FISSION TRACK CONSTRAINTS ON EXHUMATION 

AND EXTENSIONAL FAULTING IN SOUTHWEST 

NEVADA AND EASTERN CALIFORNIA, U.S.A. 

Prepared for 

U.S. Nuclear Regulatory Commission 

Contract NRC–02–07–006 

Prepared by 

David A. Ferrill,1 Alan P. Morris,1

John A. Stamatakos,2

 Deborah J. Waiting,2

Raymond A. Donelick,3

 Ann E. Blythe4

1

Department of Earth, Material, and Planetary Sciences 

Southwest Research Institute®

San Antonio, Texas 

2

Center for Nuclear Waste Regulatory Analyses 

San Antonio, Texas 

3

Apatite to Zircon, Inc. 

Viola, Idaho 

4

Department of Geology 

Occidental College 

Los Angeles, California 

September 2011
ii 

ABSTRACT 

Eastern California and southwestern Nevada is an area of Tertiary and Quaternary extensional 

and dextral transtensional deformation. We use zircon and apatite fission-track 

thermochronology to study the distribution and timing of tectonic exhumation resulting from 

extensional and transtensional detachment faulting in this area. Samples were collected from 

outcrops around Yucca Flat and Frenchman Flat, the Striped Hills, Mount Stirling, Resting 

Spring Range, Bare Mountain, Bullfrog Hills, and the eastern margin of the Funeral Mountains. 

To constrain timing of exhumation associated with crustal-scale normal faulting, sampling 

efforts were focused on Paleozoic and Precambrian clastic sedimentary and metasedimentary 

rocks of the Stirling Quartzite, Wood Canyon Formation, Zabriskie Quartzite, Eureka Quartzite, 

and Eleana Formation. Sixty-nine new apatite and zircon fission-track cooling ages from 

50 samples, analyzed in conjunction with published fission-track data from the region, indicate 

a distinct population of young (Miocene) fission-track ages and a population of irregularly 

distributed older (pre-Miocene) fission-track ages. Miocene (young population) fission track 

ages young westwards—indicating westward migration of the cooling front, consistent with 

well-documented Miocene extension of the Basin and Range. The younging pattern is also 

consistent with west-northwest displacement of the hanging wall of a crustal scale extensional 

fault system and consequent progressive footwall exhumation. The active trailing edge of the 

hanging wall of this system generally coincides with Death Valley. Migration rates of the cooling 

front in the footwall of this system are on the order of 10–11 mm/yr [0.39–0.43 in]. Based on the 

distribution of the Miocene fission-track ages, we interpret that the crustal faults that defined the 

eastern edge of the detachment system originated as separate normal faults that were linked by 

the formation of a transfer fault, similar in geometry to the Panamint Valley–Hunter Mountain–

Saline Valley fault system. The complex hanging wall of this crustal detachment system 

includes high mountain ranges, including the Panamint, Cottonwood, Argus, Inyo, White, and 

Last Chance Ranges, separated by active graben and half-graben basins, including the 

Panamint, Saline, Eureka, Deep Springs, and Owens Valleys. Extrapolation of apatite fissiontrack closure ages from two transects across the eastern margin of the Death Valley region 

suggests that exhumation along the eastern margin of the system continues beneath Death 

Valley today. 
iii 

TABLE OF CONTENTS 

Section Page 

ABSTRACT................................................................................................................................... ii 

FIGURES ..................................................................................................................................... iv 

TABLES ........................................................................................................................................ v 

ACKNOWLEDGMENTS .............................................................................................................. vi

1 INTRODUCTION ................................................................................................................1-1

2 FISSION-TRACK METHODS .............................................................................................2-1

3 SAMPLING .........................................................................................................................3-1

4 APATITE FISSION-TRACK THERMOCHRONOLOGY RESULTS ....................................4-1

5 ZIRCON FISSION-TRACK THERMOCHRONOLOGY RESULTS .....................................5-1

6 DISCUSSION......................................................................................................................6-1

7 CONCLUSIONS..................................................................................................................7-1

8 REFERENCES ...................................................................................................................8-1

APPENDIX A—APATITE FISSION-TRACK THERMOCHRONOLOGY 

APPENDX B—ZIRCON FISSION-TRACK THERMOCHRONOLOGY 
iv 

FIGURES 

Figure Page 

1-1 Digital Shaded Relief Model of the Western Basin and Range, Showing 

 Location of Detailed Study Area Within the Walker Lane Belt. ......................................1-2 

3-1 Simplified Geologic Map (Based on Workman, et al., 2002) of the Study Area 

Showing Sample Locations in Their Geologic Context ..................................................3-2 

3-2 Generalized Chart Showing Stratigraphic Position of Paleozoic Units 

 Exposed at Bare Mountain, Nevada; Death Valley, California; and the 

 Surrounding Area ...........................................................................................................3-3

4-1 Shaded Relief Digital Elevation Model of Southern Nevada and California 

Showing Locations of Apatite Fission-Track Sample Locations and Ages Sampled 

for This Study .................................................................................................................4-7 

5-1 Shaded Relief Digital Elevation Model of Southern Nevada and California 

Showing Locations of Zircon Fission-Track Sample Locations and Ages Sampled 

for This Study .................................................................................................................5-3 

5-2 Age Versus Count Plots of Zircon and Apatite Cooling Ages Based on Data in 

 Tables 4-1 and 5-1. ........................................................................................................5-4

6-1 Models of Faulting, Exhumation, and Isostatic Adjustment Illustrating Unroofing 

 of Rocks With Reset Apatite and Zircon Ages ...............................................................6-2 

6-2 (A) Digital Shaded Relief Map Illustrating the Interpreted Position of the Breakaway 

Fault, Interpretation of Domains With Respect to Detachment System, and Location 

of Transects in (B) and (C).............................................................................................6-3 
v 

TABLES 

Table Page 

4-1 Apatite Fission-Track Data.............................................................................................4-2 

5-1 Zircon Fission-Track Data ..............................................................................................5-2 
vi 

ACKNOWLEDGMENTS 

This paper was prepared as a result of work performed at the Center for Nuclear Waste 

Regulatory Analyses (CNWRA®) for the U.S. Nuclear Regulatory Commission (USNRC) under 

contract numbers NRC–02–93–005, NRC–02–97–009, and NRC–02–02–012. This work was 

initiated on behalf of the USNRC Office of Nuclear Regulatory Research as part of the Tectonic 

Processes of the Central Basin and Range research project and continued on behalf of the 

Office of Nuclear Material Safety and Safeguards. This report is an independent product of the 

CNWRA and does not necessarily reflect the views or regulatory position of the USNRC. 

The authors thank Steven Young, Lawrence McKague, Kathy Spivey, Bret Rahe, Sid Jones, 

and Don Cederquist for their assistance and Tom John for allowing us to sample in the Barrick 

Bullfrog Mine. We also thank Ron McGinnis and English Pearcy for their review comments, 

Arturo Ramos for secretarial support, and Lauren Mulverhill for editorial review. 

QUALITY OF DATA, ANALYSES, AND CODE DEVELOPMENT DATA 

DATA: All CNWRA-generated data contained in this report meet quality assurance 

requirements described in the Geosciences and Engineering Division Quality Assurance 

Manual. Sources of other data should be consulted for determining the level of quality of 

those data. 

ANALYSES AND CODES: No scientific and engineering software was used in the analyses 

contained in this report. 
1-1 

1 INTRODUCTION 

Yucca Mountain is located in the western Basin and Range Province, an area of active tectonic 

deformation. Tectonic models and interpretations of the timing and rate of tectonic deformation 

in the Yucca Mountain region have varied widely (e.g., McKague, et al., 2010). In 1993, staff of 

the Center for Nuclear Waste Regulatory Analyses (CNWRA®) began sampling for fission-track 

dating to better constrain timing and rate of crustal thinning by normal faults in the vicinity of 

Yucca Mountain. The focus was to reduce key technical uncertainties for fault-related 

processes that would need to be assessed for regulatory compliance evaluations with respect to 

long-term performance of a potential high-level radioactive waste repository at Yucca Mountain. 

