The geology, geochronology, structure and geochemistry of the

Wild Rogue Wilderness remnant of the Coast Range ophiolite, southwest Oregon:

implications for the magmatic and tectonic evolution of the Coast Range ophiolite

by

Stefan B. Kosanke

A Dissertation

Submitted to the University at Albany, State University of New York

in Partial Fulfillment of

the Requirements for the Degree of

Doctor of Philosophy

College of Arts & Sciences

Department of Earth and Atmospheric Sciences

2000

University at Albany, State University of New York

COLLEGE OF ARTS &SCIENCES

The dissertation submitted by

Stefan B. Kosanke

under the title

The geology, geochronology, structure and geochemistry of the

Wild Rogue Wilderness remnant of the Coast Range ophiolite, southwest Oregon:

implications for the magmatic and tectonic evolution of the Coast Range ophiolite

has been read by the undersigned. It is hereby recommended for acceptance to the Faculty of the University in partial fulfillment of the requirement for the degree of Doctor of Philosophy.

_________________________________ ___________________Gregory D. Harper (Date)

_________________________________ ___________________John W. Delano (Date)

_________________________________ ___________________William S.F. Kidd (Date)

_________________________________ ___________________Glenn J. MacPherson (Date)

_________________________________ ___________________Winthrop D. Means (Date)

Recommended by the Department of Earth and Atmospheric Sciences.

_________________________________, ChairVincent P. Idone

Recommendation accepted by the Dean of Graduate Studies for the Graduate Academic Council.

_________________________________

_________________________________(Date)

ABSTRACT

The Wild Rogue Wilderness ophiolite (WRWO) has been correlated with the Coast

Range ophiolite (CRO) and overlying Great Valley Sequence in California. The WRWO occurs

on the east limb of a large Cretaceous syncline within a folded thrust sheet. The basement units

strike NE, are subvertical and fault bounded and include from east to west: (1) a sheeted dike

complex having gabbro screens; (2) a ductily, but heterogeneously deformed metatonalite

containing abundant mylonites; (3) a heterogeneously deformed metagabbro having a relic

magmatic foliation overprinted by solid-state deformation at amphibolite facies and lower grade

conditions; (4) a 0.5 - 0.9 km wide, high-strain zone consisting of mafic and silicic

ultramylonites and mylonites; (5) undeformed pillow basalts cut by mafic and silicic dikes; (6)

quartz gabbro to tonalite (Half Moon Bar diorite), (7) poorly exposed metavolcanic rocks,

including at least some volcaniclastics in the uppermost section of this unit.

The following events have been identified in the Wild Rogue Wilderness: (1) pre-

ophiolite deformation and (regional?) amphibolite facies metamorphism (unit 3; ~171 Ma); (2)

formation of the ophiolite, related normal faulting and subseafloor hydrothermal alteration (units

1, 2, and 5; ~164 Ma); (3) Post-ophiolite arc-related magmatism (units 6 and 7; 153-160 Ma);

and (4) Nevadan-age ductile deformation (unit 4 and mylonites in units 2 and 3; ~149 Ma).

The trace-element analysis indicates that the WRWO consists of rocks having magmatic

affinities to normal mid-ocean ridge basalt, island-arc tholeiite, calc-alkaline basalt and boninite.

Compositional variations within units and between units cannot be explained with differences in

the degree of partial melting and/or fractionation. A highly heterogeneous source is inferred,

which was probably variably depleted by previous melting and variably re-enriched with a

subduction component.

The evolution of the WRWO is similar to that of the CRO and the Josephine ophiolite,

which is consistent with previously proposed models that invoke rifting of the volcanic arc built

on western N. America. The geochemical diversity of the WRWO is indicative of formation in a

fore-arc or intra-arc setting similar to that of the Miocene Tonga arc, SW Pacific. Rift-

propagation and melting of heterogeneous, inherited mantle may have played an important role

in the magmatic evolution of the WRWO.

ii

ACKNOWLEDGMENTS

A great deal of thanks and gratitude go to my advisor, Dr. Gregory D. Harper for his

guidance, support, and encouragement. Dr. Harper provided me with a very exciting project in

which we both shared great interest. Additional thanks go to my thesis committee members.

Their insightful comments and helpful suggestions greatly improved the quality of this work.

Also, this work benefited greatly from many productive discussions with Charles Knaack and

Richard Conrey at Washington State University regarding the precision and accuracy of trace

element analysis by ICP-MS. The trace element analysis was conducted at the Union College

Geology Department under the direction of Kurt Hollocher. I thank Kurt Hollocher for sharing

his expertise. Thanks go to Matt Heizler and Jason Saleeby, who provided the isotopic ages for

this study. Also, I like to thank my fellow students Steffi Dannenmann, Angela Coulton, Mike

Edwards, Bruno Ciscato, Nick Hayman and Young Do Park for helpful discussions. I am

particularly indebted to my wife, Tobi, for her frequent assistance and unceasing support.

Financial support for this project, including field work, ICP-MS analysis and electron

microprobe analysis was provided through Student Research Grants from the Geological Society

of America, Sigma Xi Grant in-Aid of Research, SUNY Albany Benevolent Foundation, and the

Gregg Ranch Foundation. I thank these organizations for their support.

I would like to thank the caretakers of the Rogue River Ranch, Laura and Loren Rush.

Without their generosity and help, I would not have had such pleasant and memorable field

seasons in the Wild Rogue Wilderness. Additional thanks go to Michael Haschke for assistance

in the first field season and to Sean Oakley, the forest warden, for keeping an eye on my safe

return from bushwhacks and backpack excursions.

