Internal Architecture of the Proto-Kern Canyon Fault At

INTERNAL ARCHITECTURE OF THE PROTO- KERN CANYON FAULT

AT ENGINEER’S POINT, LAKE ISABELLA, CALIFORNIA

Zachary Scott Martindale, B.S.

A Thesis Submitted to the Department of Geological Sciences California State University, Bakersfield In Partial Fulfillment for the Degree of Masters of Science in Geology

Spring 2015

Zachary Scott Martindale

2015

Acknowledgements

Completion of this project would not have been possible without the generous funding from CSUB’s NSF CREST program, the Student Research Scholarship program, and the Graduate Student Center’s Grad Student Faculty Collaborative Initiative. I thank Dr. Negrini and Andrea Medina with the CSUB CREST program for their assistance in administrative matters. Numerous individuals have dedicated their time and patience in instructing me in operating various lab equipment: Kellie Townsend and Dr. Keith Putirka at Fresno State University; Alyssa Kaess, Kelsey Padilla, and Elizabeth Powers at CSUB. I also want to thank those who helped with advice in techniques of collection and interpretation of data: Drs. Sarah Brown, Junhua Guo, Robert Horton, and Chris Krugh.

My deepest gratitude and respect is held for my advisor, Dr. Graham Andrews. His faith in me to accomplish a project of this magnitude was at times the only force pushing me forward. I would not have known how to begin any new stage without his direction.

Abstract

Faults create a structurally weak zone within the lithosphere that can be reactivated again and again through geologic time. This reactivation can occur under varying tectonic stresses, temperatures, and pressures within the fault zone. This study focuses on the complex Kern Canyon Fault zone at Engineer’s Point, Lake Isabella, California, and begins to elucidate the geologic history recorded in its structure and alteration through the damage zone and fault core. The data suggest that the Miocene - Quaternary Kern Canyon Fault is hosted within a Cretaceous ductile shear zone and hydrothermal alteration zone, the proto-Kern Canyon shear zone. The proto-Kern Canyon shear zone is heavily and complexly fractured, and probably experienced dextral shear before the cessation of shearing and the onset of exhumation. The shear zone is thoroughly hydrothermally altered and has experienced phyllic and argillic alteration during and after deformation, respectively. The Kern Canyon Fault is located within this complexly fractured and altered bedrock; estimates of future seismicity should consider propensity for creep as well as stick-slip behavior.

Table of Contents

List of Tables 4

List of Figures 5

Introduction 8

Methods 14

Results 17

Interpretation and Discussion 23

Summary 29

References 30

Tables 35

Figures 38

List of Tables

Table 1: Calculated intensity and relative abundance values

Table 2: Weight percentages of major elements by X-ray fluorescence

Table 3: Trace element abundance by X-ray fluorescence

List of Figures

Figure 1: Fault zone architecture with protolith, damage zone and fault core. From Caine et al. (1996).

Figure 2: Table showing differentiated fault rock types. Modified from Sibson (1977).

Figure 3: Fault zone architecture with depth. From Fossen (2010).

Figure 4: Map of major faulting within south-central California.

Figure 5: Earthquake epicenters around the Kern Canyon fault and the junction between the San Andreas and Garlock faults.

Figure 6: Sketch map of Engineer’s Point showing locations of sample sites for analyses.

Figure 7: Table of analyses conducted at each site.

Figure 8: Map of fault rock lithologies and interpreted structures.

Figure 9: Various structures and contacts within the map area.

Figure 10: Map of fault rock lithologies in Domain 2.

Figure 11: Photograph of Fractures within site Z01.

Figure 12: Photograph of Fractures within site Z03.

Figure 13: Photograph of fractures within site Z05.

Figure 14: Photograph of fractures within site Z06.

Figure 15: Photograph of fractures within site Z07.

Figure 16: Photograph of fractures spanning Z08-Z10.

Figure 17: Table showing summary of fracture data (stereonets, rose diagrams, fracture length distribution, fracture density) and interpretation for each station.

Figure 18: Fracture length distribution within each zone.

Figure 19: Rose diagrams of fracture orientations by zone.

Figure 19: Poles to all fractures within each zone grouped by preferred orientation.

Figure 20: Fracture lengths by zone on a log-log scale.

Figure 21: Poles to fractures in each zone grouped by orientation.

Figure 22: Histogram of filled fractures by length and zone.

Figure 23: Stereonets of poles to fractures separated by length.

Figure 24: Stereonets of poles to fractures separated by fill.

Figure 23: Poles to fractures separated by fill and length.

Figure 26: Grain size distribution of clasts >1mm within the fault gouge of Z09 and Z10.

Figure 27: Grain size distribution and statistics for Z08 grains <5 mm.

Figure 28: Grain size distribution and statistics for Z09 grains <5 mm.

Figure 29: Grain size distribution and statistics for Z10 grains <5 mm.

Figure 28: Log-log plot of Z08, Z09 and Z10 grain size distribution and linear fits where possible.

Figure 29: XRD patterns from 7° to 75° and interpreted mineralogy for each site.

Figure 30: Detailed XRD patterns for each site.

Figure 31: Compilation of XRD patterns for all sites to highlight trends through the fault zone.

Figure 32: Abundances of major minerals relative only to that particular site.

Figure 33: Abundances of major minerals relative to abundance in Z00 for each of the other sites.

Figure 34: Clay to plagioclase ratio through the fault zone. Relative abundance is fairly linear except in Z08 and Z10b.

Figure 37: Plot of major element/zirconium and selected trace element/ zirconium ratios for each station relative to Z00.

Figure 38: Plot traced element abundances for each station relative to Z00.

Figure 39: Table of hydrothermal alterations observed in each zone.

Figure 40: Phyllic alterations in Z01.

Figure 41: Argillic alteration in Z07.

Figure 42: Alteration of chlorite in Z02.

Figure 43: Fractured oligoclase in Z00.

Figure 44: Folded, fractured and altered chlorite.

Figure 45: Gouge vein suggesting pulverization of calcite vein.

Figure 46: Cataclasite with two domains of grain sizes.

Figure 47: Increased magnification of cataclasite.

Figure 48: In situ cataclasis of quartz and calcite.

Figure 49: Multiple veins filling one fracture.

Figure 50: Table of alterations within each zone.

Figure 51: Waldron (2007) model of sheared fractures.

Figure 52: Stereonet plots of preferred fracture orientations by zone showing rotation.

Introduction

Faults are not discrete planes through the lithosphere. They are instead complex zones of deformation that can vary in type and degree (e.g., Engelder, 1974; Sibson, 1977; Caine et al., 1996). These variations include lithology, structure, alteration and grain size. All are heavily influenced by the presence of fluids; particularly ions within those fluids. Because varying stress regimes induce different structural deformations and the ions within fluids can vary throughout time, it may be possible to work out a deformation history for faults that have been reactivated numerous times in the past. This study analyzes and quantifies several of the variations that occur through the Kern Canyon fault zone, a long-lived and lengthy fault, along a 180 meter transect on the western side of the fault exposed at Engineer’s Point, Lake Isabella, California.

Fault Zone Architecture

The architecture of major fault zones and the deformation and hydrothermal alteration associated with them is often complex; however, development and evolution of such features dictate fault behavior. For example, in fracture mechanics the generation of new brittle faults and ”stick-slip” fault behavior is favored in isotropic, minimally fractured, and strong (i.e. non- hydrothermally altered) lithologies. Conversely, extensive fracture and foliation development favors reactivation of slip planes by ‘creep’ (i.e. Byerlee’s Law). Moreover, weakening of rocks by alteration (hydration, clay formation, etc.) favors creep through diffuse ductile deformation. Every fault zone is composed of three major zones: (1) the wall-rock protolith, (2) the damage zone, and (3) the fault core (Fig. 1; Chester and Logan, 1986; Goddard and Evans, 1995; Caine et al., 1996). The boundaries between each of these zones strike approximately parallel to the fault plane. The fault core contains the fault plane and accommodates the majority of the strain and alteration associated with the fault zone (Goddard and Evans, 1995; Caine et al., 1996). The damage zone envelopes the core and is composed of fractured, folded, cleaved and faulted rock that accommodate some significant portion of the shear stress (Caine et al., 1996). The protolith is the undamaged and unaltered rock that envelopes the damage zone. The width of each of these zones is dependent upon numerous factors including the host rock lithology, the direction and amount of relative offset, the amount of time over which offset has occurred, and the presence of fluid within the deformed fault rocks. (Goddard and Evans, 1995; Schulz and Evans, 2000). Progressively thicker zones are favored by protracted or large magnitude strain and hydrothermal alteration.

A variety of different fault rock types exists (Fig. 2; Sibson, 1977). First order differentiations begin with determining whether the rock is cohesive or incohesive. Incohesive rocks are described based upon grain size as either breccia or gouge. Cohesive and incohesive rocks that exhibit grain size reduction but little to no shear or grain rounding are referred to as pulverized rocks (Mitchell et al., 2011). Cohesive rocks with a higher percentage of matrix are either mylonites, which have a distinct foliation, or cataclasites, with randomly oriented clasts.

The occurrence of foliation is closely linked to the pressure and temperature and therefore depth at which deformation took place. Typically, only brittle deformation occurs in the upper 10 km of the crust (Fig. 3). This brittle deformation results in the formation of fault breccias, pulverized rock, and gouge (Sibson, 1977). As the fault extends deeper into the earth it reaches higher temperature and pressure regimes that allow for ductile deformation of the minerals within the host rock (Fig. 3). This allows for preferential orientation of minerals during shearing (Simpson and Schmid, 1983; Busby and Saleeby, 1990; Passchier and Trouw, 1998); these rocks are referred to as protomylonites, mylonites and ultramylonites based upon the degree of deformation and decreasing grain size (Sibson, 1977; Brody et al, 2007

Hydrothermal alteration is the restructuring of a mineral as the crystal structure is exposed to fluids during faulting (e.g. Goddard and Evans, 1995; Ohtani et al., 2000; Uysal et al., 2006). Important phases of hydrothermal alteration in fault zones include: (1) phyllic alteration, a high temperature alteration that alters plagioclase and biotite to chlorite, white micas, and quartz; (2) argillic alteration, a low temperature alteration most recognizable as the alteration of plagioclase and K-feldspar to clay minerals and white mica; and (3) iron oxide copper gold (IOCG) alteration the leads to the precipitation of oxidized Fe-rich minerals like hematite in fissures and fractures (Klima et al., 1988; Fiebig and Hoefs, 2000; Morad et al., 2009). The fluids that induce these reactions can come from at least two sources: supersaturated fluids in the host rock immediately adjacent to the fault or other rocks that are now in hydraulic connectivity along the fault (e.g. Hammond and Evans, 2003). Ions in the newly introduced fluids react with the rocks and can induce dissolution of host rock minerals or precipitation of new minerals such as calcite, silica and iron oxides (Ohtani et al., 2000).

Geological Setting

The Kern Canyon Fault (KCF) is a 150 km long, roughly NNE-SSW trending, steeply east-dipping normal fault that dissects the central and southern Sierra Nevada in central California (Fig. 4, Nadin and Saleeby, 2010; Brossy et al., 2012). It forms part of a complex and widespread regional fault system (Fig. 5) accommodating both dextral transtension within and along the margins of the Sierran microplate (Unruh and Hauksson, 2009), and vertical displacement and uplift associated with mantle delamination beneath the southern Sierra microplate centered beneath Tulare Lake (Saleeby et al., 2009; Nadin and Saleeby, 2010). The KCF is inferred to be seismically active with both paleoseismic (trenching) and geomorphological evidence for several surface deformations in the Pleistocene and Holocene (Nadin and Saleeby, 2010; Salah-Mars et al., 2011; Brossy et al., 2012). The KCF is notable for being recognized as an active fault only recently, and that it passes beneath several communities and the auxiliary dam of the Lake Isabella Reservoir. A worst-case scenario described by Kern County Engineering Services predicts that an outburst flood from the Lake Isabella Dam would devastate communities downstream including the 300,000 person city of Bakersfield (http://esps.kerndsa.com/floodplain-management/lake-isabella-flood-area/). Concern over the

present and future integrity of the Lake Isabella Dam, including in a KCF earthquake scenario, has led to funding of a ~$500 million modification project by the U.S. Army Corps of Engineers, with operations scheduled to commence in 2017 (http://www.spk.usace.army.mil/Missions/CivilWorks/IsabellaDam.aspx).

