Contribution to Precambrian Geology No. 23

Special Publication No. 9

International Geological Correlation Programme

Project 315 Correlation of Rapakivi Granites and Related

Rocks on a Global Scale

u 1993 MISSOURI

A 0 L L A

Symposium on

Rapakivi Granites and Related Rocks

Monday, March 29-Tuesday, March 30, 1993 University of Missouri-Rolla

Rolla, Missouri, United States of America

Abstracts Volume

Edited by Eva B. Kisvarsanyi

MISSOURI DEPARTMENT Of NATURAL llSOURCES Division o f Geology and Land Survey

P.O. Box 250 Rolla, M issouri 6 540 1

Rolla, 1993

•

International Geological Correlation Programme Project 315:

Correlation of Rapakivi Granites and Related Rocks on a Global Scale

Third General Meeting

March 29-30, 1993.

Rolla, Missouri

United States of America

Hosted by the MISSOURI DEPARTMENT OF NATURAL RESOURCES

Division of Geology and Land Survey

In conjunction with the 27th Annual Meeting of the North-Central Section of

The Geological Society of America

Honorary Chairman: J. Hadley Williams

General Chairman: Eva B. K1svarsanyl

Field Trip Chairman: W. Keith Wedge

Missouri Classification Number: Ge 21 :9

Klsvarsanyi, Eva B., Editor, 1993, INTERNATIONAL GEOLOGICAL CORRELATION PROGRAMME PROJECT 315, CORRELATION OF RAPAKIVI GRANITES AND RELATED ROCKS ON A GLOBAL SCALE: SYMPOSIUM ON RAPAKIVI GRANITES AND RELATED ROCKS, ABSTRACTS VOLUME (Contribution to Precambrian Geology No. 23), Missouri Department of Natural Resources' Division of Geology and Land Survey, 46 p, 1 Illustration.

As a recipient of federal funds, the Department of Natura/ Resources cannot discriminate against anyone on the basis of race, color, national origin, age, sex, or handicap. If anyone believes he/she has been subjected to discrimination for any of these reasons, he/she may file a complaint with either the Department of Natura/ Resources or the Office of Equal Opportunity, U.S. Department of the Interior, Washington D.C., 20240

ii

FOREWORD

"Rapakivi" is a Finnish word meaning "rotten stone." It is an old name applied to Proterozoic granite in the Wiborg area of Finland because ofits predilection to break into a fine grus upon weathering. The term "rapakivi granite" was introduced to international geologi­cal literature more than a century ago by the Swedish petrologist J. J. Sederholm. The classic rapakivi is red, porphyritic biotite granite containing ovoidal orthoclase phenocrysts mantled by oligoclase; zircon, monazite, allanite, and fluorite are characteristic accessory minerals. The mantled ovoids give this rock its distinctive "rapakivi" texture whose origin is still controversial.

The St. Francois Mountains of Southeast Missouri is one of few regions in the United States where rapakivi granites and related rocks are extensively exposed. The Missouri Department of Natural Resources, Division of Geology and Land Survey (DGLS) has con­ducted ongoing research on the geology of the region during the past 25 years under the Operation Basement project. Cooperative studies with the U.S. Geological Survey were carried out within the scope of the USGS Strategic and Critical Minerals Project. Studies included surf ace and subsurface mapping, geochemical analyses, aeromagnetic mapping, structural mapping, and mineral resource assessment. The results were published as reports and maps in DGLS's "Contribution to Precambrian Geology" series, in journals, and in USGS publications.

Proterozoic rapakivi granites are now recognized on all conti­nents as significant elements in the anorogenic and post-orogenic phase of intracratonic silicic magmatism. Rapakivi and related granites (rhyolites), mangerites*, and anorthosites**-the "anorogenic trinity" of Emslie--provide important data on the evolution of continents. The International Geological Correlation Programme (IGCP) of the International Union of Geological Sciences (IUGS) recognized the need for international cooperation in studying these rocks, and in 1 991 launched Project 3 1 5, "Correlation of Rapakivi Granites and Related Rocks on a Global Scale." The principal objective of the project is to correlate the tectonic setting, petrology, geochemistry, and metallogeny of these rocks worldwide. The project addresses the areal and temporal distribution, mechanism of emplacement, bimodal character, petrographic and chemical char-

Iii

acteristics, conditions of crystallization, and petrogenesis of this distinctive suite of rocks, and provides the international scope for some 250 geoscientists from the participating countries.

The first General Meeting of IGCP Project 315 was held in Helsinki, Finland in 1991 and was attended by 65 delegates from 14 countries; the abstract volume includes 53 papers by 85 authors. The second General Meeting was held in Kyoto, Japan, in conjunc­tion with the 29th International Geological Congress in 1992; sixteen papers were submitted and published in the 29th IGC Abstract Volume.

The third General Meeting of IGCP Project 3 15, hosted by the Missouri Department of Natural Resources, Division of Geology and Land Survey, was held in Rolla in conjunction with the 27th Annual Meeting of the North-Central Section of the Geological Society of America, March 29-30, 1993. A total of 36 abstracts were submitted by authors from 10 countries; 34 of the abstracts were presented in three half-day oral sessions and one poster session. This volume contains the accepted abstracts as organized for the meeting.

The abstracts span five continents from the classic rapakivi region of the Fennoscandian Shield through the Canadian and Brazilian Shields, to South Africa, China, India, and Australia. The topics range from petrologic consideration of rapakivi origin (Gavricova et al.; Creaser) through the bimodality of rapakivi suites (Lowell and Young; Yu et al.) to mineralizations associated with them (Bettencourt et al.; Larin and Neymark).

I thank Robert F. Dymek for his assistance in reviewing the abstracts, Sandra Miller and Lois Jaquess for re-typing them, and Susan Dunn for designing the cover and the final copy of the volume.

Eva B. Kisvarsanyi

* Mangerite: A rock intermediate between monzonite and diorite.

** Anorthosite: A rock composed almost wholly of plagioclase.

Iv

TABLE OF CONTENTS

SESSION I 1. 1. 7 Ga Post-Anorogenic Magmatism Along The Western Margin

of the Svecofennian Domain, Central Sweden ..................................... 3 2. Geochemical Characteristics of the Ragunda Rapakivi

Granite-Syenite Complex, Central Sweden ........................................... 4 3. Petrography and New U-Pb Age Data on the Ahvenisto

Rapakivi Granite Complex, Southeastern Finland ................................ 5 4. Disintegration and Recrystallization of Magmatic Mafic

Enclaves in Rapakivi Granites of Southeastern Finland ...................... 6 5. Comparative Geochemistry of Mafic Rocks Associated

With Rapakivi Granite Suites in SE Finland and SE Missouri ............ 7 6. Coexisting Mafic-Felsic Magmas in the St. Francois Terrane

of Southeast Missouri: Field and Chemical Evidence from the Silvermine Granite ................................................................................. 8

7. Fine-Grained Mafic Enclaves (FGE) in Jotunite and Mangerite at the Morin Complex, Quebec: Mineralogical and Chemical Evidence for an Origin as Autoliths (Recrystallized Cumulates) ..... 9

8. Quartz Mangerites (QM): The Forgotten Member of the Anorogenic Trinity ...................................................................................... 1 0

9. The Interior Magmatic Belt in the Eastern Grenville Province, Canada ............................................................................................................ 11

10. Rapakivi Granitoids, Central Labrador: Fluids and Stable Isotopes ........................................................................................................ 1 2

SESSION 11

1. Re-Examination of Models for the Origin of Granite-Rhyolite Provinces in the Midcontinent Region, USA ....................................... 1 5

2. The Grenville-Amazon Connection in the Framework of the Sweat Reconstruction ................................................................................ 16

3. Petrography, Geochemistry and Mineralization of the Younger Granites of Rondonia, Brazil ................................................... 17

4 . The Anorogenic Magnetite-Bearing Granites of the Eastern Amazonian Craton: Implications for the Genesis of A-Type Proterozoic Granites .................................................................... 18

5. Magmatic Pulses and Architecture of Rapakivi Complexes from the ltu Province (Late Precambrian, Sao Paulo State, SE Brazil) ........................................................................................................ 1 9

V

6. Origin of Middle Proterozoic Rapakivi Granites Surrounding the Olympic Dam Cu-U-Au-Ag Deposit, South Australia ................ 20

7. Late Kinematic Large-Feldspar Granites from Southeastern Africa and Comparisons with Rapakivi Granites from Europe and North America ...................................................................... 22

8. Field Petrographic Assay on the Occurrence of Rapakivi Texture in Metadolerite and Epidiorite of Dhanbad Area, India .................................................................................................... 23

9. Bimodal Rock Association of Rapakivi Suite and Proterozoic Rifting in Northern Beijing, China .......................................................... 24

10. The Shachang Rapakivi Granite Complex, Eastern China: Petrology and Nd, Pb, and Sr Isotope Geochemistry ...................... 25

11 . Proterozoic Anorogenic Granitoids of the Ukrainian Shield and Voronezh Crystalline Massif ............................................................ 26

SESSION III

1. Geochronological Constraints on the Emplacement History of an Anorthosite-Rapakivi Granite Suite: U-Pb Zircon and Baddeleyite Study of the Korosten Complex, Ukraine ....................................................................................... 29

2. Trace Element Geochemistry of Gabbros, Anorthosites and Granites of the Ukrainian Shield .................................................... 30

3. Petrogenesis of the Anorogenic Granitoids from the Southern Aldan Shield (in Comparison to the Rapakivi-Granites) ........................................................................................................ 31

4. Quartz Porphyry - Rapakivi Granite Volcano-Plutonic Association in Karelia, Russia .................................................................. 32

5. Metallogeny of the Early Proterozoic Trans-Siberian Anorogenic Volcano-Plutonic Belt ......................................................... 33

6. Position of the Anorthosite-Rapakivi Suite Among Other Types of Igneous Rocks ............................................................... 34

7. Isostatic Geodynamic Model for the Origin of Rapakivi Granites and Related Rocks ..................................................................... 35

8. Possibilities of Rapakivi Texture Formation in the System Albite-Anorthite-Orthoclase-Quartz(-Water) ....................... 36

9. New Thermobarometric Data for the Rapakivi-Granites: Subisothermal Rise of Magmas .............................................................. 3 7

10. Origin of Banded Fabric in Bengal Anorthosite Within Chhotanagpur Gneissic Complex, Eastern India ................................ 38

vi

11. The Ancient Rapakivi-Like Granites of the Baltic Shield ................. 39

POSTER SESSION IV

1. Fluid Rates During the Formation of Rapakivi Granites and the Peculiarities of Amphibole and Mica Compositions ......... 42

2. Orbicular Rapakivi Granites from the Salmi Massif .......................... 43

vii

viii

GSA NORTH-CENTRAL SECTION, MONDAY AFTERNOON MARCH 29, 1993

SYMPOSIUM: INTERNATIONAL GEOLOGICAL CORRELA­TION PROGRAMME (IGCP) 315:

CORRELATION OF RAPAKIVI GRANITES AND RE­LATED ROCKS

ON A GLOBAL SCALE

SESSION I

211 McNUTT HALL, 1 :00 p.m. J. Hadley Williams and Robert F. Dymek, Presiding

WELCOME AND INTRODUCTION, J. Hadley Williams and Eva B. Kisvarsanyi

page no.