Finally, I wish to thank my parents. Without their continuous support and encouragement, I

would not have come this far.

iii

TABLE OF CONTENT

CHAPTER ONE

INTRODUCTION .........................................................................................................................................1

CHAPTER TWO

GEOLOGY, PETROGRAPHY AND GEOCHRONOLOGY OF THE ROGUE WILDERNESS REMNANT OF THE COAST RANGE OPHIOLITE, SW OREGON ..................................................19

2.1 INTRODUCTION ............................................................................................................................19

2.2 GEOGRAPHIC SETTING AND PREVIOUS WORK ...................................................................20

2.3 THE ROGUE WILDERNESS REMNANT OF THE COAST RANGE OPHIOLITE ...................24

2.4 SERPENTINITES ............................................................................................................................33

2.5 METAGABBRO UNIT ....................................................................................................................33

2.5.1 Lithology ................................................................................................................................33

2.5.2 Structure and metamorphism .................................................................................................34

2.5.3 Evidence for ductile deformation in the metagabbro unit ......................................................40

2.5.4 Interpretation of metamorphic hornblende and age constraints .............................................49

2.5.5 Hornblende quartz diorite in metagabbro unit .......................................................................51

2.5.6 Contact between metagabbro unit and metatonalite unit .......................................................52

2.6 METATONALITE UNIT .................................................................................................................55

2.6.1 Lithology ................................................................................................................................55

2.6.2 Evidence for magma mingling ...............................................................................................60

2.6.3 Mylonites ................................................................................................................................61

2.6.4 Metatonalite unit compared to oceanic plagiogranites ...........................................................69

2.6.5 Contact with the sheeted dike complex ..................................................................................70

2.6.6 Age constraints .......................................................................................................................72

2.7 SHEETED DIKE COMPLEX ..........................................................................................................72

2.7.1 Gabbroic screens ....................................................................................................................76

iv

2.7.2 Sheeted Dikes .........................................................................................................................82

2.7.3 Cross cutting relationships .....................................................................................................89

2.7.4 Hydrothermal metamorphism of sheeted dikes ......................................................................90

2.7.5 Age constraints .......................................................................................................................93

2.8 PILLOW UNIT .................................................................................................................................93

2.8.1 Pillowed submarine flows ......................................................................................................94

2.8.2 Dikes .......................................................................................................................................99

2.8.3 Structure ...............................................................................................................................102

2.8.4 Age constraints .....................................................................................................................103

2.9. MULE MOUNTAIN VOLCANICS .............................................................................................104

2.9.1 Volcanic breccia ...................................................................................................................106

2.9.2 Basalt and basaltic andesite flows ........................................................................................108

2.9.3 Andesites and dacites ...........................................................................................................110

2.9.4 Mudstones and sandstones ...................................................................................................113

2.9.5 Hydrothermal metamorphism ...............................................................................................115

2.9.6 Age constraints .....................................................................................................................116

2.10 POST-OPHIOLITE INTRUSIONS ..............................................................................................117

2.10.1 Muscovite garnet tonalite dikes in metagabbro unit ...........................................................117

2.10.2 Half Moon Bar Diorite .......................................................................................................121

2.11. BLOSSOM BAR SHEAR ZONE ...............................................................................................127

2.11.1 Lithology and fabric ...........................................................................................................127

2.11.2 Age constraints ...................................................................................................................137

2.12 MYRTLE GROUP ........................................................................................................................137

CHAPTER THREE

APPLICATION OF HOLLAND AND BLUNDY'S (1994) AMPHIBOLE-PLAGIOCLASE GEOTHERMOMETER: CONSTRAINTS AND IMPLICATIONS FOR THE INTERPRETATION OF THE THERMAL HISTORY OF THE HALF MOON BAR DIORITE AND THE METAGABBRO UNIT IN THE WILD ROGUE WILDERNESS, SW OREGON ............................140

3.1 INTRODUCTION ..........................................................................................................................140

v

3.2 METHOD .......................................................................................................................................143

3.2.1 Selection and analysis of coexisting plagioclase-hornblende pairs ......................................143

3.2.2 The amphibole-plagioclase geothermometer .......................................................................146

3.2.3 Restrictions for the use of the amphibole-plagioclase thermometers ...................................147

3.2.4 Recalculation of amphibole analyses ...................................................................................148

3.2.5 Classification of amphiboles ................................................................................................149

3.2.6 Calculation of temperatures .................................................................................................152

3.2.7 Uncertainties .........................................................................................................................160

3.3 PRESSURE ESTIMATES ..............................................................................................................160

3.3.1 Estimate of pressure of crystallization using geological constraints ....................................160

3.3.2 Aluminum-in-hornblende barometers ..................................................................................162

3.4 DISCUSSION .................................................................................................................................165

3.4.1 Half Moon Bar diorite ..........................................................................................................165

3.4.2 Hornblende quartz diorite in metagabbro unit .....................................................................170

3.4.3 Metagabbro unit ...................................................................................................................173

3.5 SUMMARY ....................................................................................................................................178

CHAPTER FOUR

STRUCTURAL AND METAMORPHIC HISTORY OF THE WILD ROGUE WILDERNESS REMNANT OF THE COAST RANGE OPHIOLITE ...........................................................................181

4.1 INTRODUCTION ..........................................................................................................................181

4.2 PALEOSTRESS ANALYSIS .........................................................................................................188

4.3 POST-OPHIOLITE SEDIMENTARY ROCKS AND STRUCTURES .........................................190

4.3.1 Eocene cover ........................................................................................................................190

4.3.2 Post-Mid-Eocene faults ........................................................................................................193

4.3.3 Franciscan Complex .............................................................................................................200

4.3.3.1 Yolla Bolly terrane .....................................................................................................200

4.3.3.2 Sixes River Terrane ....................................................................................................204

4.3.4 Myrtle Group ........................................................................................................................205

4.3.4.1 Riddle Formation .......................................................................................................205

vi

4.3.4.2 Days Creek Formation ...............................................................................................206

4.4 ORIENTATION OF PLANAR FEATURES IN THE PILLOW UNIT AND MULE MOUNTAIN VOLCANICS .......................................................................................................................................207

4.5 POSSIBLE RE-ORIENTATION OF THE OPHIOLITE TO PALEOHORIZONTAL ..................211

4.6 STRUCTURE OF THE SHEETED DIKE COMPLEX ................................................................212

4.6.1 Diabasic and microdioritic dikes ..........................................................................................212