This research project focuses on the part of the KCF immediately adjacent to the Lake Isabella Auxiliary Dam where exhumed fault rocks are exposed along Engineer’s Point, a peninsula formed along the uplifted footwall of the KCF.

The Late Neogene-Quaternary Kern Canyon Fault (KCF)

The KCF strikes north-south through the middle of the southern Sierra Nevada (Fig. 4). North of the town of Kernville (35°75 N, 118°43 W) it consists of a thin (cm scale) cataclastic zone that is hosted within the 2-5 km thick late Cretaceous proto-Kern Canyon Fault (pKCF) shear zone. The KCF can be traced for ~100 km based on: (1) a prominent 750 m high topographic scarp; (2) steep stream profiles west of the KCF as opposed to gentle profiles to the east; (3) changes in lithology and structure across the fault; (4) fault parallel fracture zones and breccias; (5) linear arrays of hot springs and limestone caves probably associated with fluid flow through the fault zone; and (6) north-south elongate margins of plutons (Webb, 1936; Busby and Saleeby, 1990; Nadin, 2007). Detailed geological mapping shows that strain gets distributed over an increasingly wide area until a reduction in mappable offset coincides with an increase in fractures suggesting the fault ends at latitude 36°40 N (Moore and DuBray, 1978).

In the Lake Isabella region (Fig. 4) the KCF exploits the weakened rocks of the proto- KCF shear zone and is recognized as juxtaposing metamorphic and granitic rocks against Quaternary alluvial fill (Ross, 1986; Nadin and Saleeby, 2010). These metamorphic and granitic rocks consist predominantly of five types: (1) fault breccias; (2) microbreccia; (3) fault gouge; (4) protomylonite; and (5) mylonite (Higgins, 1971; Passchier and Trouw, 1998). Linear bedrock features and aligned saddles and swales identify the KCF south of the Isabella Basin, indicating it probably trends to the southwest and possibly merges with the Breckenridge and White Wolf faults (Ross, 1986).

Motion on the KCF during the Pliocene - Quaternary has been normal sense, east side down and nearly vertical as inferred from: (1) numerous normal fault scarps (i.e. Engineer’s Point) that juxtapose elevated metamorphic and granitic bedrock to the west against subhorizontal alluvial deposits to the east, (2) earthquake focal mechanisms (Fig. 5), and (3) GPS vertical velocities of 0.45 mm/yr on the western side of the fault (Nadin and Saleeby, 2010; Brossey et al., 2013). The KCF was until recently thought to have been inactive since the Pliocene as it is partly buried by a 3.5 million year old basalt flow (Webb, 1936; Moore and DuBray, 1978). However, recent studies have shown that this basalt is heavily fractured and that during the Quaternary period the Kern Canyon Fault accommodated east-side down normal faulting, with movement as recent as 3500 years ago (Kelson et al., 2010; Nadin and Saleeby,

2010; Brossy et al., 2012). Evidence for rupture events this recent exist in fractured coal deposits and trench studies (Kelson et al., 2010; Salah-Mars et al., 2011).

Saleeby and others have suggested that the Quaternary fault motion is due to tectonic accommodation of progressive westward delamination of the mantle lithosphere and the accompanying formation and westward tilt of the Sierra Nevada microplate that is expressed in the eastern Sierra escarpment system (Fig. 4; Maheo et al., 2009; Saleeby et al., 2009; Figueroa and Knott, 2010; Nadin and Saleeby, 2010; Saleeby et al., 2012; LePourhiet et al., 2013). South of 36°24 N the westward tilt adjacent to the eastern Sierra escarpment becomes more subdued. It is possible that at this location plate deformation that allows for the tilt is accommodated by the KCF system (Figueroa and Knott, 2010; Saleeby et al., 2012). Another possible explanation is that the fault is accommodating some of the Sierra Nevada microplate’s clockwise rotation in response to relative movement between the Pacific and North American plates. The San Andreas fault to the west accommodates ~75% of the differential plate motion while the eastern Sierra escarpment system and the KCF accommodates the remaining 25% (Unruh and Hauksson, 2009; Kearey et al., 2013). It is most likely that both of these factors have had influence on relative motion of the KCF.

Relationship to the proto- Kern Canyon fault shear zone

Brittle-ductile deformation of the KCF southwest of Lake Isabella is oblique to the pKCF at a clockwise angle of ~15° (Nadin, 2007). Brittle dextral offset in the southwest mark its origins around ~86 Ma (Ross, 1986; Nadin, 2007; Nadin and Saleeby, 2010), possibly accommodating plate motion associated with rapid unroofing of the Sierra Nevada batholith (Nadin and Saleeby, 2010). By 80 Ma the pKCF had developed within the Isabella basin (Fig. 1). This can be seen in dextral ductile fabrics that diverge from the main trace of the pKCF south of Kernville (Nadin and Saleeby, 2010). The system was reactivated again in the Miocene as a dextral-slip fault serving as a transfer zone between the extensional Maricopa sub-basin to the west and the southeast Sierra extensional domain to the south (Maheo et al., 2009; Saleeby et al., 2009).

The pKCF consists of syn-intrusional, late Cretaceous episodes of ductile deformation that run through the middle of the southern Sierra Nevada from 36°35 N to 35°00 N (Busby- Spera and Saleeby, 1990; Wood and Saleeby, 1997; Nadin and Saleeby, 2008). Deformation began at latest at ~95 Ma but evidence is obscured by voluminous 90-85 Ma plutons that bound the majority of the eastern side of the fault (Nadin, 2007). Deformation in its southern segment began to wane substantially by 86 Ma, while the north continued dextral slip until ~80 Ma (Nadin, 2007). North of Kernville the pKCF fault zone can be traced in 2-5 km wide granitic mylonite zones found along the margins of late-Cretaceous aged plutons cooling through solidus conditions on its eastern side and early to mid-Cretaceous aged plutons to the west. It either passes through schistose and phyllonitic metasedimentary pendant rocks of quartzite, marble and

pelite that hosted the batholith, or is the contact between pendant rock to the west and late- Cretaceous plutons to the east (Moore and Dubray, 1978; Ross 1986; Busby-Spera and Saleeby, 1990; Nadin, 2007). South of its bifurcation from the KCF, the pKCF is hosted in a thick inlier of metamorphosed country rocks that are surrounded by Cretaceous plutonic rock (Busby-Spera and Saleeby, 1990; Wood and Saleeby, 1997; Saleeby and Nadin, 2007).

Structural features that provide evidence for the pKCF are described in depth by Nadin (2007). First are NNW striking foliations in metamorphic and pendant rocks that dip between vertical and 65° that suggest E-W shortening coupled with both vertical and N-S stretching. Second are the presence of elongate minerals within the foliation planes and small fold axes of quartzites and marbles that trend N-S. Some of these elongations are sub-horizontal and indicate dextral slip while some plunge steeply and may be the result of the vertical ascent of the adjacent plutons or early vertical motion of the pKCF. Thirdly are extensional features such as vertical dikes, joints, cleavage, and normal offset faults that all trend N-S.

Dextral strike-slip fault movement along the pKCF is inferred from mapping of pluton boundaries (Moore and Dubray, 1978; Ross, 1986) and from kinematic indicators that include S- C fabrics, asymmetric quartz ribbons, delta and sigma porphyroclasts and mica fish.

Although dextral strike-slip movement is the most obvious offset noticeable in the pKCF, detailed analyses have proved there was significant vertical offset prior to the onset of the strike- slip motion (Busby-Spera and Saleeby, 1990; Nadin 2007). Crystallization depths across the fault zone and the Sri=0.706 isopleth of the Sierra Nevada batholith suggest that the pKCF was accommodating displacement before the intrusion of the presently adjacent plutonic rock (Nadin, 2007). Crystallization depths by the Al-in-hornblende on opposite sides of the pKCF show a difference of pluton emplacement depths of over 4-6km (Nadin, 2007). Steeply dipping reverse sense ductile fabrics overprint high temperature dextral sense shear bands suggesting that reverse faulting along the pKCF juxtaposed deeper rocks in the east over shallower rocks to the west prior to the onset of right-lateral strike-slip motion (Busby and Saleeby, 1990; Nadin, 2007). These data show the most substantial vertical offset occurred along the southern portion of the fault and was possibly the result of rapid unroofing of the Sierra Nevada batholith (Wood and Saleeby, 2007).

The Bedrock Geology Adjacent to the Proto-Kern Canyon Fault

The southern Sierra Nevada consists predominantly of uplifted mid to late-Cretaceous plutonic rocks, with compositions ranging from tonalitic to granitic, and some remnants of the Paleozoic metasedimentary and metavolcanic supracrustal rocks into which the batholith was intruded (Ross, 1986; Busby-Spera and Saleeby, 1990; Nadin, 2007). These consist of a K- feldspar porphyritic granite, (the Granite of Kern River), a medium grained hornblende diorite co-mingled with the Tonalite of Bear Valley Springs, and two members of the Needles intrusive suite of Saleeby et al. (2008) which include a coarse grained biotite granodiorite, the

Granodiorite of Wagy Flat, and a fine grained biotite porphyritic granodiorite, the Granodiorite of Alta Sierra. Occasionally, metamorphosed roof pendants of the hosting country rock are also present immediately adjacent to the fault. These roof pendants consist of Jurassic-Triassic quartzites, marbles and psammitic and pelitic schists (Saleeby et al., 1978; Saleeby and Busby, 1996; Nadin, 2007).

Seismic and Other Geotechnical Hazards at the Lake Isabella Dam

Compilation of seismic data recorded by the Southern California Seismic Network show more than 100,000 earthquakes recorded in the southern Sierra Nevada region between 1981 and 2003 (Fig. 2, Unruh and Hauksson, 2009; Nadin and Saleeby, 2010; Brossey et al., 2013). A significant number of epicenters lie near the KCF trace and include six with magnitudes greater than 4.0: five along the Breckenridge fault, thought to be the southern continuation of the KCF, and one at the bifurcation of the KCF and pKCF. Recognition of recent slip along the KCF, including intense fracturing of the 3.5 Ma basalt that is covering the fault (Nadin and Saleeby, 2010; Brossey et al., 2013), led to analysis by the U.S. Army Corps of Engineers in 2009 when they found ruptured alluvium dated at 3,500 years ago, the presence of hot springs less than 2 km south of the ruptured alluvium, and ~30 m of late Quaternary sediment immediately adjacent to granitic bedrock (Kelson et al., 2010; Salah-Mars et al., 2011). These findings suggest that the Kern Canyon Fault was recently active, i.e. mid–late Holocene, and probably remains active in the present day. This has led to concern and very recent government review of the structural integrity of the Lake Isabella Auxiliary Dam, through which the KCF passes. This necessitates a much more thorough understanding of the fault than is currently available.

METHODS

Twelve different locations were studied in the pKCF and KCF at Engineer’s Point; they are grouped into three zones, the fault core, the damage zone and host rock (Fig. 1). The 160 m long transect runs roughly perpendicular to these zones (Fig. 6); sample locations were chosen based upon the degree of visible deformation or alteration relative to the host rock (sample Z00) and the availability of outcrop. Each sample location was recorded in a hand-held GPS unit. Samples were collected at sites (Z00-Z10) for a variety of petrographic, geochemical, and mineralogical analyses; these techniques are described below (Fig 7).

