Structural Analysis of the Northwest Wind Mountain Quadrangle, New Mexico: Proterozoic Shearing to Cenozoic Brittle Faulting in the Burro Mountains

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STRUCTURAL ANALYSIS OF THE NORTHWEST WIND MOUNTAIN

QUADRANGLE, NEW MEXICO: PROTEROZOIC SHEARING TO CENOZOIC

BRITTLE FAULTING IN THE BURRO MOUNTAINS

JENSEN KOHL ANGELLOZ, Bachelor of Science

Presented to the Faculty of the Graduate School of

Stephen F. Austin State University

In Partial Fulfillment

Of the Requirements

For the Degree of

Master of Science

STEPHEN F. AUSTIN STATE UNIVERSITY

December, 2017

STRUCTURAL ANALYSIS OF THE NORTHWEST WIND MOUNTAIN

QUADRANGLE, NEW MEXICO: PROTEROZOIC SHEARING TO CENOZOIC

BRITTLE FAULTING IN THE BURRO MOUNTAINS

Jensen Kohl Angelloz, Bachelor of Science

APPROVED:

Dr. Chris Barker, Thesis Director

Dr. Liane Stevens, Committee Member

Dr. R. LaRell Nielson, Committee Member

Dr. C.J. Aul, Committee Member

Richard Berry, D.M.A. Dean of the Graduate School

ABSTRACT

Preliminary investigation of the Bullard Peak metamorphic series (BPMS) in the northwestern Wind Mountain quadrangle within the Burro Mountains of southwestern New Mexico suggests a possible previously unidentified shear zone, prompting detailed (1:12,000) geologic mapping and collection of structural data. The study area has a complex tectonic history, including 1) ~1.65 Ga metamorphism during accretion of the Mazatzal terrane to Laurentia’s southern margin; 2) ~1.4 Ga intrusion of

Granite and Rhyolite Province granitoids; 3) significant uplift during the formation of the

Ancestral Rockies (~300 Ma) and the Rocky Mountains (~70-50 Ma); and 4) inversion tectonics with reactivation of compressional faults as normal and strike-slip faults during extension related to the formation of the Basin and Range and the Rio Grande Rift starting at ~37 Ma.

Evidence for northeast (031o; N31oE) shearing during accretion of the Mazatzal

Province is recorded by southwest plunging (211o; S31oW) lineations with top-to-the- northeast shear sense. Average foliation planes in the BPMS are oriented 061o/39o

(N61oE, 39oSE). Multiple folding events affected the region, likely starting during the accretion of the Mazatzal Province. Folds formed during this event are expected to be northwest verging. Abundant folding may have occurred during the intrusion of granitoids of the Granite and Rhyolite Province. These folds would have varying

i orientations caused by stress regimes formed by intruding batholiths changing orientation based on their geometry. The final folding event was caused by oblique faulting in the region. Associated fault drag folds have axial planar orientations similar to the faults that caused them. The ductile deformation seen in the BPMS is most likely a result of northeast accretion of the Mazatzal Province and intrusion of granitoids of the Granite and Rhyolite Province.

Some of the faults with slickensides in the area are strike-slip (both dextral and sinistral) with a component of oblique-slip (normal or reverse) motion. The mean vector of the mapped faults is 054o/26o (N54oE, 26oSE). The faults have two dominant orientations, northeast-southwest and northwest-southeast, making up 76% of all faults recorded. The complex pattern of faulting in the region produced previously unmapped positive flower structures, two in outcrop and one on a map scale. Two dominant trends, northeast-southwest and northwest-southeast, are expressed in the faulting and help create the complex fault system seen in the Burro Mountains. The northwest-southeast trending faults probably formed during the uplift of the Ancestral Rocky Mountains and have been reactivated during Mesozoic rifting, the Laramide orogeny, and Basin and

Range extension. The northeast-southwest trending faults most likely formed as joints during uplift of the Ancestral Rocky Mountains or the Laramide orogeny. This fault system produced the positive flower structures when the faults were reactivated during the Laramide orogeny or Basin and Range extension.

ACKNOWLEDGMENTS

I would like to thank Dr. Chris Barker for his time in helping develop this project, assistance during field work, and advisement. This project would not have reached completion without the time and help from my committee, Dr. Liane Stevens, Dr. LaRell

Nielson, and Dr. C.J. Aul. Kaitlin Askelson and Robert Schoen were wonderful help in the field as this project was beginning.

Many thanks are given to the department and faculty of geology at Stephen F.

Austin and the East Texas Geological Society for providing the opportunities I had while attending. The scholarships I received from East Texas Geological Society and the department helped cover partial costs of this project. Other funding for this project was provided through donations from Shanna Hopper, Lynette LaBorde, and Cristina Renteria and short term loans from Samuel Clayton Brown and Travis Zappe.

I would not have been able to display my data without Stereonet 9 from Richard

Allmendinger of Cornell University. Thank you for making the software available for free. Many thanks to Gary and Sally Brown for use of their ATV to reach some areas of my study area.

Many lasting friendships were made during my time at Stephen F. Austin through our mutual struggles. Many nights, evenings, and lunches were spent discussing interesting topics with Robert Schoen, Garrett Williamson, Kaitlin Askelson, Ryan

iii

Silberstorf, Jonathan Woodard, Cole Hendrickson, and Austin Wilkerson. Late night Call of Duty marathons with The Shoe will provide great memories for years to come. These acknowledgements would be remiss without thanking the faculty of Sam Houston State

Universities Department of Geography and Geology, specifically, Doctors Hill, Cooper,

Harris, Strait and Gillespie. Thank you for believing in me and preparing me for graduate school. Special thanks are deserved for Dr. Joe Hill and his wife, Kristin, for always treating me as family. The two trips to Spain will always be considered as highlights of my life.

The friendships I gained at Sam Houston benefited me greatly in graduate school, whether I was asking advice or rooming with an old friend. I expect many future memories will be made with Adam Walker, Bernie Smith, Andrea Dearing, Garrett

Ward, and Daniel Collazos.

Richard Ball, Denise Cox, Dale Short, Anita Paulssen, Rich Adams, and Fernando

Ziegler deserve credit as my industry mentors. Their encouraging words helped me set career goals and push for greater success than I imagined possible.

Last but certainly not least, eternal gratitude must be given to the people who have been there from the beginning of this long journey; my parents, Robert and Mary

Zappe; grandmother, Katherine “Kitty” Wille Angelloz; brother, Travis Zappe, brother from another mother, Sam Brown; and my second parents, Gary and Sally Brown. Many people deserve credit to pushing me to never give up and begin this journey; Travis

Zappe, Sam Brown, Justin Scheel, Steven Mayworm, Dylan and Josh Castillo, Matthew

Horrigan, and Cody Ryan. You all deserve credit for always pushing me to put my best foot forward and always having an encouraging word. Thank you for never giving up on me.

DEDICATION

This thesis is dedicated to my great grandmother Catherine “Kite” Wille for inspiring me to pursue my education above all else.

TABLE OF CONTENTS

ABSTRACT i

ACKNOWLEDGMENTS iii

DEDICATION vi

CHAPTER 1

INTRODUCTION 1

STUDY AREA 2

OBJECTIVE 5

METHODS 5

CHAPTER 2

REGIONAL SETTING AND GEOLOGIC HISTORY 7

The Proterozoic 7

Mazatzal Accretion 7

Granite & Rhyolite Province 9

Grenville Orogeny 10

Southwestern Laurentia Large Igneous Province 10

The Paleozoic Era 11

Ancestral Rocky Mountains 11

The Mesozoic Era 13

Jurassic Extension 15

vii

Laramide Orogeny 15

The Cenozoic Era 21

Basin and Range 21

Rio Grande Rift 23

Volcanism 25

Tyrone Mine and Regional Mineralization 25

LITHOLOGY 26

Metamorphic Rocks 26

The Paleoproterozoic Bullard Peak metamorphic series 26

Cretaceous Metamorphic Rocks 29

Granite and Rhyolite Province Granitoids 29

Cenozoic Igneous Rocks 30

CHAPTER 3

LITHOLOGY 31

Introduction 31

Metamorphic Rock Descriptions 31

Proterozoic Metamorphic Units 36

Quartzofeldspathic Gneiss 36

Mica Schist 36

Migmatite 39

Amphibolite 39

Cretaceous Metamorphic Unit 42

viii

Beartooth Quartzite 42

Igneous Rock Descriptions 42

Intrusive Units 42

Quartz Syenite 42

Monzogranite 43

Burro Mountain Granite 43

Diorite 45

Gabbro 45

Extrusive Units 45

Andesite 45

Andesite Porphyry 45

Green Lapilli Tuff 46

Purple Lapilli Tuff 46

Tan Lapilli Tuff 46

Lapilli-Tuff Breccia 46

CHAPTER 4

STRUCTURAL DATA 48

Foliations, Lineations, and Folding 48

Quartzofeldspathic Gneiss 56

Mica Schist 63

Migmatite 68

Amphibolite Schist 74

BPMS 83

Beartooth Quartzite 83

Faulting 88

CHAPTER 5

DISCUSSION 101

Foliation Development 101

Fold Development 105

Contact Metamorphism of the Beartooth Quartzite 108

Fault Development 108

Revised Geologic History 112

CHAPTER 6

CONCLUSION 118

Timeline of Deformation 120

Proposed Future Research 121

REFERENCES 122

APPENDICES 129

Appendix A – Planar Data 129

Appendix B – Linear Data 140

VITA 143

LIST OF FIGURES

Figure 1. Location of the Wind Mountain Quadrangle in the Burro Uplift. 3

Figure 2. Satellite imagery of the study area. 4

Figure 3. Tectonic province map of southwest North America. 8

Figure 4. Uplifts of the Ancestral Rocky Mountains (ARM). 12

Figure 5. Map depictions of the geometries of intracratonic basement uplifts caused by flat slab subduction. 14

Figure 6. Sketch of the southwest North American plate in the Late Jurassic. 16

Figure 7. Map showing the location of Laramide ranges in southwest New Mexico. 17

Figure 8. Sketch of thin-skinned and thick-skinned deformational styles and geometries. 18

Figure 9. Potential mechanism for arc magmatism during the Laramide orogeny. 20

Figure 10. The Basin and Range province within the United States is highlighted in green. 22

Figure 11. Map of the Mogollon-Datil volcanic complex showing calderas with known ages. 24

Figure 12. Map of the general geology of the Burro Mountains. 27

Figure 13. North zone of the study area. 32

Figure 14. The central zone of the study area. 33

Figure 15. The south zone of the study area. 34

Figure 16. Map key for Figures 15-17. 35

Figure 17. Outcrop of the quartzofeldspathic gneiss. 37

Figure 18. Outcrop of the mica schist. 38

Figure 19. Outcrop of the migmatite. 40

Figure 20. Outcrop of the amphibolite. 41

Figure 21. Picture of an amphibolite schist xenolith in a boulder of quartz syenite. 44

Figure 22. Location map of the north zone of the study area. 49

Figure 23. Location map of the northern-central zone of the study area. 50

Figure 24. Location map of the southern-central zone of the study area. 51

Figure 25. Location map of the south zone of the study area. 52

Figure 26. Location map along Shear Creek. 53

Figure 27. Photographs of winged porphyroclasts and sigmoidal lenses. 54

Figure 28. Photograph of an S-C fabric. 55

Figure 29. Stereonet of 29 S1 measurements in the quartzofeldspathic gneiss of the Bullard Peak metamorphic series. 57

Figure 30. Picture of an inclined antiform in the quartzofeldspathic gneiss at location 11. 59

Figure 31. Topographic map displaying the five locations of the 10 folds documented in the quartzofeldspathic gneiss. 60

Figure 32. Stereonet of fold measurements in the quartzofeldspathic gneiss of the Bullard Peak metamorphic series. 62

Figure 33. Photograph of the S1 and S2 foliation relationship in the mica schist. 64

xii

Figure 34. Stereonets of strike and dip of S1 and S2 in the mica schist of the Bullard Peak metamorphic series. 65

Figure 35. Stereonet of 16 L1 measurements from the mica schist of the Bullard Peak metamorphic series. 67

Figure 36. Stereonets of fold measurements in the mica schist of the Bullard Peak metamorphic series. 69

Figure 37. Photograph of the mica schist outcrop at location 115. 70

Figure 38. Picture of the migmatite. 71

Figure 39. Stereonet of strike and dip of 9 S1 measurements from the migmatite of the Bullard Peak metamorphic series. 73

Figure 40. Photograph of amphibolite lenses in the quartzofeldspathic gneiss at location 9. 75

Figure 41. Three stereonets displaying S1 measurements in the amphibolite of the Bullard Peak metamorphic series. 77

Figure 42. Picture of tension gashes in the amphibolite schist at location 10. 78

Figure 43. Photographs of drag folding in the amphibolite in Shear Creek, locations 121 and 122. 79

Figure 44. Stereonet of fold measurements in the amphibolite of the Bullard Peak metamorphic series. 80

Figure 45. Two tight folds at locations 147 and 122 respectively. 81

Figure 46. Three folds at location 118 that progressively become tighter towards the west. 82

Figure 47. Sketch of S- and Z- parasitic folds. 84

Figure 48. Stereonet of the mean strike and dip of foliation, S1, in the 4 units of the Bullard Peak metamorphic series. 85

xiii

Figure 49. South zone of the study area with the mean trend of foliation and lineations overlaid. 86

Figure 50. Stereonet of strike and dip of foliation measurements in the Beartooth Quartzite. 87

Figure 51. Stereonet of strike and dip of all 114 fault planes. 89

Figure 52. Photographs of fault gouge and breccia. 90

Figure 53. Stereonets of strike and dips of fault planes. 92

Figure 54. Stereonets of divided fault planes. 93

Figure 55. Photographs of faulting taken at location 110. 95

Figure 56. Photographs of faulting taken at location 117 and 110, respectively. 96

Figure 57. Block diagram of a fault bounded block. 97

Figure 58. Location map for cross section B-B’ in the central zone of the study. 98

Figure 59. Sketch of cross section line B-B’. 99

Figure 60. Box diagram of oriented foliation planes and lineations. 102

Figure 61. Diagram showing how accretion direction may have changed. 104

Figure 62. Location map for cross section A-A’ in the southern zone of the study. 106

Figure 63. Sketch of cross section line A-A’. 107

Figure 64. Sketch and photographs of drag folding in the amphibolite in Shear Creek. 109

Figure 65. Stereonets of the dominant fault orientations in the study area. 111

Figure 66. Location map for cross section C-C’ in the northern zone of the study. 116

xiv

Figure 67. Sketch of cross section line C-C’. 117

Plate 1. Geologic map and cross sections. Attached

LIST OF TABLES

Table 1. Table of axial plane (AP) and hinge line measurements of folds in the quartzofeldspathic gneiss. 61

Table 2. Table of 16 lineation measurements in the mica schist of the Bullard Peak metamorphic series. 66

Table 3. Table of axial plane (AP) and hinge line measurements of folds in the mica schist. 68

Table 4. Table of 9 migmatite strike and dip orientation measurements with locations. 72

Table 5. Table of mineral lineation orientation in the migmatite with location numbers and associated shear sense motion. 74

Table 6. Table of the regional geologic history of southwestern New Mexico from Paleoproterozoic to present. 113

Appendix A – Planar Data 129

Appendix B – Linear Data 140

xvi

CHAPTER 1

INTRODUCTION

The Burro Mountains, a basement-cored uplift in southwest New Mexico, have had a complex tectonic history. Since the late Paleoproterozoic, this region has experienced accretion, widespread plutonism, uplift, extension, volcanism, metamorphism, and deformation. The Burro Mountains expose the late Paleoproterozic

Bullard Peak Metamorphic Series (BPMS), Mesoproterozoic granitoids, Cretaceous igneous and metamorphic rocks, and Cenozoic volcaniclastic rocks (Hedlund, 1978).

