GANET PERlDOTlTE XENOLITHS FROM KIMBERLITE NEAR … · 2020-04-07 · by the presence of Paleozoic...

G A N E T PERlDOTlTE XENOLITHS FROM KIMBERLITE NEAR KIRKLAND LAKE, CANADA

Philip A. Vicker

A thesis submitted in conformity with the requirements for the degree of Master of Science Graduate Department of Geology

University of Toronto

O Copyright by Philip A. Vicker 1997

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Gai-net Peridotite Xenolitlis h+oiii Kiiiiberlite Near Kirkland Lake, Criliada.

Master of Science, 1997

Pliilip A. Vicker

Graduate Department of Geology

University of Toronto

ABSTRACT

FiRy-six pendotite xeiiolitlis Iiave beeii exainiiied fioin four kirnbeilite diatreines

(AI. A4, B30 and C14) in the Kirklaiid Lake region of Ontario, Catiada. Tlie suite is

dominated by gamet llierzolites. Xenolitli textures range fiom coarse (undeformed) to

inosaic porpliyroclastic (stroiigly deformed). Evideiice for modal inetasomatism, iioted iii

plilogopite-dominated assemblages seylaciiig gamet, exists iil 17 xerioliths. Zoiiation of

gamets, indicative of cryptic metasomatic processes, is ideiitified iii tliirteeii xeiiolitlis.

Xeiiolitlis equilibrated over a wide range of teinperatures and pressures (680-

140OC, 20-60kbar), aiid coarse-texti~red xenolitlis fonn an anay correspoiidiiig to a

relatively cool 40mW/rn2 steady-state coiiductive geotlienn. Defonned xeiiolitlis fi-on1 A 1 ,

A4, aiid B30 are iiiflected 100- 150°C above the 401n~Im' steady-state geotlieiïn.

Altliougli iiiiinerous xeiiolitlis eqiiilibsated witliiii the diatnoiid stability field, only

one of 56 peiidotite xeiiolitlis is a low-Ca ganiet Iiarzbiirgite. Tlie rarity of diainoiids iii

Kiiklaiid Lake kimbeilite is disectly propoitioiial to the paucity of low-Ca ganiet

Iiarzburgite iii tlie Kitklaiid Lake seiiolitli suite.

ACKNBWLEDGEMENTS

Ï i ~ i s tliesis would iiot liavc beeii possible withoiit tiie efforts of maiiy people. The

rocks were dotiated to U of T fioin Lac Miiierals via Clins Pegg and Joe Bniininer. Dan

Scliiilze provided the topic, tlie fuiidiiig aiid the expertise to get the project off the grouiid.

As niy supervisor, Dan allowed me abundant latitude to set rny owi agenda aiid goals, and

I'm iiot sure I would have got tliroiigli tlie process witliout the fieedoiii. Tliaiikfully, Rita,

Patrick and Nicolas always seeined to know wliere to firid Iiim. Most iinpoi~aiitly, Dan

provided me an erivirontnent tliat was both clialleiigiiig yet relaxed. 1 tluiik tliat the ability

t o "shed the mortal coil" (or pd l out tlie dtilciiner) is uiidervalued in today's Society.

This tliesis involved couiitless hours iii the inicioprobe lab aiid 1 iieed to tliaiik

Patrick Andersoli and Claudio Cermignaiii for tlieir efforts in teacliiiig me the doiiigs of

the Cameca SX-50. Claudio's insiglit and interest iiito al1 tliiiigs is both boundless aiid

iiisyiratioiial.

My coinmitee, particularly Mike Gortoii, sliowed ine tliat tliere will always be

more questiotis, and that tliey always seem to get better.

1 would also like to tliatik tlie Toronto Police Department aiid the Noi-th York

Board of Education for their patience.

1 would like to dedicate iny efforts on this tliesis to iny parents wlio put up witli it

dl , to Sliirley wlio lins put up witli soine of it, aiid to Isaac, wlio's ai-tival coiiicides witii its

coinpletioii.

.., Il l

TABLE OF CONTENTS

TITLE PAGE .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ABSTRACT . . . . . . . . . . . . . . . . . . . ... ii

... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ACLNOWLEDGEMENTS 111

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . TABLE OF CONTENTS IV

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . LIST OF TABLES vi

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . LIST OF PLATES vii

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . LIST OF FIGURES v i~ i

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . LIST OF APPENDICES IS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CHAPTER 1 . INTRODUCTION 1 1.1 General Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I 1.2 Location and Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Previous Work 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4 Metliodology 4

1.4.1 Sampling and Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4.2 Mineral Chemical Analysis 3

CHAPTER 2 . PETROGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1 General Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 . . 2.2 Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.2.1 Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.2.2 Texnire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Detailed Mineralogy 12 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.1 Primay Mineralou 12

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.1.1 Olivine 12 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.1.2 Ortliopyroxeiie ... IL.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.1.3 Clinopyroxenc 13 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.1.1 Gamet 13

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.1.5 Cbromite 18 . . . . . . . . . . . . . . . . . . . . . . . 2.3.1.6 Ilmenite, Rutile, Phlogopite, and Sulphide 18

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.2 Metasoinatic Assetnblages 19 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.3 Secoiidary Effects 30

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CHAPTER 3 . MINERAL CHEMISTRY 24 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 General Statement 24

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Prunary Minerals 25 3.2.1 Olivine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

15 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2 Ortliopyrouerie .... -- 3.2.3 Clinopyroxene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.4 Gamet 79 3.2.4.1 CaO/Cr,O, in Gamet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.5 Cliromite 36 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.6 Ilmenite 36

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . j .3 Assessinent of Priniary Equilibriiiin Asseniblaçes 39

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CHAPTER 4 . GEOTHERMOBAROMETRY 37

4.1 Geiieral Stateineiit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 4.2 Calculatioiis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

4.2.1 Tlierri~oineters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 4.7.7 Baroli~~tcrs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

4.3 Resiilts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

CHAPTER 5 . DISCUSSION AND CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 5.1 Geiieral Stateineiit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 5.2 Geotliennal Gradients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 5.3 Textiires and Eqiiilibratioii Teiuperatiires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 5.4 Modal Metasoi~iatism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 5.5 Cryptic Metasoinatisii~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 5.6 Diaiiioiid Poteiitial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 APPENDICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

LIST OF TABLES

Table 1 . 1 Minirnum detection limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table 1 . 3 Relative Precision 6

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table 2.1 Petropapliic Summary 9- 10

Table 4.1 (a) Pressures and Temperatures for Kirkland Lake Xenolitlis . . . . . . . . . . . . . . . . . . . . . . . . . . 15-16 (b) Pressures and Temperatures for Published Diarnond- and Graphite-bearing Xenolitlis . . . . . 1 7

LIST OF PLATES

Plate 7.1 Coarse Textured Gamet Lherzolite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II

Plate 2.3 Porpliyroclastic Gamet Lherzolite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Plate 7.3 Ortliopyroxene Neoblasts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Plate 1.4 Sieve-textured Clinopyroxene Grain Margins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Plate 2.5 Modally Metasomatized Ganiet Llierzolite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

Plate 7.6 DoubIy Kelyphitized Gamet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

Plate 3.1 Chemically Zoned Gamet froin XenoIith AI-P5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Figure 1.1 Location Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 3.1 Ni0 ( e h ) vs . Mg# in Olivine 36

Fiçure 3.2 Cr103 vs Ti02 iri Orthopyroxeiie . Core and Rim Compositions . . . . . . . . . . . . . . . . . . . . . . 28

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F r 3.3 Cr.0. vs Na0 in Clinopyroxene 30

Figure 3.4 Mg/(Mg+Fe) vs . Ca/(Ca+Mg+Fe) in Clinopyroxeiie . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Figure j . 5 (a) Zonation in C 14 Gamet TiO? vs . Cr.0. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (b) Zonation in Al . A3 and B30 Gamet TiO. vs . Cr203 31

Figure 3.6 Zonuig Patterns in Gamet from Xenolith A4-P5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

. . . . . . . Figure 3.7 LherzoliteMarzburgite Discrimination Plot Ca0 (wt'?!) vs Mg0 (wt%) for Gamets 35

Fiçure 3.8 Cliromite Discrimination Plot . Cr.0. (wt?/o) vs AI.0. (WtOh) for Chromite . . . . . . . . . . . . . . 37

Fiçure 3.9 Chromite Discriminatioii Plot . TiO: (wt?!~) vs Cr20, (WtOh) for Chromite . . . . . . . . . . . . . . . 38

Figure 3.10 Equilibration Discrimiiiation . Gamet-olivine vs . Gamet-Ortliopyroxene . . . . . . . . . . . . . . . . 30

Figure > . 1 1 Equilibration Discrimination . Clinopyroxene vs . Gamet-Ortliopyroxene . . . . . . . . . . . . . . . 41

Figure 3.1 Pressures and Temperatures for Published Diamond- alid Graphite-bearuiç Xenoliths . . . . . 38

. . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 4.2 (a) Pressiirelïeinperature Plot TBKN vs . PBKN for C 14 39 (b) PressureRemperature Plot TBKN vs . PBKN for Al , A4. and B30 . . . . . . . . . . . . . . . . . . 50

. (c) Press~~re/Ternperature Plot TBKN vs PNG85 for C 14 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 (d) Pressure~Temperature Plot Tl3KN vs . PNG85 for A l . A4. and B30 . . . . . . . . . . . . . . . . . 53 (e) Pressure~ernperature Plot TBKN vs . PMC74 for C 14 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 (f) PressureRemperahire Plot TBKN vs . PMC74 for Al. A4. and B30 . . . . . . . . . . . . . . . . . 54

. . . . . . . . . . . . . . . . . . . . . . . . . . . . (g) PressureKernperature Plot TOW79 vs PBKN for C 14 5 5 (h) Pressurememperature Plot TOW79 vs . PBKN for A l . A4. and B3O . . . . . . . . . . . . . . . . . 6 (i) Pressurelïemperature Plot TOW79 vs . PNG85 for C 14 . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 (i) PressureTTetnperature Plot TOW79 vs . PNG85 for A l . A4. and B30 . . . . . . . . . . . . . . . . 58 (k) PressureKemperature Plot TOU'79 vs . PMC74 for C 14 . . . . . . . . . . . . . . . . . . . . . . . . . . 59 (1) PressureKernperature Plot TOW79 vs . PMC74 for Al. A4. and B30 . . . . . . . . . . . . . . . . 60

LIST OF APPENDICES

APPENDIX A . Sainple Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

APPENDIX B . Petropapliic Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7s

APPENDIX C . Mineral Chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Olivine 90

Ortliopyroxene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cluiopyroxene 100

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gamet 106 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Primary and Metasomatic Cliromite 119

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Kelyphitic Chromite 120 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . llmeiiite 171

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . APPENDIX D . Geotliern~ometers and Geobaroiiieters 177

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . APPENDIX E . Count Times and Standards 176

CRAPTER 1

INTRODUCTION

1.1 General Statement

One ofthe most sigriificant sources of information on the composition and

geochemical evolution of the Earth's upper mantle is fiom ~Itramafic xenoliths which are

brought to the Earth's surface by alkalic rocks such as kimberlite, lamprophyre. and basalt.

These xenoiiths are primary "windows" of the upper mantle and as such provide direct

evidence of upper m a d e composition (Schulze, 1996a). Numerous studies of peridotite

xenolith suites have been presented in the literature, focussing on various properties

including mineralogy, petrology, mineral chemistry, stable and radiogenic isotopes. rare-

earth elements, and fluid inclusions. Such studies have yielded information pertaining to

the mantle environment including deformation events, geothermal gradients, mantle

structure and composition, and mantle metasomatic processes. For example, Boyd

( 1973) pioneered the use of pyroxene cliemistry to assess the equilibrium depth and

temperature of gamet lherzolite assemblages fiom nortliern Lesotho; Hearn and Boyd

( 1975) examined gamet peridotite xenoliths frorn a Montana, U.S.A kimberlite; Mitchell

( 1977) characterked ultramafic xenoliths fiom kimberlites on Somerset Island in the

Canadian Arctic; Boyd and Nixon (1978) described the ultramafic xenolith suite from

kimberlite diatremes in Kimberley, South Aûica; Murck et al. (1978) examined phase

equilibria in fluid inclusions in ultramafic xenoliths from basalts fioui Arizona, Hawaii. and

Gennany, and Menzies and Murthy ( 1 980) examined isotoyic compositions in ultramafic

nodules fiom kimberlite in Kimberley and Bultfontein. South Afnca . Also see review

volumes "Mantle Xenoliths" (Nixon, 1987) and "Mantle Metasomatism" (Menzies and

Hawkesworth, 1987).

The Superior crato~i in North Ainerica is the Eartli's largest Arclieari shield, yet

very little work lias beeii doiie to characterize tlie upper mantle below it. This study is ail

exami~iatioii of a suite of mantle xenolitlis fioiii kimberlite iiear Kirkland Lake, Ontario.

The purpose ofthe study was to assess tlie mantle euvironment beneatli the paleo-

Superior craton. Petrograpliic and mineral chemical i~ivestigatioiis were used iri

coujiuiction with recogiized geotliermobarometric calculation procedures to quanti@ the

geotliermal gradient and to identify deformation events, mantle metasomatisni. and mantle

composition.

1.2 Location and Geology

The Al , A4, B30. and C l 4 kimberlite diatremes are located approximately 20 km

northeast of Kirkland Lake, Ontano, in Arnold (A 1 and A4), Bisley (B30), and ClBord

Townships (C 14). (Figure 1.1). Kirkland Lake is located in the south-central portion of

the Archean-aged "granite-greenstonel'-dominated Abitibi SubproMnce of the Superior

craton (Jackson et al., 1990). The hoa kimberlites intrude the southern limb ofthe Blake

River synche (MERQ-OGS, 3983) which is dominated by east-west striking mafic to

felsic metavolcanic rocks (ODM Map 2283. 1969) of the 2702+/-2 Ma Blake River

assemblage (Corfù et al., 1989). Late-Archeau felsic, mafic, and ultramafic intrusive

rocks occur locally throughout the assemblage. The kimberlites near Kirkland Lake are

much younger than the host Archean supracrusta1 assemblage and have been dated by

Heaman (1 989) at 158+/-2 Ma (rnid-Jurassic). No Paleozoic rocks are located in the

area, but evidence for a Paleozoic cover at the tirne of kirnberlite emplacement is indicated

by the presence of Paleozoic linestone xenoliths in the tuffisitic breccia phases of the

Kirkland Lake kimberlites.

niere are 10 knowu dykes and diatremes in the Kirkland Lake k b e r l i t e cluster.

This cluster is central to a field of 29 kimberlites ranging from Lake Abitibi in the north to

Lake Tirniskaming in the south. This field occurs in the nortli-northwest-trending Lake

Temiskaming Structural Zone (LTSZ) (Brummer et al., 1992b). Tliese authors suggested

tliat tliis rifi system was the conduit for kimberlite magmatism in the Jurassic. Detailed

iüodels for structural emplacement of the Kirklaiid Lake Lnberlites have iiot beeii

presented in the literature.

1.3 Previous Work

Kirnberlite was first reported iii the Kirkland Lake region in Michavd To~wsliip by

Satterly (1948). Lee and Lawrence ( 1968) reported the occurrence of a kimberlite dyke

underground at the Upper Canada Miue in Gautliier Townsl~ip whicli lias also beeii

+ 4 4 + * I I

I Study Area l

Kirkland La

N

E O

Noranda

Fipure 1.1 Location Map of A l , A l , B30, and C l 4 Kimberlite~, Kirkland Lake, Ontario Locations from Zalnieriunas and Sage, (1995). Adapted from Schulze (1996a).

studied by Watkinson and Chao (1973), Mitchell (1978), and Smith et al. (1978). Micas

froin the B30 diatrerne were described by Arima et al. (1 986a.b). A review of activities

and occurrences in the Kirkland Lake kimberlite cluster was presented by Brurnmer et al.

( I WZa, b). Ten peridotite xenoliths from the C 14 diatreme were studied by Meyer et al.

(1 994). These latter authors concentrated on mineral chemical data and

pressureitemperature equilibration conditions of the xenolith suite (the current study

greatly expands this preliminary database). Recent reports on kiinberlites in the Kirkland

Lake region include Schulze and Anderson (1 992, 1994), Sage (1 996), Schulze (1 996a),

and McClenaghan et al. (1 996).

1.4 Rlethodology

1.4.1 Sampling and Preparation

Peridotite xenoliths in this study were taken from diamond drill core (BQ, NQ and

HQ sizes) donated to the University of Toronto by Lac Minerals. Sampling of peridotite

xenoliths was primarily targeted toward garnet lherzolite assemblages (garnet + olivine +

orthopyroxene + clinopyroxene +/- phloçopite +/- chromite) as this asseniblage has the

most versatility for geothermobarometry. Garnet harzburçites (çarnet + olivine -t

orihopyroxene +/- phloçopite +/- chromite) were also sampled as this mineral assemblage

permit5 some geothermobarometric caiculations, but does not allow for 2-pyroxene

therniomet~y. Several garnet-free lherzolites and dunites were also sampled.

Samples were affixed names according to their source diatreme. The depth in the

drill section from which each sample was taken is presented in Appendix A. C 14 samples

are labelled C-Pfi (Pperidotite. #=sample number), Al samples are AI -P#, A4 samples

are A4-P#, and B3O samples are B-P#.

1.4.2 Mineral Chernical Aiialysis

Minerals were analyzed using the Cameca SX-50 in the University of Toronto

Duncan Derry electron microprobe lab in the Department of Geology. Data were

corrected automatically during acquisition usinç standard SX-50 PAP procedures.

Accelerating voltage of 15 kV was utilized for garnet, orthopyroxene, and clinopyrosene,

and 20 kV for chromite and olivine. The count tirnes and standards used during

acquisition are given in Appendix E

The minimum detection limits were calculated for each inineral species

according to the standard formulae

(P-B2)E .m~-o@ m and m- E where hdDL is the minimum detection limit , a is a

desired number of standard deviations, m is calculated from results of calibration analyses,

RI is the number of background counts per second, t is the background countinç time, (1'-

B2) is the observed peak minus background counts per second of the standard, I' is the

current utilized, and E is the observed element percent in the standard. Table 1.2 lists the

minimum detection limits for each mineral analyzed in this study.

Relative precision was exatnined to assess the reproducibility of analytical results.

A sinçle homoçeneous çrain for each mineral species was analyzed on four separate

Gt

0.006

0.007

0.007

0.007

0.008

n.d.

0.0 13

0.0 17

0.071

0.022

0.0 1 X

n.d

r d

N a 2 0

M g 0 A1203

S i 0 2

P 2 0 S

U O

C a 0

Ti02

Cr203

M n 0

FcO

N i 0

Z n 0

occasions. Relative precision is calculated by the standard formulae

Iable 1.1 Minimum detection liniits in weight percent. The calcuiaticiiis arc hased ciil o \ d u c s of 2 (95.4% c«~ifidciiçc). n/a= not a n a l p d . @I=olii~irie. Cps=clinop!~r»scnc. Ops=oiZhop!~oscnc, CIii=chrtimitc. Gt=panict

S R-(-)* 100% x and n(n- 1) where R is the relative precision, S

01

n.d.

0.009

n.d.

0.008

Ops 0.008

0.006

0.005

0010

Cps 0.01 1

0.006

0.006

0.0 1 0

Chr

n.d.

O 008

0.006

0.005

n.d.

1i.d.

0.007

0.009

0.015

0.017

0.0 14

0.0 1 X

Ci.028

n.d.

n.d.

0.006

n d.

0.009

0.0 12

0.0 16

0.0 13

n.d.

n.d.

0.lJOX

0.0 17

0.014

0.019

0.02 1

0.01 1i

0.027

n.d.

n.d.