4.6.2 Igneous layering ...................................................................................................................220

4.6.3 Amphibole shear bands and amphibole veins ......................................................................221

4.6.4 Cemented faults ....................................................................................................................225

4.6.4.1 Domains A and B .......................................................................................................227

4.6.4.2 Domain D ...................................................................................................................231

4.6.4.3 Discussion of the fault geometry ................................................................................235

4.7 DUCTILE TO BRITTLE DEFORMATION IN THE BLOSSOM BAR SHEAR ZONE, METATONALITE AND METAGABBRO UNITS .............................................................................236

4.7.1 Sense of shear criteria ..........................................................................................................236

4.7.2 Deformation in the metagabbro unit ....................................................................................246

4.7.2.1 Magmatic foliation .....................................................................................................246

4.7.2.2 Shear foliation and sense of shear ..............................................................................248

4.7.2.3 Brittle deformation and crosscutting relationships ....................................................250

4.7.2.4 Estimate of temperature of solid-state deformation ...................................................251

4.7.2.5 Transition from magmatic flow to solid-state deformation? ......................................254

4.7.3 Deformation in the metatonalite unit ...................................................................................256

4.7.3.1 Shear foliation and sense of shear ..............................................................................257

4.7.3.2 Brittle deformation and crosscutting relationships ....................................................260

4.7.4 Blossom Bar shear zone .......................................................................................................265

4.7.4.1 Shear foliation and sense of shear ..............................................................................265

4.7.4.2 Brittle deformation and crosscutting relationships ....................................................266

4.7.5 Estimates of the temperatures of deformation in the metatonalite unit and Blossom Bar shear zone 266

4.7.6 Deformation of late intrusions in the rnetagabbro unit ........................................................269

4.7.6.1 Shear foliation and sense of shear ..............................................................................269

4.7.6.2 Brittle deformation and crosscutting relationships ....................................................270

4.7.7 Summary ..............................................................................................................................270

4.7.8 Using the results of the structural study ...............................................................................271

vii

4.7.8.1 Occurred ductile deformation and brittle faulting in the same stress field? ..............271

4.7.8.2 Determination of the stress tensor for ductile deformation ........................................275

4.8 DISCUSSION .................................................................................................................................279

4.8.1 Possible pre-ophiolite deformation and metamorphism .......................................................279

4.8.2 Formation of the ophiolite, related deformation and hydrothermal alteration .....................282

4.8.2.1 Direction of seafloor spreading and early normal faulting ........................................284

4.8.2.2 The fault geometry in the sheeted dike complex .......................................................289

4.8.2.3 Possible near ridge-axis rotation of sheeted dikes .....................................................294

4.8.24 Summary of oceanic deformation of ophiolite ............................................................298

4.8.3 Post-ophiolite structural history ...........................................................................................299

4.8.3.1 Late magmatism and hydrothermal alteration ............................................................299

4.8.3.2 Post-ophiolite ductile deformation .............................................................................300

4.9 SUMMARY AND CONCLUSION ...............................................................................................306

CHAPTER FIVE

THE GEOCHEMISTRY OF THE WILD ROGUE WILDERNESS REMNANT OF THE COAST RANGE OPHIOLITE, SW OREGON ....................................................................................................308

5.1 INTRODUCTION ..........................................................................................................................308

5.2 ANALYTICAL METHODS ...........................................................................................................311

5.3 ELEMENT MOBILITY .................................................................................................................313

5.4 INTERPRETATION OF CHONDRITE- AND N-MORB NORMALIZED TRACE ELEMENT PATTERNS ...........................................................................................................................................315

5.5 GEOCHEMISTRY OF IGNEOUS ROCKS FROM THE OPHIOLITE UNITS ..........................322

5.5.1 Metagabbro unit ...................................................................................................................322

5.5.1.1 Rock classification .....................................................................................................322

5.5.1.2 Magmatic affinities ....................................................................................................325

5.5.1.3 Petrogenesis ................................................................................................................3325.5.1.3a Crystal Fractionation .............................................................................................3325.5.1.3b Partial melting .......................................................................................................338

5.5.2 Hornblende quartz diorite in the metagabbro unit ................................................................339

5.5.2.1 Rock classification .....................................................................................................339

5.5.2.2 Magmatic affinities ....................................................................................................343

5.5.3 Metatonalite unit ..................................................................................................................343

viii

5.5.3.1 Rock classification .....................................................................................................343

5.5.3.2 Magmatic affinities ....................................................................................................344

5.5.3.3 Petrogenesis ................................................................................................................3515.5.3.3a Possible origin of the metatonalite unit .................................................................3515.5.3.3b Crystal fractionation models .................................................................................3535.5.3.3c Magma mixing .......................................................................................................361

5.5.4 Sheeted dike complex ...........................................................................................................364

5.5.4.1 Rock classification .....................................................................................................3645.5.4.la Gabbroic screens ....................................................................................................3645.5.4.lb Sheeted dikes ..........................................................................................................370

5.5.4.2 Magmatic affinities ....................................................................................................3775.5.4.2a Gabbroic screens ...................................................................................................3775.5.4.2b Dikes of geochemical group 1 ...............................................................................3815.5.4.2c Dikes of geochemical group 2 ...............................................................................387

5.5.4.3 Chromian Spinel in dikes of geochemical group 2 ....................................................390

5.5.4.4 Element mobility ........................................................................................................392

5.5.4.5 Petrogenesis ................................................................................................................3945.5.4.5a Crystal Fractionation .............................................................................................3945.5.4.5b Source heterogeneity and magma mixing .............................................................397

5.5.5 Pillow unit ............................................................................................................................400

5.5.5.1 Rock classification .....................................................................................................400

5.5.5.2 Magmatic affinities ....................................................................................................403

5.5.5.3 Chromian Spinel in a pillow sample ..........................................................................410

5.5.5.4 Element mobility ........................................................................................................412