These rocks exhibit a variety of evidence for ductile and brittle deformation including localized folding, mylonitization, winged porphyroclasts, fault breccia and gouge, slickenlines, and chattermarks. Shear fabrics have not been extensively described by previous workers. This project was designed to identify, describe, and analyze evidence of ductile shearing and brittle faulting to determine the significance of these events to the geologic history of the region.

The geologic history of the area began with the growth of Laurentia through accretion of terranes in the Paleoproterozoic. Protoliths of the BPMS were formed, metamorphosed, and deformed during accretion of the NE-trending Mazatzal terrane during the late Paleoproterozoic, at ~ 1.65 Ga (Karlstrom et al., 2004). Subsequent metamorphism and deformation occurred during the emplacement of granitoids from the

Granite and Rhyolite Province at ~1.4 Ga (Whitmeyer and Karlstrom, 2007; Amato,

2011). A mafic dike swarm was emplaced across southwest Laurentia at ~1.1 Ga, possibly a response to lithospheric delamination after the Grenville orogeny or the arrival of a mantle plume under southern Laurentia (Bright et al., 2014). The Ancestral Rocky

Mountains, a series of NW-trending basement-cored uplifts, formed during the late

Paleozoic (Kues and Giles, 2004; Ye et al., 1996). The Laramide orogeny uplifted the region again with basement-cored uplifts in the Cretaceous and early Cenozoic (Seager,

2004). Since the late Eocene, Basin and Range and Rio Grande Rift extension and volcanism affected southwest New Mexico (Elston, 2008).

STUDY AREA

The study area is a 7.2 square mile section in the northwest corner of the Wind

Mountain Quadrangle (Figures 1-2), approximately 20 miles southwest of Silver City,

New Mexico, in the Gila National Forest. The study area is hilly with approximately 940 feet of relief. The highest point is a benchmark near the southwestern border at 6,298 feet. Previous work in the region either focused on an area to the west of the study area

(Hewitt, 1959; Amato, 2011) or lacked detail about shear fabrics (Hewitt, 1959; Hedlund,

1978).

in in

on the the on

and is shown in in shown is and

The red polygon red Thepolygon

the location of the study area study the of location the

It is marked by the red star. red star. the by marked It is

. .

Location of the Wind Mountain Quadrangle in the Burro Uplift the Burro in Quadrangle Wind Mountain the of Location

Figure Figure Mexico New southwest indicate map topographic 2 Figure

Figure 2: Satellite imagery of the study area. The boundaries of the study are marked by the red lines.

OBJECTIVE

The overall goal of this study is to provide data aiding in reconstructing accretion kinematics of the Paleoproterozoic Mazatzal terrane and delineate the structural history of the region since accretion. A secondary objective is to determine the presence of a potential Late Paleoproterozoic shear zone that developed during Mazatzal accretion and displays a suite of strongly deformed metamorphic rocks in southwestern New

Mexico.

METHODS

This study consisted of literature review, geologic field mapping, and analysis of structural orientation data. Detailed mapping of the area at the 1:12,000 scale was undertaken during June, July and August 2016. Geologic units were delineated on a map and orientation data was collected on faults, folds, and metamorphic fabrics. Particularly good exposures of mylonitic rock outcrops in one creek (informally named Shear Creek) were mapped at the 1:3,000 scale for greater structural detail. Enlargements of the USGS

Wind Mountain topographic quadrangle were used as base maps for field mapping.

Confirmation of locations was obtained by use of the Gaia GPS application on an Apple iPhone. Structural orientation data was collected using a Brunton geologic compass. This data was converted into azimuth format from quadrant format using an Excel spreadsheet. The azimuth data was entered into Stereonet 9.5 by Richard W.

Allmendinger to display plane and pole-to-plane data on a stereographic projection,

5 calculate mean vectors, and contour pole-to-plane data to analyze the structural orientations visually.

Based on the data collected, geologic maps were created at the 1:12,000 scale for the study area and at the 1:3,000 scale for Shear Creek. Three cross-sections were made through the study area emphasizing important structures or relationships. Stereonet plots were analyzed to determine orientation patterns in the various units to better understand the deformation history of the study area.

CHAPTER 2

REGIONAL SETTING AND GEOLOGIC HISTORY

The Proterozoic

Between 2.0 Ga and 1.6 Ga, several juvenile crustal blocks, the Mojave, Yavapai and Mazatzal Provinces (Figure 3), were accreted to the southern margin of Laurentia

(Karlstrom et al., 2004; Whitmeyer and Karlstrom, 2007; Amato et al., 2008). After a period of quiescence, the Granite and Rhyolite Province was emplaced as a series of large felsic batholiths within and south of these juvenile terranes (Karlstrom et al, 2004,

Whitmeyer and Karlstrom, 2007). At ~1.1 Ga, a swarm of mafic dikes were intruded into southwestern Laurentia. It is postulated that this event was linked to the Grenville orogeny, which occurred further south and sutured the super-continent, Rodinia (Bright et al., 2014)

Mazatzal Accretion

The rocks in the Mazatzal terrane are juvenile, arc-related, igneous and sedimentary rocks (Whitmeyer and Karlstrom, 2007). Accretion occurred between 1.69

Ga and 1.65 Ga (Karlstrom, 2004; Whitmeyer and Karlstrom, 2007). The sedimentary rocks, primarily derived from weathering of rhyolites and related supracrustal rocks were deposited from 1.7-1.65 Ga and are associated with arc-related volcanism and back-arc

Figure 3: Tectonic province map of southwest North America. The yellow star is the approximate location of the study area in the Mazatzal province. The red areas represent intruded Granite and Rhyolite bodies. The northern edge of the Grenville front is marked by the thrust fault in the southeastern corner (Karlstrom et al., 2004).

8 related successions (Whitmeyer and Karlstrom, 2007; Amato et al., 2008). These units were metamorphosed, but it is unclear what grade of metamorphism occurred prior to

1.5-1.4 Ga due to regional resetting of 40Ar/39Ar ages during emplacement of anorogenic granitoids (Amato et al., 2008; Whitmeyer and Karlstrom, 2007). The amphibolite facies may have been reached in rocks in close proximity to synorogenic plutons where the thermal gradient was elevated (Whitmeyer and Karlstrom, 2007).

Geochronological data from undeformed gabbro intrusions in the Burro

Mountains suggest all pre-1.633 Ga metasedimentary and igneous rocks in the area share a common deformational fabric not caused by emplacement of the Granite and Rhyolite

Province (Amato et al., 2008). After accretion of the Mazatzal terrane, widespread emplacement of subduction-related calc-alkaline plutons occurred at 1.66-1.65 Ga, and

A-type granitoids were emplaced in intracratonic regions of the Mazatzal terrane

(Anderson and Bender, 1989; Anderson and Cullers, 1999; Whitmeyer and Karlstrom,

2007).

Granite & Rhyolite Province

After accretion of the Mazatzal terrane ceased around 1.60 Ga, a period of stabilization occurred due to a lull in tectonic activity (Whitmeyer and Karlstrom, 2007).

At 1.55 Ga, tectonic activity resumed with accretion of juvenile arc terranes (Whitmeyer and Karlstrom, 2007). Collectively, the younger terranes are called the Granite and

Rhyolite Province. The accretion of this province did not substantially affect the rocks of the previously accreted terranes; however, later magmatism associated with the Granite

9 and Rhyolite Province did affect the area (Amato et al., 2001; Whitmeyer and Karlstrom,

2007).

A large number of peraluminous (S-type) to metaluminous (I-type) granitoids were emplaced into multiple Paleoproterozoic crustal provinces between 1.4 and 1.35 Ga

(Thompson and Barnes, 1999; Whitmeyer and Karlstrom, 2007). Regional metamorphism occurred concurrently with the granitoid emplacement up to 1000 km inboard of accretion, with shortening to the northwest (Whitmeyer and Karlstrom, 2007).

Deformation this far inboard has been interpreted to have been induced by far-field stresses from plate-margin compressional stresses acting on thermally softened rocks

(Nyman et al., 1994; Karlstrom and Humphreys, 1998; Whitmeyer and Karlstrom, 2007).

Grenville Orogeny

The Grenville orogeny ended the accretionary growth of Laurentia and was part of a series of world-wide orogenies that created the supercontinent, Rodinia (Whitmeyer and Karlstrom, 2007). Protracted tectonism occurred between 1.3 Ga and 0.9 Ga, (Halls,

2015; Whitmeyer and Karlstrom, 2007) No deformation from the Grenville orogeny is recognized in southwest New Mexico.

Southwestern Laurentia Large Igneous Province

The Southwestern Laurentia Large Igneous Province was proposed by Bright et al. (2014) because of the relationship of mafic dikes, sills, sheets, and flows that intruded southwest Laurentia around 1.1 Ga. Proposed models for the formation of this province

10 are: 1) lithospheric delamination after the Grenville orogeny or 2) the presence of a mantle plume under southern Laurentia. It is likely the cause of this province also accounts for formation of the MacKenzie and Sudbury mafic dike swarms in Canada

(1.27 Ga), the Midcontinent rift (1.1 Ga), and the Central Basin platform and diabase sheets in Arizona (1.1 Ga) (Whitmeyer and Karlstrom, 2007).

The Paleozoic Era

After the rifting of Rodinia, 780-550 Ma, there was a long period of inactivity along the southwestern boundary of Laurentia (Whitmeyer and Karlstrom, 2007). This changed in the late Paleozoic with the Ouachita-Marathon orogeny, which resulted in the formation of the supercontinent Pangea (Whitmeyer and Karlstrom, 2007).

Ancestral Rocky Mountains

The ARM were Pennsylvanian to Permian intracratonic basement-cored uplifts adjacent to deep, narrow, elongate basins (Figure 4). The ARM are known from the volumes of sediment shed into adjacent basins and from exposures of the eroded roots of the former mountains. There is evidence of folding and faulting within the uplifts, but the rocks were overprinted by Laramide structures and locally covered by younger volcanic strata (Ye et al., 1996). Multiple hypotheses have been proposed for the development of the ARM (Kues and Giles, 2004): 1) Flat-slab subduction and Andean-style volcanism on the southwest margin of Laurentia (Ye et al., 1996); 2) Collision and suturing of Pangea along the Ouachita-Marathon front as deformation progressed westward during the Late-

Figure 4: Uplifts of the Ancestral Rocky Mountains (ARM). The uplifts of the Ancestral Rocky Mountains are the stippled tan regions and the basins are denoted by the syncline symbol. This map shows three tectonic fronts that may have been related to the development of the ARM (Kues and Giles, 2004).

Mississippian to Early- Permian (Alego, 1992); 3) A transform margin in northern

Mexico (Dickinson and Lawton, 2003); 4) The Sonoman orogeny, caused by subduction of oceanic crust and accretion of an island arc in the west (Burchfiel and Davis, 1972;

Burchfiel and Davis, 1975).

The Ouachita-Marathon orogeny in southern Laurentia caused northwest- southeast shortening and was more than 3000 km from the westernmost uplift of the

ARM (Ye et al., 1996). This distance and especially the orientation makes it unlikely that the Ouachita-Marathon orogeny caused the ARM deformation. The ARM shows shortening normal (northeast-southwest) to shortening caused by the formation of the

Ouachita-Marathon orogeny (Ye et al., 1996; Woodward et al., 1999). Furthermore, the

ARM are structurally similar to the Rocky Mountains of the Laramide orogeny in that they are basement-cored compressive blocks and not thin-skinned deformation like most of the Ouachita-Marathon folds (Lowell, 1985; Nelson and Lucas, 2011).The shortening direction of the ARM and geometry of the uplifts are consistent with flat-slab subduction caused uplifts (Figure 5), if subduction occurred from the southwest, as suggested by Ye et al. (1996).

The Mesozoic Era

Southwestern New Mexico during the Mesozoic experienced both extension and compression. An extensional phase possibly caused by slab rollback prior to Laramide compression resulted in magmatic activity (Lawton, 2004). This was followed by the thick-skinned deformation of the Laramide orogeny in the Late Cretaceous and Early

Cenozoic (Seager, 2004).

dipping subduction zone zone subduction dipping

ab subduction. The drawing on the right right the on drawing The ab subduction.

dern day South America, the Rocky Mountains, and the and Mountains, Rocky the America, South day dern

Map depictions of the geometries of intracratonic basement uplifts caused by flat slab subduction. flatsubduction. slab by caused uplifts basement intracratonic of geometries the of depictions Map

From left to right, the Sierra Pampeanas in mo in Pampeanas Sierra the right, to left From sl flat area of the outlines box The Mountains. Rocky Ancestral northeast a of the basedpresence on ARM the of development for model a presents 1996 al., et ARM(Ye the of southwest Figure

Jurassic Extension

During the Jurassic, the Burro Uplift was on the north flank of the Bisbee Basin, a non-marine basin that formed as a rift in conjunction with the opening of the Gulf of

Mexico (Figure 6). The rift is thought to have been formed by extensional stresses associated with Farallon slab rollback (Dickinson and Lawton, 2001; Lawton, 2004). The rift progressively extended eastward towards the Chihuahua trough in northeast Mexico

(Lawton, 2004). Normal faults trending NW-SE formed due to this rifting, which coincides with the trend of later Laramide reverse faults (Lawton, 2000; Lawton, 2004).

This led Lawton (2000) to infer that some reverse faults were reactivated normal faults from Jurassic rifting.

Laramide Orogeny

The Laramide orogeny began in the Late Cretaceous and extended into the

Eocene (Copeland et al., 2017). Laramide ranges in southwest New Mexico include the

Burro Mountains where the study area is located (Seager, 2004; Figure 7). The Laramide orogeny was a thick-skinned deformational event that uplifted basement rocks (Figure 8).

Several models have been proposed for the cause of the deformation in southern New

Mexico. These include thin-skinned deformation (Corbitt and Woodward, 1973;

Woodward and DuChene, 1981); thin-skinned deformation with basement foreland uplifts and deformation of basement in the fold-and-thrust belt (Drewes, 1978, 1988,

1991); inversion tectonics, which is a reactivation of faults (Lawton, 1996; Bayona, 1998;

Figure 6: Sketch of the southwest North American plate in the Late Jurassic. (A) Structural features include a rift shoulder (light brown) that includes the Burro Mountains and study area, and the adjacent Bisbee Basin in southwestern California and southern Arizona. (B) Structural features of the Late Albian (~105 Ma). The Bisbee Basin has moved southeastward into southwestern New Mexico and the rift is no longer active (Modified from Lawton, 2004).

Figure 7: Map showing the location of Laramide ranges in southwest New Mexico. Approximate location of study area is shown by the red star. (Seager, 2004).

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Lawton, 2000); and basement-cored block uplifts (Seager, 1983; Seager and Mack, 1986;

Seager, 2004). Crustal shortening was toward the northeast (Seager, 2004).

The controversy about the deformational style comes in part from segmentation of the structures. During the Cenozoic, these structures were partially buried under volcanic and sedimentary rocks and then separated by Basin-and-Range extension in the Neogene

(Seager, 2004).

Lawton (2000) proposed a model regarding a mechanism for magmatism during the Laramide orogeny. The Jurassic extension that created the Bisbee basin thinned the lithosphere in the region allowing the asthenosphere to rise higher than normal (Lawton,

2000). As the Farallon plate was subducted at a low angle, a wedge of asthenosphere was trapped and arc magmatism began to occur (Lawton, 2000; Seager, 2004; Figure 9).