O (107

0.0 1 O

0.013

0.OI 9

(1.070

0.01 X

0.076

1i.d.

is the standard deviation, s is the mean, n is the number of analyses. and XL is the value of

analysis a . Representative elemental values of minerai species are presented in Table 1.3

Chromitc Garnrt Cpx

llcan S.D. % Xlran S.D. O/o hlcün S.1). %

o p \

hleaii S.D.

Olivine

hlran S.D. O h

I

T:tble 1.2 Relative Precision . \ i rm \,ci~ucs (v.1 lx,) rcprcscrii four aiia~yscs pcr siiiplc griiiii (HI. S I i . is the siaiidard dcviation. and % is tlic rclaii\.c prccisiciii crror.

Relative precision error of major elenients is generally less than 1 % for al1 inineral

species, whereas relative precision error of trace elements (< 1 % of total mineral weight)

is higher. Relative precision errors of minor elements are çeneraily <5% wlien

concentrations exceed 2MDL and <1% at concentrations exceeding SMDL.

CHAPTER 2

PETROGRAPHY


Xenoliths which retain their mantle-equilibrated assemblages during and

subsequent to entrainment by kimberlite magma provide direct evidence of the mantle

source environment in which they formed. Previous studies of mantle peridotite xenoliths

have shown that it is of fundamental importance to characterize whether a xenolith

assemblage is "well-equilibrated" (e.g. Finnerty, l989), particularly for application of

thermobarometric calculations. An equilibrated assemblage may be described as a system

which remains in a stable state at a fixed temperature and pressure. It is generally

assumed that the primary mode of garnet peridotite xenoliths (olivine, orthopyroxene,

garnet, olivine) are a mantle-equilibrated assemblage unless there is evidence to the

contrary (Finnerty, 1989). Therefore it is essential to distinguish what constitutes the

primary mode for each xenolith. Petrographic examination is used to distinguish the

primary assemblage from any younger metasomatic or secondary minerals or assemblages

that may be present.

Petrographic exainination of the peridotite xenoliths from the A l , A4.330. and

C 14 kimberlite diatremes was used in this study to characterize a11 minerals and mineral

assemblages and to classi@ xenoliths accordinç to accepted rock nomenclature. Primary

mineral assemblages and metasomatic replacement assemblages were distinguished

utilizing mineral morpholoçy, grain boundary relationships, and rock texture. Also of

petrogenetic interest are relationships indicative of secondary alteration processes which

may indicate disequilibration of the mantle assemblage during ascent of the xenolith within

the kimberlite magma.

2.2 Classification

2.2.1 Mode

Classification of peridotite is based on priinary olivine/pyroxene modal proportions

according to the International Union of Geological Sciences (I.U.G.S.) scheme of

Streckheisen (1973). In studies of mantle xenoliths an accepted deviation from the

I.U.G.S. scheme is utilized wherein merely the pi.rsuicr of (primary) clinopyroxene in an

orthopyroxene-bearing peridotite is required to classi@ a nodule as a lherzolite (as

opposed to the >5% modal abundance required by the I.U.G.S. scheme) (e.5. Dawson,

1960). Names are fùrther modified by the presence of prirnary garnet, chromite, sulphide.

rutile, phlogopite. or ilmenite. The 56 xenoliths examined in this study are classified as

garnet lherzolite (33), ilmenite- phlogopite-bearing garnet lherzolite ( l ) , chromite-bearing

garnet lherzolite (6), sulphide-bearing garnet lherzolite (3). phlogopite- sulphide-bearinç

garnet lherzolite ( l ) , garnet harzburgite (3), sutphide-bearing çarnet harzburçite ( l ) ,

chromite Iherzolite ( 1 ), sulphide-bearing chromite lherzolite ( l ) , phlogopite- rutile-

bearing chromite Iherzolite (1), lherzolite (3), and dunite (2).

Mantle-equilibrated assemblages examined in this study are classified as either

primary or metasomatic. Primary assemblage includes orthopyroxene, olivine,

rtclinopyroxene, *gamet, *phlogopite, *chromite, *ilmenite, *rutile. Evidence of mantle

metasomatism is identified either petrographically or by mineral chernical analysis.

Replacement of garnet (potassium poor) by a phlogopite-dominated assemblage

(potassiun1 rich) intergrown with clinopyroxene and chromite (Plate 2.5) is petrographic

evidence that metasomatic processes have affected the primary minerals. More subtle

evidence for mantle metasomatism and disequilibration is recognized by mineral cheinical

zonation in çarnets which are petrographically homoçeneous. This zonation, termed

cryptic metasornatism, will be discussed in Mineral Chemistry - Chapter 3, Section 3.2.4.

Evidence of secondary processes, indicative of disequilibration of the primary

silicate assembla~e from mantle equilibrium, are identified as kelyphitization assemblages

comprised of a fine grained and comnionly dark brown matte of clinopyroxene,

phlogopite, and chromite replacing garnets (Plate 7.6), as sieve-textured marçins of

clinopyroxene grains (Plate 2.4), and serpenrinization of olivine.

A summary ofthe xenolith mineral assemblages and textures is presented in Table

2.1. Petrographic descriptions of al1 xenoliths are in Appendis B.

2.2.2 Texture

Xenolitlis can also be classified according to their texture, based on the descriptive

Table 2.1 - Summary of Petrography

Xenolith AI-PI A l - P 3

Al-P5 Al-P6 Al-P7 AI-PI

RockType GL D

D GL GH CL

Texture tcd n

P c c c

Primary Minerals Gt 01 Opx Cpx Chr Other * * * * - - * - - - - * - * * * * - * * * - - - * * * *

Metasomatic Minerals Phl Cpx Chr Other,

Table 2.1 - Summary of Petrography

Primary Minerals 1 Metasomatic Minerals 11

Table 2.1 Pctrographic Surnmary

Tcsturcs: c=coassc. tcd=transitional c a m e tn dcfonned. p=poiphyroclastic. mp=mosaic- porphrriiclasiic:

Rock Types: GI,=gamct Ihctmlitc. GI-[=gamet har~husgitc. Il=dunitc. CGL.=chsomitc-bcannf gainci Ihcrzoliic. CL=clirriniite Iticrr.olitc. l.=ll~ci-/olitc, PICiI.=phlogopitc. ilmcriite-hcai-ing gmict Iherzoiilc. SCiL=I;c-Ni siilphide-hcaring ganict Ilienolitc, SCil-]=Fe-Ni sulpliidc-beariiif gamet har~burgi~e. SLL=Fc-Ni sulpiiide-beasing cliromitc Ihcr/-olitc, SI'GL=I:c-Ni sulphidc-bcaring phloppiit. parnet Ilicnoliie, PRCL=nitilc-bearinp phlogopitic chromiic Ihcizolitc

Other:

terminology of Harte ( 1 977). Textural types are characterized with regard to the ratio of

olivine neoblasts to olivine porphyroclasts. According to Harte (1 977) xenoliths are

classified as coarse if <10% of olivine occurs as neoblasts (Plate 2 1 ) . A porphyroclastic

texture comprises two major olivine populations. one of porphyroclasts (N.B.

classification takes into account olivine porphyroclasts, but çarnet, clinopyroxene. and

orthopyroxene porphyroclasts may also be present) and the other of a fine çrained

neoblastic olivine rnatrix . Porphyroclasts are generally -'l mm in size. and neoblasts

generally range from <O. 1 to OSmm in size. A porpliyroclastic texture is defined as

having greater than 10% of olivine occurring as neoblasts A xenolith is termed mosaic-

porphyroclastic if greater than 90% of olivine occurs as porphyroclasts (Plate 2.2). This

study modifies the Harte ( 1 977) classification to distinguish between coarse undeformed

xenoliths and coarse xenoliths which have evidence of recrystallization and deformation

textures. Coarse xenoliths which have 540% olivine as neoblasts are classified in this

study as transitional from coarse to deformed.

The çarnet-bearinç lherzolite xenoliths include 32 coarse (of which 1 3 are

transitional from coarse to deforrned), 6 porphyroclastic, and 4 mosaic porphyroclastic.

One lherzolite is coarse and 2 are porphyroclastic. The harzburgites are subdivided into 3

coarse ( 1 transitional from coarse to deformed) and 1 porphyroclastic. The two dunites

are porphyroclastic. Note that al1 8 xenoliths with primary chromite are coarse-textured

as are 2 xenoliths with primary phlogopite. A third xenolith with primary phlogopite, C-

P 17, is porphyroclastic-textured (Plate 2.2). This xenolith is unusual in that it has botli

primary and metasomatic ilmenite, deformed phlogopite, and cryptically metasomatized

garnet (rim enrichment in Ti, rim depletion in Cr).

Olivine (and less commonly orthopyroxene) in coarse-test~ired xenoliths

coiiinionly lias undulose extinction, particularly in those whicli have yreater than trace

amounts of neoblasts. Rarely, orthopyroxene neoblasts are present in porphyroclastic

xenoliths at the boundary between orthopyroxene and garnet (Plate 2.3). Several

xenoliths have inhomogeneous texture wherein they are dominantly undeformed but

contain abundant neoblasts in small regions. These heterogeneous-textured xenoliths have

been classified as transitional coarse to deformed as they likely represent a transitional

stage between coarse and porphyroclastic textures.

2.3 Detailed Mineralogy

2.3.1 Primary Mineralogy

The primary minerals constitutinç the peridotite xenolith suite are olivine, enstatite.

diopside, pyrope, chromite, and rarely Fe-Ni sulphide, ilmenite, rutile, and phlogo pite.

Pyrope is commonly partially replaced by an assemblage of phlogopite and chromite +/-

diopside inferred to be of metasomatic origin. Primary phlogopite. chromite, rutile, and

ilmenite are distinguished from their metasomatic equivalents by being spatially and

texturally distinct from any garnet replacement assemblage. Notably. it is difficult to

distinguish between primary and metasomatic equivalents of these minerals in xenoliths in

which they are both primary and metasomatic (i.e. C-P 17. Plate 2 .2 ) . and/or where spatial

association with garnet is not seen in the third dimension (a product of thin sectioninç).

2.3.1.1 Olivine

Olivine is the dominant mineral in al1 xenoliths, generally forming 60-80% of

garnet Iherzolites, garnet harzburgites, Iherzolites, and harzburçites, and 1 00% of dunit es.

In coarse-textured xenoliths, olivine ranges from 2-1 Omm, and çrain boundaries range

from straight to sliçhtly curvinç. Olivine is comrnonly unstrained in coarse-textured

xenoliths, but in several coarse nodules olivine has undulose extinction and incipient

neoblast development on grain inarçins. In deformed xenoliths, olivine occurs as both

porpliyroclasts and neoblasts. Porphyroclasts have undulose extinction and grain sizes are

generally G m m . Neoblasts are unstrained and forin a fine çrained mosaic-textured

frainework between porphyroclasts. Neoblasts range from <O. 1 to 0.5min and range in

abundance from 0-70%. Olivine also occurs as ovoid-shaped inclusions within garnet.

occurrinç in both coarse and deformed garnet lherzolites (e.g Plate 2.2).

2.3.1.2 Orthopyroxerie

Orthopyroxene is clear in plane-polarized liçht and commonly has well-developed

cleavage. Grain sizes rançe from 1-8mm in both coarse and deformed xenoliths. In

coarse xenolitlis, ortliopyroseiie is tabiilar to lobate witli miifotm estinctiori. III several

transitioiial coarse to defoimed seiiolitlis, oitliopy-osene Iias undulose ex-iiictioii.

Porpliyroclastic o~tliopysoseiie in defonned xeiioliths is ovoid-sliaped, coininonly Iiaving

undulose extinction. Ortliopyroseiie neoblasts are rare, o c c u ~ r i g at the contact betweeii

o~tliopyroxene and ganiet (Plate 2.3). Most ortliopysoxene in the xenolitli suite is

optically clear but ortliopyroxene in xetiolitli A 1 -PI O Iias abundant fine grained

uiiidentified inclusions and higlily altered graiii tnargins. Most of tlie ortliopysoxene in

xenolitli A4-P9 also Iiave some uriidentified iiiclusions and altered grain inargitis althougli

alteration is less intense tlian A 1-P I O.

2.3.1.3 Clinopyroxene

Clinopyroxene is pale greeii iii plane-polarized liglit, and is usually <S% of

Ilierzolite assemblages, but is preseiit in concetitratiotis iip to 15% in several xeiiolitlis.

Sizes range fiom < 1 to 5mm. Grains have cutved margins and sliapes are ofien atnoeboid.

A disequilibration texture is iioted iii sieve-textured rnargins on most grains (Plate 2.4).

Development of sieve-textures varies from minor (<O. lintn) to major (entire grain).

Cliiiopysoxene po~pliyroclasts iii defoimed xenoliths are coinmonly strained, exliibitiiig

iindulose extinction and, rarely, twiiiniiig. Euhedral clinopyroxene occurs as aii inclusion

in gamet in xenolitli C-P8.

2.3.1.4 Garnet

Gai~iet is pale pink in plane-polaiized liglit and rouiided to lobate in most

seiiolitlis. Gsaiiis satige fioin 1- 12 inm and generally coiistitute 5- 15% of tlie modal

assemblage. Gamets cotninoiily enclose ovoid olivine aud rarely euliedial clinopyioxene.

A metasoinatic assemblage (descilbed fiiither iii Section 2.3.3 - Metasoniatiç

Assemblages) consisting of plilogopite, cliioinite and cliiiopyroseiie inantles gamet iii 16

senolitlis. Almost al1 gamets are iiinined by a dark b i o w , fine-grained kelypliitic

alteration assemblage compsising plilogopite, Iirowi cliroine-spinel and clinopysoxene

(disciissed fu~tlier in sectio~i 2.3.3 Secoiidary Effects). Tlie bouiidaiy betweeii kelypliite

and ganiet is sliaip in al1 xeiiolitlis. Some gai-riets have fiactiires infilled witli the

kelyphitic assemblage. Al1 gamet wliicli has not been kelyphitized is optically clear.

2.3.1.5 Chromite

Primary chromite is rare in the Kirkland Lake xenolith suite and was found in orily

8 xenoliths, al1 of which are coarse-tex-red. It is opaque to a deep reddish-brom.

Grains range fiom 0.5-2mm and are euhedral to subhedral. Frimary chromite crystals are

spatially and texturally discrete fiom metasomatic assemblages, and appear equilibrated

with the major "primary" mode.

2.3.1.6 Urnenite, Rutile, Phlogopite, and Sulphide

Ilmenite, rutile, pldogopite, and sulphide are extremely rare in the KirUand Lake

xenolith suite and are found predominately in xenoliths fiom the C 14 kimberlite. Although

some autliors have suggested that the presence of these minerals are indicative of modal

metasomatism (i.e. Harte et al. 1987) (see Section 2.3.2 - Modal Metasomatism), this

study has classiied as primary ail minerals which have no apparent association with

replacement of the primary silicate assemblage.

Primary ilmenite is present in only I xenolith. a single grain witliin mosaic-

porphyroclastic textured C-P17. It is lx2mm and opaque. The grain is lobate with sharp,

linear to curvilinear grain boundaries. It is embayed by a 0.5mm round olivine grain whicli

appears to have been resistant to deformation. The olivine embayment is coarser thaii the

neoblast mode indicating that the ilmenite sheltered it fiom the deformation event, and

thus the ilmenite is pre-deformation. l i i s xenolith also contains both undeformed

metasomatic phlogopite and phlogopite that Iias bent cleavage traces. Both of tliese

phlogopite modes are proximal to ganiet and may be ganiet replacement assemblages

fiom two separate metasomatic eveuts. The iiiitial event. prior to deformation. may bave

produced "primary" ilmenite and plilogopite. A second metasomatic event. post-

defoniiation. may have iutroduced the more typical metasoinatic assemblage of

phlogopite, cliromite, and cliliopyi~oseiie. Evideiice of metasomatisrn in this xenolith is

also iioted iii crypticaiiy zoned gamet (discussad in Minera1 Chemistry Sectiou 3.2.4 - Gamet).

Primary rutile is present in only one xenolith, coarse testured C - P Z . It occurs as

small (<O. 1-0.5rnrn). subhedral t o anhedral, honey-coloured grains, usually with altered,

opaque grain boundaries. It is commonly associated with primary phlogopite, but also

dispersed discretely throughout xenolith.

Primary phlogopite is present in three xenoliths, coarse-textured C-P20 and C-P28.

and mosaic porphyroclastic textured C-P17 (the latter is discussed above). Primary

phlogopite in the coarse-textured xenoliths are generally 0.5-2mm, subhedral, and light

beige coloured. Phlogopite grains have sharp linear to curvilinear grain boundaries and

appear to be equilibrated with the major primary mode (olivine, pyroxenes and garnet).

Primary sulphide is present in six xenoliths, coarse-textured B-P3, C-P 19 and

C-P20, and porphyroclastic-textured AI -Pl 7, C-P25 and C-P34. Sulphides are opaque in

plane-polarized light, and are probably pentlandite (as determined by EDS peaks durinç

electron microprobe examination). The sulphide in B-P3 is a single lath-like grain, Imrn

in lengh. Al1 other primary sulphide occurs as rounded blobs, 0.2-0.5mm in diameter,

both discrete and as inclusions within olivine.

2.3.2 Metasomatic Assemblages

Harte et al. (1987) stated that petrographic evidence of modal metasomatism is

distinguished by changes in modal mineralogy commonly noted by the addition of some or

al1 of the minerals ilmenite, rutile, phlogopite and sulphide. Metasomatic minerals may be

present in veins, as isolated grains, or as rims and veinlets replacing silicates (Field et al.,

1989). Veins coinprisinç nietasomatic assemblages are present in peridotite xenoliths in

the Bultfontein kimberlite, South Africa (Jones et al., 1982). Field et al. (1989) describe

several metason~atic assemblaçes which occur as isolated grains, interçrowths or clusters

of grains, or rirns and veinlets replacing other silicates in peridotite xenoliths from the

Jagersfontein diatreme, South Africa. In contrast to Field et al. (1989), this study has

distinguished between ilmenite, rutile, phlogopite and sulphide minerals which are

obviously metasomatic and those wliicli have do not appear associated with a metaso~~iatic

replacement assemblage (see Section 7.3.1.6 above).

Evidence for modal metasomatism in whicli phlogopite 5 chromite * clinopyroxene

mantle and partially replace garnet is present in 16 xenoliths ( 1 5 from C 14 and 1 from

Al) . Replacement of garnet ranges from minor (<0.5 mm of rim) to major (complete or

near complete replacement). Metasomatic phlogopite is generally coarse in comparison to

secondary kelyphitic phlogopite and commonly has intergrown chromite. Cleavage traces

of metasomatic phlogopite are bent in many cases. The garnets in samples C-P26 and C-

P27 have been nearly completely replaced by the metasomatic assemblage (Plate 2.5).

Ilmenite is present in 5 of the 16 modally metasomatized xenoliths and the ilmenite

in two of these xenoliths occur as micron-scale exsolution lamellae within metasomatic

chromite. The ilmenite in the mosaic porphyroclastic xenolith C-Pl7 appears to occur in

two modes. The first mode is characterized by a coarse (1.5mm) fractured anhedral grain

proximal to the pre-kelyphite garnet rirn but distinct from the remainder of the

metasomatic assemblage. This grain may be primary (see Section 2.3.1.6 above). The

second mode of ilmenite occurs within the thick kelyphitized garnet rim. These grains are

fine grained and rounded with irregular margins. It is unclear whether these ilmenites

were replacing garnet as a metasomatic mode or were a primary inclusion during the

growth of the garnet.

Fe-Ni sulphides are present in 8 xenoliths only 3 of which display other

characteristics of modal inetasomatism. The sulphide in the metasomatized xenoliths A l -

P 10 and C-P I O are locally associated with metasomatic phlogopite and may be of

metasomatic origin. Alternatively, sulphide in C-P34 is discrete from the metasomatic

assemblage and has been classified as primary..