5.5.5.5 Petrogenesis ................................................................................................................4135.5.5.5a Crystal Fractionation .............................................................................................4135.5.5.5b Mantle heterogeneity and magma mixing .............................................................413

5.5.6 Comparison of ophiolite units ..............................................................................................416

5.5.6.1 Metagabbro unit .........................................................................................................418

5.5.6.2 Calc-alkaline samples from the rnetatonalite unit and sheeted dike complex ...........419

5.5.6.3 Tholeiitic samples from the sheeted dike complex and pillow unit ...........................423

5.5.6.4 High Ca-boninitic component in sheeted dike complex and pillow unit ...................424

5.5.7 Geochemical diversity in modern tectonic settings ..............................................................424

5.6 GEOCHEMISTRY OF THE MULE MOUNTAIN VOLCANICS ................................................427

5.6.1 Rock classification ...............................................................................................................427

5.6.2 Magmatic affinities ...............................................................................................................431

5.6.3 Chromian spinel in a sample from the Mule Mountain volcanics .......................................440

5.6.4 Element mobility ..................................................................................................................442

ix

5.6.5 Petrogenesis ..........................................................................................................................443

5.6.5.1 Crystal fractionation ...................................................................................................443

5.6.5.2 Mantle heterogeneity and magma mixing ..................................................................448

5.7 POST OPHIOLITE INTRUSIVE ROCKS ....................................................................................448

5.7.1 Half Moon Bar Diorite .........................................................................................................449

5.7.1.1 Rock classification .....................................................................................................449

5.7.1.2 Magmatic affinities ....................................................................................................452

5.7.1.3 Fractionation ..............................................................................................................457

5.7.2 Muscovite garnet tonalite dikes in the metagabbro unit ......................................................458

5.7.2.1 Rock classification .....................................................................................................458

5.7.2.2 Magmatic affinities ....................................................................................................460

5.7.2.3 Fractionation ..............................................................................................................463

5.8 THE ZR/Y VS. ZR DISCRIMINATION DIAGRAM ...................................................................464

5.8.1 Ophiolite units ......................................................................................................................465

5.8.2 Mule Mountain volcanics .....................................................................................................465

5.9 SUMMARY ....................................................................................................................................468

5.9.1 Metagabbro unit ...................................................................................................................468

5.9.2 Metatonalite unit ..................................................................................................................469

5.9.3 Sheeted dike complex ...........................................................................................................469

5.9.4 Pillow unit ............................................................................................................................470

5.9.5 Mule Mountain volcanics .....................................................................................................472

5.9.6 Post-ophiolite intrusions .......................................................................................................473

CHAPTER SIX

RELATIONS OF THE WILD ROGUE WILDERNESS OPHIOLITE WITH THE COAST RANGE OPHIOLITE AND JOSEPHINE OPHIOLITE: IMPLICATIONS FOR THE TECTONIC AND MAGMATIC EVOLUTION OF MID- TO LATE-JURASSIC OPHIOLITES IN CALIFORNIA AND SW OREGON ............................................................................................................................................474

6.1 INTRODUCTION ..........................................................................................................................474

6.2 POSSIBLE CORRELATION OF THE WILD ROGUE WILDERNESS OPHIOLITE WITH TWO BELTS OF LATE-JURASSIC OPHIOLITES .....................................................................................476

6.2.1 Eastern belt of ophiolites ......................................................................................................481

6.2.2 Western belt of ophiolites .....................................................................................................483

x

6.2.3 The Wild Rogue Wilderness ophiolite: a bridging link ........................................................485

6.3 GEOCHEMISTRY OF THE COAST RANGE OPHIOLITE AND JOSEPHINE OPHIOLITE . .489

6.3.1 The Coast Range ophiolite remnant at Llanada, California .................................................489

6.3.2 The Coast Range ophiolite remnant at Black Mountain, California ....................................491

6.3.3 The Coast Range ophiolite remnant at Point Sal, California ...............................................492

6.3.4 The Stonyford volcanic complex .........................................................................................494

6.3.5 The Coast Range ophiolite remnant at Snow Camp Mountain, SW Oregon .......................499

6.3.6 The Josephine ophiolite, northern California SW Oregon ...................................................501

6.3.7 Summary ..............................................................................................................................505

6.4 MODELS FOR THE TECTONIC AND MAGMATIC EVOLUTION OF THE COAST RANGE OPHIOLITE .........................................................................................................................................506

6.4.1 Subduction initiation and the multi-stage evolution of the Coast Range ophiolite ..............507

6.4.1.1 The geochemical evolution of the Coast Range ophiolite, California .......................507

6.4.1.2 The geochemical evolution of the Wild Rogue Wilderness ophiolite, SW Oregon ...5106.4.1.2a Island-arc tholeiites ...............................................................................................5106.4.1.2b Boninites ................................................................................................................5116.4.1.2c Calc alkaline rocks ................................................................................................5126.4.1.2d Mid ocean ridge basalts .........................................................................................515

6.4.1.3 Discussion of the magmatic evolution of the Wild Rogue Wilderness ophiolite .......515

6.4.2 The Lau basin as a modern analogue for the Coast Range ophiolite ...................................517

6.4.2.1 The tectonic evolution of the Tonga-Lau arc/back-arc basin system .........................518

6.4.2.2 The geochemical evolution of the Tonga-Lau arc/back-arc basin system .................519

6.4.2.3 Formation of the Wild Rogue Wilderness ophiolite by fore-arc rifting .....................529

6.4.3 Discussion ............................................................................................................................531

CHAPTER SEVEN

SUMMARY ................................................................................................................................................534

APPENDIX A

PETROGRAPHIC SUMMARY OF SAMPLES FROM THE WILD ROGUE WILDERNESS, SW OREGON ....................................................................................................................................................543

xi

APPENDIX B

AGE SPECTRA, K/CA AND RADIOGENIC YIELD DIAGRAMS FOR THE DATED HORNBLENDES AND MUSCOVITES .................................................................................................561