1. Martin Ahl, 1.7 Ga POST-ANOROGENIC MAGMATISM ALONG THE WESTERN MARGIN OF THE SVECOFENNIAN DOMAIN, CENTRAL SWEDEN ........................................................... 3

2. Anders I. Persson, GEOCHEMICAL CHARACTERISTICS OF THE RAGUNDA RAPAKIVI GRANITE-SYENITE COMPLEX, CENTRAL SWEDEN ............................................................................... 4

3. Matti Vaasjoki, 0. Tapani Ramo, Reijo Alviola, and Bo S. Johanson, PETROGRAPHY AND NEW U-Pb AGE DATA ON THE AHVENISTO RAPAKIVI GRANITE COMPLEX, SOUTHEASTERN FINLAND ................................................................. 5

4. Pekka T. Salonsaari, DISINTEGRATION AND RECRYSTAL­LIZATION OF MAGMATIC MAFIC ENCLAVES IN RAPAKIVI GRANITES OF SOUTHEASTERN FINLAND ..................................... 6

5. Walter W. Boyd, Jr., Richard L. Cameron, and 0. Tapani Ramo, COMPARATIVE GEOCHEMISTRY OF MAFIC ROCKS ASSOCIATED WITH RAPAKIVI GRANITE SUITES IN SE FINLAND AND SE MISSOURI ................................................. 7

6. Gary R. Lowell and Glen J. Young, COEXISTING MAFIC­FELSIC MAGMAS IN THE ST. FRANCOIS TERRANE OF SOUTHEAST MISSOURI: FIELD AND CHEMICAL EVIDENCE FROM THE SILVERMINE GRANITE .............................. 8

7. Michael W. Rockow and Robert F. Dymek, FINE-GRAINED MAFIC ENCLAVES (FGE) IN JOTUNITE AND MANGERITE AT THE MORIN COMPLEX, QUEBEC: MINERALOGICAL AND CHEMICAL EVIDENCE FOR AN ORIGIN AS AUTOLITHS (RECRYSTALLIZED CUMULATES) ............................. 9

8. Robert F. Dymek, QUARTZ MANGERITES (QM): THE FORGOTIEN MEMBER OF THE ANOROGENIC TRINITY ......... 10

9. Charles F. Gower, THE INTERIOR MAGMATIC BELT IN THE EASTERN GRENVILLE PROVINCE, CANADA ................. 11

10. Ronald F. Emslie and Bruce E. Taylor, RAPAKIVI GRANITOIDS, CENTRAL LABRADOR; FLUIDS AND STABLE ISOTOPES .............................................................................. 12

2

1.7 Ga POST-ANO ROG EN IC MAGMATISM ALONG THE WEST­ERN MARGIN OF THE SVECOFENNIAN DOMAIN, CENTRAL SWEDEN

AHL, Martin, Department of Geology and Geochemistry, Stockholm University, 5-10691 Stockholm, Sweden.

The Transscandinavian Igneous Belt (flB) is a significant magmatic complex in central Sweden, which separates two principal crustal domains (Svecofennian [= 1J and Southwest Scandinavian [=21 Do­mains) of the Fennoscandian Shield from each other. The northeastern parts of TIB [=3aI, comprising the Siljan, Garberg, Ratan and Olden granitoids as well as the Dala Porphyries are characterized by:

a. a belt-shaped igneous complex along the margin of the Svecofennian Domain.

b. ages around =1.70 Ga. Furthermore, the Siljan and Garberg granites are peraluminous

with alkaline affinity and have high ratios of K/Na, Fe/Mg, high contents of Si0

2, Be, Nb, Sn, Rb, RE.E __________ _

(except Eu) and low contents of Ba, P and Sr. In these granites occasional Sn­Pb-Zn-Be-bearing greisen veins occur. e,~~J>°

The above mentioned features show that this group of granitoids displays , ,

' ' ' several transitional features between ' '

300 km

t,;,:,:j l -3a

~2 EHH!3b

other parts of the TIB (the postorogenic = 1.80 Ga Jama, Varmland and Smaland granitoids [=3b1) on one hand and the anorogenic=1.65-1.56 Garapakivi gran-ites in southern Finland [ =4 I on the other ....._ ____ ......___rn_gg_gl_4 _ ___,

hand. It is thus suggested that the northeastern part of TIB should be

considered as a distinct group of post- to anorogenic granitoids in the Fennoscandian Shield.

3

GEOCHEMICAL CHARACTERISTICS OF THE RAGUNDA RAPAKIVI GRANITE - SYENITE COMPLEX, CENTRAL

SWEDEN

PERSSON, Anders I., Geological Institute, Lund University, 5olveg. 13, 5-22362 Lund, Sweden.

The Ragunda massif (c. 550 km2) is one of two major Swedish massifs

belonging to the 1.65-1.54 GA Fennoscandian Rapakivi Complexes. The aero magnetic data indicate a series of more or less circular granite and syenite intrusions, younging from west to east. The country rock belongs to the 1. 9-1. 7 5 Ga old Svecofennian orogen.

The Ragunda complex includes about 25% gabbro and anortho­sitic gabbro in addition to syenite, quartz syenite, hornblende granite, biotite granite (the most frequent granitic rock) and felsic and mafic dikes. The biotite granite has normally up to 1 cm large, rectangular K-feldspar megacrysts, which occasionally are plagioclase mantled. Granophyric and even-grained varieties occur. Quartz frequently appears as drop quartz with crystals up to 8 mm in diameter.

The Ragunda granites are metaluminous to peraluminous (mo­lecular Al

20/ (CaO+Na

20+K

20) ratio 0.93 to 1.05). They are charac­

terized as A-type and within plate granites. Si02 (69.3 to 76.0 wt%), alkali contents (sums of Na

20+K

20::: 9 wt%), the K20/Na20 ratios

(average 1.53), and FeO/ FeO/MgO) ratios (ranging from 0.88 to 0. 99) are high. The abundance of CaO (average 0. 7 4 wt%) is low. The granites are high in F, Rb, Ga, Zr, Th, REE (except Eu) and have high Ga/ Al ratios (average 3. 7x 104 ). They are pronouncedly enriched in the LR.EE relative to chondrites. (La/Yb )N ratios are within the range 1 0 to 21. All granites have moderate to strong negative Eu anomalies (Eu/ Eu* = 0.2 7 to 0.09). One sample of fine-grained biotite granite has a very pronounced negative Eu anomaly (Eu/Eu* = 0.02).

The syenitic rocks have Si02

contents ranging from 58.5 to 66.6 wt%. Similarly to the granites, they have high FeO/(FeO/MgO) ratios (ranging from 0.87 to 0.98). In addition to their lower Si02 contents, they differ from the granites in having higher Al, Na and Fe abun­dances. The trace elements F and Rb are lower and Sc higher in the syenitic than in the granitic rocks.

4

'

PETROGRAPHY AND NEW U-Pb AGE DATA ON THE AHVENISTO RAPAKIVI GRANITE COMPLEX, SOUTHEAST­ERN FINLAND

V AAS/OKI, Matti, Geological Survey of Finland, 51-02150 Espoo, Finland; RAMO, 0. Tapanl, Department of Geology, University of Helsinki, P. 0. Box 115, 51-00171 Helsinki, Finland; ALVIOLA, Reljo and JOHANSON, Bo 5., Geological Survey of Finland, Sl-02150 Espoo, Finland.

The classical 161 5-1645 Ma Wiborg rapakivi granite batholith (> 18,000 km2) of southeastern Finland and adjacent Russia is flanked in the north with two smaller rapakivi granite complexes, Suomenniemi and Ahvenisto. In both of these, rapakivi granites are temporally and spatially associated with mafic rocks. We describe the petrography of and report new U-Pb zircon age data on the silicic and mafic rocks of the Ahvenisto Complex, in which the mafic rocks are much more in evidence than in any of the other Finnish rapakivi granite plutons.

The Ahvenisto Complex consists of an oval biotite rapakivi granite (240 km2

) surrounded by a horseshoe-shaped gabbroic body (70 km2), and a number of quartz-feldspar porphyry and diabase dykes. Rock types in the gabbroic body range from troctolite to anorthosite but also include monzodiorite and quartz monzodiorite. The silicic and monzodioritic rocks always cut the gabbroic rocks. The monzodiorites also form the major component in conspicuous net­veined (silicic-mafic) complexes found within the mafic body.

Zircons from two gabbroic rocks of the Ahvenisto Complex are almost concordant and yield 207Pb/2°6Pb ages of 163 7 ± 7 Ma (leucotroctolite) and 1645±5 Ma (leucogabbronorite). Zircons from a quartz-feldspar porphyry dyke that cuts all the other rock types of the Complex have an upper intercept age of 1633±2 Ma. These data show that the Ahvenisto Complex belongs to the earliest intrusive bodies of the Wiborg area. They also suggest that there probably exists a definite (ca. 5 Ma) age difference between the gabbroic rocks and the silicic dyke rocks of the Complex.

5

DISINTEGRATION AND RECRYSTALLIZATION OF MAGMATIC MAFIC ENCLAVES IN RAPAKIVI GRANITES OF SOUTHEASTERN FINLAND

SALONSAARI, Peick.a T., Department of Geology, University of Helsinki, P. 0. Box 115, SF-00171 Helsinki, Finland.

A mafic microgranular enclave {MME) is a droplet of mafic magma within a more felsic host, produced by mingling of mafic and felsic magmas. Minerals of MME's are usually identical to those in the host rock but their relative abundance and grain size may differ. Reaction of small{(/)< 2 cm) MME's with their felsic host convert the former into micro-enclaves identified as recrystallized MME's or mineral aggregates or individual crystals. The grain size of horn­blende, biotite, and plagioclase usually approaches the grain size of the host rock. A typical micro-enclave shows an abundance of magnetite grains and apatite needles that illustrate the size and shape of the primary MME.

In SE Finland, four types of partially or totally recrystallized MME's have been discovered from dark rapakivi granites of the Wiborg Batholith and the bimodal Jaala-litti Complex: 1) MME's with recrys­tallized borders characterized by growth of hornblende, biotite and occasionally plagioclase. The central parts consist of the same minerals but show smaller grain size. 2) Totally recrystallized MME's. Only individual magnetite grains, apatite needles, and plagioclase laths illustrate the primary MME shape. 3) Irregular mineral aggre­gates {usually hornblende-biotite-plagioclase) with varying amounts of magnetite and apatite. Hornblende, biotite, and plagioclase are strongly recrystallized. 4) Individual phenocryst-like grains of horn­blende and biotite with quartz, magnetite, and apatite inclusions. These are thought to derive from small primary MME's.

Recrystallization of MME's is an effective method of increasing the amount of hornblende, biotite, and plagioclase in a felsic magma, but one that may leave only little trace as to the identity of the primary components involved.

6

COMPARATIVE GEOCHEMISTRY Of MAFIC ROCKS ASSO­CIATED WITH RAPAKIVI GRANITE SUITES IN SE FINLAND AND SE MISSOURI

BOYD, Walter W.,Jr., DepartmentofGeology, University of Helsinki, P. 0. Box 115, 51-00171 Helsinki, Finland; CAMERON, Richard L., 1344 N. Bluff Rd., Collinsville, IL 62234; RAMO, 0. Tapanl, Department of Geology; University of Helsinki, P. 0. Box 115, 51-00171 Helsinki, Finland.

Evolved Fe-rich tholeiite dykes are associated temporally and spatially with rapakivi granites of the Wiborg Batholith and satellite appendages. Two sets of diabase dykes were intruded in three pulses, the latest coinciding with the intrusion of rapakivi related (quartz­feldspar porphyry) dykes. Petrologic models suggest that gabbroic assemblages were important fractionates; only plagioclase, however, appears as a phenocryst in the diabases.

Sylvester and coworkers (1981, 1985) differentiated two groups of mafic flows and intrusions associated with granites of the St. Francois Mountains in SE. Missouri on the basis of age and trace element arrays. The oldest (Silver Mines) are subalkaline olivine-free basalts occurring as dykes and thin flows coeval with the main caldera­related granite suites. The second (Skrainka) are dykes spatially associated with the caldera granites, but ca. 200 Ma younger.

Both suites span similar major element compositional ranges, lying within the field of Continental Flood Basalts (CFB). Projection into normative diagrams with superimposed phase boundaries shows a different disposition for the two suites about low pressure cotectics. Reported phenocryst assemblages confirm only part of the required fractionates; trace-element geochemistry provides further constraints on petrogenetic models involving the degree of crustal contamination and the amount of partial melting in source regions.