Compressional wrenching in southwest New Mexico caused oblique-slip faults during uplift associated with the Laramide orogeny, which then created complex fault zones that, in some cases, are potential flower structures (Hodgson, 1991; Seager, 2004).

Both dextral and sinistral movement has been argued for these faults, the majority of workers argue for sinistral movement (Seager, 2004). Drewes (1978, 1988, 1991) suggested that up to 15 km of northwest-striking sinistral movement occurred on these faults. These faults may be part of a larger system of faults related to the Texas

Lineament, a northwest trending fault zone (Muehlberger, 1980; Seager, 2004).

Figure 9: Potential mechanism for arc magmatism during the Laramide orogeny. Rifting thinned the crust, allowing the asthenosphere to draw closer to the surface. As flat-slab subduction of the Farallon plate began, a wedge of asthenosphere was trapped between the subducting Farallon plate and overriding North American plate. This trapped wedge of asthenosphere was the cause of the eastward propagating volcanism (Seager, 2004).

The Cenozoic Era

After Laramide compression ended in the early Cenozoic, the remainder of the era was dominated by extension and volcanism.

Basin and Range

Basin and Range extension (Figure 10) in southwest North America created north to northwest trending, sub-parallel mountain ranges and adjacent basins. The classic block faulting that characterizes the region obscures a prior extensional event within the

Basin and Range (Elston, 1980; Eaton, 1982). The earlier extensional event began at ~37

Ma and consisted of low angle normal faulting and development of core complexes

(Elston, 1980; Eaton, 1982). This indicates that this extensional event origniated at depths where the rocks were ductile (Elston, 1980; Eaton, 1982). The ductile extension event coincided with the climax of felsic volcanism and caldera subsidence in the southwest

(Elston, 1980; Eaton, 1982). It is possible that the ductile stage of the extension in the

Mid-Tertiary was the continental equivalent of opening an oceanic back-arc basin

(Scholz et al., 1971; Elston, 1980). The second extensional event began at approximately

17 Ma (Elston, 1980; Eaton, 1982).

This dual-stage extensional orogeny caused widespread bimodal volcanism

(Elston, 1980; Eaton, 1982). Bimodal volcanism is caused by basaltic magma creating a felsic magma through partial melting of the crust and both being emplaced (Brewer et al.,

2004; Maria and Hermes, 2001). An example is the voluminous volcanism seen in the

Figure 10: The Basin and Range Province within the United States is highlighted in green. The Rio Grande rift is outlined by the red oval in the southeast. Approximate location of the study area is marked by the red star (USGS, 2017).

Mogollon-Datil volcanic complex in southwestern New Mexico (Figure 11) (Elston,

2008).

Rio Grande Rift

The Rio Grande rift system is a north-trending rift valley, located mainly in New

Mexico, that began extending between 35 – 29 Ma (Lawton and McMillan, 1999). Both felsic and mafic volcanism was associated with the rifting. There are two hypotheses for the cause for this rifting. 1) Decompression melting related to arc abandonment. As flat slab subduction waned at the end of the Laramide orogeny, the subducted slab slowly began to retreat and sink into the mantle (Lawton and McMillan, 1999). This retreat allowed for rapid return of the mantle under the continental lithosphere causing decompression melting (Lawton and McMillan, 1999). This caused the extension of the rift and emplacement of mafic magmas (Lawton and McMillan, 1999).

2) Rotation of the Colorado Plateau (Chapin and Cather, 1994).The idea that the

Rio Grande rift system was created due to rotation of the Colorado Plateau was proposed by Chapin and Cather (1994) and suggests that the Colorado Plateau acted as its own microcontinent. As the North American Plate overrode the East Pacific Rise, it became stuck for ~15 million years prior to counter-clockwise motion of the North American

Plate (Atwater, 1970; Steiner, 1988). This rotation caused the San Andreas Fault to form at ~5 Ma (Atwater, 1970). If the Colorado Plateau rotated a few degrees clockwise relative to the North American Plate, extension would be seen on the eastern edge of the

Plateau (Steiner, 1988; Chapin and Cather, 1994).

Figure 11: Map of the Mogollon-Datil volcanic complex showing calderas with known ages. Approximate location of the study area is show by the red star. (Modified from Chapin et al., 2004).

Volcanism

Significant volcanism in the Mogollon-Datil volcanic field of southwest New

Mexico occurred between 36-24 Ma (Cather, 1990; Chapin et al., 2004). The volcanism was probably initiated by fluid enriched lithospheric mantle contacting hot asthenosphere as the Farallon Plate sunk into the mantle (Cather, 1990; Chapin et. al., 2004). This volcanism deposited multiple tuffs and lava flows on the Burro Uplift (McIntosh et al.,

1991; Chapin et al., 2004).

Tyrone Mine and Regional Mineralization

The Tyrone Mine is a gold and copper porphyry mine located a few miles southeast of the study area. The granodiorite to quartz monzonite stocks being mined at the Tyrone mine were emplaced in the Late Cretaceous to Paleocene (Horton et al.,

2017). The minerals were emplaced through a two-staged process called supergene enrichment (Zientek and Orris, 2005). Primary mineralization occurred during emplacement; low-grade copper was deposited in a network of fractures and breccias around the stock (Zientek and Orris, 2005). This occurred around 47-44 Ma in the Tyrone region (Cook, 1994; DuHamel et al., 1995). Secondary mineralization occurred as the mineralized zone was uplifted and interacted with meteoric water and the copper minerals precipitated out (Zientek and Orris, 2005). This phase occurred around 19 Ma in the

Tyrone region (Cook, 1994; DuHamel et al., 1995). Northeast-striking structures contain the highest concentration of mineralization in the Tyrone region (Cook, 1994; DuHamel et al., 1995).

LITHOLOGY

There are seven main rock units in the study area (Figure 12). Metamorphic and igneous rocks found in the thesis area constitute both basement and cover rocks.

Proterozoic rocks of the Bullard Peak Metamorphic Series and plutons of the Granite and

Rhyolite Province are exposed basement rocks. The Cretaceous Beartooth quartzite, an andesite sill, and Cenozoic tuffs are the local cover rocks and are often ridge formers in the north part of the study

Metamorphic Rocks

The metamorphic rocks in the region were first described by Paige (1916) while working in the Silver City Quadrangle as minor ill-defined metasedimentary units. In

1956, Gillerman and Whitebread mapped two units in the Black Hawk mining district, which is adjacent to the study area. The first unit is a thinly bedded quartzite containing layers of mica schist, amphibolite, and “knotted” schist, and the second unit contains rocks that may be migmatitic metasedimentary rocks (Gillerman and Whitebread, 1956;

Hewitt, 1959).

The Paleoproterozoic Bullard Peak metamorphic series

Metamorphic rocks in the region include the Bullard Peak Series and the Ash

Creek Series, but only the Bullard Peak Series is found within the study area. The main rock types of the BPMS include a quartzofeldspathic gneiss, mica schist, and amphibolite

(Hewitt, 1959; Hedlund, 1978). The units experienced high stress and temperatures that

Figure 12: Map of the general geology of the Burro Mountains. The proposed study area is outlined by the black polygon. Foliation and mineral lineation measurements are shown west of the proposed study. The white circles are U-Pb zircon locations with ages. Red circles are locations of samples that were examined for P/T conditions and/or monazite geochronology. The blue circles are 40Ar/39Ar sample locations. (Amato et al., 2011)

27 formed a well-developed foliation and are locally intensely deformed (Hewitt, 1959). The units have sharp contacts with the Burro Mountain Granite and exhibit lit-par-lit injection which is igneous material that has been injected between bedding or foliation planes, and magmatic features (Hewitt, 1959).

The biotite schist is a dark gray, fine-grained rock that is similar in outcrop pattern with amphibolite and hornblende schist (Hewitt, 1959; Hedlund, 1978). Typical outcrops consist of 40% biotite, 25% quartz, 25% feldspars, and 10% muscovite (Hewitt,

1959; Hedlund, 1978). Garnet porphyroblasts are rare (Hewitt, 1959; Hedlund, 1978).

The amphibolite varies in color from dark greenish-black to greenish-black and fine- to medium-grained (Hewitt, 1959; Hedlund, 1978). It has well defined foliations

(Hewitt, 1959; Hedlund, 1978; Amato et al., 2011). The amphibolite contains hornblende, calcic oligoclase to sodic andesine; epidote may be present (Hewitt, 1959; Hedlund

1978). Hedlund (1978) suggested the protolith for the amphibolite was marl.

The quartzofeldspathic gneiss ranges in color from orangey, light-brown to light- gray (Hewitt, 1959; Hedlund, 1978). It is fine-grained, with granoblastic quartz, perthitic microcline, and sodic oligoclase (Hewitt, 1959; Hedlund, 1978). It contains 3-12% biotite and up to 30% muscovite (Hewitt, 1959; Hedlund, 1978). This is the most abundant lithology in the Bullard Peak series. The protolith of this metasedimentary unit was most likely an arkosic sandstone (Hewitt, 1959; Hedlund, 1978).

The migmatite is medium gray in color, with up to 50% micas (Hewitt, 1959;

Hedlund, 1978). It has contorted foliation and local fibrolitic aggregates and fibrous

28 mattes of sillimanite (Hewitt, 1959; Hedlund, 1978). Garnet is rare (Hewitt, 1959;

Hedlund, 1978).

Cretaceous Metamorphic Rocks

The Beartooth Quartzite is a contact metamorphic unit in the study area. It is the basal Cretaceous unit in the region (Riess, 1990). It has an intrusive contact with the younger andesite which it contacts on three sides (Hedlund, 1978). The Beartooth

Quartzite has a maximum thickness of 150 m (Hedlund, 1978). The protolith was probably chert pebble conglomerate, sandstone, and siltstone. It is light brownish-gray to a medium dark-gray. This unit is moderately resistant and forms ridges in the region

(Hedlund, 1978). It is thought to be Cretaceous by the conformable contact with the Late

Cretaceous Colorado Formation above and the similarity to the Mancos Shale and Sarten

Formation which is Albian to early Cenomanian (Mack, 1987).

Granite and Rhyolite Province Granitoids

The Burro Mountain Granite is an aphanitic to phaneritic leucocratic granite

(Hewitt, 1959; Hedlund, 1978; Amato et al., 2011). It contains 50%-60% potassium feldspar, 30%-40% quartz, and 5%-15% plagioclase (Hewitt, 1959; Amato et al., 2011).

It has been dated to ~1.45 Ga using 40Ar/39Ar dating methods (Amato et al., 2011).

A phaneritic leucocratic granodiorite consists of ~30% white to pink potassium feldspar, ~30% plagioclase, ~15% quartz, ~15% biotite, and ~10% hornblende (Amato et al., 2011). Amato et al. (2011) has dated it to ~1.46 Ga using 40Ar/39Ar dating methods.

Cenozoic Igneous Rocks

The hornblende andesite porphyry ranges from light brownish-gray to medium- gray (Hedlund, 1978). The andesite displays bleaching and reddening attributed to limonite hematite staining (Hewitt, 1959; Hedlund, 1978). The andesite contains 25-30% oligoclase-andesine, 10% hornblende, 2% biotite in a cryptocrystalline matrix (Hedlund,

1978).

The greenish-gray ash-flow tuff is moderately welded, with flattened and aligned pumice fragments (Hewitt, 1959; Hedlund, 1978). The tuff contains about 4% oligoclase phenocrysts (Hedlund, 1978). The degree of welding increases up section and has a nodular texture (Hewitt, 1959; Hedlund, 1978).

The dark purplish-gray to light brownish-gray ash-flow tuff is welded and contains 4-5 cm devitrified, flattened pumice fragments (Hedlund, 1978). Weathered surfaces are highly pitted (Hedlund, 1978). The tuff contains approximately 3% quartz phenocrysts (Hedlund, 1978).

The light yellowish-gray ash-flow tuff is welded and devitrified (Hedlund, 1978).

The tuff contains 5-10% sanidine and plagioclase phenocrysts in a felted, recrystallized groundmass (Hedlund, 1978).

CHAPTER 3

LITHOLOGY

Introduction

The geologic map produced from this study (Plate 1) is divided into three zones based on lithology and geologic history: north (Figure 13), central (Figure 14), and south

(Figure 15); the map key is Figure 16. The southern zone is dominated by sheared

Paleoproterozoic schists and gneisses of the Bullard Peak Metamorphic Series. The central zone contains Proterozoic granitoids that were intruded during the formation of the Granite and Rhyolite Province. The northern zone contains much younger rocks and includes the Beartooth Quartzite, a large Cenozoic andesite sill and Cenozoic tuffs. Most of these units are best exposed in stream channels and along steep hillsides because weathering has created thick soils and locally abundant vegetation elsewhere.

Metamorphic Rock Descriptions

The majority of the rocks in the southern and central zones of the study are metamorphosed. In the southern and lower central zones, the metamorphosed rocks are part of the BPMS. The main unit of the BPMS is the quartzofeldspathic gneiss which crops out widely in the southern zone. The other units occur as lenses that either terminate in the quartzofeldspathic gneiss or against the surrounding igneous rocks. The

Figure 13. North zone of the study area. It consist of 4 northeast dipping tuffs, an andesite sill, a quartzite and the northern contact of the Burro Mountain Granite

Figure 14. The central zone of the study area. It consist mainly of the Burro Mountain Granite and the monzo-granite. Other units found in this zone are the andesite, diorite, gabbro, amphibolite, quartzofeldspathic gneiss, migmatite, and quartz syenite.

Figure 15. The south zone of the study area. It consists mainly of the Bullard Peak Metamorphic Series and the Burro Mountain Granite. The quartz syenite is found on the southern boundary of the study area.

Figure 16. Map key for the Figures 15-17.

Cretaceous Beartooth quartzite is found on a northwest trending ridge in the north of the study area.

Proterozoic Metamorphic Units

The four mappable units of the BPMS are described below based on the author’s field descriptions.

Quartzofeldspathic gneiss: The quartzofeldspathic gneiss (Figure 17) is the most prevalent unit of the BPMS in the study area. It weathers to an orangey-brown soil that is widespread across the southern zone of the study. This unit is strongly foliated. Both fresh and weathered outcrop surfaces are off-white to light to medium gray. It contains approximately 50-60% feldspar, 30-35% quartz, and 5-20% biotite. Some of the more weathered outcrops are friable. The quartzofeldspathic gneiss can be identified as the orange unit on the map (Plate 1) in the central and southern zone of the study area

(Figures 14; 15). The map symbol for this unit is Xqfs (Figure 16).

Mica schist: The mica schist (Figure 18) is laterally zoned with the dominant concentration of muscovite and biotite gradually changing to other mica. At a few outcrops, it appears as a “spotted schist” with up to nickel sized, circular muscovite clusters scattered across foliation planes. It weathers to an orangey-brown soil, but can be differentiated from the quartzofeldspathic gneiss soil by a higher mica content. This unit is strongly foliated and exhibits mineral stretching lineations. Winged quartz porphyroclasts and sigmoidal lenses of the mica schist are found in most outcrops. Fresh and weathered surfaces are silvery to charcoal – bluish gray with white banding.

Figure 17. Outcrop of the quartzofeldspathic gneiss. This is a weathered outcrop showing the characteristic orange soil. The foliation is dipping to the top right of the image. Hammer for scale.

Figure 18. Outcrop of the mica schist. This outcrop shows the silvery color of the mica schist. Foliation is dipping to the right of the image. Hammer for scale.

