Results of New Petrologic and Remote Sensing Studies in the Big Bend Region

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2010-01-01 Results Of New Petrologic And Remote Sensing Studies In The iB g Bend Region Stevan Christian Benker University of Texas at El Paso, [email protected]

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Recommended Citation Benker, Stevan Christian, "Results Of New Petrologic And Remote Sensing Studies In The iB g Bend Region" (2010). Open Access Theses & Dissertations. 2646. https://digitalcommons.utep.edu/open_etd/2646

This is brought to you for free and open access by DigitalCommons@UTEP. It has been accepted for inclusion in Open Access Theses & Dissertations by an authorized administrator of DigitalCommons@UTEP. For more information, please contact [email protected]. RESULTS OF NEW PETROLOGIC AND REMOTE SENSING STUDIES IN THE BIG BEND REGION

STEVAN CHRISTIAN BENKER

Department of Geological Sciences

APPROVED:

______Elizabeth Y. Anthony, Ph. D

______Richard P. Langford, Ph.D.

______Terry L. Pavlis, Ph.D.

______Thomas E. Gill, Ph.D.

______Eric A. Hagedorn, Ph.D.

______Patricia D. Witherspoon, Ph.D. Dean of the Graduate School RESULTS OF NEW PETROLOGIC AND REMOTE SENSING STUDIES IN THE BIG BEND REGION

STEVAN CHRISTIAN BENKER, MS

DISSERTATION

Presented to the Faculty of the Graduate School of The University of Texas at El Paso

in Partial Fulfillment of the Requirements for the Degree of

DOCTOR OF PHILOSOPHY

Department of Geological Sciences THE UNIVERSITY OF TEXAS AT EL PASO August 2010

ACKNOWLEDGEMENTS

Research support was in part provided by National Science Foundation Grant NSF DGE-

0538623 presented to the University of Texas El Paso. Field expenses of later portions of this work were also supported by the generosity of the Department of Geological Sciences at the

University of Texas El Paso. The author offers thanks to Dan Miggins and Don Parker whose perspectives and knowledge helped to guide this paper. Considerable time and effort were spent by Christopher Henry and Edward DuBray in reviewing earlier drafts of first chapter, thanks is offered as revisions suggested greatly assisted with clarification and progression of this work.

The author also thanks parents Steve and Maryjane, brother Jamie, and Cristina Castillo for emotional and financial support during manuscript production. Gratitude is offered to Cristina

Castillo, Steve Benker, and Michael Berube for their invaluable in field assistance. Early

Saturday morning meetings with Bill Robertson greatly aided in progression through this workload. Additionally, his generosity and that of Sarah, Judah, and Brodie Robertson, is appreciated as it provided a comfortable and quiet home in which much of this manuscript was composed. The academic advising and support of Kate Miller, Eric Hagedorn, Jeanine Kennedy, and Marybeth Harper during the UTEP GK-12 grant program also proved highly beneficial as this work was in production. Lastly, thanks to Tina Carrick for always having a willingness to listen, advise, and joke about the perils of a graduate education.

iii

ABSTRACT

The initial section of this manuscript involves the South Rim Formation, a series of 32.2-

32 Ma comenditic quartz trachytic-rhyolitic volcanics and associated intrusives, erupted and was

emplaced in Big Bend National Park, Texas. Magmatic parameters have only been interpreted

for one of the two diverse petrogenetic suites comprising this formation. Here, new mineralogic

data for the South Rim Formation rocks are presented. Magmatic parameters interpreted from these data assist in deciphering lithospheric characteristics during the mid-Tertiary.

Results indicate low temperatures (< 750 °C), reduced conditions (generally below the

FMQ buffer), and low pressures (≤ 100 MPa) associated with South Rim Formation magmatism with slight conditional differences between the two suites. Newly discovered fayalite microphenocrysts allowed determination of oxygen fugacity values (between -0.14 and -0.25

ΔFMQ over temperature ranges of 680-700 °C), via mineral equilibria based QUILF95 calculations, for Emory Peak Suite.

Petrologic information is correlated with structural evidence from Trans-Pecos Texas and adjacent regions to evaluate debated timing of tectonic transition (Laramide compression to

Basin and Range extension) and onset of the southern Rio Grande Rift during the mid-Tertiary.

The A-type and peralkaline characteristics of the South Rim Formation and other pre-31 Ma magmatism in Trans-Pecos Texas, in addition to evidence implying earlier Rio Grande Rift onset in Colorado and New Mexico, promotes a near-neutral to transtensional setting in Trans-Pecos

Texas by 32 Ma. This idea sharply contrasts with interpretations of tectonic compression and arc-related magmatism until 31 Ma as suggested by some authors. However, evidence discussed cannot preclude a pre-36 Ma proposed by other authors.

The later section of this manuscript involves research in the Big Bend area using Google

Earth. At present there is high interest in using Google Earth in a variety of scientific

investigations. However, program developers have disclosed limited information concerning the

program and its accuracy. While some authors have attempted to independently constrain the

accuracy of Google Earth, their results have potentially lost validity through time due to

technological advances and updates to imagery archives. For this reason we attempt to constrain

more current horizontal and vertical position accuracies for the Big Bend region of West Texas.

In Google Earth a series of 268 data points were virtually traced along various early

Tertiary unconformities in Big Bend National Park and Big Bend Ranch State Park. These data

points were compared with high precision GPS measurements collected in field and yielded a

horizontal position accuracy of 2.64 meters RMSE. Complications arose in determining vertical position accuracy for Google Earth because default keyhole markup language (.kml) files currently do not export elevation data. This drawback forces users to hand record and manually input elevation values listed on screen. This is a significant handicap rendering Google Earth data useless with larger datasets. However, in a workaround solution exempted elevation values can be replaced from other data sources based on Google Earth horizontal positioning. We used

Fledermaus 3D three-dimensional visualization software to drape Google Earth horizontal positions over a National Elevation Dataset (NED) digital elevation map (DEM) in order to adopt a large set of elevation data. A vertical position accuracy of 1.63 meters RMSE was determined between 268 Google Earth data points and the NED.

Since determined accuracies were considerably lower than those reported in previous investigations, we devoted a later portion of this investigation to testing Google Earth-NED data in paleo-surface modeling of the Big Bend region. An 18 x 30 kilometer area in easternmost Big

Bend Ranch State Park was selected to create a post-Laramide paleo-surface model via interpolation of approximately 2900 Google Earth-NED data points representing sections of an early Tertiary unconformity. The area proved difficult to model as unconformity tracing and interpolation were often hindered by surface inflation due to regional magmatism, burial of

Laramide topography by subsequent volcanism and sedimentation, and overprinting of Basin &

Range extensional features masking Laramide compressional features. Despite these difficulties, a model was created illustrating paleo-topographic highs in the southeastern Bofecillos

Mountains and at Lajitas Mesa. Based on the amount of surface relief depicted, inconsistency with subsequent normal faulting, and distance from magmatic features capable of surface doming or inflation, we believe the paleo-topographic highs modeled legitimately reflect the post-Laramide surface.

We interpret the paleo-surface in this area as reflecting a post-Laramide surface that has experienced significant erosion. We attribute the paleo-topographic highs as Laramide topography that was more resistant. The model also implies a southern paleo-drainage direction for the area and suggests the present day topographic low through which the Rio Grande flows may have formed very soon after the Laramide Orogeny.

Based on the newly calculated horizontal and vertical position accuracies for the Big

Bend region and results of modeled Google Earth-NED data in easternmost Big Bend Ranch

State Park, it seems Google Earth can be effectively utilized for remote sensing and geologic studies, however we urge caution as developers remain reluctant to disclose detailed program information to the public.

TABLE OF CONTENTS

ACKNOWLEDGEMENTS...... iii

ABSTRACT...... iv

TABLE OF CONTENTS...... vii

LIST OF FIGURES ...... ix

LIST OF TABLES...... xi

Chapters

1. INTRODUCTION TO PRIMARY STUDY ...... 1

2. GEOLOGIC BACKGROUND...... 3

2.1 Rio Grande Rift...... 3

2.2 The Transitional Debate...... 4

2.3 Trans-Pecos Magmatism...... 6

2.4 The South Rim Formation ...... 7

3. MINERAL CHEMISTRY...... 9

3.1 Analytical Methods...... 9

3.2 Mineral Compositions...... 9

3.2.1 Alkali Feldspar ...... 10

3.2.2 Clinopyroxene ...... 10

3.2.3 Amphibole ...... 11

3.2.4 Fayalite ...... 12

3.2.5 Fe-Ti Oxides...... 12

3.2.6 Other Phases ...... 13

3.3 South Rim Formation Magmatic Intensive Parameters ...... 13

4. DISCUSSION...... 14

vii

4.1 Mineralogic Implications on Magmatic Parameters...... 14

4.2 Magmatic and Structural Tectonic Implications...... 17

4.2.1 A Tale of Two Mindsets...... 17

4.2.2 A-type and Peralkaline Magmatism: Conceptual Clarification...... 18

4.3 Considering the Alternatives: Stress Regime Prior to 31 Ma...... 19

4.4 Rolling Back the Clock on Tectonic Transition ...... 22

5. CONCLUSIONS ...... 24

6. INTRODUCTION TO SECONDARY STUDY...... 26

7. GEOLOGIC SETTING ...... 29

7.1 Key Geologic Unconformities ...... 30

7.1.1 Javelina Formation-Chisos Group/Burro Mesa Formation (late Cretaceous-early Eocene unconformity) ...... 31

7.1.2 Hannold Hill Formation-Canoe Formation (mid-Eocene unconformity)...... 32

7.1.3 Pen Formation-Jeff Conglomerate (mid- to late Cretaceous-early Paleocene unconformity) ...... 32

8. METHODOLOGY ...... 34

8.1 Determination of Positional Accuracy...... 34

8.2 Application of Google Earth-NED Data in Paelo-surface Modeling ...... 38

9. RESULTS...... 40

9.1 Google Earth Horizontal and Vertical Position Accuracy...... 40

9.2 Paleo-Surface Model for Easternmost Big Bend Ranch State Park ...... 41

10. DISCUSSION...... 45

10.1 Factors Influencing Positional Accuracy...... 45

10.2 Post-Laramide Geology of Easternmost Big Bend Ranch State Park ...... 47

11. CONCLUSIONS...... 50

REFERENCES ...... 52

viii

APPENDIX A...... 125

APPENDIX B ...... 126

CURRICULUM VITA ...... 127

LIST OF FIGURES

Figure 1: Google Maps terrain image of central to western Big Bend National Park...... 77