7

COEXISTING MAFIC-FELSIC MAGMAS IN THE ST. FRANCOIS TERRAN£ OF SOUTHEASTERN MISSOURI: FIELD AND CHEMI­CAL EVIDENCE FROM THE SILVERMINE GRANITE

LOWELL, Gary R. and YOUNG, Glen/., Department of Geosdences, Southeast Missouri State University, Cape Girardeau, Missouri 63701.

Analogy between the St. Francois Terrane (SIT} and classic rapakivi terranes ofFinland suffers from lack of evidence for coexisting basaltic and granitic magmas. In the eastern St. Francois Mountains, Silver Mines Mafic Group (SMMG) dikes form a NE-trending swarm cutting the Silvermine Granite (-1500 Ma), largest of the "low-silica granite" ring plutons of the Butler Hill Caldera (BHC). Mapping in this pluton has revealed a 1.5 km long zone of granite-hosted hybrid mafic rocks near Tiemann Shut-in. This hybrid zone exhibits mixing/ mingling features that include: mafic pillows with quenched margins, back-veined pillows, double enclaves, mantled feldspars, quartz ocelli, and pillow fragmentation. These features are confined to medium­grained granite below the roof fades. The hybrid zone indicates that a diapir of basaltic magma intruded partially crystallized Silvermine Granite magma. Absence of silicic hybrids and prevalence of mafic pillows suggest that compositional and crystallinity contrasts between the two magmas were relatively high. The hybrid pillows and host are cut by aplite dikes that may represent local remelting of the granite near contacts with the basaltic diapir. The entire complex is cut by fracture-controlled SMMG dikes. The salient trait of the "low-silica granite" ring plutons of the BHC is the ubiquitous presence of small, rounded, tonalitic enclaves that comprise 10-20% of the pluton mass. Incompatible element ratios and REE data from these enclaves suggest correlation with the SMMG. This implies contamination of the BHC ring plutons early in their cooling history by basaltic magma which was subsequently dispersed as "inclusions" by convection. This conclusion has important implications for the use of whole rock data from the "low-silica granites" and petrologic modelling of BHC events. It also invites application of the Huppert-Sparks (1988) model for generation of granitic magmas and strengthens the SIT analogy with Finnish rapakivi terranes.

8

FINE-GRAINED MAFIC ENCLAVES (FGE) IN JOTUNITE AND MANGERITEATTHE MORIN COMPLEX, QUEBEC: MINERALOGI­CAL AND CHEMICAL EVIDENCE FOR AN ORIGIN AS AUTOLITHS (RECRYSTALLIZED CUMULATES)

ROCKOW, Michael W. and DYMEK, Robert 1., Department of Earth and Planetary Sciences, Washington University, St. Louis, MO 63130.

FGE in the Morin Complex have elliptical to rounded cross-sections (-3x5 cm), exhibit sharp contacts against their hosts, and display a distinctive "salt and pepper" appearance with homogeneous granoblastic textures. Three types have been distinguished: I 1 JType J (found exdusivelyin jotunite=monzodiorite) have the same mineralogy as their hosts (plag + opx + cpx + hbl + ilm + mgt + ap); [21 Type M 1 (found in mangerite:: qtz. monzodiorite/monzonite) have the same mineralogy as their hosts (plag + Kf + qtz + opx + cpx + hbl + ilm + mgt + ap), with a few containing larger poikilitic hbl; [3I Type M2 (found in mangerite) contain conspicuous quantities of biotite, unlike their biotite-free hosts. The compositions of plag, opx and cpx (determined by microprobe methods) in each of 20 analyzed host-FGE pairs varies by only a few mole %, although the total compositional range in the sample suite is quite large (e.g., An

46 to An

22, En

57 to En

45), with jotunite host-FGE minerals systematically more

calcic and magnesian than those in mangerites. In all cases, mineral compo­sitions in FGE are essentially identical to those in their hosts. Whole rock compositional data were acquired by XRF and INA methods on 15 host-FGE pairs. Type J FGE and their hosts have similar compositions (e.g., -4 7-52% Si02),

withlow~O,Baandh. TheamountsofTi02,P20 5,fe20 3-TandMg0arehighly variable, but can be explained by variations in the modal amounts of pyroxene, apatite and Fe-Ti oxide. Type M 1 FGE also are similar compositionally to their mangerite hosts (e.g., -52-65% Si0

2), with high K

20, Ba and a. Type M2 FGE

are distinct from their hosts, containing exceptionally high~ 0 and Ba, and low MgO and Zr. REE fractionations in type J FGE are variable with respect to their hosts. REE in types M 1 and M2 FGE have the same sense of fractionation as their hosts, with the M 1 FGE having higher REE than their hosts and M2 FGE having lower REE than their hosts.

We conclude that the types J and M 1 FGE are autoliths, probably recrystallized cumulates: this accounts for the similarities in mineral assem­blage, and mineral and whole rock compositions between hosts and FGE, as well as the variety in the type J FGE. The type M2 FGE, on the other hand, seem to be either xenoliths or contaminated M 1 FGE because they do not contain the same mineral assemblages as their hosts, nor do they have similar whole rock compositions.

9

QUARTZ MANGERITES (Q.M): THE FORGOTTEN MEMBER OF THE ANOROGENIC TRINITY

DYMEK, Robert 1., Department of Earth and Planetary Sciences, Washing­ton University, St. Louis, MO 63130.

Quartz mangerites comprise a suite of green-colored, pyroxene-bearing, granitoid plutonic rocks, broadly quartz monzodioritic to quartz monzonitic in overall composition, having Si0

2-contents in the range -57-65 wt'°k. QM are

metaluminous, with modest amounts of Al20

3 (-14-17 wt'°/o), and variable

quantities of Na2 0 (-3-5 wt'°k), Kz O (-2-5 wt:%) and CaO (-3-7 wt'°k). QM have

moderate Fe20

3-T (3-6 wt'°k) and low MgO (<1-3 wt%) yielding relatively low

values of mg(-0.2-0.4). QM have high Ti02

(1-3 wt'°/o) and P20 5 (0.8-1 .6 wt'°k), which distinguish them from virtually all other granitoids at a given level of SiO z­QM contain low concentrations of ferromagnesian trace elements (Sc, V, Cr, Co, Cu, Ni), Rb, Sn, W, U and Th. However, concentrations of high-field-strength cations (Zn, Ga, Zr, Nb, Y, REE, Hf, Ta), Ba and Sr are high. The mineralogy of QM include antiperthitic intermediate to sodic plagioclase (-An40 to An25), perthitic orthoclase (or less commonly microcline), dino- and ortho-pyroxene having intermediate XMs (-En

3s..

50), and pargasitic hornblende, likewise with intermedi­

ate XMs' containing high K (-1.5-2.0 wt'°/o) and high K/Na: such potassic compositions appear unique to QM. Additional phases include abundant ilmenite + magnetite, apatite and zircon, along with traces of biotite and sulfide; sphene is absent. Macroscopically, QM can be described in terms of a semicontinuous network of feldspar and quartz separated by streamlined mafic aggregates. The latter commonly merge into layers and/or schlieren, providing evidence for differentiation by separation of a mafic component (Fe-Ti-P liquid ?). Differentiation through plag + Kspar co-crystallization is suggested by Rb-Sr-Ba data.

QM form plutons exceeding 500 km2 in area, many of which are associated with massif anorthosite: these have been interpreted as products of crustal and mantle melting, respectively. Many QM also occur with jotunites (similar green rocks of overall monzodiorite composition, with Si02 in the range -4 7-56 wt'°k). Continuity of mineral and rock compositions from anorthosite to jotunite to quartz mangerite suggest co-magmatism among these lithologies. Such relationships are consistent with several geochemical properties of QM such as high TI/V and Ga/ Al. In either case, QM have intermediate compositions whose mere existence belie the widely held concept of bimodal magmatism applied to anorogenic suites.

10

THE INTERIOR MAGMATIC BELT IN THE EASTERN GRENVILLE PROVINCE, CANADA

GOWER, Charles F., Geological Survey Branch, Newfoundland Dept. of Mines and Energy, P. 0. Box 8700, St. John's, Newfoundland, A 1 B 4/6, Canada; TUCKER, Robert D., Dept. of Earth and Planetary Sciences, W ashlngton University, One Brookings Drive, St. Louis, MO 63130-4899, U.S.A.

The eastern Grenville Province can be divided into an Exterior Thrust Belt and an Interior Magmatic Belt. The northern Exterior Thrust Belt underlies the 200-km-wide margin of the Grenville Province and comprises parauthochthonous to allochthonous crust, largely formed during the 1710-1620 Ma Labradorian Orogeny, but re-activated during Grenvillian orogenesis.

The southern Interior Magmatic Belt (at least 250-km wide) is much less well known, but studies completed so far indicate that it is distinctly different. The differences include (i) a near absence of high­grade pelitic gneisses, comparable to the early Labradorian examples that underlie huge areas in the Exterior Thrust Belt, (ii) a lack of calc­alkaline quartz diorite to K-feldspar megacrystic granodiorite, (iii) the sporadic occurrence of lower grade, probably post-Labradorian metasediments, (iv) an overwhelming dominance of alkali-rich grani­toid rocks, certainly emplaced between 1500-14 70 Ma (Pinwarian event), and probably also at ca. 1145 Ma, (v) the prominence of presently undated rocks of the anorthosite-mangerite-charnockite­granite suite, (vi) the presence of numerous late- to posttectonic (960 Ma) rapakivi-textured Grenvillian plutons.

The thesis is advanced that the Interior Magmatic Belt is largely the product of post-Labradorian events south of the preserved Labradorian orogen. The 1500-14 70 Ma rocks are noted as compo­sitionally and temporally similar to the ca. 1460 Ma granite - rhyolite terrane of the mid-west USA and it is suggested that they belong to a tectonic environment that was common to the whoie southern flank of Laurentia-Baltica at this time. The 1145 Ma rocks are compared to those produced throughout the Grenville Province during exten­sional, anorogenic magmatism between 1180 and 11 20 Ma. The 960 Ma plutons are interpreted as the product of post-collisional effects related to Grenvillian orogenesis.

1 t

RAPAKIVI GRANITOIDS, CENTRAL LABRADOR: FLUIDS AND STABLE ISOTOPES

EMSLIE, Ronald F., and TAYLOR, Bruce E., Geological Survey of Canada, 601 Booth St., Ottawa K 1 A 0£8 Canada.

Large rapakivi granite and related felsic plutons (-1292-1322 Ma) are closely associated with anorthositic magmatism in the Nain Plutonic Suite (NPS). All of the granitoids exhibit chemical and mineralogical features of the classic rapakivi suites of the Baltic Shield but only the Makhavinekh pluton has well-developed mantled felds­par textures. Fluorine in biotite and hornblende (0. 1-4.3 and 0.2-0.8 wt%, respectively) in most granitoids is higher than chlorine in biotite and hornblende (0.01-0.2 7 and 0.14-0.52 wt%, respectively). Biotite in a late topaz-bearing dyke contains 4 .3 wt% F and has Fe# 0.986, implying exceedingly low H

20:F in some late-stage fluids. Homoge­

neous ilmenite with 2-4 mot % hematite is characteristically the sole oxide mineral in most granitoids constraining redox conditions to 1 to 3 log units below FMQ throughout crystallization.

Oxygen isotope studies indicate average 0180 values of 6.9 to 8.4, with little variation (s.d.= 1-2 permil) for the plutons, similar to other examples of anorogenic magmatism. A dominantly igneous lower crust is indicated as the magma source. High Fe/(Fe+Mg) in both biotite and hornblende resulted in large mineral-H20 (or mineral­magma) hydrogen isotope fractionations. Biotite and hornblende have low oD values (-125 to-90; mostly-110 to -90) and are in mutual equilibrium. A decrease in oD also accompanies an increase in F in these minerals, as expected. The magmatic H

20 had a oD value of

about -45, and evidence for degassing is not apparent. The stable isotope data are consistent with an origin of these rapakivi granitoids which excludes extreme degassing scenarios or involvement of upper crustal rocks or fluids. Indeed, the hydrogen isotope data suggest the magmas probably remained undersaturated in H2 0 throughout most or all of their crystallization intervals.