Mapping

Along Engineer’s Point the pKCF and KCF are hosted entirely within a coarse grained biotite granodiorite, the Granodiorite of Wagy Flat (Nadin, 2007). Mapped units were differentiated from the country rock and each other by degree and style of deformation, grain size, color, and composition. Changes in individual grains and crystals in hand sample was then used to further differentiate within both the ductile and brittle zones, with the finer grained zones, the mylonite and cataclasite zones, mapped as individual units.

Fracture Analysis

Fracture analysis was conducted at five individual sample locations (Z01, Z03, Z05, Z06, Z07) as well as at one additional location that encompassed sites Z08, Z09 and Z10 (Fig. 6). Two mutually perpendicular lines of rope, each 180 cm long, with washers at each end were fixed to the ground with 10” long, 1/2” wide stakes to form a survey target (i.e. Fig. 11). The lines were oriented so that one was parallel to 010, approximately parallel to the mapped KCF at Engineer’s Point (Ross, 1986; Nadin 2010). Each line was systematically traversed to within 10 cm of each stake, total length 160 cm, so as to avoid the recording of fractures induced by positioning of the stake. The strike, dip, length, aperture width, and the presence and color of any mineral fill were recorded for each fracture that intersected the survey target lines. Fracture density was calculated by multiplying the number of fractures that crossed the 010 line by the number that crossed the 100 line and dividing by the area sampled (160 cm x 160 cm). The composition of the fill was unknown at the time of recording, except for those that reacted to the application of dilute HCl and were therefore described by color: white, pink and red.

Grain Size Analysis

Samples of incoherent rock from the fault core (Z08 through Z10) were collected by hammering 1 1/2 inch wide x 4 inch long copper pipe into the sample area and then carefully removed by hand. Each sample was first run through sieves ranging from 4.75 mm to 1.016 mm. Approximately 2 grams were taken from the 1.016 mm fraction and analyzed using a Malvern Mastersizer 2000 particle size analyzer. Each sample was rinsed in 10 mL of deionized water and 5 mL of hexametaphospate and ran through a sonicator to loosen particles. After allowing 24 hours for the samples to settle, analyses were conducted on the total load, settled load, and suspended load. Each sample was analyzed three times and the results averaged. The data was then analyzed using GRADISTAT particle size analysis software (Blott and Pye, 2001).

X-Ray Diffraction Analysis

X-ray diffraction analysis was performed on samples from all twelve sites. Samples were collected using a hammer to break off a grapefruit sized chunk when the outcrop was coherent (Z00-Z07). Incoherent fault core (Z08-Z10b) was gathered by carefully collecting it with a trowel and placing it into resealable plastic bags. All samples were then processed through a jawcrusher and homogenized. Individual samples were further crushed and homogenized into fine powder in a circular grinder for six minutes. From this powder enough to fill a 1” diameter, ¼” thick sample tray was analyzed with a Panalytical X’Pert Pro MRD at the Fresno State Department of Geology. Cobalt was used as the anode material. Intensity values for 2Θ ranged between 5.0084° to 74.9804° with a step size of 0.0170°. Temperatures of all samples were 25° C. The X’Pert Pro data was converted to .mdi format using PowDLL conversion software. The data were then interpreted using MDI Jade 5.0 software. The relative abundance of each mineral was calculated by flattening the curve on a baseline that fit the general trend of the background noise and then calculating the area under each peak. Each value was then multiplied by that mineral’s relative intensity factor according to Cook et al. (1975) and Boski et al. (1998) and relative intensities for each mineral were plotted. The correction factors used were: 1.0 for quartz; 1.92 for calcite; 2.0 for feldspar; and 20.0 for clay.

X-Ray Fluorescence Whole Rock Geochemistry

XRF analyses were used to determine bulk chemical composition of samples at all twelve sites through the fault zone. XRF samples were collected in the same manner as the XRD samples; they were taken from outcrop when rock was coherent and dug out of incoherent outcrop. Samples were prepared and analyses were performed at Washington State University’s Peter Hooper GeoAnalytical Lab using their Thermo-ARL automated X-ray fluorescence spectrometer.

Scanning Electron Microprobe Petrography

Scanning electron microscope petrography was used to conduct microscopic analyses of structural and compositional deformation of specific minerals, determine the presence and characterization of cataclasite and mylonite and analyze fractures and their fill. Samples Z00 through Z07 were impregnated with epoxy. Samples were cut so that thin sections were oriented vertical, (i.e. roughly parallel to the plane of the fault), and parallel to the foliation of phyllosilicate minerals. A composite image was created for each sample with photo- micrographs taken on a Nikon petrographic microscope with 2X objective. The pictures were then compiled together using Adobe Photoshop CS4. Sites for SEM micro-analyses were chosen from these photos. CSU Bakersfield’s Hitachi S3400N Scanning Electron Microscope was used to generate backscatter electron photographs and in situ analyses. Samples were run at 20 kv and 100 μA. Oxford Instruments’ Inca Excite EDS software normalized against pure copper was used to determine chemical composition at selected sites on each slide.

Results

Geological Mapping

The bedrock of an approximately 800 m long section of Engineer’s Point (Fig. 6) was mapped in 2014 when Lake Isabella’s water level was historically low. The geology is divided into three domains (Fig. 8) based upon the predominant style of deformation and the relationship with identified normal faults.

Domain 1 is restricted to a horst bound to the south and east by high-angle normal faults, and is topographically higher than the adjacent domains 2 and 3. Cross-cutting relationships established by mapping suggest that the NW-trending normal fault separating domains 1 and 2 is truncated by the SSW-trending normal fault bounding Domain 3. This fault is inferred to be part of the active Kern Canyon Fault. Domain 1 exhibits primarily ductile deformation fabrics whereas domains 2 and 3 exhibit predominantly brittle deformation overprinting ductile fabrics like those in Domain 1. Domain 1 is composed of three lithologies: foliated granodiorite, protomylonite, and mylonite with ultramylonite bands and veins (Fig. 8). The foliated granodiorite is characterized by 2 cm-thick shear bands with variable but steep orientations; asymmetric white micas indicate dextral shear with some shear bands. Occasionally, brittle fractures cut through and slightly offset these shear bands suggesting these brittle fractures occurred after the shear band formation. Large, >1 m long, fractures are recognizable both in aerial photographs and at the surface; rarely, pegmatite dikes can be used to determine dextral offset in these fractures (Fig. 9 a and b).

Domain 2 is characterized by strong brittle overprinting and cataclasis of ductilely deformed rocks similar to those in Domain 1. Fractured foliated granodiorite grades eastward (i.e. towards the KCF and the center of Engineer’s Point) into foliated breccia, then cataclasite with foliated breccia lithons, and finally foliated gouge (Figs. 9e and 10). Where the foliated breccia grades into the cataclasite with foliated breccia lithons, the lithons are identical to clasts in the foliated breccia and the foliated granodiorite protolith; the orientations of the foliation vary from lithon to lithon and are not consistent.

Domain 3 is only exposed at the very eastern edge of the northern half of the map area. It consists of a friable, very fine grained white and orange gouge zone in sharp contact with the mylonite (Figs 9 d and e). The contact between the gouge and mylonite is roughly straight and strikes approximately 015 degrees, 10 degrees clockwise to the strike of the mylonite zone in Domain 1. Within the gouge of Domain 3 is an exposure of moderately fractured but otherwise unaltered lensoidal rhyolite approximately 10 meters wide on its short axis. The long axis is approximately 40 meters and runs parallel to the mylonite/gouge contact. The contact between Domains 2 and 3 is covered by alluvium and is inferred by the vertical offset suggested of deep ductile fabric against shallow fault gouge across domains 1 and 3.

The lithologies present indicate a complex shear zone transitional from ductile to brittle hosted in the granodiorite protolith. Domain 1 appears to represent an originally deeper, less brittlely deformed part of shear zone now juxtaposed against originally shallower, brittlely deformed parts (domains 2 and 3).

Fracture Analysis

The lengths, orientations and form of brittle fractures were recorded at specific stations Z01-Z10 within Domain 2 (Figs 11-16). The data collected are summarized in Figure 17. Fractures at each station were further divided into groups based upon length (Fig. 18), orientation (Fig. 19), and the presence and color of fill (Fig. 22). Second order analyses by both length and orientation are shown in Figure 23 and by length and fill in Figure 24. Third order analyses by fill, length, and orientation are shown in Figure 25.

Density and length

The fracture density in Z01 is 630 fractures per m2. The median fracture length is 6 cm with a mean of 19.1 cm. A fractal distribution of length considered a best fit line on a log/log plot yields an R2 value of 0.65 and with a k value of -0.52 with an n value of 94 (Fig. 20). Fracture density is highest in Z03 at 862 fractures per m2. Median fracture length is again 6 cm with an average of 13.80 cm. Z03 has an R2 value of 0.64 and a k value of -0.57 with an n value of 103. In Z05 fracture density is 676 fractures per m2 with a median length of 6 cm and an average of 32.48 cm; it has an R2 of 0.43 and a k of -0.47 with an n of 106. Z06 fracture density is 494 fractures per m2; median length is 7 cm, and the mean is 20.84 cm; it has an R2 of 0.65 and a k of -0.47 with an n value of 85. Fracture density in Z07 is 530 fractures per m2 with a median length of 5 cm and a mean of 28.49; it has an R2 of 0.60 and a k of -1.49 with an n of 83. Sites Z01 to Z07 all show fractal fracture length distributions from 1 to 10 cm fracture lengths. Sites Z06 and Z07 are fractal to 50 cm and 30 cm, respectively. Fractures within Z08-Z10 are substantially different with a fracture density of 14 fractures per m2, a median length of 27 cm and a mean of 49.55 cm. Fracture length distributions have an R2 of 0.14 and a k of -0.13 with an n of 55.

Orientation

Fractures show typically two to three preferred orientations within each zone (Figs. 19). A 1% percent contouring of fractures was made and used to determine the strikes and dips of preferred fracture orientations (Fig. 21). The preferred orientations in Z01 are 093, 8°; 227, 11°; and 355, 2°. Preferred orientations in Z03 are 116, 14°; 248, 03°; and 350, 4°. Z05 preferred orientations are 112, 24°; 077, 11°; and 004, 00°. Z06 has only two preferred orientations 110, 4°; and 203, 12°. Z07 has three 137, 26°; 039, 17°; and 265, 3°. Z08-Z10 has only one 277, 24°. All fractures within Z08-Z10 strike NNE and dip near vertical. The fractures in each zone appear to rotate clockwise from Z01 to Z05; in Z06 there are only two sets of preferred orientations that follow the projected clockwise trend for sets II and III.

Fracture fill

Fractures differentiated by fill are shown in (Fig. 22). None of the fractures in Z01 are filled. 17% of the fractures in Z03 are filled with iron oxide and 4% with calcite. 36% of Z05 fractures are

filled; fill is about equally split between iron oxide (11%), calcite (13%) and gouge (8%). 36% of Z06 fractures are filled with gouge (20%) or calcite (13%). 42% of fractures in Z07 are filled with calcite (22%) or iron oxide (20%). 87% of the fractures within Z08-Z10 are filled; 62% of those with calcite, 19% with gouge and 19% with iron oxide. Cross cutting relationships between these fractures are varied and non-systematic.