2.3.3 Secondary Effects

Evidence that secondary processes have affected the mantle assemblage are

present on al1 garnets and clinopyroxenes exainined in this study, noted in kelyphitic

rin~ming of garnets and as sieve-textured marçins to clinopyroxene (Plate 2.4). Both

processes Vary from minor rimming to comylete replacement. Additionally, olivine is

commonly serpentinized, particularly proxiinal t o fractures and at xenolith inaigins.

Kelyphitic replacement of çarnet is commonly composed of a fine grained dark to

almost opaque assemblage of phIogopite, chromite, and clinopyroxene. It is usually easily

distinguished fiom the metasomatic assemblage by its grain size. Kelyphitic cliromite lias

dirty brown grain margns in plane-polarized liglit. as opposed to the opaque or deep red

for mantle-equilibrated chromite.

One gamet apparently has two generations of kelyphitization (Plate 2.6). It

appears that the entire garnet was rimmed by kelppliite , and then the xenolitli was

fiactured tlirough the garnet grain and the newly exposed surface in contact witli the

kimberlite was kelyphitized.

CHAPTER 3

MINERAL CHEMISTRY

3.1 General Staternent

Chemical compositions of the prirnary silicate phases olivine, orthopyroxene.

clinopyroxene, and garnet were deterinined by electron microprobe analysis. Primary and

metasomatic chromites were also analyzed. Ilrnenite was analyzed in five xenoliths. In

most cases, two grains of each rnineral were analyzed in each xenolith to assess

homogeneity within the xenolith. In addition, cores and margins were analyzed on each

grain to assess rnineral chemical zonation. Minimum detection limits and precision of

analyses are presented in Section 1.4 - Methodology. Count times and standards are

shown in Appendix E. All mineral chernical analyses are tabulated in Appendix C.

The mineral compositions discussed in this section, in particular those of the garnet

lherzolites and harzburgites, are used for the geothermobarometric calculations in Chapter

4. Finnerty (1 989) stated that "in applying thermobarometric calculations to a rock it is

assumed that the chemical compositions of the minerals in the rock reflect equilibration at

a single temperature and pressure". Within an equilibrated assemblage, element

partitioning between phases shouid be well-correlated. Evidence that a mineral has

deviated from equilibrium conditions may be fùrther identified in inhomogeneities within

grains or across xenoliths.

Within the 56 xenoliths examined in this study, 25 of these have some evidence of

mineral zonation in one or more minerals. Attempts were made to determine the cause of

zonation in each of these xenoliths. Most of the elemental zonation found in olivine,

orthopyroxene and clinopyroxene was minor and could be correlated to secondary

alteration processes particularly witli regard to sieve-textured clinopyroxene marçins

which are reduced in jadeite component. As these minerals are othenvise homogeneous,

their core cliemistries are likely to reflect chemical compositions in equilibration with other

phases in the rock. In zoned gamets, rim compositions could not be correlated to

petrographic evidence of secondary alteration (N.B. "true" garnet rims are obscured due

to kelyphitization, and al1 rims were analyzed as near to kelyphitized marçin as possible

yet remaining within optically clear garnet). These zoned gamets may show chemical

evidence of mantle metasomatic processes as discussed by Smith and Boyd (1987, 1989.

19%). At m t l e temperztures wid pressures garnet presewes evidence of past histones

better than other phases due to slower diffusion rates (Smith and Boyd, 1989). The rim

composition of a zoned gamet is most likely representative of the most recent event and

therefore is the most likely part ofthe gamet to be in equilibrium with the peridotite

assemblage .

3.1 Primary Minerals

3.2.1 Olivine

Core and rim compositions of either coarse or porphyroclastic olivines were

determined in each xenolith. Two xenoliths contain chemically zoned olivine: oliviue in C-

P22 (gamet Iherzolite) and C-P28 (chromite Iherzolite) are Fe-enriched (and Mg-depleted)

fiom core to margin on the order of 1.4 wt% Fe0 and 0.8-0.9 wt% Mg0 (tabulated in

Appendix C). No other signifkant heterogeneities in olivine compositions, within

precision parameters, were noted within the remainder of the xenolith suite.

Trace elements Cr, Mn, and Ca compositions are mostly within one standard

deviation to their respective minimum detection lirnits. Mg#'s of olivines in the xenolitli

suite (defiiied as molar Mg/(Mg+F%,,,)) are within the range 0.85 1-0.933, with most

>0.90. Seveii xenoliths are relatively Fe-enriclied in cornparison to the remainder ofthe

suite, iiicluding garnet lherzolites A4-P5, C-P26, and C-P34, dunites Al-P3 and Al-P5,

clirornite Ilierzolite AI-P8, and Iherzolite A4-PI 1. Witliin tliese "Fe-enriclied" olivines.

N i 0 increases proportionaly witli Mg# (Figure 3.1).

3.2.2 Orthopyroxene

Orthopyroxene is present in al1 samples except the dunites. Cores and margins

were analyzed on al1 grains. The trace elements Ni and Mn are generally witliin one

standard deviation to minimum detection and are therefore unreliable. K is at or below

minimum detection in al1 xeiioliths. Most xenoliths have Ti, Cr, and Na contents well

above minimum detection, and all have Ca and Al well above minimum detection.

Mg contents of ortliop~~oxene are inversely proportional to Na, Fe, Ca, Mn, Ti, Cr

and Al. Mg# values are witliin the range 0.871-0.944, and most are over 0.91. Five

0.84 0.86 0.88 0.9 0.92 0.94 MgI(Mg+Fe) Olivine

O Garnet Lherzolite

Dunite

Garnet Harzburgite

Lherzolite

Chromite Lherzolite

A Chromite-bearing Garnef Lherzolite

seiiolitlis coiitaiii oitliopyroxeiie wliicli is relatively Fe-enriclied in coinpaiison to the

remainder of the suite, iticludiiig ganiet Ilierzolites A4-P5, C-P26. aiid C-P34' chroinite

Ilierzolite AI-P8, and Ilierzolite A4-P 1 1. Tliese seiiolitlis also have Fe-eiiiicfied oliviiie

indicatiiig tliese xenolitlis are Fe-eiinclied tliiougliout the plimniy assemblage .

Seveii of tlie 54 oi~tliopyi~oxeiie-beaii~ig xenolitlis Iiave inarkedly zoiied

oitliopyroxeiies, paiticularly witli respect to the trace elemeiits. Most otlier xenolitlis

have ininor ortliopyroxe~ie zonatio~i witli respect to at least one or more trace elemeiits.

The effects of tliese ortliopyroxene zonatioiis on tliennobaroinetric calculations of the

ganiet Ilierzolites is discussed in Cliapter 4. Detailed study of ortlioyyroxeiie zonation

(i.e. zoning profiles) was tiot undertaken. Specifics of sigiiificant orthopyroxene zoiiatioii

in gamet llierzolites is as follows. Relative to cores, AI-PI0 Iias margiiis eiiriclied in Fe,

Ca, and Ti, aiid depleted iii Mg and Al, A4-P6 Iias rnargins eiiriclied iii Mg aiid depfeted in

Al and Cr, A4-P9 Iias margins etiriclied in Na, Ca, Ti, Al, and Cr and depleted iii Mg, alid

B-P 1 Iias margins depleted in Ca. In cliromite Ilierzolites B-P3 and A 148,

ortliopyroxenes Iiave rnargins depleted in Al witli respect to tlieir cores. Ortlioyyroxene iii

Ilierzolite C-P3 1 Iias iiicreasiiig Ci. fioiii core to inargiii. Rini coinpositioiis are weakly

Cr-enriclied (-O. I wt%) in I I C 14 xenolitlis (Figure 3.2a).

Two of tliese xenolitlis (A4-P9 aiid AI-PlO) display drastic zoiiatioti with respect

to major and iniiior elemeiits (Figure 3.2b). The ortliopyroxe~ie in botli of tliese senolitlis,

and AI-Pl0 in particular, are altered (as discussed in Petrograpliy Section 2.3.1.2) aiid

theii clieinical vaiiatioiis caii be asciibed to tliis alteration. Witliiii tlie reinaiiiing xeilolitlis

in the Kirklniid Lake suite, iio con.elatioii caii be niade betweeii oi-thopyroxeiie zotiatioii

and eitlier defoni~atioii or modal inetasoinatisin. The clieniical zonation of oitliopyroxeiie

in tliese seiiolitlis Inay be ilidicative of iiicipieiit secoiiclaiy riltewtioti.

3.2.3 Clinopyi-oxene

Cliiiopyoxeiie is preseiit iii al1 Ilieizolites alid gaillet Ilierzolites. K aiid Ni viiliies

are geiieially at or below iiiiiiiinuiii detectioii liinits, aiid tlie imairidci of the aiialyzecl

Solid = Core

O 0.05 0.1 0.15 0.2 0.25 0.3 Ti02 (wt%) Orthopyroxene

O 0.05 0.1 0.15 0.2 0.25 0.3 Ti02 (wt0/0) Orthopyroxene

0.9

Figure 3.2 - Cr203 vs T i 0 2 in Orthopyroxene - Core and Rim Compositions (a) C 14 - Minor nui enrichment of Cr is common. (b) AI. A4, B30 - Most ortliopyroxeile uuzoned to weakly zoned

Al-Pl0 is riin -eiiriclied in Ti, A4-P6 is rim-depleted in Cr, A4-P9 is rini- enriclied in Cr, Ti

- Al, A4, B30 Orthopyroxene Zonation 0.8- Ct203fi01 43

elements are well above minimum detection. -411 clinopyroxenes have some degree of

alteration of grain margins, noted petrograpiiically as sieve textures, and atteinpts were

made to obtain mineral chemical analyses in the most optically fresh margins available. In

several cases this was not possible. In these cases the grain margin results are particularly

reduced with respect to the cores in Na and Al (orjadeite component) and commonly

increased in Ca and Ti. This mineral chernical zonation compounded with textural

evidence of alteration indicates that clinopyroxene marçins have lost their mantle-

equilibrated compositions. This disequilibration likety occurred durin; ascent of the

xenolith in the kjmberlite magma. In a few samples, the clinopyroxene is entirely sieve-

textured, and the jadeite component is low throughout the grains. Mantle related mineral

chemistry zonation, or cryptic metasornatism (see Section 3.2.4 - Garnet, below), was not

observed, possibly due to secondary-process disequilibration of clinopyroxene grain

margins or lack of preservation due to rapid difision rates in clinopyroxene.

Clinopyroxenes are essentially diopsidic in composition, with Mç#'s ranging from

0.865-0.947, and molecular Cal(Ca+Fe+Mg) values ranging from 0.3495-0.485. Na,O

(wt%) values range from 0.5-3.5 wt% and Cr@, values range fronl 1-4 wt% (Figure 3.3).

Xenoliths AI-P8, A4-P5, A4-P11, C-PX, and C-P34 are enriched in Fe compared to the

remainder of the xenolith suite (Fiçure 3.4).

3.2.4 Garnet

Garnet was analyzed in garnet lherzolites, chromite-bearing çarnet Iherzolites, and

garnet harzburgites. Phosphorous contents were al1 at or below minimum detection limits.

Due to the presence of kelyphitic rimining on al1 garnets. "rims" were analysed within 10-

20 microns of the kelyphite, and are not "true" rim compositions. Cryptic zonation exists

in the garnets of thirteen xenoliths (Al-P 1 , AI-P 10, Al -P 17, A4-P3, A4-PS, A4-P 13, C-

P l , C-P l O, C-P 17, C-Pl 9, C-PX, C-P27, and C-P34). It is possible that apparently

unzoned garnets in other xenoliths may have been zoned prior to kelyphitization, but

evidence has been obscured by the kelyphitic assemblage. Most of the detected çarnet

Na20 (wt%) in Clinopyroxene

a 4- c ai 8 3.5: L X

3' s .- 0 2.5: s . - - 2 1 s CI

3 - 1.5: Ô L Ir O 0.5<

0 -

a C a A4-P5, Al-P8, A4-P11,

O 0 C-P26, and C-P34 have 0, A >r Fe-enriched clinopyroxene. (1 O

O Tliese xenoliths are also Fe- C .- - O cbO A I -P8 enriched in al1 other primary O O - 0.9 silicates. AI-PI O is altered.

0.96

0.33 0.37 0.41 0.45 0.49 Ca/(Ca+Mg+Fe) in Clinopyroxene

Figure 3.3 - Cr@, vs Ea,O in Clinopyroxene

Cores of clinopyroxene have p o s i t ~ e correlation behveeii Cr and Na. Note that the chromite lherzolite B-P3 lias elevated Cr content of clinop yroxene

" EbP3

O

O O

0 &O O

O Ct3 O O

0 0 O

0 0°80 " d o AI 0A Al

80 0 A

Figure 3.4 - Mgl(Mg+Fe) vs. Cal(Ca+Mg+Fe) in Clinopyroxene

A A4 V B30

v .

; 1 , , q , , 1 , , , , 1 . ,

O Cl4 l

O Al A A4

- Ho110 IV = Rim

O Cl4 l2 -1 Zonation in C 14 Gamet 2 vs Cr203

Figure 3.5 (a) - Zonation in Cl4 Garnet Ti02 vs. Cr@, Accordin; to the classification of Smith and Boyd (1997). zonation patterns in C-Pl 0, C-P 17. C-P 19. and C-P27 correspond to Type 1 (rim-enrichment in Ti, decrease in Cr), C-PI is Type IV (slight zonation in Ti sympathetic to Cr). The remainder of C 14 garnets are relatively homogeneous and correspond to Type II.

Zonationin Al , A4, B30 Gamet Ti2 vs Cr203

Figure 3.5 (b) - Zonation in A l , A4 and B30 Garnet TiO, vs. Cr203 Accordinç to the classification of Smith and Boyd (1992), zonation patterns in A1 -P 17, A4-P3, and A4-P5, correspond to Type I (rim-enrichment in Ti, decrease in Cr), A 1 -P 1 O is Type III (decrease in Cr, no change in Ti), AI -Pl and A4-P 1 3 are Type IV (slight zonation in Ti sympathetic to Cr). The remainder of A 1, A4, and B3 O garnets are relatively homogeneous and correspond to Type II.

zonation is reflected in Ti a n d h Cr composition (Figure 3.5). Eight ofthe zoned

xenoliths' gamets (Al-P17, A4-P3, A4-P5, C-PIO, C-P17, C-P19, C-P25, and C-P27)

have sigruficant increases in Ti and decreases in Cr fiom core to margin (except C-P25

which hasno change in Cr). Gamets in xenoliths AI-Pl, A4-P13, and C-Pl have slishht

decreases in Ti sympathetic to decreases in Cr. Al-Pl0 gamet is rim-reduced in Cr with

no Ti change. Gamet in C-P34 has reduced Mg# fiom core to margin with no sikgdïcant

change in Cr or Ti. With regard to the classification of Smith and Boyd (1992) these

zonation patterns correspond to their Type 1 (increasiig Ti and other incompatibles), Type

III (no change in Ti with decreasiig Cr fiom core to margin), Type IV (slight decrease in

Ti sympathetic to change in Cr), and Type VI (zonation not related to Cr or Ti). The

remainder of the gamet peridotite xenoiiths from the Kiridand Lake suite have relatively

unzoned gamets and correspond to Type II. ûther patterns detected include increasiiig

Na, Fe and Ai, and decreasing Ca. Mg# increases from core to margin in Al -P I O and A 1 - P17, and decreases in A4-P5 and C-P34.

Xenolith A4-P5 displays marked chemical zonation of gamets for all detected

elements. Traverses were made across a gamet in A4-P5 to better define the zonation

(Plate 3.1 and Figure 3.6). The gamet is concentrically zoned with decreased Mg and Cr,

and increased Fe, Ti, Na, and Mn fiom core to margin. Zonation patterns of Ca, Al, Si

and Cr are generally concentric but heterogenous, wherein the lower left portion of the

grain (shown in Plate 3.1) is enriched in Ca and reduced in Al and Si compared to the core

composition, and the upper right portion of the grain is reduced in Ca and enriched in Al

relative to the core composition. Cr content varies inversely fiom Al, but the core Cr

cornponent is higlier than al1 r i tn conipositions (Figure 3.6). This heterogeneous zonation

may be indicative of 2 separate metasomatic events. An initial event may have generated

the concentric zoiiatioii pattern of aii elements. A second metasomatic event inay have

affected only part oftlie grain (eitlier the upper riglit or lower lefi portion oftlie grain in

Figure 3.6) and thus ody partially overpritited the initial event.

Plnte 3.1 Pliotoiiiicrogri~pli of Cbeiiiiçiilly Zuiied Gsrnet froni Xeiiotitli AJ-PS Note the gnrilei lias a vcry tliiii kelypliitic riiii. Eqiiilibratioii teriiperatiire aiicl prcssiii-e ~iiiliziiig gasiiet ririi for oliviiic-gariict tliciinoiiietq aiid Al-in-opx baroiiictry 1 190- 12-30 "C', 43-53 kbar. C'liciiiical data i s inbrtlaierl i i i Appciidrx C. Traverse tiiirs aiid aiialysis poiiits Iloiii wliicli tlic coiitoiired prolilcs iii I3yirc 3.0 wcrc gctisrated arc prcsciited iii Appciitlix C.

Gi~iticy ( 1984) fouiitl tli;it 85% of ;il1 pcriciotite suite giii-xts iiicliidcd i ~ i diaiii»iitl

wcre low iii calçiliiii iiiid lie dcliiictl iiii "85%-hic" oii ;i C;iO vs. Ci.!O, 1ii1i;iiy plot (Figliit

3.7). 'l'liis liiie i-oliglily correl;itcs to tlic lowcr liiiiit ot'tlic ilici~ilitc licld dciiiicd Iiy tlic

Kiik1;iiitl L,iike g;iriict Ilieizolites. 0iiIy oiic of the sis Iiiiizliiirgiiic g;iilicts (A 1 - 1'7) plots

iii tlic Iiiiixbiiigite iield as ;i low-C;t g;iilict. Tlic Iiigli Cii:C'r ialio i i i ilic giisiict of'tlic o~lici.

fivc Iiiirzl~ui~gitcs. al1 ol'wliiçli plot iii tlic Iiici~zolitc lield. iiitliciitcs t l i r i ~ tlicv iniiy Iiiivc

FeO*

Figure 3.6 Zoiiing Patterns in Garnet from Xenolith 84-P5 Refer to photomicroçraph Plate 3.1. Note that zonation is concentric and symmetrical with regard t o FeO, TiO?, and MçO, and asyrninetric in Cr,O,, A120,, and Cao.

Harzburgite

O 2 4 6 8 10 12 14 Cr203 (wt%) in Garnet

Al Ganiet llierz~lite

A1 Gamet HaIiburgire

A A4 Gamet i i iml i te

7 B30 Gamet Lhemliie

O C 14 Ganiet Lheiaobte

O C 14 Chrode Gamet Lhemlite

CI4 GanietHarzblngite

Figure 3.7 Lher~oliteNar~burgite Discrimination Plot - C a 0 (wtit%) vs M g 0 (ivt%) for Carnets 'I'lic 85% line is delincd as 85% of al1 peridoiite-suite gamet inclusions in d imonds plot helow it (Gumc!.. 1983). 'l'lie apparent base of the Kirkland Lake ihe~zolite fidd is roughl!. dcfined hy tlic 85% linc. Notc that al1 but one hanburgitr (A1 4'7) plots \vitIlin the lhemcilitc îkld

3.2.5 Chromite

Both m t l e equilibrated and secondaq chromites (the lztter associated vd!i

kelyphitized gamets) were analyzed in this study. Fe3+ values were calculated

stoichiometrically based on the method of Droop (1987). Secondary kelyphite-associated

chromites are typically readily distinguished petrographically fiom mantle-equilibrated

chromites. Generally, secondary chromites have Al,03 27-45% and CrzO, < 38%

(tabulated in Appendk C). Conversely, m a d e equilibrated chornites have A,03 < 13%

and Cr.0, > 40% (Figure 3.8).