12

GSA NORTH-CENTRAL SECTION, TUESDAY MORNING MARCH 30, 1993

SYMPOSIUM: INTERNATIONAL GEOLOGICAL CORRELA­TION PROGRAMME (IGCP) 315:

CORRELATION OF RAPAKIVI GRANITES AND RELATED ROCKS ON A GLOBAL SCALE

SESSION II

211 McNUTI HALL, 8:00 a.m. Eva B. Kisvarsanyi and Ronald F. Emslie, Presiding

1. W.R. Van Schmus, RE-EXAMINATION OF MODELS FOR THE ORIGIN OF GRANITE-RHYOLITE PROVINCES

page no.

IN THE MIDCONTINENT REGION, USA ....................................... 15

2. Georg R. Sadowski and Jorge Bettencourt, THE GRENVILLE-AMAZON CONNECTION IN THE FRAMEWORK OF THE SWEAT RECONSTRUCTION .................. 16

3. Jorge S. Bettencourt, Washington B. Lette, Jr., and Bruno L. Payolla, PETROGRAPHY, GEOCHEMISTRY AND MINERALIZATION OF THE YOUNGER GRANITES OF RONDONIA, BRAZIL ............................................. 1 7

4 . Roberto Dall'Agnol, Marilia S. Magalhaes, and Carlos E.M. Barros, THE ANOROGENIC MAGNETITE-BEARING GRANITES OF THE EASTERN AMAZONIAN CRATON: IMPLICATIONS FOR THE GENESIS OF A-TYPE PROTEROZOIC GRANITES ............................................................... 18

5. Eberhard Wernick, MAGMATIC PULSES AND ARCHITECTURE OF RAPAKIVI COMPLEXES FROM THE ITU PROVINCE (LATE PRECAMBRIAN. sAo PAULO STATE, SE BRAZIL) ............................................................................. 19

13

6. Robert A. Creaser, ORIGIN OF MIDDLE PROTEROZOIC RAPAKIVI GRANITES SURROUNDING THE OLYMPIC DAM Cu-U-Au-Ag DEPOSIT, SOUTH AUSTRALIA .................... 20

7. Alan Kerr and RobertJ. Thomas, LATE KINEMATIC LARGE-FELDSPAR GRANITES FROM SOUTHEASTERN AFRICA AND COMPARISONS WITH RAPAKIVI GRANITES FROM EUROPE AND NORTH AMERICA ..................................... 22

8. Santosh Kumar, FIELD PETROGRAPHIC ASSAY ON THE OCCURRENCE OF RAPAKIVI TEXTURE IN METADOLERITE AND EPIDIORITE OF DHANBAD AREA, INDIA ......................... 23

9. Jian-Hua Yu, Hui-Qin Fu, and Fang-Xiao-Fang Wan, BIMODAL ROCK ASSOCIATION OF RAPAKIVI SUITE AND PROTEROZOIC RIFTING IN NORTHERN BEIJING, CHINA .................................................................................. 24

10. 0. Tapani Ramo, llmari Haapala, Matti Vaasjoki, Jian Hua Yu, and Huei Qin Fu, THE SHACHANG RAPAKIVI GRANITE COMPLEX, EASTERN CHINA: PETROLOGY AND Nd, Pb, AND Sr ISOTOPE GEOCHEMISTRY ...................... 25

11. Yu. T. Sukhorukov and K.I. Sveshnikov, PROTEROZOIC ANOROGENIC GRANITOIDS OF THE UKRAINIAN SHIELD AND VORONEZH CRYSTALLINE MASSIF .................................................................................................. 26

14

t

RE,.EXAMINATION OF MODELS FOR THE ORIGIN Of GRANITE,. RHYOLITE PROVINCES IN THE MIDCONTINENT REGION, USA

VAN SCHMUS, W.R., Department of Geology, University of Kansas, Lawrence, KS 66045.

New isotopic data for the 1.4 7 Ga Eastern Granite-Rhyolite Province and the 1.3 7 Ga Southern Granite-Rhyolite Province require re-examination of models for the origin of these suites of rock. For the most part, eNd(t) values for the granite-rhyolite provinces and A-type plutons intrusive into adjacent Early Proterozoic basement are compatible with origin through melting of 1.8 Ga continental crust (Nelson and DePaolo, 1985). However, new data (Bowring et al., 1992) show that southeastern parts of the granite-rhyolite provinces yield positive eNd(t) values, which can only be explained by derivation from 1.5 Ga continental crust. The transition from older substrate ( 1.8 Ga) to younger substrate ( 1 .5 Ga) occurs along a NE-SW line from Detroit, Ml to eastern Oklahoma; it probably represents the edge of the pre-1.6 Ga craton. A further variation in eNd(t) data is an E-W trending belt of intermediate values in northern Oklahoma; eNd(t) data south of this belt, in S. Oklahoma, are equivalent to that in Kansas and Nebraska, reflecting ca. 1.8 Ga lower crust.

The granite-rhyolite provinces are not related to any well defined tectonic event, and they have commonly been referred to as" anorogenic." The thermal event responsible for producing the silicic melts may have been associated with an extensional regime, in view of the A-type character of the granites. However, the 1.5 Ga crust underlying the SE parts of the granite-rhyolite provinces suggests that there may be a 1.5 Ga magmatic arc accreted to the margin of the 1.6 Ga craton. Formation of this arc must have been followed within a few tens of m.y. by a major rise in the geotherm which melted not only its lower crustal regions, but also Early Proterozoic crust throughout the U.S. A similar event must have followed about 100 m.y. later, affecting the south­central region. The intermediate eNd(t) values in Oklahoma may denote an E­W zone of crustal extension in which melts formed from 1.8 Ga crust with a significant contribution from 1.3 7 Ga mantle-derived magmas (fractional crystallization of mafic magmas at the base of the crust?). The heat for the regional 1.4 7 Ga magmatism is problematical, but the presence of a continental margin along the SE edge of the craton suggests a tectonic regime similar to that which produced voluminous felsic volcanic suites of the Cordillera (shallow subduction of delamination of continental lithosphere?). Restriction of melting to Early Proterozoic provinces resulted either because the Archean craton was not fertile enough to produce A-type melts, or because a deeper keel to the Archean craton prevented an influx heat.

15

THE GRENVILLE-AMAZON CONNECTION IN THE FRAME­WORK OF THE SWEAT RECONSTRUCTION

SADOWSKI, Georg R., BEITENCOURT, Jorge, lnstltuto de Geodendas, Unlversldade de Sao Paulo, SP, Brasil.

Possible paleogeographic connection between the Grenville and Rondonia-Sunsas provinces is reinforced by the timing of thermo­metamorphic and plutonic events. Equivalent terms of regional geological time scales are: Ketilidian=Transamazonian; Paleohelikian or Elsonian = Rondonian-San Y gnacio; N eohelikian or Grenvillian=Sunsas; Hadrynian=Brasiliano. Remobilization of older crust is another common feature affecting both provinces in Helikian time. Two pulses of potash rich plutonism responsible for granitoid intrusions from about 1.1 to 0.95 Ga may be detected in Grenvillfa from Labrador to Texas and in the Rondonian-Sunsas Province of the Amazon Craton. Differences between the provinces include the large anorthositic massifs of Northeastern Laurentia whose equivalents in Rondonia are small, layered mafic and gabbroid bodies, basic and mangeritic/charnockitic intrusions and the large extensional and transtensional features of Sunsas age in the SW Amazon.

Significant AMCG plutonism in Grenvillian times roughly coeval with the transtensional features in the Amazon Craton allow two models of evolution to be postulated:

a. Amazonian transtensional features originated in response to collision along the Grenville front similar to the reactivation of the Asian continent due to the Himalayan push (diva basins and magmatism on the Sinian Platform).

b. Major continental extension preceding separation of Laurentia from Amazonia long before the Cambrian.

16

PETROGRAPHY, GEOCHEMISTRY AND MINERALIZATION OF THE YOUNGER GRANITES OF RONDONIA, BRAZIL

BETTENCOURT, Jorge S., IGc-USP, C.P. 20.899, CEP 05508, Sao Paulo­SP; LEITE, Washington B., Jr.; PAYOLLA, Bruno L., IGCE-UNESP, C.P. 178, CEP 13.500, Rio Claro-SP, Brazil.

The younger Granites of Rondonia occur as epizonal multiphase batholiths and stocks. They consist of several kinds of granites emplaced about 1.05 to 0.95 Ga (Rb-Sr ages) into medium- to high­grade metamorphic terrains of the Rio Negro-Juruena ( 1. 7 5-1.50 Ga) and Rondonian ( 1.45-1.25 Ga) Provinces.

Early intrusive phases are coarse-grained porphyritic biotite (±hastingsite) monzogranite and syenogranite, with local rapakivi texture. Intermediate intrusive phases are porphyritic to equigranular biotite syenogranite and alkali-feldspar granite. The latest intrusive phases are protolithionite-albite granite. Granites are metaluminous to slightly peraluminous rocks characterized by high Fe/(Fe+Mg) and K(K + Na) ratios as well as by high Ga, Rb, Zr, Y, F and REE contents. They show the geochemical characteristics of subalkaline A-type granites and within-plate granites. Tin, tungsten, niobium, tantalum, beryllium, fluorine and sulphide mineralizations are associated with two latter phases, mostly as: pegmatite with topaz and beryl, albite granite with cassiterite and columbite-tantalite(?), greisen bodies with cassiterite, and quartz veins with cassiterite, wolframite, beryl and Cu-Pb-Zn-Fe sulphides.

17

THE ANOROGENIC MAGNETIT£...8EARING GRANITES OF THE EASTERN AMAZONIAN CRATON: IMPLICATIONS FOR THE GENESIS OF A-TYPE PROTEROZOIC GRANITES

DALL'AGNOL, Roberto; MAGALHAES, Marilla 5., BARROS, Carlos E.M., Centro de Geoclenclas, Caixa Postal 1611, 66075-900, Belem, PA, Brazil.

The anorogenic granites are widespread in the Amazonian Cra­ton. The Jamon ( 1 .6 Ga, Rb-Sr isochron), Musa and Cigano (both with 1.88 Ga, zircon U-Pb ages) are not foliated, shallow level granites, cross-cutting Archean terranes. (Amphibole)- biotite monzo-and syenogranites, metaluminous to slightly peraluminous, are the domi­nant fades. These granites crystallized under relatively high f0

2 near

the NNO and HMlTQ buffers. Oxide mineral assemblages include magnetite + ilmenite (±pyrite). These rocks have geochemical characteristics of A-type, within-plate granites, and display relatively high Y /Nb ratios (A2 type). They show some geochemical similarities with the Fennoscandian shield rapakivi granites, although they gener­ally contrast in f0

2 and textural aspects with them. Concerning the f0

2 conditions the studied granites are similar to the Middle Proterozoic A-type granites of Southern California. Geochemical and petrological aspects, associated to the high 87Sr/86Sr ratios found in the Jamon, Musa and Cigano granites, indicate that they were derived by high temperature anatexis of lower crust Archean terr an es. An origin of the Proterozoic A-type granites by crustal anatexis has been generally assumed in the North American province, as well as in the Fennoscandian shield. This points to a peculiar evolution for the Proterozoic granite genesis on a global scale and strengthens the tectonic links between the Amazonian craton and the aforementioned provinces.

18

MAGMATIC PULSES AND ARCHITECTURE Of RAPAKIVI COMPLEXES FROM THE ITU PROVINCE (LATE PRECAM­BRIAN, SA.O PAULO STATE, SE BRAZIL)

WERNICK, Eberhard, Departamento de Petrologla e Metalogenla, UNESP, P. 0. Box 178, 13500 Rio Claro, SP, Brazil.