Figure 2: Alkali feldspar chemical variation plots...... 78

Figure 3: Clinopyroxene chemical variation plot ...... 79

Figure 4: Amphibole cationic variation plot...... 80

Figure 5: TiO2-FeO-Fe2O3 ternary composition diagram...... 81

Figure 6: Alkaline magma series chemical variation diagram...... 82

Figure 7: The Big Bend region and areas from which unconformities were targeted...... 83

Figure 8: Generalized stratigraphic column for the Big Bend region...... 84

Figure 9: Distribution of all virtually collected Google Earth-NED data points in Big Bend National

Park and localized geologic maps...... 85

Figure 10: Distribution of all virtually collected Google Earth-NED data points in Big Bend Ranch

State Park and localized geologic map...... 89

Figure 11: Distribution of field truthed data points used in determining horizontal and vertical

position accuracy in the Big Bend region...... 91

Figure 12: A) Post-Laramide paleo-topographic model of easternmost Big Bend Ranch State

Park and B) Post Laramide paleo-topographic map draped with geologic map...... 94

Figure 13: Simplistic example illustrating potential effects of different cell positioning on values

reported by a cell...... 96

LIST OF TABLES

Table 1: South Rim Formation mineral assemblage by suite ...... 97

Table 2 (A-E): Mineral chemistry for chemical suites of the South Rim Formations...... 98

Table 3: Pre-31 Ma alternative tectonic stress regime considerations...... 104

Table 4: Horizontal position calculations between 268 Google Earth and field truthed positions in the Big Bend region ...... 105

Table 5: Vertical position offset calculations between 268 Google Earth and NED positions in the Big Bend region ...... 115

1. INTRODUCTION TO PRIMARY STUDY

The Rio Grande Rift is a series of interconnected grabens beginning in Colorado and extending to its southern U.S. extent in Trans-Pecos Texas (Chapin, 1979; Baldridge et al., 1995;

Keller and Baldridge, 1999). Trans-Pecos Texas contains much structural and magmatic rift- related evidence; unfortunately, it can be difficult to resolve due to the regional imprint of previous Laramide deformation.

There has been an abundance of research performed on the Trans-Pecos Magmatic

Province (TPMP) in efforts to better understand the complex landscape and which components of it were produced from a Laramide volcanic arc and relative compression versus subsequent

Basin and Range normal faulting and extension. Currently there exists considerable debate over the approximate timing of this tectonic transition and the initiation of southern Rio Grande Rift in Tran-Pecos Texas.

We present and interpret new mineralogic data from the 32.2-32 Ma South Rim

Formation, a series of comenditic quartz trachytic through rhyolitic volcanics and associated intrusives, which erupted and were emplaced in central Big Bend National Park (southern

TPMP) proximal to the period of transitional debate (Figure 1). These data provide a variety of information pertaining to magmatic parameters that assists in evaluating petrogenesis and resolving the tectonic environment in which magmatism commenced.

Ultimately, we attempt to correlate structural and petrologic evidence from Trans-Pecos

Texas and adjacent regions in order to evaluate the stress regime that existed during extrusion of the South Rim Formation and constrain timing of transition from Laramide compression to Basin and Range extension as well as onset of the southern Rio Grande Rift. Examination of this

evidence invokes conceptual concerns and discussion over amount and extent of rift-relative information that is obtainable from petrologic evidence in general.

2. GEOLOGIC BACKGROUND

2.1 RIO GRANDE RIFT

The Rio Grande Rift is a zone of attenuated lithosphere, with a surface expression

comprised of an extensive series of interconnected asymmetrical grabens, that extends from

Leadville, Colorado, south to El Paso, Texas, where it diverts southeastward toward Presidio,

Texas, before passing into Chihuahua and Coahuila, Mexico (Chapin, 1979; Baldridge et al.,

1995; Keller and Baldridge, 1999). While the rift extent in Mexico remains unresolved,

McDowell and Clabaugh (1979), Dayvault (1979), and McDowell and Mauger (1994) have described peralkaline volcanism that may be Rio Grande Rift related as far south as central

Chihuahua.

Forces initiating Basin & Range extension, which persists to present time, associated with the Rio Grande Rift remain difficult to resolve. Despite its great distance ( > 1000 kilometers)

from the western margin of the North American Plate, several authors proposed extension

resulted from complications associated with subduction of the Farallon Plate (i.e. triple junction

realignment, slab rollback, shallow angle, or slab breakage; Lipman et al., 1972; Christiansen

and Lipman, 1972; Lawton and McMillan, 1999; McMillan et al., 2000). McMillan et al. (2000)

suggest the consequence of slab failure was asthenospheric upwelling into space previously

occupied by the subducted slab, in turn convection of hot asthenosphere against the base of the

lithosphere heating the sub-continental mantle and initiating extension. Henry et al. (1991)

suggested extension may be related to the change from a convergent to a transform margin at

western edge of the North American Plate. However, due to the distance from the western

margin of the North American Plate and because the timing and distribution of extension do not correspond well with kinematics of the Pacific, Farallon, and North American plates, it is difficult to directly (and fully) credit this extension to forces produced by plate boundary interactions (Townsend and Sonder, 2001). These authors also mention possibility of extension initiating (circa 29 Ma) contemporaneously with collision of the East Pacific Rise and paleotrench (Stock and Molnar, 1988). Numerous authors (Sonder and Jones, 1999, Townsend and Sonder, 2001, and references therein) alternatively attribute western U.S. extension to

gravitational buoyancy forces from a combination of previously thickened crust, thinned mantle

lithosphere, or density contrast in the crust or mantle.

2.2 The Transitional Debate

The timing of tectonic transition from Laramide compression to Basin and Range

extension and timing of southern Rio Grande Rift initiation during the mid-Tertiary has been

debated considerably. Interpretations generally involve subduction-related arc magmatism with

varying degrees of compression approaching the mid-Tertiary, a period of transition, and

ultimately tectonic extension, with temporally proximal southern Rio Grande Rift onset, prior to

36 Ma or circa 31 Ma.

Tectonic transition and rift onset prior to 36 Ma has been proposed (Lawton and

McMillan, 1999; McMillan et al., 2000; Chapin et al., 2004; McIntosh and Chapin, 2004; Parker

and White, pers. comm) on the basis of: 1) global plate circuit analysis showing an abrupt

decrease, from 11-14 cm/yr to 6-9 cm/yr, in Farallon-North American plate convergence rates

after ~ 45 Ma (Stock and Molnar, 1988) along with presence of several low relief erosion

surfaces underlying later Eocene to Oligocene sedimentary rocks and potentially extension-

related volcanism (i.e. the 36.7 Ma Wall Mountain Tuff and magmas of the San Juan volcanic

field) (Atwood and Mather, 1932; Larsen and Cross, 1956; Cather et al., 2003; Chapin et al.,

2004), and 2) structural and petrologic evidence from New Mexico and central Colorado including a) suggestions by Parker et al. (2005) that the voluminous intermediate rocks of the

San Juan volcanic field adopted their orogenic geochemical signatures through multi-level and

extensive assimilation of ancient orogenic and anorogenic continental crust and b) the emplacement of a porphyry copper system (whose formation is typical of zones where the magmatic arc is in a nearly neutral stress regime, usually during transitions in or out of subduction (Chapin et al., 2004)) in the Jarilla Mountains between 48 and 42 Ma (Beane et al.,

1975).

Alternatively, the ~31 Ma tectonic transition and rift onset age is hypothesized (Price and

Henry, 1984; Henry and McDowell, 1986; Henry and Price, 1986; Henry at al., 1991; James and

Henry, 1991) because of: 1) change in regional paleostress direction from north-northwesterly

minimum principal stress (σ3) and east-northeasterly maximum principal stress (σ1),

characterizing compression until 32 Ma to east-northeasterly σ3 and vertical σ1, definitive of

extension thereafter (Price and Henry, 1984; Henry and McDowell, 1986); 2) differences in

Zr/Nb, Y/Nb, and Ba/Nb in pre- and post-31 Ma basalts (James and Henry, 1991); and 3) onset

of magmatism prior to < 28 Ma normal faulting in Trans-Pecos Texas (Dickerson and

Muehlberger, 1994; Henry et al., 1991; James and Henry, 1991). This proposed ~31 Ma tectonic

transition is also consistent with spatial and temporal patterns of continental arc migration in the

western United States and Mexico (i.e., Coney and Reynolds, 1977).

2.3 Trans-Pecos Magmatism

TPMP magmatism was voluminous between 48-27 and 24-17 Ma (McDowell, 1979;

Henry and McDowell, 1986); compositions were increasingly alkalic eastward in parallel with

Cenozoic magmatic trends throughout the North American Cordillera (Barker, 1977; James and

Henry, 1991). Barker (1977) initially described TPMP magmatism as “rift-related” based on

comparisons with the Kenya Rift in eastern Africa. Contrastingly, an orogenic and compressional origin for early TPMP magmatism was interpreted by Henry at al. (1991) and

James and Henry (1991); on the basis of structural and trace element evidence (noted in the

previous section) these authors alternatively suggested 48-31 Ma TPMP magmatism as

continental arc-related. However, Henry et al. (1991) note that pre-31 Ma data may could be

interpreted as anorogenic implying a weakly compressional to nearly neutral stress regime

(perhaps representative of transition between approximately 31 and 28 Ma) despite their

suggestion of compression. Compression was proposed by Henry et al. (1991) and James and

Henry (1991) primarily due to absence of Basin and Range normal faulting in Trans-Pecos Texas until ~28 Ma (Dickerson and Muehlberger, 1994).