Disthguishing between prirnary and metasomatic chromite petrographically was

difficult in xenoliths, particularly those in whicli cliromite is both discrete (primary?), and

intergrown with phlogopite (metasomatic) replacing gamet. M a r y (apparently)

chromites generally have Ti0, <l.S%. An exception is a primary chromite included in a

discrete clinopyroxene grain (in xenoiith C-P2) which has 4.5% TiO,. Metasomatic

chromites have TiOz 0.33-7.81% (Figure 3.9). Two analyses with TiOz contents of 6.15%

and 7.8% (C-P27 and C-P26 respectively) are of chromite lameilae exsoived from

tnetasomatic ilmenite.

In addition, chrornite compositions are quite variable in many xenoliths, and

individual grains are coininonly zoued. Details of chromite zonation were not determined.

3.2.6 Umenite

ninenite was analyzed in five xenofths, C-P3, C-P17, C-P26, C-P27 and C-P34.

Analyses were generated by the calibratioii for cliromite wliich may have introduced small

accuracy deviations. Detailed statistical analysis was not doiie.

Ihnenite compositions range fiom 13.0- 14.6 wt% MgO, 25.4-3 1 . 1 % F e 0 (total),

5 1.7-56.8% TiO-,, 1.37-4.93% Ci,O,, and 0.03-0.96% A120,. It is notable that tlie lowest

Cr content of 1.37% is fiom an ilmenite with exsolution lamellae of chromite (xenolitli C-

P26). These compositions are generally within the range of ilmenite in xenoliths from tlie

Matsoku kimberlite in Lesotho (Harte et al., 1987).

Figure 3.8 Cliromite Discrimination Plot - Cr,O, (wt%) vs AI,O, (wt%) for Chromite Most cliromite was distlliguislied petrogaphically. Mantle-equilibrated chromite overlap but are generally <20% A120,. Kelypliitic chromite generally havelow Fe,O, (<7%) and hi& N20, (>270/0). Dotted line ouilims the field of primary chrornites, daslied h ie outlines the field of kely phitic cliromites.

25 30 35 40 45 50 Cr203 (wt%) in Chromite

Figure 3.9 Chromite Discrimination Plot - TiO, (wt%) vs Cr,O, (wt%) for Chrornitc Geiierally kelyphitic chromite is low in CIO, (09%) . Primary cluoiiiite is geiierally low iii TiO- (< l .S%) witli the exception of C-PZ wliich has elevated TiOz (4.5%). Tliiç chromite is an hclusion in clbiopyroxeiir. Dotted line outliiies the field of primary chromites. daslied line outlines the field of kelypliitic chro~nitzs.

3.3 Assessrnent o f f r imaq Equiiibrium Assenihlnges

Two xenolith assemblages (A4-P9 and Al-P 1 O) were identified both

petrographically and through chemical zonation to have non-equilibrated orthopyrosenes.

The clinopyroxenes in xenoliths A4-P6. C-P3. and C-P34 are entirely sieve-testured (due

to secondary alteration) and therefore are not in equilibrium with the primary garnet

lherzolite assemblage.

In assessing chemical correlation between minerals in garnet lherzolite xenolirhs in

kimberlite frorn northern Lesotho, Finnerty and Boyd ( 1 984) compared ratios of major

element Fe, Mg, and Ca among olivine, orthopyroxene, clinopyroxene, and garnet. FeO-

Mg0 partitioning between garnet and olivine are correlated with Ca-Mg partitioning in

garnet and orthopyroxene Figure 3.10. Xenoliths C-P34 and C-P26 (also A4-P5 and C-

P27 if core compositions of garnet are used) plot below the equilibration trend of Lesotho

lherzolites of Finnerty and Boyd (1 9841, and xenolith C-P2 plots above the trend. The

remainder of the xenoliths correspond well with the equilibrium trend of Finnerty and

Boyd (1 984). Rim compositions of garnets for xenoliths C-P27 and A4-P5 lie on the

equilibration trend . In Figure 3.1 1 Ca-Mg ratios of clinopyroxene are compared with the

Ca-Mg ratios of garnet-orthopyroxene exchançe and xenoliths C-P3, A4-P9, A4-P6, and

Al -P 10 plot off of the equilibration trend Therefore, these data are not acceptable for

use in pressure-temperature calculations for which equilibrated assemblages are required.

3.2 O

a, . E q & h Trend of gamet IhenoPes h m Lesotho !z .- > . - (Finne@ aud Boyd, 1984) - O

O O 2.8-

s + C-l?? O a, LL V 5 2.4- a,

5 a,

E C3 - h 2- O

f d a, LL 5 I .6- a, k

1 6 20 30 40 [Ca/(C a+Mg)] Garnetl[Ca/(Ca+Mg)] Orthopyroxene

Figure 3.10 Equilibration Discrimination - Carnet-olivine vs. Carnet-Orthopyroxene The solid line is comparable to the eqiiilibrium treiid of Lesotho gamet IIierzolites (Firinerty and Boyd, 1984). Xeiiolitlis C-P34, C-P26 and C-PI plot off of the equilibratioii treiid. The cores o f mned gamets iii A4-P5 aiid C-P27 plot below the eqiiilibration trend and the inargiris of gamets appear 10 be in equilibrated witli orthopyroxene, and olivine.

Equiiibh Trend of gmet niemlites h m Lesotho (Fhm and Boyd, 1984)

O 10 20 30 40 50 [Cal(Ca+Mg)] Garnetl[Ca/(Ca+Mg)] Orthopyroxene

Figure 3.11 Equilibration Discrimination - Clinopyroxene vs. Carnet-Orthopyroxene The solid Iule is comparable to Uie equilibrium trend of Lesotho gamet lherzolites (Finnerty aiid Boyd, 1981). Xziiolitiis C-P3, A4-P9, A4-P6, and Al-PI0 plot off of the equilibriuin trend.

CBAFTER 4

GEOTHERMOBAROMETRY


Geothermobarometric equilibration conditions have been calculated for al1 ganiet

bearing xenoliths. Calculations utilize the chemical compositions of equilibrated phases to

estirnate the pressure and temperature of equilibration.

Accepted geothemobarometers have been reviewed in Finnerty and Boyd (1987)

and Brey and Kohler (1 990). Pressure calculations utilized in this study are based on the

Al content of orthopyroxene in equiiibrium with gamet (e.g. Brey et al., 1990,

MacGregor, 1974, Nickel and Green, 1985). Temperature calculations are based on the

olivine-ganiet and two-pyroxene thennotneters of O'Neill and Wood (1979) and Brey et

al. ( 1990) respectively (with the O'NeiU ( 198 1 ) correction applied to the O'Neill aiid

Wood (1979) thermometer) An independent evaluation of geotl~ennobaroinetric methods

was made to ensure that the prefened methods conform to published data for graphite atid

diatnond bearing gamet Iherzolites. The chosen geothermobarometric methods are

considered to be reliable as tliey place graphite- and diamond-bearing peridotite xenoliths

into, within error limits, their respective stability fields (as defined by the Kennedy and

Kennedy (1 976) diamond-graphite boundary (Figure 4.1)). Details of each calculatioii

method are presented in Appendir; D. A brief discussion of each metliod is presented iii

Section 4.2.

4.2 Calculations

4.2.1 Tlierniometers

Tlie tliermometer ofBrey et al . (1990). Iiereafier referred to as TBKN, is a two-

pyroseiie tlierrnoineter usefiil ai temperatures > 900 "C and pressures of 10-60 kbar. The

method is based on temperature-dependent CaiMg partitioning between clinopyroxeiie

and orthopyroxene. Compositiorial variables involved in TBKW calculatioiis iilclude Fe,

Mg, Ca, and Na contents of ortliopyroxeiie and clinopyroxeiie. This rnetliod is usehl iii

calculating temperatures for lherzolites, but not liarzburgites (clinopyroxene absent). Brey

aiid Kohler ( 1990) claimed that TBKN is accurate to within 15 "C for natural assemblages.

TBKN cannot be applied to the lherzolite xenoliths in which clinopyroxene has been

altered (i.e. clinopyroxene is disequilibrated fiom orthopyroxene) due to the increase of Ca

and reduction of Al and Na compoiients. Fresh clinopyroxene core compositions were

used to avoid the effects of alteration on temperature results.

l i e thermometer of OWeill and Wood ( 1979) with the O'Neill (1 98 1) correction.

hereafter referred to as TOW79, is based on temperature dependent Fe-Mg partitioning

betweeii co-existing olivine and gamet, and Ca contents of gamet, between 900°C and

1400 "C at pressures up to 60 kbar. This themorneter is utilized in calculating

temperatures for gamet-olivine assemblages. and is particularly usefiil for harzburgites

(lacking clinopyroxene) to whicli two-pyroseiie thennometers are iiot viable. O'Neill and

Wood (1979) suggest temperature estimates below 1300°C are accurate to within 60 OC,

and errors may be larger at temperatures above 1300°C. Finnerty and Boyd (1984)

suggest that errors in this thermometer may anse due t o uncertainty in estimating Fe3'/Fe"

compositions in silicates at hi& temperature and pressure.

4.2.2 Barometers

l i e barometer of MacGregor (1974), hereafier caiied PMC74, is based on the

temperature depeudence of Al,O, partitioning between orthopyroxene in equilibrium Gtli

ganiet at temperatures 900-1 600 OC and pressures > 15 kbar in experimental assemblages

of the Mg0-AIzO,-Si0, system. The author suggested tliat values are generally accurate

to withiii 5%. Brey and Koliler (1990) stated that this metliod is unsuitable for applicatioii

to iiatural assemblages due to oversimplificatioli. Fiiinerty and Boyd (1987) prefer

PMC74 as it provides a good fit of data to the diamolid-graphite stability field. As

opposed to the other barometers used in this study, PMC74 permits calculation of

pressures for lherzolite xe~iolitlis witli altered ganiet.

The barometer ofNicliel and Green (1985), liereafier called PNG85, modeIs Cr

escliange effects betweeii orthopyroxeue and ganiet in the Cr,O,-MgO-AI,O,-SiOZ systerii

at temperatures 1000- 1400 Y and pressures 20-40 kbar. Compositional variables

involved in their equations include Cr, Mg, Fe, Al in orthopyroxene and Cr, Mg, Fe, Al,

and Ca in gamet. Suggested error is estimated at 5 kbar, although Brey and Kohler

(1990) indicated that error mar,& of PNG85 widen at liigh temperatures.

The barorneter of Brey et al. (1990), hereafier termed PBKN, models Al content

of orthopyroxene in equilibrium Mt11 gamet with corrections involving site occupaiicy

effects of other elements in orthopyroxene. Compositional variables used in PBKN

include Ca, Mg, Fe, Cr, Al, and Mn of gamet, and Ca, Mg, Fe, Cr, Al, Mn, and Na of

orthopyroxene. The authors estimated that errors in PBKN-calculated pressure,

depending on the thermometer utilized, range from 5-7 kbar.

4.3 Results

AU pressures and temperatures were calculated with the software program PT of

Brey (unpublished) for al1 oftbe gamet-beating xenoliths in the present study. The two

thennometers utilized in this study, TOW79 and TBKN, are iteratively paired in the P T

program with three barometers, PMC74, PNG85, and PBKN yielding six

thermobarometer combinations: TOW79-PMC74, TOW79-PNGS5, TOW79-PBKN,

TBKN-PMC74, TBKN-PNG85, and TBKN-PBKN. The first three thermobarometric

pairs are used for gamet lherzolites and gamet harzburgites, and the latter three are only

viable for garnet lherzolites.

Pressures and temperatures were also calculated for several published mineral

chernical analyses of diamond and graphite-bearing xenoliths (Figure 4.1 and Table 4.1 b).

Pressures and temperatures are not presented for xenoliths A 1 -P 1 O, A4-P9, aiid C-P34

due to evidence that these xenolitlis do tiot have equilibrated assemblages. Two-yyrosene

tliei-iiionietiy was iiot used for ganiet Iiarzburgites Al-P7, Al-Pl 5, C-P24 and C-P34 due

to the absence of cluiopyroxeiie. and is not used for xenoliths A+P6 and C-P2 due to

secondary alteration of clinopyroxene. Gamet-olivine thennoinetry is not used for

xenolith C-P26 due to evidence tliat olivine and gamet are 11ot il] equilibnum (Figure

3.10). Results of al1 pressure and temperature calculations are presetited iii Table 4.1.

Pressure-temperature plots oftlie garnet peridotite suite are presented in Figure 4.2 a-h.

The Kirkland Lake ganiet peridotite xenolitli suite correlates with the conductive

Table 4.1 (a) - Pressure and Temperature for Kirkland Lake Garnet Peridoites Xenolith (Rock Typ 1 Texture (TBKN PBKN (TBKN PNGSS

Al-PI GL tcd 897 37.9 902 41.2 Al-P6 GL c 788 31.1 793 35.0

A ~ - P I 2 1 GL 1 tcd 1 12 14 49.5 1 12 15 49.6 A4-Pl3 GL tcd 1243 59.4 1243 59.7

B-Pl GL P 1376 58.9 1369 56.2

C-P3 GL tcd 1029 41.3 1037 46.3 C-P4 CGL c 885 32.6 892 36.9 ' C-P5 CL tcd 986 39.7 992 43.5- C-P6 CL tcd 1030 43.9 1076 48.9

1 C-P9 1 GL 1 tcd 1 1036 43.1 1 1041 45.9

Table 4.1 (a) - Pressure and Temperature for Kirkland Lake Garnet Peridoites Xenolith I ~ o c l c Typ 1 Textiire ~ T B K N PBKN ~ T B K N ~ ~ ~ 8 5 1 TBKN ~ ~ ~ 7 4 ~ 0 ~ 7 9 PBKN 1 ~ 0 ~ 7 9 PNGXS 1 ~ 0 ~ 7 9 PMC74

C-P33 GL c 686 20.3 692 25.1 691 24.3 773 24.8 806 30.7 1 8 1 4 32.3 C-P35 GH tcd * * * * * * 1107 41.6 i l24 45.3 1 1145 50.3

C-PI0 C-PI 1 C-Pl2 C-Pl3

Table 4.1 a) Pressures and Teniperatures for Kirkland Lake Xenolith Suite Thennonieters and barometers are described in text. Symbols and abbreviatioiis iised in table include: Rock Types: GL=garnet Iherzolite, CGL=cliromite-bearing ganiet Iherzolite, GH=gamet harzburgite Textures: c=coarse, tcd- transitional coarse to defomed, p=porpliyroclastic, mp=mosaic porphyroclastic Symbols: *=unable to calciilate 2-px thennometer due to lack of clinopyroxene, **=unable to calculate

GL CGL GL GL

2-ps thennometer due to secondary alteration of 6esh clinopyroxeiie, ***=unable to caIculate olivine- ganiet themiorneter

tcd c c c

IO88 48.1 938 35.4 932 39.2 911 37.8

1088 48.0 947 40.9 937 42.7 919 42.8

1090 49.4 949 42.0 938 43.0 917 41.9

1172 54.6 929 40.7 896 40.2 1041 50.3

1167 53.5 1 1162 52.2 889 32.4 874 35.7 ! O 1 2 43.6

926 39.9 898 40.6 1030 47.6

m . . ? ? - m . ? . m C I I - O O O ' o a P I W d d c l c l * ' n ' D \ D

E E E E 0 0 0 0 c t L t & c t ; c o u 0 ,I .C W .i: - - - - o o o c 2 t? t? 2 2 2 2 2 C - d l = =

- /

600 / I I

15 35 55 Pressure (kbar)

1600

0 15 35

55 IPressure)

TBKN 1 PMC 73

/

TBKN PNGRS

600 15 35 5 5

Pressure (kbar)

I U W I Y

I 4 O 0 - PBKN

1200 - / O / : , /O

1 O00 -

d O / 600 I I

15 35 55 7 5 Pressure (kbar)

1600 /

Pressure (kbar)

l 6 O 0 0

15 35 55 75 Pressure (kbar)

Figure 4.1 - kessure/Temperature Plots for Diamoiid- and Graphite-beariiie Xenolitlis Symbols: circies represent graphite-bearing xenoiiths; diamonds represent diamond- beariiig xeiiolitlis; solid hie is diamoiid graphite boundary of Ketiiiedy and Kennedy (1976), dashed curve is 40mW/m2 steady-state geotlierm of Pollack and Cliapmati (1976). Data is tabulated in Table 4. I(b).

1375 Temperature Method BKN

with Pressure Method BKN

1275 Applied to Cl4 Xenoliths /

/

51175 / 6 a,

/'

n V

1075 3 U

m

975

? 875

775 / /

675 / , I I I I I 1 . 1

25 30 35 40 45 50 55 60 65 Pressure (kbar)

Cl4 Coarsa Garnet Lherzolite

Cl4 Transitional Coarse to Deformed Garnet Lherzolitr

Cl4 Deforrned Garnet Lherzolitr

Cl4 Coarse Chromite-bearing Garnet Lherzolice

Cl4 Transitional Coarse to Deformed Chromite-bearing

Garnet Lherzolice

Figure 4.2 ri) PressureRemperature Plot TBKN vs. PBKN for Cl4 Tcmperaturc calculated witli tlie BKN ttieniiometer, pressure calculated with BKN barometer. The solid line is tlie diarnoiid-graphite transition of Kennedy aiid Kennedy (1976), dashed line is the 40mWim2 conductive geotlierm of Pollack and Cliapniaii ( 1 977).

T e r n p e r s t u r e N e t h o d 1 3 7 5 -

BKN w i t h Pressure

- Method BKN Applied to

1 2 7 5 - A l , Ac, a n d B30

X o n o l i t h s

- " 1 1 7 5 -

bi al

2 al 1 0 7 5 - Li 3 ci m Li al 9 7 5 - a 5 B

8 7 5 -

/ 7 7 5 - h

/'

6 7 5 ,

1 . 1 I I 1 ' 1 ' 1 2 0 25 3 0 3 5 4 0 4 5 5 0 55 6 0

P r e s s u r e ( k b a r )

Al Coarçe Garnet L h e r i o l l t e

]&) Aï Tranç i t iona l Coarse t o Deformed Gamet L h e r z o l i t e

O AZ De fonnid Gamet Lherzol i t e

L] A4 Tranç i t iona l Coarçe t o Deformed Garnet Lherzo l i t e

A4 Defonned Gamet Lherzo l i t e

A B3C Deformed Gürnet L h e r z o l i t e

Figure 4.2 b) Pressure~Tcrnperature Plot TBKN vs. PBKN for A l , A4, and B30 Teinperatirre calculated witli the BKN thermoineter, pressure calculated with BKN barorneter. The solid luie is tlic diamond-gaphite transitioii of Keiiiiedy and Kennedy (1 976). daslied line is the 40mW/m2 conductive geotlienn of Pollack and Cliaprnaii (1 977).

1375-

1275- Temperature Method BKN .with Pressure Method N G 8 5

1175- Applird to Cl4 Xenoliths

1 O75 -

975 -

875 - /

775 - / /

675 I I I I I I I I I

25 30 35 40 45 50 55 60 65 Pressure (kbar)

Cl4 Coarse Garnet Lherzolite

Cl4 Transitional Coarse to Deformed Garnet Lherzolité

C l 4 Deformed Garnec Lherzolite

C l 4 Coarse Chromite-bearing Garnet Lherzolite

Cl4 Transitional Coarse to Deformed Chromite-bearing

Garnet Lherzolite

Figure 4.2 c) PressurelTemperature Plot TBKN vs. PNG85 for Cl4 Teinperahire calculated witli the BKN thennorneter, pressure calculated with Ne85 barorneter. n ie solid lins is the diamolid-graphite transition of Kennedy arid Kennedy ( 1976), dashed line is the 40mWhn2 conductive geotlienn of Pollack and Cliapmari (1977).