Early analyses focused on Bare Mountain (the mountain range west of Yucca Mountain across 

Crater Flat Basin) and were presented by Ferrill, et al. (1995). Sampling was later expanded to 

provide a broader regional context and tie in other published fission-track data sets. In this 

report, we present the entire fission-track data set collected from the Yucca Mountain region by 

CNWRA, include other published data from the region, and present a summary of these results 

and constraints provided by the data on the timing and rate of lower crustal exhumation in the 

Yucca Mountain region. 

Oblique motion between the Pacific and North American plates produces a transtensional 

tectonic regime in the western Basin and Range Province of eastern California and southern 

Nevada (Harland, 1971; Atwater, 1970; Frisch, et al., 2011). Active deformation in this region is 

manifested by an interconnected network of large-scale north-south striking normal faults and 

northwest-trending strike-slip faults, an area Stewart (1988) referred to as the Walker Lane Belt 

(Figure 1-1). Although there is debate about the total amount of extension in the region 

(e.g., Serpa and Pavlis, 1996) and the details of fault block definition and displacement style 

(e.g., Snow and Wernicke, 2000), there is consensus that rapid and continuing displacement on 

this network of basin-controlling faults is producing pull-apart basins linked by strike-slip faults 

(Zoback, et al., 1981; Burchfiel, et al., 1987; MIT 1985 Field Geophysics Course and Biehler, 

1987; Dixon, et al., 2000, 1995; Rahe, et al., 1998; Sims, et al., 1999; McQuarrie and 

Wernicke, 2005). 

Slow rates of erosion and sedimentation, combined with high slip rates, have generated starved 

basins (where rate of subsidence exceeds rate of sedimentation) with several kilometers of 

structural and topographic relief. Most of these active basins have developed since the late 

Miocene (e.g., MIT 1985 Field Geophysics Course and Biehler, 1987; Snow and Wernicke, 

2000), although there is also evidence of Eocene, Oligocene, and early Miocene basin 

development in the region (Axen, et al., 1993; Ridgway, et al., 2011). Along the eastern margin 

of this region of active and rapid basin formation is the Death Valley–Furnace Creek fault 

system. East of this fault system, displacement on normal faults initiated in the Miocene and 

has exhumed rocks from depths of 10 to 15 km [6 to 9 mi] (Hodges, et al., 1987; Hoisch and 

Simpson, 1993; Hoisch, et al., 1997; Holm and Dokka, 1993, 1991). Exhumation of deep 

footwall rocks during deformation led to progressively more brittle overprinting of earlier formed 

ductile deformation features at the northern end of the Panamint Range (Hodges, et al., 1989), 

the Black Mountains (Cowan, et al., 2003; Miller and Pavlis, 2005; Hayman, 2006), and the 

Funeral Mountains (Hoisch and Simpson, 1993). Isostasy is presumed to have produced uplift 

of footwalls relative to hanging walls, placing rocks from 10- to 15-km [6- to 9-mi] depths at the 

same elevation as uppermost crustal rocks (e.g., Asmerom, et al., 1990; Wernicke, 1992). 

Analog modeling that simulates brittle deformation of the upper crust above more ductile 

lower crustal material has reproduced many of the key structural elements seen in the region 

(Brun, et al., 1994). 
1-2 

Figure 1-1. Digital Shaded Relief Model of the Western Basin and Range, Showing 

Location of Detailed Study Area Within the Walker Lane Belt. Coordinate Projection Is 

Universal Transverse Mercator, Zone 11, NAD 27. 
1-3 

The purpose of this report is to summarize fission track cooling ages and related distribution and 

timing of fault-related exhumation of crustal rocks in the vicinity of Yucca Mountain, Nevada. 

These results provide important constraints on tectonic models of the Yucca Mountain area. 

We use fission-track ages from apatite and zircon as a basis for interpreting the distribution and 

timing of exhumation for pre-Miocene rocks in southwest Nevada and eastern California. We 

present 69 new apatite and zircon fission-track ages collected from Paleozoic and Precambrian 

rocks throughout the study area. The fission-track ages indicate exhumation ages of the 

sample host rocks as these rocks cooled through the fission-track closure temperatures of 

apatite and zircon. Our results define an area of Miocene crustal extension exhumed by normal 

faulting. Spatial distribution of the fission-track ages is also used to infer the original 

configuration of crustal faults that define the detachment system.
2-1 

2 FISSION-TRACK METHODS 

Fission tracks are linear damage zones caused by spontaneous fission of uranium atoms in 

U-bearing minerals such as apatite and zircon. U-238 decay occurs at a known rate unaffected 

by temperature or pressure, and the number of fission tracks per unit area of crystal in 

conjunction with the uranium concentration gives a measure of the time since track 

accumulation began (Wagner and Van den Haute, 1992). Fission tracks are not permanent 

features of a crystal and are subject to healing or annealing if the crystal is heated above its 

closure temperature for a period of ~106

 years (Tagami and O’Sullivan, 2005). While at 

temperatures above the closure temperature, rates of fission-track formation within the crystal 

are balanced by rates of annealing and there is no net fission-track accumulation. Below the 

closure temperature, however, annealing is inhibited and fission tracks accumulate within the 

crystal. Thus a fission-track age is a measure of the time elapsed since the latest cooling of the 

crystal through its closure temperature. If the rock in which the mineral sample resides had 

been buried to depths at which the ambient temperature was greater than the fission-track 

closure temperature for that mineral, then the fission-track age also represents the time at which 

the rock was exhumed by erosion, extensional faulting, or a combination of these processes. 

Typical long-term (geological) cooling rates for crustal rocks exhumed by these processes 

would be on the order of 10–100°C/my [18–180°F/my]. 

For fast-annealing, typical Ca-F-rich apatite, the closure temperature is estimated to be 

130–146 °C [266–295 °F] for cooling rates of 10–100 °C/my [18–180 °F/my] (Ketcham, et al., 

1999). For slow annealing, oftentimes Cl-rich and possibly Mn-, Fe-, and/or REE-rich 

apatite, the closure temperature is estimated to be as high as 172 °C [342 °F] for cooling rates 

of 10–100 °C/my [18–180 °F/my] (Ketcham, et al., 1999). Fast-annealing apatites are typically 

less soluble in the nitric acid used to reveal the tracks for observation and measurement. The 

mean diameter of fission-track etch pits (Dpar) on the apatite surface being studied is usually 

less than 2 μm [0.000079 in] for the etching conditions used in this study (e.g., Carlson, et al., 

1999; Donelick, et al., 2005). As discussed in Appendix A, the apatite grains in this study 

were dominantly fluorine-rich, as indicated by their small fission-track etch pit diameters. 

Assuming an average surface temperature of 15°C [59°F] and a constant geothermal gradient 

of 30 °C/km [87 °F/mi] (Ferrill, et al., 1995; 1996a), an apatite closure temperature of 138 °C 

[280 °F] would equate to a depth of approximately 4.1 km [2.55 mi]. 

Zircon has a higher estimated closure temperature. Early estimates of zircon closure 

temperatures ranged from 175 ± 25 °C [347 ± 45 °F] (Harrison and McDougall, 1980) 

to 230 ± 5 °C [446 ± 9 °F] for cooling rates of 10 to 30 °C/my [18 to 54 °F/my] Brandon and 

Vance (1992) modeled from annealing data of Zaun and Wagner (1985) and Tagami, et al. 

(1990) and closure temperature equations of Dodson (1979, 1973). More recently, borehole 

data from the Vienna basin (Tagami, et al., 1995), laboratory annealing data (Yamada, et al., 

1995), and natural annealing data from the contact metamorphic aureole around a granite 

pluton (Tagami and Shimada, 1996) have suggested a significantly higher temperature range 

for the zircon annealing zone, ~230 to ~330 °C [446 to 626 °F], and a zircon closure 

temperature of 250 °C [482 °F] for cooling rates of 10–100 °C/my [18–180 °F/my] (Tagami and 

Shimada, 1996; Foster, et al., 1993). Assuming an average surface temperature of 15 °C 

[59 °F] and a constant geothermal gradient of 30 °C/km [87 °F/mi] (Ferrill, et al., 1995; 1996a), a 

zircon closure temperature of 250°C [482 °F] would equate to a depth of approximately 

7.8 km [4.85 mi].
3-1 

3 SAMPLING 

Samples were collected from outcrops around Yucca Flat and Frenchman Flat (on the 

Nevada Test Site), the Striped Hills, Mount Stirling, Resting Spring Range, Bare Mountain 

(Spivey, et al., 1995; Ferrill, et al., 1996a), Bullfrog Hills, and the eastern margin of the Funeral 

Mountains (Figures 1-1 and 3-1). Sampling sites were selected to expand upon previous 

fission-track results that concentrated on mountain ranges along the eastern margin of 

Death Valley, the Bullfrog Hills, and the northwest corner of Bare Mountain. To constrain timing 

of exhumation associated with crustal-scale normal faulting, we focused our sampling efforts 

on Paleozoic and Precambrian clastic sedimentary and metasedimentary rocks of the 

Stirling Quartzite, Wood Canyon Formation, Zabriskie Quartzite, Eureka Quartzite, and 

Eleana Formation (see Figure 3-2 for stratigraphic positions and data tables in Sections 4 and 5 

for details on sampled rock types). 