Since there exists evidence for an earlier, pre-31 Ma, Rio Grande Rift onset age in New

Mexico and Colorado, it becomes important to note the existence of several isolated patches of

peralkaline and A-type magmatism throughout Trans-Pecos Texas. The rhyolite and trachyte (~

44 Ma) in the Hen Egg and Christmas Mountain areas (Lonsdale, 1940; Cameron et al., 1986;

Henry and McDowell, 1986; Henry et al., 1989; Parker, pers. comm) are perhaps the oldest documented peralkaline activity in this region. Approximately 37-35 Ma peralkaline volcanism

has also been recorded from the Chinati Mountains, the Davis Mountains, and north and west of the Solitario laccocaldera (Noble and Parker, 1974; Parker and McDowell, 1979; Parker, 1983;

1986; Henry et al., 1992; Henry et al., 1994; Henry et al., 1997; Parker and White, 2008). A- type magmas such as the Bracks Rhyolite, Star Mountain Formation, and Crossen Trachyte also were emplaced in the Davis Mountains during this time. Peralkaline activity in Big Bend

National Park began at 32.2 Ma and ceased by 29.4 Ma (Miggins et al., 2004, 2007). Although outside of the region, it is worth noting peralkaline volcanism from 30.5-27 Ma just south of the

TPMP in portions of north and central Chihuahua (Dayvault, 1979; Bockoven, 1981; Mauger and Dayvault, 1983; McDowell and Mauger, 1994).

2.4 The South Rim Formation

The South Rim Formation is composed of 32.2 to 32 Ma (Miggins et al., 2004, 2007) comenditic quartz trachytic-rhyolitic lavas and tuffs forming the upper Chisos Mountains (Pine

Canyon Rhyolite, Boot Rock Member, and Emory Peak Rhyolite) in Big Bend National Park

(Maxwell et al., 1967; Ogley, 1978; Barker et al., 1986; Holt, 1998; Parker, 2002; Adams, 2004).

Over time this formation has undergone several reinterpretations and stratigraphic revisions as new geologic evidence was discovered (Becker, 1976; Ogley, 1978; Barker et al., 1986; Henry et al., 1989; Holt, 1998; Urbanczyk and White, 2000; White, 2002; Parker, 2002; Adams, 2004), a summary of these can be found in Benker (2005). For this manuscript, we utilize South Rim

Formation nomenclature of Benker (2005) and White et al. (2006).

Numerous petrogenetic studies have been performed on rocks of the South Rim

Formation. Investigations by Benker (2005) and White et al. (2006) revealed two distinct

geochemical groupings for South Rim Formation rocks capping the high Chisos Mountains, the

Pine Canyon Suite (Pine Canyon Rhyolite, Boot Rock Member, and Lone Mountain and Little

Nugent intrusions) and Emory Peak Suite (Emory Peak Rhyolite and intrusions at Hayes Ridge,

K-Bar, Panther Pass, Lost Mine Trail, and Appetite Peak) which implicate petrogenetic diversity among the South Rim Formation. Geochemical modeling by White et al. (2006) suggests origination of Pine Canyon Suite quartz trachyte via approximately 60-70% fractionation of alkali basalt in conjunction with assimilation of a shale-type wall with more evolved rocks were the product of roughly 70% subsequent fractionation and Emory Peak Suite by ~5% crustal anatexis of a deep mafic granulite that experienced volatile (fluorine) enrichment with compositional variation of these rhyolites most likely due to subsequent fractionation. White et al. (2006) noted these petrogenetic mechanisms, while diverse, were more consistent with those operating in extensional rather than compressional environments and that ascent of viscous high- silica rhyolite from deep within the crust would be facilitated in an extensional stress regime and inhibited in a compressional one.

3. MINERAL CHEMISTRY

Mineralogic data can provide important petrogenetic information that is useful in determining magmatic source region. In previous investigations by Benker (2005) and White et al. (2006) limited mineralogic data were collected and petrogenetic models proposed were base predominantly on whole rock geochemical modeling. Here, we attempt to resolve magmatic parameters such as oxidation state, associated pressure, and temperatures from mineral assemblage and chemistry in order to evaluate the previously proposed petrogenetic models and better understand the crustal depth of source materials generating South Rim Formation magmas.

3.1 Analytical Methods

Mineral data were obtained via electron probe microanalysis at the University of Texas,

El Paso, with a Cameca SX50 electron microprobe. Operating conditions utilized 15 keV accelerating voltage, 20 nA beam current, 5-10 μm beam size, and a 20 second peak count time.

Calibration and internal standards are from Smithsonian, Astimex Scientific, Ltd., and Siemens

Nuclear Labs collection. Calibration and internal standards were analyzed to monitor accuracy and precision; results indicate our accuracy for abundances > 0.5% are better than 5% relative with a precision better than 1%. Mineral assemblages are summarized in Table 1 and mineral compositions are presented in Tables 2A through 2E.

3.2 Mineral Compositions

3.2.1 Alkali Feldspar

Alkali feldspar in each suite are up to 5 millimeters in length forming euhedral to

subhedral phenocrysts and are also a groundmass component. Most Pine Canyon Suite sanidine

phenocrysts (Or41) have lower Or contents than Emory Peak Suite sanidine phenocrysts (Or46), both suites exhibit very low An content (An < 3 mol. %) (Figure 2). Pine Canyon Suite alkali feldspar are perthitic but those in Emory Peak Suite are unexsolved. Highly albitic (Ab>94) stringlets and patches occur in and adjacent to high orthoclase sanidine (Or>93) in perthitic Pine

Canyon Suite alkali feldspar. Rare turbid patches and almost pure end-member compositions

suggest that perthite represent deuterically mediated exsolution representative of interaction

reactions between feldspar and aqueous fluids (Parsons and Brown, 1983).

3.2.2 Clinopyroxene

Clinopyroxene are sparsely distributed throughout the South Rim Formation; most are subhedral in Pine Canyon Suite rocks versus anhedral or rounded in Emory Peak Suite rocks, all grain sizes are generally < 2 millimeters. Clinopyroxene in both Pine Canyon Suite (Wo44Fs55

AVG) and Emory Peak Suite (Wo44Fs57 AVG) rocks are ferroaugite border lining ferrohedenbergite composition (Figure 3). These clinopyroxene have very low En contents; Emory Peak Suite

ferroaugite contain < 0.5 mol. % En while Pine Canyon Suite ferroaugite contain < 4 mol. % En.

Except for one acmitic ferroaugite (Ac17) from the Pine Canyon Suite (BC-02), most of these

have < 5 mol. % Ac. Ac abundances do not vary systematically with increasing peralkalinity.

3.2.3 Amphibole

Sodic amphibole in rocks of the South Rim Formation are euhedral to subhedral,

commonly < 2 millimeters in length, and are the most abundant volumetrically minor (<1 vol. %)

phase in each suite. Sodic amphibole exemplify the highly evolved and alkalic nature of these rocks; these amphibole have sodic B sites (NaB 1.60-1.87 pfu), highly sodic A sites ([Na + K]A

1.16-1.46 pfu), and high Fe+2 and Fe+3 contents befitting their classification as near end member

arfvedsonite. Giret et al. (1980) determined that amphibole compositions are correlative with

magma alkalinity from which they crystallize; thus, the peralkaline character of South Rim

Formation rocks is in accord with unusually sodic amphibole. The CaO content of arfvedsonite

in samples of each suite differs; Pine Canyon Suite arfvedsonite frequently contains ≥ 1 wt. %

CaO whereas Emory Peak Suite arfvedsonite does not. A single Pine Canyon Suite amphibole

(PC-01) has a less sodic B site (NaB = 0.70 pfu) and completely filled sodic A site (NaA = 2.00

pfu) which is consistent with classification as ferrorichterite. Although cationic abundances of

Si+Na+K (~ 10.50-10.75 pfu) in all South Rim Formation rocks are very similar, Pine Canyon

Suite amphibole have higher Ca+ivAl in their A, B, and T sites (~ 0.4-1.4 pfu) (Figure 4) relative

to Emory Peak Suite amphibole (~ 0.2-0.35 pfu).

3.2.4 Fayalite

Olivine forms minor to trace phenocrysts and microphenocrysts exclusively in rocks of

the Emory Peak Suite. Grains are a deep green and often alter to iddingsite. Olivine

compositions range from fayalite (Fa98) to a slightly higher SiO2, lower FeO olivine that may be

hortonolite. The presumed hortonolite is also Mg-poor and contains minor amounts (< 1 wt. %) of Fe2O3.

3.2.5 Fe-Ti Oxides

South Rim Formation rocks contain magnetite and ulvöspinel as discrete

microphenocrysts or as exsolved products. Magnetite TiO2 contents are generally 2-3 wt. % but approach 6 wt. % in some samples (Figure 5). Microphenocrysts of a pseudobrookite series solid solution mineral, nearly the composition of ferropseudobrookite (FeTi2O5), are also present in Emory Peak Suite samples and in one Pine Canyon Suite sample (PJ-01). In samples of both suites ilmenite form microphenocrysts, with near end member compositions (Ilm>92), and form

rims and/or small patches on pseudobrookite solid solution series minerals. Ilmenite rimming

some pseudobrookite solid solution series minerals suggest the presence of primary

ferropseudobrookite in South Rim Formation (Stähle and Koch, 2003). Magnetite-ulvöspinel

and ferropseudobrookite-pseudobrookite exsolution are evidence for interaction with aqueous

fluid. A number of magnetite grains are altered and contain up to 5 wt. % SiO2.

3.2.6 Other Phases

Additional phases for both Pine Canyon Suite and Emory Peak Suite rocks include

zircon, apatite, and quartz. However, there are several minerals that are present solely in the

Pine Canyon Suite rocks such as pyrrhotite, Ce enriched bastnasite, and a Ce enriched phosphate

likely representative of monazite (such a phase was reported by White et al. (2006)). Ti bearing

(up to 8 wt. % TiO2) aenigmatite also forms as microphenocrysts in those Pine Canyon Suite

samples where alkali feldspar compositions approach anorthoclase (~Or35). Emory Peak Suite

rocks offer different mineral exclusivity such as Fe enriched biotite (compositionally annite, with

some grains containing up to 2.48 wt. % F), in rocks where alkali feldspar exhibit Or>40, and Ce enriched chevkinite.