1375- BKN with Pressure - Method NG85 Applied

1275- t o Al, A4, and B30 Xenoliths

ô 1175- 0, al 0

1075- 3 CI

E E 975- E

875 -

775 -

675 I I I I I I I

20 25 30 35 40 45 50 55 60 65 Pressure (kbar)

Aï Coarse Gamet Lherzolite

@ Aï Transitional Coarse to Deformed Garnet Lherzo l i te

O Aï Defomed Gamet Lherzolite

fj A4 Transitional Coarse to Defomed Gamet Lherzolite

[7 A4 Defomed Garnet Lherzolite

A E30 Deformed Gamet Lherzolite

Figure 4.2 d) Pressure/Temperature Plot TBKN vs. PNG85 for A l , A4, and E30 Temperature calcrilated witli the BKN thennoiiieter, pressure calculated witti NG85 baroineter Tlis solid h ie is the diarnond-gaphite transition of Iietitiedy and Kennedy (I976), dashed h i e is tlic 40mW/m2 conductive geothem of Pollack and Chapman (1977).

1 3 7 5 -

12" - Temperature Method BKN /

.with Pressure Method M C 7 4 - u 1175 Applied to Cl4 Xenoliths

- Y1 a, G - , 1075- J.4 3 w m ii ai 9 7 5 - a L5 c-

8 7 5 -

/ 775- /

/ 6 7 5 ,

1 . 1 ' 1 1 ' I 20 215 20 315 40 45 50 55 60 6'

Pressure i kbar)

Cl4 Coarse Garnet Lherzolite

@ Cl4 Transitional Coarse to Deformod Garnet Lherzolite

O Cl4 Deformed Garnet Lherzolite

Cl4 Coarse Chromite-bearing Garnet Lherzolite

a Cl4 Transitional Coarse to Deforrned Chromite-bearing Garnet Lherzolite

Figure 3.2 e) Pressure/Temperature Plot TBKN vs. PILlC74 for Cl4 Temperature calculated witli the BKN tlienno~ueter. pressure calculated with MC74 baroineter. The solid h i e is the diamolid-gapliite transition of Keniiedy and Keimedy (1976). dashed hie is the 401nW11n' cotiductive geotlienn of Pollack atid Cliapinati ( 1977).

1375 -

1275 - Temperature Method BKN with Pressure

- Method MC74 Applied y1175- to Al, A4, and830 m a, -0

Xenol i ths - . 1075- 4 7 4J a L4 ai 9 7 5 - a 5 b

875 -

775-

/ ' 675 /

I I I 1 l l I 20 25 30 35 40 45 5 0 5 5 60

Pressure [ k b e r )

() Al Coarse Garnet Lherzolite

@ Al Transitional Coarse to Deformed Garnet Lherzolite

O Al Deforrned Garnet Lherzolite

Q] A4 Transitional Coarsr to Deformed Garnet Lherzolite

II7] A4 Deformed Garnet Lherzolite

A B30 Deformod G a r n t t Lherzolite

Figure 4.2 f) Pressure/Teniperature Plot TBKN vs. PMC74 for A l , A4, and B30 Temperature calculated witli tlie BLN tliennoineter. pressure calculated witti MC74 baroinetcr. Tlir: solid line is tlie diainoiid-graphite traiisitioti of Kennedy and Kennedy ( 1976). daslied liiie is the 40inW/m2 coiiductive geotlienii of Pollack aiid Chap~ilan (1 977).

20 25 30 35 40 45 50 55 60 65 Pressure (kbar)

Cl4 Coarse Gamet Lherzolite

@ C14 Transitional Coarse to Defomed Gamet Lherzoiite

O C14 Deformeci Gamet Lherzolite

C14 Coarse Ckromite-bearing G a m e t Lherzolite

Cl4 Transitional Coarse to Deforneci Chromite-bearing G a m e t Lherroli~e

A Cl4 Coarse Gamet Harzburgite

A Cl4 Transi tional Coarse to De f ormed Gamet Harzburgite

1375-

1275-

' 1175- cn a, n V

a, 1075- L 3 C

2 a 975- E e

875 -

775 -

675

Figure 4.2 g) Pressure/Teniperature Plot TOW79 vs. P B W for Cl4 Teniperaturs calculated witli the OW79 themoineter, pressure calculated witli BKN barorneter. The solid h i e is the diamoiid-graphite trarisitioii of Kennedy aiid Kennedy (1976), daslied liiie is the 40iiiW/iii' coriductive geotlienn of Pollack and Cliapinari ( 1 977).

Dlamond

Temperature Method 0W79 /'

w i c h Pressure Methoà BKN /

Appiied t o Ci4 Xenoliths 9'

/

/ ; I I ' I I ' I I I

Temperature Method 0W79 with Pressure

Method BKN Applied to Al, A4, and B30 Xenoliths

O

20 25 30 35 40 45 50 55 60 65 Pressure (kbar)

Al Coarçe Garnet Lherzolite

@ A l Transitional Coarçe to Deforrned Garnet Lherzolite

O Al Deformed Garnet Lherzolite

Al Coarse Garnet Harzburgite

Al Deforrned Garnet Harzburgite

A4 Transitional Coarçe to Deforrned Garnet Lherzolite

A4 Deforrned Garnet Lherzolite

A4 Coarçe Chrornite-bearing Garnet Lherzolite

A B30 Deforrned Garnet Lherzolite

Figure 1.2 h) Pressure/Temperature Plot TOW79 vs. PBKN for A l , A4, and B30 Temperature calculated witli the OW79 tliennometer, pressure calculated with BKN barorneter. The solid h i e is the diamorid-gaphite traiisition of Kennedy and Ke~inedy ( 1976), daslied liiie is the 40inW/rn2 conductive geotlierm of Pollack aiid Cliapmaii ( 1 977).

Temperature Method OW79 I with Pressur? Method N G 9 5 / Applied to Cl4 Xenoliths / /

20 25 30 35 40 45 50 55 60 65 Pressure (kbar)

Cl4 Coarse Gamet Lherzolite

@ C l 4 Transitional Coarse to Defonned Gamet Lherzolite

O Cl4 Defonned Gamet Lberzolite

Cl4 Coarse Chornite-bearing Gamet Lhertoli te

Cl4 Transitional Coarse to Daformeci Chrornite-bearing Garnet Lherzol

Cl4 Coarse Garnet Harzburgite

A Cl4 Transitional Coarse to Defomed Gamet Harzburgite

Figure 4.2 i) Pressure/Temperature Plot TQW79 vs. PNG85 for C l 4 Teniparahire calciilated with the 0W79 themorneter, pressure calculated with NG85 baroineter. The solid Iule is the diamond-graphite transition of Kennedy and Kennedy (1976). daslied Iliie is the 40inW/tn2 coiiductive geotlierm of Pollack and Chaprnan (1977).

Tempora tu r? Method 0W79

~ i t h Pressure Method N G 8 5 / * / 4pplied to Al, A4, and

330 Xenoliths / /O

20 25 30 35 40 45 50 55 60 65 Pressure (kbar)

0 Al Coarse Gamet Lherzolite @ Al Transitional Coarse to Deformed Gamet Lherzolite

0 A1 Deformed Gamet Lherzolite

Al Coarçe Garnet Harzburgi te

v Fii Defonned Gamet Harzburgite

0 A4 Transi t i o n ~ l Coarse to Do£ ormed Gamet Lhe r -ml i te

a A? Defonned Gamet Lherzolite

b A4 Coarçc Chromite-bearing Gamet Lherzoli te

A 830 Defoïmed Garnet Lherzolite

Figure 4.2 j) PressureA'emperature Plot TOW79 vs. PN685 for Al , .44, and B30 Temperature calculated witli the 0 W 7 9 tliennoineter, pressure calciilated witli NGS5 bamiieter. The solid line is the diamoiid-graphite transition of Keniiedy and Kennedy (1976). daslizd h i e is the 10mWim' conductive çeotlienn of Pollack and Cliapinaii (1977).

Graphl t e

/'

Diamond '3751 1275 / Ternperature Msthod OW79 /

20 25 30 35 40 45 50 55 60 65 Pressure (kbar)

Cl4 Coarse Gamet Lherzo l i t e

@ C14 T r a n s i t i o n a l Coarse t o Deformed Garnet L h e r z o l i t e

0 Cl4 Deiormed Gamet Lherzo l i t e

C14 Coarçe Chroinite-bearing Garnet Lherzol i te

Cl4 T r a n s i t i o n a l Coarse to Deformcd Chrornite-bearing Garnet Lherzol i te

C14 Coarse Gamet Harzburgite

A Cl4 T r a n s i t i o n a l Coarse t o Deformed Garnet H a r z b u g i t e

Figure 4.2 k) PressurelTemperature Plot TOW79 vs. PMC74 for C l 4 Ternperaturr calculated with the OW79 thermomefer, pressure calculated with MC74 barorneter. The soiid line is the diamond-graphite transition of Kennedy and Kennedy (1 976). daslied line is the 40rnW/m2 conductive geotliemi of Pollack and Chapman (1977).

Temperature Method 0W79

w i t h Pressure Method MC74

Applied to Al, A G , and

B30 Xenoliths

20 25 30 35 40 45 50 55 60 65 Pressure (kbar)

Al Coarse Gamet Lherzolite

@ Al Transitional Coarse to Defonned Garnet Lherzolite

O Al Deformed Gamet Lherzolite

7 Al Coarçe Gamet Harzburgite

V Al Deformed Gamet Harzburgite

M Transitional Coarçe to Defonned Garnet Lherzolite

A4 Defomed Gamet Lherzolite

A4 Coarse Chrornite-bearing Gamet Lherzolite

A B O Deformed Garnet Lherzolite

Figure 4.2 1) Pressure/Temperature Plot TOW79 vs. PMC74 for Al , A4, and B30 Temperature calculated witli the 0W79 thennometer, pressure calculated witli MC74 baroineter. The solid line is the diamond-graphite transition of Kennedy and Kennedy (1 976), daslied line is the 40mWim2 conductive geothem of Pollack and Chapman ( 1977).

geothenn corresponding to a surface heat flow of 40aiW/m2 of Pollack and Chapmaii

(1977), over a wide raage of tenperature and pressure (- 675 O C - 1375 "C' 20-60 kbar) .

C 14 xenoliths yield predominately low to moderate temperatures and pressures (675 "C.

20-25 kbar to 1175-1200 O C , 50-55 kbar). A l , A4, and B30 xenoliths equilibrated at

moderate to hi& temperatures and pressures (>IO50 "C, 40 kbar), althougii 3 coarse

xenoliths and one transitional coarse to deformed xenolith equilibrated at lower

temperature and pressures. Xenolitiis from AI, A4 and B30 which equilibrated above 40-

45 kbar yield temperatures 100-200" above the 40mW/m2 geotherm. Al1 gamet

peridotites fiom C 14 lie on the 40mW/m2 geotherm.

Most defonned (iucluding trarisitional coarse to deformed, poryhyroclastic. and

mosaic porphyroclastic textures) xenoliths fiom the Kirlcland Lake suite equilibrated in the

diamond stability field as defined by the Kennedy and Kennedy (1976) graphiteldiarnoiid

univariant phase boundary. Four coarse xenolitlis fiom C 14 have also equilibrated iri the

diamond stability field.

There is no apparent correlation between equiiibration temperature and

metasomatism (modal andior csptic) witfiin the Kirkland Lake suite. Modally

metasotnatized xenoliths, predominately fiom C 14, al1 lie on the 40mW/m2 conductive

geotherm. Xenoliths fiom Al, A4 and B30 wliicli have csptically zoned gamets (rini-

enrichmerit iii Ti) yield temperatures above the 40mW/m2 conductive geotherm, yet

xenoliths fiom C 14 with cryptically zolied gamets plot aloug the 40inW1mz conductive

geothenn.

CBAPTER 5

DISCUSSION -4ND CONCLUSIONS

5.1 General Staternent

The Kirkland Lake xenolith suite represents a cross-section of the upper portion of

the upper mantle beneath the Superior craton during the Jurassic. Petrographic and

mineral chernical investigation of 56 xenoliths indicates that the xenoiith suite is dominated

by gamet Iherzolites (* chromite, phlogopite, ilmenite and sulphide; 44 xenolitlis) with a

lesser amount of gamet harzburgite (i sulphide; 4 xenoliths), chromite lherzolite (*

phlogopite, rutile and sulphide; 3 xenoiiths), lherzolite (3 xenoliths) and dunite (2

xenoliths). Xenoiith textures range fiom coarse (undeformed) to mosaic porphyroclastic

(strongly deformed). Evidence of modal metasomatism is present in 16 xenoliths fiom

Cl4 and 1 xenolith fiom A l , Zonation of gamets, indicative of cryptic metasomatic

processes, was identified in thirteen xenoliths. Althougli characteristics of secondary

processes, including serpentinization of olivine, kelyphitic nmming of garnet and sieve-

textured margins of ciinopyroxene, arc present in most xenoliths, most of the pendotite

xenoliths examined in this study have retained evidence of mantle equilibrium conditions

during and subsequent to entrainment by kimberlite magma. Xenoiiths equilibrated over a

wide range of temperatures and pressures (680- 1400°C, 20-60kbar), and coarse-textured

xenoliths fonn an array corresponding to a relatively cool 40mW/m2 steady-state

conductive geothem Defonned xeuoliths fiotn Cl4 are also on this gradient, but

deformed xenoliths f?om Al. A4, and B30 are inflected to hi& temperatures, 100- 150°C

above tlie 40mW/m2 steady-state geotlierm. Many of tlie xenoliths equilibrated within the

diainond stability field.

The results of the current study overlap and eqaiid upou a preliiniriary

investigation of I O peridotite xenoliths (6 of wliich contain gamet) from the C l 4

kirnberlite by Meyer et al. (1993). These autliors calculated equilibratioii temperatures

and pressures lyirig on a steady-state geotlienn of 40niW/rn; and ideutîfïed evidence of

incipient modal ruetasomatism in severai xenolitlis. l ie i r study also examitied a mosaic

porpliyroclastic garnet lherzolite fiom C 14. No mosaic porphyroclastic gamet pendotites

were found fiom C 14 in tlie current study.

5.2 Geothermal Gradients

A geothemal gradient corresponding to a surface heat flow of 40mW/m2 is

considered to be typical for stable continental lithosphere (Fhmerty and Boyd, 1987).

Meyer et al. (1994) suggested that the pressureltemperature array corresponding to a

su~face heat flow of 40mW/m2 for Cl4 xenoliths indicates that the sub-Kirkland Lake

upper mantle is positioned "non-marginal" with respect to the North Amencan craton.

Simiiar gradients have been calculated for numerous xenolith suites within, or marginal to'

stable Archean cratons. Locahies include Kimberley, West End. Finsch, Jagersfontein,

Premier, Northern Lesotho, Frank Smith and Koffiefontein kimberlites fiom the Kaapvaal

craton, Afiica (Finnerty and Boyd, 19871, Attawapiskat kimberlites within the northem

Superior craton in Canada (Scliulze and Iietman, 1997), and Udachnaya in Siberia

(Finnerty and Boyd, 1987). The xenolith suites from Premier, Northeni Lesotho, and

Frank Smith al1 have high temperature inflections above the 40mW/m2 geothemal

gradient.

Peridotite xenolith localities not directly associated with Archean cratons tend t o

have steeper (hotter) geothemal gradients. Jacques et al. (1990) examiiied gamet

peridotite xenoliths fiom the Argyle, Australia lamproite (within a Proterozoic orogenic

belt). These xenolitlis equilibrated on a 42mw/m2 geotherm and high temperature

xenoliths are inflected above the geothenn. Additionally, kimberlitic gamet peridotite

xenoliths fiom Somerset Island, Canada equiiibrated on a 44mW/m2 geotherm,

(Kjarsgaard and Peterson, 1992). Ganiet peridotite xenolitlis fiom an alnoite in Malaita.

Soiitli Pacific form an array with considerably lower pressures and luglier temperatures

tlian that of a conti~iental steady-state geotherm, reflectiug the more dynamic heat flow

regitue of 0cean.i~ crust (Fiimerty a d Boyd, 1987). Scliulze (1996b) presented similar

pressure/temperature values to tliose from Malaita for the Ile Bizard alnoite near

Montreal, Canada.

5.3 Textures and Equilibration Temperatures

At C 14, coarse-textured xenoliths generally have low to moderate equilibrium

temperatures and pressures, and defonned xeiioliths equilibrated at rnoderate to hi@

temperatures and pressures along the steady-state geotherm. The 3 coarse-textured _parnet

peridotites fiom A l and A4 (including the gamet harzburgite Al-P7) equilibrated at low

temperatures and pressures on the 40mW/m2 steady-state geotherm. Deformed xenoliths

from Al , A4 and B3O equilibrated at high temperatures and pressures within the diamond

stability field. Temperatures for these xenoliths are 100- 150°C above the 40rnw/rn2

steady-Gate geotherm. The transition horn low temperature (coarse) to high temperature

(deformed) xenoliths is thought by some workers to occur at the lithosphere-

asthenosphere boundary (Finnerty and Boyd, 1987). Alternatively, Schulze ( 1987) noted

that defomed gamet peridotites with high temperatures off of the steady-state geotherm

have equilibration pressures and temperatures which overlap the calculated crystallizatioii

temperatures of the Cr-poor oithopyroxene megacrysts in kimberlite fiom Hamilton

Braiich Kentucky. The author suggeaed that these high equilibration temperatures may

have been generated by heating fiom the parent magma to the Cr-poor megacryçt suite.

Schulze (1996a) identified the presence of Cr-poor megacryçts within Kirkland Lake

liùnberlites, and it is possible that the high temperature deformed gamet pendotites in Al.

A4, and B30 were heated by the parent magma of these megacrysts.

5.4 Modal Metasomatism

Modal metasomatism is evident within the Kirkland Lake xenolith suite, and

primarily noted in C 14 peridotite xenoliths. The dominant metasomatic assemblage is a

ganiet replacement assemblage compnsed of phlogopite + cliromite + clinopyroxene. This

metasomatic replacement of gamet requires an input of potassium which was, pnor to

metasomatisq not an abundant constituent in the gamet pendotite. Metasomatic ilmenite

is present in 5 of tlie modally metasomatized xenolitlis, indicating that the source

metasomatic fluids of these xenoliths were also eiiriched iii Ti. Summers ( 1989) described

the modal inetasomatism of tlie gamet peridotites at the Moiiastery kimberlite, South

&ca and noted that metasomatic ainphibole/plilogopite assemblages are preseiit in place

of inetasornatic clinopyroxene/phlogopite assemblages at low pressures and temperatures

(--GOkbar-900°C). The author suggested tliat tliis is approximately the upper limit for

edenitic amphibole. Al1 Kirkland Lake ganiet peridotites have equilibrated at temperatures

and pressures above the 30kbar-900°C arn~~hibo~e/clinopy~or;ene transition deflned by

Summers ( 1989). Metasomatized gamet peridotite xenoliths from the KirMand Lake suite

lack ampliibole and commonly contain clinopyroxene within the metasomatic asseii~blages

replacing ganiet.

