University of Nevada

Reno

REMOTE SENSING ANALYSIS

OF

SOUTHERN WALKER LANE

A thesis submitted in partial fullfillment of the requirements for the degree of Master of Science

by

Nancy Denning Walker

April, 1986 The thesis of Nancy Denning Walker is approved:

Thesis Advisor d Department Chair

University of Nevada

Reno

April, 1986 IV

ACKNOWLEDGEMENTS

I would like to thank my major advisor, D. B. Slemmons, for his assistance and encouragement throughout my stay atMackay School of Mines, and especially during the course of this study. John Bell of the Nevada Bureau of Mines supplied the initial idea for this topic, and numerous helpful discussions along the way. Much of the imagery used in the study was available through the efforts of Dr. J. V. Taranik, Dean of Mackay School of

Mines. The U. S. Nuclear Regulatory Commission recognized the need for such a study and provided funds which were distributed by Lawrence Livermore National Laboratories.

Larry McKague and Danny Chung, of Lawrence Livermore National Laboratories, provided much logistical and academic assistance. Larry McKague made valuable suggestions which were incorporated into the paper. On the Nevada Test Site, the help of

Bill McKinnis, Becky El wood, and Casey Schmidt, of Lawrence Livermore National

Laboratories, was invaluable.

Finally, I would like to thank my husband, Michael Walker, whose continued good humor and moral support made this endeavor possible. V

ABSTRACT

A comprehensive analysis of Landsat 4 and 5 Thematic Mapper (TM) imagery, and topographic, geologic, and aeromagnetic maps demonstrates that the Walker Lane is a continuous feature through the southwestern Nevada volcanic field. A strong northwest pattern of lineaments is apparent in rock units older than 9.5 m.y. These lineaments correspond to sites of aligned preferential erosion, and at intersections with lineaments of different trends, may be northwest-trending vertical fractures and faults. The lineaments in volcanic rocks are thought to owe their origin to movement on northwest-trending structures in the underlying Paleozoic basement.

A conspicuous lack of northwest-trending lineaments occurs in rock units younger than 9.5 m.y. The lack of the lineaments in young volcanic units may suggest that movement on the underlying structures ceased by the time of, or soon after, their deposition. Relative ages of the gradual cesssation of movement are provided by tuff units of the Black Mountain and Stonewall Mountain calderas. The 8.5 to 6.3 m.y. ages of the calderas agree with other evidence which supports a clockwise rotation of the stress regime at about the same time. The lineament distribution therefore suggests the cessation of movement along northwest-trending structures is directly related to a change in the orientation of the stress regime.

The lineament analysis also demonstrates the advantages of the multiband format of

Landsat TM imagery. Linear features not apparent in bands 1-4 were noted in the longer wavelength bands. This is due to spectral reflectance and resolution differences between bands. Bands 5, 6, and 7 were found to be most useful for structural analysis of the southwestern Nevada region. TABLE OF CONTENTS

Page

ACKNOWLEDGEMENTS...... iv ABSTRACT...... ;...... v TABLE OF CONTENTS...... vi INTRODUCTION...... 1 Study Objectives...... I Study Area...... 2 DATA SOURCES...... 5 Imagery...... 5 Landsat Imagery...... 5 SIR-B Imagery...... 7 Aerial Photographs...... 7 Maps...... 8 Topographic Maps...... 8 Geologic Maps...... 8 Aeromagnetic Maps...... 8 GEOLOGIC SETTING...... 9 Regional Geology...... 9 Walker Lane...... 10 GEOLOGY OF THE SOUTHERN WALKER LANE...... 15 Cenozoic Tectonic History...... 15 Extensional History...... 18 Cenozoic Volcanic Rocks...... 20 Effects of a Change in Stress Regime...... 25 Faults in the Southern Walker Lane...... 27 Northwest Faults...... 27 Northeast Faults...... 29 North-South Faults...... 30 LINEAMENT ANALYSIS OF THE SOUTHERN WALKER LANE.....32 Introduction...... 32 Methods of Lineament Mapping on Landsat Imagery...... 33 Evaluation of Image Bands...... 36 Discussion of Lineaments...... 44 Age of Northwest Faulting in the Southern Walker Lane...... 58 Aeromagnetic Lineaments...... 63 Topographic Lineaments...... 67 DISCUSSION AND CONCLUSIONS...... 69 REFERENCES...... 73 vii

Table of Contents (Cont.)

APPENDIX A The Landsat Imaging Satellites...... 82 Filtering Techniques for Digital Landsat Data...... 87 APPENDIX B Histograms of the Yucca Mountain Subscene...... 98 APPENDIX C Stereonets from Northwest-Trending Lineaments...... 107 APPENDIX D Aeromagnetic and Geologic Map Coverage of the Study Area 112 1

INTRODUCTION

Study Objectives

Analysis of lineaments on imagery, in conjunction with field verification of

geomorphic features, has proven to be a successful method for delineating structures and

zones of weakness in the crust (Glass and Slemmons, 1977; Rowan and Purdy, 1984). A

lineament analysis of Landsat thematic mapper images of the southern Walker Lane was

undertaken to determine if any evidence of recent Walker Lane-style deformation is present

in southwestern Nevada. The study fulfills in part requirements for a Master of Science

degree in Geology from the University of Nevada, Reno. Funding for the study was by

grants from the Nuclear Regulatory Commission through Lawrence Livermore National

Laboratories, and the Chevron Corporation.

The purpose of this study was to utilize remote sensing imagery and other data to determine the regional structural relationships in southwestern Nevada. Of particular

interest was the nature of the northwest-trending Walker Lane structural system through the

southwest Nevada volcanic field. Yucca Mountain, a proposed high level nuclear waste repository site, is situated along the trace of the Walker Lane on the southern boundary of

the southwest Nevada volcanic field. A thorough understanding of the regional structural

setting is important to determine the suitability of Yucca Mountain as a repository site. 2

The objectives of the study were to use remote sensing imagery to answer

the following questions:

1. Is the Walker Lane a continuous feature through the southwest Nevada volcanic

field?

2. If continuous, is the Walker Lane an active northwest-trending right-lateral shear

system?

As defined by Slemmons and McKinney (1977), a fault is active if it has

shown evidence of activity in the present seismotectonic regime; if there

is geomorphic, stratigraphic, or seismogenic evidence of activity; or if

there is potential of recurrence in the present seismotectonic regime.

3. Is satellite-generated remote sensing imagery useful in neotectonic analyses?

Study Area

The area chosen for study encompasses the projected trace of the Walker Lane through the southwest Nevada volcanic field in southern Nye County from latitudes 38° to

36°, and longitudes 117°10' to 115°50' (fig. 2). The longest east-west and north-south dimensions are 108 km by 221 km (69 miles by 138 miles).

Nearly all of the study area is within the Nellis Air Force Range, the Nevada Test

Site, and the Las Vegas Bombing and Gunnery Range. Public access to these areas is not permitted. Therefore towns and roads are sparse. U.S. Highway 95 crosses the western side of the study area from south to north, connecting Las Vegas with Tonopah. The larger towns include Beatty, Pahrump and Mercury. Mercury is situated on the Nevada

Test Site and entry is restricted to test site workers and guests only. 3

The topography of the study area is a combination of typical Basin and Range style topography and the volcanic terrain of the southwest Nevada volcanic field. Basin and

Range topography is characterized by closed basins separated by ranges, while the southwest Nevada volcanic field is made up of eruptive volcanic centers, broad plateaus and mesas composed of extensive ash flow tuff sheets, narrow canyons, washes, and open alluvial basins often termed "flats". Elevations in the study area increase from south to north. Elevations within the basins range from approximately 750 m (2,500 feet) in the south to 1,800 m (6,000) feet in the north. The mountains rise from 300 m to 1,800 m

(1,000 to 6,000 feet) above the basins. Many mountains exceed 2,100 m (7,000 feet) in elevation. Kawich Peak, the highest peak in the study area, has an elevation of 2,866 m

(9,404 feet). Pahute Mesa, a large mesa in the central part of the study area, has an elevation of greater than 1,800 m (6,000 feet).

Vegetation in southern Nye County is zoned according to altitude. In the lower valleys, where the water table is close to the surface, common plants include mesquite, salt grass, greasewood, and rabbit brush. On the alluvial fans and lower slopes, where the water table is relatively deep, Mormon tea brush, barrel cactus, and yucca are found, though creosote brush predominates. Joshua trees occur between about 1,150 m and

1,500 m (3,800 and 5,000 feet) in elevation, and grasses, pinon pine and juniper are abundant above 1,500 m (5,000 feet) (Cornwall, 1972). 4

Figure 2. Location map of study area. 5

DATA SOURCES

This study involves a comprehensive analysis of Landsat 4 and 5 Thematic Mapper images, topographic, geologic, and aeromagnetic maps, and review of 1:60,000 scale aerial photographs. Lineaments were mapped from Landsat imagery, topographic maps and aeromagnetic maps. Criteria for lineament mapping on each type of imagery will be given in each individual section. Comparison of lineaments with geologic maps, topographic maps and aerial photographs, and ground checking at selected locales helped decipher the nature and significance of the lineaments and lineament trends.

Imagery

Landsat Imagery Landsat 4 and 5 Thematic Mapper (TM) images of the Bald Mountain, Death Valley, Las Vegas, and Goldfield scene were the primary sources of information for lineament mapping. Landsat 4 images are 16" by 20" hard copies generated by Santa Barbara Research Center. These images were taken on November 17, 1982, along a flightline trending about SI0°W. Scale of a 16" by 20" scene is approximately 1:555,000. In addition to the above mentioned scenes, eight subscenes from the Bald Mountain scene were also generated by the Santa Barbara Research Center. The scale of a 16" by 20" subscene is approximately 1:125,000. Coverage of Landsat imagery is shown in figure 3. Landsat 5 TM images used in the study were taken on June 26, 1985. Computer compatable tapes were aquired by Mackay School of Mines from

7

EROS Data Center. EROS performed image restoration and processing procedures on the raw data to correct for errors, noise, and distortion. The data was then analyzed, enhanced by filtering and/or contrast stretching, and images generated by the author on a VAX 11/780 computer using the IDIMS (Interactive Digital Image Manipulation System) image processing system. Scale on Landsat 5 imagery varied depending on the size of the image area and the type of film used (prints or slides). A detailed description of the Landsat imaging system and computer enhancement techniques is given in Appendix A.

SIR-B Imagery From October 5-13, 1984, the thirteenth flight of NASA's manned Space Shuttle carried a side-looking, L-band imaging radar system. This system, named Shuttle Imaging Radar- B (SIR-B), is the second generation synthetic aperature system carried aboard a space shuttle. However, a short in the system s antenna power cable produced weak and variable signals, greatly reducing image quality and coverage. Seven bands over Nevada were aquired by the SIR-B. Four of these bands cross the study area. Unfortunately, the images over the Nevada Test Site and Nellis Air Force Base were particularly dark and noisy. SIR-B images were therefore excluded from the study.

Aerial Photographs Stereoscopic viewing of 1:60,000 scale aerial photographs helped delineate the nature and significance of lineaments and lineament trends mapped from Landsat imagery. These photos are AMS (Aerial Mapping Service) 109 series photos, taken in the fall of 1952. 8

Maos

Topographic Maos Topographic linear features were mapped on U. S. Geological Survey l° i 2° sheets (1:250,000) of the study area. Lineaments mapped on Landsat imagery were transferred tol 5' (1:62,500 scale) and 7.5' (1:24,000 scale) quadrangle maps in order to determine if the lineaments corresponded to topographic features, and to locate the lineaments on the ground.

Geologic Maps Lineaments mapped on Landsat imagery were compared with geologic maps of the study area to determine if the lineaments correspond to mapped geologic features such as contacts, faults, or joint patterns. A list of geologic map coverage of the study area is given in Appendix D.

Aero magnetic Maos Aeromagnetic maps of Nevada show a strong northwest linear and curvilinear magnetic anamoly patterns which correspond to the trace of the Walker Lane. The trends of the magnetic anomolies indicate the Walker Lane is a through-going crustal feature along the total length of western Nevada. Linear magnetic gradient patterns were mapped in the study area from the 1:500,000 scale aeromagnetic map of Nevada. A list of aeromagnetic map coverage of the study area is given in Appendix D. 9

GEOLOGIC SETTING

Regional Geology

The study area, located along the Walker Lane trend in southern Nye County, is situated in the southcentral Great Basin subprovince of the Basin and Range physiographic province. Other subprovinces within the Basin and Range province include the Mojave and

Sonoran Deserts, the southern Columbia Plateau, and the Snake River Plain. The topography of the Basin and Range province is largely controlled by Late Cenozoic extensional tectonism which has formed predominantly north to northeast trending, fault- bounded, linear mountain ranges separated by broad alluvial basins.

A closed drainage system characterizes the Great Basin subprovince. The Great

Basin is bound on the south by the Mojave and Sonoran Deserts, on the west by the Sierra

Nevada, on the north by the Columbia Plateau and Snake River Plains, and on the east by the Rocky Mountains and the Colorado Plateau. It is an area of high average elevation and topographic relief, reflecting the active extensional tectonism of the region. Mountain ranges are 2000 - 3000 m high (6,000 - 9,000 feet), while the valley floors lie at 900 -

1500 m (2,100 - 4,500 feet). Locally, ranges and valleys are interrupted by caldera complexes and associated dissected volcanic plateaus.

Rocks of the Great Basin are predominantly Precambrian metamorphic, sedimentary and igneous rocks, Paleozoic eugeosynclinal clastic rocks west of miogeosynclinal carbonate rocks, Mesozoic and Tertiary plutonics, and volcanics, plutonics, and sediments of Cenozoic age (Sinnock, 1982). The Great Basin has experianced a complex tectonic history. During Paleozoic and Mesozoic time the region underwent extreme crustal shortening resulting in numerous, large-scale, low-angle thrust faults. In the Tertiary period, however, there was a change to crustal extension, strike-slip faulting, and extensive 10 volcanism in the Great Basin (Ekren, 1968, Carr, 1974). A detailed discussion of the

Cenozoic extensional history of the Great Basin is given in a future section.

A northwest-trending zone of strike-slip faulting separates the thick crust of the essentially quiescent Sierra Nevada range on the northwest and the Inyo-Mono region of the southwest from the thin crust and active extensional tectonism of the Basin and Range province to the east. This zone, the Walker Lane, is thought to have been active through much of the Tertiary and possibly as early as late Mesozoic (Longwell, 1960). The southern segment of the Walker Lane is the topic of this study.