3.3 South Rim Formation Magmatic Intensive Parameters

Barometric conditions prevailing during Emory Peak Rhyolite crystallization were

indeterminable in previous studies; however, in this study, the discovery of fayalite

microphenocrysts in one Emory Peak Rhyolite sample permitted use of the geothermobarometric

calculator. Using ferroaugite-olivine-ilmenite equilibria from this sample, QUILF95 (Andersen

et al., 1993) was used to calculate oxygen fugacities between -0.14 and -0.25 ΔFMQ over a

temperature range of 680-700 °C (at 100 MPa).

4. DISCUSSION

4.1 Mineralogic Implications on Magmatic Parameters

White et al. (2006) noted that both Pine Canyon Suite and Emory Peak Suite magmatism could be designated as A-type due to high total alkalis, low CaO, high FeOT/MgO, and elevated

HFSE concentrations. The low feldspar content (generally < 10 vol. %), microphenocrystic size

of Fe-Ti oxides, and occurrence of ferroaugite and near end member fayalite are consistent with

A-type mineral recognized in early anorogenic suites in continental regions described by Bonin

(2007). The mineral assemblages of rocks in each South Rim Formation suite are also consistent

with those commonly exhibited in peralkaline rocks (i.e. the Gedemsa caldera, Eburru Volcanic

Complex, Greater Olkaria Volcanic Complex, Mounts Abu-Kharif and El-Dob, Pantelleria;

Peccerillo et al., 2003; Omenda, 1997; Ren et al., 2006; Davies and Macdonald, 1987; Abdel-

Rahman, 2006; Civetta et al., 1984, 1988, 1998; Avanzinelli et al., 2004; White et al., 2005;

Parker and White, 2008). Numerous similarities also exist between the mineral assemblages

observed in the two South Rim Formation suites and assemblages crystallized under reduced

conditions in pantellerite during laboratory experiments by Scaillet and Macdonald (2001, 2003).

Mineral assemblage and chemistry can place constraints on magmatic oxidation for the

two South Rim Formation suites. The scarcity of clinopyroxene in, and comenditic nature

mentioned by White et al. (2006) of, South Rim Formation rocks may be a preliminary indicator

for reduced conditions; Martin (2006) discusses the necessity of low oxygen fugacity in order to

destabilize alkali-bearing clinopyroxene during melt reactions to initiate production comenditic

melts from quartzofeldspathic sources. Low oxidation state of Pine Canyon Suite magmas is

further promoted by the presence of aenigmatite, whose upper stability limit is between NNO

and FMQ buffers (Ernst, 1962; Lindsley, 1971), and its coexistence with ferrorichterite (Scaillet

and Macdonald, 2001). These inferences are supported by QUILF95 (Andersen et al., 1993)

calculations for the Pine Canyon Suite that determined oxygen fugacities ranging from -1.7 to -

1.9 and -1.5 ΔFMQ for the Pine Canyon Rhyolite and Boot Rock Member (White et al., 2006),

respectively. Reducing conditions are also suggested by assemblages in the Emory Peak Suite;

Dachs (1994) documents annite + sanidine + magnetite equilibration at oxygen fugacities

defined by the FMQ buffer (at 100 MPa). These mineralogic implications are consistent with

new QUILF95 calculated oxygen fugacity values for the Emory Peak Suite, between -0.14 and -

0.25 ΔFMQ, presented in this investigation. In comparison, calculated oxygen fugacities suggest

Emory Peak Suite magmas were relatively more oxidized than those of the Pine Canyon Suite.

Overall low magmatic temperature and pressures can be interpreted from examined

mineral assemblages. The previously noted coexistence of aenigmatite and ferrorichterite

suggest temperatures < 750 °C (Scaillet and Macdonald, 2001) for Pine Canyon Suite. Ti bearing

aenigmatite similar to that of the Pine Canyon Suite has been synthesized at 700 °, 100 MPa

(PH2O), and oxygen fugacity controlled by the iron-wüstite buffer (Deer et al., 1992; Marsh,

1975; Thompson and Chisholm, 1969). At 100 MPa, the Emory Peak Suite assemblage annite +

sanidine + magnetite has been recorded to equilibrate at temperatures between approximately

680 and 690 °C (Dachs, 1994).

Volatile interaction with these magmas was speculated by White et al. (2006) due to

fluorian enrichment in ubiquitous groundmass arfvedsonite (1.50 wt. % F) of rheomorphic tuff

and via fluorine content of annite (2.21 wt. % F) in the Emory Peak Suite. This speculation is supported by detection of additional fluorine enriched annite (2.48 wt. % F) in Emory Peak Suite

rocks. The discovery of bastnasite (Ce enriched carbonate) may indicate some degree of volatile interaction also involved with Pine Canyon Suite magmas.

Mineralogic interpretations suggest low pressure (< 100 MPa) and likely shallow magma

chamber depths for South Rim Formation magmas. Additionally, it can be inferred from mineral

assemblages and oxygen fugacity calculations that these magmas experienced reducing

conditions, along FMQ buffer or lower, albeit to different degrees in each suite. The low

temperatures, similar to those approximating the solidus of crustal compositions, and low

oxidation states interpreted for the South Rim Formation are likely buffered or inherited from the

protolith and can be reasonably interpreted as products of crustal anatexis (i.e. Carmichael, 1991;

Frost and Frost, 1997; Anthony, 2005; Ren et al., 2006). However, low oxidation states can also

indicate direct derivation from mantle melting or anatexis of mantle-derived source rocks; thus,

the assimilation-fractional crystallization origin for Pine Canyon Suite proposed by White et al.

(2006) also cannot be precluded, especially when considering fractionation trends implied by

their Pearce element ratio diagrams and results of geochemical modeling. Furthermore, Martin

(2006) also acknowledges that some A-type granitic magmas do arise via efficient fractionation

of a mantle-derived basaltic magma. Thus, the diverse petrogenetic models proposed for the two

South Rim Formation suites are supported by this mineralogic study. Interestingly, when whole

rock geochemistry (White et al., 2006) and feldspar chemistry are plotted together trends

expressing petrogenetic differences in each suite can also be observed; Emory Peak Suite whole

rock and alkali feldspar compositions are representative of K-series alkaline magmatism whereas

Pine Canyon Suite whole rock and alkali feldspar compositions are representative of Na-series

alkaline magmatism (Figure 6).

4.2 Magmatic and Structural Tectonic Implications

4.2.1 A Tale of Two Mindsets

It seems that when examining the complicated tectonic environment associated with

Trans-Pecos Texas and the southern Rio Grande Rift during the mid-Tertiary there are two

paradigms in which one views evidence: structural and petrologic. While the structural mindset

and petrologic mindset often complement one another in deciphering tectonic scenario, in Trans-

Pecos Texas evidence provokes theoretical head-butting between these two mindsets due to pre-

31 Ma emplacement of A-type and/or peralkaline magmatism and the later occurrence of major

Basin and Range faulting (circa 28-24 Ma).

From a structural perspective, rifting is likely considered strictly as formation of grabens throughout Trans-Pecos Texas. Thus, it is most reasonable to place extensional onset where major regional normal faulting is established and graben production occurs. However, this approach may only quantify when extension reaches upper crustal levels. On the other hand, a petrologic perspective utilizes rock composition to ascertain magmatic conditions, from upper to lower crustal and beyond, and predict relative stress. It is greatly difficult to assess which mindset is better for interpreting onset of southern Rio Grande rifting in Trans-Pecos Texas; with this stated, the remainder of this section will attempt to correlate temporally overlapping petrologic and structural evidence from Trans-Pecos Texas and adjacent areas in an effort to better constrain mid-Tertiary extensional initiation estimates.

4.2.2 A-type and Peralkaline Magmatism: Conceptual Clarification

Due to the debatable nature of the mid-Tertiary tectonic scenario in Trans-Pecos Texas and presence of A-type and peralkaline magmatism, an important consideration before discussing petrologic evidence is the conceptual clarity concerning implications of such magmatism. In a recent paper, Bonin (2007) discusses in detail the ambiguities associated with the term A-type magmatism and concludes: 1) emplacement ages for these magmas are apparently unrelated to proximal major orogenic events, 2) Fe-rich mafic mineralogy encountered in these rocks is predominantly the result of reducing conditions, and 3) geochemically, A-type rocks are marked by high alkali, LILE, and HFSE contents, high Fe/Mg ratios, and OIB-type compositions. Martin (2006) also concluded A-type granitic magmatism is intimately tied to nepheline syenite and carbonatite origination; all of these are manifestations of anorogenic magmatism and are linked to processes going on in the upper mantle and lower crust.