APPENDIX C

COMPOSITION OF CLINOPYROXENE, PLAGIOCLASE AND CR-SPINEL IN SAMPLES FROM THE WILD ROGUE WILDERNESS, SW OREGON (ELECTRON MICROPROBE ANALYSIS) ................................................................................................................................................566

APPENDIX D

FAULT SLIP DATA AND SENSE OF SHEAR DETERMINED IN FOLIATED AND MYLONITIC ROCKS FROM THE WILD ROGUE WILDERNESS, SW OREGON ..............................................581

APPENDIX E

QUALITY CHECK OF THE TRACE ELEMENT ANALYSIS BY INDUCTIVELY COUPLED PLASMA MASS SPECTROMETRY (ICP-MS) AT THE UNION COLLEGE GEOLOGY DEPARTMENT, SCHENECTADY, NY ..................................................................................................598

E.1 INTRODUCTION .........................................................................................................................598

E.2 SAMPLE PREPARATION ............................................................................................................599

E.2.1 Internal standards .................................................................................................................599

E.2.2 Acid digestion procedure .....................................................................................................599

E.2. 1.1 Weighing and dissolution procedure ........................................................................600

E.2.1.2 Dilution procedure .....................................................................................................604

E.3 ICP-MS INSTRUMENT OPERATION ........................................................................................604

E.3.1 Instrumentation ....................................................................................................................604

E.3.2 Drift ......................................................................................................................................606

E.3.3 Interference ..........................................................................................................................606

E.4 CALIBRATION .............................................................................................................................607

E.4.1 Sequence of analysis ............................................................................................................607

E.4.2 Standards ..............................................................................................................................607

E.4.3 Blanks ...................................................................................................................................611

E.5 CALCULATION OF CONCENTRATIONS .................................................................................612

xii

E.6 EVALUATION OF DATA .............................................................................................................613

E.6.1 Determination of detection limits ........................................................................................613

E.6.2 Determination of precision ..................................................................................................614

E.6.3 Determination of accuracy ...................................................................................................615

E.6.3.1 Comparison with standards ........................................................................................615

E.6.3.2 Inter-laboratory comparison ......................................................................................617

E.7 TEST RUNS ...................................................................................................................................617

E.7.1 First test run, 06/12/1995, synthetic standard used ..............................................................617

E.7.1.1 Strategy and methods .................................................................................................617

E.7.1.2 Limits of detection .....................................................................................................619

E.7.1.3 Precision ....................................................................................................................619

E.7.1.4 Accuracy ....................................................................................................................623

E.7.1.5 Inter-laboratory comparison ......................................................................................623

E.7.1.6 Problems with Ta and Nb ..........................................................................................628

E. 7.1.7 Evaluation of dissolution ..........................................................................................630

E.7.2 Second test run, 11/17/95, NIST-278 and NTST-688 used as standards .............................631

E.7.2.1 Strategy and methods .................................................................................................631

E.7.2.2 Limits of detection .....................................................................................................632

E.7.2.3 Precision ....................................................................................................................632

E.7.2.4 Accuracy ....................................................................................................................635

E.7.2.5 Inter-laboratory comparison ......................................................................................635

E.7.2.6 Problems with Ta and Nb ..........................................................................................639

E.8 ANALYTICAL RUNS ...................................................................................................................640

E.8.1 Introduction ..........................................................................................................................640

E.8.2 First analytical run, 02/23/96 ...............................................................................................642

E.8.2.1 Limits of detection .....................................................................................................642

E.8.2.2 Precision ....................................................................................................................642

E.8.2.3 Accuracy ....................................................................................................................642

E.8.2.4 Resolution of problem with Ta and Nb ......................................................................647

E.8.3 Second analytical run, 08/19/96 ...........................................................................................648

E.8.3.1 Limits of detection .....................................................................................................648

E.8.3.2 Precision.....................................................................................................................648

E.8.3.3 Accuracy ....................................................................................................................648

E.8.3.4 Evaluation of dissolution ...........................................................................................653

xiii

E.8.4 Third analytical run, 09/10/97 .............................................................................................654

E.8.4.2 Limits of detection .....................................................................................................654

E.8.4.3 Precision ....................................................................................................................655

E.8.4.4 Accuracy ....................................................................................................................655

E.8.5 Fourth analytical run, 09/19/97 ............................................................................................660

E.8.5.1 Limits of detection .....................................................................................................660

E.8.5.2 Precision ....................................................................................................................660

E.8.5.3 Accuracy ....................................................................................................................665

E.8.5.4 Selection of data ........................................................................................................665

E.9 COMMENTS ON USE OF ICP-MS AT UNION COLLEGE AND CONCLUSIONS ................665

E.10 SUPPLEMENT: EVALUATION OF THE FIFTH ANALYTICAL RUN; ANALYSIS OF SAMPLES FROM THE COAST RANGE OPHIOLITE REMNANTS AT LLANADA AND BLACK MOUNTAIN .........................................................................................................................................668

E.10.1 Introduction ........................................................................................................................668

E.10.2 Fifth analytical run, 11/11/97 .............................................................................................677

E.10.2.1 Limits of detection ...................................................................................................677

E.10.2.2 Precision ..................................................................................................................677

E.10.2.3 Accuracy ..................................................................................................................677

E.10.2.4 Varying performance of the ICP-MS instrument or incomplete dissolution? .........682

E.10.3 Comparison with XRF and INAA data ..............................................................................683

E.10.3.1 Comparison with XRF data .....................................................................................683

E.10.3.2 Comparison with INAA data ...................................................................................683

E.10.4. Summary ...........................................................................................................................684

APPENDIX F

ANALYTICAL DATA OBTAINED BY ICP-MS AT THE UNION COLLEGE GEOLOGY DEPARTMENT, SCHENECTADY, NY (WILD ROGUE WILDERNESS, SNOW CAMP MOUNTAIN, BLACK MOUNTAIN AND LLANADA) ........................................................................689