In a few cases, we sampled younger igneous rocks to provide an independent check of dating 

results and additional geochronologic constraints. For these purposes, samples were collected 

from Cretaceous granite and Tertiary diorite and latite dikes at Bare Mountain, Mesozoic 

monzogranite of the Climax Stock (northwest Yucca Flat), and Rainier Mesa tuff from the 

Bullfrog Hills. In total, 50 new samples were collected for dating. Apatite and zircon mineral 

separates were isolated from each sample following procedures outlined in Dumitru (1999) 

using standard gravimetric and magnetic mineral separation techniques. The apatite mineral 

separates consist of fluorine-rich apatite. Apatite fission-track ages were measured at Apatite to 

Zircon, Inc. by Raymond A. Donelick (analyst RAD; see Appendix A) using the external detector 

method (e.g., Gleadow, 1981). Zircon grains from 16 samples were analyzed using zircon 

fission-track thermochronology techniques (e.g., Wagner and Van den Haute, 1992). Eleven of 

the zircon fission-track age analyses were performed at University of California at Santa 

Barbara by Ann E. Blythe (analyst AEB), and 5 were performed at Apatite to Zircon, Inc. 

(analyst RAD; see Appendix B). All analyses were performed using the external detector 

method (e.g., Gleadow, 1981). Fission track analyses are detailed in Appendices A and B. 
3-2 

Figure 3-1. Simplified Geologic Map (Based on Workman, et al., 2002) of the Study Area 

Showing Sample Locations in Their Geologic Context. Qs = Quaternary Sedimentary 

Units, Qv = Quaternary Volcanic Units, Ts = Tertiary Sedimentary Units, Ti = Tertiary 

Igneous Units, Mz = Mesozoic Units, Pzu = Upper Paleozoic Units, Pzl = Lower Paleozoic 

Units, pC = Precambrian Units. H etal 97 = Hoisch, et al., 1997; H&S 93 = Hoisch and 

Simpson, 1993; H&D 93 = Holm and Dokka, 1993. 
3-3 

Figure 3-2. Generalized Chart Showing Stratigraphic Position of Paleozoic Units 

Exposed at Bare Mountain, Nevada; Death Valley, California; and the Surrounding Area 

(After Poole, 1974; Poole, et al., 1992; and Monsen, et al., 1992). Gray Areas Show Gaps 

in the Geologic Record Due to Nondeposition, Faulting, or Erosion. 
4-1 

4 APATITE FISSION-TRACK THERMOCHRONOLOGY RESULTS 

Except for the Miocene silicic porphyry dikes at Bare Mountain (apatite fission-track ages 

10.9 to 16.0 Ma) (Monsen, et al., 1992), the Rainier Mesa Tuff from the Bullfrog mine 

(apatite fission-track age 21.3 Ma), and the Climax stock (apatite fission-track age 76 Ma) 

(Naeser and Maldonado, 1981) in northern Yucca Flat (Figure 1-1), all apatite fission-track ages 

reported here (Table 4-1) are significantly younger than the host rocks. Of the 53 ages reported 

here (including 2 duplicates and 1 combined), 50 exhibit Dpar values less than or equal to 2 μm 

[0.000079 in], indicating that the apatites can be treated as fast annealing for interpretation 

purposes. In general, fission-track ages that are younger than the host rock indicate heating 

above the temperatures required for total fission-track annealing after deposition or 

crystallization of the host rocks. Thus, the ages are not inherited (e.g., from rocks of a 

previously eroded terrain); rather, they represent cooling of the host rocks through the 

fluorine-rich apatite closure temperature, presumably during exhumation. In addition to our 

53 new ages, we include 10 published ages from the Black Mountains (Holm and Dokka, 1993), 

the Funeral Mountains (Holm and Dokka, 1991; Hoisch and Simpson, 1993), and the Bullfrog 

Hills and northwest corner of Bare Mountain (Hoisch, et al., 1997). 

Apatite fission-track ages fall into a population of diverse pre-Miocene ages and a population of 

Miocene and younger ages (Figure 4-1). Pre-Miocene ages generally lie to the east of Miocene 

ages at a given latitude in the study area and range from 25–115 Ma. To assess spatial 

variation of the Miocene and younger ages, we subdivided these ages into three groups: 

(i) early Miocene (16.6–23.7 Ma), (ii) middle Miocene (11.2–16.6 Ma), and (iii) late Miocene 

(5.3–11.2 Ma) and younger (Figure 4-1). The youngest ages are found along the eastern 

margin of Death Valley in the Funeral Mountains and Black Mountains. Miocene cooling ages 

generally young to the west or northwest. The Funeral Mountains and Bare Mountain include 

ages belonging to both the Miocene and pre-Miocene populations, which allows us to delineate 

these age transitions in bedrock within these ranges. 
4-2 

Table 4-1. Apatite Fission-Track Data

Site Rock Type Easting Northing ρs Ns ρi Ni ρd Nd Grains Q χ2 Dpar Pooled Age Mean Age 

Analyst RADBFH1 Wood Canyon 

Formation (schist)

522200 4082050 0.116 88 2.361 1792 5.238 4105 25 0.998 P 1.60 14.6 ± 1.7 14.7 ± 1.2 

BFH2 Wood Canyon 

Formation (schist)

521130 4081680 0.127 96 3.390 2560 5.249 4105 25 0.210 P 1.58 11.2 ± 1.2 9.9 ± 1.5 

BFH3 Stirling Quartzite 

(D member)

521130 4081660 0.095 66 2.810 1951 5.259 4105 22 0.129 P 1.66 10.1 ± 1.3 13.0 ± 2.4 

BMN1 Granite 523380 4083170 0.035 19 0.909 489 5.158 4105 25 0.729 P 1.61 1.4 ± 2.7 11.9 ± 3.2 BMN2 Diorite Dike 522950 4083130 0.113 15 2.151 285 5.324 4105 18 0.945 P 1.65 15.9 ± 4.2 14.7 ± 5.1 BMN4 Zabriskie Quartzite 530360 4080190 0.270 81 5.205 1559 5.335 4105 25 0.035 F 1.79 15.8 ± 1.9 20.2 ± 4.4 BMN5 Zabriskie Quartzite 524640 4082730 0.049 28 1.311 749 5.345 4105 25 0.788 P 1.49 11.4 ± 2.2 13.4 ± 4.0 BMN10 Zabriskie Quartzite 526671 4080373 0.219 31 8.421 1191 5.356 4105 13 0.177 P 1.65 7.9 ± 1.5 7.5 ± 2.9 BMN13 Eureka Quartzite 530130 4081726 0.139 62 3.037 1351 5.086 4236 22 0.575 P 1.69 13.3 ± 1.8 13.6 ± 3.3 BMN15 Zabriskie Quartzite 529163 4079903 0.279 58 5.471 1138 5.074 4236 15 0.788 P 1.73 14.7 ± 2.0 15.8 ± 2.7 BMN16 Quartz Latite Dike 533093 4082128 0.050 19 0.925 353 4.578 4116 24 0.706 P 1.70 14.0 ± 3.3 10.7 ± 3.0 BMN19 Wood Canyon 

Formation (quartzite; lower member unit D)

522933 4083039 0.059 15 1.523 384 5.057 4236 23 0.207 P 1.61 11.2 ± 3.0 7.8 ± 3.4 

BMN20 Eureka Quartzite 529724 4082811 0.331 21 5.556 352 5.003 4236 9 0.774 P 2.16 17.0 ± 3.8 12.8 ± 5.2 BMN21 Eureka Quartzite 531044 4084040 0.104 1 6.042 58 4.995 4236 1 n.a. n.a. 1.55 4.9 ±4.9 4.9 BME1 Eleana Formation 