5.5 Cryptic Metasomatism

Cryptic metasomatism in garnet pendotites is recognized in zonation of ganiets

whicli appear to have slower diffusion rates for some elements than the remainder of the

primary silicate assemblage (Smith and Boyd, 1989). This metasomatism is thouglit to

occur witliin a relatively short time. tens to thousands of years, pnor to entrainment in the

kimberlite magma (Boyd et al., 1993, Smith and Boyd, 1992). Cryptic mineral zonation is

interpreted by some authors to be caused by eitber introduced fluid, increase in

temperature, or by phases partially re-equilibrating due to deformational stress (Sinith and

Boyd, 1989). Schulze (1995) suggested that Ca-enrichment of gamet rims iu low-Ca

gamet harzburgite xeuoliths fiom Kimberley, South Africa, was caused by re-equilibration

of gamet harzburgite toward the predorninant diopside-saturated gamet lherzolite bulk

composition of the upper mantle. These Ca-zoned harzburgitic gamets have no zonation

witli respect to Ti, and Ti contents are considered low (Scliulze, 1995). Ca enriched-

garnet r ims were not recognized within the Kirkland Lake xenolith suite, although 3 of 4

petrographically-defined gamet harzburgites (clinopyroxene absent) examined in this

study have high-Ca unzoned ganiets and aypear to bave equilibrated with a lherzolite

assemblage. It is dficult to distuiguisli whetlier tliese rocks are actually clinopyro~eiie-

poor lherzolites or Ca-enriclied (tnetasomatized) harzburgites.

An additional type of cryptic metasornatism is recognked in Fe, Ti and other

incompatible-element enrichient of garnet rims. Unlike Ca eiirichment, tliere is no

obvious identifiable source for the influx of these incompatible elements. Smith and Boyd

(1 989) suggest that ganiet zonation, particularly noted in Ti-enriched gamet rims of

iiiflected gamet peridotites, is caused by silicate melt infiltration (metasomatism) with melt

temperatures ranging fiom 1200- 1400°C. Tliese authors also suggest that the hjgli

temperature silicate melts are the lieat source for high temperature inflected garnet

peridotites. They further note that Ti-rich zoried gamets are absent in coarse-tex-tured, iow

temperature gamet peridotites.

The present study identified incompatible element enriched gamets in both high

temperature gamet lherzolites (Al-P17, A4-P3, and A4-P5) and steady-state gamet

lherzolites (C-PIO, C-P17, C-P19, C-P25, and C-P27). These C 14 xenoliths range from

coarse-textured, undeformed (C-Pl9 and C-P27) to defonned (C-PIO, C-P17, and C-P25)

which is in contrast to the conclusion of Smith and Boyd (1989) that coarse, low

temperature gamet pendotites do not have Ti-enriclied rims. It can be concluded that the

cryptic metasomatic process that generates incompatible-element enrichment of gamet in

the upper mantle is not necessariiy directly associated with an increase in equilibration

temperatures.

If a silicate magma (e.g. the parent magma to the Cr-poor megacryst suite) is

responsible for both increase in equilibration temperature and incompatible-element

eurichment, it is possible that the same magma is also the cause of incompatible-element

enriciunent independent of temperature (discussed below). A silicate magma chamber

would likely generate a thermal aureole, influencing a large volume of upper mantle

matenal analogous to metamorphic aureoles generated around plutons in the upper crust.

The silicate ma,pa may also be the source of incompatible-elements, which migrate

outward fiom the magma chamber in dykes, veins or veinlets, metasomatizing the heated

and deformed country rock wi th the aureole. This mechanism may explain the hi&

temperatures in deformed xenolitlis containing cryptically metasomatized gamets. but it

does not account for the xenolitbs with cryptically metasomatized gamets fiorn C 14 which

equilibrated on the 40mWlm~eothem.

A silicate dyke, comprised of fertile magma necessary for metasomatic enrichent

of country rock, exteildirig beyond the t h e m l aureole of the source cliainber would have

minimal thermal impact on country rock. If enrichinent of gamet r-ims (and comylete re-

equilibratiou of the remainder of the country rock assemblage) is via p orous-medium

~nantle flow as Iiypothesized by Nielson aud Wilsliire (1993), then an intrusive dyke would

only chemically influence a region of up to tens of meters proximal to its margks. A

dyke-related delivery mechanism for incompatible-element enriched metasomatic fluids

would influence a significantly smaller portion of the upper mantle compared to the region

thennally and metasomatically affected by the source chamber itself. This volume

difference may explain the paucity of recogiized low-temperature undefomed steady-

state geothenn cryptically metasomatized, undefomed garnet peridotites in the studies of

Smith and Boyd (1989 and 1992). The two coarse textured xenoliths with Ti-enriclied

gamet rims from C 14 may represent a fortuitous sampling event by the entraining

kimberlitic magma en route to the surface.

5.6 Diamond Potential

Kirkland Lake kirnberlites sampled a wide range of the diamond stability field yet

diamond contents of the kimberlites are considered to be low (Schulze, I996a). Gumey

(1984) correlated diamond content of kimberlites fiom the Kaapvaal craton in South

Afiica with the abundance of low-calcium xenocrystal gamets. Gurney (1 984) also

showed that 85% of all pendotite-suite gamets included in diamond were low in calcium

and defined an "85%-line" on a C a 0 vs. Cr,O, binary plot (shown in Figure 3.7). This line

roughly correlates to the lower limit of the lherzolite field for the Kirkland Lake gamet

lherzolite xenoliths. Only one ofthe four harzburgitic gamets (Al-P7) plots in the

harzburgite field as a low-Ca garnet. The higlier Ca:Cr ratio in the gamet ofthe other

t h e e harzburgites, all of which plot in the lherzolite field, indicate that tbey may have

equilibrated with clinopyroxeiie.

Low-Ca gamet kimberlite xenocryst populations have been correlated to the

presence of garnet harzburgite xenolitlis in South Afiïcaii kunberlites (Schulze. 1995).

This relationship is consistent within the Kirkland Lake kimberlites. Schulze and

Anderson (1992) noted that low-Ca xenocrystal gamets are rare in KirkIand Lake

kitnberlite, and in this study only one of 56 peridotite xeiiolitlis has been identified as a

low-Ca garnet harzburgite. The rarity of diamonds in Kirkiand Lake kimberlite is directly

proportional to the paucity of low-Ca garnet harzburgite in the KirMarid Lake xenolith

suite.

Au additioiial source of information on the relationship between diamond content

and iipy er rnantle composition is peridotitic xeiiolitlis that contai11 diatnonds.

Diatnondiferous peridotites are extremely rare, but they provide obvious iiisight toward

the nature of diamondiferous upper mantle. Most diamondiferous pendotites are

harzburgite and dunite: but diamondiferous lherzolite xenoliths have also been fouiid.

Textures are generally coarse, and equilibration conditions are generally <lOOO"C (Boyd

and Finnerty, 1980). Coarse-textured gamet pendotite xenoliths that equilibrated in the

diamond stability field and at temperatures < 1000°C are absent fiom Al , A4, and B30.

and are well-represented at C 14 (3 to 10 xenoliths dependmg upon the

geotliemobarometer used). The highest diamond content reported fi-om Kirkland Lake

kimberlite is 1.99 caratdl00 tonnes in C 14 (Brummer, l99Zb). A4 and B30 contain 0.71

and 0.54 caratsIl00 tonnes respectively. The diamond content of A l has not been

repoxîed. Although these data are based on small bulk samples and are only hui;catiorrs of

actual diamond contents ofthe kimberlites, they show that there is at least a qualitative

relationship between diamond content in Kirkland Lake kimberlite and abundance of

coarse-textured gamet lherzolites which equilibrated in the diamond stability field at

temperatures 1 OOO°C.

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Scliulze, D.J., and Andersoii, P.F., (1 992): Coinpositioii and significance of xenociystal gamet, cliroinite, and ilineiiite from diamoiid-beaiiiig kimberlites of tlie Kirklaiid Lake cluster; Ontario Miiies and Miiierals Symposium, Miaistty of Nortlieni Developrnent and Mines. p.52.

Scliulze, D.J., and Aiidersoii, P.F., ( 1992): Iiidicator inineral clieinistiy of Kirklaiid Lake kimberlites; Geological Association of Caiiada/MitieraIogic,11 Association of Canada, Prograin witli Abstracts. 19, p A 100.

Sliee, S.K., Gui~iey, J.J., aiid Robiiison, D.N., (1982): Two diainoiid-beariiig peiidotite xeiiolitlis fioni tlie Finscli kiinberlite, Solith Afiica. Co/itrib. hlitrera/. Petru!., 81, pp. 79-87.

Siiiitli,D., & Boyd,F.R., ( 1987): Compositioiial Iieterogeiieities in a Iiigli-teinperatiii.e lliei-zolite nodule aiid iinplicatioiis for inaiitle processes. i i ~ M a d e Xeiiolitlis. (ed) P.H. Nixon. Wylie, Loiidon, pp. 55 1-56 1.

Sinitli,D., & Boyd,F.R., (1989): Co~npositioiial lieterogeiiei~ies iii iiiiiierals of slieared Ilierzolite iiicliisioiis fiorii Afncaii kimberlites. i ~ r Kiinberlites and rclated rocks, vol 2: tlieir inaritle/ci.iist settiiig, diaiiionds. aiid diamond exploration, Proceedi~igs of tlie Foui-th Ititei-iiatioiial Kiriiberlite Coiifereiice, Geoloçical Society of Australia Special Piiblicatioii No. 14, pp. 709-724.

Sinitli,D., & Boyd,F.R.. (1992): Coriipositioiial zoiiatioii iii çaniets iii peiidotite seiiolitlis. Cotttrib. Mirrerrrf. Petrol. i 12, 134- 147.

Sinitli. J.V., Breiiiischoltz, R.. and Dawsoii, J,B.. (1978): Clieinistry of inicas froin kiinberlites and xeiiolitlis; 1. Micaceoiis kiinberlites. Geochinl. Cosn~ochi~u. Acta. 42. pp. 959-97 1.

Streckheisen, A.L., ( 1973): Plutonic rocks: Classification aiid iiomeiiclatiire recotnineiided by the IUGS Subcointnission on the Systeinatics of Igneous Rocks. Geotimes. Oct.. pp. 26-30.

Sumrrters, R.W.: ( 1989): A study of the petrograpliy and geocliemistry of metasoinatised gamets iii xenoliths from the Moiiasteiy kimberlite pipe. BSc Tliesis, Queeii's University, Kingston, Ontario, Caiiada. 56 p.

Viljoen,K. S., Swasli, P.M., Otter, M. L., Scliulze, D. J., and Lawless, P.J., ( 1992): Diarnoiidiferous gamet liarzburgites froin the Fiiiscli kiinberlite, Northeni Cape. Soutli Afiica. Co~itrib. Mirlerd Petrof., 110, pp. 133- 138.

Watkiiisoii, D.H., aiid Chao, G.Y., (1973): Shor-tite in kirnberlite froin the Upper Caiiada initie, Oiitario. J. Geol., 81, py. 229-233.

Zaliiieiiuiias, R.V., and Sage, R.P., (1995): Ktiowi kimberlites of easter-ii Oiitario; Oiitario Geological Survey, Prelitniiiary Map P. 33 2 1.

APPENDIX A

Sample Locations

Appendix A - Location of Samples

B-P3 1 ~ul~hidc-kar ing Chrottiite Llierzolite

f

A-&Pl3 ( Garnet Lherzolite 1 A-4 unknown 1 21 6 :: :. .:... :.:.:::.:,;.;j;j;:,j:j:j:;:j:; >>,;i;j,::;;; .;i;;::ji.; ,;? .;::j:j:j::::':::::!:::j;;>: >>>>;> :,.> ::..:::::::;:;:*::,:::

i.;.; :: :;j:i::i.:.i:::jj:jj:::::j.>: ............. :.:::::.>:.:,:,::E, 'i:lj:'jiji::::;::::.:;:::.::::.: ....

B-30

B-30

.:;. ,?.:'::.;:.:::.-Y..;:...:.:

unknowvn

unknown

;j:,;:::;:;$,i:jk;:::::i; ::::.:. .;.:;::: ;.;:i;;;~,:,i;2~jl;;$jj;ji,ii;:j:j.j .jji:Jjjjj;:jjjjji:jjjji;.:-::: .::;:.:.::..::j:::;,i:; ........................ ;; .:<... <:.:;:.: ..................................................................................................................................... ;:; ?::; .:,:;>:::::::.: .."\. . .<.'..... ;;.. ,,; . __, ... . ..,,.. . . < .............. / .......... .. ....,., .; ........ < :.. < ................................. ,..... /. . ) . .. . . : ~.~......... , :,, , ,.! . ' . . . ..,.,h: . ;i:. , ,.,.,.,, . .. , , . . . . . .:..... ~.:.:...:.:..,:,.,:, ... .................... .,., ,:. .,. ., ... , ...............,... , , , . .,.,... . . . . ..:. ...-.'... .., , . , . . . .. . .i.i.....ri...ri , , ., . . : ..... ,'::::::: ::> :.:.;i:r:.jc::. -.:w:'.:--:: .:::.:.:.::.:::

888

171.5 B-Pl

B-P2

Garnet Llierzolite

Garnet Llierzolite

Appendix A - Location of Sampies

enolithIRock Type 1 Pipe Hole l ~ e p t h (m)

1 C-PX

APPENDIX B

Detailed Petrography

Xenolith Al-Pl Transitional coarse to porpliyroclastic gamet lberzolite with 5-7% olivine

neoblasts. The xenolith is very small(2cm) and the outer 0.5 cm is serpentinized. Graiii sizes are as follows: olivine 3- 5 mm; orthopyroxene 0.5-2.0 mm; clinopyroxene 1.5 mm: gamet 5 mm. The loae clinopyroxene grain lias a sieve-textured rnargin and a fiesh core. Olivine and orthopyroxene have undulatory extinction. Kelyphitic rirnming of gamet is thin (< 0.2 mm).

Xenoiith AbP3 Porphyroclastic dunite. Olivine porpliyroclasts have undulatory extinction and

range in siie fiom 5-7 mm. OlMne neoblasts constitute 50% of xenolith and range fiom O. 1- 1.0 mm.

Xenolith Al-P5 Transitional porphyroclastic to mosaic porphyroclastic dunite. Olivine

porphyroclasts have undulatoiy extinction and range in size fiom 5-7 mm. Olivine neoblasts constitute 60% of xenolith and range fiom <O. 1- 1 .O mm.

Xenolith Al-P6 Coarse gamet Iherzolite. Grain sizes are as follows: o l ~ n e 3-6 mm;

orthopyroxene 1-2 mm; clinopyroxene 0.5- 1.5 mm; gamet 3-4 mm. Clinopyroxene margins are sieve-texhired, but most have fiesh cores. Kelyphitic rimmùig of gamet is tliin (< 0.05 mm).

Xenolith A b P 7 Coarse gamet harzburgite. Xenolith is small(2 cm) witli outer 0.5cni

serpentinized. Grain sizes are as follows: olivine 3-6 mm; orthopyroxene 1-2 mm; gamet 3-4 mm. Clinopyroxene is absent. Kelyphitic rirnming of gamet is thin (< 0.05 mm).

Xenolith Al-P8 A coarse chromite Iherzolite. Grain sizes are as follows: olivine 3-8 mm;

o~thopyroxeiie 1-2 mm; clinopyroxeue 1-2 mm; chromite 0.1-0.5 mm. Clinopyroxene inargins are sieve-textured, but most have fi-es11 cores. Chromite is subhedral comprisiiig upto 10% of xenolith and appears to be primary.

Xenolith Al-Pl0 Weakly metasomatized coarse gamet Iherzolite. Grain sizes are as follows:

olivine 3-8 mm; ortliopyroxene 0.5-2 mm; clinopvoxene 0.5 mm; gamet 3-4 mm. Clinopyroxene is entirely sieve-textured, only one grain found in section. Kelyphitic riiiiming of gamet is thin (< 0.5 mm). Metasomatic phlogopite and very fine chroinite m a d e gamet, and occur also in xeuolitli fractures. Orthopyroxene is abundant (10- 15% of section), and have tliin (<50 microns) browi gruiigy, unresolvable alteratioil- assemblage rims. Orthopyroxene commonly coiitains 5- 10% fine inclusions impartixig a siinilar appearaiice to that of sieve-textured clinopyroxeue.

Xenolith Al -Pl 5 Porphyroclastic gamet liarzburgite. Xenolith is small(1 cm). Neoblasts are 25-

30% of xenolith. Grain sizes are as follows: olivine 2-8 mm; orthopyroxene O S - 1 mm: gamet 5 mm. Olivine aiid orthopyroxene grains show a strained extinction. Clinopyroxene has mottled margins. There is one fine-grained, anhedral blob of Fe-Ni sulpliide included in orthopyroxene. Gamet kelyphite is 0.5- 1.0 mm thick.

Xenolith Al-Pl7 Transitional porphyroclastic to mosaic-porphyroclastic gamet lherzolite. n i e

xenoiith is small ( km). Neoblasts are 40-50% of section. Lone gamet is 0.5mm and rounded. Onhopyroxene ranges fiom 1-2mm and commonly bas thin unresohrable reaction rims (secondary?). Clinopyroxene ranges from 1-3mm with thin sieve-textured margins.

Xenolith A4-Pl Transitional coarse to porphyroclastic (locally) gamet lherzolite. Gamet is

generally Imm; olivine ranges from 1 -6mm; orthoppoxeoe 1-3mm; clinopyroxene 2-3mm. Gamet is strongly kelyphitized. Clinopyroxene has very thin sieve-textured margUis. Orthopyroxene rarely contains rounded olivine. One portion of xenolith has abundant neoblasts and Iiighly strained o h e , and other sections have coarse olivine without neoblasts. indicating that this xenolith is variably deformed. Olivine, orthopyroxene, and clinop yroxene have undulatory extinction.

Xenolith A4-P3 Porphyroclastic to mosaic porphyroclastic gamet Iherzolite. Gamet ranges fiom

1 - h m ; olivine porphyroclasts 2-5mm, neoblasts <O. 1-0.5mm; orthopyroxene 1-4mm: clinopyroxene 1-2mm. Olivine and orthopyroxene have undulatory extinction. Clinopyroxene has minimal sieve-textured margiiis, and kelyphitic rimrning on gamet is veiy minor. There is minor extremely fine-grained orthopyroxene neoblast development.

Xenolith A4-P4 Mosaic porphyroclastic gamet lherzolite. Gamet ranges frorn 1-3mm; olivine

porphyroclasts 1 -2mq neoblasts <O. 1-0.2mm; orthopyroxene 1 -2mm: chopyroxene 0.5- 2min. Olivine aiid orthopyroxene porphyroclasts have undulatory extinction. Clinopyroxene has ininirnal sieve-textured margins, and kelypliitic rimming on ganiet is tliin (0.2mm). Neoblasts constitute 60-65% of section, and 90% of the total olivine.

Xenolith A4-PS Transitional coarse to deformed ganiet 1herzolite.Ganiet ranges fiom 2-5rnin;

olivine from 2- 1 Omm; orthopyroxene 1 -3mm; aiid clinopyroxene 1 -2mm. Gamets have very minor kelypl~ite rirnming and grains are subhedral. Soine clinop yroxenes are entirely sieve-textured, and only one grain lias optically clear margiii.

Xenolith A 4 P 6 Coarse cliromite-bearing gamet Iherzolite. Garnet ranges fion] 4-8mm; olivine 2-

6mm; orthopyroxene 4-6mm; and clinopyroxene is O . 5 m . A trace amount of discrete. anhedral chromite, apparently prima-, occurs locally. It is deep red in plane polarized light. One entirely altered (mottled and sieve-texmred) clinopyroxene is present. Olivine and orthopyroxene appear uostrained.

Xenolith A4-P7 Transitional coarse to porphyroclastic gamet lherzolite. Gamet ranges fiom 1-

2mm; olivine 2-6mm; orthopyroxene 0.5-2mm; and clinopyoxene 1-2mm. Olivine neoblasts are heterogenously distributed throughout section. A portion of the xenolitli is porpliyroclastic. Coarse olivine is strajned. Most gamet is entirely kelyphitized.