Therefore the term A-type magmatism , as used here, refers to rocks demonstrating aforementioned characteristics and indicative of an anorogenic (approximately neutrally stressed) environment. Peralkaline magmas are geochemically defined as those where molar alkali content exceeds the molar alumina. A good explanation of environments where peralkaline magmas are encountered is provided by Avanzinelli et al. (2004) who stated:

“Peralkaline suites are generally found in continental intraplate settings, affected by rifting (e.g.,

Pantelleria, Tibesti, Ethiopia, Afar, Kenya, Cameroon line, British Columbia, Basin and Range,

South Greenland, Villari, 1974; Barberi et al., 1975; MacDonald, 1974; Bailey and McDonald,

1987; Trua et al., 1999), but examples from oceanic islands close to active mid-ocean ridges are also found (e.g., Socorro Is., Easter Is., St. Paul Is., Iceland, and Azores; Mungall and Martin,

1995; Bailey, 1974, Sørensen, 1974; Fitton and Upton, 1987; Bohrson and Reid, 1997). More

rarely, peralkaline felsic rocks and alkali basalts are associated with orogenic magmatic suites

(e.g., New Zealand, Japan, Papua New Guinea, Mexico, Sardinia; Nelson and Hegre, 1990;

Bailey, 1974, Sørensen, 1974, Fitton and Upton, 1987).” Many other descriptions concerning

tectonic environments of peralkaline rock formation are similar in noting their presence in

orogenic associated settings; however, subsequent papers addressing generation of these specific

peralkaline magmas attribute their existence, generally as minor members of these orogenic

suites (Macdonald, 1974), to complicated tectonic interactions involving zones of extension or

relatively small localized extension that has manifested in rare convergent margins (i.e. each of

the locational examples associated with orogenic magmatism listed by Avanzinelli et al. (2004)

is linked to some degree of, or association with, extension by Mahood, 1984; Yamaji and

Yoshida, 1998; Stolz et al., 1993; Nelson and Hegre, 1990; Cioni et al., 2001). Furthermore,

peralkaline magmatism in the upper crust cannot be invalidated as it may represent a distant and

downplayed expression of extensional activity in the lower crust and upper mantle. Particularly

for segments of the Rio Grande Rift in New Mexico, findings by Wilson et al. (2005) conclude that lower crustal extension is distributed over an area four times the width of the rift’s surface expression. Therefore it should not be inferred that peralkaline magmatism at the surface, even if minor, is void of expressing some degree of tectonic tension.

4.3 Considering the Alternatives: Stress Regime Prior to 31 Ma

Due to the presence of A-type and peralkaline magmatism in the TPMP, an alternative

mid-Tertiary stress scenario is considerable. Formation of A-type and peralkaline magmas

before ~31 Ma suggest the possibility of a near-neutral to perhaps transtensional environment, with the possibility of legitimate extension at greater lithospheric depths, prior to occurrence of major Basin and Range faulting at the surface. While this view sharply contrasts with the orogenic setting interpreted by Henry et al. (1991) and James and Henry (1991), we believe that although magmatism preceded major regional normal faulting that there is sufficient evidence indicating anorogenic to transtensional stress regime by at least 32 Ma when the South Rim

Formation erupted. Thus, in this section we examine petrologic and structural evidence supporting anorogenic magmatism or some degree of lithospheric extension by 32 Ma (Table 3).

Cameron et al. (1986) and Henry et al. (1989) have documented ~44 Ma peralkaline intrusions near the Christmas Mountains; these intrusions have been proposed by Parker and

White (pers. comm) as possibly representing the earliest extension-related magmatic activity.

Thus, there is potential for a gap of up to 22 Ma between the first indication of extension and significant Basin and Range faulting in Trans-Pecos Texas. At approximately 37 Ma peralkaline tuffs erupted from the Infiernito caldera north of the Chinati Mountains (Henry et al., 1992).

From 36.8-35 Ma peralkaline eruptions occurred throughout the Davis Mountains Volcanic Field

(i.e. Buckhorn caldera, Paisano volcano, etc.) (Parker et al., 1983; Parker and White, 2008) ; it was during this time that the Bracks Rhyolite, Star Mountain Formation, and Crossen Trachyte, all of which are geochemically A-type, formed (Henry et al., 1983). At approximately 35.4 Ma, peralkaline rhyolitic domes were formed to the north and west of the Solitario laccocaldera

(Henry et al., 1997). Eruptions of peralkaline and A-type rocks creating the South Rim

Formation from 32.2-32 Ma suggest a near-neutral to transtensional tectonic regime before 31

Ma. Comenditic trachytic-rhyolitic magmas comprising the South Rim Formation (as stratigraphically redefined here) erupted from 32.2-32 Ma (Miggins et al., 2004, 2007). While

their peralkalic nature suggests some degree of extensional relation, their A-type granitic characteristics are indicative of an anorogenic setting (White et al., 2006).

Perhaps the earliest structural evidence suggesting an alternative stress regime by 32 Ma is the emplacement of a 48-42 Ma porphyry copper system documented by Beane et al. (1975) in adjacent New Mexico near the Jarilla Mountains; according to Chapin et al. (2004), such formation is typical in zones where the magmatic arc is in a nearly neutral stress regime, usually during transitions in or out of subduction. Also in New Mexico, McMillan et al. (2000) document intercalation of the Bell Top Formation and a conglomerate deposited in a half graben at ~36 Ma as further suggestive of earlier extension. Furthermore, Bell Top Formation and Uvas

Volcanic Field basalts (that are generally accepted as extensional) demonstrate similar incompatible trace element patterns with earlier (~38 Ma) Rubio Peak Formation basalts;

McMillan et al. (2000) proposed each of these lavas were generated via various degrees of partial

melting from the same subcontinental lithospheric source. Therefore, some degree of extension

may be perceivable by approximately 38 Ma. Just south of the TPMP in northern Chihuahua, a

~37 Ma carbonatite complex exists near Villa Ahumada that preliminarily suggests near-neutral

to neutral stress regime (Nandigam, 2000). Extensional stress is also interpretable through

formation of the Goodsight-Cedar Hills half graben in New Mexico between 35 and 28.5 Ma

(Mack et al., 1994; Mack, 2001). Further evidence of extensional stress at this time are dikes

preferably striking N40°W in the Organ Mountains of New Mexico (Newcomer et al., 1983). A

7 kilometer long dike just across from the TPMP near the San Carlos caldera complex in

northern Chihuahua generally strikes northerly implying extension at 32 Ma (Chuchla, 1981;

Gregory, 1981).

The fact that South Rim Formation magmatism pre-dates the beginning of Basin and

Range faulting in Trans-Pecos Texas between roughly 28 and 23 Ma (Dickerson and

Muehlberger, 1994) is a significant counter argument against the concept of near-neutrality or

transtension; however, investigations by Ebinger et al. (2000) document East African Rift

System volcanism that precedes faulting by ~20 Ma and 8 Ma in southern Ethiopia in northern

Kenya, respectively. Closer to Trans-Pecos Texas, Axen et al. (1993) report extensional

volcanism preceding 32-30 Ma volcanism in the Dry Lake Valley area of Nevada; these authors

attribute this precedence to the structural state of the upper crust. Additional evidence for a near-

neutral to transtensional environment by 32 Ma is found in notation by Henry et al. (1991)

admitting that: 1) σ1 could range from east-northeasterly to vertical, thereby indicating north-

northwest extension, but such an interpretation was overruled because faulting [only noticeable

at the surface] accompanying magmatism was negligible (p. 13,551), and 2) there exists

considerable scatter in dike and vein orientations suggesting a small difference in magnitude

between σ1 and σ3, and that this can be characteristic of tectonically inactive regions as suggested

by Delaney et al. (1986) (p. 13,552).

4.4 Rolling Back the Clock on Tectonic Transition

While the debate over timing of the mid-Tertiary tectonic transition from compressional

to extensional tectonic regime continues, evidence discussed here offers a new perspective.

While workers such as Price and Henry (1984), Henry and McDowell (1986), Henry and Price

(1986), Henry at al. (1991), and James and Henry (1991) recommend a ~31 Ma tectonic

transition age and proximal onset of the southern Rio Grande Rift, we note petrologic and

structural evidence that suggest a near-neutral or transtensional stress regime in Trans-Pecos

Texas at 31 Ma. Evidence discussed suggests at least preliminary transition from Laramide compression to Basin and Range Extension initiated a minimum of 1 Ma earlier than the age proposed by the aforementioned authors. Furthermore, due to the generation of isolated patches of peralkaline magmatism as far back as ~44 Ma and the difficulties in recognizing expressions of deeper crustal and upper mantle tension at the surface, evidence presented here cannot preclude the pre-36 Ma tectonic transition and southern Rio Grande Rift onset age interpreted by

Lawton and McMillan (1999), McMillan et al. (2000), Chapin et al. (2004), McIntosh and

Chapin (2004), Parker and White (pers. comm.).

5. CONCLUSIONS

Mineral assemblages and chemistry suggest South Rim Formation magmatic conditions

were characterized by reducing conditions (generally below the FMQ buffer), low temperatures

(< 750 °C), and pressures likely less than 100 MPa. Because fayalite microphenocrysts were discovered in an Emory Peak Rhyolite sample during this investigation, new oxygen fugacity values between -0.14 and -0.25 ΔFMQ were calculated from mineral equilibria with the program

QUILF95. Overall, conditions associated with Emory Peak Suite magmas appear to have been less reduced than those of the Pine Canyon Suite. The two South Rim Formation suites also demonstrate small differences in their low temperatures. Mineralogic results presented here are consistent with the diverse petrogenetic model for Emory Peak Suite and Pine Canyon Suite proposed by White et al. (2006) that was predominantly based on geochemistry. Mineralogic results suggest magmatic conditions that are more consistent with those encountered in extensional over compressional settings.

In our discussion we emphasize the potential for under appreciation of magmatic deformational evidence, specifically lower lithospheric thinning in areas of extension, and resultant crustal interpretations due to the sharpness of structural evidence expressing deformation, perhaps to a lesser degree, at the surface. A number of the mid-Tertiary structural and magmatic features discussed show correlations that, when lower lithospheric processes are considered, justify rolling back the proposed ~31 Ma timing for tectonic transition in Trans-

Pecos Texas and southern Rio Grande Rift onset inferred by some authors (Price and Henry,

1984; Henry and McDowell, 1986; Henry and Price, 1986; Henry at al., 1991; James and Henry,

1991) to approximately 32 Ma. Magmatism from 48-31 Ma has been interpreted as orogenic and

arc-related (Henry et al., 1991; James and Henry, 1991); however, such interpretation is

inconsistent with eruption of the 32 Ma peralkaline and A-type South Rim Formation and other

structural and petrologic evidence noted. We propose that Trans-Pecos Texas experienced a

near-neutral to transtensional stress regime by at least 32 Ma and that the region did not

experience true compression at this time. Structural and petrologic evidence discussed during

this examination cannot preclude the pre-36 Ma tectonic transition and southern Rio Grande Rift onset age suggested by some authors (Lawton and McMillan, 1999; McMillan et al., 2000;

Chapin et al., 2004; McIntosh and Chapin, 2004; Parker and White, pers comm).