(conglomerate)

532430 4080400 0.136 38 3.528 989 5.270 4105 25 0.143 P 1.61 11.5 ± 1.9 12.9 ± 4.5 
4-3 

Table 4-1. Apatite Fission-Track Data (continued)

Site Rock Type Easting Northing ρs Ns ρi Ni ρd Nd Grains Q χ2 Dpar Pooled Age Mean Age 

BME2 Quartz Latite Dike 532780 4080120 0.035 15 0.857 368 5.287 4105 24 0.462 P 1.76 12.3 ± 3.2 11.6 ± 3.7 BME3 Wood Canyon 

Formation (quartzite)

533000 4071100 0.039 5 0.891 114 5.308 4105 9 0.900 P 1.50 13.2 ± 6.1 7.4 ± 6.0 

BME6 Quartz Latite Dike 530456 4075819 0.038 27 0.641 451 4.576 4116 23 0.766 P 2.37 15.6 ± 3.1 16.0 ± 3.0 BME17 Quartz Latite Dike 533452 4081028 0.143 12 2.684 225 5.024 4236 11 0.594 P 1.57 15.2 ± 4.5 15.4 ± 8.9 BME18 Stirling Quartzite 

(E member)

532490 4075863 0.250 79 5.032 1591 5.011 4236 24 0.930 P 1.67 14.1 ± 1.7 15.7 ± 1.8 

BMW1 Stirling Quartzite 

(schist; C member)

526475 4076240 0.026 11 0.440 189 5.173 4105 23 0.321 P 1.50 17.1 ± 5.3 19.0 ± 6.8 

BMW2 Wood Canyon 

Formation (quartzite; lower member, unit A)

530880 4069920 0.027 11 0.707 286 5.190 4105 20 0.535 P 1.60 11.3 ± 3.5 16.1 ± 7.4 

BMW3 Stirling Quartzite 

(D member)

532300 4069380 0.161 92 3.563 2032 5.206 4105 24 0.575 P 1.57 13.4 ± 1.5 20.3 ± 3.3 

BMW5 Zabriskie Quartzite 528730 4075260 0.057 14 1.643 406 5.212 4105 22 0.238 P 1.60 10.2 ± 2.8 12.3 ± 5.8 BMW6 Stirling Quartzite 

(D member)

522690 4079300 0.072 33 1.630 752 5.045 4236 25 0.956 P 1.88 12.6 ± 2.3 11.3 ± 2.1 

BMW12A Stirling Quartzite 

(D member)

522677 4079457 0.094 19 1.830 369 5.367 4105 20 0.899 P 1.66 15.7 ± 3.7 18.1 ± 3.7 

BMW12B Diorite Dike 522677 4079457 0.084 12 2.463 350 5.036 4236 14 0.575 P 1.56 9.8 ± 2.9 10.9 ± 4.0 BMW13 Stirling Quartzite 

(A member)

533455 4067605 0.013 2 0.800 125 4.987 4236 8 0.645 P 1.58 4.5 ± 3.2 4.3 ± 3.8 

BMW15 Stirling Quartzite 

(A member)

530632 4071735 0.104 19 2.530 463 4.970 4236 18 0.840 P 1.75 11.6 ± 2.7 11.4 ± 2.8 
4-4 

Table 4-1. Apatite Fission-Track Data (continued)

Site Rock Type Easting Northing ρs Ns ρi Ni ρd Nd Grains Q χ2 Dpar Pooled Age Mean Age 

BMW16 Eureka Quartzite 528139 4078281 0.938 15 28.750 460 4.962 4236 2 0.343 P 1.68 9.2 ± 2.4 16.2 ± 10.4 BMW17 Stirling Quartzite 

(schist; C member)

526251 4076808 0.110 11 3.576 357 4.953 4236 12 0.829 P 1.54 8.7 ± 2.7 5.7 ± 2.8 

DFBM61 Zabriskie Quartzite 534210 4066361 0.644 134 3.663 762 4.585 4116 24 0.126 P 1.83 45.7 ± 4.5 40.7 ± 6.5 DFBM62 Zabriskie Quartzite 534135 4065850 1.258 128 6.899 702 4.587 4116 10 0.824 P 1.79 47.4 ± 4.8 49.1 ± 8.0 DFSH1 Zabriskie Quartzite 559253 4055732 0.588 164 2.476 691 4.945 4236 14 0.038 F 1.99 66.4 ± 6.1 65.9 ± 9.8 DFSH2 Wood Canyon 

Formation (quartzite)

559409 4055393 0.768 290 2.781 1050 4.937 4236 25 0.320 P 1.97 77.1 ± 5.6 87.9 ± 8.3 

DFBFM1 Rainier Mesa Tuff 516010 4083130 0.047 4 1.140 97 4.583 4116 13 0.170 P 1.76 10.7 ± 5.5 21.3 ± 12.0 DFM2 Eureka Quartzite 590572 4063062 0.938 239 2.120 540 4.589 4116 25 0.292 P 1.89 115 ± 10 128 ± 14 DFM2 (dup) Eureka Quartzite 590572 4063062 2.128 301 5.253 743 4.612 4116 22 P 2.03 105 ± 8 102 ± 11 DFMS1 Stirling Quartzite 582236 4032599 1.454 388 5.141 1372 4.592 4116 24 0.679 P 1.78 73.5 ± 4.8 78.5 ± 5.6 DFMS2 Stirling Quartzite 582845 4031897 0.915 339 2.968 1100 4.594 4116 23 0.376 P 1.84 80.1 ± 5.5 83.9 ± 9.8 DFRSR1 Stirling Quartzite 573252 3998158 2.146 239 5.532 616 4.596 4116 16 0.511 P 1.89 101 ± 8 99.4 ± 9.3 DFRSR2 Stirling Quartzite 572878 3997924 1.478 123 4.303 358 4.598 4116 16 0.094 P 1.75 89.3 ± 9.7 106 ± 19 DFYF1 Monzogranite (Climax) 584257 4120177 0.371 336 1.246 1129 4.600 4116 25 0.597 P 1.77 77.4 ± 5.3 76.0 ± 5.2 DFYF2 Eleana Formation (cng.) 572878 4114429 0.266 40 2.832 426 4.603 4116 13 0.106 P 1.73 24.5 ± 4.1 23.3 ± 8.8 DFYF3 Eleana Formation (ss) 572112 4102051 1.515 159 14.558 1528 4.605 4116 20 0.612 P 2.00 27.2 ± 2.4 21.9 ± 4.0 DFYF3 (dup) Eleana Formation (ss) 572112 4102051 0.401 77 3.911 751 4.580 4116 23 0.323 P 1.77 26.7 ± 3.3 26.0 ± 6.2 DFYF4 Eureka Quartzite 579570 4094021 0.600 76 4.253 539 4.607 4116 20 0.758 P 1.90 36.9 ± 4.6 47.4 ± 5.3 DFYF7 Eureka Quartzite 579289 4093685 1.019 191 4.586 860 4.609 4116 20 0.542 P 1.89 58.0 ± 5.0 72.6 ± 10.9 
4-5 

Table 4-1. Apatite Fission-Track Data (continued)

Site Rock Type Easting Northing ρs Ns ρi Ni ρd Nd Grains Q χ2 Dpar Pooled Age Mean Age 

RJBD1-1A Stirling Quartzite 531012 4050377 0.082 137 4.137 707 4.853 4175 22 0.000 F 1.70 53.3 ± 5.2 67.4 ± 11.9 RJBD1-1B Stirling Quartzite 531012 4050377 1.060 217 4.165 853 4.838 4175 24 0.712 P 1.71 69.6 ± 5.7 65.1 ± 11.8 RJBD1-2 Stirling Quartzite 531012 4050377 0.762 122 3.212 514 4.822 4175 20 0.916 P 1.70 64.8 ± 6.8 72.4 ± 18.7 RJBD1-3 Stirling Quartzite 531012 4050377 0.953 97 4.452 453 4.807 4175 15 0.820 P 1.74 58.3 ± 6.8 71.8 ± 13.7 RJBD1 (all) Stirling Quartzite 531012 4050377 0.899 573 3.964 2527 4.853 4175 81 0.027 F 1.71 62.3 ± 3.4 69.1 ± 7.1 Previously PublishedCC-61 (H&S 93)