Walker Lane

The Walker Lane is a northwest-trending zone of disrupted topography along the

Califomia/Nevada border. It is characterized by an en echelon pattern of northwest­ trending, right-slip faults, shorter northeast-trending left-slip faults and minor north-south normal faults. No single fault or closely aligned fault zone can be mapped continuously along the Walker Lane, but the zone everywhere is marked by changes in range trends and by other topographic discontinuities. Aeromagnetic maps of Nevada (Zeitz, et al,

1977,1978) show a 30-60 km wide, northwest pattern of magnetic anamolies and igneous intrustions which corresponds to the trace of the Walker Lane. This pattern indicates the

Walker Lane is a major crustal feature. The Walker Lane parallels the San Andreas fault, trending about N40^W to N45^W, and is believed be the result of transmitted right-lateral shear stress caused by the interaction of the Pacific and North American plates along the

San Andreas transform (Atwater, 1970).

The Walker Lane extends for more than 600 km from Las Vegas, Nevada northwest to Honey Lake, California (Gianella and Callaghan, 1934; Locke and others,

1940; Bell and Slemmons,1979). It can be segmented, on the basis of geomorphic expression and left-lateral shear zones, into the northern Walker Lane, the central Walker

Lane, and the southern Walker Lane (fig. 4). The northern Walker Lane contains the northwest-trending right-lateral Pyramid Lake fault zone and a number of short, northeast­ trending left-slip fault zones (Slemmons and others, 1979). Numerous geomorphic features characteristic of strike-slip fault zones are displayed along the northern Walker

Lane in Late Pleistocene and Holocene sedimentary deposits and landforms. These features include: recent scarps, offset stream channels, linear gullies, elongate troughs and depressions, sag ponds, vegetation alignments, sidehill and shutter ridges, and rhombohedral and wedge-shaped enclosed depressions (Bell and Slemmons, 1979;

Sanders and Slemmons, 1979). Historic seismicity, including a magnitude 6.7 earthquake in 1869 along the Olinghouse fault zone, attest to the seismic potential of the northern

Walker Lane zone (Ryall, 1977, Slemmons and others, 1965).

The central Walker Lane extends from the Walker Lake area southeast to the

Excelsior Mountains lineament. Detailed mapping by Hardyman and others, (1975) defined the central part of the Walker Lane as a regional northwest-trending shear zone about 30 km (19 miles) wide consisting of at least five major right-slip faults. Combined apparent right lateral displacement across the five mapped strike-slip faults is at least 48 km

(30 mi). Historic activity within the central Walker Lane includes a magnitude 7.3 earthquake with right-slip movement on the north-northwest trending Cedar Mountain fault in 1932 (Gianella and Callaghan, 1934) and left-slip movement on the northeast-trending

Excelsior Mountain fault in 1934 (Callaghan and Gianella, 1936).

South of Tonopah, Nevada, the continuity of the Walker Lane becomes suspect.

From Tonopah to the northern extent of the Las Vegas Valley shear zone around Mercury, obvious topographic expression of the Walker Lane is hidden by the young volcanics and calderas of the southwestern Nevada volcanic field. Although through-going, northwest trending structures do not appear on geologic maps of the southwestern Nevada volcanic field, the location of the calderas are apparently influenced bya northwest-trending zone of 12

Figure 4. Map of Nevada showing Walker Lane segments (modified from Albers, 1967). weakness. Timber Mountain, Black Mountain, Mount Helen, and the Cactus Range calderas are located along a nearly straight line extending northwest from the northernmost known position of the Las Vegas Valley shear zone. Carr (1974) suggests volcanic eruptive centers may be associated with northeast trending zones of left-slip between terminations of right-lateral en echelon systems. He considers these northeast-trending, left-slip faults to be conjugate to the larger right-lateral system. Where the northeast- and northwest-trending faults intersect they are mutually offsetting. Though northwest­ trending faults are presently considered inactive in the southern Walker Lane, northeast­ trending faults are active. Presently active left-slip faults in the southern Walker Lane include the Mine Mountain, Cane Springs, and Rock Valley fault zones (Rogers, et al,

1983; U. S. G. S„ 1985).

The Las Vegas Valley shear zone, a northwest-trending strike-slip fault zone, is traceable from Las Vegas northwest to Mercury. Albers (1967) proposed oroclinal flexuring of north-south trending mountain ranges at the northern end of the Las Vegas

Valley shear zone to explain the disappearance of the shear zone to the north. He suggested that stike-slip movement in the basement was expressed by oroclinal bending of the sedimentary cover. Estimations of offset along the Las Vegas Valley shear zone, based on bends and offsets of Paleozoic facies markers and oroclinal flexuring, range from 50 km

(Stewart, 1967) to 72 km (Fleck, 1970). However, recent paleomagnetic studies show no rotation of Mesozoic plutons, indicating another mechanism must be responsible for the apparent bending of the mountian ranges. This mechanism may decrease or increase the estimated amount of shearing along the zone (Oldow and Geissman, 1982). Based on the amount of deformation of Tertiary volcanic units in the sheared and "bent" mountain ranges, Longwell (1974) suggests much of the movement along the Las Vegas Valley shear occurred between 17 and 11 m.y. ago.

The eastern and western boundaries of the Walker Lane are conjectural. In the northern and central Walker Lane, deformation occurs in a zone about 30 km to 60 km in width. In the southern Walker Lane, the boundaries are speculative. Stewart (1984) and

Carr (1984) include the Death Valley-Furnace Creek fault zone in the Walker Lane, with the boundaries of the lane stepping westward on the Excelsior Mountain fault at the southern end of the central Walker Lane segment. The aeromagnetic map, however, show a 50 km -

60 km wide zone of anamolies along the entire length of the Walker Lane from the

California border on the north to the Las Vegas Valley shear zone on the south. Although right-slip displacement on northwest-trending faults is on-going in the Death Valley-

Furnace Creek fault zone, the width of the zone of deformation in the northern and central

Walker Lane, and the magnetic patterns suggest the Death Valley-Furnace Creek structure is separate from the Walker Lane structure. For these reasons I am not including it in the

Walker Lane zone. 15

GEOLOGY OF THE SOUTHERN WALKER LANE

Cenozoic Tectonic History

Gneisses, schists, quartzites and dolomite of Precambrian age occur throughout the

Walker Lane in southern Nye County. During the latest Proterozoic and Paleozoic eras, southern Nye County was part of the Cordilleran miogeosyncline, a subsiding trough on the submerged western edge of the North American continent. Nearly 30,000 feet of carbonates and terrigenous detrital rocks were deposited on the shelf during this time. In the Late Devonian and Early Mississippian, an orogenic highland, the Antler Orogenic Belt, formed along the continental margin, shedding detritus eastward into a marine trough known as the Antler foreland flysch basin. The argillite, quartzite, conglomerate and sparse limestone detritus was overlain by the Pennsylvanian and Permian limestone. These rocks were complexly folded and thrust faulted during several periods of compressive deformation in the Mesozoic (Barnes and Poole, 1968). Intrusion of granitic plutons accompanied these mountain building episodes.

A complex history of extensional tectonism followed the compressional deformation of the Basin and Range, and was initiated by major changes in subduction geometry beneath the western North American continent. Three phases of extension have occurred since about 37 m.y. ago (Zoback and others, 1981; Eaton, 1984). The first phase, which took place between about 37 and 22 m.y. ago in a convergent plate boundary setting, was a result of subduction of the Farallon plate beneath North America. At this time the Basin and Range was characterized by a diffuse zone of calc-alkaline, intermediate composition volcanism, indicating extension was occurring in an intra-arc environment

Eaton (1984) suggests the change from compression to extension in the Great Basin is related to a change in the rate of convergence between the Farallon and North American plates. Work by Carlson (1982) and Engebretson and others (1982) on chronological relations of plate interactions demonstrate that the rate of convergence of the plates increased between 135 m.y. and 43 m.y. ago from about 25 mm/yr to about 170 mm/yr.

Between 42 and 43 m.y. ago, the convergence rate dropped sharply to less than 100 mm/yr, and continued dropping to 65 mm/yr at 37 m.y. ago. The earliest well-documented extension in the Great Basin began at about 37 m.y. ago, indicating that intra-arc extension began at a time of rapidly declining rates of plate convergence.

About 20 to 30 m.y. ago, the Farallon-Pacific Ridge collided with the trench and initiated the formation of the San Andreas transform (Atwater, 1970). Though the southern

Great Basin did not immediately respond to this change in plate interactions, by about 17-

18 m.y. ago the zone of diffuse arc-related volcanism in the Basin and Range had become a well-defined and continuous andesitic volcanic arc situated along the western margin of the

Great Basin in the south and the locus of the Cascade range in the north. Behind the arc, a bimodal distribution of basalt and highly silicic volcanics was erupting in the southern

Great Basin. The distribution and character of the volcanism, and a subtly developed geophysical and topographic bilateral symmetry is evidence that in the mid-Miocene the

Great Basin was an actively extending back-arc region (Eaton, 1982).

During intra-arc and back-arc extension, the Great Basin was extending in a west- southwest direction, normal to the orientation of the trench. The west-southwest extension direction parallels the earlier compression direction in the Great Basin, both being the result of subduction of the Farallon plate beneath the North American plate (Zoback and others,

1981). Some time after 10 m.y ago the direction of the least principal stress rotated clockwise to west-northwest extension. Eaton (1984) suggests the change in the least principal stress direction is due to maturation of San Andreas transform geometry and its resultant influence on tectonic activity inland. West-northwest extension has produced the present style of basin and range crustal extension. The topography is characterized by north to northeast trending, fault-bounded, linear mountain ranges, and basins filled with 17 several hundred meters of alluvium and colluvium eroded from the ranges, floodplain deposits, eolian sand sheets, and scattered spring, pond, and lacustrine deposits.

The present direction of the least principal stress, determined by recent fault slip data, bore-hole breakouts, and hydraulic fracture measurments at the Nevada Test Site region, is oriented at about N5(Pw (Zoback and Frizzell, 1985; Ander, 1984; Springer and others, 1984). Ander (1984) suggests this continued clockwise rotation may be due to increasing influence of the transform boundary on extensional deformation causing the extension direction to swing in an arc which follows the progress of the Mendocino triple junction as it travels northward. Extensional History

Distinct differences in degree of extension, styles of faulting, and type of igneous

activity distinguish pre-Basin and Range extension from Basin and Range extension.

Estimates of up to and greater than 100% extension is suggested for early- and mid-

Miocene time in the Great Basin during west-southwest extension (Wernicke and others,

1984; Guth, 1982; Proffitt, 1977). Extension occurred on high angle listric and block

faults, and low angle detachment surfaces. In the Sheep and Desert Ranges south of the

Nevada Test Site, Guth (1981) suggests low angle faults originated during surficial gravity

sliding, in response to topograpy produced by extension along the high angle faults. In

this theory, strike-slip faults such as the Las Vegas Valley shear zone are related to extensional faulting as boundaries of domains with differences in style or magnitude of extension (Wernicke and others, 1984). The zone of brittle deformation was shallow at

this time, with faulting usually restricted to the upper 5 km of the crust (Zoback and others,

1981).

Large, steep-walled caldera complexes emitted huge volumes of igneous material during pre-Basin and Range extension, with activity slowing down and finally ceasing soon after the onset of Basin and Range faulting. Volcanism associated with Basin and

Range faulting is primarily basaltic or bimodal rhyolite and basalt of limited proportions relative to the earlier volcanic activity. Degree of extension also decreases dramatically during Basin and Range extension, with estimates of about 20 to 30% for the Great Basin

since the onset of the west-northwest extensional regime (Zoback and others, 1981;

Stewart, 1980; Proffitt, 1977).

The present zone of extensional failure takes place in the upper 20 km or so of crust, with aseismic deformation occurring below 20 km (Eaton, 1980). Models for basin and range-forming geometry include listric faulting, planar faults producing tilted blocks, and horsts and grabens (Stewart, 1980). Listric and planar faults may merge with a zone of continuous extensional deformation below the seismic zone, while the geometry of horsts and grabens necessitate a shallow and local zone of extension beneath the grabens.

Strike-slip faulting also exists in the basin and range regime. Strike-slip faults which are parallel or subparallel to the direction of extension may bound areas within which the amount, rate or sense of normal faulting is different from the adjacent on strike areas

(Anderson, 1984).

Zoback and others (1981) point out that the differences in the amount of extension and type of volcanism indicate a contrast in the thermal regimes characterizing the extensional events. The broad zone of major igneous activity, and the extreme amount of extension in the pre-Basin and Range extensional era suggest a hot and thermally weakened lithosphere. The change to Basin and Range extension with faulting penetrating the upper

15-20 km of crust suggests overall cooling of the crust and tapping of subcrustal magmas to produce basaltic volcanism. n n a

20

Cenozoic Volcanic Rocks

Tertiary volcanic rocks cover a large portion of the study area. Silicic pyroclastic tuffs and associated lavas and intrusives are the most common, though at least two generations of basaltic lavas and domes are also present.

Following a period of intermediate to silicic calc-alkalic volcanism in the early and mid-Tertiary, a period of voluminous silicic and associated minor basaltic volcanism began about 16 m.y. ago in the southern Great Basin (Christiansen and Lipman, 1972). In the study area, these silicic and associated basaltic rocks are part of the southwestern Nevada volcanic field, a group of related source complexes within an area of about 1800 km2. Ash flow tuffs cover an area of about 11,000 km2, forming extensive volcanic plateaus which surround a group of clustered, overlapping calderas and eruptive centers (Christiansen and others, 1977). The plateaus have since been disruped by normal faulting, erosion and sedimentation though their essential character is still partly preserved in Pahute Mesa,

Rainier Mesa, Yucca Mountain and Shoshone Mountain. Timber Mountain, Black

Mountain, and Stonewall Mountain, the youngest calderas in the field, (9.5-11.3 m.y, 6-

8.5 m.y, and 6.3 m.y., respectively) are still well preserved. Table 1 lists the stratigraphy and ages of the silicic volcanics in the study area.