Xenolith A4-P8 Transitional coarse to porphyroclastic gamet herzolite. Gamet is 0.5-1.0 mm;

olivine is 2-5mm; orthopyroxene 1-2mm; and clinopyroxene 0.5-lmm. Coarse tabular (0.1-0.3mm) olivine neoblasts are abundant ( 10- 13% of section). Oiiviiie and orthopyroxene have undulose extinction. Portions of xenolith are porphyroclastic. Gamets constitute 10% of section, have thin (O. lmm) kelrphitic rims, and occur locally as inclusions in orthopyroxene.

Xenolith A4-P9 No thin section available, xenolith <lem. Examination of poiished surface

indicates this xenoiith is a coarse gamet iherzolite. Clinopyroxene 2-3 mm, gamet 3-5 mm, orthopyroxene 3-5 mm, and olivine 5-7 mm.

Xenolith A4-Pl1 No thin section available, xenolith <I cm. Examination of polislied surface

indicates this xenolith is a porpliyoclastic iherzolite.

Xenolith A4-Pl2 Transitional coarse to porpliyroclastic garnet Iherzolite. Garnet is 0.5mm; olivine

2-5uim; ortliopyroxeiie 0.5-lmm; and clinopyroxene 0.5-Imm. Olivine neoblasts are very fine graiiied and constitute 10-15% of xenolith. Kelyphitic rimmuig on gamet has nearly completely altered al1 ganiet. Olivine and orthopyroxene have undulose ex-iinctioii.

Xenolitli Ad-Pl3 Transitional coarse to deformed gamet lherzolite. Gamet Imm; olivine 1-8mm;

oithopyroxene 1-5mm; cliuopyroxene 0.5-2mm. Olivine is cominonly strained, and fine grained neoblasts occur locally. Gamets are highly kelyplutized and clinopyroxenes are mostly sieve-textured. ûptically clear clinopyroxene cores are rare.

Xenolith B-Pl Porphyroclastic ganiet Iherzolite. Olivine neoblasts constitute 20% of xenolitli.

Grain sizes ofporpliyroclasts are as follows: olivine 2-6 mm; orthopyroxene 0.5-2.0 mm:

clinopyrosene 0.5-2.0 mm; gamet 0.5- 1.5 mm. Garnet is abundant (10- 15%). Olivine and orthopyroxene porphyroclasts have undulose extiriction. Chopyroxene porphyroclasts appear unstrained witfi very thU: sieve-textured margins. Kelyphitic rirnmi~g of gamet is minimal.

Xenolith B-P2 Transitional porphyroclastic to mosaic porp hyroclastic gamet Iherzolite. Olivine

neoblasts constitute 1520% of xenolith, and locally up to 50%. Grain sizes of porphyroclasts are as follows: olivine 2-10 mm; orthopyroxene 0.5-3.0 mm; clinopyroxene 0.5-2.0 mm; gamet 0.5-2.0 mm. Gamet is abundant (5-10%). OlMne and orthopyroxene porphyroclasts have undulose ex~inction. Clinopyroxene porphyroclasts have iittle to no sieve-textured margins. Kelyphitic rimming of gamet is minimal.

Xenolith B-P3 Coarse chromite lherzolite. Grain sizes of are as foilows: o h i n e 2-5 mm;

orthopyroxene 1-4 mm; clinopyroxene 1-3 mm; chromite c0.5 mm; phlogopite 0.5-2.0 mm. Clinopyoxene is rnostly pseudomorphed by a serpentine rich fine grained assemblage. Chromite occurs both discretely throughout xenolith and as an inclusion nithin clinopyroxene. Phlogopite is rare and discrete and may be primary. A single lath of Fe-Ni sulphide O. 1 mm is present.

Xenolith C-Pl Transitional coarse to deformed chromite-bearing gamet lherzolite. Grain sizes are

as follows: olivine 3-8 mm; orthopyroxene 1-4 mm; cliuopyroxene 1-3 mm; gamet 3-3 mm; chromite 0.1-0.5 mm. Strained extinction is common in olivine and rare in orthopyoxene. Clinopyroxene is locally sieve-textured on grain margins. Gamet is rounded and highiy fiactured with thin kelyphitic margins and abundant kelyphjte withiri fractures. Chromite is rounded to amoeboid (1 grain) and does not appear to have formed at the expense of gamet (primary?). There is a trace presence of olivine neoblasts (< 0.1 mm), and locally constitute 5% of xenolitli. Small (O. 1-0.3mn) orthopyroxenes occur rarely as inclusions within oliviue.

Xenolith C-P2 Coarse chromjte-beariiig gamet lherzolite. Grain sizes are as follows: olivine 2-6

mm; orthopyroxene 1-3 mm; clinopyroxene <0.5 mm; gamet 3-4 mm; chromite 0.2-0.5 mm. Strained ex-tinction is locally present in olivine and orthopyroxene. Cliuopyroxei~e is strongly sieve-tex~ured on grain margins. Gamet is rounded and kelypliitic margin up to 0.5 mm. Chornite occurs as rounded, anliedral, and subliedral, cO.5- 1.0mm. Most grains are discretely dispersed thraughout the xenolitli. One grain of chromite is subhedral and appears equilibrated with the lherzolite assemblage. A single euhedral chromite is included in clinopyroxene.

Xenolitli C-P3 Transitional coarse to deformed weakly metasomatized gamet lherzolite. Grain

sizes are as follows: olivine 2-10 mm; orthopyroseue 1-4 mm; clinopyroxene 1 .O mn: gamet 3-4 mm. Strained extinction is locally present in olivine and orthopyroxene. Fine (0.1 mm) tabular olivine neoblasts constitute 3-5% of xenolith. Gamet is rounded and kelypliitic margin is <O. 1 mm. Gamet has a coarse inclusion assemblage of olivine + clinopyroxene + pldogopite + chornite. A metasomatic assemblage is found proximal to gamet and may also occur apart fiom gamet. The metasomatic assemblage consists of phîogopite + chromite + ilmenite (locally with very fine rutile exsolution) rt clinopyroxeiie. Chromite is anhedral with indistinct grah boundaries and does not appear primary.

Xenolith C-P4 Coarse chromite-bearing gamet Iherzolite. Grain sizes are as follows: olivine 3-6

mm; orthopyroxene 1-3 mm; clinopyroxene 1 mm; gamet 3-4 mm; chromite 0.1-0.5 mm; phlogopite 3mm. Trace presence of o M e neoblasts. Gamet is rounded and kelyphitic margin is 0.5- 1 .O mm. Primary chromite is subhedral to anhedral with sharp grain boundaries. A single discrete tabular phlogopite grain may be primary. A secondary kelyphitic assemblage mantling garnet consias of phlogopite + chromite (fine, anhedral with fùzzy grain boundaries) + clinopyroxene.

Xenolith C-P5 Transitional coarse to deformed gamet lherzolite. Grain sizes are as follows:

olivine 2-7 mm; orthopyroxene 1-3 mm; clinopyroxene O S - 1.0 mm; gamet 3-6 mm. Garnet is rounded and kelypliitic margin is 0.5- 1 .O mm. There is trace to 3% olivine neobla st S. A secondary kelyphitic assemblage commonly mantles gamet and hcludes phlogopite + chromite + clinopyroxene. Clinopyroxene is completely sieve-textured. Gamet kelyphite is thin, 0.5 mm.

Xenolith C-P6 Transitional coarse to defomed gamet lherzolite. Grain s'izes are as follows:

olivine 3-7 m; orthopyroxeiie 1-4 mm; clinopyroxene 1-2 mm; garnet 2-5 mm. There is a trace to 2% presence of olivine neoblasts along coarse olivine grain margins. Some of the larger olivine grains have strained extinction. Clinopyroxene is randomly distributed and most have fresh cores and sieve-textured margins. Secondary kelyphitic assemblage of phlogopite + spinel k clinopyroxene partially mantles gamets. The secondary cliiiopyroxene is fine grained (<OS mm), irregular shaped, and strongly sieve-textured. The secondary chromite is very fine grained (<O. lmm), euhedrai, and included in plilogopite. Gamet kelypliite is 0.2- 1 .O mm tliick.

Xenoli th C-P7 Coarse gamet lherzolite. Grain sues are as follows: oliviue 2-8 min;

ortliopyroxene 1-4 rnm; cliuopyroxeiie 1-4 mm; gamet 2-5 mm. O h e grains show a stiained exhction. Clinopyroxene is randomly distributed and most have fiesh cores with sieve-textured marghs. Some clinopyroxenes have amoeboid shapes. Secondary plilogopite mantles gamets. One rouiided spinel (0.5 mm) mantled by plilogopite appeass associated witli the secondary assemblage. Garnet kelyphite is OS- 1 .O mm thick.

Xenolitli C-Pt3 Ti-ansitioiial coarse to deformer! weakly inetasoinatized gamet lherzolite. Grain

sizes are as follows: olivine 2-6 inin: ortliopyroxene 1-3 mm; clinopyroseiie 1-3 mm; ganiet 5-6 Inin. Clinopyroxene is raiidomly distiibuted and most grains are t otally sieve- texqured. Fresli euliedral clinopyroxene (0.5 mm) is rarely included in ganiet. A metasomatic assemblage of phlogopite + fine grained (<0.5 mm) clinopyroxene + spinel mantle ganiet. Ganiet kelypliite is < 0.5 min. Xenolitli constitutes trace to 5% oliviiie neoblasts locally.

Xenolith C-P9 Transitional coarse to deformed weakly inetasotnatized ganiet Ilierzolite. Grain

sizes are as follows: olivine 2-9 min; orthopyroxene 2-4 mm; clinopyroxene 1-2 min; ganiet 5- 1 1 mm. Olivine and orthopyroxene porpliyroclasts have strained extinction. Olivine iieoblasts locally make up 5% of xeiiolitli. A clinopyroxene associated witli coarse phlogopite Iias lamellar twinniiig. Metasotnatic plilogopite is rare, occurring adjacent to strained clinopyroxene and gamet. It is tabular and very liglit browi in colour (plane- polarized liglit). Routided olivine chadacrysts (0.5- 1 .O min) are commoii inclusions iii gamet. Metasoinatic pliIogopite is rare, inantles ganiet, aiid oRen contains very fine (<O. Iinm) inclusions of euliedral clirornite. Ganiet kelypliite rimming is tliiii (c0.5 mm).

Xenolith C-Pl0 Transitional coarse to porphyroclastic weakly inetasoinatized ganiet llierzolite.

Tiiere is up to 35% olivine neoblasts. Grain sizes are as follows: olivine (coarse) 2-5 niin; olivine (iieoblasts) <O. imm; ortliopyroxene 2-4 mm; cliiiopyroxene 1-2 mm; ganiet 5-7 mm; plilogopite <O. 5 mm. Olivine and ortliopyroxene have strained extiiictioiis. Clinopyroxene is rare and is oiily found proximal to ganiet. Clinopyroxene is randornly dispersed witli sieve-textured grain inargiiis aiid one grain Iias lamellar twinning. All plilogopite present is spatially associated witli clinopyroseiie. Rounded olivine cliadacrysts (0.5-2.0 inin) are coininon iiiclusiotis iii ganiet. Fine graiiied iroti-nickel sulpliide blobs are locally present (<O. 1 %). Ganiet kelypliite rimmiiig is tliiii (<O. 5 min).

Xenolitli C-Pl 1 Coarse cliroinite-beariiig gamet Ilierzolite. Grain sizes are as follows: olivine 5-

1 1 iiiin; oitliopyroxetie 0.5-2.0 inin; cliiiopyroxene 2-4 inm; gamet 3-6 mm: clisoinite c0.5 min. Clinopyroxeiie is iaiidomly dispersed aiid lias tliiii sieve-texqiired graiii inargiiis. One aiiliedral clinopyroseiie is iiicludetI in gamet. A fractured cliromite graiii prosimal to ganiet may be piiinaiy. A kelypliitic assemblage coinposed of plilogopite -1 spinel * cliiiopyroxene ~ ims a vety fine grained dask browi kelypliite arowid gamet. Gaiiiet kelypliite riininiiig is tliin (<0.5 niin).

Xenolitli C-Pl2 Coarse weakly inetasoinatized gaillet llierzolite. Grain sizes are as follows:

olivine 2-8 min: oi.tliopyroseiie 0.5-3.0 iniil; clino~~yroxene 0.5-4.0 mm; gamet 4-5 inin. Clinopyroxe~ie is randoinly dispersed and Iias tliiii sieve-tex%ured grain maigins. A tliin

inetasomatic :issetnblage coiisists of plilogopite t spi~ieI -1- cliiiopyroseiie mantles and partially replaces ganiet. The spiiiel appears to be exsolviiig out of the plilogopite. Ganiet kelypliite ïiinitiiiig is tliiii (<0.5 nini).

Xenolith C-Pl3 Coarse weakly inetasoinatized ganiet 1lierzolite. Graiii sizes are as follows:

oliviiie 2-6 mm; orthopyroxeiie 1-3 min; cliriopyrosene 1-3 mm; ganiet 3-4 iiim. Oliviiie Iias straiued extinction. Priinary clinopyroxene Iias sieve-textured grain margiiis. Clinopyroxeiie cores locally esliibit lainellar straiii features. A metasoinatic assemblage coinposed of phlogopite + spinel+ cliiiopyroxene inaiitles ganiet. Ganiet kelypliite iiminiiig is tliiti (<O. 5 mm).

Xenolith C-Pl4 Coarse weakly metasornatized gamet Ilierzolite. Graiii sizes are as follows:

olivitie 3-7 mm; onliopyroxene 1-3 rniii; cliiiopyroxene 1-3 inin; gamet 3-4 min. Olivine Iias strained extiiictioti. Olivine cliadacrysts are locally iiicluded in ganiet. Tliere is a trace presence of oliviiie neoblasts. Cliiiopyroxene is rare and is stroiigly sieve-textiired. A inetasomatic assemblage coinposed of plilogopite t. spinel + cliiiopyroxeiie inaritles ganiet. Kelyphitic replacement of ganiet ranges fioin moderate (1 Inin riiid), to coinplete.

Xenolith C-Pl5 Coarse metasomatized ganiet Ilierzolite. Graiii sizes are as follows: olivine 3-7

inin; oitliopyroxeiie 1-3 mm; cliiiopyroxene 1-3 inin; ganiet 4-8 min. Oliviiie Iias strained extinctioii. Oliviiie chadacrysts are locally iiicluded iii gamet. Clinopyroxeiie Iias sieve- textured riins aiid fiesli cores. A metasoniatic asseinblage coinposed of plilogopite + spinel + cliiiopyroxeiie inaiitles ganiet. The inetasomatic phlogopite is coarse ( 1-5inin). Kelypliitic replacement of ganiet is minimal (10.2 mm).

Xcnolith C-Pl6 Coarse ganiet Ilierzolite. Grain sizes are as follows: olivine 3-6 inin;

orthopy-oxene 1-2 inin; cliiiopyroxeiie 0.5-2.0 mm; ganiet 3-4 inin. Clinopyroxeiie inargins are sieve-textured, but most Iiave fiesli cores. Oliviiie corn~nonly lias strained extiiictioii. Kelypliitic rirnmiiig of ganiet is tliin (< 0.2 ~nni).

Xenolitli C-Pl7 Mosaic poipliyroclastic inetasoinatized (ilinetiite-lieaiiiig?) gamet Ilierzolite.

Oliviiie iieoblasts coiistitute 70% of xeiiolitli. Grain sizes of poipliyroclasts are as follo~vs: oliviiie 1-3 inin; ortliopyroxe~ie 2-4 inin; cliiiopyroxeiie 2-3 inm; ganiet 3-5 min; iltneiiite 2 inin. Ilineiiite is bitnodal existiiig as large (2 mm) anliedial, fiactiired graiiis and as sinall(<.2 inin) roiuided iiiclusioiis iii the gamet kelypliite asseinblage. The large fiiictured giiiiiis inay repieseiit a pie-inetasoiiiatic os 1)riinii~ pliase of iliiie!iite. 01-tliopyroxeiie poipliyroclasts Iiave straiiied ek$iiictioii. Clinopyroxeiie poipliysoclasts appear undefonned altlioi~gli one grain appears cataclasticly brokeii. Cli~iopyroxenes Iiave sieve- tcx?iii.ed ~nargiiis. Uiidefoimed roiriided olivine cliadaciysts are locally iiicluded in gaillet. A tnetasoriiatic assemblage coinposed of plilogopite t clinopysosene + iltneiiite * spiiiel

iiiaiitles ganiet. Soine coarse plilogopite lias beiit cleavage. Kelypliitic iiininiiig of ganiet ranges fioin < O S inin to iiearly complete.

XenoIith C-Pl8 Mosaic porpliyroclastic inetasoinatized gamet Ilierzolite. Olivine iieoblasts

coiistitute 60% of xeiiolitli. Graiii sizes of poiyliyroclasts are as follows: olivine 1-3 min; ortliopyroxeiie 2-3 min; cliiiopyroseiie 2-3 inm; gamet 3-5 mm. Ortlioyyroxene poryliyroclasts have strained extiiictioii. Clinopyroxene y orpliyroclasts app ear uiidefonned althougli one grain Iias fine straiii lamellae. Clinoppxeiies have sieve- textured margiiis. A metasomatic assemblage composed of phlogopite + cliiiopyroxeiie %

cliromite mantles ganiet. The cliromite occiirs as essolution out of ylilogopite. Kelypliitic nmmiiig of ganiet ranges fioin <0.5 mm to iiearly complete.

Xenolith C-P19 Coarse ganiet Iherzolite. Grain sizes are as follows: olivine 2- 10 inm;

oithopyroxene <O. 5- 1 .5 mm; cliiioy yroxeiie 0.5 mm; ganiet 2 ina. Clinopyroxeiie aiid oithopyroxene combiiied coiistitute <5% of xenolitli. Tlie cliiiopyroxetie lias sieve- textured margins. A small (O. linm) ailliedrai iroii-nickel sulpliide blob is iiicluded in an olivine. Kelyphitic rimtning of gamet <O. 5 mm.

Xenolith C-P20 Coarse (plilogopite-beaniig?) gamet llierzolite. Grain sizes are as follows: olivine

3- 10 mm; orthopysoxene 1.5 inin; clitiopyroseiie 0.5-2 mm; ganiet 5 inin; ylilogopite 0.5 mm. Plilogopite is tabular and discrete and does tiot appear associated with a metasornatic assemblage. The clinoyyroxene Iias sieve-textured inargitis. An Fe-Ni sulpliide blob (0.5mm) is iticluded iii olivine. Kelypliitic ~iminiiig of gamet <O. 1 min.

Xenolith C-P21 Mosaic y oryhyroclastic weakly inetasomatized gamet llierzolite. Tlie textiiie is

inosaic porpliyroclastic. Oliviiie iieoblasts coiistitute 55% of xenolitli. Grain sizes of poq~hyroclasts are as follows: oliviiie 0.5-4 inin; ortliopyroxeiie 0.5-2 inin; cliiiopyroxeiie 1-2 inin; gamet 3-5 min. Cliiioyyroxeiie graiiis (<.5 min) occiir as botli poryliyroclasts aiid as a fiiier grained (0.5 min) assemblage associated with plilogopite inaritliiig ganiet. Olivine poipliyroclasts are iiearly wliolly reciystallized to iieoblasts. Ortliopyroseiie poi=pliyroclasts Iiave straiiied extinction. Cliiiopyroseiie poi-phyroclasts appear iiiidefoi~ned but 11 ave tliiii sieve-textured inargiii S. Kelypliit ic iiiniiiiiig of ganiet is rniiiiiiial.