Fracture length vs. orientation

Fracture orientations within each zone are separated by length in Figure 18. Z01 fractures less than 3 cm in length trend NW/SE. Trends are not apparent in the 3-20 cm range. In those greater than 20 cm there is a tendency towards N/S and E/W oriented fractures. Z03 fractures less than 3 cm do not have a noticeable preference toward any orientation; fractures with lengths between 3 and 20 cm trend to the NW/SE and ENE/WSW, most fractures greater than 20 cm trend to the NW/SE. There is some preference toward a N/S orientation in Z05 fractures less than 10cm long; however, no trends are obvious in fractures with lengths between 10 and 100 cm. Fractures greater than 100 cm trend N/S and E/W. Z06 fractures less than 3 cm long trend approximately NW/SE; those greater than 10 cm trend NNE/SSW. There is no preference in orientation in Z07 fractures less than 3 cm; those greater than 3 cm show a slight tendency towards NW/SE, except for those greater than 100 cm which trend N/S. All fractures in Z08- Z10 trend roughly N/S, there is no preference based upon fracture length.

Fracture fill vs. orientation

Fractures grouped by fill and orientation are shown in Figure 24. Z01 has no filled fractures. Hematite-filled fractures in Z03 have random orientations, the few calcite-filled fractures in Z03 trend NNW/SSE. In Z05 gouge-filled fractures are randomly oriented; those with hematite fill are oriented E/W, whereas those with calcite are oriented N/S. Z06 fractures filled with gouge are oriented NNE/SSW whereas calcite-filled fractures are oriented NNE/SSW or NNW/SSE. In Z07 hematite-filled fractures are generally oriented N/S while calcite-filled fractures are N/S or NNE/SSW. Z08-Z10 fractures are all oriented N/S.

Fracture fill vs. length

Fractures separated by the presence and type of fill are then further differentiated by length (Fig. 22). Open fractures trend towards shorter lengths in all zones. Gouge-filled fractures show no preference to fill based upon length. Hematite-filled fractures only show a preference of length in Z05, where these fractures are typically >100 cm long. Calcite-filled fractures show some preference to longer lengths, particularly in Z07 and Z08-Z10.

Fracture fill vs. length vs. orientation

Fractures separated by fill, length, and orientation are shown in Fig. 25. Open fractures in Z01 that are less than 20 cm long are randomly oriented. Fractures greater than 20 cm are oriented E/W or N/S. Open fractures in Z03 less than 20 cm show no preference in orientation, those greater than 20 cm are oriented NNW/SSE. Z05 open fractures show no preference toward orientation at any length. Z06 open fractures less than 10 cm have no preference in orientation; fractures with lengths between 10 cm and 20 cm are oriented N/S; Z06 open fractures greater than 20 cm in length are too few to be

statistically relevant. Open fractures in Z07 less than 10 cm in length have no preference in orientation, those greater than 10 cm trend N/S. Open fractures in Z08-Z10 have no apparent preference in orientation.

Conversely, the wide range of lengths for gouge-filled fractures does not correlate with a preferred orientation for any specific length. Calcite-filled fractures in Z03 and Z05 have no preference in orientation. Z06 fractures with calcite-fill and lengths between 3 and 10 cm are oriented WNW/ESE, fractures greater than 10 cm in length are oriented NNE/SSW. Z07 fractures less than 100 cm long show no preference in orientation, those with lengths greater than 100 cm are oriented N/S. All calcite-filled fractures in Z08-Z10 trend N/S. Hematite-filled fractures only show preference to lengths in Z05 and Z07. In Z05 hematite-filled fractures greater than 100 cm long trend E/W. In Z07 hematite-filled fractures greater than 100 cm in length trend N/S.

Grain Size Analysis

Grain size analyses were conducted on samples within the friable fault gouge of sites Z08, Z09, and Z10. Results from sieving are shown in Figure 26. The data for Z08 was lost before being recorded. Particles less than 1mm make up close to 40% of the Z09 samples. Z10 samples have a high percentage of 4 mm grains largely due to one large (~2 cm diameter) chunk that did not disaggregate.

The distribution curves and calculated statistics of all particle sizes less than 1 mm in Z08, Z09 and Z10 are shown in Figures 27, 28, and 29, respectively. Z08 and Z10 show similar characteristics with three humps at approximately 600, 100, and 3 μm, have a mean grain size of coarse silt and are coarsely skewed. Z09 is distinctly different (Fig. 28); there are two humps, one at approximately 700 μm and the other at 4 μm, a mean grain size of very fine sand, and is very finely skewed.

X-Ray Diffraction

Detailed intensity curves for each sample with all data through 2Θ = 65° are shown in Figure 30; curves for all sites plotted together are in Figure 31. Samples Z00 – Z10b consist predominantly of quartz (2Θ = 20.65°, 20.85°, and 50.14°), K feldspar and plagioclase (2Θ = 23.69°, 27.76°, and 28.07°), undifferentiated chlorites (2Θ = 6.16°, 12.504°, 18.89°, and 25.37°), undifferentiated micas (2Θ = 8.75° and 24.27°) and composite clays (2Θ = 19.94°). An attempt was made to distinguish between chlorites, micas and clays and is tentative at best. The calculated abundance of each mineral, except micas, relative to other major minerals in that zone is shown in Figure 32 and 33. There are two peaks in every sample at 36.58° and 60.02° that maintain an intensity of 6% and 9%, respectively; these peaks are close to those recognized for ++ +++ several smectites, in particular iron rich saponite (Ca0.3(Fe , Mg,Fe )3(Si,Al)4O10(OH)2•4(H2O)).

Quartz generally maintains its relative abundance through the fault. Feldspars make up 60% of the total rock in the protolith (Z00) and decrease in abundance to less than 5% of the

dark green and grey fault gouge (Z08 and Z10b) and less than 30% of the rest of the fault core in Z05, Z06, Z07 and Z09. Composite clays increase in relative abundance from 9% to 45% and appear to compensate for the loss of feldspar. There is also a steady, if less significant, increase in the abundance of calcite from 2% to 11%. The 8.72° mica peak shows a decrease in abundance into the fault core while the 24.27° peak shows no change.

Mineral abundances were also normalized relative to Z00 (Fig. 33a). Clay and calcite are enriched and increase through the damage zone and fault core. Quartz does not vary. The ratio of clay to plagioclase is shown in Figure 33b. The ratio is consistent through the fault zone, except in Z08 and Z10b where it increases by an order of magnitude relative to other stations. Figures 34a and b show the ratio of clay to plagioclase through the fault zone. There is no correlation between the two; however there are two distinct peaks in Z08 and Z10b.

X-Ray Fluorescence Whole Rock Geochemistry

Major element abundances in each zone are shown in Table 2 and trace element abundances in Table 3. Figure 37 depicts element-zirconium ratios normalized to the inferred protolith (Z00). Ca and Sr covary being depleted in Z02, Z10a, and Z10b, and enriched in Z03 (Fig. 37a). Na does not consistently covary with Ca and Sr; instead it is strongly depleted in Z08, Z10a and Z10b, and is strongly enriched in Z09. K and Ba are strongly covariant and do not vary significantly. Water-soluble metals including U, Cu, and Cr are typically slightly enriched except in Z06 but otherwise do not covary well (Fig. 37b). Cr is significantly enriched in Z08, Z10a, and Z10b, but depleted in Z09; it therefore anti-correlates with Na.

Figure 38 shows a broader selection of Z00-normalized trace elements. Samples Z01- Z07 and Z09 and Z10a covary strongly; Z08 and 10a covary with each other but not with the majority of samples. Sample Z09 is the least enriched (or most depleted) in the majority of elements. All samples show minor to moderate depletion in Ba and Sr. All samples show minor enrichment in Y and Cu, and moderate to major enrichment in U. Zr and Ga are neither enriched nor depleted. Samples Z08 and Z10a are the dark green gouge in the fault core; they are both highly enriched in metals Cr, Sc, Y, Cu, and U.

Scanning Electron Microprobe Petrography

SEM petrography of polished thin sections was conducted for two primary purposes: (1) to observe mineralogical alteration and (2) to observe microscopic structures within the damage zone and outer fault core (Z00-Z07). Z08 – Z10 proved too friable to produce suitable thin sections.

Mineralogical Alteration

Alteration of four of the five primary minerals (albite, oligoclase, orthoclase and biotite) increases with proximity to the fault core (Fig. 39). Oligoclase is present in Z00 only and is inferred to be completely altered to albite in Z01 and Z02. Albite alteration to kaolinite and white mica is observed in Z01, Z02 and Z07 (e.g., Fig. 40 and Fig. 41) and is tentatively inferred to be occurring throughout the fault zone. Orthoclase remains unaltered within the damage zone and begins to alter in the fault core first to albite and then to quartz and white mica (Fig. 40). Biotite alters to white mica (muscovite or phengite) and chlorite at the periphery of the damage zone with full chloritization by Z02. Second order alteration of chlorite to white mica and silica occurs within the crystals along planes parallel to cleavage in the outer part of the damage zone and along planes both parallel and perpendicular to cleavage in the inner part of the damage zone (Figs. 42 and 44). Alteration of chlorite also occurs on the periphery of chlorite-filled fractures (Fig. 45). Some quartz crystals in the damage zone and fault core contain S, Au and Pb; this suggests that these crystals are secondary to those that crystallized in the protolith.

Micro-structure

Microstructural deformation in the damage zone begins with heavy fracturing and accompanying dissolution of Ca-plagioclase and minor fracturing of quartz (Fig. 43). Fractures are both intra- and inter- granular. Brittle deformation increases in intensity first in Na plagioclase and later in orthoclase and quartz. Fractures are typically (1) open at the periphery of the damage zone; (2) filled predominantly with calcite in Z01 and Z02, and (3) filled with calcite, hematite and occasional pyrolusite, (a manganese oxide found in hydrothermal deposits), in the rest of the fault zone. In Z01, and then throughout the damage zone, chlorite shows ductile deformation in bent cleavage planes (Fig. 44).

Thin (~1 cm thick) cataclasite bands are present in the margins of the damage zone at Z05, and increase in thickness through Z07 (Figs. 45, 46, 47, and 48). The microbreccia is very poorly sorted and consists of quartz, calcite, white mica, albite and orthoclase at all scales. The brecciated clasts are typically angular and in some instances loosely grouped by composition (Figs. 47 and 48). These clasts are spaced and no obvious ‘cement’ exists to hold them in place. Albite within the fault core that is altering to clay is cut by veins of calcite and hematite (Fig. 40).

Interpretation and Discussion

Lithology

Engineer’s Point exposes the Quaternary Kern Canyon Fault (KCF) hosted within variably altered and deformed rocks of the proto-Kern Canyon Fault (pKCF) shear zone. The lithologies exposed in domains 1, 2, and 3 probably represent parts of the pKCF that have been exhumed differently and now occur adjacent to one another. Domain 1 is exposed in the footwall of two obliquely converging normal faults (i.e. a horst), with domains 2 and 3 on the hanging-walls of each fault, respectively (Fig. 8). Domains 2 and 3 contain lithologies typical of shallow-level shear zones transitioning from ductile to brittle behavior (Sibson, 1977): (1) fractured protolith (Fig. 8); (2) bands and lenses of foliated breccias, cataclasites, and gouges (Figs 8 and 10), (3) separated by faulted or sheared contacts (Fig. 9c, d), and (4) over-printed by discordant fractures (Fig. 9b). In contrast, Domain 1 is composed of sheared and fractured protolith that transitions rapidly into protomylonite, and then to mylonite with veins of ultramylonite (Fig. 8). Domain 1 is over-printed by the same discordant fractures as domains 2 and 3 but does not preserve non- or weakly-lithified cataclastic rocks. Domain 1, therefore, is composed of shear zone rocks formed during ductile deformation, rather than at the ductile- brittle transition (Fig. 3).