The southwestern Nevada volcanic field was active between about 16 and 6 m.y ago. Alignment and clustering of the calderas along the Walker Lane trend indicate that the

Walker Lane influenced their location, although many calderas are located outside the

Walker Lane. Aerial distribution and thickness variations, of the extensive ash-flow tuffs indicate basin and range normal faulting was occurring before, during, and after the volcanic field was active (Noble, 1972; Ekren and others, 1968). Still, much of the faulting that produced the topography of the present field occurred in the late stages and following silicic volcanism, beginning in the southern Great Basin sometime between 13 and 10 m.y. ago in a back-transform setting (Christiansen and others, 1977; Zoback and 21

ERUPTIVE CENTER FORMATION M EM BERS OR AGE- RELATED UNITS i o % i. y .

STONEVALL MOUNTAIN STONEWALL MTN TUFF 6 .3 CALDERA

BLACK MOUNTAIN THIRSTY CANYON TUFF LABYRINTH CANYON MEMBER CALDERA GOLD FLAT MEMBER TRAIL RIDGE MEMBER 6 -8 SPEARHEAD MEMBER ROCKET VASH MEMBER

TIMBER MOUNTAIN TIMBER MTN TUFF RHYOLITES OF SHOSHONE MTN CALDERA ■ M AFIC LAVAS OF DOME MTN RHYOLITES OF 40-MILE CANYON 9 5 - TUFFS OF CROOKED CANYON 1 1.5 & BUTTONHOOK VASH AMMONIA TANKS MEMEBER RAINIER MESA MEMBER

VAHM O NIE - VAHMONIE FM MULTIPLE RHYOLITE, ANDESITE 1 2 -1 3 MT. SALYER AREA SALYER FM BRECCIAS, FLOWS, & TUFFS

RHYOLITE FLOWS TWA CANYON MEMBER CLAIM CANYON PAINTBRUSH YUCCA MTN MEMBER 1 2 - 13 CALDERA - TUFF PAH CANYON MEMBER CALICO HILLS TOPOPAH SPRINGS MEMBER CALICO HILLS FM RHYOLITES OF CALICO HILLS 1 3 - 14

SILENT CANYON STOCKADE VASH TUFF 1 3 -1 5 CALDERA BELTED RANGE TUFF 1 3 -1 5

CRATER FLAT AREA - PROW PASS MEMBER SLEEPING BUTTE CRATER FLAT TUFF BULLFROG MEMBER 1 4 -1 5 CALDERA TRAM MEMBER RED ROCK VALLEY TUFF

M T . HELEN TOUCH A PEAK TUFF MULTIPLE COOLING UNITS > 14

KANE SPRINGS WASH KANE VASH TUFF MULTIPLE COOLING UNITS 1 4 -1 5 CALDERA LAV A FLOWS

CACTUS - KAWICH RHYOLITE LA V A FLOW'S O'BRIEN'S KNOB, CACTUS PEAK 1 4 -1 5 RANGES BELTED PEA K , OCHER RIDGE

CATHEDRAL RIDGE FRACTION TUFF MULTIPLE COOLING UNITS 1 5 -1 8

INTERMEDIATE FLOW'S 1 8 -2 2 MT. HELEN, WHITE BLOTCH MULTIPLE COOLING UNITS 2 4 -2 5 CACTUS - KAWICH SPRING TUFF RANGES ANTELOPE VLY TUFF MULTIPLE COOLING UNITS 2 6 -2 7

Table 1. Volcanic stratigraphy in study area (modified, from Sinnock, 1982). Thompson, 1978). On Yucca Mountain, members of the Timber Mountain tuff, dated at

11.1 m.y. to 11.4 m.y. old, are restricted to topographic basins and rest against the uniformly distrubuted Paintbrush Tuff (12.5 - 13 m.y. old) with buttress unconformity

(Scott and Bonk, 1984). In Yucca Flat, however, Timber Mountain tuff is uniformly distributed. Contour maps of unit thicknesses suggest Basin and Range style normal faulting did not begin in Yucca Flat until after 11 m.y. ago. At this same time activity along faults at Yucca Mountain is thought to have dramatically declined (Ander,1984; Carr,

1984). These relationships indicate initiation of Basin and Range sytle faulting varied within a very short distance, and may suggest that activity along faults transfers from place to place without major readjustments of the stress regime.

A presently important volcanic-structural element of the southern Great Basin has been termed the Death Valley - Pancake Range basalt belt by Crowe and others (1983).

This north to northeast-trending belt is a relatively youthful feature, with a higher than average concentration of Quaternary faulting, seismicity, and basaltic volcanism (Carr,

1974; Rogers and others, 1983) (fig. 5).

Two temporal groupings of basalt which erupted in the last 10 m.y., occur within the Death Valley - Pancake Range belt The first are older basalts, spatially related to large volcanic centers and erupted during the waning stages of silicic volcanism (Noble and others, 1984). These older "rift" basalts occur as dikes and flows younger than 8.5 m.y. on Pahute Mesa, and between 6.3 and 8.7 m.y. old in Paiute Ridge, Yucca Flat, and Nye

Canyon. Dikes associated with the flows consistently strike north to N15°W (Byers and

Barnes, 1967; Henrichs and McKay, 1965). Basalts of the same age at Silent Canyon strike north to N30°E. The strike of most of the older basalts indicate they were emplaced in a stress regime favoring intrustion along north-northwest trends, consistent with the west-southwest least principal stress regime suggested for the Great Basin in mid-Miocene time (Zoback and Thompson, 1978; Anderson and Ekron, 1977). The variation at Silent

Canyon may be a local effect from the Silent Canyon caldera. 100 kilometers Figure 5. Map showing location of Death Valley-Pancake Range basalt belt, (after Carr, 1984). The second type of basalts are younger rift basalts, spatially unrelated to the silicic volcanic centers. These basalts are small volume, isolated scoria cones and lavas. The basalts of Crater Flat and north of Beatty are among these younger basalts. They are about

4 m.y old or younger, and show a fairly consistent northeast trend in alignment of eruptive centers and dikes. These basalt have been erupted in a stress regime favoring intrusion along a north-northeast trend, suggesting a northwest least principal stress direction.

Although time constraints vary from place to place (Bamhard and Anderson, 1984), the trends of the two basalts groups in the Death Valley - Pancake Range belt suggest the change from southwest to northwest-trending extension may have occurred as recently as

6.3 m.y. ago, and was underway by at least 4 m.y. ago. 6.3 m.y. is the age of the last of the older rift basalts and the age of Stonewall Mountain caldera, the youngest caldera in the southwest Nevada volcanic field. Effects of a Change in Stress Regime

Change in the stress regime from southwest to northwest extension implies a concomitant change in behavior and activity along faults of specific orientations. In southwestern Nevada, three major fault groups were active in the southwest-trending extensional regime. They are northwest-trending right-slip faults associated with the

Walker Lane; northeast-trending left-slip faults, presumably complementary and even conjugate to the northwest faults; and normal faults trending about N10°W to N10°E

(Carr, 1974). Evidence of a relatively recent (between 10 and 6 m.y. ago) major reorientation of the stress regime should be supplied by changes in the rate and style of movement along these faults. With the present N50°W extension direction, northwest faults may be undergoing compression and therefore be inactive or be acting as boundaries between regions with different styles and degrees of extension (Anderson, 1984), northeast faults should show a dominant normal or normal-oblique component, and north-south faults should display a right-lateral component (fig. 6).

Ongoing work by Zoback and Frizzell (1985) suggests temporal variations in the present stress regime may control the sense of movement along a fault. Fault slip data from the east-northeast trending Rock Valley Fault and an unnamed parallel fault 2 km to the south demonstrate left-lateral oblique offset of Late Tertiary and Quaternary sediments.

Slip measurements indicate a bimodal distribution of slip angles (rakes). The first group, with 75° to 90° rakes, are normal dip slip faults. These faults cluster at a strike of about

N30°-50°E, and dip 65° to 80°. The second group are strike-slip faults with rakes of less than 20°. These faults strike bimodally about a dominant node of N35°-40°E (right- and left-lateral offset and dip 80°-90°. Using a method developed by Jacques Angelier (1979) to determine the mean deviatoric principal stress tensor, Zoback and Frizzel determined a "normal faulting stress regime" for the region ( the greatest principal stress direction, Si, vertical). S3, the least principal stress direction, is horizontal and oriented at about N

PRESENT STRESS AND FAULT ORIENTATION AT N.T.S.

Figure 6. After Carr, 1984. 2 6

N58°W. S2, the intermediate principal stress, is oriented at N32°E and plunges 8°.

Strike-slip faulting on northeast-trending faults is therefore inconsistent with the stress orientation data, though slip data shows lateral movement of the sediments.

Angelier and others (1985) see a similar pattern in Neogene faults at Hoover Dam.

They describe a "mixed mode" faulting pattern with normal and strike-slip movement occurring on similarly oriented faults or superposed on the same fault during a single extensional stress regime. They suggest this is due to temporal oscillations between S \ and

S2 while the orientation of S3 stays constant. These relationships may indicate that in a primarily extensional regime activity along a fault is determined by the orientation of the least principal stress direction. However, the sense of movement along the fault is determined by the orientation of the greatest and intermediate principal stresses which may oscillate without major readjustments of the regional stress regime. ■ ...... ■

27

Faults in the Southern Walker Lane

Mapped major faults in the vicinity of the study area are shown in figure 7.

Northwest Faults

Northwest-trending faults which have been mapped in the study area include the

Las Vegas Valley and La Madre faults (included in the Las Vegas Valley shear zone system), the Yucca-Frenchman Rat fault, five northwest-trending washes on the east side of Yucca Mountain, faults cutting Timber Mountain, and northwest faults bounding and cutting the Cactus Range in the northwestern part of the study area. The Las Vegas Valley shear zone, the Yucca-Frenchman Flat fault, and the northwest-trending washes cutting

Yucca Mountain have displayed right-slip movement. From a short seismic record, stratigraphic evidence, and the lack of geomorphic expression of recent faulting on northwest-trending faults, it appears that in the southwestern Great Basin faults with a northwest orientation are presendy quiescent (Carr, 1984; Rogers and others, 1983).

The Las Vegas Valley shear zone, a major structural and topographic feature, was discussed earlier in the Walker Lane section.^ Much of the movement on the shear zone is thought to have occurred between 17 m.y. ago and 10 m. y. ago, with estimates of shear zone displacement ranging between 40 and 65 km (Longwell, 1974). Guth (1981) and

Wernicke and others (1985) have suggested the Las Vegas Valley shear zone marks the boundary between two regions with differential Tertialry extension.

Northeast-trending structures bend in a right lateral sense as they approach the

Yucca-Frenchman fault (Rogers and others, 1983), and ranges to the east of the fault display the typical north-south trend of the Basin and Range. This may suggest the Yucca-

Frenchman fault marks the eastern boundary of the Walker Lane in that area, with the

Walker Lane stepping eastward from the Las Vegas Valley shear zone on a northeast-

ujCX7- 117* 116* 113* I I I EXPLANATION -Exult or fracture «2 *.y. (fault known or suspected l Tonopah to have had lurface movement In last 2 m.y. In Calif., probably Includes some faults with surface Holocene movement)

Holocene fault or fracture (Includes historic fractures In frenchman. Tucca, Groom, and Antelope playas)

-UllHlu l Inear mountain front (unusually linear mountain front segment where young deposits are not obviously offset, but where persistent fault activity has been young enough to maintain a prominent scarp-1 He steep linear mountain front) or fault /one <3 - >1 m.y. (age range of last Important aovoment; some of these /-VX faults have had minor ^ O V-R«cenl ' " , / \ K displacement after I m.y.) — —v r-Hracture f f ------Other selsmlcally active or ,- k . 1 4 Important fault /ones s* ' (o '* ' A >2 m.y.

I h X Basalt "rift" <2 m.y. YM Yucca Mountain V°0» o^o^ I L o t V tg a t

20 30 AO 30 ml. i— r1—i—h— H-r -I \ 0 10 20 30 40 50 60 70 km.

Figure 7. Generalized map of Pliocene and Quaternary faults and seismic zones. ro After Carr, 1984. oo 29

trending left-slip fault. Though the Yucca-Frenchman fault is presently quiescent, active

northeast-trending left-slip faults to the southwest are truncated by it (Carr, 1984).

Scott and others (1984) discuss the origin and activity of the northwest-trending

washes cutting Yucca Mountain. They conclude that these washes are sites of right-slip

faults coincident with the right-slip faults of the Walker Lane-Las Vegas Valley shear

zones. Stratigraphic evidence indicates most of the faulting on the northwest-trending

faults occurred prior to 11.5 m.y. ago. This date is based on the age of normal faults on

Yucca Mountain which cut the washes. Major displacement on the normal faults is

bracketed by displacement of the Tiva Canyon Member of the Paintbrush Tuff (13 m.y.

old) and the lack of displacement of the Rainier Mesa Member of the Timber Mountain Tuff

(11.5 m.y. old) in that area.

The Timber Mountain resurgent caldera and the Cactus Range volcanic complex are

elongated in a northwest-southeast direction. Northwest-oriented faults may be the result

of this primary elongation, reflecting stresses occurring at the time of their development.

Northeast Faults

Northeast-trending, left-slip faults may have originally been conjugate to northwest­

trending right-slip faults in the Walker Lane. However, since northeast-trending faults are presently seismically active while the northwest-trending faults are considered inactive

(Rogers and others, 1983), the conjugate relationship may no longer exist.

An important northeast-trending structural feature which crosses the Nevada Test

Site is the Spotted Range - Mine Mountain zone. This zone crosses the projected trace of

the Walker Lane extending from the Furnace Creek fault on the west to the Yucca-

Frenchman fault on the east. Seismically active faults within the Spotted Range - Mine

Mountain zone include the Cane Springs, Rock Valley, Frenchman Flat and Mine Mountain

faults (Carr, 1974,1984). Fault slip data and trenches across the Rock Valley fault attest to

Quaternary left-slip and normal offset on the fault (Zoback and Frzzell, 1985; D. B. 3 0

Slemmons, pers. comm., 1986). Other seismically active northeast-striking faults in the area area are the Lake Mead fault zone south of Las Vegas, the Pahranagat shear zone to the northeast of the Nevada Test Site, and faults on Pahute Mesa. Seismic studies indicate that these areas are sites of high tectonic activity (McKague, 1985; Rogers and others, 1983).

Focal plane mechanisms show recent earthquakes are produced by left-lateral movement on northeast-trending faults, though short, north-south fault segments within the larger Pahranagat shear zone display right-lateral movement On Pahute Mesa (Hamilton and others, 1971) and at Lake Mead (Rogers and Lee, 1976) normal fault earthquakes on northeast-trending faults were recorded.