REFERENCES ..........................................................................................................................................713

xiv

LIST OF FIGURES

Chapter 1

1.1 Generalized geologic map of central and northern California and SW Oregon ........................................3

1.2 Simplified geological map of SW Oregon .................................................................................................5

1.3 Tectonostratigraphic diagram comparing CRO and Josephine ophiolite ..................................................7

1.4 Model postulating a mid ocean ridge origin for the Coast Range ophiolite ..............................................9

1.5 Model postulating the CRO formed in an exotic island arc terrane ........................................................11

1.6 CRO and Josephine ophiolite formed by rifting of the volcanic are built on western N. America .........13

1.7 Model postulating the CRO formed during the initiation of subduction (infant arc crust) .....................15

1.8 Model of Cretaceous continental margin of western North America ......................................................17

Chapter 2

2.1a Simplified geologic map of SW Oregon ................................................................................................22

2.1b Interpretative cross section through Snow Camp Mountain terrane .....................................................23

2.2a Simplified geologic map of the Wild Rogue Wilderness .......................................................................27

2.2b Geological cross sections through Wild Rogue Wilderness along lines BB' and CC' ...........................28

2.3 Schematic reconstruction of the ophiolite ...............................................................................................31

2.4 Photograph of typical medium grained gabbro of the metagabbro unit ..................................................36

2.5 Close up photograph of outcrop in metagabbro unit ...............................................................................37

2.6 Photograph of compositionally layered metagabbro ...............................................................................38

2.7 Photograph showing the relationship between three different phases of gabbro ....................................39

2.8 Photomicrograph of fine grained mafic dike in metagabbro ...................................................................42

2.9 Photomicrograph of plagioclase in weakly foliated mafic dike in metagabbro ......................................43

2.10 Photograph of slabbed and polished sample from a mylonite zone in the metagabbro unit .................44

2.11 Photomicrograph of typical mylonitic metagabbro ...............................................................................45

2.12a Photomicrograph showing typical plagioclase porphyroclasts in the metagabbro unit .......................46

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2.12b Photomicrograph showing typical augen-shaped hornblende porphyroclast in the metagabbro unit . 46

2.13 Photomicrograph showing a shear band cut by an epidote vein (metagabbro unit) ..............................47

2.14 Photograph of slabbed and polished metagabbro protomylonite ..........................................................53

2.15 Photograph of prominent brittle fault with shear zone exposed at mile 46 at the Rogue River ............54

2.16 Photograph of metatonalite and dioritic enclaves in the metatonalite unit ............................................57

2.17 Photograph of metatonalite containing two globular fine-grained dioritic enclaves .............................58

2.18 Photomicrograph of granophyric texture in metatonalite ......................................................................59

2.19 Photograph of a zone of strongly foliated rock within the metatonalite unit ........................................63

2.20 Photomicrograph showing fabric of typical mylonite (type 1) in the metatonalite unit ........................64

2.21 Photomicrograph showing fabric of typical mylonite (type 2) in the metatonalite unit ........................65

2.22 Photomicrograph of porphyroclast of albite in matrix of recrystallized quartz (metatonalite) .............66

2.23 Photomicrograph of large, relic quartz grain in a monomineralic layer of quartz (metatonalite) .........67

2.24 Photograph of fault contact between the metatonalite unit and the sheeted dike complex ...................71

2.25 Outcrop map of sheeted dikes in the Rogue River canyon near Stair Creek Falls ................................74

2.26 Photograph of layered cumulate gabbro screen in the sheeted dike complex .......................................77

2.27 Photograph of layered cumulate gabbro in sheeted dike complex near the Coffee Pot ........................78

2.28 Traced thin section showing relict igneous texture of cumulate gabbro ...............................................79

2.29 Photograph of polished hand sample showing a narrow shear band in cumulate gabbro .....................80

2.30 Photograph of a quartz-bearing dike of group two intruding a gabbroic host rock ...............................84

2.31 Photomicrograph showing texture typical of aphyric diabasic dikes (sheeted dike complex) ..............86

2.32 Slabbed and polished sample of a microdioritic dike containing olivine xenocrysts ............................87

2.33 Photomicrograph showing translucent brown Cr-spinel in partially resorbed olivine xenocryst .........88

2.34 Photograph of an exposed fault surface with patches of pistachio green ep+qtz mineralization ..........91

2.35 Photograph of one of several faults across which an abrupt change in dike orientations was observed ...92

2.36 Photograph of water polished outcrop of pillows ..................................................................................96

2.37 Photograph of pillow exposed in Huggins Canyon ...............................................................................97

2.38 Photomicrograph of center of pillow showing typical intergranular texture .........................................98

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2.39 Photomicrograph of granophyric texture in dikes intruding pillows ...................................................100

2.40 Photograph of leucocratic dike in the pillow unit near Brushy Bar ....................................................101

2.41 Photograph of hand sample of typical breccia in the Mule Mountain volcanics .................................107

2.42 Photomicrograph of the intergranular texture of the basalt sample O/C-81a (Mule Mountain) .........109

2.43 Photomicrograph of the trachytic texture of an aphyric andesite (Mule Mountain volcanics) ............111

2.44 Photomicrograph of plagioclase phenocryst in dacite (Mule Mountain volcanics) ............................112

2.45 Photograph of sedimentary rocks in the uppermost Mule Mountain volcanics ...................................114

2.46 Photograph showing outcrop of late tonalitic dikes in the metagabbro unit ........................................118

2.47 Photomicrograph showing the texture of a foliated tonalite dike (metagabbro unit) ..........................119

2.48 Polished sample of muscovite-garnet tonalite dike having S/C-type fabric ........................................120

2.49 Photograph of a net-vein breccia about 200 m west of the fault exposed at Brushy Bar ....................123

2.50 Photograph of medium-grained Half Moon Bar diorite intruded by a porphyritic dike .....................124

2.51 Photomicrograph of amphibole in sample O/C-377 from the HMB diorite ........................................125

2.52 Photograph of S/C-type mylonite from the Blossom Bar shear zone ..................................................129