The ductile-brittle transition (e.g., Fossen, 2010) is not a simple fixed depth in the crust as shown in Figure 5, and is moderated by parameters such as fluid pressure and composition, temperature, and strain rate. The pKCF rocks have clearly experienced significant and complex fluid-enhanced alteration events (e.g., phyllitic and argillic alteration,Fig. 50) and enrichment in fluid-mobile metals (Fig. 37b); therefore the precise role of fluids is unconstrained. The pKCF is inferred to have been active, and perhaps initiated, in the Cretaceous (ca. 95 Ma; Nadin, 2007) during construction of the Sierra Nevada batholith (Busby-Spera and Saleeby, 1990), and active until at latest 86 Ma (Nadin, 2007). The pKCF therefore developed in a high-temperature crustal environment, presumably at metamorphic conditions even at relatively shallow depths (i.e. low pressures). The presence of andalusite and sillimanite-bearing metamorphic rocks in adjacent roof pendants (Saleeby et al., 2008) is testament to the high-temperature, low-pressure conditions during the Cretaceous. Accepting that such high temperatures were prevalent during the formation and early development of the pKCF implies that the brittle-ductile transition was elevated to shallower depths as the strength of the lithosphere is primarily controlled by the temperature-dependent rheology of crustal rocks. Therefore, the brittle-ductile transition could have been less than 10 km from the surface.

It is, however, reasonable to infer that Domain 1 formed at deeper and hotter conditions than domains 2 and 3 through the presence of mylonites and sheared protolith rather than exclusively cataclastic rocks (Fig. 8). In the absence of evidence to the contrary, I tentatively infer that Domain 1 is a discrete piece of the pKCF shear zone from the upper-middle to lower-

upper crust (Fig. 3); potentially as deep as 10 – 15 km depth, but probably shallower. Domains 2 and 3 on the other hand were formed at undoubtedly shallow depths within the pKCF (i.e. < 10 km depth), and corresponding lower temperatures and higher rock strengths.

All three domains are over-printed by the horst-forming normal faults (Fig. 8) and subordinate fracture sets (Fig. 9b). The eastern of the two faults (Fig. 8) is inferred to be the surface trace of the Quaternary KCF or a recently abandoned branch of it (Nadin and Saleeby, 2010). If this is correct then Quaternary, or possibly Miocene (Saleeby et al., 2009), brittle fault motions are likely responsible for (1) juxtaposing the different domains, and (2) that the domains themselves are older than that brittle fault motion (e.g., Nadin, 2007). This interpretation is supported by the observation that the modern KCF is an east-side-down normal fault (Nadin and Saleeby, 2010; Brossy et al., 2012), and therefore, Domain 1 is in the (presumably) uplifted footwall. Furthermore, the formation of mylonites and other foliated and annealed fault rocks is favored by higher temperatures because of enhanced intercrystalline diffusion, especially if catalyzed by fluids. Suitable fluid-saturated, high-temperature conditions existed in the pKCF and wall-rocks during the Cretaceous, and are unlikely to have existed in the Cenozoic (Saleeby et al., 2009).

In conclusion, the pKCF at Engineer’s Point is interpreted to have been disrupted by the Quaternary KCF normal faulting such that domains of pKCF rocks from different depths and metamorphic conditions are now juxtaposed against each other. Lithologies in Domain 1 were formed at elevated temperatures at or immediately below the ductile-brittle transition. The ductile-brittle transition was likely shallower than in typical continental lithosphere (e.g., Fig. 3) due to the great thermal gradient associated with formation of the contemporaneous Sierra Nevada batholith. Domains 2 and 3 were formed under exclusively brittle deformation conditions. All three domains are over-printed by relatively young fractures associated with the Quaternary KCF.

Alteration

Rocks in the pKCF and Domain 2 specifically are altered from their original compositions and lithologies. The alteration history of the pKCF rocks has not been described before, and knowledge of the alteration history is limited to recognition of vein-hosted gold- silver mineralization along strike from Engineer’s Point at the Big Blue Mine (Prout, 1940). Mineralization and associated metasomatism are expressed as pervasive alteration of cataclastic pKCF rocks (breccia, cataclasites, and gouges) and demonstrably later cross-cutting veins (e.g., Fig. 16).

Pervasive alteration of the pKCF lithologies becomes more intense towards the fault core and correlates with decreasing grain size and increase in cataclastic deformation (breccia to cataclasite to gouge). Increases in alteration intensity are recognized using a range of geochemical and mineralogical values: (1) increasing loss-on-ignition (Table 2); (2) increasing

clay/plagioclase ratio (Fig. 31); (3) increasing clay and calcite content (Fig. 33); and (4) decreasing feldspar content (Fig. 33).

Two types of pervasive alteration are inferred: phyllic and argillic (Fig. 39). Phyllic alteration is the result of the circulation of high-temperature, low pH hydrothermal fluids leading to the alteration of (1) biotite to white mica (muscovite, phengite, sericite) and chlorite (Fig. 39); (2) chlorite to white mica and quartz (Fig. 39); (3) plagioclase (oligoclase) to albite; (4) K- feldspar (orthoclase) to albite; (5) albite to white mica and quartz; and (6) precipitation of secondary quartz enriched in Au. The various white micas are difficult to distinguish by XRD methods (e.g., Fig. 30) but are confirmed by electron dispersive spectrometry (EDS) and backscatter electron microscopy (Fig. 42). Phyllic alteration appears to have affected all parts of the pKCF at Engineer’s Point. Argillic alteration is the result of the circulation of low-temperature (i.e. meteoric), high pH water in the shallow subsurface (supergene) and is expressed in several sites by the breakdown of albite to kaolinite (e.g., Fig. 41). Argillic alteration is recognized in sites both distal and proximal to the fault core and I tentatively infer that it is ubiquitous across all sites in the pKCF (Fig. 39).

My interpretation of argillic alteration is supported by the differing behaviors of Na and K between samples Z08 and Z10a, and sample Z09. Z08 and Z10 are distinctive dark green, incredibly fine-grained (Figs. 27 and 29), gouge bands separated by a thick band of foliated, orange, fine-grained gouge (Z09). Samples Z08 and Z10b are very clay-rich (clay / plagioclase ratio ≥10; Fig. 34) compared to all other samples including Z09 (clay / gouge ratio ~1). Samples Z08 and Z10 are distinctly depleted in Na (Fig. 37a) relative to the protolith (Z00) but not in K, Ca, Ba, and Sr. Conversely, Z09 is very enriched in Na but not in K, Ca, Ba, and Sr. The mobility of Na but not the other base metals indicates the loss of albite (Na-rich feldspar) in Z08 and Z10. K and Ba are buffered by growth of white mica (e.g., muscovite) and Ca and Sr are buffered by precipitation of calcite; the alumni-rich residue crystallizes as kaolinite. The enrichment in Na in Z09 (Fig. 37a) may reflect horizontal transfer of Na from the adjacent dark green gouge bands (Z08 and Z10), possibly due to lateral thermal and water flux gradients. Furthermore, large magnitude fluid flow through the dark green gouge bands is supported by major enrichment of water-soluble metals including Cr, Cu, and U (Fig. 38).

All sites within the pKCF on Engineer’s Point appear to have experienced phyllic and argillic alteration. Phyllic alteration is typically followed and over-printed by argillic alteration as the alteration zone is exhumed and cooled, and introduced into the meteoric environment. Demonstrating a retrograde reaction assemblage where argillic alteration over-prints older phyllic mineral reactions has not been possible in the scope and timeframe of this study; however, future studies have potential. Prograde (i.e. argillic to phyllic) reactions are not observed in any pKCF samples, so a retrograde evolution is a reasonable conclusion as the pKCF must have been exhumed from some depth (e.g., Domain 1) to the shallow subsurface were meteoric water-driven reactions occur.

Veins are filled by calcite (white), hematite (red), and clay, or are not filled (“open fractures”). Open fractures predominate in sites more than 15 m away from the fault core (site Z10) especially at short and medium fracture lengths (Fig. 22). Open fractures are absent in the 5 m closed to the fault core where the pKCF is gouge-dominated. Calcite veins are only observed within 70 m of the fault core and are only dominant in the most proximal site (Z10). Calcite veins occur at all lengths and have a preferred orientation of NNW-SSE oblique to the pKCF and KCF (Fig. 25). Hematite and clay-filled veins do not show significant trends in length or orientation except in proximal to the fault core where hematite-veins are preferentially orientated NNW-SSE like the adjacent calcite veins. The transition from dominantly open fractures to calcite veins, and to a lesser extent hematite veins, towards the fault core is interpreted to be the result of mineral precipitation from Cenozoic hydrothermal fluids concentrated in fractures within the fault core rather than disseminated fluid-flow throughout the shear zone. This mineralization is inferred to be relatively young (i.e. not Cretaceous) because it is always vein-hosted (i.e. brittle deformation) and it cross-cuts both ductile and earlier brittle deformation features (e.g., foliation planes) and lithologies (e.g., domains 1 and 2). Calcite and hematite veins probably formed contemporaneous with each other and with fracturing of the pKCF. This is best demonstrated in Figure 49 where alternating calcite and hematite bands fill the margins of a contemporaneous fracture. If this is interpretation is correct then oxidized, carbonate-rich fluids hydro-fractured the pKCF rocks and precipitated calcite and hematite in an alteration assemblage similar to that encountered in the later stages of the formation of iron oxide copper gold (IOCG) deposits (Fig. 50; Groves et al., 2010) and some skarns. IOCG deposits are exclusively associated with silicic magmatic bodies so, if as seems likely, these veins are relatively young, then IOCG-type mineralization is not to be expected. The origins of these mineral veins deserve further study.

Three distinct types of alteration and mineralization are identified in the pKCF. Phyllic and argillic alterations are typical of hydrothermally-altered fault zones (e.g., Fiebig and Hoefs, 2002; Morad et al., 2009; Arancibia et al., 2014). IOCG-like mineralization is not documented as being associated with major faults and rather with plutonic intrusions. Argillic and to a lesser extent phyllic alteration are important processes in the evolution of major crustal shear zones because they directly weaken the rocks present. Hydrothermal alteration is enhanced by contemporaneous deformation and grain size reduction because (1) increasing lithostatic and hydrostatic stresses increase mineral solubility (dissolution) in the host rock, and (2) grain size reduction and elevated temperature increase the effectiveness of diffusion. Reaction (i.e. alteration) rates increase, therefore, in actively deforming shear zones. The breakdown of relatively strong minerals (e.g., feldspars) to phyllosilicates (i.e. micas and clays) weakens rocks, and is not compensated for by the addition of quartz and calcite. The possible presence of the smectite mineral saponite in all pKCF samples (Fig. 31) is important because saponite has been identified to increase the potential for creep (Lockner et al., 2011; Richard et al., 2013). Therefore there is a positive feedback where continued deformation in the presence of a

hydrothermal fluid reduces grain size and alters strong rocks to comparatively weaker rocks that, in turn, localize more strain and sustain deformation (Fossen, 2010).

The pKCF appears to have followed this pattern where phyllic, and possibly then argillic, alteration occurred during ductile and ductile-brittle deformation. Exhumation of the pKCF to the near-surface continued or initiated argillic alteration and was contemporaneous with continued (Cretaceous) or renewed (Miocene) cataclasis to the dark green gouges (Z08 and Z09) in the fault core. Much younger, likely Quaternary KCF deformation, led to the development of calcite and hematite-filled fractures over-printing both the argillic and phyllic alterations. It seems likely that all deformations within the pKCF and KCF were associated with hydrothermal flow and alteration or mineralization.

Grain Size

Gran size analysis of the fault core gouge bands reveals differences between Z08 and Z10 (dark green) and Z09 (orange). Z09 and Z10 are similar in the sieved sand and fine pebble-sized fractions (1 – 4 mm diameter; Fig. 26). In the ≤ 1 mm fraction analyzed by laser particle size analyzer differences emerge between the dark green gouges (Z08 and Z10) and the intervening orange gouge (Z09). Sample Z08 shows a characteristic and very atypical trimodal grain size distribution (Fig. 27). Samples Z09 and Z10 show atypical bimodal grain size distributions (Figs 28 and 29). In all three samples the primary mode grain size is 677 μm. Samples Z08 and Z10 differ from Z09 in the secondary and tertiary modes. The secondary mode is 2.7 μm in Z08 and Z10 in contrast to 5.4 um in Z09. Z08 has a prominent tertiary mode at 112 μm; this corresponds to noticeable “humps” in Z09 and Z10 where the >100 μm ranges are negatively-skewed, and all three are probably related.