6. INTRODUCTION TO SECONDARY STUDY

The use of Google Earth (Google Inc., 2009a), a virtual globe program, is becoming increasingly popular in the scientific community as well as with the general public. This is due to the fact that it is very user friendly, widely available, does not require a state-of-the-art computing system, and most importantly is downloadable free of cost (at least the basic version).

Additionally, it is fast becoming a program of choice over, or in combination with, popular GIS programs because there is no need for extensive training (De Paor et al., 2009). Google Earth has potential in itself to become a powerful remote sensing tool; however, currently very limited information has been disclosed by developers concerning processing techniques involved with and accuracy of incorporated imagery.

Despite Google Earth’s benefits, the scientific community generally expresses reservations about its use. This is because Google Inc. representatives attest values reported by

Google Earth are only estimations and make no claims as to their accuracy (Google Inc., 2008,

2009). This disclaimer is understandably put forth by Google Inc. for liability purposes.

However, independent investigations by Potere (2008) and Jain and Ravibabu (2008) have placed initial constraints on Google Earth horizontal and vertical position accuracy allowing

Google Earth utilization in scientific research to some degree.

In comparing positions of 436 data points between Google Earth and Landsat Geocover scenes, Potere (2008) conservatively determined a horizontal position accuracy of 39.7 meters root means square error (RMSE). Such accuracy was deemed adequate for use in analysis of moderate resolution remote sensing imagery (Potere, 2008). Jain and Ravibabu (2008) investigated vertical position accuracy of varying scale (1:10000 through 1:50000) based digital

terrain models that were extracted from Google Earth. At a scale of 1:50000, these authors

determined a vertical position accuracy of ± 10 meters (Jain and Ravibabu, 2008).

While these are valid efforts that place constraints on horizontal and vertical position

accuracies, developers have likely updated Google Earth imagery archives at frequent intervals

(and perhaps fragmentally). Addition of higher resolution imagery and technological advances

with time may very well have increased horizontal and vertical position accuracy. It has been

two years since the conclusions of Potere (2008) and Jain and Ravibabu (2008) were published;

while these authors provided benchmark constraints for Google Earth accuracy there is need for

re-assessment due to the likelihood of technological and imagery updates over this time.

If present accuracy of Google Earth has improved since that reported by Potere (2008)

and Jain and Ravibabu (2008) then Google Earth-NED data could be applied to other

investigatory methods such as construction of three-dimensional paleo-surface models derived from targeted geologic interest points. A second section of this investigation uses acquired

Google Earth-NED data from sections of the early Tertiary unconformity, present after Laramide deformation and uplift occurred, to construct a paleo-surface model for easternmost Big Bend

Ranch State Park. The area’s rugged terrain and complex geologic history pose numerous complications that can limit data collection and paleo-surface modeling. Challenges include burial of the targeted unconformity and Laramide topography beneath subsequent late Eocene-

Oligocene volcanics and clastic sediments, inflation and doming of the paleo-surface from regional intrusions, and differentiation between structural features associated with Laramide compressional stresses versus Basin & Range extensional stresses. With hopes of overcoming noted challenges, we attempt to determine if relict Laramide topography can be observed through modeling sections of the targeted early Tertiary unconformity. Successful paleo-surface

modeling in this area will support use of Google Earth techniques and data even in more geologically complicated areas throughout the United States.

7. GEOLOGIC SETTING

In the Late Cretaceous the Big Bend region (Figure 7) experienced far inland

compressional effects of the Laramide Orogeny; several geologic features formed via

compressional faulting and folding between approximately 90 and 50 Ma (Muehlberger, 1980,

Erdlac, 1991; Lehman, 1991; Henry and Muehlberger, 1996; Henry, 1998). In Big Bend

National Park, the park bounding Sierra del Carmen-Santiago Mountains (Conn and Poth, 1980;

Muehlberger, 1980; Muehlberger and Dickerson, 1989) and Mesa de Anguila (Erdlac, 1990) monoclines were formed via left-lateral shear. Between these mammoth monoclines several major anticlines such as Cow Haven, Mariscal Mountain, and San Vicente also developed

(Maxwell et al., 1967; Lehman, 1991). In easternmost Big Bend Ranch State Park the Terlingua

Uplift and Contrabando Lowlands were separated as the Fresno-Terlingua Monocline and relative faulting developed pushing up the Terlingua Uplift (or Terlingua-Solitario structural

Block) (Henry and Muehlberger, 1996, and references therein; Erdlac, 1990, 1996).

During the late Eocene (Lawton and McMillan, 1999; McMillan et al., 2000; Chapin et

al., 2004; McIntosh and Chapin, 2004) to early Oligocene (Price and Henry, 1984; Henry and

McDowell, 1986; Henry and Price, 1986; Henry et al., 1991; James and Henry, 1991) the Big

Bend region began to experience effects of Basin & Range extensional stresses [which persist to present]. By late Oligocene the region was also marked by major normal faulting associated with Basin & Range extensional stresses (Henry and Price, 1986). In Big Bend National Park some byproducts of this stress are numerous grabens south and west of the Chisos Mountains and fault belts such as the Punta de la Sierra, Burro Mesa, and Castolon-Terlingua Abaja

(Maxwell et al., 1967). In easternmost Big Bend Ranch State Park numerous grabens and faults,

such as the larger Yellow Hill and Terlingua faults, formed atop the Terlingua Uplift and

throughout the Contrabando Lowlands via Basin & Range extensional stresses (Henry and

Muehlberger, 1996, and references therein; Henry et al., 1996a, Henry and Erdlac, 1996; Henry,

1998) at this time.

Also approaching the mid-Tertiary, the Big Bend region (and the remainder of West

Texas) experienced widespread and voluminous magmatism (Henry and McDowell, 1986).

Earliest magmatism in the Big Bend region initiated 46.5 Ma in Big Bend National Park with the

oldest lava flows of the Chisos Group (Maxwell et al., 1967; Miggins et al., 2008). Magmatism

continued throughout the Big Bend region until about 18 Ma with extrusion of Closed Canyon

Formation volcanics in Big Bend Ranch State Park (Henry, 1998).

7.1 Key Geologic Unconformities

Modeling the post-Laramide surface in the Big Bend region is difficult due to limited exposures of target early Tertiary unconformities. However, in areas where there are numerous

or prominent exposures of these unconformities post-Laramide three-dimensional paleo-surface

models can be interpolated [pending suitable Google Earth accuracy] and can assist in depicting

a post-Laramide surface thereby complementing our understanding of pre- and post- Laramide

geologic structures in the region. Three geologic unconformities varying in age and strata

(Figure 8) were examined in this investigation; we generally describe appearance and age of

bounding strata creating these unconformities throughout Big Bend National Park and Big Bend

Ranch State Park. Detailed stratigraphic descriptions can be found in Maxwell et al. (1967) for

units in Big Bend National Park and Henry et al. (1996a) and Henry (1998) for units in

easternmost Big Bend Ranch State Park. These authors also produced detailed non-digitized geologic maps that assisted in virtually locating targeted unconformities.

7.1.1 Javelina Formation-Chisos Group/Burro Mesa Formation (late Cretaceous-early Eocene

unconformity)

Throughout Big Bend National Park there are numerous localities where Chisos Group or

Burro Mesa Formation flows unconformably overlay Javelina Formation clays (Maxwell et al.,

1967; Benker, 2005; White et al., 2006). The Javelina Formation is a series of late Cretaceous multi-colored (mustard yellow, dull gray, pink, and maroon) clays with poorly indurated sandstone layers (Maxwell et al., 1967). The late Eocene Chisos Group varies considerably in lithology by location; it has been grouped into three basal basaltic flows, a rhyolitic tuff, and a trachyandesitic flow that are all separated by undifferentiated tuffs and tuffaceous sedimentary rocks (Maxwell et al., 1967; Henry and Davis, 1996; Miggins et al., 2008). The Oligocene

Burro Mesa Formation (formerly included in Maxwell et al.’s (1967) South Rim Formation) includes rhyolitic tuffs and flows centered in the Castolon Graben (Benker, 2005; White et al.,

2006). Together these rocks predominantly form the Chisos Mountains.

In the Castolon Graben the dull gray clays of the Javelina Formation sharply contrast with reddish tinted Burro Mesa Formation flows. The unconformity is easily identifiable and it is perhaps the most conspicuous of all targeted in this investigation. The Javelina Formation-

Chisos Group/Burro Mesa Formation unconformity was field truthed along two ridges in the

Castolon Graben; it was virtually traced in Google Earth at this location, in the southern Chisos

Mountains, and at Dogie Mountain and adjacent areas (Figures 9A-B, 11A).

7.1.2 Hannold Hill Formation-Canoe Formation (mid-Eocene unconformity)

An angular unconformity exists between early Eocene Hannold Hill Formation clays and

overlaying mid-Eocene basal sandstone of the Canoe Formation and is exposed mainly in

Tornillo Flat. Each of these formations is predominantly comprised of multi-colored (dull gray,

brown-yellow, and maroon) clays that are often marly; the most prevalent difference is presence

of a massive white to yellow colored basal sandstone locally, termed the Big Yellow Sandstone

(Maxwell et al., 1967) in the Canoe Formation (Maxwell et al., 1967).

This unconformity can be challenging to detect where the Big Yellow Sandstone is

absent due to the similarity of these formations. However, in most areas traced in Google Earth

the size and contrast between the Big Yellow Sandstone and/or its eroded debris contrast against duller or darker colored underlaying clays. This unconformity was traced with a GPS unit along ridges and cliffs in two areas of Tornillo Flat and was virtually traced in Google Earth at these

locations as well as isolated ouctrops north of the Chisos Mountains (Figures 9C-D, 11B-C).