It contains approximately 25-55% biotite, 5-35% muscovite, 10-20% feldspar, and 10-

20% quartz. The mica schist can be identified as the green lenses on the map (Plate 1) in the southern zone of the study area (Figure 15). The map symbol for this unit is Xms

(Figure 16).

Migmatite: The migmatite (Figure 19) is the least extensive unit in the BPMS.

This unit is strongly foliated and lineated and presumably represents very high grade metamorphism with partial melting resulting in the ptygmatic bands. It consists of alternating pinkish to off white and silvery – gray to black bands. Outcrops are extremely hard and smooth. It weathers to an orange – brown soil. The migmatite can be identified as the gray lenses on the map (Plate 1) in both the central and south zones of the study area (Figures 15; 16). The map symbol for this unit is Xmg (Figure 16).

Amphibolite: The amphibolite (Figure 20) is found as lenses and discontinuous layers throughout the BPMS. It weathers to a dark soil that is easily identifiable against the orange soils of the other units of the BPMS. Outcrops on top of hills and the sides are more red-brown, whereas outcrops in stream beds are blue-black. This unit is strongly foliated and lineated. Fresh surfaces are dark greenish-black to dark bluish-black, often with white specks. Weathered surfaces are a reddish-brown to a bluish-gray and rarely greenish-gray. It contains approximately 80% amphibole and 20% plagioclase. A few highly deformed and weathered outcrops are friable. The amphibolite can be identified as the blue lenses on the map (Plate 1) in the central and southern zone of the study area

(Figures 14; 15). The map symbol for this unit is Xas (Figure 16).

Figure 19. Outcrop of the migmatite. Located in the red square, biotite and hornblende have the appearance of flowing off the outcrop. Notice the mixing of the felsic and mafic minerals. Hammer for scale.

Figure 20. Outcrop of the amphibolite. The white lineations are plagioclase preferentially oriented with the foliation. The dark spots are rain drops. The red color is iron oxidizing out of the amphibolite. Hammer for scale.

Cretaceous Metamorphic Unit

Beartooth Quartzite: The Beartooth Quartzite ranges from a quartzite to a metaconglomerate. The weathered surface is light-medium gray to an orangey-red. Some surfaces are mineralized with iridescent black, purple, blue, red, and green colors. Fresh surfaces are light to medium gray in the quartzite and dark gray with some variability in the metaconglomerate. Clasts in the metaconglomerate are up to 1 inch in diameter.

Fossilized shells are rare. The Beartooth Quartzite can be identified as the gray unit on the map (Plate 1) in the north zone of the study area (Figure 13). The map symbol for this unit is Kbq (Figure 16).

Igneous Rock Descriptions

Within the study area there are eleven igneous rock types, six intrusive units and five extrusive units. They range in age from Proterozoic to Cenozoic. The extrusive units are found only in the northern zone of the study area, whereas the intrusive bodies are found throughout the area (Plate 1). All rock descriptions in this section are based on the author’s field descriptions.

Intrusive Units

Quartz syenite: This is a leucocratic, coarse-grained phaneritic rock. Weathered surfaces are a pinkish to dull-red. Fresh surfaces are white to gray. It contains approximately 30-40% feldspar, 20-25% biotite, 10-15% plagioclase, 10-15% hornblende, 10-15% quartz, and less than 5% muscovite. Feldspar crystals are up to 1.5

42 inches long and are euhedral to subhedral. Other minerals are subhedral to anhedral.

Xenoliths of amphibolite are present in some outcrops (Figure 21). The quartz syenite can be identified as the red unit on the map (Plate1) in the south zone of the study area

(Figure 15). The map symbol for this unit is Yqs (Figure 16).

Monzogranite: This is a leucocratic, course-grained phaneritic rock. Weathered surfaces are light tan with dark spots to a pinkish-orange. Fresh surfaces are 60% white and 40% black. It contains approximately 40-45% biotite, 20-25% plagioclase, 20-25% feldspar, 10% quartz, and up to 5% hornblende. Mineral crystals are subhedral to anhedral. The monzo-granite has an alignment of biotite and hornblende crystals in a possible flow fabric. The monzo-granite can be identified as the pink unit on the map

(Plate 1) in the central zone of the study area (Figure 14). The map symbol for this unit is

Ymg (Figure 16).

Burro Mountain Granite: This is a leucocratic, relatively fine-grained, phaneritic rock. Weathered surfaces are red-brown while fresh surfaces are pink with orange to red spotting. It contains approximately 60% potassium feldspar, 20-30% quartz, 5% hornblende, 5% plagioclase, and up to 5% biotite. Mineral crystals are subhedral to anhedral. Large xenoliths of the monzo-granite are found near the contact of these two intrusive bodies. The Burro Mountain Granite can be identified as the brown unit on the map (Plate 1) in the central and south zones of the study area (Figures 14; 15). The map symbol for this unit is Ybmg (Figure 16).

Figure 21. Picture of an amphibolite xenolith in a boulder of quartz syenite.

Diorite: This is a leucocratic, coarse-grained phaneritic rock. Weathered surfaces are light tan and black to a pinkish-orange. Fresh surfaces are approximately 50% white and 50% black. It contains approximately 40-50% hornblende, 20-25% plagioclase, 10-

15% feldspar, 10% quartz, and 10% biotite. Mineral crystals are subhedral to anhedral. It has an alignment of biotite and hornblende crystals in a possible flow fabric. The diorite can be identified as the gold unit on the map (Plate 1) in the central zone of the study area

(Figure 14). The map symbol for this unit is Ydi (Figure 16).

Gabbro: This is a melanocratic, phaneritic rock. Weathered and fresh surfaces are black. Crystals of 35-45% pyroxene and 55-65% plagioclase are up to 5 mm. The gabbro can be identified as the dark teal unit on the map (Plate 1) in the central zone of the study area (Figure 14). The map symbol for this unit is Xgb (Figure 16).

Extrusive Units

Andesite: This is a mesocratic, aphanitic rock. Weathered surfaces are red-brown to maroon-brown. Fresh surfaces are medium gray with spots of white and black. The matrix is 85% of the rock and dark gray. Small (< ~1mm) euhedral hornblende crystals make up about 5% of the rock. Subhedral plagioclase (up to 2 mm) crystals make up

~10% of the rock. The andesite can be identified as the dark red unit on the map (Plate 1) in the north zone of the study area (Figure 13). The map symbol for this unit is Cza

(Figure 16).

Andesite Porphyry: This is a melanocratic, aphanitic porphyritic rock. Weathered surfaces are red-brown with some light gray. Fresh surfaces are greenish-brown to black.

Matrix is ~80% of the rock; the other 20% is porphyritic, euhedral to subhedral gray to white plagioclase crystals up to 2 cm. The andesite porphyry can be identified as the peach unit on the map (Plate 1) in the central zone of the study area (Figure 14). The map symbol for this unit is Czap (Figure 16).

Green Lapilli Tuff: This rock has a light-gray weathered surface. Fresh surfaces are gray-brown to light gray-green. It contains 30% lapilli lithic fragments in a grayish groundmass. Lithic fragments are up to 2 cm in length. The green lapilli tuff can be identified as the sky blue unit on the map (Plate 1) in the north zone of the study area

(Figure 13). The map symbol for this unit is Czgt (Figure 16).

Purple Lapilli Tuff: This rock has a brown weathered surface. Fresh surfaces are purplish-brown. Blocks up to 5 cm and lapilli consist of andesite porphyry, rhyolite porphyry, and pumice in the groundmass. Small vesicles are flattened. The purple lapilli tuff can be identified as the purple unit on the map (Plate 1) in the north zone of the study area (Figure 13). The map symbol for this unit is Czpt (Figure 16).

Tan Lapilli Tuff: The weathered surface of this rock is a pale orangey-brown.

Fresh surfaces are whitish. The crystals and lapilli up to 5mm are biotite, feldspar, and pumice are in a gray groundmass. The tan lapilli tuff can be identified as the tan unit on the map (Plate 1) in the north zone of the study area (Figure 13). The map symbol for this unit is Cztt (Figure 16).

Lapilli-Tuff Breccia: The weathered surface of this rock is light pinkish to reddish-brown. Fresh surfaces are light pinkish to tan-gray. Brecciated blocks and lapilli contain small biotite and quartz crystals. The lapilli-tuff breccia can be identified as the

46 maroon unit on the map (Plate 1) in the north zone of the study area (Figure 13). The map symbol for this unit is Czmt (Figure 16).

CHAPTER 4

STRUCTURAL DATA

Ductile and brittle structures were identified in the field and their orientations were measured. Those features included mainly foliations, lineations, folds, and faults.

Figures 22-26 show locations where measurements were made.

Foliations, Lineations, and Folding

The Paleoproterozoic BPMS and Cretaceous Beartooth Quartzite are the only metamorphic rocks in the study area that have easily measurable foliations. Not surprisingly, foliation orientations in the BPMS and Beartooth quartzite are unrelated.

However, the individual units of the BPMS all share an overall northeast-striking, southwest-dipping foliation. Metamorphic lineations and folding were only found in the units of the BPMS. Foliations, lineations, and folds are described by unit in the following sections.

A creek in the southern zone of the study area was designated as “Shear Creek” due to numerous and varied exposures of highly sheared rocks of the BPMS (Figures 25,

26). These outcrops displayed several types of deformational and shear fabrics, including winged porphyroclasts, sigmoidal lenses, S-C fabrics, mineral lineations, mica fish, and multiple foliations (Figure 27; Figure 28). The winged porphyroclasts are larger quartz and feldspar σ-type clasts that have stair-stepping wings. The sigmoidal lenses consist of

Figure 22. Map of locations in the north zone of the study area. The red dots are locations were data was recorded. Locations found in this zone are: 23-37; 42-65.

Figure 23. Map of locations in the northern central zone of the study area. The red dots are locations where data was recorded. Locations in this portion of the map are: 2-6; 112-113; 180-212; B-77-78; B-186-195; B218-228.

Figure 24. Map of location in the southern central zone of the study area. The red dots are locations where data was recorded. Locations found in this zone are: 145-179; B-196.

Figure 25. Map of locations in the south zone of the study area. The black rectangle is around Shear Creek (Figure 20). The red dots are locations where data was recorded. The locations are so dense in the creek they are not shown in this figure. Locations found in this zone are: 1; 7-22; 67-91; 133-134; 137-144.

140. 140.

111; 114 111;

22; 9 22;

Map of locations along Shear Creek, which is in the southern portion of the study study the of portion southern the in is which Creek, Shear along locations of Map

Figure 26 Figure area. The red dots indicate locations where data was recorded. Locations found in this this found in Locations recorded. was data where locations indicate red Thedots area. 7 are: segment

Figure 27. Photographs of winged porphyroclasts and sigmoidal lenses. Top) Picture of winged porphyroclasts. Two are outlined in red showing sinistral movement. View to the southeast. Bottom) Picture of sigmoidal lenses indicating sinistral movement. View to the southeast.

C fabric marked by yellow red and yellow by marked fabric C

C fabric indicates sinistral movement. Brunton for scale Brunton movement. sinistral indicates fabric C

C fabric. Left) Unmarked photograph of the quartzofeldspathic gneiss gneiss quartzofeldspathic the of photograph Unmarked Left) fabric. C

Photograph of a S a of Photograph

ectively. The orientation of the S the of The orientation ectively.

Figure 28 Figure the S with photograph Same Right) the tosoutheast. looking resp lines,

55 a penetrative fabric that bounds bundles of rock and lean toward shear direction. It does not appear the bounding fabric of the lenses separate differences in the rocks mineralogy as the term suggests. The S-C fabric consists of the foliation and planes that form antithetic to shear direction. The acute angle formed by the foliation and C-fabric point in the direction of shear. The mineral lineations are aligned along foliation planes and indicate movement. The mica fish formed as sigmoidal mica pods tilted in shear direction. On exposed foliation planes, the mica fish reflect in the sunlight in what is known as a “fish flash.”

Quartzofeldspathic Gneiss

The quartzofeldspathic gneiss is the most prevalent unit of the BPMS and covers the majority of the southern zone of the study. Twenty-nine strike and dip measurements were taken on foliation within this unit. This foliation was designated as S1 as there is no evidence of foliations being formed before. If a foliation had formed in a previous event, it was annihilated by the event which formed this foliation.

These measurements were plotted on a stereonet (Figure 29) and displayed as orange arcs to correspond with the unit color on Plate 1. The poles were calculated and contoured using the 1% contouring method. The mean vector was calculated and displayed as a pole with 90% confidence. The average strike and dip of foliation (S1) in the quartzofeldspathic gneiss is 052o/38o (N52oE, 38oSE). This average foliation trend matches unit boundaries in the southern zone of the study area (Plate 1; Figure 16).

Figure 29. Stereonet of 29 S1 measurements in the quartzofeldspathic gneiss of the BPMS. The S1 measurements are displayed as orange arcs which corresponds with the unit color on Plate 1. The poles of the S1 planes are displayed as black dots. They have been contoured using the 1% method; each pole represents 3.4% of the total number of poles. The mean vector is denoted by the larger black dot. The circle around the mean vector pole denotes 90% confidence. The dip of the mean vector will change to 45o when the 3 northwest dipping arcs are removed from the calculation.

Two lineations on foliation planes in the quartzofeldspathic gneiss were measured at locations 9 and 19 (Figures 25; 26). They were designated as L1 as they are stretching

o o lineations on the S1 foliation plane. The measurements for the two lineations are 35 /204 and 21o/200o (35o, S24oW; 21o, S20oW), respectively. Since they plunge to the southwest, they plot in the southwest quadrant on a stereonet. Winged porphyroclasts and sigmoidal lenses were also identified at the same locations. When viewed from the northwest looking southeast, they indicate oblique sinistral-thrust shear occurred, with tops moving to the northeast.

Folds were small, wavelengths < 18 inches, and localized in the quartzofeldspathic gneiss (Figure 30). The strike and dip of the axial plane of ten folds in the gneiss were recorded at five locations (Figure 31; Table1). Plunge and trend measurements on fold hinges were also recorded (Table 1) for all but one heavily weathered fold. Of the 10 axial plane measurements, 9 strike east-northeast and one strikes southeast (Figure 32). The trends for the 9 fold hinge measurements vary with 6 trending southwest, 2 northeast, and 1 southeast (Table 1; Figure 32).

Figure 30. Picture of a small inclined antiform in the quartzofeldspathic gneiss at location 11. The fold hinge is marked by the red lines. The rock is in place and bounded by joints.

Figure 31. Topographic map displaying the five locations of the 10 folds documented in the quartzofeldspathic gneiss.

Axial Plane Fold Hinge Location Number Strike Dip Plunge Trend 9 115o 55oSW 29o 110o 11 085o 21oSE 15o 215o 79 040o 74oSE 42o 205o 79 064o 64oSE 55o 237o 132 079o 50oSE 26o 200o 144 025o 72oSE 25o 190o 144 020o 75oSE - - 144 015o 75oSE 12o 210o 154 019o 39oSE 31o 031o 154 045o 47oSE 40o 022o

Table 1. Table of axial plane (AP) and hinge line measurements of folds in the quartzofeldspathic gneiss.

Figure 32. Stereonet of fold measurements in the quartzofeldspathic gneiss of the BPMS. A) Stereonet of ten axial plane strike and dip measurements. All but one, strike to the east-northeast. B) Stereonet of nine fold hinge line plunge and trend measurements. The majority (6) of the fold hinges plunge toward the southwest.