North-South Faults

Characteristically, north-south faults in the Great Basin are normal faults, consisiting of steeply dipping horsts and grabens, tilted blocks bound by planar faults, and rotated blocks bound by downward flattening or listric faults. Normal fault blocks in the study area are primarily tilted blocks, though there is some evidence of the Baneberry fault in northwestern Yucca Flat, the Yucca Fault, and faults on Yucca Mountain flattening of curving slighdy with depth (Elwood and others, 1985; Scott, 1984; Carr, 1974).

Mapping by Scott and Bonk (1984) on Yucca Mountain shows a series of west-dipping normal faults with hundreds of meters of offset which break the Miocene volcanic strata into north-trending blocks. Within the major blocks are abundant minor west-dipping normal faults with less than three meters of offset which further break up the larger blocks.

Scott (1984) notes that dips of major normal faults decrease about 10° down 200 m of vertical exposure, suggesting curved fault surfaces. He explains the abundant minor faults within the major blocks as secondary faults caused by internal readjustment of the hanging wall block to movement over curved normal fault surfaces.

Cores from three bore holes on Yucca Mountain show coatings of calcite and opal on fractures. Uranium-series dating on the calcite and opal samples group at 28,000 +/- 31

5.0000 years, 170,000 +/- 30,000 years, 280,000 +/- 50,000 years, and older than

400.000 years. These dates suggest there has been at least four episodes of recent recurrent faulting at Yucca Mountain (Szabo, 1984).

Downhole motion pictures in boreholes on Yucca Flat show an upward decrease in bedding in alluvium on the hanging wall of a buried, east-dipping normal fault. Elwood and others (1985) suggest the upward decrease in dip is due to rotation of the downthrown block during syncontemporaneous listric faulting and alluvial deposition. The lack of rotation of the uppermost 250 m of alluvium indicates listric faulting ceased prior to its deposition.

Focal plane mechanisms from seismically active north-south trending faults in the study area show that many of the earthquakes are produced by right-slip movement

(Rogers and others, 1983). Areas displaying such movement include Sarcobatus Flat,

Pahute Mesa, Jackass Flat, Indian Spring Valley, and Thirsty Canyon. Right-lateral movement on north-trending faults is in accordance with least principal stress direction of

N50^W. The ubiquitous presence of normal-oblique faults may indicate that transmitted right-lateral shear stress associated with the transform configuration of the Pacific and

North American plates is ongoing in the southwestern Great Basin and is now displayed on north-trending rather than northwest-trending faults. 32

LINEAMENT AN AT .YSIS OF THE

SOUTHERN WAITER T .ANF

Introduction

The use of Landsat imagery in structural interpretations is based on the concept of morphotectonics, or the regional study of landforms (Gold, 1980). In a morphotectonic interpretation, internal structures and external forms and outlines of major topographic units such as mountains, basins, and plateaus, are analyzed for their tectonic significance. This is possible because of the great influence of structure on the geomorphology of landforms.

The morphological pattern developed on the surface often represents subsurface structural elements.

Landsat satellites are passive imaging systems, using solar-derived electromagnetic radiation in the visible and infrared wavelengths to view the two dimensional configuration of rock structures, and to analyze discontinuities. Discontinuities, as viewed by the imaging system sensor, are contrasting adjacent features. Primary discontinuities are inherent features of the rock. Examples are bedding, lithologic contacts, or differential weathering characteristics. Secondary discontinuities are imposed on the rock via deformation. Secondary discontinuities are analogous to structural discontinuities such as faults, shears, or folds. Since features forming structural discontinuities tend to weather easily, they often produce valleys, drainages, saddles or other erosional landforms.

Discontinuities are often expressed as linear features. There are three main categories of linear features: 1) Lineations derived by point or segment alignment, such as hot springs, volcanic centers, drainages or ridges; 2) Linear truncation and offsets of contours; and 3) Linear boundaries between structural domains (Gold, 1980). The definition of lineaments set forth by O'Leary and others (1977) was used in this analysis of the southern Walker Lane. Lineaments are mappable linear features that differ distinctively from adjacent landscape features and may reflect subsurface phenomena.

Lineaments on Landsat imagery were defined by alignments of geomorphic features such as straight streams, valley segments, or landform boundaries, and by linear tonal differences due to differences in vegetation, soil or rock composition, or moisture content. Lineaments are both simple, formed by a single type of feature, and composite, defined by a combination of features. Often, the nature of the feature producing the lineation is not resolvable at imagery scale. Comparison of lineaments with topographic and geologic maps helped to discern their origin.

Methods of Lineament Mapping on Landsat Imagery

As mentioned earlier, lineaments were mapped on clear mylar overlays from

Landsat 4 and 5 Thematic Mapper images of the Bald Mountain, Death Valley, Goldfield, and Las Vegas scenes, and from eight subscenes made from the western half of the Bald

Mountain scene. Because of the regional nature of the study and to eliminate distracting noise, only linear features greater than 1 mile (1.6 km) were mapped as lineaments. All seven bands and the false and real color composites of the Yucca Mountain subscene were mapped. Comparison of image quality and lineament frequency indicated that bands 5, 6, and 7 were most useful for structural analysis in the study area. Therefore, in five of the remaining seven subscenes, lineaments were mapped from bands five, six and seven, and from the false color composite. The Pahute Mesa and the Kawich Valley subscenes, however, were available only in the false color composite (band 2=blue, band 3=green, and band 4=red). Lineaments from those areas were derived from the false color composite and the Bald Mountain scene. 34

The factors which most greatly affect the ability to discern lineaments on imagery are spatial resolution and sun elevation angle and azimuth. The ideal resolution of Landsat

Thematic Mapper imagery is determined by the instantaneous field of view of the imaging system, or the dimensions of one picture element (pixel). The size of a pixel on TM imagery, bands 1 through 5 and band 7 is 28.5 m by 28.5 m (94 ft by 94 ft). A band 6 pixel is 120 m by 120 m (394 ft by 394 ft). The actual spatial resolution, however, is determined by several factors including pixel size, quality of the imaging system, atmospheric conditions, image reproduction methods, and the contrast ratio of the scene.

Contrast ratio, the ratio between the brightest and darkest parts of the image, is the result of electromagnetic response differences between individual objects, atmospheric scattering, and the sensitivity of the remote sensing system and recorder (Sabins, 1978). Images with low contrast ratios are generally not as useful for lineament mapping as those with higher ratios.

The second primary factor in lineament recognition is the angular relationship between the linear feature and the illumination source, the sun in Landsat images. Linear features trending perpendicular to the sun azimuth will be enhanced, whereas features trending parallel to it will be subdued. A low sun elevation angle will also greatly enhance linear features. Landsat 4 images used in the study were taken in the early morning on

November 17, 1982. The sun azimuth at this time is from the southeast and the sun elevation low. Therefore northeast-trending features would tend to be enhanced. Landsat

5 images were taken in the early morning on June 26,1985. At this time the sun is from the northeast and the elevation angle low. Therefore northwest-trending features should be emphasized. Filtering is a often used method of improving image quality and enhancing features for lineament analysis. To highlight lineaments in the Black Mountain-Thirsty Canyon

Tuff region of the study area, I built a number of filters for Landsat 5 Themetic Mapper digital data of bands 5 and 7, using Mackay School of Mines' VAX-IDIMS image 35 processing system. Lineaments were mapped from low pass, high pass, Laplacian, northeast and northwest directional filtered images. A discussion of filtering and the filters used in this study is given in the appendix.

Scale is important in determining the character and continuity of linear features. For example, range fronts which appear irregular at subscene scale (1:125,000 for a 16" by 20" hardcopy) may appear to be linear at scene scale (1:555,000 for a 16" by 20" hardcopy).

Or, linear features which are aligned but not continuous at subscene scale may appear continuous at scene scale. To compensate for scale differences, lineaments from each subscene band, the color composites and scenes were combined and transferred to a

1:250,000 scale topographic composite of southern Nye County. Map reductions and enlargements were made using a Gordon Enterprise Map-O-Graph. Total lineaments were tallied and their trends determined. A 0.75" by 0.75" square grid system was used to increase the accuracy of determining attitudes and counting linear features. Each square measured 4.8 km by 4.8 km (3 miles by 3 miles). Lineaments were counted one time for each grid square. If a lineament crossed grid squares, it was counted once in each square.

This method was employed to give equal weight to long and short lineaments. Trends and frequencies were plotted as histograms and rose diagrams.

The orientation and frequency of faults mapped on the southern Nye County geologic map (Cornwall, 1972) were tallied in the same method as the lineaments. These trends were also plotted as histograms and rose diagrams for comparison with the lineaments. Geologic maps were also used to determine the relationship between the geology and the lineaments. F.valuation of Image Bands

The benefits of the Thematic Mapper's multiple band format for structural analysis was demonstrated in the study of the Yucca Mountain subscene. Table 2 describes the characteristics of each spectral bands. Bands 1, 2, and 3 correspond to the visible portion of the spectrum (blue, green, and red, respectively), band 4 is in the photographic infrared, bands 5 and 7 are in the middle infrared portion of the eletromagnetic spectrum, and band 6 is in the thermal infrared portion.

For the study of the Yucca Mountain subscene, all seven bands, and the false and real color composites of Landsat 4 imagery were used. Comparison of lineament frequency and image quality between bands determined that, in general, bands 5, 6, and 7, the near infrared and thermal bands, were found to display more structural information than bands 1 through 4 and the color composites. Histograms of azimuth vs. frequency illustrate different populations of lineament groups between the bands. The histograms are displayed in Appendix B. The histograms show band 1, the shortest wavelength band, has two distinct popoulation groups trending north-south and northwest. Bands 2, 3, 4, 5, and

7 have three groups trending north-south, northwest, and east-west. Band 6 has a fourth distinct population trending northeast, and a very strong northwest population. The difference between lineament population groups can be explained by spectral reflectance and resolution differences between wavelength bands.

Landsat 4 images of the study area were taken in mid-November, 1982. At this time there was snow at the higher elevations and a sparse cloud cover. In bands 1 through

4, snow has a very high reflectance and clouds are impenetrable (Dozier, 1984). On images from these bands, areas covered with snow or shadowed by clouds are marked by saturated returns. In these areas, which are bright white on imagery, the contrast ratio is essentially zero, and the overall resolution of the images decrease. The real color images are produced by compositing bands 1, 2, and 3. The false color images are produced by 37

Table 2 Thematic Mapper Spectral Bands (after Salomonson and others, 1980)

Wavelenath Characteristics

0.45 to 0.52 um Blue-green. Maximum penetration of water; useful for bathymetric mapping in shallow water. Good for distinguishing soil from vegetation; deciduous from coniferous plants.

0.52 to 0.60 um Green. Sensitive to green reflectance by healthy vegetation.

0.63 to 0.69 um Red. Sensitive to chlorophyll absorption for plant species differentiation.

0.76 to 0.90 um Reflected IR. Sensitive to near infrared reflectance of healthy vegetation for biomass surveys, and useful for mapping shorelines.

1.55 to 1.75 um Reflected IR. Indicates moisture content of soil and vegetation. Penetrates thin clouds. Good contrast between vegetation types.

10.-40 to 12.50 um Thermal IR. Useful for nighttime mapping, and estimating soil moisture.

2.08 to 2.35 um Reflected IR. Sensitive to vegetaion moisture and to hydroxyl ions in minerals for geological mapping. 38 compositing bands 2, 3, and 4. The masking effect of snow and cloud cover which characterizes bands 1 through 4 also occurs in the composite imagery, thereby decreasing the spatial resolution. In the longer wavelength bands, 5 and 7, snow has a very low reflectance and clouds are penetrable. Contrast increases, therefore the overall spatial resolution of the scene increases, and a greater amount of information is available for detailed lineament analysis.

In band 6, important regional information for lineament analysis is evident. Band 6 images in the thermal infrared portion of the electromagnetic spectrum. The imagery depicts the pattern of heat emitted and reflected by surface materials. The ability to discriminate between adjacent materials depends on the thermal contrast between the materials. The time at which the imagery is aquired determines in part the thermal contrast.

Landsat 4 TM imagery was aquired in the early morning when the sun azimuth was southeast and the sun elevation angle low. In the early morning, the thermal contrast between materials is at a minimum. However, because of the low sun angle at this time, northwest-trending highs produced long shadows, and northwest-trending valleys were shadowed. These areas emitted lower temperatures and are characterized by dark signatures on the thermal images. At the same time northeast-trending topography was in full sunlight and therefore had a warm temperature. The thermal image signature on northeast features is bright In addition, the low resolution of band 6 images acts in the same manner as a low pass filter, removing extraneous topographic noise and emphasizing the orientation of regional landform boundaries. The low resolution and topographic effects in the band 6 image work together to emphasize aligned northeast and northwest features. These effects are well illustrated in the Timber Mountain area of the Yucca

Mountain subscene. In the visible and near infrared wavelength bands, northwest-trending lineaments are not readily apparent, possibly due to noise caused by the radial drainage pattern, cooling joints, and caldera collapse features. In the thermal band, however, northwest lineaments define the dominant structural grain through Timber Mountain. Photographs of bands 1, 5, and 6, illustrating the contrast differences are shown as figures

8, 9 andlO.

The greater applicability of bands 5 ,6, and 7 for structural analysis of the Yucca

Mountain subscene is demonstrated by the graph of total lineaments per band (fig. 11).

Bands 4, 5, 6, and 7 show the greatest number of lineaments per band. Though band 4 is useful for accentuating vegetative differences, much information is lost due to the high reflectance in areas with snow or cloud cover. For these reasons bands 5, 6, and 7 were evaluated preferentially over the other bands in the remainder of the study area. To obtain vegetation lineaments of band 4 and any information that may be on bands 2 and 3, false color composites were also mapped.

43

Chart showing lineament frequency per band.

LINEAMENTS/BAND

N U M B E R OF LINEAMENTS

BAND

Figure 11. Graph of total lineaments per band for the Yucca Mountain subscene. 44

Discussion of Lineaments

The lineament map of the study area is shown in figure 12. Lineament length ranges from 1.6 km (1 mile) to 32 km (20 miles). Many of the longest lineaments represent range boundaries, though a lineament extending northwest from Shoshone

Mountain through Timber Mountain is almost 24 km (15 miles) long. In general, northwest lineaments in the study area are the most lengthy, though there are also short northwest lineaments, north-south trending lineaments are both long and short, and northeast trending lineaments tend to be short.