7.1.3 Pen Formation-Jeff Conglomerate (mid- to late Cretaceous-early Paleocene

unconformity)

In easternmost Big Bend Ranch State Park there are numerous localities where the Jeff

Conglomerate unconformably overlays Pen Formation clays (McKnight, 1970; Henry and Davis,

1996; Henry et al., 1996a; Henry, 1998). The mid- to late Cretaceous Pen Formation is

comprised of finely laminated calcareous clays, often marled in appearance, and minor flaggy limestone sections (Lehman, 1985; McCormick et al., 1996; Henry et al., 1996a; Henry, 1998).

The mid-Eocene Jeff Conglomerate is mainly the byproduct or erosion from the Fresno-

Terlingua Monocline; it consists of poorly to moderately sorted chert and limestone clasts (up to

40 cm in diameter) bound by strong calcitic cementation and locally contains lenses to thick layers of coarse sandstone (McKnight, 1970; Henry et al., 1996a; Henry et al., 1996b; Henry and

Davis, 1996; Henry, 1998). The Jeff Conglomerate is actually a basal conglomerate of the

Devil’s Graveyard Formation, exposed north and northeast of Big Bend Ranch State Park, but was mapped separately by McKnight (1970) and Henry and Davis (1996).

In field this unconformity is easily recognized due to the textural differences between finely laminated clays and pebble and cobble filled conglomerate. In Google Earth these units are somewhat more difficult to distinguish but can be differentiated by the mottled appearance of blue-grey Pen Formation clays—often weathering yellowish or greenish—contrasting against darker blue-grey tinted and more resistant Jeff Conglomerate. Field truthing through GPS location collection for this unconformity was obtained at two locations in the Contrabando

Lowlands while the unconformity was virtually traced in Google Earth at these and other locations throughout the Contrabando Lowlands as well as a few locations atop Fresno-Terlingua

Monocline (Figures 10A-B, 11D-E).

8. METHODOLOGY

8.1 Determination of Google Earth Positional Accuracy

With the assistance of non-digitized geologic maps by Maxwell et al. (1967) and Henry

et al. (1996a), aforementioned unconformities in the Big Bend region were targeted and virtually

traced using the polyline tool in Google Earth (v. 4.3). This process was aided by the three-

dimensional visualization and image manipulation offered by Google Earth. Upon completion

of tracing, five unconformity sections were selected for field data point collection using a high

precision (< 1 meter) GPS unit [Geo Trimble XH] (Figure 11A-E). These GPS collected data points would act as independent sources of higher accuracy from which Google Earth unconformity traces could be compared in order to calculate positional accuracy.

Data points uploaded from the GPS unit were saved as an comma separated value (.csv)

files which were then loaded into ArcMap (v. 9.2) (Environmental Systems Resource Institute,

2009) and converted to shape (.shp) files. Data points from the Google Earth polyline tracing

were saved as default keyhole markup language (.kml) files. However, because the .kml file

format is not programs (at present) widely recognized by other GIS and three-dimensional

visualization programs, conversion to a more universally compatible file format was required.

We opted to convert Google Earth default .kml files into ArcMap .shp files to compliment file

format of data previously uploaded from the GPS. ArcMap alone cannot perform this type of

file conversion; however, scripts and add-in tools for such conversions are now freely available

on the developer’s website [htto://arcscripts.esri.com] due to increased popularity in Google

Earth use. Alternatively, we describe lengthier manual method for conversion of .kml to .shp

files that is more suitable if attempting to also determine vertical position accuracy (as described

later in this section) and in cases where Google Earth based data are being used for three-

dimensional modeling.

It is important to note that Google Earth provides options to alter geographic coordinate

formats (DMS, decimal degrees, UTM) for ease of matching with a geographic coordinate

format of a GPS unit. With geographic coordinate formatting matched, saved .kml data were

opened in Microsoft Excel and saved as a text (.txt) file. Often times such data opened from .txt

files are not distributed properly (i.e. inclusion of spaces between values, null values included,

etc.) for use in global positioning. To resolve this issue .txt files were re-opened and imported

text (comma and space delimited) data were converted to columns. Through copying, transpose

pasting, and IF function use (created to differentiate longitude and latitude values) coupled with

a “hide zero value” option and mass blank cell deletion in Excel, latitudinal and longitudinal data

were separated into respective columns. Once separated, exclusively latitudinal values were

saved as a .txt file and re-imported (space delimitated) into Excel as a column of all latitude values. The same procedure was followed for longitudinal data. Upon completion data in their appropriate columns were pasted into a blank Excel worksheet and saved as a comma separated value (.csv) file. These .csv files were then loaded into ArcMap and converted to .shp files (sans vertical position measurements).

Once all GPS and Google Earth data were in .shp file format (utilizing a World Geodetic

System 1984 (WGS84) datum) they were re-projected in ArcMap to a Universal Transverse

Mercator (UTM) grid system so calculations and measurements could utilize meter increments.

Horizontal root mean square error (RMSEr) was next calculated following the Geospatial

Positioning Accuracy Standards of the United State’s Federal Geographic Data Committee

(Subcommittee for Base Cartographic Data, 1998). Latitudinal and longitudinal offset distances

between Google Earth and GPS positions were calculated for 268 points (Figures 9A, 9C, 10A)

with results squared. Squared latitudinal and longitudinal offset distances were then added together and the square root of the sum was taken to determine individual RMSEr per point. To

determine RMSEr for all 268 points, squared latitude and longitude offset distances were

combined and averaged with the square root of the resulting value taken (Table 4).

Determination of Google Earth vertical position accuracy proved challenging because 1)

our GPS traces of unconformities were often along cliff ledges or atop scree piles in mid-sections

of cliff walls, thus vertical positions may be offset from surface vertical positions listed in

Google Earth and 2) vertical position data listed on screen in Google Earth is excluded and

replaced by null values when saved in .kml files. We determined two workaround solutions for these complications. First, vertical position data list on screen in Google Earth can be hand recorded and manually entered into alongside horizontal position data in aforementioned .csv files. Vertical position data for 268 points along targeted unconformities were hand recorded and manually entered into .csv files for part of this investigation. While this method is effective, it proves inefficient to impossible if large point datasets (perhaps > 100 points) are used.

Second, since these unconformities are located in the United States, we decided vertical positions could be adopted from the United States Geological Survey’s National Elevation Dataset (NED)

[http://seamless.usgs.gov] (Gesch, 2002; Gesch et al., 2007). We describe this second batch input method in detail below.

A digital elevation model covering areas where unconformities were located was downloaded from the NED website and loaded into the Fledermaus 3D (IVS 3D, 2010) three- dimensional visualization software. At the same time a series of .shp files (created as previously

discussed) containing (only) horizontal position data, originally derived from Google Earth, were

datum converted to match the North American Datum 1983 (NAD83) utilized by the NED and

then imported into Fledermaus 3D. In Fledermaus 3D the .shp files were draped over the digital

terrain model and coordinates were exported as a graph coordinate file (.xyz). This created a

semi-functional .xyz file with stored longitudinal and latitudinal values and a blank data column

for vertical position data. We then imported the same data as the newly created .xyz file and

repeated the drape and export procedure. In the end a fully functional .xyz file was produced

with merged horizontal and vertical position data. This method is recommended when users are

working with larger datasets.

Because no information has been publicized by developers regarding vertical position

accuracy in Google Earth, we compared vertical positioning of data points listed on screen in

Google Earth with the NED (for which an overall vertical position accuracy of 2.44 meter RMSE

was determined by Gesch, (2007)). Vertical position accuracy was determined in a similar

fashion to horizontal position accuracy. Vertical root mean square error (RMSEz) was again calculated following the Geospatial Positioning Accuracy Standards of the United State’s

Federal Geographic Data Committee (Subcommittee for Base Cartographic Data, 1998).

Vertical position offset distances between adopted NED values and Google Earth on screen values were calculated for 268 points (Table 5). Squared vertical offset distances were then added together and the square root of the sum was taken to determine individual RMSEz per

point. To determine RMSEz for all 268 points squared vertical position offset distances were

combined and averaged then the square root of the resulting value was taken.

8.2 Application of Google Earth-NED Data in Paelo-surface Modeling

An 18 x 30 kilometer area in easternmost Big Bend Ranch State Park was selected to trace the early Tertiary unconformity in an attempt to model the post-Laramide paleo-surface.

The unconformity contact was traced using the polyline tool in Google Earth. Vertical position data were adopted from the NED and merged with horizontal position data acquired in Google

Earth as described in above sections. The combined Google Earth-NED data points were then interpolated to construct a paleo-surface model of the area.

Data points following the unconformity mainly trace the eastern limits of the Bofecillos

Mountains, select areas in the southern Contrabando Lowlands, and northern Lajitas Mesa

(Figure 12A). Originally a large dataset of approximately 4300 data points was collected for interpolation in this area. However, roughly 1/3 of these points formed a linear trend extending around the Solitario and did not allow three-dimensional modeling. Therefore, only about 2900 data points south of 29°24’30” latitude were used. Our ~2900 point dataset also represents cropping to avoid interpolating data points across extensively large distances (~ 5 kilometers). It is important to note that large gaps in data are less accurately interpolated and modeled compared to areas with dense coverage. Unfortunately, this type of data distribution tends to be characteristic of geologic outcrops examined in the Big Bend region.

Our paleo-surface model was interpolated via kriging. Kriging uses distances between irregularly spaced data points as a function to help characterize topography; however, unlike other interpolation methods utilizes a weighting system allowing more closely spaced points to have a greater influence on a surface (Yilmaz, 2009, and references therein). Weighting

assigned to data points during the kriging process can be affected by the proximity to a location

being estimated, redundancy between data values (i.e. cluster points would carry less weight than isolated points at the same distance), and the magnitude of elevation variability (Bohling, 2005).

The specific type of kriging algorithm can also affect vertical position accuracy. Fencík and

Vajsáblová (2006) evaluated various kriging methods and determined vertical position accuracy was best (between 4.44 and 4.88 meters RMSE) for the linear algorithm, which was used for the

Trans-Pecos data. Regardless of interpolation method utilized, it is important to recall 1) that better results are obtained if data are fairly dense and uniformly distributed throughout an area

versus fewer locations that are clustered together and 2) almost all interpolation algorithms will underestimate highs and overestimate lows (inherent to averaging) (Isaaks and Srivastava, 1989;

Bohling, 2005).