The presence of a significant proportion of sand-sized particles (>100 μm) is atypical of fault gouges (e.g., Engelder, 1974). Grain size distributions evolve to smaller mean sizes with deformation. The rate of grain size reduction is related to strain, strain rate, temperature, and fluid composition. Assuming that a plutonic protolith starts with a coarse, equigranular (i.e. unimodal) grain size distribution, homogeneous deformation would gradually but uniformly reduce the grain size. However, heterogeneous deformation where the protolith first fractures into large (i.e. larger than the component crystals) blocks is likely; this introduces poor-sorting in the fault breccia that continues during grain size reduction to cataclasite, and eventually gouge. Mixing between cataclasite and gouge bands and the development of later gouge bands over cataclasite will produce the same complex grain size distributions. Most studies of gouge grain size distributions are limited to very well-sorted, very fine-grained, experimentally-produced gouges (e.g., Engelder, 1974; Marone and Scholz, 1989; Wilson et al., 2005; Keulen et al., 2007) and I have been unable to find a similar study of natural gouges like those in the pKCF. I tentatively infer that the gouges of the pKCF are relatively immature (i.e. coarse and poorly

sorted) and have developed from cataclasite but are not so far evolved that they would be typical of gouges elsewhere.

Structure

Fracture analysis reveals distinct differences between the damage zone and fault core. Fracture length distributions (Fig. 18) in samples from the damage zone (Z01 to Z07) are bimodal and strongly skewed to shorter fracture lengths (2 – 4 cm); long (>50 cm long) fractures are abundant but fractures between 15 – 50 cm are uncommon. Abundant short fractures in two or three orientations form dense networks (Fig. 23). In contrast, fractures in the fault core (Z08 – Z10) are (1) unimodal with a mode of >50 cm-long (Fig. 18); (2) have a low fracture density (Fig. 17); and (3) a strong N-S preferred orientation (Fig. 19). The low fracture density and high unimodal fracture length characteristic of the fault core is typical of new faults disrupting otherwise weakly fractured rock (i.e. the gouge bands of the fault core). The soft gouge bands formed during deformation and alteration within the pKCF core probably overprinted earlier fracture networks preserved in the damage zone (Z01 – Z07). Development of the Quaternary KCF likely generated a new set of through-going, low density fractures.

The various vertical fracture orientations preserved in the damage zone (Z01 – Z07) are typical of long-lived strike-slip shear zones (e.g., Twiss and Moores, 2007; Fossen, 2010). Fracture orientations in Z01 fit those of antithetic Reidel shears, reverse thrusts, and P structures in right-lateral strike-slip shear zones (Twiss and Moores, 2007). The same three orientations are found mirrored in analyses of left-lateral strike-slip faulting in a Sierra Nevadan pluton to north of Lake Isabella (Griffith et al., 2009).

The principal orientations of fractures rotate clockwise from Z01-Z07. Strain within a transtensional shear zone can allow for pre-existing fractures and faults to rotate in the direction of shear (e.g., Waldron, 2005; Fig. 51). The degree of rotation of each fracture is dependent upon the angle the fracture initially made with the shear plane, the amount of shear experienced by the fault zone, and the angle the transtensional vector makes with the pure strike-slip plane. This model suggests that with enough shear all fractures should become parallel to the fault plane; it also explains the trend seen in fractures in the pKCF damage zone where fractures all rotate with a dextral sense of shear and by differing angles (Fig. 52). Most notably, fracture set II does not rotate once it becomes parallel to the fault plane, and fracture set III appears to rotate until it is parallel to set II and becomes impossible to distinguish from set II. This is inferred to be due to both sets now paralleling the fault core.

Summary

The exposure at Engineer’s Point provides insight into a deep, long-lived shear zone that has been reactivated numerous times throughout its lifespan as it has been exhumed to shallower and shallower depths. Three distinct alterations have been identified: (1) a low pH high temperature phyllic alteration exhibited by alteration of biotite to white mica and chlorite, chlorite to white mica and quartz, plagioclase to albite, K-feldspar to albite, albite to white mica and quartz, and precipitation of secondary quartz enriched in Au; (2) a high pH low temperature alteration exhibited by alteration of albite to kaolinite; and (3) possible IOCG alteration inducing iron-oxide veins and precipitation of gold-bearing quartz. Fractures suggest alternating fluid composition through recent (KCF) fractures. Fracture sets through the fault zone suggest post- brittle deformation shear. Grain size distribution through the core of the pKCF is atypical and requires further analyses. The pKCF undoubtedly strikes through Engineer’s Point; its core hosts the Quaternary, brittle KCF.

Long lived fault zones can be reactivated over and over under different tectonic stress regimes, depths, and fluid compositions. It is, however, possible to differentiate deformation events using a variety of analyses. It is suggested that now that these different patterns have been established for each analysis, perhaps further studies can be conducted to allow for an integrated, comprehensive deformation history of the pKCF zone at Engineer’s Point.

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(after Calculated Cook et Relative Peak Intensity Intensity al. Abundance 1975) distance Sample from total total total quartz plag. calcite quart plagio. calcite SUM quartz plag. calcite clay/plag # fault clay clay clay core (m) Z00 1000 12395 822944 802539 24646 247900 822944 1605078 47320 2723242 9.10 30.22 58.94 1.74 0.15 Z01 173 31155 894210 521190 65435 623100 894210 1042380 125635 2685325 23.20 33.30 38.82 4.68 0.60 Z02 126 29454 883282 271815 77882 589080 883282 543630 149533 2165525 27.20 40.79 25.10 6.91 1.08 Z03 70 27022 699222 469201 64942 540440 699222 938402 124689 2302753 23.47 30.36 40.75 5.41 0.58 Z04 55 33896 865615 336133 31335 677920 865615 672266 60163 2275964 29.79 38.03 29.54 2.64 1.01 Z05 18.75 25766 678661 223928 109556 515320 678661 447856 210348 1852185 27.82 36.64 24.18 11.36 1.15 Z06 15.45 37165 843147 341993 54380 743300 843147 683986 104410 2374843 31.30 35.50 28.80 4.40 1.09 Z07 12.65 32629 876656 220866 132128 652580 876656 441732 253686 2224654 29.33 39.41 19.86 11.40 1.48 Z08 5.86 43381 722783 34865 82808 867620 722783 69730 158991 1819124 47.69 39.73 3.83 8.74 12.44 Z09 1.5 32833 747148 209865 113638 656660 747148 419730 218185 2041723 32.16 36.59 20.56 10.69 1.56 Z10A 0.01 30736 611608 275322 92514 614720 611608 550644 177627 1954599 31.45 31.29 28.17 9.09 1.12 Z10B 0 45340 713096 29223 99455 906800 713096 58446 190954 1869296 48.51 38.15 3.13 10.22 15.52

Table 1: XRD determined peak and calculated distributed intensity values, as described by Cook et al., 1975, used to quantify relative abundance of major minerals. Relative abundances are graphed in Figure 32 to show trends. Ratio of clay to plagioclase is also calculated for each zone.

Z00 Z01 Z02 Z03 Z04 Z05 Z06 Z07 Z08 Z09 Z10a Z10b

Unnormalized Major Elements (Weight %): SiO2 65.10 63.68 66.09 62.10 66.75 64.16 64.88 66.90 60.78 68.08 65.77 61.20 TiO2 0.655 0.614 0.676 0.578 0.467 0.531 0.559 0.501 0.568 0.326 0.466 0.612 Al2O3 16.70 15.52 16.48 14.74 15.39 13.57 14.06 12.81 13.69 12.02 13.64 14.51 FeO* 3.62 3.33 3.69 3.69 2.91 2.89 3.37 2.88 2.94 1.88 3.15 3.54 MnO 0.062 0.076 0.066 0.066 0.041 0.056 0.062 0.060 0.058 0.057 0.058 0.053 MgO 1.32 1.31 1.27 1.40 1.22 1.16 1.36 1.18 1.44 0.72 1.20 1.40 CaO 3.80 3.42 0.99 4.62 2.02 4.95 3.78 4.20 5.93 5.32 3.94 4.64 Na2O 4.06 3.40 2.44 3.25 2.56 3.11 2.88 1.74 0.77 2.89 1.83 0.16 K2O 2.41 3.06 3.63 2.70 4.33 2.49 2.73 2.69 2.86 2.08 2.87 3.83 P2O5 0.336 0.147 0.153 0.140 0.116 0.125 0.132 0.119 0.113 0.087 0.106 0.104 Sum 98.05 94.56 95.49 93.28 95.79 93.04 93.81 93.07 89.15 93.46 93.02 90.05 LOI % 0.94 4.58 3.32 5.60 3.30 5.70 4.87 5.38 9.37 5.81 5.92 8.56 Normalized Major Elements (Weight %): SiO2 66.39 67.34 69.21 66.58 69.68 68.96 69.17 71.88 68.18 72.84 70.70 67.96 TiO2 0.669 0.650 0.708 0.620 0.487 0.571 0.596 0.538 0.638 0.348 0.501 0.680 Al2O3 17.03 16.41 17.26 15.80 16.06 14.58 14.98 13.76 15.36 12.86 14.66 16.11 FeO* 3.69 3.53 3.86 3.95 3.04 3.10 3.60 3.09 3.30 2.01 3.39 3.93 MnO 0.063 0.080 0.069 0.071 0.043 0.060 0.066 0.064 0.065 0.061 0.063 0.059 MgO 1.35 1.39 1.33 1.50 1.27 1.25 1.45 1.27 1.62 0.77 1.29 1.56 CaO 3.88 3.62 1.04 4.95 2.11 5.32 4.03 4.51 6.65 5.69 4.24 5.15 Na2O 4.14 3.59 2.55 3.48 2.68 3.34 3.07 1.87 0.87 3.10 1.97 0.18 K2O 2.46 3.24 3.80 2.90 4.52 2.68 2.91 2.89 3.20 2.22 3.09 4.25 P2O5 0.342 0.155 0.160 0.150 0.121 0.134 0.140 0.127 0.127 0.093 0.114 0.115 Total 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00

Table 2: Unnormalized and normalized weight percentages of major elements as determined by X-ray fluorescence analysis. Data is graphed in Figure 37 to demonstrate trends in the data.

Z00 Z01 Z02 Z03 Z04 Z05 Z06 Z07 Z08 Z09 Z10a Z10b

Unnormalized Trace Elements (ppm): Ni 3 1 2 2 1 3 3 15 7 3 1 16 Cr 5 9 9 9 7 8 9 8 32 5 7 71 Sc 4 5 6 5 6 5 6 4 7 4 5 11 V 55 57 58 56 52 49 55 51 58 31 46 73 Ba 733 535 542 424 700 442 459 460 387 318 355 372 Rb 80 113 136 99 127 84 90 101 150 72 117 203 Sr 549 316 100 206 216 216 228 188 352 289 226 214 Zr 152 132 137 121 99 115 121 113 148 79 101 208 Y 6 14 13 11 8 11 10 10 13 11 10 22 Nb 5.6 8.6 9.6 8.0 5.9 7.5 7.5 6.5 9.3 6.0 6.7 12.3 Ga 22 18 21 17 18 15 17 16 16 12 16 19 Cu 2 2 4 5 7 7 4 7 8 3 9 19 Zn 103 65 69 68 63 62 72 52 51 36 76 62 Pb 14 11 13 7 12 15 12 7 18 15 19 17 La 25 17 15 23 8 9 12 14 23 16 20 34 Ce 45 38 36 37 16 23 26 29 48 25 30 65 Th 8 10 10 11 4 5 9 8 11 8 15 15 Nd 15 18 20 17 9 12 12 14 21 12 14 29 U 0 2 2 1 1 3 1 1 3 2 3 5 Cs 72 41 As >/= 32 375 148 36 20 42 110 24 44 70

Table 3: Trace element abundances (parts per million) as determined by X ray fluorescence.