The emplacement of the rapakivi complexes from the ltu Prov­ince which surround the Parana Basin is controlled by an expressive bundle of transcurrent faults. Three main types of intrusions are recognized: 1. circular bodies located nearby the transcurrent faults (e.g. the ltu complex); 2. droplike shaped intrusions located on transcurrent faults and cut by them (e.g. the Sao Francisco complex); 3 . "S"-shaped wormlike intrusions located on conjugated faults which connect major parallel transcurrent faults.

In all cases the complexes are of multiple nature, either mono­(subalkaline potassic) or pluriserial (calc-alkaline+subalkaline potassic+alkaline) and built up by at least three magmatic cycles each evolving from basic to acidic compositions. In all cases the input of a new magma cycle is related to a well defined longitudinal, lateral or vertical growing phase of the complexes which reflect successive reactivation phases of the faults. In this way the magmatic evolution and architecture of the rapakivi complexes is quite similar to that of true calc-alkaline ones.

19

ORIGIN Of MIDDLE PROTEROZOIC RAPAKIVI GRANITES SURROUNDING THE OLYMPIC DAM Cu-U-Au-Ag DEPOSIT, SOUTH AUSTRALIA

CREASER, Robert A., Dept. of Geology, University of Alberta, 1-26 Earth Sciences Bldg., Edmonton, Alberta Canada T6G 2E3.

The Olympic Dam Breccia Complex (ODBC) and Cu-U-Au-Ag deposit comprise part of the subsurface Burgoyne batholith (BB) on the northern Stuart Shelf, South Australia. All BB granites are metaluminous and vary from quartz monzodiorite (56% Si0

2) to

granite (ss) with rapakivi texture (71 o/o Si02), and all have high K, Ba,

Rf.E, U, Th, Zr, Nb, F and low Mg, Cr, Ni, V relative to average Phanerozoic granites. Two distinct suites are recognized from the BB; one suite (Wirrda Suite; WS) is considered here. All WS granites have similar initial Sr (0.7087) and Nd (ENd = -5.0) isotopic compositions and emplacement ages ( 1590 Ma; U-Pb zircon/titanite). The local host for the ODBC is a felsic rapakivi granite, the Roxby Downs Granite (RDG). Hornblende geobarometry from mafic granites and the presence of related volcanic rocks intruded by granite dykes indicate sub-volcanic crystallization of the BB.

Origin of the rapakivi RDG is linked to crystal accumulation and fractionation processes in a subvolcanic environment. Gradational contacts, compositional heterogeneity and cumulate textures in mafic WS granites suggest an origin via crystal accumulation; this is sup­ported by their geochemical characteristics. Felsic rapakivi granites such as RDG are compositionally uniform and represent the fraction­ated liquid complement to the crystal accumulation process that generated the mafic granites. This is suggested by both the geochem­istry of felsic granites and intrusive relationships within the WS, where felsic granites are consistently younger than mafic ones. No WS granite is representative of a "primary magma" from which fraction­ated and cumulate granites could have been derived. Voluminous, chemically homogeneous quartz latites (QL) from the area have identical ages and similar initial isotopic compositions to WS granites, and are a viable primary magma. Geochemical modelling suggests that crystal fractionation and accumulation from such a QL magma can

20

yield the diverse, related suite ofWS granites seen; about 25% removal of QL phenocrysts (cpx, plag, biot, oxides) is required to generate the rapakivi ROG.

Isotopic and trace element modelling suggests that the primary QL magma is unlikely to originate by mixing of mantle derived magma and existing crustal material; an origin by crustal partial melting is proposed. Simplistic modelling of a homogeneous crustal source suggests that broadly tonalitic to granodioritic source compositions can satisfy the observed geochemical characteristics of the primary QL magma. The high eruption temperatures (950-1000°C) and low water content ~2%) recorded for these QL magmas are consistent with both experimental and modelled partial melting behavior for source rocks of these compositions. The high geothermal gradients necessary for crustal melting at these temperatures are preserved in contemporaneous granulite terranes of the region.

21

LATE-KINEMATIC LARGE-FELDSPAR GRANITES FROM SOUTHEASTERN AFRICA AND COMPARISONS WITH RAPAKIVI GRANITES FROM EUROPE AND NORTH AMERICA

KERR, Alan, Geology Dept., University of Natal, Durban 4001, South AhlCct; THOMAS, Robert J., Geological Survey, P. O. Box 900, Pletermarltzburg 3200, South AhlCct.

Late-kinematic, large K-feldspar granites (the Oribi Gorge Suite) of late Proterozoic age (± 1050 Ma) occur as ten major plutons within a north-south erosional inlier in Natal, southeastern Africa.

Petrographically, biotite- and/or hornblende-bearing types pre­dominate, but charnockitic members, which are found locally within some of the northern intrusions, dominate the southern plutons. Garnet and allanite are ubiquitous in many of the plutons. All plutons show rapakivi textures to a greater or lesser degree. No fluorite has been recognized, but fayalite occurs in a number of charnockite­dominated plutons, which rarely contain minor clinopyroxene.

Chemically, the rocks have A-type, within-plate characteristics. They are subalkalic, peraluminous to metaluminous, ilmenite-type granites which have high Fe/Mg, Ga/Al, Na+K/Ca ratios and high contents of Ba, Zr, Nb, Y and P. Total REE concentrations are high, with high LREE/HREE ratios, and Eu anomalies are very variably developed. Notably, Rb contents are low.

No associated basic magmatism, so typical of northern hemi­sphere rapakivi granite suites, has been recognized. Many plutons display a strongly-deformed, often brecciated, and chemically hetero­geneous border fades. Current thought is that these granitoids were intruded at a late stage of the collisional (accretionary} orogenic phase. Suggested analogues in the Namaqualand area, to the west, are locally associated with anorthositic bodies. Comparisons with some rapakivi granites from Europe and North America show many similarities in chemistry and mineralogy. ltis proposed that the Natal "rapakivi-Iike" granites are transitional towards the rapakivi granites (sensu stricto) of Finland.

22

FIELD PETROGRAPHIC ASSAY ON THE OCCURRENCE Of RAPAKIVI TEXTURE IN METADOLERITEAND EPIDIORITE Of DHANBAD AREA, INDIA

KUMAR, Santosh, Geology Dept., Banaras Hindu University, V aranasl-221 005, U. P., India.

Rapakivi textures as originally defined by Sederholm have been reported in the granitoids and related rocks of Champawat, Dhanbad, Erinpura and Singhbhum in India by several workers. Typical rapakivi texture has been identified in the (meta)dolerite, (epi)diorite and porphyritic granitoid (injection gneiss) of Dhanbad in the classical note of N. L. Sharma. The field petrographic relationships between these rock-types containing rapakivi of Dhanbad area have been discussed. The studied rock-types probably belong to the Satpura orogenic cycle of Mid-Proterozoic age and are exposed in association near Dhaiya and Baliapur villages. The contact between acid and basic members is sharp and occasionally gradational. Rapakivi in basic rocks is found to be more frequent near contacts but less common outwards. Rare undigested felsic enclave hosted in dolerite is also seen near contacts. Frequent circular, elliptical and angular ovoids of aligned untwinned K-feldspars (up to 5 cm across) usually surrounded by felsic rim of plagioclase and quartz are embedded in fine- to medium-grained doleritic/dioriticgroundmass. The mafic mineral assemblage includes px-hb-bt-gt with zircon and epidote as accessory. The origin of rapakivi textures found in the rocks of Dhanbad area and its tectonic association is being examined to confirm whether they have been originated due to decompression of a closed system approaching equilibrium, or by the process of magma-mixing attaining disequilibrium.

23

BIMODAL ROCK ASSOCIATION OF RAPAKIVI SUITE AND PROTEROZOIC RIFTING IN NORTHERN BEIJING, CHINA

YU, /Ian-Hua, FU, Hui-Qin, WAN, Fang-Xiao, Geological Institute of Beijing, No. 24 Huangsl St. Deshengmenwal, Beijing 100011, P. R. China.

Along the north boundary of Mid-Proterozoic ( 1.85-1.60 Ga) Beijing rift, there occurs a 1 50 km long rock belt made up of bimodal rock association (quartz syenite, K-rich granite, rapakivi granite and anorthosite/gabbro). Previously they were assigned to Archean migmatites or Mesozoic intrusions, but the U/Pb concordant age of quartz syenite ( 1698. 7 Ma, J. K. Mortensen) proves they belong to Mid-Proterozoic. The anorthosite is composed of plagioclase cumu­lates with V-Ti-mineralization. The latter intruded quartz syenite contains low Si0

2 (63%), high K

20 (5.5-6.1 %), and fayalite (Fa=96%),

hypersthene, Fe-augite (Fs=57%), Fe-horneblende, and the accessory minerals are of ilmenite-zircon type. The K-rich granite is transitional with quartz syenite by increased Si0

2 (69-71 %) and Fe-biotite, and the

rapakivi granite occurs in the marginal fades of some massifs. A WPG pattern of LILE-rich character and the curves of right slope in LREE portion and horizontal line in HREE portion are suitable for their rift setting. The quartz syenite possibly represents a relatively basic initial granitic magma.

This rock belt serves as a key linking the abyssal anorthosite­norite-mangerite complex (1735 Ma) in the north with the hypabyssal rapakivi granite massif ( 1 700 Ma) and potassic alkali basaltic-phono­litic volcanics (1625 Ma) in the south making up four parallel rock belts. They represent different levels of emplacement successively from north to south due to their tectonic setting with respect to rifting and extensional faulting.

24

THE SHACHANG RAPAKIVI GRANITE COMPLEX, EASTERN CHINA: PETROLOGY AND Nd, Pb, AND Sr ISOTOPE GEO­CHEMISTRY

RAMO, 0. Tapanl, Department of Geology, UnlversltyofHelslnld, P. 0. Box 115, SF-00171 Helslnld, Finland; HAAPALA, llmarl, Depart­ment of Geology, Unlve_rslty of Helslnld; V AAS/OKI, Matti, Geologi­cal Survey of flnland, SF-02150 Espoo, Finland; YU, /Ian Hua, Geological Institute of Beijing, No. 24 Huangsl St. Deshengmenwal, Beijing 100011, China; FU, Huel Qin, Geological Institute of Beijing.

In the northwestern part of the Sino-Korean Craton, near Beijing, there exists a small (20 km2) rapakivi granite complex that is, in terms of its mode of occurrence, lithologic association, petrography, geo­chemistry, and age (1665±6 Ma, U-Pb from zircon), quite like the classical Finnish rapakivi granites. Unlike the Finnish granites, how­ever, the Shachang Complex intrudes an Archean crustal domain and is, in fact, the only known Proterozoic rapakivi granite complex not associated with crustal provinces formed in the Early Proterozoic. To shed light on the origin of the Shachang Complex, we present Nd, Pb, and Sr isotopic data on granites of the Complex and its immediate country rocks.

The granites of the Shachang Complex have initial £Nd values ranging from -6.1 to -5.5 and T oM model ages of 2.24 to 2.34 Ga. Pb isotopic data on K-feldspars and whole rocks fall on a 1689±96 Ma (26; MSWD=0.85) isochron and, in the 207Pb-206Pb space, far below average crustal Pb evolution (K-feldspar S~K µ

2 values range from 8.63 to

9 .13 ). Charnockitic country rocks have £Ni2460 Ma) values of 0.0 and +0.9, T

0M model ages around 2.6 Ga, and feldspar µ

2 values averaging

9.19. Preliminary Sr isotopic data indicate a distinctly lower 87Sr/86Sr ratio (at 1665 Ma) for the rapakivi granites (0. 7058) than for the country rocks (0. 7106).

The granites of the Shachang Complex are felsic and homoge­neous throughout and may reasonably be thought to have crystallized from anatectic melts generated at deeper levels within the crust. The isotopic data advocate an old lower crustal protolith characterized by the low long-term Sm/Nd and Rb/Sr ratios as well as very retarded Pb isotopic evolution.