Pelitic Schist 511207 4061043 5.6 ± 1.4

900008 (H&D 91)

Muscovite Granite 504614 4062871 6.6

IH1-BIO (H&D 93)

pC Basement 551756 3970035 10.2

DKH-IH2 (H&D 93)

pC Basement 550690 3972248 9.9

DKH-JP (H&D 93)

pC Basement 538500 3973665 8.4

988-25 (H&D 93)

Gabbro Diorite 529423 3989528 6.9

89-MP (H&D 93)

pC Basement 522373 3987474 7.6

BM-TH-14ab (H etal 97) 

Schist 521999 4082379 11.1
4-6 

Table 4-1. Apatite Fission Track Data (continued)

Site Rock Type Easting Northing ρs Ns ρi Ni ρd Nd Grains Q χ2 Dpar Pooled Age Mean Age 

BF-TH-9AB (H etal 97)

Amphibolite 510361 4082461 10.0

BF-TH-10 (H etal 97)

Schist 510454 4082564 10.6

Notes: Easting and Northing are UTM (Zone 11, NAD 27) locations in meters. All errors are reported at 1σ; zeta calibration factor for analyst RAD of 113

and P.F. Green. “The Zeta Calibration of Fission Track Dating.” Isotope Geosciences. Vol. 1. pp. 285–317. 1983.) relative to CN-1 dosimeter glass (39 

determined using Durango and Fish Canyon Tuff apatite standards irradiated with these samples; mean spontaneous track lengths for Durango and Fish 

standards are 14.47 ± 0.06 μm, and 15.35 ± 0.06 μm, respectively. Rock types are defined in Monsen, et al. (1992). ρs, ρi, and ρd, are spontaneous, ind

tracks, respectively, given in units of in 106 tracks per cm2. Ns, Ni, and Nd are the number of spontaneous, induced, and dosimeter fission tracks, respec

of apatite grains. Q is the probability that χ2 value would be greater than reported for a population of apatite grains having a common history and commo

history; χ2 Test, P (pass) for Q 0.05, F (fail) for Q <0.05. Dpar is the mean etch pit diameter parallel to the crystallographic c-axis for the grains measured end-member fluorapatite). Pooled Age is the fission-track age based on sum total of spontaneous and induced tracks for all grains measured (reliable wh

bold font) given in Ma. Mean Age is the arithmetic mean of the individual grain ages (reliable when χ2 Test is F, indicated by bold font) given in Ma. NT is 

measured. Mean length is average track length in μm. σ is one standard deviation about the mean of the track length measurements. U is the concentrat
4-7 

Figure 4-1. Shaded Relief Digital Elevation Model of Southern Nevada and California 

Showing Locations of Apatite Fission-Track Sample Locations and Ages 

Sampled for This Study. Other Regional Data Sources Are Indicated Thus: 

H etal 97 = Hoisch, et al., 1997; H&S 93 = Hoisch and Simpson, 1993; 

H&D 93 = Holm and Dokka, 1993. 
5-1 

5 ZIRCON FISSION-TRACK THERMOCHRONOLOGY RESULTS 

Sixteen fission-track samples were processed for zircon fission-track analysis (Table 5-1). Most 

of the zircon fission-track ages are much younger than the ages of their host rocks, indicating 

that the host rocks were heated above the total fission-track annealing temperature of zircon 

after deposition. With two exceptions, the zircon fission-track ages reflect resetting of the host 

mineral grains and cooling of the host rocks, presumably during exhumation, through the zircon 

fission-track closure temperature, rather than being inherited from a previously eroded terrain or 

recording primary cooling. 

One exception is the sample from the silicic porphyry dike (BME-2; Table 5-1) sampled from 

Bare Mountain, which yields a zircon fission-track age of 11.9 ± 1.2 Ma, concordant with the 

apatite fission-track age of 12.3 ± 3.2 Ma. A conventional K/Ar age of 13.8 ± 0.2 Ma was 

measured from biotite from this dike (Monsen, et al., 1992). Based on data from Marvin, et al. 

(1989), Noble, et al. (1991), Monsen, et al. (1992), and Weiss (1996), conventional K/Ar and 

Ar-40/Ar-39 dates from the silicic porphyry dikes along eastern Bare Mountain, of which this is 

part, range from 14.9 to 13.8 Ma. However, textural features and K/Ar dates from alunite 

indicate epithermal and hydrothermal activity contemporaneous with the later stages of silicic 

volcanism (circa 11.0 to 12.5 Ma), especially associated with altered margins of the silicic 

porphyry dikes. Our apatite and zircon fission-track ages are consistent with resetting due to 

epithermal or hydrothermal activity, or the fission-track ages can be considered concordant with 

the conventional K/Ar biotite age. 

The second exception is Eureka quartzite (DFM-2) sampled from the south side of Frenchman 

Flat at Mercury Ridge, which yielded a fission-track age older than the depositional age of the 

rock. This age relationship suggests that the fission-track age records provenance age of the 

host rock from which the Eureka quartzite grains were derived. The Eureka quartzite at this 

location was apparently never buried sufficiently deep to reset the zircon fission tracks. Apatite 

grains from the same sample yield Cretaceous ages, indicating that the apatite grains were 

reset after deposition in the Ordovician. 

In addition to our 16 new zircon fission-track ages, we include 15 published ages from the 

Black Mountains (Holm and Dokka, 1993), Funeral Mountains (Holm and Dokka, 1991), and 

Bullfrog Hills, and northwest corner of Bare Mountain (Hoisch, et al., 1997). Like the apatite 

fission-track ages, zircon fission-track ages fall into a population of pre-Miocene ages and a 

population of Miocene and younger ages (Figures 5-1 and 5-2). Pre-Miocene ages generally lie 

to the east of Miocene ages at the latitude of the Funeral Mountains, Bullfrog Hills, and Bare 

Mountain (Figure 5-1; see Figure 1-1 for place names). Zircon ages range from 25 to 115 Ma 

(Figures 5-1 and 5-2). As with the apatite fission-track ages, we subdivided the Miocene and 

younger zircon fission-track ages into three groups: (i) Early Miocene (16.6 to 23.7 Ma), 

(ii) Middle Miocene (11.2 to 16.6 Ma), and (iii) Late Miocene (5.3 to 11.2 Ma) and younger 

(Figures 5-1 and 5-2). The youngest ages are found along the eastern margin of Death Valley 

in the Funeral Mountains and Black Mountains. Miocene cooling ages are generally younger to 

the west or northwest. The Funeral Mountains and Bare Mountain include ages belonging to 

both the Miocene and pre-Miocene populations. 
5-2 

Table 5-1. Zircon Fission-Track Data

Site Rock Type Easting Northing ρs Ns ρi Ni ρd Nd Grains Q χ2 

BFH-1 Wood Canyon 

Formation (schist) 

522200 4082050 2.09 155 4.450 330 0.20 1272 11 0.89 P 

BFH-2 Wood Canyon 

Formation (schist) 

521130 4081680 2.80 246 7.460 664 0.20 1272 11 0.01 F 

BMW-6 Stirling Quartzite 

(D member) 

522690 4079300 2.58 554 5.370 1155 0.19 1223 20 0.16 P 

BME-2 Quartz latite dike 532780 4080120 2.45 135 6.840 376 0.20 1260 8 0.56 P BMN-5 Zabriskie Quartzite 524640 4082730 2.73 579 3.580 759 0.19 1248 16 0.99 P BMN-10 Zabriskie Quartzite 526671 4080373 4.49 628 4.200 588 0.19 1235 20 0.56 P BMW-2 Wood Canyon 

Formation (quartzite; lower member, unit A) 

530880 4069920 6.31 606 4.840 465 0.19 1223 13 0.37 P 

BMW-3 Stirling Quartzite 

(D member) 

532300 4069380 5.10 1291 3.600 911 0.19 1217 17 0.24 P 

BME-3 Wood Canyon 

Formation (quartzite)

533000 4071100 3.61 419 2.970 344 0.20 1260 16 0.60 P 

BMN-4 Zabriskie Quartzite 530360 4080190 18.36 1964 2.040 216 0.19 1248 20 0.34 P BMN-15 Zabriskie Quartzite 529163 4079903 16.50 2230 1.940 221 0.19 1235 20 0.28 P DFSH-1 Zabriskie Quartzite 559253 4055732 11.62 729 0.925 58 0.56 2053 10 0.75 P DFSH-2 Wood Canyon 