2.53 Photograph of mylonite and ultramylonite (Blossom Bar shear zone) ................................................130

2.54 Photograph of a strongly foliated, mafic rock (Blossom Bar shear zone) ...........................................132

2.55 Photograph of a strongly foliated chlorite schist (Blossom Bar shear zone) .......................................133

2.56 Photograph of an undeformed and a foliated volcanic breccia (Blossom Bar shear zone) .................135

2.57 Photograph of hand sample of 1.5 m wide epidote+actinolite zone (Blossom Bar shear zone) . .......136

Chapter 3

3.1 Columnar section, showing reconstruction of ophiolite ........................................................................142

3.2 Photomicrograph of HMB diorite showing typical, strongly zoned plagioclase ...................................145

3.3 Classification of amphiboles using electron microprobe data ...............................................................151

3.4 Diagram illustrating P-T conditions of equilibration of hornblende-plagioclase pairs (HMB diorite). .167

3.5 Temperature variations versus Mg-# in samples O/C-118a and O/C-376 (HMB diorite) .....................168

3.6 Diagram illustrating P-T conditions of equilibration of hornblende-plagioclase pairs (O/C-229) ........171

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3.7 Temperature variations versus Mg-# in sample O/C-229 (hbl qtz gabbro in metagabbro unit) ............172

3.8 Diagram illustrating P-T conditions of equilibration of hbl-plag pairs (metagabbro unit) ...................176

3.9 Temperature variations versus Mg-# in samples from the metagabbro unit ..........................................177

Chapter 4

4.1a Simplified geologic map of SW Oregon ..............................................................................................184

4.1b Interpretative cross section along line AA' in figure 4.1a ...................................................................185

4.2 Stratigraphic nomenclature in the Tyee Basin after Baldwin (1974) .....................................................192

4.3 Stereographic projections of faults after the method of Hoeppner (1955) ............................................196

4.4 Stereographic projections of post-Eocene faults and results of paleostress analysis ............................198

4.5 Stereographic projections of structural data from the Dothan Formation .............................................203

4.6 Stereographic projections of poles to planar features (pillow unit and Mule Mountain volcanics) ......209

4.7 Geologic map showing structural domains A through F in the sheeted dike complex ..........................215

4.8 Stereographic projection of pole to mean dike orientations for domains A through F ..........................217

4.9 Stereographic projections of poles to dikes after correcting for Tertiary and Cretaceous folding ........218

4.10 Results of the paleostress analysis of structural data from domains A and B .....................................224

4.11 Results of the paleostress analysis of structural data from domains A and B (continued) ..................229

4.12 Results of the paleostress analysis of structural data from domain D .................................................233

4.13 Summary of the criteria used to infer the sense-of-shear in mylonitic rocks ......................................239

4.14a Photomicrograph of fabric in a mafic mylonite from the metagabbro unit (O/C-374b.4) ................243

4.14b Photomicrograph of a C/C'-type fabric in a chlorite-rich mylonite from the metatonalite unit ........243

4.14c Photomicrograph of plagioclase porphyroclast having a low-angle, synthetic microfault ................244

4.14d Photomicrograph of plagioclase porphyroclast having two high-angle, antithetic microfaults ........244

4.14e Photomicrograph of mylonite consisting of alternate layers of quartz and epidote ± chlorite ..........245

4.15 Stereographic projections of foliations and lineations in samples from the Wild Rogue Wilderness. 259

4.16 Results of paleostress analysis of cemented faults in the metatonalite unit ........................................263

4.17 Determination of the shear stress τ on Ct and Csz for different stress fields (after Means, 1989) .......274

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4.18 Determination of stress tensor (shearing in Blossom Bar shear zone and metatonalite unit) .............278

4.19 Summary and interpretation of isotopic ages in the Rogue Wilderness remnant of the CRO .............280

4.20 Stereographic projections of structural data (domains A and B) after correcting for folding .............287

4.21 Model for fault block rotation in the sheeted dike complex ................................................................288

4.22 Analysis of unfolded structural data of domains A, B and D ..............................................................292

4.23 Model of the spreading and fault geometry of the Troodos ophiolite .................................................297

4.24 Stereographic projections of foliations and lineations after correcting for folding .............................304

4.25 Cartoons depicting the directions of spreading (~164 Ma) and thrusting (~150 Ma) .........................305

Chapter 5

5.1 Simplified geologic map of the Wild Rogue Wilderness and sample localities ....................................310

5.2 Chondrite and N-MORB normalized REE and trace element patterns (reference samples) .................318

5.3 Chondrite and N-MORB normalized REE and trace element patterns (metagabbro unit) ...................327

5.4 Cr vs. Y tectonic discrimination diagram (metagabbro unit) . ..............................................................330

5.5 Hf/3-Th-Ta tectonic discrimination diagram (metagabbro unit) ...........................................................331

5.6 MgO variation diagrams of samples from the metagabbro unit ............................................................336

5.7 Chondrite and N-MORB normalized REE and trace element patterns (hbl qtz diorite in metagabbro) ...342

5.8 Chondrite and N-MORB normalized REE and trace element patterns (metatonalite unit) ..................348

5.9 MgO variation diagrams of samples from the metatonalite unit ...........................................................355

5.10 Incompatible trace element ratios in tonalite-trondhjemite samples plotted against SiO2 .................358

5.11 N-MORB normalized trace element patterns showing the effects of allanite fractionation

(metatonalite) ................................................................................................................................360

5.12 N-MORB normalized trace element diagram showing the effects of mixing (metatonalite unit) ......363

5.13 MgO variation diagrams of samples from the sheeted dike complex .................................................372