The distribution and orientation of lineaments illustrate a possible boundary between the Walker Lane Belt and the Basin and Range province to the east. Northwest­ trending linear features are concentrated west of an imaginary line extending northwest from Yucca Flat to Cactus Flat. The Yucca-Frenchman fault, a northwest-trending shear zone located in the eastern Nevada Test Site, lies along this boundary. It was suggested in an earlier section that the Yucca-Frenchman fault may represent the eastern boundary of the

Walker Lane in that area. A westward step of the eastern boundary may occur along a northeast-trending left-slip fault at the southern end of the Yucca-Frenchman fault, connecting it to the Las Vegas Valley shear zone to the south (see figure 7).

East of the boundary, in the northeast comer of the lineament map, the north-south trending Kawich, Belted, and Reveille Ranges display more typical basin and range topography. The southern end of these ranges, however, are slightly concave westward.

This may suggest their orientation has been influenced by right-lateral shear. The westward curvature of the Desert and Spring Ranges to the south has been attributed to oroclinal flexuring. This oroclinal flexuring is though to be the result of right-lateral drag along the northeast boundary of the Las Vegas Valley shear zone (Albers, 1967). The analogous, though not as extreme, westward curvature of the Kawich, Belted, and Reveille

Ranges is further evidence of the position of the eastern Walker Lane boundary.

The trends of 608 lineaments were tallied from the composite lineament map (fig.

13). From these trends a rose diagram of lineament azimuth vs. frequency, normalized to

100%, was produced. The rose diagram shows strong northwest and north-south populations (Fig. 14). Lineaments oriented N30°W to N50°W make up 29% of the total population, while those oriented N10°E to N10°W make up 18%. Concentrations of northeast-trending lineaments occur at N20° E to N30°E and N50°E to N60°E, but these combined areas make up only 10% of the total lineaments.

In order to better discern the nature of the linear features, the lineament map was compared with the geologic map of southern Nye County (Cornwall, 1972). Many lineaments correlate with mapped faults and contacts, though lineaments tend to be longer than the corresponding geologic features. This may reflect the regional, small scale character of satellite imagery. Features which look continuous at Landsat imagery scale and resolution may be isolated though aligned on the ground. Not all lineaments correspond to a mapped geologic feature.

To further compare lineament trends and frequencies with those of mapped structures, the trends of 672 mapped faults in the study area were tallied (Fig. 15). A rose diagram of mapped fault trends and frequencies (fig. 14), with frequencies normalized to

100%, shows an approximately equal distribution of faults around a node at NIO^W to

N 10°E (27% of the total faults). The rose diagrams of the mapped faults and the mapped lineaments illustrate the lineament population does not correspond to the fault population.

Lineaments trending N30°W to N50°W make up 29% of the total lineaments, while faults trending N30°W to N50°W make up only 11% of the total faults. 13% of the total lineaments trend N10°W to N10°E compared to 27% of the total faults. The percentages of northeast-trending faults and lineaments are approximately the same (N40°E to N70°E

11% of total faults and 10% of total lineaments). The greater percentage of north-south faults than percentage of north-south lineaments is an expression of the difference between the number of northwest-trending 47

LINEAMENT MAP, SOUTHERN NYE COUNTY

AZIMUTH

FREQUENCY

Figure 13. Histogram of lineament trends vs. frequency, from the composite lineament map of Southern Nye County. LINEAMENTS MAPPED FAULTS

ROSE DIAGRAMS SHOWING AZIMUTH VS. FREQUENCY

Figure 14. Rose diagrams of lineaments and mapped fault trends, Southern Nye County, Nevada.

oo 49

MAPPED FAULTS, SOUTHERN NYE COUNTY

AZIMUTH

FREQUENCY

Figure 15. Histogram of mapped fault trends vs. frequency, from the geologic map of Southern Nye County. faults (11%) and lineaments (29%). By subtracting the number of lineaments and faults striking N30°W to N50°W from the total number of lineaments and faults, and recalculating the percentages, it is possible to directly compare other population groups without the influence of the northwest population. The recalculations show lineaments striking N10°W to N10°E make up 25% of the lineaments without the northwest population, and faults of the same orientation make up 31%. Both northeast-trending lineaments and faults make up 14% of the lineaments and faults without the northwest population. Therefore, though there are slightly more faults than lineaments, the relative populations of both the north-south and northeast faults are in accordance with lineament populations of the same trend. The question therefore is what is the origin of the northwest-trending lineaments?

In some areas, such as the Cactus Range and in northwest-trending washes on

Yucca Mountain, northwest-trending lineaments do correspond to faults. On Timber

Mountain a radial fault pattern with a strong northwest fabric is evident. This pattern is associated with caldera resurgence, and the Timber Mountain caldera is elongated in a northwest trend. Northwest-trending lineaments which cross Timber Mountain, however, continue southeastward through rocks of different ages and lithologies. The lengthy, northwest-trending lineaments which cross Timber Mountain, Dome Mountain, Shoshone

Mountain, and Busted Butte were ground checked to determine their origin. Low altitude aerial photographs were used in conjunction with Landsat imagery during ground checking of lineaments. In many places the lineaments corresponded to sites of preferential erosion, such as valleys, saddles, or canyon (fig. 16). Stereonets of joints and fractures, located in

Appendix C, show no regular northwest-trending fracture system or rotation of joint attitudes to a northwest trend along the length or across these lineaments. (See stereonets of the Busted Butte linemant, Chukar Canyon, and Dome Mountain Canyon). However, at some intersections of northwest-trending lineaments with linear features of different orientations (north-south or northeast) there is evidence of northwest-trending, closely

52 spaced fractures, some of which show movement (fig. 17). (See stereonets of the mouth of Dome Mountain Canyon, and the drainage southwest of Chukar Canyon). Figure 18 is a photograph of an offset tuff sequence at the intersection of north-south trending 40-Mile

Canyon and a northwest lineament cutting Dome Mountain. The fault is vertical, striking

N30°W, with 1 m of vertical offset. In contrast is a 1-2 m wide gouge zone at the intersection of 40-Mile Canyon and the northwest-trending Chukar Canyon lineament, about 1 mile to the north of the previously mentioned lineament. The gouge zone contains clasts with horizontal striations indicating horizontal movement.

To summarize the characteristics of northwest-trending lineaments: A single northwest-trending lineament may correspond to a mapped fault at one end, strike into an area of aligned preferential erosion with no apparent signs of deformation, and at the intesection of the northwest lineament with a lineament of a different orientation, may display closely-spaced northwest-trending vertical fractures with or without signs of movement If there is movement it can be horizontal or vertical.

The continuity, parallelism, and total number of northwest-trending linear features suggest that they are related to a northwest-trending structural system. An explanation for their complicated and contrasting characteristics is differential surficial expression of movement along underlying northwest-trending bedrock faults. Except at the exact location of the calderas, volcanic rocks of the southwestern Nevada volcanic field blanket Paleozoic basement. South of the southwestern Nevada volcanic field, northwest-trending valleys and ranges which characterize the Las Vegas Valley shear zone, and oroflexural bending of ranges bounding the shear zone to the northeast, illustrate the strong control of the northwest-trending structure on topography. Analogous structural control of the distribution, orientation, and pre-existing topography of Paleozoic rocks underlying the volcanic rocks of the southwestern Nevada volcanic field is probable. The northwest alignment of claderas in the volcanic field, the northwest elongation of Timber Mountain caldera, and the westward curvature of ranges bounding the proposed eastern boundary of Figure 17. Northwest-trending closely spaced fracture at intersection of a northwest lineament cutting Dome Mountain and north-south trending 40-Mile Canyon. BBBIMWBIB'IMIffllli****"*'""------— IILUlUUUHimillM

55 the Walker Lane are evidence of a northwest-trending structural system underlying the southwestern Nevada volcanic field.

Figure 19 is a photograph of southwestern Yucca Mountain, which shows the north-south trending spurs of Yucca Mountain offset in an apparent right-lateral sense along a northwest trend. This relationship is shown on the lineament map. Mapping of the easternmost of these spurs by Scott and Bonk (1984) shows the offset is caused by primarily vertical movement along northwest-trending faults. Some striations along the faults, however, are horizontal. This situation is analogous to slip data along the Rock

Valley fault zone (Zoback and Frizzell, 1985) and at Hoover Dam (Angelier and others,

1985), which show both vertical and horizontal movement along faults of the same orientation. As mentioned earlier, Angelier and others relate this phenomena to temporal variations in the greatest and intermediate stress directions during a regime with a constant least principal stress direction. In the mid to late Miocene (about 20 m.y. to 10 m.y ago), the direction of the least principal stress in the southern Great Basin was oriented at about

S70°W (Zoback and others, 1981). In this stress orientation, northwest-trending structures would be in a primarily extensional mode, although movement along northwest faults may be horizontal, vertical or oblique. Surficial expression in the volcanic cover of movement along bedrock faults may be variable. At sites of enhanced tectonic susceptibility, such as calderas or at the intersections of faults with differing orientations, movement along the faults may reach the surface, being displayed as either faults or fractures. However, at other locales, rocks at the surface may simply experience extension or pulling apart, thus becoming sites of preferential erosion without apparent deformation.

The orientation, continuity, and parallelism of northwest-trending lineaments in the volcanic rocks of the southwestern Nevada volcanic field, in combination with evidence of northwest-trending topography and structures, the northwest elongation of Timber

Mountain caldera, and the westward curvature of ranges northeast of the area of concentrated northwest-trending linear features imply that the Walker Lane is continuous throuth the southwestern Nevada volcanic field. However, the evidence also shows it is not a major shear system. What then is the age of faulting associated with the Walker Lane in the southwestern Nevada volcanic field? 58

Apt*, of Northwest Faulting in the Southern W a lV e r T ^

The distribution of lineaments through volcanic units of different ages is indirect evidence of the timing of a change in the stress regime in the southern Great Basin from a regime with the least principal stress oriented at about S70®W to the present regime with the least principal stress oriented at about N50°W. A simplified geologic map of the study area, with lineaments mapped from Landsat imagery overlain on it, is presented as figure

20. On the map, units older than 9.5 m.y., the age of the Shoshone Mountain Rhyolite of the Timber Mountain Tuff are shown in grey; silicic volcanic rocks younger than 9.5 m.y. are red, pink, and orange; young basalts are blue, and alluvial deposits are yellow.

The map shows that northwest lineaments are essentially absent from all units younger than 9.5 m.y. old. The alignment of Black Mountain caldera (6 - 8.5 m.y. old) and Stonewall Mountain caldera (6.3 m.y. old) along the Walker Lane trend, and the northwest distribution of the tuffs between Black Mountain and Stonewall Mountain indicate the influence of northwest-trending stresses until about 6.3 m.y. ago. However, the apparent truncation by the Thirsty Canyon Tuff (8.5 m.y. old) of northwest-trending lineaments which cross Timber Mountain and Shoshone Mountain, the scarcity of northwest lineaments in the tuffs erupted from Black Mountain and Stonewall Mountain calderas, and the lack of silicic volcanism after 6.3 m.y. ago indicate that stresses associated with the formation of northwest-trending lineaments declined sometime after 9.5 m.y. ago, and ceased after 6.3 m.y. ago.

The timing of the decline and cessation of a stress regime favoring activity along northwest-trending structures, as determined from linear features on Landsat imagery, is in agreement with temporal groupings of basalts in the Death Valley - Pancake Range belt.

Basalts between 6.3 m.y. and 8.7 m.y. old are associated with the waning stages of silicic volcanism (Noble and others, 1984). These basalts strike consistently north to N15°W, indicating they were emplaced in a stress regime o 10 20 30 km

36 00' Simplified Geologic Map of Southern Nye County

Explanation

Q a Quaternary Alluvium

b Basalt flows and plugs, younger than 8.5 rn.y

T w Welded Tuff, undifferentiated

Tth Thirsty Canyon Tuff

Tr b Rhyolite of Black Mountain

Tt r Trachyte of Black Mountain

U Undifferentiated rock units older than 8.5 rn.y.

Lineaments from Landsat TM imagery

Geologic data from : Henry Cornwall (1972), Geology of Southern Nye County with a west-southwest least principal stress direction. The younger grouping of basalts in the belt are about 4 m.y. old or younger, and show a fairly consistent northeast trend in alignment of eruptive centers and dikes. These basalts have been erupted in a stress regime favoring intrusion along a north-northeast trend, indicating a northwest least principal stress direction (Carr, 1984). The basalt data suggests the present stress regime was in existance by 4 m.y. ago, and possibly as early as 6.3 m.y. ago.

Listric faulting along north-south trending faults in Yucca Flat and Pahute Mesa may be evidence that the stress regime rotated clockwise and did not simply jump from

S70°W to N50°W. According to Elwood and others (1985), listric faulting in Yucca Flat occurred during deposition of alluvium, but ceased before deposition of the uppermost 250 m. Pure dip-slip movement, which is favorable for listric faulting, would occur on north- south faults during a stress regime with an east-west least principal stress direction. During continued rotation of the stress direction, movement on north-south faults becomes oblique, possibly causing listric faulting to cease. The deposition rate or age of listric faulting in Yucca Flat is not known (L. McKague, pers. comm., 1986), but listric faulting on Pahute Mesa began after the deposition of the Thirsty Canyon Tuff, 8.5 m.y. ago. The gradual slowing down of silicic volcanism and activity along northwest-trending structures, suggested by the scarcity of northwest-trending linear features crossing rock units younger than 9.5 m.y. old, may be further evidence of the continuous clockwise rotation of the stress regime.

In the present stress regime, northwest structures are parallel or subparallel to the direction of least principal stress. In this orientation, northwest-trending faults may be experiancing compression across them and therefore be inactive. Anderson (1984), however, has suggested that presently in the Basin and Range active northwest faults may be separating regions of differential extension. The lack of northwest-trending lineaments in rocks younger than 9.5 m.y. old in the study area suggests that major activity along northwest structures has not occurred since their deposition. The study therefore suggests that while the Walker Lane is a continuous feature through the study area, major activity along structures associated with the Walker Lane declined and possibly ceased after 6.3 m.y. ago. This is in response to a clockwise rotation of the least principal stress direction from an orientation of S70°W to the present orientation of N50°W sometime after deposition of the Shoshone Mountain Rhyolite, 9.5 m.y. ago. 63

Aeromagnetic Lineaments

An aeromagnetic map of a region which includes the study area is shown in figure

21. To compare magnetic anamoly trends in the study area with lineament trends mapped from Landsat Thematic Mapper imagery, magnetic anamoly trends were mapped from the

1:500,000 scale aeromagnetic map of Nevada (Zietz and others, 1977). This map is shown in plate 1. Criteria for mapping magnetic lineaments included alignments of high or low anamolies, abrupt changes in intensity values, and overall intensity patterns. The lineament map was reduced, using a Gordon Enterprise Map-O-Graph, to fit as an overlay on an 8.5" by 11" map of the study area.