Figure 1: Fault zone architecture showing several fault cores of gouge, mylonite and cataclasite within a larger damage zone that make up an entire fault zone, from Caine et al., 1996

Figure 2: Different fault rock types as grouped by Sibson, 1977. First-order differentiation is by cohesiveness of rock, the second-order is by proportion of matrix. Pulverized rocks are included as a distinct group after Mitchell et al., 2011.

Figure 3: Fault zone differences with depth. Ductile mylonitic rocks are formed when temperature and pressure allow rocks to shear. At shallower depths and lower temperature/pressure regimes rocks deform brittlely. If pressure is high enough fluids will precipitate cement and ‘lithify’ the fault rocks. At shallow depths the rocks remain incohesive. From Fossen, 2010

Figure 4: Regional tectonic framework discussed in text. At Lake Isabella the two Kern Canyon fault bifurcate; the older pKCF travels south while the younger KCF continues to the southwest. Modified from Nadin and Saleeby, 2010. Locations for Msb and sSed from Maheo et al., 2009

Figure 5: Earthquake epicenters recorded by the Northern and Southern California Seismic Networks from 1981 to 2008 (Brossy et al., 2012). F LI – Lake Isabella; WB – Walker Basin; BF – Breckenridge fault; GF – Garlock fault; WWF – White Wolf fault

Engineer’s Point

Figure 6: Sketch map of Lake Isabella and Engineer’s Point. Locations of sample sites are indicated as Z00 through Z08-Z10B. The lake is shown in blue; the main and auxiliary dams are in black.

Figure 7: Analyses performed for each location. Note that for fracture analysis one analysis covered stations Z08-Z10b. The friable nature of Z08-Z10b allowed for grain size analyses but not for thin sections construction to conduct SEM analyses.

100 m

Figure 8: Map of fault rock lithologies and interpreted structures at Engineer’s Point. A NW/SE trending fault is inferred between the ductile deformed rocks in the north and the brittlely deformed rocks in the south.

a) b)

c) d)

e) f)

Figure 9: Various structures and contacts exposed at Engineer’s Point. a) A dike offset along ENE-WSW trending fracture. b) ENE trending fractures with sinistral offset observable in aerial photographs. c) Contact between Z07 (boudinaged granodiorite) and Z08 (dark green fault gouge). d) Contact between mylonite and fault gouge in northeast map area. e) Another view of mylonite/gouge contact with dacite on the far east of picture (view is looking north). f) Ultramylonite of pKCF

Figure 10: Smaller scale map of Domain 2. Sample sites for fracture and chemical analyses are shown for Z05, Z06 and Z07. Sites for structural data for Z08-Z10 are also shown. Chemical and grain size analyses were conducted through four sites through the orange and green and dark green and grey gouges of Z08-Z10. Inset is view looking NNE from the southeast side of the map.

Figure 11: Area Z01 fracture analysis. Open fractures are blue. Note three preferred orientations: NNW/SSE, NE/SW and E/W. Length of rope between stakes is 190 cm.

Figure 12: Area Z03 fracture analysis. Open fractures are blue. Filled fractures are not apparent in the photograph. The N/S trending zone about one third of the way down the photograph is interpreted as a ~40 cm thick gouge zone. Length of rope between stakes is 190 cm.

Figure 13: Area Z05 fracture analysis. Open fractures are blue; calcite-filled fractures are white; hematite- filled fractures are red and gouge-filled fractures are yellow. Inset is smaller scale photograph to show preferred orientations for fractures of smaller lengths. Length of rope between stakes is 190 cm.

Figure 14: Area Z06 fracture analysis. Open fractures are blue, calcite-filled fractures are white, and gouge- filled fractures are yellow. Note three preferred orientations: N/S, NNE/SSW and E/W. Length of rope between stakes is 190 cm.

Figure 15: Area Z07 fracture analysis. Hematite-filled fractures are red; calcite-filled fractures are white; gouge-filled fractures are yellow. Note three preferred orientations: N/S, NW/SE, and NE/SW, although anastomosing form makes this somewhat ambiguous. Brecciated granodiorite is visible in the top half of the photograph.

Figure 16: Area Z08-Z10 fracture analysis. Calcite-filled fractures are white, hematite-filled fractures are red, and gouge-filled fractures are yellow. Note the general N/S trend for fractures.

FRACTURE FRACTURE ROSE FRACTURE LENGTH DENSITY STATION ORIENTATION DIAGRAMS ZONE INTERPRETATION (#/m2) (cm)

Undeformed granodiorte hosting Z00 N/A N/A N/A N/A WALL ROCK the pKCF.

30 pKCF damage zone with numerous Z01 630 0 small fractures that indicate dextral 2 8 14 20 35 50+ DAMAGE slip of the entire pKCF. Fracture 30 ZONE orientations rotate clockwise Z03 862 0 further indicating dextral slip. 2 8 14 20 35 50+

Z05 676 0 2 8 14 20 35 50+

30 Fractures indicate both pKCF and

BRECCIA KCF movement; vertical offset and Z06 494 0

2 8 14 20 35 50+ CORE length distinguish the two

30 FAULT Z07 530 0 2 8 14 20 35 50+ FAULT

30 Z08- KCF normal, long and anastomosing 14 0

FAULT FAULT fractures within pKCF gouge Z10 2 8 14 20 35 50+ GOUGE

Figure 17: Summary of fracture data and preliminary interpretations. There are typically three preferred fracture orientations except in Z08-Z10. Fracture densities vary but are an order of magnitude lower in Z08-Z10 compared to the other zones. Fractures show preference to shorter lengths except in Z08-Z10. These data combined suggest the KCF is exploiting the weakened core of the pKCF. 54

Z01 Z03 n = 94 30 30 n = 103

20 20

10 10

0 0

Number of of Number fractures 2 6 10 14 18 25 35 45 of Number fractures 2 6 10 14 18 25 35 45 Length (cm) Length (cm)

Z05 Z06 n = 106 30 30 n = 85 25 25 20 20 15 15 10 10 5 5 Number of of Number fractures 0 of Number fractures 0 2 6 10 14 18 25 35 45 2 6 10 14 18 25 35 45 Length (cm) Length (cm)

Z07 Z08-10

n = 83 30 30 n = 55 25 25 20 20 15 15 10 10 5 5

0 of Number fractures 0 Number of of Number fractures 2 6 10 14 18 25 35 45 2 6 10 14 18 25 35 45 Length (cm) Length (cm)

Figure 18: Fracture length distribution by station. Z01 through Z07 have tendency toward short fracture lengths (i.e. less than 15 cm), while Z08-Z10 have longer fracture lengths (i.e. greater than 45 cm).

N = 94 N = 103 N = 106 Z01 Z03 Z05

N = 85 N = 83 N = 55

Z06 Z07 Z08-Z10 Figure 19: Rose diagrams of fracture orientations for each zone. There are generally three preferred orientations for each zone except in Z08-Z10, which has only one.

100 Z01 100 Z03

n = 94 n = 103

2 2 10 10

per m per -0.57 y = 7.768x-0.515 m per y = 11.291x R² = 0.6474 R² = 0.6428 number of of number fractures number of of number fractures

1 1 1 10 100 1000 1 10 100 1000 Fracture length (cm) Fracture length (cm)

100 Z05 100 Z06

n = 106 n = 85

2 2 -0.388 10 y = 5.9359x 10 y = 7.5147x-0.465 per m per

R² = 0.4305 m per R² = 0.645 number of of number fractures number of of number fractures

1 1 1 10 100 1000 1 10 100 1000 Fracture length (cm) Fracture length (cm)

100 Z07 100 Z08-

n = 83 Z10

2 n = 55 2

10 10 y = 1.9988x-0.129 per m per per m per y = 7.6523x-0.494 R² = 0.1363 R² = 0.599 number of of number fractures number of of number fractures

1 1 1 10 100 1000 1 10 100 1000 Fracture length (cm) Fracture length

Figure 20: Fracture length distribution on a log-log scale.

ALL pKCF I pKCF II pKCF III KCF

Z01

N = 94 N = 11 N = 17 N = 19

Z03

N = 106 N = 20 N = 6 N = 26

Z05

N = 103 N = 19 N = 17 N = 18

Z06

N = 85 N = 10 N = 26

Z07

N = 83 N = 12 N = 8 N = 20 Z08 – Z10 N = 44 N = 14

Figure 21: Poles to all fracture orientations for each zone with 1% area distribution used to distinguish trends in orientation. Fracture orientations within the 2% contour line were averaged and are plotted as colored dots.

Open fractures <3 3 to 10 40 10 to 20 20 20 to 50 number 50 to 100 0 100 Z01 Z03 Z05 Z06 Z07 Z10

Clay-filled fractures <3 12 3 to 10

8 10 to 20

number 4 20 to 50 50 to 100 0 Z01 Z03 Z05 Z06 Z07 Z10 100

Hematite-filled fractures <3 12 3 to 10

8 10 to 20 20 to 50 number 4 50 to 100 0 100 Z01 Z03 Z05 Z06 Z07 Z10

Calcite-filled fractures <3 12 3 to 10

8 10 to 20

number 20 to 50 4 50 to 100 0 100 Z01 Z03 Z05 Z06 Z07 Z10

Figure 22: Histograms of fracture lengths for each station. Z10 refers to Z08-Z10 described in earlier figures and text. Open fractures prefer shorter lengths and are absent in Z10. Hematite- filled fractures vary in length while calcite-filled fractures increase in abundance through Z10.

ALL < 3 cm 3 to 10 10 to 20 20 to 50 50 t 100 > 100cm

Z01

N = 94 N = 29 N = 27 N = 12 N = 13 N = 5 N = 4

Z03

N = 106 N = 28 N = 36 N = 19 N = 12 N = 5 N = 3

Z05

N = 103 N = 35 N = 24 N = 14 N = 6 N = 8 N = 11

Z06

N = 85 N = 27 N = 24 N = 10 N = 9 N = 7 N = 4

Z07

N = 83 N = 27 N = 24 N = 7 N = 10 N = 1 N = 10

Z08 – Z10

N = 55 N = 4 N = 8 N = 10 N = 14 N = 8 N = 9

Figure 23: Poles to all fracture orientations for each zone separated by length.