Formation (quartzite)

559409 4055393 10.60 631 1.140 68 0.57 2053 10 0.11 P 

DFBM61 Zabriskie Quartzite 534210 4066361 8.48 662 0.794 62 0.59 2053 10 0.13 P DFBM62 Zabriskie Quartzite 534135 4065850 10.02 782 0.961 75 0.60 2053 10 0.01 F DFM2 Eureka Quartzite 590572 4063062 18.01 784 1.330 58 0.61 2053 9 0.00 F 900009 (H&D 91) Muscovite Granite 504614 4062871 IH1-BIO (H&D 93) pC Basement 551756 3970035 DKH-IH2 (H&D 93) pC Basement 550690 3972248 DKH-JP (H&D 93) pC Basement 538500 3973665 AM2a-M (H&D 93) pC Basement 529759 3979177 DKH-FS (H&D 93) Gabbro Diorite 529979 4002655 DKH-SMG (H&D 93) Granite 531557 3980662 89-CC (H&D 93) pC Basement 523851 3995981 DKH-IH2 (H&D 93) pC Basement 550690 3972248 DKH-JP (H&D 93) pC Basement 538500 3973665 AM2a-M (H&D 93) pC Basement 529759 3979177 DKH-FS (H&D 93) Gabbro Diorite 529979 4002655 DKH-SMG (H&D 93) Granite 531557 3980662 89-CC (H&D 93) pC Basement 523851 3995981 988-25 (H&D 93) Gabbro Diorite 529423 3989528 89-MP (H&D 93) pC Basement 522373 3987474 BWT-B (H&D 93) pC Basement 521275 4126312 TQM-GW-B (H&D 93) Granite 557384 3983751 BM-TH-14ab (H etal 97) Schist 521999 4082379 BF-TH-9ab (H etal 97) Amphibolite 510361 4082461 BF-TH-10 (H etal 97) Schist 510454 4082564 Notes: Explanations of table headings are the same as in Table 1. Ages determined using zeta calibration factor of 335 ± 20 relative to SRM 962a dosimeter glass (analyst AEdosimeter glass (analyst RAD). The age for sample BFH-2, which failed the χ2 test, is the mean age instead of the pooled age. 
5-3 

Figure 5-1. Shaded Relief Digital Elevation Model of Southern Nevada and California Showing 

Locations of Zircon Fission-Track Sample Locations and Ages Sampled for This Study. Other 

Regional Data Sources Are Indicated Thus: H et al 97 = Hoisch, et al., 1997; H&S 93 = Hoisch 

and Simpson, 1993; H&D 93 = Holm and Dokka, 1993. 
5-4 

Figure 5-2. Age Versus Count (Cumulative Number of Data Points) Plots of Zircon and Apatite 

Cooling Ages Based on Data in Tables 4-1 and 5-1. Ages for Both Apatite and Zircon Data Are 

Color Coded as in Figures 4-1 and 5-1. 
6-1 

6 DISCUSSION 

Large normal fault displacements can thin the crust and exhume rocks from depths beneath the 

apatite- and zircon-annealing depths. This is especially true where the absence of 

syndeformational sedimentation permits the footwall of the system to respond to unloading by 

isostatic uplift (Stewart, 1983; Wernicke, et al., 1987; Wernicke and Axen, 1988; Wernicke, 

1992; Asmerom, et al., 1990; Block and Royden, 1990). Prior to deformation, apatite and zircon 

grains within the footwall of the extensional system are hotter than their respective closure 

temperatures and are continuously annealed [Figure 6-1(A)]. 

Uplift generated by displacement of the hanging wall causes the footwall and its associated 

population of apatites and zircons to move toward the Earth’s surface and down the geothermal 

gradient to progressively cooler conditions. The fission-track ages represent the time elapsed 

since the mineral passed through its closure temperature on its way to the Earth’s surface. 

Because the unroofing process is progressive and at large scale directional, the pattern of 

cooling ages in the exposed footwall will show a pattern of decreasing ages in the direction of 

hanging wall displacement [Figure 6-1(B)]. Fault slivers stranded on the footwall will contain 

fission-track younging patterns broadly similar to the fundamental footwall [Figure 6-1(C)]. 

Structural complexities in some areas, such as the stranding of a hanging wall fault sliver, may 

partially occlude this broad pattern [Figure 6-1(C)]. Based on this model, Bare Mountain, the 

Bullfrog Hills, the Funeral Mountains, and the Black Mountains were all unroofed differentially 

during the Miocene (Maldonado, 1990; Holm and Dokka, 1991; Hoisch and Simpson, 1993; 

Serpa and Pavlis, 1996), and this interpretation is in accord with large-scale structural 

relationships and small-scale deformation features, including brittle extensional structures 

that overprint ductile extensional deformation fabrics (Wernicke and Axen, 1988; 

Wernicke, 1995, 1992). 

In this work (Figures 4-1 and 5-1), we note that the eastern half of Bare Mountain exhibits 

pre-Miocene cooling through 250 °C [482 °F], followed by Miocene cooling through 130–146 °C 

[266–295 °F]. Northwest Bare Mountain cooled through both 250 °C [482 °F] and 130–146 °C 

[266–295 °F] since the beginning of the Miocene. South and east of Bare Mountain, including 

the southeasternmost Funeral Mountains and the Resting Spring Range but excluding the Black 

Mountains, apatite closure ages are pre-Miocene. West of this broadly defined line, apatite 

ages show a consistent younging trend to the west. 

We interpret Miocene and younger apatite and zircon cooling ages to indicate exhumation of the 

rocks through the 130–146 °C [266–295 °F] (apatite) and 250 °C [482 °F] (zircon) closure 

temperatures in response to the west-northwest-directed tectonic removal of overlying crust. 

The initiation of the breakaway at Bare Mountain occurred at about 13 Ma (this work and 

Hoisch, et al., 1997). Our fission-track results do not indicate tectonic exhumation east of Bare 

Mountain, which refutes earlier interpretations by Hamilton (1988, 1987) and Scott (1990) that a 

shallow regional detachment extends beneath and east of Yucca Mountain. We suggest that 

the Death Valley–Furnace Creek fault zone (Figure 3-1) represents the current position of the 

easternmost surface trace of the west-northwestward-moving hanging wall (consistent with 

Stewart, 1983, and Serpa and Pavlis, 1996). Projecting the apatite age data horizontally and 

parallel to the traces of the extensional fault segments onto transects that are parallel to the 

regional extension direction over the last 12 million years (represented by the Furnace Creek 

fault trace; McQuarrie and Wernicke, 2005) yields graphs which illustrate the sharp break 

between older (pre-Miocene) ages to the east-southeast and younger (Miocene) ages to the 

west-northwest [Figures 6-2(B,C)]. Considering only the Miocene and younger ages 
6-2 

Figure 6-1. Models of Faulting, Exhumation, and Isostatic Adjustment Illustrating 

Unroofing of Rocks With Reset Apatite and Zircon Ages: (A) Crustal Cross Section 

Before Deformation. Dashed Line Within Orange Is an Arbitrary Marker for Reference. 

(B) Detachment Faulting With Isostatic Adjustment of the Footwall and Illustrating the 

Case Where a Single Hanging Wall Fault Sliver Is Adjacent to the Main Hanging Wall 

Block. (C) Detachment Faulting With Isostatic Adjustment of the Footwall and Illustrating 

the Case Where a Single Hanging Wall Fault Sliver Is Stranded on the Footwall Block. 
6-3 

Figure 6-2. (A) Digital Shaded Relief Map Illustrating the Interpreted Position of the 

Breakaway Fault, Interpretation of Domains With Respect to Detachment System, and 

Location of Transects in (B) and (C). Squares are Horizontally Projected Onto the 

Northern Transect Line [Figure 6-2(B)] Along an Azimuth of 190°, Diamonds Are 

Horizontally Projected Onto the Southern Transect Line [Figure 6-2(C)] Along an Azimuth 

of 170°. (B) Transect Along Azimuth 123°, Parallel to the Furnace Creek Fault Zone 

Sharing Apatite Fission-Track Cooling Ages Plotted Against Distance Along Transect. 