Magnetic source rocks in Nevada fit five broad categories (Zietz and others, 1977).

These categories are Precambrian metamorphic and intrusive rocks, Mesozoic gabbroic rocks, Mesozoic granitic rocks, Tertiary calc-alkalic volcanic and intrusive rocks, and

Upper Cenozoic basalts and associated rhyolites. Areas with weak aeromagnetic signatures may be due to rocks with originally weak magnetization such as carbonates and silicic tuffs with a low iron content, or rocks whose original magnetism has been destroyed by hydrothermal or other alteration.

In the study area, two regions with low magnetic gradients are apparent (Plate 1).

The first region, in the north-central part of the study area, corresponds to the Cactus Flat -

Gold Flat alluvial basin. The low gradient may be interpreted as a great depth below the surface of the basin to the source rock. The second area with a low magnetic gradient is in the southern part of the study area, extending northeast to include the Yucca Flat area. The low gradient may be due to the combination of a deep source rocks in the basins, and the inherent low magnetic signature of Paleozoic and Mesozoic carbonate and detrital rocks which outcrop in that region.

The overall pattern of aeromagnetic anamolies in the study area trend northwest and east-west. Northwest-trending anamolies correspond to the trace of the Walker Lane and are concentrated in a region about 50 km wide. A similar north west-trending pattern of aeromagnetic anamolies of approximately equal width is traceable along the length of the

Walker Lane north to the California border. High gradients along the trend are caused by igneous intrusions. Northwest-trending anomalies crossing the Timber Mountain area corresponds almost precisely to lineaments mapped from Landsat imagery. The anamoly may be due to a buried intrusive body underlying the caldera region, alignment of Cenozoic basaltic rocks along the trend, or fault zones transposing rock units of different magnetic intensities. Bath and Jahren (1984) suggest that northwest-trending magnetic anamolies at

Yucca Wash and the Armagosa Desert, determined by air and ground magnetic surveys, represent fault zones in those areas.

East-west trending anamolies occur in the central part of the study area. In the

Yucca Mountain area, the east-west anamoly is interpreted as a tabular body of sedimentary rocks containing magnetite (Bath and Jahren, 1984). The sedimentary source rock is thought to be magnetized argillite of the Paleozoic Eleana Formation. Because the Eleana

Formation is not typically highly magnetized, magnetization was probably induced by the heating effects of an underlying pluton which converted pyrite to magnetite. In general, east-west anamoly trends are ubiquitous in western and eastern Nevada. They are thought to represent zones of crustal weakness along which intrusive masses were emplaced (Carr,

1984).

In general, northwest-trending aeromagnetic lineament correspond nicely to northwest-trending lineaments mapped from Landsat imagery. North-south and northeast­ trending linear features, which are evident on Landsat imagery, are scarce on the aeromagnetic map of the study area. North-south trending anamolies bound the Reveille,

Belted, and Kawich Ranges in the northeast part of the study area, but are generally absent in other areas. Highly detailed magnetic surveys in the Yucca Mountain and Yucca Flat areas by Bath and Jahren (1984) indicate a number of north-south trending parallel negative and positive anamolies that they interpret as being the result of vertical faults. These anamolies are not apparent at a regional scale. The absence of northeast-trending anamolies from the map is surprising in light of the northeast-trending Death Valley - Pancake Range basalt belt. Except in the Yucca Mountain subscene, east-west lineaments which are prominent on the aeromagnetic map are not strongly represented by lineaments on Landsat imagery. This may be expected since the east-west aeromagnetic anamolies are thought to be due to aligned intrusive masses which may or may not surface.

The northwest pattern of aeromagnetic lineaments is further evidence that the

Walker Lane is continuous through the study area, and that the Walker Lane is a major zone of crustal weakness along which igneous intrusions and faulting have occurred. 67

Topographic Lineaments

Major regional landforms, such as mountain ranges, plateaus, and basins, are typically related to the effects of diastrophism, or crustal warping and deformation. The landforms are continually modified by erosion, with the most powerful landscape modifier being water. Topography, which is in essence the modified landforms, is a direct reflection of the underlying geology. A combination of the physical and chemical characteristics of the rock determine topographic features. Physical characteristics include dip and strike, jointing, foliation, and stratification; the most important chemical characteristic is the rock's resistance to erosion (Easterbrook,1969).

In the southwestern Great Basin, the tensional forces of the Basin and Range and shearing forces of the Walker Lane are responsible for producing the landscape. In the study area, these forces work on the extensive volcanic terrain of the southwestern Nevada volcanic field. Drainage patterns, which modify the landscape, reflect structural and/or lithologic control. On volcanic plataeus, such as Pahute Mesa, the drainage pattern is parallel; on domes or resurgent calderas, such as Timber Mountain or Black Mountain, the pattern is radial. Often deep, straight canyons are formed in the volcanic terrain. Canyon location may be structurally controlled, or may be the result of differential erosion of tuff units. The overall drainage pattern is centripital, with a number of streams from surrounding high areas emptying into a single basin. The drainage pattern in the basins is usually braided. Any study of linear features on topographic maps will mirror the landform boundaries and the drainage patterns. While the landform boundaries are indicative of the regional tectonics, drainage patterns may not be.

Topographic lineaments were mapped from 1:250,000 scale topographic maps.

Though 1:24,000 and 1:62,500 scale maps (7-1/2' and 15' quadrangles) were examined and used in the study, the smaller scale maps better illustrate relationships of landforms to one another over a larger area. Linear features associated with drainage patterns, landform 68 boundaries, linear valleys and ridges, and slope changes were mapped on clear mylar overlays. Only lineaments longer than 1.6 km (1 mile) were mapped. For direct comparison with aeromagnetic and Landsat lineaments, the topographic lineaments maps were reduced, using a Gordon Enterprises Map-O-Graph, to fit as an overlay on an 8-1/2" by 11" map of the study area (plate 1).

Topographic lineaments which correspond to landform boundaries correlate closely to Landsat lineaments in the same areas. Many drainage-related lineaments also are similar.

Lineaments within the major landforms, however, are not correlative. This is because the origin of Landsat lineaments is much more diverse than topographic lineaments.

Lineaments on Landsat imagery may be due to vegetative differences, geologic features such as joint patterns or rock and soil contacts, or moisture content, as well as landform boundaries and drainage patterns. Topographic lineaments, though informative, have a much more limited origin. 69

DISCUSSION AND CONCLUSION

The lineament study demonstrates that the Walker Lane is a continuous feature through the southwestern Nevada volcanic field. The question of the activity of faults associated with the southern Walker Lane is not so easily determined. If the origin of many of the northwest-trending lineaments is movement on underlying faults, the lack of northwest-trending lineaments in young volcanic units may suggest that movement on the underlying structures ceased by the time of, or soon after, their deposition. This being the case, the volcanic units erupted from Stonewall Mountain and Black Mountain calderas provide relative ages of the time of cessation of movement along structures with a northwest trend. The 8.5-6.3 m.y. ages of these units agrees nicely with other evidence that supports a clockwise rotation of the least principal stress direction at about the same time. The lineament distribution therefore suggests that since cessation of movement along northwest-trending structures is directly related to a change in the orientation of the stress regime, all northwest-trending structures in the same stress regime must be inactive.

To follow this line of reasoning two questions must be answered. First, is it valid to assume that northwest-trending structures upon which movement could occur are present in basement rocks underlying the area now covered by tuffs erupted from Stonewall

Mountain and Black Mountain calderas? Secondly, assuming the lack of northwest­ trending lineaments are caused by cessation of movement along northwest-trending structures in that area, does this imply all other northwest-trending structures in the same stress regime are inactive?

It is possible that the lack of lineaments with a northwest-trend in the Stonewall

Mountain and Black Mountain areas may be due to an en echelon step in the Walker Lane.

This westward step would occur on a northeast-trending left-slip fault south of the Cactus

Range and north of Timber Mountain. However, there is no evidence of a northeast­ trending structure in that area on the geologic or aeromagnetic maps, and the northwest alignment of the Black Mountain and Stonewall Mountain calderas suggest that their location may be structurally controlled. The distribution of Thirsty Canyon Tuff in a relatively naixow northwest trend between the two calderas also may imply that its distribution was controlled by a northwest-trending topographic low. The evidence supports the asssumption that northwest-trending basement structures along which movement could occur are present in the area.

The second question is not so easily answered. Two possiblities exist for northwest-trending faults in the present northwest-trending stress regime. The faults may be feeling compression across them, and therefore, in this primarily extensional regime, be inactive; or northwest-trending faults are active and separating regions with different styles and magnitudes of extension. Seismological and geomorphic evidence suggests that northwest oriented faults are presently inactive in the southern Great Basin (Rogers and others, 1983). Unfortunately the seismological record is very brief. The northwest­ trending Death Valley - Furnace Creek fault zone, directly west of the study area, is active though it is presently seismologically quiescent. Its youthfulness, however, is evident in its geomorphic expression. Does the activity along the Death Valley - Furnace Creek fault zone indicate northwest-trending faults in the southern Walker Lane are also potentially active? A related question is why are northwest-trending faults of the central and northern

Walker Lane active, while faults of the southern Walker Lane appear to be inactive?

Perhaps these questions can be answered in terms of differential extension.

According to Anderson (1984), northwest-trending faults which are active in the present stress regime are separating regions with different styles and magnitudes of extension.

Seismologic and geomorphic evidence indicate that the southern Great Basin is tectonically quiescent compared to the central and northern Great Basin (Zoback and others, 1981).

The Death Valley - Furnace Creek fault zone may separate the active Inyo-Mono region to the west from the more quiescent southern Great Basin to the east Faults of the central and northern Walker Lane may be separating the relatively quiescent Sierra Nevada block to the 7 west from the actively spreading northern and central Basin and Range to the east. In this

scenario, northwest-trending faults of the southern Walker Lane may have become inactive

when the boundary between regions of differential extension moved westward to the Death

Valley - Furnace Creek fault zone. Lineament, volcanic and fault data suggest this is

related to the change in the stress regime.

Presently in the southern Great Basin, right-slip movement is occurring on north-

south trending faults. Normal faulting should be occurring on northeast-trending faults; focal plane solutions show both normal and left-slip movement along these faults (Rogers and others, 1983). However, there are not many faults which trend northeast. Perhaps the general paucity of northeast-trending faults along which extension can take place is a cause of the reduced rate of extension in the southern Great Basin. The overall slow rate of extension and right-slip movement on north-south faults make right-slip movement on northwest-trending faults unnecessary and therefore unlikely in the southwestern Great

Basin.

Still, it is possible that the close proximity of the active northwest-trending Death

Valley-Furnace Creek fault zone indicates northwest-trending faults of the southern Walker

Lane are potentially active, though presently quiescent Resolving the question of activity along specific northwest-trending faults is not possible in this study, although the study does indicate there is a higher risk of activity along north-south or northeast-trending faults than along northwest-trending faults.

This dilemma leads to the third objective of the study which was to consider the usefulness of satellite-generated remote sensing imagery in neotectonic analysis. The study indicates satellite imagery is possibly most useful in neotectonic analysis as a tool for analyzing regional relationships. Resolution is the limiting factor of satellite imagery for neotectonic analysis. Although the digital nature of imagery data allows for hardcopies of any scale to be obtained, the inherent resolution of the scene stays the same. The 72 dimensions of a band 5, thematic mapper pixel is about 30 m (90 ft) whether the image scale is 1:500,000 or 1:60,000.

A sense of regional relationships is essential in any neotectonic study. For example, the continuity of the Walker Lane was questionable in southern Nevada.

However, the multiband format of Landsat Thematic Mapper imagery allowed recognition of linear features through the young volcanics of the southwestern Nevada volcanic field that demonstrate the Walker Lane is a through-going structure from Honey Lake, California to Las Vegas, Nevada. The data also indicates that movement along northwest-trending structures in the southern Walker Lane may have ended 6 m.y. ago. Therefore, in future, detailed studys of recent fault activity in the southern Walker Lane vicinity it may be more efficient to concentrate on north-south or northeast-trending structures preferentially over northwest-trending structures. The study also illustrates the importance of intersections of structures as sites of enhanced tectonic susceptability. In conclusion, small scale, satellite­ generated imagery is useful in neotectonic analysis as a tool for making intelligent choices as to where to look more closely for recent fault activity. However, to determine the activity of a specific fault or group of faults it is necessary to use larger scale imagery and

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Livaccari, R. F., and Engebretson, D. C., 1984, Late Cenozoic basin and range extension: transtension tofree-face tectonics: Geol. Soc. Amer. Abst. Programs, v. 16, no. 5, p. 577.

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------, 1974, Measure and date of movement on the Las Vegas Valley shear zone, Clark County, Nevada: Geol. Soc. Amer. Bull., v. 85, p. 985 - 990.

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McKee, E. H., 1968, Age and rate of movement of the northern part of the Death Valley - Furnace Creek fault zone, California: Geol. Soc. Amer. Bull., v. 79, p. 509 - 512.

Moik, Johannes G., 1980, Digital processing of remotely sensed images: NASA Spec. PubL 431,330 p.

Narendra, P. M„ 1981, A separable median filter for image noise smoothing: IEEE Trans, on Pattern Analysis and Machine Intelligence, v. PAMI-3, no. 1, p. 21 - 29.

NASA, 1982, Landsat data users NOTES: U. S. G. S. Eros Data Center. Issue No. 23, 16 p. 78

Noble, D. C, 1972, Some observations on the Cenozoic volcano-tectonic evolution of the Great Basin, western United States: Earth and Planet. Sci. Letters, v. 17, p. 142 - 150.