5.14 Rock classification of diabasic and microdioritic dikes in the Zr/TiO2 vs. Nb/Y diagram .................376

5.15 Chondrite and N-MORB normalized REE and trace element patterns (gabbro screens) ....................379

5.16 Hf/3-Th-Ta tectonic discrimination diagram (sheeted dike complex) .................................................382

xix

5.17 Chondrite and N-MORB normalized REE and trace element patterns (sheeted dikes) ......................385

5.18 Cr vs. Y tectonic discrimination diagram (sheeted dike complex) ......................................................388

5.19 Composition of Cr-spinels in dikes of geochemical group 2 ..............................................................391

5.20 Diagrams showing effects of mixing of MORB with IAT and IAT with CAB (sheeted dike complex) .399

5.21 Rock classification of samples from the pillow unit in the Zr/TiO2 vs. Nb/Y diagram .......................404

5.22 Chondrite and N-MORB normalized REE and trace element patterns (pillow unit) ..........................407

5.23 Hf/3-Th-Ta tectonic discrimination diagram (pillow unit) ..................................................................408

5.24 Cr vs. Y tectonic discrimination diagram (pillow unit) .......................................................................409

5.25 Composition of Cr-spinel in a sample from the pillow unit ................................................................411

5.26 Diagrams illustrating the effects of mixing vs. variable degrees of partial melting (pillow unit) .......415

5.27 Th/Yb vs. Ta/Yb tectonic discrimination diagram (Wild Rogue Wilderness ophiolite) ......................421

5.28 Rock classification of samples from the Mule Mountain volcanics in the Zr/TiO2 vs. Nb/Y diagram ...432

5.29 Chondrite and N-MORB normalized REE and trace element patterns (Mule Mountain volcanics) . .435

5.30 Hf/3-Th-Ta tectonic discrimination diagram (Mule Mountain volcanics) ..........................................438

5.31 Cr vs. Y tectonic discrimination (Mule Mountain volcanics) .............................................................439

5.32 Composition of Cr-spinel in a sample from the Mule Mountain volcanics ........................................441

5.33 MgO variation diagrams of samples from the Mule Mountain volcanics ...........................................446

5.34 Rock classification of diabasic dikes intruding HMB diorite using the Zr/TiO2 vs. Nb/Y diagram....453

5.35 Chondrite and N-MORB normalized REE and trace element patterns (Half Moon Bar diorite) ........455

5.36 Hf/3-Th-Ta tectonic discrimination diagram (Half Moon Bar diorite) ................................................456

5.37 Chondrite and N-MORB normalized REE and trace element patterns (Musc-gar-tonalite) ...............462

5.38 Zr/Y vs. Zr tectonic discrimination diagram of Pearce and Norry (1979) and Pearce (1983) ............467

5.39 Cross section showing the units of the Wild Rogue Wilderness, sample ages, and magmatic affinities 471

Chapter 6

6.1 Generalized geologic map of California and SW Oregon showing major accretionary terranes ..........478

6.2 Tectonostratigraphic diagram comparing two belts of Jurassic ophiolites ............................................480

xx

6.3 Cr-Y discrimination diagram showing data from the Coast Range ophiolite ........................................496

6.4 Hf/3-Th-Ta discrimination diagram showing data from the Coast Range ophiolite .............................497

6.5 Tb/Yb and Ta/Yb discrimination diagram showing data from the Coast Range ophiolite ....................498

6.6 Cr vs. Y tectonic discrimination diagram showing the fields for Josephine lavas and dikes ................503

6.7 Hf/3-Th-Ta discrimination diagram showing the fields for Josephine lavas and dikes .........................504

6.8 Hf/3-Th-Ta tectonic discrimination diagram showing samples from the Rogue Wilderness ophiolites ...514

6.9 Location map of the Lau Basin after Hergt and Farley (1994) ..............................................................521

6.10 Diagrams showing the tectonic evolution of the Lau Basin ................................................................522

6.11 Th/Yb vs. Ta/Yb discrimination diagram showing data from the Lau Basin, SW Pacific ..................526

6.12 Hf/3-Th-Ta discrimination diagram showing data from the Lau Basin, SW Pacific ...........................527

Chapter 7

7.1 Simplified geologic map of the Wild Rogue Wilderness ......................................................................540

7.2 Cross section showing units of the Wild Rogue Wilderness, sample ages and magmatic affinities .....541

List of Plates

Plate 1: Geological map of the Wild Rogue Wilderness, southwest Oregon (scale 1:24,000)

(in back pocket)

xxi

List of Tables

Chapter 2

Table 2.1a: Summary of 40Ar/39Ar apparent ages .......................................................................................32

Table 2.1b: Summary of U/Pb zircon ages ....................................................................................................32

Table 2.2: List of mineral abbreviations ........................................................................................................32

Chapter 3

Table 3.1: Microprobe analyses of hornblende in samples from the Half Moon Bar diorite ......................154

Table 3.2: Microprobe analyses of hornblende in O/C-229 (hornblende quartz diorite in metagabbro unit) .156

Table 3.3: Microprobe analyses of hornblende in samples from the metagabbro unit ................................157

Table 3.4: Chemical analyses and proportional formula for run products (Poli, 1993) and results of

temperature calculations using the geothermometers of Blundy and Holland (1994) ..................180

Chapter 5

Table 5.1a: Major and trace element compositions of samples from the metagabbro unit .........................323

Table 5.1b: Major and trace element composition of hornblende quartz diorite in the metagabbro unit.....340

Table 5.2: Major and trace element compositions of samples from the metatonalite unit ..........................345

Table 5.3a: Major and trace element compositions of samples from the sheeted dike complex (gabbro

screens) ..........................................................................................................................................365

Table 5.3b: Major and trace element compositions of samples from the sheeted dike complex (diabasic and

microdioritic dikes) .......................................................................................................................367

Table 5.4: Major and trace element composition of samples from the pillow unit .....................................401

Table 5.5 Major and trace element composition of samples from the Mule Mountain volcanics ...............428

Table 5.6: Major and trace element composition of samples from the Half Moon Bar diorite ...................450

Table 5.7: Major and trace element composition of dikes in the metagabbro unit ......................................459

xxii