Color Coding as in (A). Gray Area Represents Range of Best Fit Lines Within 

±1 Standard Deviation From the Mean. Least Squares Best Fit Line to the Miocene and 

Younger Data Is Provided. The Southeastern Projection to 13 Ma Coincides With the 

Inferred Trace of the Footwall Cutoff of the Detachment System. The Northwestward 

Projection to 0 Ma Indicates That Rocks at the Far Northwest End of the Transect, at the 

Appropriate Depth, Are Currently Passing Through the Apatite Closure Geotherm. The 

Inverse Slope of the Best Fit Line Is 10 mm Per Year [0.394 in/yr]. (C) Transect Along 

Azimuth 123° (Parallel to the Furnace Creek Fault Zone), Apatite Fission-Track Cooling 

Ages Are Plotted Against Distance Along Transect. The Inverse Slope of the Best Fit 

Line Is 11 mm Per Year [0.433 in/yr]. 
6-4 

[Figures 6-2(B,C)] reveals a west-northwest younging trend that results from migration of the 

apatite cooling front. Migration of the front was comparable in the Bare Mountain–Bullfrog Hills 

area {10 mm/yr [0.394 in/yr]; Figure 6-2(B)} and in the Black Mountains {11 mm/yr [0.433 in/yr]; 

Figure 6-2(C)}. Projecting the Black Mountain data eastward to 13 Ma indicates that the 

location of the breakaway in that area was just to the west of the Resting Spring Range 

[Figure 6-2(A)]. This also agrees with Stewart’s (1983) placement of the Panamint Mountains 

prior to faulting and subsequent restored positions of the Panamint Range interpreted by Snow 

(1994), Serpa and Pavlis (1996), and Snow and Wernicke (2000). 

South of Bare Mountain, the position of the breakaway is constrained between the location for 

our sample locality RJBD1 along the northeastern margin of the Funeral Mountains 

(mean apatite age of 69.1 Ma), and samples CC-61 (apatite age of 5.6 Ma; Hoisch and 

Simpson, 1993) and 900008 (apatite age of 6.6 Ma; Holm and Dokka, 1991). From here the 

trace must step laterally to pass to the east of the Late Miocene ages from the Black Mountains 

and west of the 89.3 Ma apatite fission-track age from the Resting Spring Range. This step 

corresponds to the surface trace of the Furnace Creek fault. The precise location of the footwall 

cutoff in the vicinity of the Funeral Mountains is not well constrained by our data. However, 

although Workman, et al. (2002) show the location from which we collected sample RJBD1 as 

being separated from the main Funeral Mountains by a fault, more detailed mapping by Wright 

and Troxel (1993) shows that the geologic layers and layer orientations (including marker beds 

and folds) at RJBD1 correlate with geology along strike in the Funeral Mountains. We have, 

therefore, chosen to link the trace directly to the Furnace Creek fault zone as shown in 

Figure 6-2(A), but there may be more complexity than this indicates. 

Large-magnitude displacement on a dipping fault (e.g., in the vicinity of the detachment-fault 

breakaway) results in differential unloading and, therefore, differential footwall uplift. This 

differential uplift tilts the footwall in the direction opposite to the hanging wall transport direction 

(Figure 6-1). This differential uplift is controlled by lateral variation in thickness of removed 

hanging wall rock above the dipping fault. Apatite and zircon grains deeper than their 

corresponding annealing depths are progressively unroofed and cooled, resulting in 

accumulation of fission tracks and younging of fission-track ages in the direction of hanging wall 

transport. Rocks exposed in the exhumed footwall will contain mineral grains that exhibit a 

variety of cooling age patterns depending upon the depth to detachment of the major fault 

system, the geothermal gradient during exhumation, and the depth of erosion following footwall 

uplift. Our interpretation of detachment faulting related to crustal exhumation in the 

Death Valley region is illustrated in Figure 6-1. Exhumed footwall rocks adjacent to the surface 

trace of the breakaway fault and initially shallower in the crust than the apatite fission-track 

closure temperature geotherm exhibit preexhumation ages for both apatites and zircons. Within 

the footwall and in the direction of transport of the hanging wall, there will be a zone in which 

apatite will yield exhumation cooling ages but zircon will not. Finally, there is a zone in which 

both zircon and apatite yield exhumation cooling ages. Fission-track ages for a given mineral 

will be younger in the direction of transport of the hanging wall reflecting progressive 

exhumation (e.g., Holm and Dokka, 1993, 1991; Hoisch and Simpson, 1993; Hoisch, et al., 

1997). Complications to this general pattern arise if slivers of the hanging wall are left on the 

exhumed footwall [e.g., Figure 6-1(C); Wernicke and Axen, 1988; Wernicke, 1992]–each sliver, 

however, represents a small version of the overall footwall pattern. 

Our interpreted configuration of the footwall and hanging wall cutoffs of the Death Valley–

Furnace Creek regional detachment system places Crater Flat basin immediately adjacent to 

the footwall cutoff and in the footwall of the system [Figure 6-2(A)]. Yucca Mountain lies at the 

eastern edge of Crater Flat basin and is a series of cuestas formed by west-dipping normal 
6-5 

faults with displacements on the order of a few hundreds of meters [up to more than 1,000 ft] 

(e.g., Ferrill, et al., 1999; Ferrill and Morris, 2001; Morris, et al., 2004). Crater Flat basin is a 

half-graben controlled by displacement on the east-dipping Bare Mountain fault, which has a 

maximum displacement of 3 to 5 km [1.9 to 3.1 mi] (Faulds, et al., 1994; Ferrill, et al., 1996b; 

Brocher, et al., 1998). Faulting at Yucca Mountain and on the Bare Mountain fault was at least 

in part contemporaneous with Miocene tuff emplacement (Carr, 1990; Monsen, et al., 1992), 

began approximately 13 million years ago, and has continued into the Quaternary 

(Ferrill, et al., 1997, 1996b). Fault displacements and associated extensions within the Bare 

Mountain–Crater Flat–Yucca Mountain system are one to two orders of magnitude less than 

those faults in the Bullfrog Hills (just north and west of Bare Mountain) and within the Death 

Valley–Furnace Creek detachment system. Fault slivers within the Bullfrog Hills contain a 

highly extended sequence of Miocene volcanic rocks (Maldonado, 1990). The Bare Mountain–

Crater Flat–Yucca Mountain system likely represents footwall damage that developed coevally 

with the large Miocene displacement on the Death Valley–Furnace Creek detachment system 

and its consequent footwall uplift (Stamatakos, et al., 2011). 
7-1 

7 CONCLUSIONS 

Apatite and zircon fission-track cooling ages from the Death Valley region of southern Nevada 

show (i) a belt of Miocene ages and a broad region of pre-Miocene ages; (ii) the belt of Miocene 

ages corresponds to an area of large-magnitude crustal extension by normal faulting and is 

segmented, with an area of Miocene fission-track ages in the Bare Mountain–Funeral Mountains 

area and in the Black Mountains; (iii) the eastern edge of Miocene fission-track ages is mapped 

in Bare Mountain and the Funeral Mountains, then steps eastward (to the south) to east of the 

Black Mountains and west of the Resting Spring Range; and (iv) fission-track ages within the 

belt of Miocene exhumation young westward, suggesting progressive westward or 

northwestward progression of exhumation. 