Mica Schist

Two foliations were identified in the mica schist, S1 and S2. S1 is correlatable to the other units in outcrop and is the main foliation that is found throughout the BPMS

(Figure 33). S2 is a secondary foliation found locally in a few outcrops. Forty-nine S1 and six S2 foliations were measured and plotted on a stereonet (Figure 34). Poles were plotted

o o o and contoured using the 1% method for S1. The mean vector for S1 is 070 /39 (N70 E,

39oSE). The confidence is greater for the mean vector in the mica schist than the quartzofeldspathic gneiss due to less variability in S1 measurements. The mean vector for

o o o o S2 is 220 /53 (S40 W, 53 NW). Confidence in this measurement is low due to the range in orientation for S2 measurements.

In the mica schist mineral lineations on foliation planes, L1, were documented at multiple locations (Table 2). All measurements are similar and plot in the southwest

o o o quadrant on a stereonet (Figure 35) and have a mean vector for L1 is 23 /212 (23 ,

S32oW). Sigmoidal lenses and other shear sense indicators were identified at many locations (Table 2) where lineations were measured; with oblique sinistral-thrust shearing being the primary movement indicated when foliation is viewed to the southeast. A few shear indicators were found showing opposite shear sense (Table 2). Since most foliation dips to the southeast, this indicates shearing with tops to 032o (N32oE).

Figure 33. Photograph of the S1 and S2 foliation relationship in the mica schist. Location 17; pencil for scale. View to the south.

Figure 34. Stereonets of strike and dip of S1 and S2 in the mica schist of the BPMS. A) The S1 strike and dips are displayed as green arcs to correspond with the unit color on Plate 1. The poles of the S1 planes are displayed as black dots and have been contoured using the 1% method; each pole represents 2% of the total number of poles. The mean vector is denoted as a pole by the larger black circle. The large empty circle around the mean vector pole denotes 90% confidence. o o o o The mean strike and dip is 070 /39 (N70 E, 39 SE). B) The S2 strike and dips resulted in two bundles of green arcs. The mean vector of the measurements is marked by the larger black dot; however, the validity of this mean is questionable due to the low number of measurements and the scatter in orientations.

Location Number Plunge Trend Shear Sense 8 17o 181o Sinistral 12 36o 221o Sinistral 17 14o 210o Sinistral 17 15o 212o Sinistral 18 15o 220o Sinistral 18 20o 222o Sinistral 22 13o 242o Dextral and Sinistral 22 12o 235o Dextral and Sinistral 22 26o 231o Dextral and Sinistral 22 19o 214o Dextral and Sinistral 22 21o 205o Dextral and Sinistral 69 35o 190o Sinistral 69 57o 210o Sinistral 98 20o 195o Sinistral 101 14o 210o Sinistral 143 26o 184o N/A

Table 2. Table of 16 lineation measurements in the mica schist of the BPMS. All of the measurements plot in the southwest quadrant on a stereonet. Shear sense when viewed from west-northwest, mostly indicates sinistral shear, meaning tops moved to the northeast.

Figure 35. Stereonet of16 L1 measurements from the mica schist of the BPMS. The lineations are displayed as green dots on the stereonet to correspond with the unit color on Plate 1. The mean o o o o vector is 23 /212 (23 /S32 W). This vector along with shear sense indicates tops to the northeast.

Six folds were found in the mica schist (Table 3; Figure 36). The strike orientations of four of the axial planes trend northwest-southeast, one due north, and one northeast. Five of the six fold hinges plunge southeast and one southwest (Figure 36).

Three folds were found at location 115, a small, inches wide, tight antiform-synform pair, and a large, approximately 1.5 foot wide, open synform (Figure 37).

Axial Plane Fold Hinge Location Number Strike Dip Plunge Trend 12 131o 77o 43o 125o 17 059o 26o 15o 216o 18 329o 68o 46o 136o

115 000o 69o 38o 175o 115 340o 50o 46o 175o

115 115o 55o 45o 175o Table 3. Table of axial plane (AP) and hinge line measurements of folds in the mica schist. There were 3 folds at location 115, all with hinge lines that trend in the same direction (175o; S5oE).

Migmatite

A few outcrops of migmatite (Figure 38) are found as lenses in the southern zone of the study area. The migmatite is compositionally similar to the quartzofeldspathic gneiss but is not as prevalent (Plate 1). Roof pendants of migmatite are found in several locations in the Burro Mountain Granite (Plate 1) and may represent partially melted pieces of quartzofeldspathic gneiss. Nine S1 measurements (Table 4; Figure 39) were recorded in the migmatite; the average mean was 064o/42o (N64oE, 42oSE).

Figure 36. Stereonets of fold measurements in the mica schist of the BPMS. A) Stereonet of strike and dip of six axial planes. Four of the six axial planes trend northwest-southeast, 1 strikes due north and 1 strikes to the northeast. Green arcs are used to match the unit color on Plate 1. B) Stereonet of the 6 fold hinge line plunge and trend measurements. Five plunge to the southeast and 1 plunges southwest.

Figure 37. Photograph of the mica schist outcrop at location 115. The three folds that were documented are labeled A, B, and C. A) Small tight antiform with an axial plane and hinge line measurement of 340o/50o (N20oW, 50oNE) and 46o/175o (46o, S5oE), respectively. B) Small close synform with an axial plane and hinge line measurement of 000o/69o (N0oW, 69oNE) and 38o/175o (38o, S5oE), respectively. C) Large open synform with an axial plane and hinge line measurement of 115o/55o (S65oE, 55oNE) and 45o/175o (45o, S5oE), respectively.

Figure 38. Picture of the migmatite. S1 is shown by the red lines on the bottom left. This picture is from location 104. View to the northeast.

Location Number Strike Dip 104 066o 30oSE 105 040o 26oSE 106 050o 66oSE 108 052o 31oSE 108 052o 35oSE 130 049o 59oSE 140 070o 19oSE 174 112o 70oSW 174 074o 59oSE

Table 4. Table of 9 migmatite strike and dip orientation measurements with locations. Eight of the nine measurements strike northeast, which is similar to the trend of other units in the BPMS. One measurement at location 174 strikes southeastward with a much steeper dip than the other measurements.

Figure 39. Stereonet of strike and dip of 9 S1 measurements from the o o o o migmatite of the BPMS. The mean vector is 064 /42 (N64 E/42 SE). The mean vector is plotted as the large black pole. The surrounding circle is the 90% confidence area.

Four mineral lineations, L1, were recorded in the migmatite (Table 5). Of the four measurements, three plunge to the southwest and one plunges to the northeast. Shear sense indicators were found at location 104 showing both sinistral and dextral movement.

It is possible some of the indicators were rotated when the migmatite was formed. Most of the lineations plunge toward the southwest, which is consistent with most lineations in the study area.

Location Number Plunge Trend Shear Sense 104 22 187 Dextral and Sinistral 106 27 194 Sinistral; few dextral 130 10 050 Sinistral; few dextral 140 12 204 N/A

Table 5. Table of lineation orientation in the migmatite with location numbers and associated shear sense motion. Shear sense was recorded when viewed from the northwest.

One tight, plunging, inclined fold was found in the migmatite, at location 108.

The orientation of the axial plane for the fold is 045o/46o (N45oE/46oSE). The plunge and trend for the hinge line of the fold is 28o/190o (28o/S10oW).

Amphibolite

Amphibolite is the second most prevalent unit in the BPMS. It is found as large- and small-scale lenses throughout the other units of the BPMS (Figure 40). It is also occasionally found as roof pendants in the Burro Mountain Granite. A total of 84 S1

Figure 40. Photograph of amphibolite lenses in the quartzofeldspathic gneiss at location 9. The amphibolite lenses are outlined in red. Hammer on bottom left for scale. View to the south.

75 foliation measurements were recorded in the amphibolite. Tension gashes were also found on three outcrops. These measurements were recorded as LT lineations.

The S1 measurements were plotted on a stereonet as poles due to the large data

o o o o set. The mean strike and dip for this data is 059 /39 (N59 E/39 SE). Out of the 84 S1 measurements (Figure 41), 60 poles plot in the northeast quadrant (Figure 41) with a mean strike and dip of 051o/48o (N51oE/48oSE); this mean closely matches the orientation of contacts in the BPMS. The other 24 poles plot erratically in the other three quadrants of the stereonet (Figure 41). The mean vector for these measurements is

167o/28o (S13oE/28oSW). Tension gashes (Figure 42) were only found in the amphibolite and will be discussed in the faulting section.

Folding (Figure 43) was prevalent in the amphibolite and 21 folds were recorded in this unit (Figure 44). The mean orientation of axial planes is 085o/36o (N85oE, 36oSE).

The trends of the hinges of the folds are variable, but 13 out of 18 hingelines trend to the south (Figure 44). In some areas, the foliation was tightly folded into small parasitic chevron folds (Figure 45), while in other areas boudinage of felsic materials occurred

(Figure 45). This suggests the possibility of multiple strain events.

Folding in the amphibolite at location 118 displays large scale parasitic folding

(Figure 46). Three folds are present at this location, across approximately 30 feet of creek bank on the south side of Shear Creek. Only one limb is exposed above the stream on the eastern side of the outcrop. The geometry of this one limb suggests it may be a broad fold with vergence towards the east. The middle fold is an S fold (when viewed to the south)

SE). The 90% confidence ring ring confidence 90% The SE).

E, E, 48

riking foliations. These poles are are poles These foliations. riking

(N51

SW). There is no confidence ring on this this on ring confidence no is There SW). o

/48

E, 28 E,

northeast st northeast

(S13

/28

hows the 90% confidence circle around it. B) Stereonet of 60 S 60 of Stereonet B) it. around circle confidence the 90% hows

measurements in the amphibolite of the BPMS. A) Stereonet of all 84 84 all of A) Stereonet BPMS. the of amphibolite the in measurements

measurements for non measurements

SE).The mean vector pole s pole vector mean SE).The

E, E, 39

measurements. The poles are contoured using the 1% method. The mean vector for the amphibolite is is amphibolite the for vector mean The method. 1% the using contoured are The poles measurements.

Three stereonets displaying S displaying stereonets Three

(N59

/39

Figure 41 Figure for S poles 059 051 is poles these for vector mean The foliations. striking northeast 24 S of Stereonet C) thanin A. tighter is 167 is vector mean Their location. their in erratic more measurement.

Figure 42. Picture of tension gashes in the amphibolite at location 10. Field book for scale.

E, E,

(N90

/44

the south side of Shear Creek. The strike and dip dip and strike The Creek. Shear of side south the

SE). B) Tight inclined amphibolite drag fold. This fold This fold. drag amphibolite inclined Tight B) SE).

E, E, 31

(N70

/31

Photographs of drag folding in the amphibolite in Shear Creek, locations 121 and 121 locations Creek, in Shear amphibolite the in folding of drag Photographs

Figure 43 Figure Tight A) geometry. fold the mark lines Red movement. sinistral indicates folds of This pair 122. on is fold This fold. drag amphibolite inclined 070 is plane the axial of 090 is plane axial the of dip and The strike Creek. Shear of side north on the is 44

Figure 44. Stereonet of fold measurements in the amphibolite of the BPMS. A) Stereonet of 21 axial plane measurements. Blue arcs are used to match the unit color on Plate 1. B) Stereonet of 21 fold hinge line plunge and trend measurements. No fold hinge in the amphibolite plunges to the northwest.

is seen in the the in seen is

This

It is a large outcrop scale fold at location 122. The The 122. fold location at scale outcrop large a It is

top) limb of the drag fold. drag the of limb top)

Two tight folds at locations 147 and 122, respectively. Left). The foliation forms small parasitic parasitic small forms foliation The Left). respectively. 122, and 147 locations at folds tight Two

chevron folds. These folds are more heavily weathered than folds without this fabric this without folds than weathered heavily more are folds These folds. chevron line. red the by outlined is geometry crenulation The 147. fold location at scale outcrop large a hingeof The position. original from its away pulled was as fold it the drag of limb the on formed Boudins Right) ( southern the is shown limb boudins. the of necks the mark lines red diagonal 45 Figure

synform pairs. The folds progressively close their interlimb interlimb their close folds progressively The pairs. synform

ometry of the two paired folds pictured would be parasitic to the the to be parasitic would pictured folds paired two the of ometry

Three folds at location 118 that progressively become tighter to the west. The broad fold limb limb fold broad The west. the to become tighter progressively that 118 location folds at Three

n A is ten feet left of the left margin of B. Fold geometries are outlined by red lines. A) Upper limb limb Upper A) red lines. by outlined are geometries Fold B. of margin left the of left feet ten is A n

pictured pictured i antiform Two fold. B) amphibolite open of an geThe isoclinal. is fold third the until angle limbs. the of upper geometry the mimics limb buried the if in A, fold 46 Figure

82 and contains an antiform-synform pair, approximately 15 feet to the west. This set of folds are close folds with the same eastern vergence. The final fold at this location is approximately 15 west and is an inclined, plunging isoclinal S-fold (when viewed to the south). The second and third folds, being S-folds, at this outcrop predict the antiformal closure in the direction of the first, broad fold (Figure 47).

BPMS

In summary, the mean trend for strike and dip of foliation from the four units of the BPMS is 061o/39o (N61oE/39oSE), which matches the trend of unit contacts in the southern zone of the geologic map (Plate 1; Figure 15) Foliation (S1) in the units of the

BPMS is remarkably consistent (Figure 48). The mean trend for plunge and trend of lineations from the four units of the BPMS is 24o/211o (24o, S31oW). Shear was determined to be top-to-the-northeast. This indicates sinistral oblique-thrust shear occurred to 031o (N31oE) (Figure 49).

Beartooth Quartzite

The Beartooth Quartzite caps a northwest-trending ridge that stretches across the study area (Figure 13). The foliation in this unit is equivalent to the original bedding planes prior to contact metamorphism, which was caused by intrusion of andesite sills above and below the quartzite (Plate 1; Figure 13). The mean vector of 13 foliation measurements in the quartzite is 305o/26o (N55oW/26oNE; Figure 50). This northwest- striking foliation is essentially perpendicular to the trend of foliation in the BPMS.

Figure 47. Sketch of S- and Z- parasitic folds. These folds can be used to identify the direction of an antiformal closure and which limb they are located. S-folds are found on the right limb of an antiform. Z- folds are found on the left limb of an antiform.

Figure 48. Stereonet of the mean strike and dip of foliation, S1, in the 4 units of the BPMS. Each arc represents the mean strike and dip of foliation in one of the four units of the BPMS. The arcs are colored coded for the unit they represent; orange: quartzofeldspathic gneiss, green: mica schist, black: migmatite, blue: amphibolite. The mean vector of the 4 mean vectors of the BPMS is 061o/39o (N61oE/39oSE). This shows that foliation is very consistent in the BPMS.

Figure 49. South zone of the study area with the mean trend of foliation and lineations overlaid. The red arrow indicates the direction of shear that occurred within the BPMS.

Figure 50. Stereonet of strike and dip of foliation measurements in the Beartooth Quartzite. The mean vector is 305o/26o (N55oW/26oNE). Note that the orientation of foliation in the Beartooth Quartzite is very different than S1 in the BPMS.

Faulting

There is abundant evidence of both ductile deformation and brittle faulting in the study area. Ductile deformation, presumably at depths at or below the ductile/brittle transition zone (approximately 10-15 km), resulted in development of a distinctive shearing fabric in rocks of the Bullard Peak metamorphic series. This series is exposed in the southern part of the study area (Figure 15) where the rocks have many shear indicators. In addition to the ductile structures, the area also has many brittle faults that formed after significant exhumation of the region.

Brittle faulting was recorded in all zones of the study area. A total of 114 fault measurements were recorded. Fault plane orientations varied widely on both small and large faults (Figure 51). The width of faults and fault zones also varied widely: from < .5 inch gouge zones to 100+ feet wide breccia zones (Figure 52). A few faults had slickenlines with chattermarks, which are useful for determining displacement directions.