25

PROTEROZOIC ANOROGENIC GRANITOIDS Of THE UKRAI­NIAN SHIELD AND VORONEZH CRYSTALLINE MASSIF

SUKHORUKOV, Yu. T., Institute of the Lithosphere, 1091 BO, Mos­cow; SVESHNIKOV, K. I., L'vov State University, 290005, L'vov, Ukraine.

In the Ukrainian shield the anorogenicgranitoids are represented by the Korosten and Korsun-Novomirgorod rapakivi massifs, East­Peri-Asovskii complex of subalkaline granites, syenites and nepheline syenites; Perzhanskii complex of subalkaline granites and rare-metal metasomatites. The rapakivi granitoids are similar in tectonic setting and composition; controlled by ring and linear structures; close to each other in composition and age. The East-Peri-Azovskii and Perzhanskii complexes show many features in tectonic setting and composition, which are contiguous to those of the rapakivi granitoids. The anorogenic massifs display a chain-like distribution along a major transregional north-western Early Proterozoic lineament, which coin­cides with the Dnepr-Donetsk Trough.

The Early Proterozoic anorogenic granitoids of the Voronezh crystalline massif are the most widespread in its eastern part. Here they are confined to a north-western peri-cratonic depression, filled with weakly metamorphosed volcanosedimentary rocks. The anorogenic granitoids are composed of subalkaline biotite and biotite­muscovite granites with associated rare-metal greisens and pegmatites. The granites constitute small size isometric or elongated bodies, controlled mainly by north-western faults.

The anorogenic granitoids of the Ukrainian shield and Voronezh crystalline massif formed at the later stage of the Early Proterozoic consolidation of the mature crust, but they differ in composition and tectonic setting.

26

GSA NORTH-CENTRAL SECTION, TUESDAY AFTERNOON MARCH 30, 1993

SYMPOSIUM: INTERNATIONAL GEOLOGICAL CORRELA­TION PROGRAMME (IGCP) 315:

CORRELATION OF RAPAKIVI GRANITES AND RELATED ROCKS ON A GLOBAL SCALE

SESSION Ill

211 McNUTI HALL, 1 :00 p.m. Bernard Bonin and 0. Tapani Ramo, Presiding

1. Yu. V. Amelin, L.M. Heaman, and V.M. Verkhogliad, GEOCHRONOLOGICAL CONSTRAINTS ON THE EMPLACEMENT HISTORY OF AN ANORTHOSITE­RAPAKIVI GRANITE SUITE: U-Pb ZIRCON AND BADDELEYITE STUDY OF THE KOROSTEN COMPLEX,

page no.

UKRAINE ................................................................................................ 29

2. Konstantin Ye. Esipchuk and Yevgeny M. Sheremet, TRACE ELEMENT GEOCHEMISTRY OF GABBROS, ANORTHOSITES AND GRANITES OF THE UKRAINIAN SHIELD ........................................................................... 30

3. S.N. Gavricova, M.S. Nikolaev, and S. Yu. Sokolov, PETROGENESIS OF THE ANOROGENIC GRANITOIDS FROM THE SOUTHERN ALDAN SHIELD (IN COMPARISON TO THE RAPAKIVI-GRANITES) ........................... 31

4. Linata P. Sviridenko, QUARTZ PORPHYRY - RAPAKIVI GRANITE VOLCANO-PLUTONIC ASSOCIATION IN KARELIA, RUSSIA ................................................................................ 32

5. Anatoly Larin and Leonid Neymark, METALLOGENY OF THE EARLY PROTEROZOIC TRANS-SIBERIAN ANOROGENIC VOLCANO-PLUTONIC BELT ................................ 33

27

6 . Dmitriy A. Velikoslavinsky, POSITION OF THE ANORTHOSITE-RAPAKIVI SUITE AMONG OTHER TYPES OF IGNEOUS ROCKS .......................................................................... 34

7. Anatoly M . Belyaev, ISOSTATIC GEODYNAMIC MODEL FOR THE ORIGIN OF RAPAKIVI GRANITES AND RELATED ROCKS ................................................................................. 35

8. Eugenia I. Kravtsova, POSSIBILITIES OF RAPAKIVI TEXTURE FORMATION IN THE SYSTEM ALBITE-ANORTHITE-ORTHOCLASE-QUARTZ(-WATER) .......................... 36

9. Aleksey D. Shebanov, NEW THERMOBAROMETRIC DATA FOR THE RAPAKIVI-GRANITES: SUBISOTHERMAL RISE OF MAGMAS .............................................................................. 3 7

10. Dipankar Mukherjee and N. C. Ghose, ORIGIN OF BANDED FABRIC IN BENGAL ANORTHOSITE WITHIN CHHOTANAGPUR GNEISSIC COMPLEX, EASTERN INDIA ................................................................................... 38

11. Valeri Vetrin, THE ANCIENT RAPAKIVI-LIKE GRANITES OF THE BALTIC SHIELD ..................................................................... 39

28

GEOCHRONOLOGICAL CONSTRAINTS ON THE EMPLACE­MENT HISTORY Of AN ANORTHOSITE- RAPAKIVI GRANITE SUITE: U-PB ZIRCON AND BADDELEYITE STUDY Of THE KOROSTEN COMPLEX, URKRAINE

AMELIN, Yu. V., HEAMAN, L.M., Geochronology Ltboratory, Royal Ontario Museum 100 Queen's Park, Toronto, Ontario, Canada, M5S 2C6, and VERKHOGLIAD, V.M., Institute of Geochemistry and Mineral Physics, Ukrainian Academy of Science, Klev, Ukraine, 252 680.

U-Pb zircon/baddeleyite ages obtained for the Korosten anortho­site-rapakivi granite complex, Ukrainian shield, suggest that different magmatic phases were emplaced during a period of ca. 30 m.y. as a series of distinct igneous episodes. The earliest 1789.1 ±2.0 Ma anorthite anorthosites were followed by 1781 .3±3.2 Ma diabases. The emplacement of a major rapakivi granite phase took place at 1 7 6 7 .2 ± 2.2 Ma, and was followed by intrusion of labradorite anortho­sites, diabases and gabbronorites between 1761-1758 Ma. The alternation of basic and felsic magmatism indicated by the geochro­nological data is in agreement with interlayering of basic rocks and granites that extends to a depth of ca. 20 km as inferred from gravity and deep seismic sounding results. Comparison of age distributions in the Korosten and other anorthosite-granite complexes shows that the 30 m.y. duration of magmatism and its episodic nature is a common feature of these complexes providing evidence for similar mechanisms of their formation. The rate of plate migration over a hypothetical middle Proterozoic mantle "hot spot" estimated from spatial and temporal distribution of anorthosite-rapakivi granite com­plexes of the East European platform is 1.0-1.8 cm/year, if all the complexes are assumed to be generated by a single "hot spot."

29

TRACE ELEMENT GEOCHEMISTRY Of GAB BROS, ANORTHO­SITES AND GRANITES Of THE UKRAINIAN SHIELD

ESIPCHUK, Konstantin Ye., Institute of Geochemistry and Physics of Minerals, Ukrainian Academy of Sciences, Klev-142, Palladln Av. 34, Ukraine; SHEREMET, Yevgeny M., Polytechnlcal Institute, Donetsk-66, Artem 5tr. 58, Ukraine.

Gabbros and anorthosites of the Korosten complex are character­ized by slightly higher ( 1.5 times) F, B, Ba, Mo, Pb abundances and lower ( 1.5-1 2 times) Co, Ni, Cr, Cu abundances compared to their averages in basic rocks. Their Zn and V distribution is very irregular.

From gabbro to anorthosite F, Rb, Zn contents decrease, and Sr contents increase; concentration of B, Li, Ba, Mo, Pb, Co, V, Cu, Ni and Cr do not considerably change.

In granites F, Li, Rb, Be, Sr abundances correspond to average values for acid rocks, but V, Cr, Co and Ni contents are 1.5-2 times lower than the average. From granites of early to those of later phases one can observe Li, Ba, Zn concentrations to be reduced 1.2-1.5 times and Pb to increase. Li and Rb contents are determined by biotite abundance in the rocks.

Chondrite-normalized REE plots show positive Eu anomalies in gabbro and anorthosite; in granites, Eu anomalies range from zero to a distinct minimum. Titanomagnetites from granites and basic rocks are different in Zr, Ge and Zn abundances.

Trace element distribution in rapakivi granites and related acid and basic rocks allows to conclude that these two groups of rocks were formed from different parent magmas: the first group from mantle tholeiitic, the second one from crustal granite.

30

PETROGENESIS OF THE ANOROGENIC GRANITOIDS FROM THE SOUTH­ERN ALDAN SHIELD (IN COMPARISON TO THE RAPAKIVI-GRANITES)

GA VRICOVA, S.N., Geologlcal Institute, Russian Academy of Sciences, Pyzhevsk.ly per. 7, l 09017 Moscow, Russia; NIKOLAEV, M.S., Moscow Institute for Geologlcal Research, 117485 Moscow, Russia; SOKOLOV, S. Yu., Moscow State University, 119899 Moscow, Russia.

Anorogenic granitoids are widely distributed in the southern part of the Aldan Shield. They form stock-shaped, post-collisional plutons emplaced during Permian to Late Jurassic times. As a rule, the plutons are composed of granodiorites and granites which were intruded into Late-Archaean tonalitic gneisses and Early­Proterozoic granulites.

The granodiorites and granites contain biotite and amphibole, are enriched in magnetite and sphene, and have affinity to lshihara's magnetite series on the 0 18

-

Si02 plot. In contrast to rapakivi-granites from the Baltic and Canadian shield and anorogenic granites from SW Australia, they are characterized by moderate crystal­lization temperatures (lower 780-750°C).

Anorogenic granites from the Aldan Shield are depleted in Rb, Ba, Zr, Nb, Y and REE but are enriched in Sr compared to rapakivi-granites. The granitoids and their mafic minerals are characterized by a lower ferricity index than those for rapakivi­granites and the Australian anorogenic granites. The granitoids have higher l5r values (0. 706-0. 708) than the rapakivi-granites (0. 705-0. 706).

The features of the Aldan Shield anorogenic granitoids indicate that they formed through assimilation of the middle crust by mantle-derived basaltic melts. As a result, andesitic magmas were formed, with certain distinctions having been established in both ferricity and alkalinity depending on the composition of the assimilated crust. The entire diversity of the granitoid composition is controlled by the processes of the andesitic melt fractionations and the crust-derived quartz-albite melts. In contrast. generation of the parent magmas for the rapakivi-granites and anorogenic granites from SW Australia occurred within the lower crust composed of granulites, which have been repeatedly depleted due to the production of granitic melts (Clements et al.. 1986, Emslie, 1991 ). Peculiarities in geochemistry and petrology of the rapakivi­granites and their related rocks (anorthosites) make it possible to suggest that melting of the lower crust occurred under the influence of both water-alkaline mantle fluid and heat from intruded or underplated basalts. Hence, significant distinction between the two groups of anorogenic granitoids is caused by profoundly different mechanisms responsible for their formation.

31

QUARTZ PORPHYRY-RAPAKIVI GRANITE VOLCANO-PLU­TONIC ASSOCIATION IN KARELIA, RUSSIA

SVIRIDENKO, Unata P., Institute of Geology, Karellan Research Center, Russian Academy of Science, Pushklnskaya 11, 185610 Petrozavodsk.

Quartz porphyry-rapakivi granite association in Karelia is only an episode of long magmatic activity related to the formation of a suture zone which separated the 2. 7 Ga Late Archean crust of the Karelian geoblock from the 1.8 Ga Early Proterozoic crust of Svecofennian geoblock in the Fennoscandian Shield. It is represented by the Salmi pluton, confined to the tectonic suture, and a parallel belt consisting of 12 echelon-like quartz porphyry, granite porphyry and trachyandesite dikes. The deep structure of the Salmi pluton is characterized by the fact that igneous rocks can be traced throughout the entire Earth's crust and that granites alternate with gabbroids. The pluton has been found to consist of gabbro-norites, pyroxenites, anorthosites and monzonites as well as three structural varieties of rapakivi granites and two varieties of non-ovoid biotite granites.

