STRUCTURAL INTERPRETATION OF THE ELK RANGE THRUST SYSTEM WESTERN COLORADO, USA by Justin Edward Tully 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 2009 ©COPYRIGHT by Justin Edward Tully 2009 All Rights Reserved ii APPROVAL of a thesis submitted by Justin Edward Tully This thesis has been read by each member of the thesis committee and has been found to be satisfactory regarding content, English usage, format, citation, bibliographic style, and consistency, and is ready for submission to the Division of Graduate Education. Dr. David R. Lageson Approved for the Department of Earth Sciences Dr. Stephen G. Custer Approved for the Division of Graduate Education Dr. Carl A. Fox iii STATEMENT OF PERMISSION TO USE In presenting this thesis in partial fulfillment of the requirements for a master’s degree at Montana State University, I agree that the Library shall make it available to borrowers under rules of the Library. If I have indicated my intention to copyright this thesis by including a copyright notice page, copying is allowable only for scholarly purposes, consistent with “fair use” as prescribed in the U.S. Copyright Law. Requests for permission for extended quotation from or reproduction of this thesis in whole or in parts may be granted only by the copyright holder. Justin Edward Tully April 2009 iv ACKNOLEDGEMENTS The field work and academic effort behind this thesis was facilitated by research grants, scholarships, donations and intellectual support from professional societies, industry and private parties. Without these generous organizations and individuals this thesis would certainly not have been possible. Thank you all! The Geological Society of America The Colorado Scientific Society (Ogden Tweto Memorial Scholarship) Rocky Mountain Association of Geologists (Norman H. Foster Memorial Scholarship) The Billings Geophysical Society United States Geological Survey Colorado Geological Survey Anschutz Exploration Corporation Dan Bean and Pricilla Spears Margot and Ned Timbel Dr. James C. Coogan Dr. Bruce Bartleson Andrew Lockman and Erin Ganser Elizabeth Helmke John & Judith Tully Alicia Tully v TABLE OF CONTENTS 1. BACKGROUND AND FOCUS ......................................................................................1 Introduction ......................................................................................................................1 Previous Work .................................................................................................................5 Research Problem ............................................................................................................9 2. DESCRIPTION OF MAP UNITS AND MECHANICAL PROPERTIES ...................12 Cretaceous ......................................................................................................................12 Jurassic ...........................................................................................................................14 Mechanical Properties 18 Triassic ...........................................................................................................................18 Pennsylvanian-Permian ..................................................................................................19 Mechanical Properties ................................................................................................22 Mississippian..................................................................................................................23 Mechanical Properties ................................................................................................23 Devonian ........................................................................................................................24 Mechanical Properties ................................................................................................24 Silurian-Ordovician........................................................................................................29 Mechanical Properties ................................................................................................30 Cambrian ........................................................................................................................30 Mechanical Properties ................................................................................................33 Precambrian ...................................................................................................................33 Mechanical Properties ................................................................................................36 Intrusive Rocks ..............................................................................................................37 3. GEOMETRY OF STRUCTURAL FEATURES ...........................................................42 Major Faults ...................................................................................................................42 Elk Range Thrust .......................................................................................................42 Brush Creek Thrust ....................................................................................................44 Rustlers Gulch Lateral Ramp .....................................................................................45 Sawatch Front ............................................................................................................46 Italian Creek Lateral Ramp/Star Basin Window .......................................................47 Cement Mountain Block ............................................................................................48 Major Folds ....................................................................................................................50 Schofield Syncline .....................................................................................................50 Whiterock Anticline ...................................................................................................50 Flag Creek Syncline ...................................................................................................52 Spring Creek Park Syncline .......................................................................................53 vi TABLE OF CONTENTS – CONTINUED American Flag Anticline ............................................................................................53 Cement Mountain Arch ..............................................................................................54 4. STRUCTURAL SYSTEM.............................................................................................55 Surface Continuum ........................................................................................................56 Thrusted Margin.........................................................................................................57 Faulted Basement Blocks ...........................................................................................58 Subsurface Continuum ...................................................................................................60 Geometric Model .......................................................................................................65 Disciplinary Context ..............................................................................................66 Kinematic Model .......................................................................................................67 Regional Continuum ......................................................................................................69 5. SUMMARY AND DISCUSSION ................................................................................72 Conclusions ....................................................................................................................72 Further Research ............................................................................................................73 REFERECES CITED.........................................................................................................81 vii LIST OF FIGURES Figure Page 1. Major Tectonic Features of Colorado and Location of the Elk Range Thrust System.................................................................................................3 2. Local Structural and Topographic Features of the Elk Range Thrust System ..................................................................................................................4 3. Thesis Map Area with respect to Published Mapping and Existing Theses ..............................................................................................................11 4. Mechanical Stratigraphy of the Elk Range Thrust System ............................................15 5. Cretaceous Mancos Formation in Footwall of the Hunter’s Hill Thrust Segment ........................................................................................16 6. Brecciated Gothic & Belden Formations on the Flank of Italian Mountain .............................................................................................................25 7a. Outcrop Photo of Typical Belden Shale and Limestone Beds..............................................................................................................................26 7b. Contact Metamorphosed Belden Formation at the Summit