Some faults had just slickenlines, but most had no indicators of movement. Many faults lacked dip information because the fault was visible only as a trace or was exposed in a prospect pit that was too deep to safely measure the dip.

Faults are subdivided by the type of movement that occurred, including sinistral- thrust, sinistral-normal, dextral-thrust, dextral-normal, sinistral, and dextral. Of 27 faults;

11 were found to have sinistral thrust oblique-slip movement, 3 dextral thrust oblique- slip, 3 sinistral normal oblique-slip, 1 dextral normal oblique-slip, 3 sinistral strike-slip,

Figure 51. Stereonet of strike and dip of all 114 fault planes. The mean vector is 054o/27o (N54oE/27oSE), but the orientation of fault planes is highly variable.

Figure 52. Photographs of pseudotachylite and breccia. A) Anastomosing pseudotachylite veins in a fault zone a few centimeters wide. Pencil for scale. B) Fault gouge zone approximately 1 foot wide with brecciated margins. Rock hammer for scale.

90 and 6 dextral strike-slip (Figure 53). On many fault planes where movement was identifiable, slickenlines and chattermarks were faint.

Tension gashes were found on 3 outcrops of amphibolite schist adjacent to fault planes. At two locations, 117 and 128, the tension gashes indicated sinistral movement.

At location 10, the tension gashes suggest dextral movement.

The faults are divided by strike orientation to determine if there is a dominant orientation in the area. The north-south and east-west orientations are 20o slices, 10o either direction from 0o and 90o, respectively. It was discovered that 48 faults were oriented northeast-southwest, 39 were northwest-southeast, 22 were east-west, and 5 were north-south (Figure 54). Two dominant orientations were found, northwest- southeast and northeast-southwest. These two trends account for 76% of all faults recorded in the study.

In some parts of the study area, especially in Shear Creek, multiple fault planes in close proximity to each other were found with opposing orientations and movement.

Multiple hypotheses were considered to explain the observed data including: fault wobble

(faults that change dip orientation); wrench faulting; a horse or rider fault system (riders and horses are fault-bound blocks in extensional and compressional environments, respectively). None of the proposed ideas were able to explain the orientation relationship and type of movement.

This relationship was most noticeable at locations 108 and 110 (Figures 25; 26), where the fault trends were similar, but dips and movement were opposite. The fault at

The arcs are color coded for lateral for lateral coded color are arcs The

slip faults where only lateral movement was detected was movement lateral only faults where slip

Stereonets of strike and dips of fault fault planes. of dips and strike of Stereonets

Figure 53 Figure 4 of Stereonet B) faults. thrust oblique 14 of A) Stereonet dextral. = red = sinistral, blue movement; strike 9 of Stereonet C) faults. normal oblique

Figure 54. Stereonets of divided fault planes. A) North-South trending faults make up 4% of the total faults. B) East-West trending faults make up 19% of the total faults. C) Northwest-Southeast trending faults make up 34% of the total faults. D) Northeast-Southwest trending faults make up 42% of the total faults.

93 location 108 had an orientation of 050o/66o (N50oE, 66oSE) and had dextral oblique movement. The fault at location 110 had an orientation of 265o/72o (S85oW, 72oNW) and had sinistral thrust movement. An exposed fault plane in Shear Creek at stop 110 helped resolve this issue. At stop 110, the creek bed drops approximately three feet and exposes a small positive flower structure adjacent to this fault plane (Figure 55; Figure 56). The fault planes in the small flower structure displayed similar attributes, similar trend and opposite dipping planes, as the fault planes at locations 108 and 110. Determining movement on the small planes proved difficult due to a lack of slickenlines and chattermarks.

If one east-west oriented fault bounded block is considered (Figure 57), the movement relationship can be resolved. If the east end of the block drops and moves west, then the west end must rise and move west in response. If the faults dip toward each other, a dextral oblique normal fault formed in the east and sinistral oblique thrust- oblique fault formed in the west. Cross section line B – B’ crosses a larger positive flower structure (Figure 58; Figure 59). The faults exhibit the palm tree geometry that is characteristic of positive flower structures. The topography also exhibits characteristics of a positive flower; the faults are found in streams and the surrounding areas rapidly rise in elevation.

SE). Red box indicates indicates box Red SE).

, 89 ,

(

/89

110. A) Two intersecting fault planes in Shear in Shear fault planes intersecting Two A) 110.

NW); Fault 2: 073 2: Fault NW);

e. View is to the towest. is View e.

W, 72

(S85

/72

Photographs of faulting taken at location taken at faulting of Photographs

larger fault planes pictured in A. All of the fault planes taper to one plane at the bottom of the the of bottom the at plane toone taper planes fault the of All A. in pictured planes fault larger Creek.Fault 1: 265 1: Creek.Fault the of juncture the at flower structure positive Small B) scale. for book Field B. Picture of location for scal book Field photograph. 55 Figure

re of the larger fault planes at location 110. All of the fault planes taper to one one to taper planes fault the of All 110. at location planes fault larger the of re

Photographs of faulting taken at location 117 and 110, respectively. A) Fault with multiple multiple with A) Fault respectively. 110, and 117 location taken at faulting of Photographs

structure at the junctu the at structure Figure 56 Figure flower positive B) Small scale. for book Field structure. flower a to similar symmetries with planes west. the tois View for scale. book Field photograph. the of the at bottom plane

block moves up and right, right, and up moves block

xpression of the faults. The blue lines mark the faults in the faults in the mark lines blue The faults. the of xpression

Block diagram of a fault bounded block. The green lines mark mark lines green The block. fault bounded a of diagram Block

formed. In response, the west side of the of side west the response, In formed. Figure 57 Figure e the surface the east If block. bounded fault the of top the are red Thelines subsurface. fault is normal oblique dextral a right, and down moves block the of side fault. thrust oblique sinistral a forming

Figure 58. Location map for cross section B-B’ in the central zone of the study. The section line crosses five faults and three lithologies; Burro Mountain Granite: brown; Monzo-granite: pink; Gabbro: green.

B’. The geometry of the faults and the raised topography topography raised the faults and the of geometry The B’.

Sketch of cross section line B line section cross of Sketch

Figure 59 Figure present. being flower structure positive of a the probability faults the indicates between

In the north and central zones of the study, large brecciated zones are found.

These breccias do not exhibit indicators of what type of movement occurred. Previous workers in the region were also unsuccessful in identifying movement of the faults. They are found in the stream banks and disappear into the large streams in the north and central zones. The topography is most likely controlled by these faults.

100

CHAPTER 5

DISCUSSION

Multiple types of structural features and fabrics are found in the study area. These structural elements can be attributed to multiple events that affected the region through its history. This chapter interprets the deformational history of the observed structures.

Foliation Development

o o o o The strike of foliation (S1) is (061 /39 ; N61 E, 39 SE), which is consistent with the northeast-southwest trend of the Mazatzal Province. The foliation (S1) in the BPMS was probably formed during regional metamorphism caused by accretion of the juvenile arc terranes of the Mazatzal Province. The average orientation of L1 measurements in the

BPMS plunges southwest (24o/212o; 24o, S32oW). These mineral lineations indicate shearing, presumably by movement of foliation planes. Since the average strike and dip of foliation is 061o/39o (N61oE, 39oSE), and the average plunge and trend of lineations is

24o/212o (24o, S32oW), then the lineations indicate oblique-slip movement of the foliation planes and of rocks beyond the zone of shearing (Figure 60). To determine shear sense it was necessary to look at indicators parallel to the lineation and perpendicular to the foliation. Shear sense indicators were numerous in the BPMS, particularly in the intermittent stream named Shear Creek, and occurred as winged porphyroclasts, mica

101

Figure 60. Box diagram of oriented foliation planes and lineations.

The red arrows above the lineations show the direction of movement along foliation planes. They indicate oblique sinistral thrust movement on the foliation planes.

102 fish, and most abundantly, as sigmoidal lenses (Figures 27-28). When viewed to the southeast, most shear indicators showed sinistral shear with tops to the northeast (though a few indicated dextral shear). If the rocks are still in the same general orientation as when they developed this structural fabric, then this indicates that as the Mazatzal terrane accreted, tops moved northeast (032o) resulting in thrust faulting with a component of sinistral offset.

The oblique-slip nature may indicate a two-stage development history for this fabric. Stage 1 may have been northwest-directed compression that created a northeast- striking foliation. Northwest vergence of possible folds would have created southeast dipping axial-planar cleavage during regional metamorphism. Stage two may have been a shift to northeast-directed transpression with creation of lineations on foliation planes and shear sense indicators that formed in a sinistral thrust oblique-slip shear zone or region of shearing (Figure 61).

The S2 in the mica schist of the BPMS may be associated with the intrusion of the granitoids of the Granite and Rhyolite Province. Whitmeyer and Karlstrom (2007) noted deformation occurred to thermally-softened country rock when granitoids were emplaced.

Amato et al. (2011) proposed the formation of a gneiss dome at 1.4 Ga due to the emplacement of the Burro Mountain Granite. A gneiss dome is normally formed in an extensional environment where the oldest rock is found in the core and surrounded by younger metasedimentary rocks. Also, a large igneous body would not create a well- defined foliation in the country rock, but could create a new fabric. The emplacement of

103

Figure 61. Diagram showing how accretion direction may have changed. A) The northeast trend of accreted volcanic arcs of the Mazatzal Province occurs due to northwest movement. B) Clockwise rotation of the overriding plate may have developed in the subduction zone. A bend in the accreting arcs could have produced the northeast shear seen in the study area.

104 the Burro Mountain Granite and associated intrusions did however metamorphose the

BPMS to the amphibolite facies based on zircons in amphibolite and monazites in the metapelite (Amato et al., 2011). The grade of metamorphism prior to 1.45 Ga is unknown

(Amato et al., 2011). This study interprets the BPMS as a pendant in the intruding granitoids as shown in cross section line A-A’ (Figure 62; Figure 63).

Fold Development

There are two probable scenarios for development of folding in the BPMS: 1) all folding occurred during one event, or 2) there were multiple stages of folding. Different events could have caused the folding to occur. Northwest-verging folds may have formed during accretion of the Mazatzal terrane. Another event that may have caused folding was intrusion of granitoids of the Granite and Rhyolite Province. The orientations of the folds formed would vary depending on the stress produced from the intruding batholith.

Deformation caused by intrusions and far-field stresses have been documented on country rock (Nyman et al., 1994; Karlstrom and Humphreys, 1998; Whitmeyer and

Karlstrom, 2007). The folds would have subsequently been reoriented through faulting.

Folding in the BPMS may have occurred in multiple stages of deformation. The first folding event may have occurred when the granitoids of the Granite and Rhyolite

Province were emplaced. This may also have produced a second foliation in the mica schist, S2. In the amphibolite, parasitic folding occurred in fold hinges. These folds are recognized because their axial planes trend northwest-southeast on the stereonet.

105

Figure 62. Location map for cross section A-A’ in the southern zone of the study. The section line crosses four faults and five lithologies; Burro Mountain Granite: brown; Quartz syenite: red; Quartzofeldspthic gneiss: orange; Amphibolite schist: blue; Mica schist: green.

106

A’. The units of the BPMS are interpreted to be roof pendants pendants roof tobe are interpreted BPMS the of units The A’.

Sketch of cross section line A line section cross of Sketch

the granitoids of the Granite and Rhyolite Province. The amphibolite, blue, and mica schist, green, green, schist, mica and blue, amphibolite, The Province. Rhyolite and Granite the of granitoids the

Figure 63 Figure in orange. gneiss, quartzofeldspathic the in are lenses

107

The second folding event is related to fault drag. This event is identified by the relationship of amphibolite folds and fault planes. This is evident in Shear Creek at location 121 and 122 where paired fold hinges were found (Figure 64). The displacement between the drag fold hinges is approximately 100 feet with sinistral movement. If the folding developed during the accretion of the Mazatzal terrane, one would expect more northwest verging folds and possibly a large regional fold.

Contact Metamorphism of the Beartooth Quartzite

The Beartooth Quartzite was deposited on a transitional margin, originally onlapping the Paleozoic granites (Riess, 1990). The foliations in the Beartooth Quartzite are probably original bedding planes that were metamorphosed by contact with an andesite sill that intruded above and below it. The andesite is most likely related to the andesites that erupted as part of the Mogollon-Datil volcanic field approximately 40 miles north of the study area.

Fault Development

Brittle faults in the area display mainly oblique-slip and strike-slip movement.

The majority however were either only fault traces or breccia zones where no movement could be determined.

The faulting found in the study area was most likely caused by multiple events, including to the formation of the Ancestral Rocky Mountains, Laramide orogeny, Basin

108

Figure 64. Sketch and photographs of drag folding in the amphibolite in Shear Creek. This pair of folds indicates sinistral movement on a probable fault that Shear Creek uses as a conduit. Approximate displacement is 100 feet.

109 and Range and Rio Grande Rift extension, and Cenozoic igneous activity. Most of the older faults may have been reactivated during Basin and Range extension. Some possibly started as joints and then those planes were used to disperse the stress placed on the Burro

Mountains from compression, extension and shearing. The dominant fault orientations in the study are northwest-southeast and northeast-southwest (Figure 65). These orientations are the same as the trends of the major regional fabrics. The northeast-southwest trend was created by the accretion of juvenile volcanic arcs of the Mazatzal terrane. The northwest-southeast trend formed when the Ancestral Rocky Mountains were uplifted

(Figure 65).

The orientations of the fault planes in the study area and their relationship to other major faults in the area suggest a complex regional fault system. The Mangus Fault to the north of the Burro Mountains is a northwest-southeast trending normal fault with the downthrown side to the southwest (Gillerman, 1970). To the south, the Taylor and

Malone Faults are northwest-southeast trending, northeast dipping, thrust and normal faults, respectively (Gillerman, 1970). Negative flower structures formed by transtensional stresses have been noted to create basins in southwestern New Mexico

(Hodgson, 1991). Two small flower structures were identified in Shear Creek. One was identified as a positive flower structure. The other is more difficult to interpret due to weathering on the creek bank; however, the bend of the outermost fault with tension gashes used as movement indicators, suggests that it is also a positive flower structure.

This evidence, along with the orientations of the other faults in the study, specifically

110

Figure 65. Stereonets of the dominant fault orientations in the study area. A) Stereonet displaying 39 northwest-southeast trending fault planes. The mean orientation is 110o (N70oW). This orientation formed with the uplift of the ARM. B) Stereonet displaying 48 northeast-southwest trending fault planes. The mean orientation is 044o (N44oE).

111 cross section B-B’ (Figures 58; 59), suggests that there may be a regional positive flower structure in the area that generally trends east-west.

The pattern of a flower structure allows for individual, fault bounded slivers of rock to have multiple orientations. The discovery of a small positive-flower structure adjacent to a fault that has opposite dip- and strike-slip movement but trends in the same general direction as a fault 100 feet downstream is a strong indicator of transpressional kinematics in the region.

This structure could have formed during uplift caused by the Laramide orogeny or in response to the external forces of Basin and Range extension acting on the rigid Burro

Uplift. Basin and Range stress could have torqued the uplift, reactivating the internal faults. This could have created a positive flower structure within the Burro Uplift, in spite of an overall, regional extensional stress.

Revised Geologic History

Context of geologic history is needed when examining the field observations to develop plausible hypotheses that work within the known history. The following discussion outlines the regional geologic history from deposition of Mazatzal sediments to present and is summarized in Table 6.