We interpret that early Miocene apatite ages are near the breakaway (footwall cutoff) of the 

regional detachment faulting and that the original crustal faults which defined the edge of the 

detachment system may have originally been separate normal faults linked by a transfer zone, 

similar to fault system architecture in the Panamint Valley–Saline Valley region today. Migration 

rates of the cooling front in the footwall of this system are on the order of 10 to 11 mm/yr 

[0.394 to 0.433 in/yr]. Extrapolation of apatite fission-track closure ages from two transects 

across the eastern margin of the Death Valley region suggests that exhumation along the 

eastern margin of the system continues beneath Death Valley today. East of the footwall cutoff 

of this system, extensional basins, such as the Crater Flat basin, either did not experience 

enough extension in the last 13 million years to produce footwall exhumation sufficient to be 

recorded in cooling ages, or Miocene basin filling with volcanic and alluvial material occurred too 

rapidly for isostatic footwall uplift to occur.
8-1 

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APPENDIX A 

APATITE FISSION-TRACK THERMOCHRONOLOGY
A–1 

APPENDIX A—APATITE FISSION-TRACK THERMOCHRONOLOGY 

Apatite fission-track ages were measured by Raymond A. Donelick (analyst RAD) using the 

external detector method (e.g., Gleadow, 1981). The natural apatite fission tracks were etched 

in 5.5N HNO3 for 20.0 ± 0.5 seconds at 21 ± 1 EC [69.8 ± 1.8 EF]. Thermal-neutron irradiations 

for age measurement were of 1-hour duration in position A-8 of the Texas A&M University 

nuclear reactor while the reactor was operating at 1 MW power output, yielding a 

thermal-neutron fluence of approximately 1016 neutrons/cm2

. All mica detectors were etched in 

48 percent HF at 24 ± 1 °C [75 ± 1.8 °F] for 12.0 ± 0.25 minutes to reveal induced fission tracks 

for use in determining apatite grain uranium concentrations. Fission-track length distributions 

were measured for all samples that yielded apatite fission-track ages following procedures 

Dumitru (1999, and references therein) outlined with the added step Cf-252 irradiation to 

enhance their measurability (Donelick, 1991). All measurements were made with a 

binocular microscope in nonpolarized light at 1562.5 × magnification (100 × dry objective, 

1.25 × projection tube, 12.5 × oculars). With few exceptions, the apatite grains studied 

were dominantly fluorine rich as indicated by their small fission-track etch pit diameters 

(e.g., Burtner, et al., 1994; Carlson, et al., 1999). The closure temperature for small etch pit, 

fluorine-rich apatite fission tracks is approximately 130–146 °C [266–295 °F] {cooling rate of 

100 °C/my [180 °F/my]; Ketcham, et al. (1999)}. 

The apatite fission-track ages reported in this paper include remeasurements performed using 

grain mounts from some samples reported on earlier (Ferrill, et al., 1996; Spivey, et al., 1995). 

In our reanalysis, images of all apatite grains were recorded on videotape. The videotapes 

were then reviewed in detail (for every apatite grain dated) while tracks were simultaneously 

counted on the mica detector. This procedure ensured proper counting of the mica detector. In 

addition, we re-irradiated all of the original grain mounts during a single neutron irradiation 

session and the remeasurements were performed within a 3-week period. The zeta calibration 

(Hurford and Green, 1983) factor used to calculate the fission-track ages for the reanalyses was 

determined using only age calibration standards irradiated simultaneously with the samples in 

this study. Parameter Dpar (Carlson, et al., 1999; Donelick, et al., 2005) was measured for 

each apatite grain dated, and the mean value of the dated grains for each sample is reported in 

Table 4-1. 

References:

Burtner, R.L., A. Nigrini, and R.A. Donelick. “Thermochronology of the Lower Cretaceous 

Source Rocks in the Idaho-Wyoming Thrust Belt.” American Association of Petroleum 

Geologists Bulletin. Vol. 78. pp. 1,613–1,636. 1994. 

Carlson, W.D., R.A. Donelick, and R.A. Ketcham. “Variability of Apatite Fission-Track Annealing 

Kinetics: I. Experimental Results.” American Mineralogist. Vol. 84. pp. 1,213–1,223. 1999. 

Donelick, R.A., P.B. O’Sullivan, and R.A. Ketcham. “Apatite Fission-Track Analysis.” 

Mineralogy and Geochemistry. Vol. 58. pp. 49–94. 2005. 

Donelick, R.A. “Crystallographic Orientation Dependence of Mean Etchable Fission Track 

Length in Apatite: An Empirical Model and Experimental Observations.” American Mineralogist. 

Vol. 76. pp. 83–91. 1991. 
A–2 

Dumitru, T.A. “Fission-Track Geochronology in Quaternary Geochronology; Applications in 

Quaternary Geology and Paleoseismology, Volume 1.” J.S. Noller, J.M. Sowers, and 

W.R. Lettis, eds. Washington, DC: American Geophysical Union, Geophysical Monograph 

Series. 1999. 

Ferrill, D.A., G.L. Stirewalt, D.B. Henderson, J.A. Stamatakos, K.H. Spivey, and B.P. Wernicke. 

NUREG/CR–6401, “Faulting in the Yucca Mountain Region, Critical Review and Analyses of 

Tectonic Data from the Central Basin and Range.” Washington, DC: U.S. Nuclear Regulatory 

Commission. 1996. 

Gleadow, A.J.W. “Fission Track Dating Methods: What Are the Real Alternatives?” 

Nuclear Tracks. Vol. 5. pp. 3–14. 1981. 

Hurford, A.J. and P.F. Green. “The Zeta Calibration of Fission Track Dating.” 

Isotope Geosciences. Vol. 1. pp. 285–317. 1983. 

Ketcham, R.A., R.A. Donelick, and W.D. Carlson. “Variability of Apatite Fission-Track Annealing 

Kinetics: III. Extrapolation to Geological Time Scales.” American Mineralogist. Vol. 84. 

pp. 1,235–1,255. 1999. 

Spivey, K.H., D.A. Ferrill, J.A. Stamatakos, A.P. Morris, R.A. Donelick, and S.R. Young. “Uplift 

and Cooling History of Bare Mountain, Nevada, From Apatite Fission Track Thermochronology.” 

Geological Society of America Abstracts with Programs. Vol. 27, No. 6, A-389. 1995. 
APPENDIX B 

ZIRCON FISSION-TRACK THERMOCHRONOLOGY 
B–1 

APPENDIX B—ZIRCON FISSION-TRACK THERMOCHRONOLOGY 

Zircon grains from 16 samples were analyzed using zircon fission-track thermochronology 

techniques (e.g., Wagner and Van den Haute, 1992). Eleven of the zircon fission-track age 

analyses were performed at University of California at Santa Barbara by Ann E. Blythe 

(analyst AEB), and 5 were performed by analyst RAD. All analyses were performed using the 

external detector method (e.g., Gleadow, 1981). The natural zircon fission tracks were etched 

in an eutectic melt of KOH–NaOH at 220 °C [428 °F] for 18–24 hours, the duration being 

optimized for each sample. Thermal-neutron irradiations were performed at the Cornell 

University nuclear reactor (results for analyst AEB) or at Texas A&M University (results for 

analyst RAD); the duration position, duration, and reactor power levels were optimized to 

provide thermal-neutron fluences of approximately 1015 neutrons/cm2

. All mica detectors were 

etched in 48 percent HF at 18 ± 1 °C [64.4 ± 1.8 °F] for 30.0 ± 0.25 minutes (analyst AEB) or 

24 ± 1 °C [75.2 ± 1.8 °F] for 12.0 ± 0.25 minutes (analyst RAD) to reveal induced fission tracks 

for use in determining zircon grain uranium concentrations. All measurements were made with 

a binocular microscope in unpolarized light at 1,250 × magnification (100 × dry objective, 

1.25 × projection tube, 10.0 × oculars; analyst AEB) or 1,562.5 × magnification 

(100 × dry objective, 1.25 × projection tube, 12.5 × oculars; analyst RAD). The thermal 

annealing characteristics of zircon fission tracks are not as well constrained as for apatite 

fission tracks. In this study, we consider the zircon fission-track data in terms of a zircon 

partial annealing zone of 230 to 330 °C [446 to 626 °F] and a closure temperature of 

approximately 250 °C [482 °F] {cooling rate of 10 °C/my [18 °F/my]; Tagami and Shimada, 

1996; Foster, et al., 1993)}. 

References:

Foster, D.A., A.J. Gleadow, S.J. Reynolds, and P.G. Fitzgerald. “Denudation of Metamorphic 

Core Complexes and the Reconstruction of the Transition Zone, West Central Arizona: 

Constraints From Apatite Fission Track Thermochronology.” Journal of Geophysical Research. 

Vol. 98, B2. pp. 2,167–2,185. 1993. 

Gleadow, A.J.W. “Fission Track Dating Methods: What Are the Real Alternatives?” 

Nuclear Tracks. Vol. 5. pp. 3–14. 1981. 

Tagami, T. and C. Shimada. “Natural Long-Term Annealing of the Zircon Fission Track System 

Around a Granitic Pluton.” Journal Geophysical Research. Vol. 101. pp. 8,245–8,255. 1996. 

Wagner, G.A. and R. Van den Haute. Fission Track Dating. Dordrecht, Netherlands: 

Kluwer Academic Publishers. 1992.