METALAMPROPHYRE DIKE DEFORMATION IN THE HOMESTAKE RESERVOIR QUADRANGLE, LEADVILLE, COLORADO by Michael Geoffrey Frothingham A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Earth Sciences MONTANA STATE UNIVERSITY Bozeman, Montana April 2017 © COPYRIGHT by Michael Geoffrey Frothingham 2017 All Rights Reserved ii ACKNOWLEDGEMENTS Colin A. Shaw is gratefully acknowledged as my supervisor and for the direction and revision of this project. Additional committee members are Mary S. Hubbard and David W. Mogk. This work was undertaken with partial financial assistance from the Graduate School at Montana State University, the United States Geological Survey EDMAP grant number G15AC00175, the Montana Association of Geographic Information Professionals, the Barry C. Bishop Scholarship at Montana State University, and NSF award number 1525590 to Concord University (J. Allen and S. Kuehn). I would also like to thank my family, friends, Flysch, undergraduate research assistants Natali Kragh and Matthew Mersen, fellow graduate students in the bullpen, and Chester A. Ruleman of the USGS; because of whom my life, research, and future career as a field geologist are fundamentally metamorphosed. iii TABLE OF CONTENTS 1. INTRODUCTION .......................................................................................................... 1 Location .......................................................................................................................... 2 Geologic Setting of the Northern Sawatch Range .......................................................... 5 Regional Tectonic History .............................................................................................. 5 Paleoproterozoic ..................................................................................................... 5 Mazatzal Province — Model 1 ............................................................................... 6 Mazatzal Province — Model 2 ............................................................................... 7 Mesoproterozoic ..................................................................................................... 9 Late Mesoproterozoic to Neoproterozoic ............................................................. 13 Phanerozoic ........................................................................................................... 13 Previous Mapping ......................................................................................................... 14 2. METHODS ................................................................................................................... 16 Field Work .................................................................................................................... 16 Data Collection and Field Mapping ...................................................................... 16 Sample Collection ................................................................................................. 17 Laboratory Work .......................................................................................................... 18 Map Digitization ................................................................................................... 18 Stereonets .............................................................................................................. 19 Thin Section Preparation....................................................................................... 20 Microscope Petrography ....................................................................................... 20 TitaniQ Thermometry ................................................................................................... 21 3. ROCK DESCRIPTIONS .............................................................................................. 23 Paleoproterozoic Gneiss ............................................................................................... 23 Biotite Gneiss ........................................................................................................ 23 Hornblende Gneiss ................................................................................................ 26 Micaceous Quartzite ............................................................................................. 28 Calc-Silicate Gneiss .............................................................................................. 30 Mesoproterozoic Igneous Rocks .................................................................................. 32 Metalamprophyre .................................................................................................. 32 St. Kevin Granite .................................................................................................. 37 Mesoproterozoic Shear Zone Tectonites ...................................................................... 39 Mylonite Shear Tectonites .................................................................................... 39 Pseudotachylyte Shear Tectonites ......................................................................... 41 iv TABLE OF CONTENTS — CONTINUED 4. STRUCTURAL DOMAINS ......................................................................................... 42 Structural Domain I — Homestake Shear Zone ........................................................... 44 Structural Domain II — Hornblende Gneiss, Calc-Silicate Gneiss, and Metalamprophyres .............................................................. 45 Structural Domain III — Slide Lake Shear Zone ......................................................... 46 Structural Domain IV — St. Kevin Batholith .............................................................. 47 Structural Domain V — Paleozoic Sedimentary Cover ............................................... 48 Structural Domain VI — Upper Arkansas Basin ......................................................... 48 Summary ...................................................................................................................... 48 5. KEY FIELD RELATIONS ........................................................................................... 50 Paleoproterozoic Gneiss ............................................................................................... 50 Location ................................................................................................................ 50 Orientation ............................................................................................................ 51 Age ........................................................................................................................ 51 Mesoproterozoic Metalamprophyres ............................................................................ 52 Location ................................................................................................................ 52 Orientation ............................................................................................................ 52 Age ........................................................................................................................ 54 Mesoproterozoic St. Kevin Granite .............................................................................. 56 Location ................................................................................................................ 56 Orientation ............................................................................................................ 56 Age ........................................................................................................................ 56 Mesoproterozoic Shear Deformation ........................................................................... 57 Location ................................................................................................................ 57 Orientation ............................................................................................................ 57 Shear Sense Indicators .......................................................................................... 57 Age ........................................................................................................................ 60 6. TEMPERATURE OF DEFORMATION ..................................................................... 62 Metalamprophyres and St. Kevin Granite .................................................................... 62 Deformation Textures ........................................................................................... 62 TitaniQ .................................................................................................................. 63 Regional Deformation .................................................................................................. 65 v TABLE OF CONTENTS — CONTINUED 7. DISCUSSION ............................................................................................................... 67 Timeline of Geologic Events ........................................................................................ 67 Inherited Structural Control .......................................................................................... 71 Temperature of Deformation ........................................................................................ 72 Continuum of Deformation .......................................................................................... 74 Intracontinental Deformation