The rocks of the BPMS were deposited as sediments weathered from arc-related volcanic deposits in an accretionary basin from 1.7 – 1.65 Ga (Whitmeyer and Karlstrom,

112

Age Event Units Deformation Metamorphism (Ma) Basin and Inversion 37-2 Range; Rio Tuffs Tectonics; Grand Rift Extension 50-37 Erosion Passive Inversion Beartooth Tectonics; Laramide 70-50 Quartzite; Andesite Basement Cored Contact orogeny Sill Intrusion Uplift; Exposed basement 105- Deposition and Passive 70 Erosion Inversion 154- Bisbee Basin Tectonics; Normal 105 Faulting 307- Deposition and Passive 154 Erosion Formation of Northwest trending 315- Ancestral faults; Basement 307 Rocky Cored Uplift Mountains 1400- Deposition and Passive 315 Erosion Granite & Burro Mountain Secondary Contact; 1450- Rhyolite Granite; Quartz Foliation; First Amphibolite 1400 Province Syenite Folding Event Grade Bullard Peak 1650- Mazatzal Metamorphic Foliation; Regional; 1600 Accretion Series; Gabbro; Lineations Unknown Grade Monzo-Granite

Table 6. Table of the regional geologic history of southwestern New Mexico from Paleoproterozoic to present.

113

2007; Amato et al., 2008). As sinistral-oblique accretion progressed to the northeast, the rocks were regionally metamorphosed and foliation and shear fabrics developed. Based on field observations, the amphibolite may have been intruded as a mafic dike and sill complex while accretion was ongoing. This complex could be associated with an undeformed gabbro emplaced nearby at 1.633 Ga (Amato et al, 2008). Accretion of the

Mazatzal terrane formed a northeast-southwest regional trend.

After accretion concluded, a period of quiescence ensued until approximately 1.45

Ga when the Granite and Rhyolite Province terranes were accreted to the southeast and granitoids were emplaced in the region. During this event, folding may have occurred in the region. Folding may have been caused by intrusion of the granitoids adding heat to the country rock and folding being a result of far-field stresses induced by accretion to the southeast (Nyman et al., 1994; Karlstrom and Humphreys, 1998; Whitmeyer and

Karlstrom, 2007).

The region was not tectonically active again until the Pennsylvanian when the

Ancestral Rocky Mountains (ARM) formed in western Laurentia. The uplifts of the ARM formed northwest trending faults that are normal to the northeast trend of the Mazatzal

Province. This was the first event to uplift the basement in the region.

The Jurassic formation of the Bisbee Basin in eastern Arizona, southwest of the

Burro Uplift, most likely reactivated ARM bounding faults to drop the basin (Lawton,

2000; Lawton, 2004). These faults were then reactivated again during Laramide

114 compression as the region was uplifted (Lawton, 2004). During uplift positive flower structures may have formed.

In the late Cretaceous, the Beartooth Quarzite was deposited on a transitional margin onlapping the Burro Mountain Granite (Riess, 1990). It was subsequently metamorphosed by contact metamorphism through the emplacement of an andesite sill

(Plate 1; Figure 66; Figure 67).

During Basin and Range extension, the northwest trend of the rigid Burro Uplift may have been torqued by the east-west directed tensional stress acting on the uplift.

These stresses would have been dispersed through the uplift by movement on existing faults and by formation of new faults. This complex system of faults may have then formed a large positive flower structure. Possible evidence for this was found in Shear

Creek in the form of small scale positive flower structures and by map scale fault orientations (Figure 53; Figure 54).

Volcanism in the region began at the end of the Eocene with felsic calderas, while mafic and intermediate volcanism didn’t begin until the Early Oligocene (Mack, 2004).

By the Late Oligocene, all volcanism had ended (Mack, 2004).

115

Figure 66. Location map for cross section C-C’ in the northern zone of the study. The section line crosses six lithologies (Plate 1; Figure 17).

116

unger tuffs to be tobe tuffs unger

C’. The Beartooth Quartzite was deposited on the Burro Burro the on deposited was Quartzite Beartooth The C’.

cross section line C line section cross

Sketch of of Sketch

Figure 67 Figure of Erosion the quartzite. below and above sill large a as intruded was Andesite Granite and Mountain yo the and exposed be to the andesite allowed Quartzite the Beartooth the units surface. erosional the on deposited

117

CHAPTER 6

CONCLUSION

Field mapping was conducted in the northwest Wind Mountain quadrangle in southwest New Mexico, in an area of varying rock types and deformational styles, located approximately 15 miles southwest of Silver City. The study identified both ductile and brittle deformational features. The ductile structures include multiple foliations, sigmoidal lenses, mineral lineations, mica–fish and winged porphyroclasts.

Brittle structures include tension gashes, fault gouge, fault breccia, mineralized fault planes, and possible flower structures. The brittle structures must have formed much later, after significant erosion had exhumed the ductilely deformed rocks.

At least six events contributed to the deformation seen in the study area. They are:

1) 1.65-1.6 Ga Mazatzal accretion likely formed northeast trending S1 foliation, L1 lineation, and shearing that resulted in left-lateral, thrust oblique-slip motion with top-to- the-northeast; 2) 1.45-1.4 Ga Granite and Rhyolite Province accretion and emplacement of granitoids may have formed an S2 foliation and locally folded the Bullard Peak metamorphic series; 3) 315-307 Ma Ancestral Rocky Mountains uplift produced northwest-trending faults normal to the older northeast structural trend; 4) 154-105 Ma nearby Bisbee Basin formed by inversion tectonics (reactivated faults), possibly reactivated the northwest-trending faults into normal faults; 5) 70-50 Ma Laramide

118 orogeny compression reactivated the northwest-trending normal faults possibly turning them into reverse faults; 6) 37-2 Ma Basin and Range and Rio Grande Rift extension created major normal faults in the area, and/or reactivated older thrust faults as normal faults, and created regional horsts and grabens. Extension may have torqued the Burro

Uplift to create a positive flower structure.

Questions remain on timing and extent of how some of these and other events may have affected the region.

119

Timeline of Deformation

Age (Ma) Event Deformation Metamorphism

37-2 Basin and Range; Rio Grande Rift Inversion Extension Tectonics; Formation of Regional Positive Flower Structure

70-50 Laramide orogeny Inversion Tectonics; Reactivation of faults

154-105 Bisbee Basin Southwestward dipping normal faults; Burro Uplift is a rift shoulder

315-307 Ancestral Rocky Mountains Formation of Formation northwest trending bounding faults

1450-1400 Granite & Rhyolite Emplacement Formation of S2 in Contact; Amphibolite and Accretion the BPMS; First Facies folding event

1650-1600 Mazatzal Accretion Formation of S1, L1; Regional; unknown and shear sense grade indicators in the BPMS; created NE structural trends

120

Proposed Future Research

More research is needed in the region to further delineate the history of ductile and brittle deformation and the possibility of mineral enrichment.

The region would benefit from further studies in geochronology, geochemistry, structural mapping. A structural mapping study should focus on the Bullard Peak metamorphic series. The objectives would be to delineate the extent of the shear and to determine a solid answer for the formation of migmatite in the area. This project would help support or refute the gneiss dome hypothesis proposed by Amato et al. (2011).

Another mapping project could focus on regional faulting. Determining the extent of the faulting and the size of the possible regional flower structures in the Burro Uplift could help with the understanding of the kinematics that caused the faults to form.

A project could be developed to examine the microstructures of the Bullard Peak metamorphic series. A petrographic analysis of oriented samples may find fabrics unidentifiable in outcrop due to weathering processes. This project could also identify protoliths using XRF analysis.

A geochronological study could be developed to determine the ages of the monzogranite to determine when emplacement occurred. This would help ascertain if the fabric seen in the rock is a flow fabric or if the rock would qualify as an L- or S-tectonite.

121

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Appendices

Appendix A – Planar Data

Appendix A Key

Unit: Xqfg – Quartzofeldspathic Gneiss Xms – Mica Schist Xmg – Migmatite Xas – Amphibolite Kbq – Beartooth Quartzite VC – Volcanic Clastics Czan – Andesite

MeXasurement Type: So – Original Bedding S1 – First Foliation (Primary) S2 – Secondary Foliation AP – Axial Plane of a Fold

Location Unit Measurement Strike Dip Notes Type

7 Xqfg S1 056 30 Xqfg S1 064 31 Xqfg S1 075 60 Xas S1 027 54 Xas S1 009 49 8 Xms S1 061 23 9 Xqfg S1 081 46 Xqfg S1 067 35 Xqfg S1 070 46 Xqfg S1 061 32 Xas S1 063 29 Xas S1 048 17 Xas S1 052 25 Xas S1 064 13 Xqfg Fold AP 115 55 10 Xas S1 051 30

129

11 Xqfg Fold AP 085 21

12 Xms S1 086 50 Xms Fold AP 131 77

13 Xms S1 087 55 15 Xas S1 154 70 Xas S1 310 59 15 Xas S1 175 49 Xas S1 128 53 Xas S1 128 56 Xas S1 135 50 16 Xas S1 053 25 Xas S1 078 20 17 Xms S1 088 17 Xms S1 083 16 Xms S2 208 72 Xms S2 192 62 Xas S1 078 20 Xms Fold AP 059 26

18 Xms S1 111 19 Xms S1 350 56 Left limb of Fold Xms S1 054 49 Xms S1 141 19 Right limb of Fold Xms Fold AP 329 68

19 Xqfg S1 025 42 Xas S1 082 55 20 Fault Plane 214 82 21 Fault Plane 042 90 Fault Plane 044 57

22 Xms S1 069 60 Xms S1 065 64 Xms S1 115 30 Xms S1 110 27 Xms S1 061 36 Xms S1 054 38 Xms S1 105 30 Xms S1 086 28 Xas S1 071 65 Xas S1 061 56 Xas Fold AP 200 83 Fault Plane 321 90 Fault Plane 323 89 Fault Plane 245 36

130

23 Vc S0 346 20 24 Vc S0 342 34 Vc S0 304 42 Vc S0 292 24 Vc S0 331 40 Vc S0 306 42 25 Vc S0 205 73 26 Vc S0 319 26 Vc S0 306 28 Vc S0 306 30 Vc S0 297 34 27 Vc S0 316 17 28 Vc S0 317 11 Vc S0 308 20 Vc S0 309 40 Vc S0 304 24 29 Vc S0 310 25 Vc S0 295 29 Vc S0 324 28 Vc S0 284 29 32 Vc S0 310 54 Vc S0 305 43 35 Vc S0 313 46 42 Vc S0 205 49 43 Czan S0 288 29 Possible Czanesite Sill or sheet flow plane

44 Vc S0 281 34 45 Czan S0 334 10 Possible Czanesite Sill or sheet flow plane

46 Czan S0 309 27 Possible Czanesite Sill or sheet flow plane

47 Czan S0 316 25 Possible Czanesite Sill or sheet flow plane

50 Czan S0 310 41 Possible Czanesite Sill or sheet flow plane Czan S0 295 54 Possible Czanesite Sill or sheet flow plane

Czan S0 248 38 Possible Czanesite Sill or sheet flow plane

56 Czan S0 325 41 Possible Czanesite Sill or sheet flow plane

58 Kbq S1 306 26

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Kbq S1 305 27 Kbq S1 290 19 59 Kbq S1 273 8 Kbq S1 282 6 60 Kbq S1 296 45 Kbq S1 296 28 61 Kbq S1 309 28 62 Kbq S1 305 40 63 Kbq S1 300 32 64 Kbq S1 298 19 Kbq S1 305 20 66 Kbq S1 338 46 67 Xqfg S1 025 33 Xas S1 055 64 Xas S1 047 75 Xas S1 055 44 Xas S1 042 69 68 Xas S1 135 55 Xas S1 102 50 Xas S1 072 59 69 Xms S1 060 49 Xms S1 060 65 Xms S1 068 49 Xas S1 076 39 Xas S1 084 37 Xas Fold AP 076 44 69 Xas Fold AP 065 50

70 Xas S1 092 27 Xas S1 065 43 Xas S1 035 40 71 Xms S1 067 31 Xms S1 061 20 Xms S1 070 49 Xms S2 312 62 72 Xms S1 100 30 Xms S1 055 35 73 Xms S1 052 61 74 Xas S1 122 66 Fold limb Xas S1 084 35 Fold limb Xas S1 084 35 Fold limb Xas S1 178 52 Fold limb Xas Fold AP 105 40

132

Xas Fold AP 122 58

75 Xms S1 080 16 76 Xas S1 198 76 77 Xas S1 021 84 Fold limb Xas S1 150 67 Fold limb Xas Fold AP 130 60

78 Xas S1 026 50 Xas S1 194 63 Xas S1 210 74 Xas S1 238 88 79 Xqfg S1 037 51 Xqfg Fold AP 040 74 Xqfg Fold AP 064 64

80 Xqfg S1 045 58 Xqfg S1 059 74 81 Xas S1 060 70 Xas S1 065 65 82 Xqfg S1 087 66 83 Xms S1 075 63 Xms S1 076 81 84 Xms S1 073 48 Xms S1 051 61 85 Xqfg S1 039 47 Xqfg S1 065 50 Xqfg S1 067 56 86 Xas S1 075 60 87 Xas S1 224 60 Possible wobbling fault plane intersecting

Xas S1 045 65 Possible wobbling fault plane intersecting

88 Xms S1 058 58 89 Xms S1 065 40 Xms S2 111 81 Xms S1 060 23 89 Xms S1 047 25 Xas S1 071 26 Xas S1 065 19 90 Xms S1 065 28 91 Fault Plane 219 84 Possible sinistral movement Fault Plane 110 64 Fault Plane 321 80

92 Xms S1 015 59

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Xas S1 050 21 93 Xas S1 040 74 Fault Plane 213 90 Fault Plane 342 82 Fault Plane 344 78 Fault Plane 002 72 Fault Plane 022 56 94 Fault Plane 095 25 Wall of amphibolite on the north wall of shear creek Fault Plane 342 90 Fault Plane 063 82

95 Xas S1 080 12 Fault Plane 015 49 96 Fault Plane 102 67 Fault Breccia Plane Fault Plane 275 78 Fault Breccia Plane Fault Plane 277 45 Fault Plane 280 88 Fault Plane 270 63 Fault Plane 245 80

97 Xas S1 045 54 98 Xms S1 054 39 Xms S1 049 49 99 Xms S1 080 39 100 Xas S1 036 39 101 Xms S1 063 24 102 Xms S1 107 53 Possible Fault Drag Xms S1 050 20 Fault Plane 138 72 Normal Fault

103 Xms S1 057 32 104 Xmg S1 066 30 Fault Plane 065 35 Fault Plane 152 67 Fault Plane 153 60 Fault Plane 228 59 Fault Plane 137 61 105 Xms S1 045 35 Xmg S1 040 26 Fault Plane 140 86 Fault Plane 165 84 LARGE FAULT MIDDLE OF CREEK

106 Xmg S1 052 31 106 Fault Plane 323 90 107 Fault Plane 146 84

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Fault Plane 012 80 Fault Plane 247 70

108 Xmg S1 050 66 Xmg S1 050 35 Xmg Fold AP 045 46 Fault Plane 050 66 110 Fault Plane 265 72 Fault Plane 266 70 Fault Plane 073 89

111 Xms S1 055 54 112 Fault Plane 238 57

114 Xas S1 040 60 115 Xms S1 070 20 Xms S1 039 24 Xms S2 200 68 Xms Fold AP 000 69 Antiform Xms Fold AP 340 50 Synform Xms Fold AP 115 55 Synform