ALL GOUGE? CaCO3 ALL NO FILL FeO FILL FILLED FILL FILL

Z01

N = 94 N = 94

Z03

N = 106 N = 88 N = 18 N = 14 N = 4

Z05

N = 103 N = 66 N = 37 N = 8 N = 12 N = 14

Z06

N = 85 N = 55 N = 30 N = 17 N = 11

Z07

N = 83 N = 48 N = 35 N = 17 N = 18

Z08 – Z10

N = 55 N = 7 N = 48 N = 8 N = 9 N = 31

Figure 24: Poles to all fracture orientations for each zone separated by fill. The most notable trend is towards fill (hematite and calcite) in NNE/SSW trending fractures within stations Z07 and Z08-Z10. 61

OPEN CALCITE-FILL

ALL < 3 cm 3 to 10 10 to 20 20 to 50 50 t 100 > 100cm ALL < 3 cm 3 to 10 10 to 20 20 to 50 50 t 100 > 100cm

Z01 Z01

N = 94 N = 29 N = 27 N = 12 N = 13 N = 5 N = 4

Z03 N = 94 Z03

N = 88 N = 25 N = 31 N = 16 N = 6 N = 4 N = 1 N = 4 N = 3 N = 1

Z05 Z05

N = 66 N = 28 N = 15 N = 6 N = 7 N = 14 N = 5 N = 5 N = 4

Z06 Z06

N = 66 N = 25 N = 17 N = 6 N = 3 N = 16 N = 5 N = 1 N = 3 N = 3 N = 4

Z07 Z07

N = 55 N = 24 N = 14 N = 3 N = 2 N = 18 N = 9 N = 1 N = 3 N = 5

Z08- Z08- Z10 Z10

N = 7 N = 4 N = 3 N = 31 N = 3 N = 7 N = 11 N = 4 N = 6

HEMATITE-FILL

ALL < 3 cm 3 to 10 10 to 20 20 to 50 50 t 100 > 100cm

Z01

Z03

N = 14 N = 3 N = 4 N = 2 N = 3 N = 1 N = 1

Z05 Figure 25: Poles to all fracture orientations for each N = 12 N = 2 N = 2 N = 1 N = 7 zone separated by fill and length. A) Open Z06 fractures typically have no preferred orientation. B) Calcite-filled fractures tend towards two lengths (3-

Z07 10 cm and greater than 50 cm) and strike N/S. C)

N = 17 N = 2 N = 1 N = 3 N = 5 N = 1 N = 5 Hematite-filled fractures only show preference to Z08- length in Z05 and Z07, where they are typically Z10 >100 cm. N = 9 N = 1 N = 2 N = 2 N = 2 N = 2

45 Clump

40 35 30 25 Z09 20 Z10

Percentage of of Total Percentage 15 10 5 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 FINER COARSER Grain Size (mm)

Figure 26: Results of grain size from sieving. Grains less than 1 mm in size make up approximately 40% of Z09 and 15% of Z10. Z10 grain size distribution is skewed by one large clump that did not disaggregate upon sampling.

Figure 27: Grain size distribution of fault gouge in Z08.

Figure 28: Grain size distribution of fault gouge in Z09.

Figure 29: Grain size distribution of fault gouge in Z10.

Z00 Q 90000 P/K 80000

70000 60000 M 50000

40000 30000 Q M? 20000 P K Ca Ca Ca Sm(?) Q Sm(?) 10000

0 0 10 20 30 40 50 60 70 2Θ

120000 Q Z01

100000

80000 P/K 60000 M Ch 40000 M Ch Q ? Ca 20000 P K Ca Ca Sm(?) Q Sm(?)

0 0 10 20 30 40 50 60 70 2Θ

Q 100000 Z02 90000 80000 70000 60000 M 50000 40000 P/K 30000 Ch Q M? Ch K Ca Ca Sm(?) Q Sm(?) 20000 P Ca 10000 0 0 10 20 30 40 50 60 70 2Θ

90000 Q 80000 Z03 70000 60000 50000 P/K 40000 M 30000 M Ch Ch Q ? 20000 P Ca Ca Ca Sm(?) Q Sm(?) 10000 K 0 0 10 20 30 40 50 60 70 2Θ Figure 30: XRD patterns for Z00-Z03. Q = quartz; M = undifferentiated mica; Ch = chlorite; P = plagioclase; K = K feldspar; Ca = calcite; and Sm = smectite. ? = a peak prominent in all samples that was not matched in these analyses. 67

Q Z04

80000

70000 60000 M 50000

40000 P/K 30000 Ch Q M 20000 Ch K Ca Ca Sm(?) Q Sm(?) P ? Ca 10000

0 0 10 20 30 40 50 60 70 2Θ

Q 80000

70000 Z05

60000 50000 P/K 40000

30000 M Ch Q M 20000 Ch P ? Ca Ca Ca Sm(?) Q Sm(?) 10000 K

0 0 10 20 30 40 50 60 70 2Θ

120000 Q 100000 Z06

80000 M

60000 P/K 40000 Ch Q M? Ch K Ca Ca Ca Sm(?) Q Sm(?) 20000 P

0 0 10 20 30 40 50 60 70 2Θ

120000 Q

100000

80000 Z07 P/K 60000 M 40000 M Ch Ch Q ? Ca 20000 P K Ca Ca Sm(?) Q Sm(?)

0 0 10 20 30 40 50 60 70 2Θ

Figure 30: XRD patterns for Z04-Z07. Q = quartz; M = undifferentiated mica; Ch = chlorite; P = plagioclase; K = K feldspar; Ca = calcite; and Sm = smectite. ? = a peak prominent in all samples that was not matched in these analyses. 68

Q 90000 Z08 80000

70000 60000 M 50000 40000 P/K 30000 Ch Q M Ch K Ca Ca Sm(?) Q Sm(?) 20000 P Ca 10000 ?

0 0 10 20 30 40 50 60 70 2Θ

90000 Q 80000

70000 60000 Z09 50000 P/K 40000

30000 M Ch Q M 20000 Ch ? Ca Ca Ca Sm(?) Q Sm(?) 10000 P K 0 0 10 20 30 40 50 60 70 2Θ

Q 70000

60000

50000 Z10a M 40000

30000 P/K Ch Q M 20000 Ch K Ca Ca Sm(?) Q Sm(?) P ? Ca 10000

0 0 10 20 30 40 50 60 70 2Θ 80000

70000 Q

60000

50000

40000 P/K 30000 Z10b M M 20000 Ch Ch Q Ca Ca Sm(?) Q 10000 P K ? Ca Sm(?) 0 0 10 20 30 40 50 60 70 2Θ Figure 30: XRD patterns for Z08-Z10b. Q = quartz; M = undifferentiated mica; Ch

= chlorite; P = plagioclase; K = K feldspar; Ca = calcite; and Sm = smectite. ? = a peak prominent in all samples that was not matched in these analyses.

meters PLAG MICA MICA

from FC ILLITE KSPAR CALCITE CALCITE CALCITE QUARTZ QUARTZ QUARTZ CHLORITE CHLORITE SMECTITE SMECTITE PLAG/KSPAR COMPOSIT CLAY Z00 1000

Z01 173

Z02 126

Z03 70

Z04 35

Z05 18.75

Z06 13.43

Z07 12.65

Z08 3.86

Z09 1.5

Z10a 0.01

Z10b 0.0

0 10 20 30 40 50 60 70

Figure 31: Compilation of all XRD curves analyzed to highlight trends. Plagioclase, chlorite and the undifferentiated mica peak at 8.75° decrease through the fault zone. Quartz, calcite and the 24.27° mica maintain intensity throughout the entire sample area.

60.00

50.00 y = -3.3238x + 48.411 R² = 0.6146 y = 2.3275x + 14.958 y = 0.3133x + 33.799 R² = 0.6441 R² = 0.092 40.00

total clay

30.00 quartz plag. calcite 20.00

y = 0.683x + 2.8324 R² = 0.5126 10.00

0.00 Z00 Z01 Z02 Z03 Z04 Z05 Z06 Z07 Z08 Z09 Z10A Z10B

Figure 32: Abundance of major minerals (% of total minus complex phyllosilicates), relative to abundance of other minerals at that station. Total clays increase towards the fault core while plagioclase decreases.

7 A)

4 total clay quartz 3 plag. calcite 2 abundance relative abundance relative to Z00

0 Z01 Z02 Z03 Z04 Z05 Z06 Z07 Z08 Z09 Z10A Z10B

7 B)

4 clay 3 quartz plag

abundance relative abundance relative to Z00 2 calcite 1

0 180 160 140 120 100 80 60 40 20 0 distance from fault core [Z10b] (m)

Figure 33: Abundance of major minerals relative to their abundance in Z00: a) by zone; b) by distance from fault core.

a) 100

clay/plag 10 ratio abundance relative abundance relative to Z00

1 Z01 Z02 Z03 Z04 Z05 Z06 Z07 Z08 Z09 Z10A Z10B

1000 b)

100

10 abundance relative abundance relative to Z00

1 180 160 140 120 100 80 60 40 20 0 distance from fault core (m)

Figure 34: Clay/plagioclase ratio at stations through the fault zone:. a) by station; b) by distance from fault core.

Figures 37a and b: Major element and trace element zirconium relative ratios normalized to Z00

10.00

Z01 Z02 Z03 Z04 Z05 Z06 1.00 Z07 Z08 Z09 abundance normalized to Z00 abundance Z10a Z10b

0.10 Ni Cr Sc V Ba Rb Sr Zr Y Nb Ga Cu Zn Pb La Ce Th Nd U

Figure 38: Distribution of trace elements relative to their abundance in Z00.

Figure 39: Hydrothermal alteration of major wall rock elements through the damage zone and periphery of the fault core. 76

Mu Ch Al Ch Ch

Q Q Al Ap

Figure 40: Phyllitic alteration of albite within Z01. Also note alteration of chlorite to muscovite and albite to muscovite and calcite around the periphery of the fracture. Al – albite; Q – quartz; Ap – apatite; Ca – calcite; Ch – chlorite; Mu - muscovite

Mu Al

Al Ka Al

Figure 41: Argillic alteration of albite to kaolinite in Z07. Calcite and muscovite-filled fractures cut through and probably post- date the kaolinization. Al – albite; Ca – calcite; Ka – kaolinite; Mu - muscovite

Figure 42: Phyllitic alteration of chlorite pseudomorph (Ch) of biotite in Z02 partially altered to quartz (Q) and muscovite (Mu) along cleavage planes and sub perpendicular fractures.

Q Ol

Bi Ol

Figure 43: Fracturing in Z00 of dominantly oligoclase (Ol); quartz (Q) and biotite (Bi) are relatively undeformed.

Q Ap Cl

Cl Mu

Figure 44: Folded and fractured chlorite pseudomorph (Ch) of biotite with quartz (Q) alteration along cleavage and muscovite alteration parallel and perpendicular to cleavage. Shortening probably induced the folding with fractures generated once the interlimb angle of the fold was less than ~60°.

Ca Ca Q

Q Q

Figure 45: Gouge vein suggesting pulverization of a pre-existing calcite-filled vein. Ca – calcite; Q – quartz.

Ca Mu Mu

Q Q

Figure 46: Cataclasite within Z05 consisting of angular and fragmented calcite (Ca), quartz (Q), and muscovite (Mu). Within the yellow outline is a finer-grained domain.

Al Ca Mu Q

Mu Ca Mu

Ca Al Al Q

Figure 47: Increased magnification on cataclasite of Figure 46. Crystal fragments are highly angular and show little hydrothermal alteration. Al – albite; Ca – calcite; Q – quartz; Mu - muscovite

Q Ca

Mu Q

Ca Q

Figure 48: Cataclasite of quartz (Q) and calcite (Ca) within Z05. Clasts are highly angular and loosely grouped by composition, (suggesting in situ cataclasis rather than flow), and show no sign of hydrothermal alteration. Mu - muscovite

Ca He Ca

He Al Al

Figure 49: Fracture albite (Al) in Z03 showing multiple reactivations of one fracture. Note alternating fill of calcite (Ca) and hematite (He).

Figure 50: Alterations observed and associated alteration types. Phyllic alteration is inferred to have occurred prior to argillic. Relative timing of Iron oxide-copper-gold (IOCG) alteration is ambiguous.

Z05 Z03 Z01

Z07

Z05

Z01

Z05 Z03 Z03 Z06

Z01 Z07

Z06

Figure 52: Plots of preferred fracture orientations for Z01 through Z07. Set I orientations are blue, set II are red and set III are orange. Pink set is assumed to be both set II and III following the same orientations in Z06 and Z07. Preferred fracture orientations rotate clockwise from the periphery of Figure 51: Shear induced rotation of fracture the damage zone into the fault core. sets as suggested by Waldron (2005). Highlighted fractures are color coordinated with those in Figure 52.