Noblo, D. C., Vogol, T. A., WoiM, S. T., Erwin, J. W., MeKoo, E. H.,

Oldow, J. S. and Geissman, J. W., 1982, Oroflexural deformation in west- central Nevada reassessed: evidence from paleomagnetic data (abstract), EOS Trans. AGU, v. 63, p. 309.

O'Leary, D. W., Friedmon, J. D., and Pohn, N. A., 1976, Lineament, linear, lineation: some proposed new standards for old terms: Geol. Soc. Amer. Bull., v. 87, p.. 1463-1469.

Rogers, A. M. and Lee, W. H. K., 1976, Seismic study of earthquakes in the Lake Mead, Nevada-Arizona region: Bull. Seis. Soc. Amer., v. 66, p. 1657 - 1681.

Rogers, A. M., Harmsen, S. C, and Carr, W. J., 1983, Southern Great Basin seismological data report for 1981 and preliminary data analysis: U. S. G. S. Open-file Report 83-669, 240 p.

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Zoback, M. L., Anderson, R. E... and Thompson, G. A., 1981, Cainozoic evolution of the state of stress and style of tectonism of the Basin and Range province of the western United States: Phil. Trans. R. Soc. Lend A300 p. 407 - 437.

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Appendix A

THE LANDSAT IMAGING SATELLITES

Five Landsat satellites have been launched since the deployment of the first Landsat satellite by NASA in July, 1972. (This first satellite was originally called the Earth Resources Technology Satellite, or ERTS). Designated Landsat l through 5, launching dates of the satellites are: Landsat 1 on July 23, 1972; Landsat 2 on January 22, 1975; Landsat 3 on March 4, 1978; Landsat 4 on July 16, 1982; and Landsat 5 on March 1. 1984. These satellites have been supplying images of the Earth through means of the multispectral scanner (MSS) sensing instrument. In addition to the MSS, Landsat 4 and 5 carry a second generation Earth resource observation system, the Thematic Mapper (TM). The descriptions of the Landsat satellites in this report are primarily summarized from NASA's Landsat Data Users Notes (1982). The MSS and the TM sensors are object-space scanners which use moving mirror assemblies to scan in the crosstrack direction (perpendicular to the spacecraft ground track) and the orbital motion of the spacecraft to scan the along-track direction. Both sensors generate multispectral image data in a digital format. The TM, however, was designed to achieve finer spatial resolution, sharper spectral separation, improved geometric fidelity, and greater radiometric accuracy and resolution than the MSS (Engel and Weinstein, 1982). Design of the Landsat 4 and 5 satellites are identical, and differ significantly from the earlier Landsat satellites (fig. 22). The most conspicuous features are the single-wing solar power array, and the mast 83

A) Landsat 1,2, and 3 with the MSS

B) Landsat 4 and 5 with the MSS and the TM

Figure 22. Landsat satellites (after Sabins, 1978, and NASA, 1982) and antenna assembly. The mast and antenna assembly of Landsat 4 and 5 was designed for transmitting data via the Tracking and Data Relay Satellites (TRDS). The TRDS. in a geostationary orbit around the Earth, relays data from the Landsat satellites to a single ground recieving station at White Sands, New Mexico. This eliminates the need for onboard recorders as well as the extensive network of ground recieving stations required by Landsats 1 through 3. The orbits of Landsat 4 and 5 differ from the orbits of Landsat 1, 2, and 3. Landsat 4 and 5 travel in a repetitive, circular, sun-synchronous, near-polar orbit at a nominal altitude of 705 km over the equator. The satellites cross the equator at approximately 9:45 a.m. during the descending (north to south) portion of each orbit. The TM can also acquire thermal data during the satellites ascending (south to north) orbit which crosses the equator at 9:45 p.m. Each orbit takes almost 99 minutes, with the spacecrafts completing just over 14.5 orbits a day. Due to rotation of the Earth, the distance between ground tracks for two consecutive orbits is 2752 km at the equator. This orbital configuration creates a 16 day repeat cycle for the same ground track. The time interval between adjacent tracks is seven days. Landsat 1 through 3 traveled at altitudes of 920 km and completed each orbit in 103 minutes, 14 times a day. The orbital cycle was 18 days, resulting in a one day interval between orbits over adjacent tracks. Comparisons of Landsat orbits and systems is given in Table 3. Major differences exist between the basic design of the MSS and the TM. The MSS acquires data in four spectral bands in the regions between 0.5 and 1.1 um. The instantaneous field-of view, the size of one picture element, or pixel, of the MSS is 82 m by 82 m (269 ft by 269 ft). The TM 85 aquires data in seven spectral bands, covering the visible, near infrared, middle infrared, and thermal infrared regions of the electromagnetic spectrum. The instantaneous field-of-view of the TM is 28.5 m by 28.5 m (94 ft by 94 ft) in bands 1 through 5 and band 7, and 120 m (394 ft by 394 ft) in band 6. MSS data are acquired only as the scan mirror moves from west to east; no data are acquired during the return scan. The TM acquires data during both the forward (west to east) and reverse (east to west) sweeps of its scanning mirrors. The bidirectional approach for the TM reduces the rate of oscillation of the scan mirror and increases the dwell time of the individual detectors upon the Earth s surface, thereby increasing the radiometric sensitivity. Another major difference involves signal detectors. The MSS transmits incoming radiation from the Earth through fiber optics onto its detector arrays. The TM detector arrays, however, are located within the primary focal plane of the instrument, allowing incoming light to be reflected directly onto the detectors without transmission through fiber optics. The MSS uses 6 detectors for each of its four spectral bands, while the TM uses 16 detectors for bands 1, 2, 3, 4, 5, and 7, and four detectors for band 6 (the thermal band). These configurations minimize any loss in the intensity of incoming radiation and increase spatial resolution. Data is then quantified to 256 levels (8 bit) which allows detection of very small differences in reflected light energy. Comparison of the MSS and TM systems is given in Table 4. 86

TABLE 3 COMPARISON OF LANDSAT ORBITS AND SYSTEMS ( after Sabins, 1982)

Landaat 1. 2. 3. Landsat 4

Altitude 920 km 705 km Orbits per day 14 14.5 Number of orbits (paths) 251 233 Earth covered in 18 days 16 days Operational from 1972 - 1982 1982 on Onboard data storage Yes No Imaging systems: Multispectrai scanner Yes Yes Return beam vidicon Yes No Thematic Mapper No Yes

TABLE 4 COMPARISON OF MSS AND TM SYSTEMS (after Sabins, 1982)

Multispectrai Thematic Scanner Manner

Spectral bands 4 7 Angular field of view 11.60 14.90 Image swath width 185 km 185 km Image sidelap at Equator 14 X 7.6% Instantaneous field of view: Visible and reflected 0.087 mrad 0.043 mrad Thermal IR 0.17 mrad Spatial resolution: Visible and reflected IR 82 m 28.5 m Thermal IR (band 6) 120 m Picture elements per band 7.3 i 10^ 38 x 106 Picture elements per scene 29 i 106 266x 106 87

FILTERING TECHNIQUES FOR DIGITAL LANDSAT DATA

The digital Tor mat of Landsat data allows the processor or interpreter to mathematically alter the image, pixel by pixel, to increase contrast, emphasize subtle tonal differences, or highlight and group ranges of spectral signatures. Image manipulation can be a valuable tool for lineament studies, as linear features of various orientations can be enhanced (Chavez, 1983). Filtering is an often used method of improving image quality and enhancing features for photointerpretation. To highlight lineaments in the Black Mountain-Thirsty Canyon Tuff region of the study area, I built a number of filters for Landsat 3 TM digital data using the VAX-IDIMS image processing system. A description of filtering and filters used follows.

Filtering

Filtering may be performed in either the spatial or frequency domain by modifying the spatial frequency characteristics of an image. Frequency filtering involves multiplication of the Fourier transform of the image by the frequency response of the filter, and re-transformation of the product to produce an image in the spatial domain (Gillespie, 1976; Moik, 1980). Spatial filtering alters the gray level of a pixel according to its relationship with the gray levels of the other pixels in the immediate vicinity. This study was 88 limited to spatial filtering. For a detailed description of frequency filtering and Fourier transforms, see Moik, 1980. The spatial information on an image consists of low and high frequency components. Low frequency components are large areas of constant brightness. On Landsat imagery, low frequency components usually reflect albedo or color information. High frequency components consist of brightness changes that occur over a short spatial dimension. These often represent contrast in slope attitude or topography, or contrast in brightness at boundaries between different geologic units (Chavez, 1983). In general, the higher frequency components contribute to the sharpness of edges in the image, while the lower frequency components contribute to the overall contrast of the image. Spatial filtering works to enhance either the low or high frequency components at the expense of the other. Low pass filters smooth the detail and reduce the gray level range of an image. High frequency components are attenuated. A high-pass filter, however, retains the high frequency components while subduing or removing the low frequency components. This tends to sharpen features on the image. Directional filters are high pass filters which accentuate features in a specified vertical or diagonal direction. Digital spatial filtering is a pixel by pixel operation, involving convolution of the original image data with a moving weight matrix, the filter kernel. The value of the output image at any point (x,y) is given by the weighted summation of the input signal in the vicinity of (x,y) (Showengerdt, 1983). The weighting and geometry of the convolution kernel is determined by the type of feature the processor or interpreter wishes to enhance. A filter kernel may be one dimensional (linear) or two dimensional, symmetrical or nonsymmetrical. A two dimensional, uniform weight convolution or filter kernel is known as a box filter. Low pass boi filters can be implemented by averaging the pixels in the vicnity of each piiel of the original image and using the average as the pixel gray level in the processed image (Showengerdt, 1983). A high-pass filtered image can be produced simply by subtracting the low-pass filtered image from the original image. This produces an image which displays deviations from the local average brightness. In digital spatial filtering, a high pass filter can be built using a convolution kernel with a positive weight for the central pixel and negative weights for the surrounding pixels. Directional filters are non-symmetrical, combining both negative and positive weights in an orientation designed to highlight features of a specific trend. However, linear artifacts may be produced by directional filters since directions are weighted inequally (Gillespie, 1976). Filters Used in This Study

For this study, 3X 3 filter kernels were used to build low-pass, high pass, Laplacian, northwest directional, and northeast directional filters. On the VAX-IDIMS software, the filters were built using the KERNEL function and convoluted with the original image using the CONVOL function. The filtered images were then added back to the original images using the ADD function. The filtered images may be added back at any fraction to the original simply by specifying the ratio, e. g„ ADD (1 .5) indicates add half the weight of the filtered image to the full weight of the original image. If no ratio is specified, the filtered image and the original image are given equal weight. Qualitative contrast stretching by Trackball Linear Mapping (TLM) was performed on all images. Photographs of unfiltered, low pass, high pass and northwest directional filtered images of the Black Mountain area are shown as figures 23 and 24. An edge enhancement of the original image was performed using the EDGE function. This function is much quicker than the CONVOL function and produces a sharp image with high contrast. The exact nature of this filter is not known. 91

The following filter kernels were used:

Low oass filter: 1 1 1 1 2 1 i i i

\ High pass filter: 0 -1 0 -1 5 -1 0 -1 0

Laplacian filter: -1 -1 -1 -1 8 -1 -1 -1 -1

NW-SE directional 2 -1 -2 filter: -1 4 -1 -2 -1 2

NE-SW directional -2 -1 2 filter: -1 4 -1 2 -1 -2 92 Low Pass Filter The low pass filtered image smooths edges while keeping the contrast high. Adding it back to the original improves both the contrast and the sharpness, while maintaining the slightly blurred effect. Low pass filtering may be useful for regional lineament mapping, or for any mapping based on subtle tonal differences.

High Pass Filter The high pass filtered image of Black Mountain displays a sharp though slightly grainy teiture with enhanced edges and moderately subdued subtle tonal differences. Adding back the original slightly improves the contrast and removes the graininess but decreases the clarity of the image. The high-pass filtered image, though somewhat grainy, appears to display the greatest amount of information before it is added back to the original. The slight improvement in contrast by adding it back to the original is not worth the loss of image clarity. Much of the graininess of the high- pass filtered image may be due to contrast streching of the image since the dynamic range of its brightness values is limited. High-pass filtering may be especially useful preprocessing for mapping and classification purposes.

Laplacian Filter A laplacian filter is a high-pass filter whose total kernel weight adds to zero. High frequency components are dramatically enhanced and low frequency components are greatly subdued. Consequently, laplacian filtered images are speckled and grainy along distinct boundaries, and subtle tonal 93 differences are almost completely lost. Adding back the original greatly improves the background and foreground contrast.

Northwest and Northeast Directional Filters Diagonal directional filters are laplacian filters whose negative and positive weights are diagonally symmetrical in order to highlight features in the desired direction. For example, the northwest directional filter highlights boundaries and edges trending northwest while subduing boundaries in all other directions. However, linear artifacts oriented orthogonally to the directional filter are produced, i.e., the northwest filtered image has a strong northeast trending grain, and the northeast filtered image has a strong northwest trending grain. In addition to the linear artifacts, the directionally filtered images have very low contrast, and an irritatingly blurred appearance as though each successive line of pixels was slightly offset from the previous one.