Xenolitli C-P22 Coarse gamet llierzolite (Iiaizbuigite?). Graiii sizes are as follows: oliviiie 4- 10

inin; cliiiopyroxeiie 0.5inin; oitliop yroseiie 0.5-2.0 min; cliroinit e 0.5 inin. Several rouiidecl oliviiie graiiis are iiicludecl iii ganiet. A sobliedral cliroiiiite grain is iiicliided iii ganiet aiid inay be piiiiiaiy?. Kelypliite lias iiearly coinpletely alteied ganiet. Tlie loiie grain of discrete cliiiopyroseiie is proxiiiial to a fi-actiire, is veiy altered, aiitl inay be iiot be priinaiy.

Xcnolitli C-P24 Traiisitioiial coai-se to defor-ined pai-iiet liai-zburgite. Graiii sizes are as follows:

oliviile 5- 10 nini; oitliopyi-osetie 0.5 tiiiii; gamet 3- 10 iiiiii. Rouiided olivine nlso occ~irs as a cliadaciyst witliiii gamet. Olivine iieoblasts occur locally, upto 3% of section. Kelyphitic riinmitig of ganiet is tliiii (< 0.5 intn).

Xenoiith C-P25 Tratisitional porpliyroclastic to inosaic porpliyroclastic ganiet Ilierzolite. Graiii

sizes are as follows: olivine 4-6 mm; ortliopyroxeiie 1-4 mm; cliiiopyroxene 1-2 mm. Olivine grains are commonly iiicluded in ortliopyroxeiie. Neoblasts constitute 40-50% of xeiiolitli. Porpliyroclastic olivine lias straiiied extiiictioii. Gamet kelypliite riin is tliiii.

Xenolith C-P26 Traiisitional coarse to porpliyroclastic metasomatized garnet Ilierzolite. Oliviiie

iieoblasts coristitute 10% of xeiiolitli. Grain sizes of porpliyroclasts are as follows: oliviiie 2-6 mm; ortliopyroxeiie 1-3 mm; clinopyroxeiie 2-3 mm; garnet 3-5 inm. Plilogopite graiiis (<.5-3min) occur in clusters associated witli clinopyroxetie as a inetasoinatic assemblage replacing gamet. Fine grained cliromite and ilmenite with rutile exsolution is exsolvitig fiom metasomatic phlogopite. Tliis assemblage lias replaced one garnet porpliyroclast prefereiitially on one side, termitiatirig at ail olivirie cliadacryst suc11 that the relict gamet core is fetal diaped witli the oliviiie in the Iiirige point. Ortliopyroxeiie porpliyroclasts have strained extinction. Cliiiopyroxeiies have sieve-textured inargiiis. Plilogopite coinmonly has beiit çleavages. Kelypliitic rimmiug of gamet <0.5 mm.

Xenolith C-P27 Coarse inetasoinatized ganiet Ilierzolite. Grain sizes are as follows: olivine 2-6

mm; oitliopyroxeiie 0.5-2.0 inin; cliiiopyroxerie 0.5- 1 .O mm; gamet 3-5 inin. Plilogopite graiiis (<.5-3inin) occur iii clusters associated witli clinopyroxene, cliromite, aiid ilineiiite as a tnetasoinatic assemblage replaciiig ganiet. Fine graiiied cliromite aiid ilineiiite are exsolviiig from plilogopite. Cliiiopyroxeiies have sieve-textured inargiiis. Kelypliitic iiinmiiig of ganiet <0.5 inin.

Xenolith C-PB Coarse plilogopitic cliromite-beariiig Ilierzolite. Graiii sizes are as follows: oliviiie

2-4 min; ortliopyroxene 1-5 inni; cliiiopyroseiie 0.5- 1 .O iiiin; cliroiiiite 0. 1-0.25 iiitn; plilogopite 1-3 inin. Plilogopite graitis occiir raiidoinly tliroiiglioiit the xeiiolitli. Cliroinite is coiiiinoiily iiicluded in ~Iiiioyyroxeiie. Cliroinite graiiis are aiiliedraI. Cliiiopyroserie is abuiidaiit aiid inost have sieve-textured inargiiis. Tliei-e is iio evideiice for a prectissoin gamet aiid the plilogopite aiid cliromite appear p~imaiy.

Xenolith C-P30 No tliiii scctioii available, xeiiolitli I m. Esatiiiiiatio~i of polislied surface

iiidicates tliis senolitli is a coarse Ihei.zoIite. Cliiiopyroseiie 2-3 min, ortliopyoxeiie 1-2 inin, aiid oliviiie 2-7 iniii.

Xenolith C-P31 No tliiti sectioii available, seiiolitli < 1 cm. Esainiiiatio~i of polislied surface

indicaies iliis seliolith is a poiyiiysoclastic ganiet Ilierzolik. Cliiiopy oseiie 2-3 inni ( I grain), ganiet 3 inm (inostly keIyptiitized), ortliopyroxetie 1-2 inin, and olivine neoblasts.

Xenolitli C-P32 No tliiii sectioii available, senolitli < 1 cm . Exainiiiatioii of polished suiface

indicates tliis xenolith is a coarse ganiet Ilierzolite. Cliiiopyroseiie 1 mm, ganiet 3-5 inm witli Iinm kelyphite, oithopyroxene 1-2 inin, and olivine 2-5 mm.

Xenolith C-P33 Coarse weakly metasomatized ganiet Ilierzolite. Graiii sizes are as follows: oliviiie

2-6 mm; orthopyroxene 2-4 mm; clitiopyroxetie <0.5 mm; ganiet 4-6 mm; cliroinite 0.5 mm. Plilogopite grains (<OS-)mm) occur in clusters associated witli clitiopyroxene and cliroinite as a metasomatic assemblage replacing ganiet. Clinopyroxeiie is both associated with plilogopite, and aIso occurs as fine graiiied inclusions in gamets. Sotne fine graitied clirotnite is discrete aiid inay be primary. Kelypliitic rimmiiig of ganiet is iiearly complete.

Xenolith C-P34 Transitional porpliyroclastic to mosaic porpliyroclastic metasomatized gamet

Ilierzolite. Olivine neoblasts constitute 50% of xeiiolitli. Graiii sizes of porpfiyroclasts are as follows: olivine 1-3 mm; ortliopyroxene <0.5-4 mm; ganiet 5-9 mm. Ortliopyroseiie and oliviiie porphyroclasts Iiave strained extiiictioii. Cliiiopyroxeiies are foutid in spatial associatioii with the metasomatic plilogopite, and Iiave sieve-textured margins. The metasomatic assemblage composed of plilogopite + clinopyroxene * ilmenite malitles ganiet. Tlie ilmenite occurs as exsolution out of plilogopite. Discrete fiiie giaiiied aiihedral Fe-Ni sulpliide species is present locally. Kelyphitic riinining of ganiet ratiges fioin <0.5 inln to iiearly complete.

Xenolith C-P35 No tliiii sectioii available, xeiiolitli < I cm. Exainiiiatioii of polislied surface

iiidicates tliis xeiiolitli is transitional frorn coarse to poipliyroclastic ganiet Iiarzburgite. Gamet 2-3 mm, ortliopyroxene 0.5- 1 inin, and olivine 1-2 inin.

APPENDIX C

Mineral Chemistry

Appendix C- Microprobe Analyses of Olivine

Appendix C- Microprobe Analyses of Olivine

- Xenolith

, C-P35 msrgin

Fe0 7.409

Cr203 0.063

Ca0 0.069

Si02

40.771

Mg0 1 M n 0 N i 0 0.392 50.393

Total 99.599 0.1 13

Appendix C- Microprobe Analyses of Orthopyroxene

~4.p.l 1 margin 1 0.238 1 5.053 1 1.044 1 35.031 11 A4-H 1 core 1 0.254 1 7.502 1 0.971 33.238

A4-P6 core 0.023 4.469 0.181

A4-P6 margin 0.030 4,529 0.1 95 37.165 1 0.096 1 1 1

A4-W corf 0.307 4.942 1.005 34.927

A4-P7 margin 0.310 4.933 1.044 34.797 1 0.1 1 1

A4-P8 core 0.195 4.700 1.497 34.829

A4-P9 margin 0.162 4.913 0.567 35.914 1 0.138 1 A4-Pl1 core O. 189 7.057 1.325 33.879 1 0.125 1

1 1

A4-Pl1 margin 0.207 6.915 1.378 33.930

A4-Pl2 fore 0.080 5.306 1.081 35.440 [ 0.1 16 1 I

A4-Pl2 margin 0.081 5.266 1.101 35.351

Appendix C- Rlicroprobe Analyses of Qrthopyroxene

Na20 Fe0 CnO Mg0 Mn0 Ti02 AI203

C-P3 mnrgin 0.131 4.624 0.444 36.474 0.121 0.013 0.707

C-P4 fore 0.067 4.134 0.229 37.062 0.087 0.01 4 0.71 O

C-P4 ma 1 C-P core 1 0.160 1 4.645 1 0.561 / 36.123 1 0.141 1 0.171 1 05-13

C-P margin 1 0.165 1 1.720 0.563 1 36.086 1 0.131 O. 184 0.861

core 1 0.122

A p ~ e n d i x C- Microprobe Analyses of Orthopyroxene


corc 1 0.232 , d-Pl0 1 core 1 0.225 1

hl-Pl7 ( core 1 0.405

A4-PI msrgin 0.335 56.991 0.000 0.137

A4-P3 corc 0.368 56.859 0.001 0.129

A4-P3 mrirgin 0.393 56.752 0.002 0.094 100.005

II A4-P4 1 core 1 0.421 [ 56.904 1 0.020 1 0.122 1 100.164 I

A4-P4 margin 0.381 [ 56.794 [ 0.000 1 0.138 1 100.159 I l . .-.

A4-F'5 core 0.240

A4-F'5 margin 0.205 55.289 [ 0.000 1 0.094 1 99.2-11 I -. . . .- - - - .-

A4-P6 core 0.163

A4-P6 margin 0.287 56.810 1 0.000 1 0.05

II A4-W 1 margin 1 0.797 1 56.567 1 0.001 1 0.090 1 100.103

II A4-PS 1 core 1 0.531 1 56.518 1 0.007 1 0.114 1 100.110 100.368 II A4-PS 1 margin 1 0 573 1 56.539 1 0.003

II A4-F9 1 core 1 0.334 1 57.058 1 0.000 1 0.090 1 100.184 1

C-Pl

C-PZ

A4-F9

A4-Pl1

A4-Pl1

corc

margin

corc

margin

CO rc

1) C-PZ 1 morgin 1 0.393 1 56.752 1 0.002 1 U.0' 1 1

margin

core

margin

core

0.535

0.153

0.225

56.923

56 153

56 150

0.000

0.005

0.001

0.084

O. 136

O. 185

100.416

100.597

100.690



Appendix C- ICIicroprobe Analyses of Clinopyroxene

Appendix C- Microprolie Analyses of Ciinopyroxene

Appendix C- Microprobe Analyses of Clinopyroxene

Ti02

0.067

0.369

0.484

AI203 3.804

2.672

1.045

Mg0 14.491

15.921

17.009

Xenolith

C-P33 C-P34

C-P34

hl nO

0.081

0.119

0.125

Na20

3.856 2.629 1.355

margin

core

margin

Fe0

2.112

4.445

4.002

Ca0

18.404

27.795

M.311

Appendix C- Microprobe Analyses of Clinopyroxene

Appendir C- Microprobe Analyses of Clinopyroxene

Appendix C- Micioprobe Analyses of Clinopy~oxene

Total

99.914 99.333

99.682

N i 0 O. C63 O. 003 O El

Xenolith

C-P33

C-P34

C-P34

Si02

53.851

53.312

52.844

K20 0.005

0.006

0.012

margin core

margin

Cr203

3.51 1

2.067 2.445

Appendir C- Microprobe Analyses of Garnet

Appendix C- Microprobe Analyses of Garnet

C-P34

C-P34

C-P35

C-P35

core

mnrejn

core

core

0.076 7.712 6.01 1

0.080 5.836

5.569

6.012

8.812

19.011

18.167

20.379

20.269

0.057 6.214

0.394

0.062

0.377

0.298

0.305 6.323

0.426 18.524

0 352

0.3 14

18.702

18.681

0.399 1x453

Appendix C- Microprobe .4nalyses of Garnet



Xenolith

C-PI5

C-P26

C-PZ6

C-P27

C-P27

margin

core

margin

core

margin -

C r 2 0 3

7.224

7.257

7.492

7.970

6.985

C-P32

C-P32

C-P33

C-P34

C-P33

C-P35

C-P35

0.016

0.030

0.045

0.015

0.03 1

Si02

4 1.050

40.530

40.742

40.476

40.71G

99.502

99.705

99.375

99.297

99.437

core 40.795

margin

margin

core

margin

core

core

PZ05

0.026

0.016

0.014

0.030

0.01 i ---

0.01 6

0.03 1

Tot31

100 153

99.604

100.063

100.050

100.22 1

7.309

4.861

6.338

6.066

6.43 1

6.950

99.293

100.165

40.671

41.132

40.689

40.614

4 1.336

31.351

Analyses Locations for Garnet in Xenolith A4-P5 (Refer t o Plate 3.1)

X-Y CO-ordinates and individual analyses are tabulated on the proceeding pages. The diniensions of the box below are 4x4mm.

5 2 1: ++ 94 , ç i + +

++ l + + 4- I - t 4

Appendix C- Microprobc Analyses of Garnet from A4-PS

Refer to Plate 3.1 and Preceeding Teinplate (X,Y = distance in microns froni origin)

Appendix C- Microprobe Analyses of Garnet from A4-PS

Refer to Plate 3.1 and Preceeding Template (X,Y = distance in microns froni origin)

Appendix C- Microprobe Analyses of Garnet froni A4-PS

Refer to Plate 3.1 iind Preceeding Teniplate (X,Y = distance in microns froiii oiigin)

A4-P5 Ca0 4.705

Analysis 94

Mg0 19.223

Mn0 0.325

X 3661

Y 2995

Ti02 0.806

Na20 0.104

Fe0 10.011

Appendix C- Microprobe Analyses of Giirnet from A4-P5

Refer to Plate 3.1 and Preceeding Teniplate (X,Y = distance in microns from origin)

Appendix C- Microprobe Analyses of Garnet from ,444'5

Refer to Plate 3.1 and Preceeding Teniplate (X,Y = distance in inicrons froni origin)

Appendix C- Microprobe Analyses of Gamet from A4-PS

Itefer to Plate 3.1 and Preceeding Teiiiplate (X,Y = distance in iiiicrons froni origin)

Mantle-equilibrated Chromite

Metasomatic Chrornite 1 Si02 1 Mn0 ] C a 0 1 A12031 Zn0 1 Cr2031 Mg0 1 Fe0 I~e203'1 Ti02 Ni0 ]Total INotes

0.109 (98.794 Ihtergrown with metasomatic phlog

* Fe203 re-calciil;ited frorii FeO(tota1) hy niethod of Drooli (1987)

* Fe203 re-calculated from FcO(total) by method of Droop (1987)

llmenite from Cl4 Xenolitlis

Z n 0 ~ r 2 0 3 ] Mg0 Fe0 Ti02 Ni0 Total 0.035 4.518 14.616 25.483 55.201 0.214 100.575

Notes li llmenite intergrom Ath metasomatic

Primary ilmenite

llmenite exsolving from metasornatic chromite Ilmenite exsolving from metasomatic chromite Discrete ilmenite, may be metasomatic

APPENDIX D Geothermometers and Geobarometers

APPENDIX D

Thermometer 0W79 (O'Neill and Wood. 1979)

eq. 1

eq. 2

temperature (degrees Kelvin) factor of thermal expansion and compressibility, eq. 2 below (Md@k+Fe)md *\,,, (Fef(M~+Fe)rn,i.,iinnc pressure (kbar) (Mç/(Mg+Fe+Ca),,,,, (Fe/(Mg+Fe+Ca),dp, (Ca/(Mg+Fe+Ca),d,,d distribution coefficient for the reaction (almandine+forsterite)=@yropetfayalite)

Thermorneter BKN (Brey and ~ o l i l e r , 1990)

wliere K , = (l-Ca*)qxl(l-Ca*)v Ca* = CasC/( 1 -NaxC) Xi.? = Fe/(FetMg)

- Tl,,,

- temperaîure (degrees kelvin)

P - - pressure (kbar)

Baronleter BKN ( Brey aiid Loliler. 1990, pg. 1372)

wliere

and R - - 8.3 143JKmol T - - temperature (degees Kelvin)

witli site occupai~cies (from Brey and Koliler (1990) after Nickel and Green, 1985 and Carswell and Gibb ( 1987) ( 1 ) pyroxenes

( a ) X,u"'qAl+Na-Cr-Fe"'-2Ti)i2 (b) X,,l,l,h"=AI"l du e to Tschem~ak's coniponent

jadeite=Na-Cr-Fe"-3Ti (b,) ifjadritec0, tlien X,, ,'"=(Al+jadeitc)/? (b,) if jadeite>O, tlieii X,,, ,:!'=(Al-jadeite)/2

(c) Mg and Fe on M 1 and M2

Xt:'=Xh,, hyl-XSI,.) X,,,."'==(l -X,,,'"-Cr-Fe3'-Ti)

1-Ca-Na-Mn) X,,,.=M&Mg+Fe)

(2) gamets X,,,@=AV(AI+Cr) X,,"=Cr/(Al+Cr) X,.,+Ca/(Ca+Mg+Fe+Mn) X,.,P-Fe/(Ca+Mg+Fe+Mn) X,,~=Mç/(Ca+Mg+FetMii)

Baroiiieter NC8S (Nickel and Green, 1985)

where

x,ulll = (Al-Cr-2Ti+Na)/l - - Al occupancy of Ml ui opx

XBPJ>'' = 1 -&"'-Cr-Ti - - MI sites occupied by Mg and Fe in opx XlP,,.,.hC = 1 -X,,lh"-Cr-Ti - - M2 sites occupied by Mg and Fe in opx X181'1 = [M_&lg+Fe]X,,,,,,"" - - Ml sites occupied by Mg only, in opx x, ,, l l l = [Fe~g+FeIX, , , ,~" - - Ml sites occupird by Fe o~iIy, in opx

- X,,,"" - ~M@8+Fel&.!F.~chc - - M2 sites occupied by Mg only. in opx X~ = [Fe/Mg+Fe]X,S,,,"' - - M2 sites occupied by Fe only. in opx k

Xr::' = [Ca/CaMg+Fe+MnILT X,;,F = [FrlCaMg+Fe+Mn]fl X,,? = [AlIAl+Cr]p X,.,P = [Cr/Al+CrJP P - - pressure ut kilobars

T - - temperature in degrees Kelviti

Barometer MC74 (MacGregor. 1974. equation solution in Fiiiiierty aiid Boyd, 1984)

wliere

a - - -3736 (307) wliere iiuttibers in brackets represetit 1 o iincertauities b - - -97.1 (3.5)

C - - 1.46 (0.71 1

T - - temperature in degrees Kelvin

P - - pressure in kilobars

APPENDIX E Count Times and Standards

APPENDlX E Count Times and Standards

Count Times Leiigth oftime (seconds) used to acquire element peaks of standards and xeiiolit mitierals. Count times for given elements Vary for eacli mineral species analyzed

"Standards ]=bustamite ~ = P Y ~ ~ P K 1 l=etistatite 2=gahnite 7=MnTiO, 1 2=liyperstlieiie 3=cliroinite 8yxTiAl 1 3=microclitie 4=Ni0 <)=albite 14=olFo85 5=SrTiO, I O=apatite {- )=tiot aiialyzed

APPLIED = IMAGE. lnc

O 1993, Applicd Image. Inc , All Righls Rosctvfd

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