116 Xas S1 035 60 117 Fault Plane 064 85 Fault drag shows dextral movement Fault Plane 060 70 Fault drag shows dextral movement

118 Xas S1 032 71 Xas S1 066 62 Xas S2 056 35 Xas Fold AP 055 45 Xas Fold AP 053 54

119 Xas S1 036 68 Left limb of fold Xas S1 248 25 Right limb of fold Xas S2 021 56 Xas Fold AP 012 31 Fault Plane 135 79 Fault Plane 000 43 Fault Plane 096 65 120 Fault Plane 242 43

121 Xas S1 058 66 Upper limb of fold Xas S1 082 50 Lower limb of fold Xas Fold AP 075 56 Fault drag Fault Plane 250 31

122 Xas S1 104 77 South limb of fold Xas S1 010 74 North limb of fold Xas Fold AP 090 44 Fault drag Fault Plane 065 79 Probable fault causing folding

135

123 Fault Plane 090 55 FAULT BRECCIA

124 Xas S1 343 42 Xas S1 350 57 Fault Plane 090 67 Appears to be a normal fault

125 Xqfg S1 020 45 Xas Fold AP 052 56 Fault Plane 230 82 Fault Plane 251 76 Fault Plane 290 26 Fault Plane 089 78

126 Xas S1 016 62 127 Xas S1 080 36 129 Xas S1 040 43 130 Xmg S1 049 59 Fault Plane 290 75 Fault Plane 092 58

131 Xas S1 015 64 Xas S1 028 74 132 Xas S1 065 64 Xas Fold AP 082 47 Xas Fold AP 074 44 Xas Fold AP 100 50 Xqfg Fold AP 079 50 Fault Plane 272 58

133 Xas S1 054 62 Xas Fold AP 184 80

134 Xas S1 004 58 Fault Plane 345 64

135 Xas S1 084 70 136 Fault Plane 348 90 137 Fault Plane 156 14

138 Xas S1 014 55 Fault Plane 163 88 Fault Plane 110 80

139 Xqfg S1 359 17 140 Xmg S1 070 19 Fault Plane 334 79

141 Xqfg S1 040 48 142 Xqfg S1 029 57 143 Xms S1 035 70 Xms S2 300 87 144 Xqfg Fold AP 025 72 Large synform

136

Xqfg Fold AP 020 75 Synform Xqfg Fold AP 015 75

145 Xas S1 330 87 Limb meXasurement on a large fold with a hidden hinge

Xas S1 334 79 Limb meXasurement on a large fold with a hidden hinge

Xas S1 077 71 Limb meXasurement on a large fold with a hidden hinge

Xas S1 045 63 Limb meXasurement on a large fold with a hidden hinge

146 Xas S1 334 83 Right limb of a large tight fold Xas S1 098 43 Left limb of a large tight fold Xas Fold AP 350 47 147 Xas Fold AP 053 44 Fault Plane 088 50 148 Xas S1 014 73 Xas Fold AP 130 39 149 Xas Fold AP 226 74 Xas Fold AP 358 74 150 Fault Plane 090 50 BRECCIA 151 Fault Plane 335 65 BRECCIA W/ GREEN MINERALIZATION 152 Fault Plane 022 60 153 Fault Plane 053 59

154 Xqfg S1 010 47 Xqfg S1 243 39 Xqfg Fold AP 341 39 Xqfg Fold AP 315 47 156 Fault Plane 080 - No plane exposed to meXasure dip

157 Xqfg S1 059 58 158 Fault Plane 300 61 159 Fault Plane 300 60 160 Fault Plane 135 74 Appears to run length of Silver Dale Canyon Czan beyond study area 161 Fault Plane 042 90 162 Fault Plane 060 70 163 Fault Plane 095 66

164 Xqfg S1 057 65 165 Xqfg S1 052 40 166 Xqfg S1 228 72 167 Fault Plane 095 47 Wall of amphibolite Fault Plane 050 51

137

168 Xqfg S1 080 51 169 Fault Plane 078 51

170 Xas S1 115 44 171 Fault Plane 355 90

172 Xqfg S1 030 36 174 Xmg S1 112 70 Xmg S1 074 59 176 Xqfg S1 230 65 177 Fault Plane 132 65 178 Fault Plane 026 70 179 Fault Plane 340 - No plane exposed to meXasure dip 180 Fault Plane 232 89 Location of a prospect mine 181 Fault Plane 085 55 182 Fault Plane 053 80 183 Fault Plane 055 - Deep prospect pit. No chance to meXasure dip 185 Fault Plane 170 90 186 Fault Plane 040 28 187 Fault Plane 345 64 Fault Plane 356 64 188 Fault Plane 027 86 189 Fault Plane 022 46 190 Fault Plane 118 74 192 Fault Plane 090 62 193 Fault Plane 155 85 194 Fault Plane 064 59 195 Fault Plane 159 86 Fault Plane 069 63 196 Fault Plane 175 81 197 Fault Plane 065 66 198 Fault Plane 045 40 199 Fault Plane 078 58 200 Fault Plane 192 78 202 Fault Plane 060 80 203 Fault Plane 247 76 204 Fault Plane 020 76 Fault Plane 004 75 Fault Plane 279 59 205 Fault Plane 180 55 206 Fault Plane 275 47 208 Fault Plane 290 69 Fault Plane 045 67

138

211 Fault Plane 030 56

139

Appendix B – Linear Data

Appendix B Key

Unit: Xqfg – Quartzofeldspathic Gneiss Xms – Mica Schist Xmg – Migmatite Xas – Amphibolite

Measurement Type: L1 – Primary Lineation L2 – Secondary Lineation LT – Tension Gashes LS – Slickenlines FH – Fold Hinge

Lineation Location Unit Type Plunge Trend Notes 8 XMS L1 17 181 9 XAS L1 16 198 XQFG L1 35 204 XQFG FH 29 110

10 XAS LT 18 071 Tension Gashes XAS L1 22 197 Possible Slickensides XAS L1 04 204 Possible Slickensides 11 XQFG FH 15 215

12 XMS L1 36 221 XMS FH 43 125

15 XAS L1 27 160 17 XMS L1 14 210 XMS L1 15 212 XMS FH 15 216

18 XMS L1 15 220 XMS L1 20 222 XMS FH 46 136

19 XQFG L1 21 200 22 XMS L1 13 242 XMS L1 12 235 XAS L1 00 245 Mineralization on the Plane

140

XMS L1 26 231 XMS L1 19 214 XMS L1 21 205 XAS FH 30 200

69 XMS L1 35 190 XMS L1 57 200 69 XAS FH 42 115 XAS FH 03 058 74 XAS FH 30 255 XAS FH 63 240 77 XAS FH 40 235 79 XQFG FH 42 205 XQFG FH 55 237

91 LS 29 039 LS 60 235 LS 79 050 93 LS 46 090 94 LS 40 063 98 XMS L1 20 195 101 XMS L1 14 210 104 XMG L1 22 187 XMG LS 20 295 106 XMG L1 27 194 XMG LS 22 143 108 XMG LS 17 225 XMG FH 28 190

110 LS 57 045 115 XMS FH 38 175 Anitform XMS FH 46 175 Synform XMS FH 45 175 Synform

117 XAS LT 16 110 Exhibits dextral movement 118 XAS L2 36 226 Parasitic crenulations XAS FH 21 063 XAS FH 24 070

119 XAS L2 15 194 Parasitic crenulations XAS FH 08 205 121 XAS FH 41 080 Fault drag 122 XAS FH 55 135 Fault drag 125 XAS FH 40 255

128 XAS LT 29 123 130 XMG L1 10 050 132 XAS FH 53 190

141

XAS FH 37 204 XAS FH 55 194 XQFG FH 26 200 133 XAS FH 29 185

137 XMG LS 09 177 140 XMG L1 12 204 142 XQFG L1 42 195 143 XMS L1 26 184 XMS L2 70 110 144 XQFG FH 25 190 Large synform XQFG FH Synform XQFG FH 12 210 146 XAS FH 26 158 147 XAS FH 38 144 148 XAS FH 39 165 149 XAS FH 41 020 XAS FH 53 006 154 XQFG FH 31 031 XQFG FH 40 338 Shows that fault 167 is a dextral

167 XAS LS 10 090 oblique fault 177 LS 06 306 Sinistral movement 195 LS 29 192 Sinistral normal movement 199 LS 30 085 Sinistral normal movement 203 LS 26 075 Sinistral thrust movement 208 LS 32 290

142

Vita

Jensen Kohl Angelloz grew up in Hallettsville, Texas, graduating from Hallettsville High School in 2005. In 2006, he began his collegiate career at Blinn Community College in Brenham, Texas. In summer of 2011, he transferred to Sam Houston State University in Huntsville, Texas. He was hired as a historical geology teaching assistant in 2013 and began research entitled “Using Porosity to Differentiate Sedimentary Facies within Bahamian Carbonates” in spring 2014, his final semester. He attended the University of Missouri’s field camp in Lander, Wyoming during the summer of 2014. He graduated in August of 2014 with a double major in Geology and GIS. He then began a job as surveyor in Victoria, Texas. He changed jobs in November 2014 after an opportunity to work as a mudlogger in West Texas was presented. After the petroleum market crashed, he enrolled in the graduate program at Stephen F. Austin State University in the fall of 2015. He was subsequently hired as graduate teaching assistant where he taught 131 and 132 geology labs. He was hired by South Dakota School of Mines as a teaching assistant for their Spain field camp in the summer of 2017. During his final semester at Stephen F. Austin State University, he was taken on as the lab assistant for Seismic Methods. Jensen received his Master of Science degree in Geology from Stephen F. Austin State University on December 16, 2017.

Permanent Address: 501 N. Ridge Hallettsville, TX 77964

GSA style guide

This thesis was typed by Jensen Kohl Angelloz

143

Geologic Map and Cross Sections Plate 1 Structural Analysis of the Northwest Wind Mountain Quadrangle, New Mexico: Proterozoic Shearing to Cenozoic Brittle Faulting in the Burro Mountains MAP EXPLANATION C C Czmt Lapilli Tuff Breccia: fresh surface: light pinkish to tan-gray; weathered surface: light pink to reddish-brown. Brecciated blocks and lapilli contain small biotite and quartz crystals. e n Cztt Tan Lapilli Tuff: fresh surface: white; weathered surface: pale orangey-brown. Crystals and lapilli (up to 5mm) consist of biotite, feldspar and pumice in matrix.

o Czpt Purple Lapilli Tuff: fresh surface: purplish-brown; weathered surface: brown. Blocks (up to 5 cm) and lapilli consist of andesite porphyry, rhyolite porphyry and pumice. Small flattened vesicles could be removed lapilli. z o Czgt Green Lapilli Tuff: fresh surface: gray-brown to light gray-green; weathered surface: light gray; 70% matrix, 30% lapilli lithic fragments. Lapilli up to 2 cm. i Czap Andesite Porphyry: Melanocratic, aphanitic andesite porphyry; fresh surface: greenish-brown to black; weathered surface: red-brown with light gray spots; matrix 80%; porphyrytic eu- to subhedral plagioclase (up to 2 cm) crystals 20 %. M c e Cza Andesite: Mesocratic, aphanitic andesite; fresh surface: medium gray with white and black spots; weathered surface: red-brown to maroon-brown; matrix 85% is dark gray, subhedral plagioclase up to 2mm 10%, < ~1mm euhedral hornblende crystals 5%. s Beartooth Quartzite: Grades from a metaconglomerate at the base to a quartzite; fresh surface: light to medium gray in the quartzite and variable shades of dark gray in the metaconglomerate; weathered surface: light medium grey to an orange-red. Some Kbq C’ o surfaces are mineralized with an iridescent black-purple-blue-red-green color. Pebbles in the metaconglomerate are up to an inch in length.

z Quartz Syenite: Leucocratic, course-grained phaneritic quartz syenite; fresh surface: white to gray; weathered surface: pink to dull-red; mineralogy: 30-40% feldspar, 20-25% biotite, 10-15% plagioclase, 10-15% hornblende, 10-15% quartz, < 5% muscovite. Yqs Feldspar crystals are up to 1.5 in and are eu- to subhedral. Other crystals are sub- to anhedral. Xenoliths of amphibolite are found in some outcrops. B o

i Ybmg Burro Mountain Granite: Leucocratic, fine-grained phaneritic granite; fresh surface: pink with orange-red spotting; weathered surface: red-brown; mineralogy: 60% potassium feldspar, 20-30% quartz, 5% hornblende, 5% plagioclase, up to 5% biotite. Crystals are P sub- to anhedral. Xenoliths of monzogranite and amphibolite are found around the boundaries of the Burro Mountain Granite. c Ydi Diorite: Leucocratic, course-grained phaneritic diorite; fresh surface: 50% white and 50% black; weathered surface: light tan and black to a pink-orange; mineralogy: 40-50% hornblende, 20-25% plagioclase, 10-15% feldspar, 10% quartz, 10% hornblende. Crystals r are sub- to anhedral.

o Monzogranite: Leucocratic, course-grained phaneritic monzogranite; fresh surface: 60% white and 40% black; weathered surface: light tan and black to a pink-orange; mineralogy: 40-45% biotite, 20-25% plagioclase, 20-20% feldspar, 10% quartz, 5% hornblende. Ymg t Crystals are sub- to anhedral. There appears to be a flow fabric caused by the alignment of biotite and hornblende.

e Xgb Gabbro: Melanocratic, phaneritic gabbro; fresh surface: black; weathered surface: black; Pyroxene crystals are up to 5mm. r Amphibolite: Strongly foliated and lineated schist; fresh surface: dark green to dark blue-black with white spots; weathered surface: reddish-brown, occasionally green; mineralogy: 80% amphibolite, 20% plagioclase. Weathered fold hinges are extremely friable. Xas o Weathers to a black soil. B’ z Xmg Migmatite: Strongly foliated and lineated migmatite; fresh surface: orangey-pink with gray-black banding; weathered surface: orangey-pink to an off-white with silvery-dark gray banding. o

Mica Schist: Strongly foliated and lineated schist; fresh surface: charcoal gray with bands of white; weathered surface: charcoal gray with bands of white; mineralogy: 25-55% biotite, 5-35% muscovite, 10-20% feldspar, 10-20% quartz. Muscovite and Biotite Xms i concentrations are zoned, grading into the other. Weathers to an orange soil with high mica content. Winged, sigmoidal porphyroclasts are prevalent in this unit c Xqfg Quartzofeldspathic Gneiss: Strongly foliated gneiss; fresh surface: off-white to light-medium gray; weathered surface: off-white to light-medium gray; mineralogy: 50-60% feldspar and plagioclase, 30-35% quartz, 5-20% biotite. Weathers to orange soil. Strongly weathered outcrops are friable.

MAP SYMBOLOGY

65 36 36 Fault Unit Contact Strike and Dip of Foliation Fault with known dip Strike and Dip of Bedding

36 Inferred Unit Contact Strike and Dip of Foliation and Potential Fault A the Plunge and Trend of Lineation ? 15 Thrust Fault with Oblique movement

CROSS-SECTIONS A A’ B B’ 6,000’ 6,000’ 5,600’ 5,600’ Xas Ymg 5,000’ Ybmg Xqfg 4,600’ 4,600’ Yqs 5,000’ Ybmg Ybmg A’ 4,000’ 4,000’ 3,600’ 3,600’

SCALE: N 1:12,000 C C’ No VE 5,600’ Czpt 5,600’ 1,000 ft. Czgt Cza 1000’ 4,600’ Ybmg 4,600’ 1000’ 3,600’ 3,600’ 0’

Jensen Kohl Angelloz; December 2017 Stephen F. Austin State University