Edge Enhancement Filter The edge enhanced filtered image is sharp with good contrast and a generally pleasing appearance. Edge enhancement filters are supposed to be high pass filters and this image has an appearance similar to the high pass filtered image. However, the histogram of this filter is shaped like the histogram of the low pass filter, though the edge enhancement filter histogram is centered on the high brightness value end while the low pass filter histogram is centered on the low brightness value end. Perhaps this filter is a combination of a low and high pass filter or a filter of a larger kernel size. Whatever it is, it is quicker to use than the KERNEL and CONVOL functions and equally as satisfactory. 94

Summary of Filter Characteristics

The degree and style of modification of the original image by filtering is dependent of the type of filter used, its weighting factor, and the ratio by which it is added back to the original image. The edge enhancement and high pass filters may be valuable for improving overall image quality. Lapiacian filters can be implemented when enhancement in very specific directions is desired, though their uses are limited for geologic mapping or classification purposes. Low pass filtered images highlight subtle tonal differences and can accentuate regional linear features which are sometimes lost in too much detail. In general, the usefulness of the individual filters is dependent on the character, size and frequency of the features the interpreter wishes to enhance, and experimentation may be necessary to obtain the best results. Figure 231 Computer-generated photographs of Black Mountain area. a) unfiltered image b) low pass filtered image 96

1.d)

Figure 24. Computer-generated photographs of Black Mountain area. a) high pass filtered image b) image with northwest directional filter t**#ww9iw*5 e a i niiTrriiiinnTiiiimnrnrwTTr

Appendix B

B A N D 1

AZIMUTH

FREQUENCY

Yucca Mountain subscene, band 1 Appendix B

B A N D 2

AZIMUTH

FREQUENCY

Yucca Mountain subscene, band 2 100 Appendix B

B A N D 3

E / W - N 8 0 W N80W - N70W N70W - N60W N60W - N50W ■ ■ 10 N50W - N40W N40W - N30W N30W - N20W N 2 0 W - N 1 0 W ■ H 3 N 1 0 W - N /S AZIMUTH N / S - N 1 0 E ■ H H B i 14 N 1 0 E - N 2 0 E ■ H i 12 N20E - N30E ■ ■ ■ ■ I■ Qj N30E - N40E ■ 1 1 N40E - N50E ■ 3 N50E - N60E N60E- N70E "mmm N70E-N80E ' N 8 0 E - E /W H |2

6 8 10 12 1 4 1 6 FREQUENCY

Yucca Mountain subscene, band 3 101 Appendix B

B A N D 4

AZIMUTH

FREQUENCY

Yucca Mountain suDscene, band 4 Appendix B

B A N D 5

AZIMUTH

FREQUENCY

Yucca Mountain subscene, band 5 103

Appendix B

B A N D 6

AZIMUTH

FREQUENCY

Yucca Mountain subscene, band 6 104

Appendix B

B A N D 7

AZIMUTH

FREQUENCY

Yucca Mountain suoscene, Dand 7 105

Appendix B

FALSE COLOR COMPOSITE

AZIMUTH

FREQUENCY

Yucca Mountain subscene, False Color Composite 106 Appendix B

REAL COLOR COMPOSITE

AZIMUTH

FREQUENCY

Yucca Mountain subscene, Real Color Composite 107 Appendix C

Busted Butte Lineament

S o - fractures x - cooling joints

Stereonet

Poles to fractures/joints 108 Appendix C

Chukar Canyon

S o - fractures x - cooling joints

Stereonet

Poles to fractures/joints Appendix C

Dome Mountain Canyon

fractures cooling joints

Stereonet

Poles to fractures/joints 110 Appendix C

Mouth of Dome Mountain Canyon

o - fractures x - cooling joints

Stereonet

Poles to fractures/joints Appendix C

SW drainage off Chukar Canyon

o - fractures x - cooling joints

Stereonet

Poles to fractures/joints Appendix D

Aeromagnetic Map Coverage of the Study Arsa

Boynton, G.R., and Vargo, J. L., 1963a, Aeromagnetic map of the Cane Spring Quadrangle and parts of the Frenchman Lake, Spector Range, and Mercury quadrangles, Nye County, Nevada: U. S. Geol. Survey Geophys. Inv. Map GP-442.

------, 1963b, Aeromagnetic map of the Topopah Spring quadrangle and part of the Bare Mountain quadrangle, Nye County, Nevada: U. S. Geol. Survey Geophys. Inv. Map GP-440.

Boynton, G. R., Meuschke, J. L., and Vargo, J. L., 1963a, Aeromagnetic map of the Timber Mountain quadrangle and part of the Silent Canyon quadrangle, Nye County, Nevada: U. S. Geol. Survey Geophys. Inv. Map GP-443.

------, 1963b, Aeromagnetic map of the Tippipah Spring quadrangle and parts of the Papoose Lake and Wheelbarrow Peak quadrangles, Nye County, Nevada: U. S. Geol. Survey Geophys. Inv. Map GP-441.

Philbin, P. W. and White, B. L., Jr., 1965a, Aeromagnetic map of the Belted Peak quadrangle and part of the White Blotch Springs quadrangle, Nye County, Nevada: U. S. Geol. Survey Geophys. Inv. Map GP-514.

______, 1965b, Aeromagnetic map of the Black Mountain quadrangle, Nye County, Nevada: U. S. Geol. Survey Geophys. Inv. Map GP-519.

______,1965c, Aeromagnetic map of the Cactus Spring quadrangle and part of the Goldfield quadrangle, Esmeralda and Nye Counties, Nevada: U. S. Geol. Survey Geophys. Inv. Map GP-511.

______, 1965d, Aeromagnetic map of parts of the Cactus Peak and Stinking Spring quadrangles, Nye County, Nevada: U. S. Geol. Survey Geophys. Inv. Map GP-517.

______,1965e, Aeromagnetic map of parts of the Kawich Peak and Reveille Peak quadrangles, Nye County, Nevada: U. S. Geol. Survey Geophys. Inv. Map GP-516. 113

------,1965f, Aeromagnetic map of the Mellan quadrangle, Nye County, Nevada: U. S. Geol. Survey Geophys. Inv. Map GP-518.

------,1965g, Aeromagnetic map of the Quartzite Mountain quadrangle, Nye County, Nevada: U. S. Geol. Survey Geophys Inv Map GP-515.

------, 1965h, Aeromagnetic map of the Sarcobatus Flat area, Esmeralda and Nye Counties, Nevada: U. S. Geol. Survey Geophys. Inv. Map GP-512.

------, 1965i, Aeromagnetic map of the Silent Canyon quadrangle, Nye County, Nevada: U. S. Geol. Survey Geophys. Inv. Map GP-520.

------, 1965j, Aeromagnetic^nap of the Wheelbarrow Peak quadrangle and part of the GKroom Mine quadrangle, Nye and Lincoln X Counties, Nevada: U. S. Geol.Purvey Geophys. Inv. Map GP-513.

Zeitz, I., Gilbert, F.P., and Kirby, J. R., 1978, Aeromagnetic map of Nevada: Color coded intensities. Scale 1:1,000,000: U. S. Geol. Survey Geophys. Inv. Map GP-922.

Zeitz, I., Stewart, J. H., Gilbert, F.P., and Kirby, J. R., 1977, Aeromagnetic map of Nevada. Scale 1: 500,000: U. S. Geo. Survey Misc. Field Studies Map MF-902. Appendix D

Geologic Mao Coverage of the Study Area

Barnes, Harley, Christiansen, R.L., and Byers, F.M., Jr., 1965, Geologic map of the Jangle Ridge quadrangle, Nye and Lincoln Counties, Nevada: U S. Geological Survey Geologic Quadrangle Map GQ-363.

Barnes, Harley, Houser, F. N., and Poole, R. G., 1963 Geologic map of the Oak Spring quadrangle, Nye County, Nevada: U.S. Geological Survey Geologic Quadrangle Map GQ-214.

Byers, F. M., Jr., and Barnes, Harley, 1967, Geologic map of the Paiute Ridge quadrangle, Nye and Lincoln Counties, Nevada: U. S. Geological Survey Geologic Quadrangle Map GQ-577.

Byers, F. M. Jr., and Cummings, D., 1967, Geologic map of the Scrugham Peak quadrangle, Nye County, Nevada: U.S. Geological Survey Geologic Quadrangle Map GQ-695.

Byers, F. M. Jr.,Rogers, C. L., Carr, W. J., and Luft, S. J., 1966, Geologic map of the Buckboard Mesa quadrangle, Nye County, Nevada: U.S. Geological Survey Geologic Quadrangle Map GQ-552.

Byers, F. M„ Jr., Carr. W. J., Orkild, P. P., Quinlivan, W. D., and Sargent, K. A., 1976, Volcanic suites and related cauldrons of Timber Mounatin-Oasis Valley caldera complex, Southern Nevada: U. S. Geological Survey Professional Paper 919, 70 p.

Carr, W. J., and Quinlivan W. D., 1966, Geologic map of the Timber Mountain quadrangle, Nye County, Nevada: U.S. Geological Survey Geologic Quadrangle Map GQ-503.

Christiansen, R.L. and Lipman, P. W., 1965, Geologic map of the Topopah Spring NW Quadrangle, Nye County, Nevada: U. S. Geological Survey Geologic Quadrangle Map GQ-444.

Christiansen, R.L. and Noble, D. C., 1968, Geologic map of the Trail Ridge Quadrangle, Nye County, Nevada: U. S. Geological Survey Geologic Quadrangle Map GQ-774. Colton, R. B., and McKay, E. J„ 1967, Geologic map of the Yucca Flat Quadrangle, Nye County, Nevada: U. S. Geological Survey Geologic Quadrangle Map GQ-582.

Colton, R. B., and Noble, D. C„ 1967, Geologic map of the Groom Mine SW Quadrangle, Nye and Lincoln Counties, Nevada: U. S. Geological Survey Geologic Quadrangle Map GQ-719.

Cornwall, H. R„ 1972, Geology and mineral deposits of southern Nye County, Nevada: Nev. Bur. Mines and Geol., Bull. 77, 49 p.

Cornwall, H. R. and Kleinhampl, F. J., 1961, Geology of the Bare Mountain quadrangle, Nevada: U. S. Geological Survey Quadrangle Map GQ-157, 1:62,500.

______, 1964, Geology of the Bullfrog quadrangle and ore deposits related to the Bullfrog Hills caldera, Nye County, Nevada and Inyo County, California: U. S. Geological Survey Professional Paper 454-J, 25 p.

Denny, C. S., and Drewes, H., 1965 , Geologic map of the Ash Meadows Quadrangle, Nevada-California: U. S. Geological Survey Bull 1181 -L.

Ekren, E. B„ Anderson, R. E., Orkild, P. P., and Hinrichs, E. N„ 1966, Geologic map of the Silent Butte Quadrangle, Nye County, Nevada: U. S. Geol. Surv. Geologic Quadrangle Map GQ-493-

Ekren, E. B., Anderson, R. E., Rogers, C. L., and Noble, D. C., 1971, Geologyof northern Nellis Air Force Base Bombing and Gunnery Range, Nevada: U. S. Geol. Surv. Prof. Paper 65-

Ekren, E. B., Rogers, C. L., Anderson, R. E. and Botinelly, T„ 1967, Geologic map of the Belted Peak Quadrangle, Nye County. Nevada: U. S. Geol. Surv. Geologic Quadrangle Map GQ-606.

Ekren, E. B. and Sargent, K. A., 1965, Geologic map of the Skull Mountain Quadrangle, Nye County, Nevada: U. S. G. S. Geologic Quadrangle Map GQ-387.

Gibbons, A. B„ Hinrichs, E. N.,Hansen, W. R., and Lemke, R. W., 1963, Geologic map of the Rainier Mesa Quadrangle, Nye County, Nevada: U. S. Geol. Surv. Geologic Quadrangle Map GQ-215. 116

Hinrichs, E. N„ 1968, Geologic map of the Camp Desert Rock Quadrangle, Nye County, Nevada: U. S. Geol. Surv. Geologic Quadrangle Map GQ-726.

Hinrichs, E. N., Krushensky, R. D., and Luft, S. J„ 1967, Geologic map of the Ammonia Tanks Quadrangle, Nye County, Nevada: U. S. Geol. Surv. Geologic Quadrangle Map GQ-638.

Hinrichs, E. N., and McKay, E. J., 1963, Geologic map of the Plutonium Valley Quadrangle, Nye and Lincoln Counties, Nevada: U. S. Geol. Surv. Geologic Quadrangle Map GQ-384.

Lipman, P. W. and McKay, E. J., 1965, Geologic map of the Topopah Spring SE quadrangle: U. S. G. S. Geologic Quadrangle Map GQ-439.

Lipman, P. W., Quinlivan, W. B., Carr, W. J., and Anderson, R E., 1966, Geologic map of the Thirsty Canyon SE quadrangle: U. S. G. S. Geologic Quadrangle Map GQ-489.

McKay, T. J. and Sargent, K. A., Geology of the Lathrop Wells quadrangle, Nye County, Nevada: U. S. G. S. Geologic Quadrangle Map GQ-883.

McKay, T. J. and Williams, W. P., 1964, Geology of the Jackass Flats quadrangle, Nye County, Nevada: U. S. G. S. Geologic Quadrangle Map GQ-368.

Noble, D. C., and Christiansen, R. L., 1968, Geologic map of the southwest quarter of the Black Mountain quadrangle, Nye County, Nevada: U. S. G. S. Misc. Inv. Map 1-562.

Noble, D. C., Krushensky, R. D., McKay, E. J., and Ege, J. R., 1967, Geologic map of the Dead Horse Flat quadrangle, Nye County, Nevada: U. S. G. S. Geologic Quadrangle Map GQ-614.

O'Conner, J. T., Anderson, R. E., and Lilpman, P. W., 1966, Geologic map of the Thirsty Canyon quadrangle, Nye County, Nevada: U. S. G. S. Geologic Quadrangle Map GQ-524.

Orkild, P. P„ 1963, Geologic map of the Tippipah Spring quadrangle, Nye County, Nevada: U. S. G. S. Geologic Quadrangle Map GQ-213-

______1968, Geologic map of the Mine Mountain quadrangle, Nye County, Nevada: U. S. G. S. Geologic Quadrangle Map GQ-746. 117

Orkild, P. P., and 0;Connor, J. T., 1970 , Geologic map of the Topopah Spring quadrangle, Nye County, Nevada: U. S. G. S. Geologic Quadrangle Map GQ-849.

Poole, F. G., 1965, Geologic map of the Frenchman Flat quadrangle, Nye, Lincoln, and Clark Counties, Nevada: U. S. G. S. Geologic Quadrangle Map GQ-456.

Poole, F. G.,Elston, D. P., anc Carr, W. J., 1965, Geologic map of the Cane Spring quadrangle, Nye County, Nevada: U. S. G. S. Geologic Quadrangle Map GQ-455.

Rogers, C. L., and Noble, D. C., 1970, Geologic map of the Oak Spring Butte quadrangle, Nye County, Nevada: U. S. G. S. Geologic Quadrangle Map GQ-822.

Sargent, K. A., Luft, S. J., Gibbons, A. B., and Hoover, D. L„ 1966,, Geologic map of the Quartet Dome Quadrangle, Nye County, Nevada: U. S. G. S. Geologic Quadrangle Map GQ-496.

Sargent, K. A., McKay, E. J., and Burchfiel, B. C., 1970, Geologic map of the Striped Hills Quadrangle, Nye County, Nevada: U. S. G. S. Geologic Quadrangle Map GQ-882.

Scott, R. B. and Bonk, Jerry, 1984, Preliminary geologic map of Yucca Mountain with geologic sections, Nye County, Nevada: U. S. G. S. Open-file Report 84-494, 1:12,000.