It has been inferred by comparing the petrographic characteris­tics of chemically identical granites and quartz porphyries that K­feldspar and quartz are the subliquidus minerals of rapakivi granite magma and water-bearing minerals are subsolidus minerals. The fluid composition of quartz porphyry and ovoidal rapakivi granites is characterized by somewhat increased CO, CO

2 and CH

4 contents.

The paragenesis of rock-forming minerals and reaction relations of K-feldspar to oligoclase and biotite are strongly affected by oxygen fugacity. When these dry high temperature granite melts are crystal­lized, conditions required for cotectic crystallization of K-feldspar and plagioclase are never created. Differences in the composition of non­ovoid and ovoid granite are due to differences in the partial melting of the lower-crust granulitic complex caused by upward movement of the crystal magmatic source. This was facilitated by the preheating of the crust and the subsidence of its blocks along the tectonic suture.

32

METALLOGENY Of THE EARLY PROTEROZOIC TRANS-SIRE,. RIAN ANOROGENIC VOLCANO-PLUTONIC BELT

LARIN, Anatoly, and NEYMARK, Leonid, Institute of Precambrian Geology and Geochronology, Russian Academy of Science, Makarova emb. 2, St. Petersburg, 199034, Russia.

The Trans-Siberian (T-S) volcano-plutonic belt can be traced more than 4000 km along the southern margin of the Siberian platform. The igneous rocks of this belt show bimodal composition features: subalkaline, alkaline and peralkaline granitoids including rapakivi granites, and gabbro-anorthosites. They exhibit within-plate charac­teristics and granites are represented by A-type granites.

U-Pb zircon ages for the rocks from east to west increase from 1. 73-1. 70 Ga to 1.87-1.82 Ga. The T-S belt contains a number of ore deposits of several types: Fe-Ti-P, Au, base metal, rare metal and fluorite. The economic ore deposits are related to the youngest magmatic complexes of the Ulkan-Dzhugdzhur region only where the largest Fe-Ti-Pore deposits are localized in 1.73 Ga gabbro-anortho­sites, and rare metal ore deposits occur in the differentiated granites. Sn-W greisen ore occurrences are genetically linked to the alkaline granites of the major intrusive phase ( 1. 72 Ga), and ore deposits of Be, Ta, Nb, Zr, Rf.E are related to the latest per alkaline granites ( 1. 70 Ga). There are five economic types of these ores: peralkaline pegmatites, fenites, hematite-feldspar, quartz-magnetite and quartz-chlorite metasomatites.

33

POSITION Of THE ANORTHOSITf...RAPAKIVI SUITE AMONG OTHER TYPES Of IGNEOUS ROCKS

VELIKOSLA VINSKY, Dmltrly A., Institute of Precambrian Geology and Geochronology, Russian Academy of Science, Malcarov emb. 2, St. Petersburg, 199034, Russia.

Every pluton may be represented by its natural sequence of magmas (rocks). Two types of natural sequences may be distin­guished: epigenetic and syngenetic. Epigenetic natural sequence represents a consecutive order of intrusive phases of a pluton, formed during differentiation of magma in an intermediate magma chamber. Syngenetic natural sequence is represented by fades varieties formed within separate intrusive phases.

Mean chemical analyses of phases and f acies of 80 plutons were plotted on variation diagrams, the most important of which was (Fe0+Mg0)-Ca0-2A1

20

3-Si0

2 (excepting FeO amalgamated in ore

minerals). Consideration of the natural sequences of magmas (rocks) in this and other variation diagrams permits their assembly into ten associations. The natural sequences (or vectors of differentiation) of plutons of the anorthosite-rapakivi suite (as natural sequences of all other associations) occupy their own definite place in the diagram.

Such complexes as the Berdiaush pluton (southern Ural) and the potassic granite plutons of Karelia and Kola Peninsula designated as "rapakivi," occupy quite different positions from the rapakivis of the anorthosite-rapakivi association in the diagram.

34

...

ISOSTATIC GEODYNAMIC MODEL FOR THE ORIGIN Of RAPAKIVI GRANITES AND RELATED ROCKS

BEL YAEV, Anatoly M., Department of Geology, St. Petersburg Uni­versity, University Embanlcment 7/9, 199034, St. Petersburg, Russia.

The anorogenic rapakivi granites and related rocks of the Baltic shield formed in a geodynamic setting of continental crustal strain resulting from plate movement. The displacement listric fracture zones were formed in anorogenic continental crust that had gentle dips in the upper parts, steep dip in the lower crust, and subhorizontal dip near the Moho boundary. Initial basaltic magmas for the early gabbros and anorthosites were melted from the foot of listric fractures. The upper mantle rocks were recrystallized under isostatic decompression be­low the listric fractures, and undepleted garnet lherzolites of the deeper zones changed into less dense, depleted spinel lherzolites. The thermal energy of phase transformation was released, and hot, mantle-derived fluids saturated with K, Rb, Ba, F, Cl were formed. They transferred the mantle heat and substance. The ascent of hot mantle fluids into listric fracture zones caused preliminary metasomatic transformation of cataclased, lower crustal basic rocks into monzo­nites or monzosyenites. Such metasomatically transformed basic rocks were partially melted, and hybrid, anatectic "migmas" were formed. Differentiation of such "migmas" gave rise to rapakivi granite magmas. Diabase dikes appeared as a result of partial melting of mantle rocks during the entire period of rapakivi granite formation.

35

POSSIBILITIES OF RAPAKIVI TEXTURE FORMATION IN THE SYSTEMALBITE--ANORTITE--ORTHOCLASE-QUARTZ (WATER)

KRAVTSOVA, Eugenia I., Institute of Precambrian Geology and Geochronology, Russian Academy of Science, Makarova emb. 2, St. Petersburg, 199034, Russia.

Published experimental and theoretical data on feldspar systems with and without Qz at different PH10 have been examined in order to construct the low-temperature part of the system Ab-An-Or-Qz (H

2 0).

Sections of the cotectic curve Pl-Or-Qz with peritectical crystallization of acid after basic Pl at PH

2o>0.5 kbar are distinguished. This is due to

the effect of the emergence of a Pl-miscibility gap and Na-Kfsp after Or at PH20=0.5-1.5 kbar, as the result of the T m1n solidus shift in the Or enrichment direction.

In these specific areas, rapakivi granite compositions fall at PH10=0.5-1 kbar. The beginning of Pl mantle formation seems to be stimulated by either first or second types of peritectical reactions, depending on magma composition. It starts early at a slight PH10

increase after Or crystallization under dry conditions. Pl-Pl change may be due to the reaction of the melt with An-domains dissolved in Or. Rim formation continues with the crystallization of Olig-Ab as the PH20 rises to more than 1.5 kbar. The addition of F removes areas of peritectical crystallization, or causes the melt composition to fall into the Pl-field of the quaternary granite system because the Pl-Or surface shifts to the Ab-Or-Qz face.

Partial melting of Or at sharp P FI increase may precede the resorption and redistribution of components at a lower T. Other models of rapakivi texture formation at appropriate conditions have been observed as well.

36

NEW THERMOBAROMETRIC DATA FOR THE RAPAKIVI­GRANITES: SUBISOTHERMAL RISE OF MAGMAS

SHEBANOV, Aleksey D., Department of Mineralogy, Geological faculty, The St. Petersburg State University, St. Petersburg, 199034, Russia.

Mineral associations in the main phases of rapakivi-granites from the Wiborg massif indicate different conditions of formation. The first association includes early biotite (Bt-1) + amphibole (Amph) ± plagio­clase (Pl) localized mostly as inclusions in the core zones of KFsp­ovoids. The second association comprises biotite of a later generation (Bt-Z) ± Amph ± Pl found in the groundmass of rocks and partially, in the rim zone of ovoids. In order to determine the parameters of crystallization, a number of different Amph-Bt-Pl thermobarometers were used. The data obtained for the lappee-granite are:

T1=780 ± 30° C, P

1=6 kbar (first association data)

T 2 = 7 60 ± 30° C, P

2 = 1 kbar (second association data),

and for the wiborgite and the trachytoid granite:

T1=7ZO ± Z0° C, P1=5.5 kbar

T2=680 ± Z0° C, P

2=Z.5 kbar and 1.5 kbar,

respectively. By the method of homogenization of primary fluid inclusions in porphyritic quartz, parameters of the last alteration stages at T

3 =490° to 5 7 0° C with P

3 = 1 to 1 .5 kbar were obtained.

These data permit the construction of evolution trends for rapakivi-granite magmas at P-T coordinates displaying subisothermal rise during decompression of the melt source. Ovoid core zones are interpreted as the hypogene formations undermelted during the rise of magmas.

37

ORIGIN OF BANDED FABRIC IN BENGAL ANORTHOSITE WITHIN CHHOTANAGPUR GNEISSIC COMPLEX, EASTERN INDIA

MUKHERJEE, Dlpankar, Geological Survey of India, Kankarbagh, Patna-800020, India, GHOSE, N. C., Geology Dept., Patna University, P atna-800006, India.

The "Bengal Anorthosite" is comprised of a coarse grey anortho­site at the core surrounded by equigranular white anorthosite with a transitional variant in between. Occasionally the peripheral white anorthosite exhibits a conspicuous banded fabric defined by metabasic bands of varied dimension. Such banded fabric in "Bengal anortho­site" has been attributed to secondary gneissic banding, primary flow layering and other noncommittal terms by earlier workers.

The significant features of Bengal anorthosite are: (i) restricted development of banded fabric in close proximity to older metabasics which show non-comagmatic relationship with anorthosite, (ii) devel­opment of banded fabric both in the anorthosite and the adjoining metabasic xenoliths as thin penetrative layers, and the gradual disappearance away from the contact, (iii) the uniform character of mafic minerals both in the mafic bands within the anorthosite, and in the metabasic country rock, and (iv) development of planar and linear fabric defined by the parallel-oriented metabasicxenoliths. The above features do not support the hypothesis that the banded fabric owes its origin to gravity separation of minerals as in a stratiform body, or represents a secondary gneissic banding from metamorphic differen­tiation. On the contrary, the fabric is attributed to "flow structure" where the flow layers/lines are defined by the parallel arrangement of metabasic xenoliths formed by preferential emplacement of anortho­site along pre-existing foliation planes or lithocontacts in the metabasic country rocks.

38

THE ANCIENT RAPAKIVI-LIKE GRANITES Of THE BALTIC SHIELD

VETRIN, V alerl R., Geological Institute, Kola Science Center, Russian Academy of Science, 14 fersman Str., 184200, Apatlty, Russia.

The ancient rapakivi-like granites of the Baltic Shield (2760±30 Ma, Pb-Pb age, zircon) form some massifs in the northeastern and central parts of the Kola Peninsula over an area of 500 km2• The post­tectonic intrusives have been located along large fault zones and were em placed later than the massifs of the gabbro-anorthosites; zones of fine-grained granites with granophyric textures formed at the margins of the granite massifs. The rocks are subalkaline or normal granites and leucogranites, near the chemical composition of typical rapakivi granites of the Baltic Shield. The sequence of mineral crystallization is the following: plagioclase + ferrosalite (f =6 7) + ferrohastingsite (F=90-96) + K-Na-feldspar (phenocrysts) + ilmenite + K-Na-feldspar (the bulk of crystals) + quartz + lepidomelane (F=89-93) + zircon + sphene + allanite. The formation of the massifs occurred at a depth of not more than 2.5-3.0 km, and crystallization took place from the margins toward the centers under conditions of increasing water solubility and decreasing temperatures (granophyre granites: PH

2o=

2-2.5 kb, T-710-720°C, granites of the central parts of the massifs: PH

2o=3.5-5 kb, T 680°C).

39

..

1 I

40 I j

GSA NORTH-CENTRAL SECTION, MONDAY AFTERNOON MARCH 29, 1993

POSTER SESSION: INTERNATIONAL GEOLOGICAL COR­RELATION PROGRAMME (IGCP) 315:

CORRELATION OF RAPAKIVI GRANITES AND RELATED ROCKS ON A GLOBAL SCALE

POSTER SESSION IV

COMMONS ARE.A, 2ND FLOOR. McNUTI HALL, 1 :00 p.m. - 5:00 p .m.

1. Aleksey D. Shebanov and Anatoly M. Belyaev, FLUID RATES DURING THE FORMATION OF RAPAKIVI GRANITES AND THE PECULIARITIES OF AMPHIBOLE

page no.

AND MICA COMPOSITIONS ........................................................... 42

2. Anatoly Belyaev, Aleksey Shebanov, and Dina Michailova, ORBICULAR RAPAKIVI GRANITES FROM THE SALMI MASSIF ............................................................................ 43

41

FLUID RATES DURING THE FORMATION OF RAPAKIVI GRAN­ITES AND THE PECULIARITIES OF AMPHIBOLE AND MICA COMPOSITIONS

SHEBANOV, Aleksey D., and BELYAEV, Anatoly M., Department of Mlneralogy, Geologlcal faculty, The St. Petersburg University, St. Petersburg, 199034, Russia.

Amphibole, biotite, and plagioclase thermobarometric data in some rapakivi-granites from the Wiborg massif show that hydrous mafic minerals coexisted in the melt and isolated from it under pressures from about 5 to 6 kbar in the early-magmatic association of the ovoid core-zones, to about 1.5 kbar in the late-magmatic associa­tion of the ovoid rim-zones and the groundmass. Mass-spectrometric data for amphibole and mica grains of the first abyssal association indicate a F:Cl ratio of 1 to 3; this ratio increases 5 to 11 in the minerals of the second, hypabyssal association. Chemical analyses show that the reason for this is the decrease of Cl content from 0.35-0.65% in the earlier association, to 0.00-0.12% in the later one. The value F = (Fe'"/ Fe"'+ Fe") x 100 is 7 to 16 and 15 to 22 in the earlier and later minerals, respectively. These data permit the assumption that at the early stage, hypogene melts contain considerable amounts of dissolved, mostly halogene fluids with a little prevalent F over CJ, and a rather low water content. Decompression at subisothermal conditions during the rise of magma caused an increase in oxygen activity. The rise of magma must have caused a boiling of the melt; both the melt and the whole system were losing more volatile halogenes, especially CL The sum of our data allows the supposition that fluid separation causes mass isolation of the main minerals of granites.

42

ORBICULAR RAPAKIVI GRANITES FROM THE SALMI MASSIF

BELYAEV, Anatoly, SHEBANOV, Alebey, Department of Geology, St. Petersburg University, 199034, St. Petersburg, Russia; MICHAJLOVA, Dina, Karella expedition, Petrozavodsk, Russia.

A dike of the orbicular granites cuts across ovoid-bearing rapakivi granites of the Salmi batholith. Orbicules commonly occur as rounded forms (0. 1 to 0 .2 m in diameter) with nuclei of KFsp ovoids (2 to 5 cm) which are sometimes mantled with Pl. Mantles of the orbicules are composed of granite-aplite matter with microgranular granophyric structure, and macrocrystalline pegmatitic matrix is present between them.

It has been established, that the F /Cl ratio in Amph and Bt from the mantles of the orbicules and the pegmatitic matrix is 2 to 5 times higher than that in the KFsp of the nucleus.

We propose that the fracture zone at shallow levels of the rapakivi granites was filled by anchicotectic residual granitic melt from the lower zones of the crystallized intrusive. This melt contained rare xenocrysts of KFsp ovoids and Qz, and was saturated with F and Cl. Such a melt boiled under retrograde boiling conditions as a result of decompression, and F and Cl were removed in the gas phase. Due to the volatile element loss, the temperature of crystallization of the melt rose and rapid crystallization of the anchicotectic melt took place. Ovoids of KFsp have been the centers of crystallization for the orbicules. The evolution of the residual melt and fluid phase continued under closed system conditions that caused the crystallization of the pegmatitic matrix.

43

44

CONTRIBUTIONS TO PRECAMBRIAN GEOLOGY

Reports and maps are pub/Jshed by the Missouri Department of Natural Resources, Division of Geology and Land Survey, In a special series "Contributions to Precambrian Geology."

CP-1. E.xposed Prec:ambrlAn Roe.ks In Southeast Missouri, (Report of Investigations 44), by Carl Tolman and Forbes Robertson, 74 p., 2 pis., 3 figs., 1969. Out of print.

CP-2. Ash-flow luffs of Prec:ambrlAn Age In Southeast Missouri, (Report of Investi­gations 46), by R. Ernest Anderson, 56 p., l pl., 8 figs., l tbl., 1970. Out of print.

CP-3. Mafk Intrusive Roe.ks of Precambrian Age In Southeast Missouri, (Report of Investigations 47), by Dewey H. Amos and George A. Desborough, 28 p., 3 pis., 3 figs., 2 tbls., 1970. Price $2.00.

CP-4. Petrochemlstry of a Precambrian Igneous Province, St. Francois Mountains, Missouri, (Report of Investigations 51 ), by Eva B. Klsvarsanyl, 51 p., l pl., 7 figs., 3 tbls., 2 app., 1972. Price $2.00.

CP-5. Data on Precambrian In Drlllholes of Missouri lndudlng Rock Type and Surface Conflguradon, (Report of Investigations 56), by Eva B. Klsvarsanyl, 24 p., l pl., l tbl., 1975. Out of print.

CP-6. Studies In Prec:ambrlu Geology with a Gulde to Selected Parts of the St. FrAncols Mountains, Missouri, (Report of Investigations 61 ), edited by Eva B. Klsvarsanyl, 200 p., 75 figs., 5 pis., 8 tbls., 1976. Price $5.00.

CP-7. GeologlcMapofthePrecambrlanofMlssourl,byEvaB.Klsvarsanyl, 1:1,000,000, 1979. Price $2.00.

CP-8. Geology of the Prec:ambrlAn St. FrAncols Terrane, Southeastern Missouri, (Report of Investigations 64), by Eva B. Klsvarsanyl, 58 p., 9 figs., 10 tbls., l :250,000-scale map, 1981. Price $4.00.

CP-9. Guidebook to the Geology and Ore Deposits of the St. Francois Mountains, Missouri, (Report of Investigations 67), by Eva B. Klsvarsanyl, Arthur W. Hebrank. and Richard F. Ryan, 119 p., 75 figs., 8 tbls., 198 t. Price $4.00.

CP-10. Geologic Map of Exposed Prec:ambrlAn Roe.ks In the Iron Mountain uke Quadrangle, Missouri, (Open-file Map 83-160-MR), by Robert L. Nusbaum, 1 :24,000, 1983. Price $2.00.

CP-11. Geologic M.-p of Exposed Precambrian Roe.ks In the Wachlta Mountain (Fredericktown NWI/,) QuadrAngle, Missouri, (Open-file Map 83-161-MR), by M.E. Bickford and J.R. Sides, l :24,000, 1983. Price $2.00.

CP-12. Geologic Map of Exposed PrecambrlAn Roe.ks In the uke Klllamey Quad­rangle, Missouri, (Open-file Map 83-16Z-MR), by J.R. Sides, l :24,000, 1983. Price $2.00.

CP-13. Geologic Map of E.xposed Prec:ambrlM Roe.ks In the Des Arc Quadrangle, Southeast Missouri, (Open-flle Map 84-198-MR), by Vernon M. Brown, 1:24,000, 1983. Price $2.00.

45

CP-14 The Magnetic. Anomaly Map of Missouri With an Interpretation of Prec.am­brlan Struc.ture, (Part A and B), 1984. Prlc.e $3.00. Part A-The Magnetic Anomaly Map of Missouri, by Isidore Zietz Kevin R. Bond, and Frederic E. Riggle, 1:1 ,000,000. Part B-The Precambrian Tectonic Framework of Missouri as Interpreted from the Magnetic Anomaly Map, by Eva B. Kisvarsanyl, 19 p.

CP-15. Struc.ture Contour Map of the Prec.ambrlan Surfac.e In Missouri, (Open-file Map 84-207-GJ), by Eva B. Kisvarsanyl, 1 :500,000, 1984. Prlc.e $3.00.

CP-16. Inventory, Logging, and Sampling of Basement Cores, (Open-file Report 87-58-GIJ, by Eva B. Klsvarsanyl, 11 p., 1987. Prlc.e $1.00.

CP-17. Spec.trographlc. Analyses of Drill Core from Prec.ambrlan Rodes In the Burled Prec.ambrlan Basement Terranes of Missouri (Open-flle Report 88-68-GJ), by Gregory M. Lovell, 11 p. Prlc.e $1.00.

CP-18. Boss-Bixby, A High Temperature Iron-Copper Deposit In the Prec.ambrlan of the MJdc.ontlnent United States (Open-file Report 88-72-Gl), by Geza Klsvarsanyl and Fredenck J. Smith, University of Missouri-Rolla, 8 p., 1988. Prlc.e $1.00.

CP-19. Appraisal of the Prec.ambrlan Basement Complex In the Harrison 1 x 2 Degree Quadrangle, Missouri and Arkansas, (Open-flle Report 89-74-GJJ, by Eva B. Klsvarsanyl, 10 p., 1989. Prlc.e $1.00.

CP-20a. Mine Geology Map of the Pea Ridge fe-Rll Deposit, 2440 Sublevel, Map 1, (Open-flle Map 89-25 fa-GJ), by Mark A. Marlkos and Cheryl M. Seeger, 1 :240, 1989, (computer-generated colored map). Prlc.e $5.00.

CP-20b. Mine Cieology Map of the Pea Ridge fe-RIE Deposit 2370 Sublevel, Map 1, (Open-flle Map 89-251 b-GJ), by Mark A. Marlkos, Laurence M. Nuelle, and Cheryl M . Seeger, 1 :240, 1989, (computer-generated colored map). Prlc.e $5.00.

CP-20c.. Mine Cieology Map of the Pea Ridge fe-RIE Deposit, 2370 Sublevel, Map 2, (Open-flle Map 89-251 c-GJJ, by Laurence M . Nuelle, Cheryl M. Seeger, and Mark A. Marikos, 1 :240, 1989, (computer-generated colored map). Prlc.e $5.00.

CP-21. Ciold, Rare Earth Element, and Other Potential By-Produc.ts of the Pea Ridge Iron Ore Mine, Washington County, Missouri, (Open-flle Report 89-78-MRJ, by James R. Husman, 19 p. Prlc.e $2.00.

CP-22a. Map of Drill Holes that Bottom In Prec.ambrlan Basement In Missouri, (Open-flle Map 90-257-G/J, by Eva B. Klsvarsanyl and Cheryl M. Seeger, 1 :500,000, 1990. Prlc.e $4.00.

CP-22b. Ust of Basement Drlllholes In Missouri, by Eva B. Klsvarsanyl and Cheryl M. Seeger, (Open File Report - 93-92-GS), 1993, 40 p., 2 figs. Prtc.e $5.

CP-23. International Cieologlc.al Correlation Programme ProJec.t 315: Correlation of Rapaklvl Granites and Related Roe.ks on a Cilobal Sc.ale--Abstrac.ts Volume, edited by Eva B. Klsvarsanyl, (Special Publlcatlon No. 9), 1993, 46 p., 1 fig. Prlc.e $5.

46

MISSOURI DEPARTMENT OF NATURAL RESOURCES DIVISION OF GEOLOGY AND LAND SURVEY

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INnRNATIONAL GEOLOGICAL CORRELATION PROGRAMME. CoRRELATION OF llAPAKIVI GRANIT£S AND R£LAno RocKs ON A GLOBAL SCALE-­

ABSTRACTS VOWME.

MISSOURI DEPARTMENT Of NATURAL RESOURCES Division of GeoloBY and Land Survey

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