It is the proximity and relatively intricate distribution of exposures in Big Bend Ranch

State Park that provides us with the opportunity to obtain a relatively detailed paleo-surface model using the post-Larmide unconformity. The early Tertiary unconformity extends along the

eastern margin of the Bofecillos Mountains, passes eastward across the creek dissected

Contraband Lowlands, and ultimately laps against the buttress formed by the Fresno-Terlingua

Monocline (Figure 12A). Most of the Buttes are less than 3 km in diameter throughout this area.

Lajitas Mesa, trending 10 km east-west and 5 km north-south is the largest of these buttes. In this area, the unconformity is typically exposed along walls of canyons cut into the Bofecillos

Mountains and in the sides of isolated buttes and mesas within the Contrabando Lowlands

(Figure 12A). The average spacing between continuous outcrops is less than 2 km across most

of the area.

9. RESULTS

9.1 Google Earth Horizontal and Vertical Position Accuracy

In the remote Big Bend region many areas along targeted unconformities are difficult to

access, thus it is important to determine horizontal and vertical position accuracy of Google

Earth if coordinate data are to be collected virtually and applied in other remote

sensing/modeling tachniques. Five areas in the Big Bend region were selected for field tracing

[ground truthing] using a high precision (< 1 meter accuracy) handheld GPS unit to precisely locate the respective unconformity in three-dimensions. A continuous line data collection method was utilized while unconformities were traversed and traced in each area. In western Big

Bend National Park an area of the Javelina Formation-Chisos Group/Burro Mesa Formation unconformity totaling approximately 1.63 kilometers in length were traced. A series of 60 high precision data points were extracted from this trace (bb8a). In eastern Big Bend National Park two areas of the Hannold Hill Formation-Canoe Formation unconformity totaling about 0.60 kilometers in length was field traced. A total of 135 high precision data points were extracted from this trace (unc1i and unc1g). In easternmost Big Bend Ranch State Park two areas of the

Pen Formation-Jeff Conglomerate unconformity totaling approximately 0.32 kilometers in length were traced with the GPS unit. A series of 73 high precision data points were extracted (unc4 and unc17).

These 268 high precision data points were compared to previously collected Google

Earth virtual line traces along the respective unconformities that were collected remotely.

Comparisons yielded a horizontal position accuracy of 2.64 meters RMSEr with respect to actual horizontal field positions recorded. Horizontal offset distances ranged from 0.09 to 49.71 meters.

An arithmetical mean offset distance of 6.95 meters was calculated. Horizontal position offset

distances and accuracy calculations are presented in Table 4.

While complexities have been noted with determination of vertical position accuracy,

comparisons between 268 Google Earth points and (horizontal position matched) adopted

vertical surface position points from the NED, for which a 2.44 meter RMSE is known (Gesch,

2007), yielded a vertical position accuracy of 1.63 meters RMSEz . Vertical position offsets

ranged from 8.35 meters lower than the unconformity to 29.13 meters above it. The arithmetical mean vertical position offset between Google Earth data points and those adopted from the NED was 0.28 meters. Vertical position offset distances and accuracy calculations are presented in

Table 5.

9.2 Paleo-Surface Model for Easternmost Big Bend Ranch State Park

Distribution of data in easternmost Big Bend Ranch State Park allowed us to model a paleo- surface from the post-Laramide unconformity, including valleys described in outcrop by Henry et al. (1996a) and Henry (1998). The resulting model is shown in Figure 12A. After the

Laramide Orogeny, easternmost Big Bend Ranch State Park experienced the effects of voluminous magmatism and major Basin & Range normal faulting. These factors make interpretation of paleo-surface models challenging. Comparison of paleo-surface models with geology can better assess the validity of post-Laramide surface features versus byproducts of subsequent faulting and/or magmatism. Thus a generalized geologic map is overlain on the

model in Figure 12B. The model covers an 18 x 30 kilometer area. Elevations associated with

the unconformity range from 1300 to 700 meters, providing a maximum relief of 600 meters.

The interpolated model expresses two paleo-topographic highs. The first, the higher of

the two features, is located in the southeastern Bofecillos Mountains. It exhibits a maximum

paleo-elevation of 1300 meters. While this is the highest elevation on the paleo-surface, in

reality scattered and sparse exposures of the unconformity are present across the Terlingua Uplift that was raised by northwest-southeast trending Laramide derived Fresno-Terlingua Monocline.

Outcrops of Santa Elena Limestone between 3600 and 4000 meters high, atop the crest of the

Terlingua Uplift, mark a minimum elevation of the post–Laramide unconformity, although the surface must have been eroded during the late Tertiary. Our model suggests paleo-elevations of up to 1060 meters occurring in the northeast in the Terlingua Uplift area; however, we consider these values to be less representative of the paleo-surface due to aforementioned reasons and potential for late Tertiary erosion. Paleo-elevations between the Terlingua Uplift and the paleo- topographic high gradually drop from about 920 to less than 720 meters southwestward. South of the Terlingua Uplift, another topographic high is centered in the Lajitas Mesa area. It exhibits a maximum paleo-elevation of 980 meters. The feature is centered in a Laramide syncline and the unconformity is exposed mainly along the northern and western walls of Lajitas Mesa.

In the southeastern Bofecillos Mountains deformation associated with three faults can be reasonably projected beyond their extent mapped by Henry et al. (1996a) further into the

Bofecillos Mountains based on the model. Perhaps the best example of fault depiction and/or projection occurs west of and along the western side of Lajitas Mesa.

Faults appearing on the model are also valuable tools for assessing structural paleo- topographic highs. A number of normal faults truncate the paleo-topographic high in southeastern Bofecillos Mountains (Henry et al., 1996a; Texas Water Development Board,

1999). Fault deformation is visible as northeast trending steps represented by the modeled unconfomirty. However, fault offsets are small compared to the relief of the unconformity.

Locally, fault offsets associated can be as much as 200 meters. Faulting is less prominent at the

Lajitas Mesa paleo-topographic high. However, fault deformation is likely not an important factor in the shape of the unconformity. For Example, the area north of Lajitas Mesa is upthrown by a series of faults on the mesa’s northern margin, however, the modeled unconformity demonstrates lower elevations for this area and higher elevations associated with the graben centered at Lajitas Mesa. If the high paleo-elevation associated with Lajitas Mesa was produced by subsequent normal faulting it is highly likely this area would be instead downthrown. The Lajitas Mesa paleo-surface shows between 100 and 160 meters of relief.

These modeled paleo-topographic highs may have been formed via erosion of the post-

Laramide surface. However, appearance of younger Pen Formation clays at lower elevations than older Boquillas Formation clays and limestones in the southernmost portion of easternmost

Big Bend Ranch State Park (Henry et al., 1996a) suggest that these paleo-topographic highs were eroded into and that Laramide folding was cut across. Much of the paleo-topography suggests high relief (between 300 and 320 meters) at this location. Furthermore, the axis of the paleo- topographic high in the southeastern Bofecillos Mountains is oriented northeasterly- southwesterly perpendicular to sub-perpendicular to direction of regional major Basin & Range normal faulting (Henry et al., 1991).

Magmatic upwelling and doming also cannot be precluded as a factor in each of these paleo-topographic highs. However, the degree and extent of upwelling are often shrouded by subsequent magmatism. The paleo-topographic high in the southeastern Bofecillos Mountains could be related to a buried intrusion or source vent. Such a vent may be related to the distal

Primero Dome located approximately 5.5 kilometers to the northwest (Henry, 1998). The Lajitas

Mesa paleo-topographic high may be related to intrusions mapped by Henry et al. (1996a) associated with Contrabando Dome or a large intrusion along Fresno Creek within a few kilometers to the north and northwest (Figure 12B).

Our model illustrates the likely direction of paleo-drainage to be south to southwesterly.

Drainage perhaps flowed in this direction into post-Laramide highs formed in adjacent northeastern Chihuahua, Mexico. The density of data points in the southeastern Bofecillos

Mountains also depicts a number of paleo-valleys that likely encompassed paleo-drainage tributaries (Figure 12A). Paleo-valleys A and B are roughly 100 and 40 meters deep, respectively. Each of these paleo-valleys run level for just under 3 kilometers before transitioning into steeper terrain. Paleo-valley C is about 120 meters deep and with a continuously gradual decline. Paleo-valley D is the largest paleo-valley observed in the model.

Although it only reaches about 100 meters depth it is nearly 1.5 kilometers wide. Paleo-valley D gradually declines in a similar fashion to that of C.

10. DISCUSSION

10.1 Factors Influencing Positional Accuracy

Several factors can affect horizontal and vertical position accuracies of geologic features

traced remotely using Google Earth. These factors can include data point mis-picking in Google

Earth by the user, improper coordinate system or datum selection, low georectification quality in

image processing, poor horizontal positioning resulting in inaccurate reported vertical positions,

and perhaps the positioning of the remotely sensed cell itself.

Potentially the most significant source for error is point mis-picking by the user. This

issue has been in effect since onset of remote sensing and photogrammetry and is generally

attributed to poor resolution or to instances where stratigraphic features are indistinguishable.

Data point mis-picking can directly affect horizontal position accuracy. Perhaps the best method to avoid point mis-picking is through use of digitized geologic maps to help guide initial location

of the points. However, it is important to caution that many digitized geologic maps have been

partly created using aerial photographs, and therefore suffer from the same problems with data

miss picks. While horizontal position accuracy has potential for errors in such maps, this

investigation suggests digitized maps can still be utilized to more accurately identify geologic

beds for more appropriate data point selection. We also found appropriate data point selection

was aided by three-dimensionally manipulating surfaces displayed in Google Earth. This

allowed viewing the contact as a three-dimensional surface and allowed separation of

stratigraphic contacts from igneous intrusions and other artifacts.

Google Earth uses a Simple Cylindrical projection with a WGS84 datum (Google Inc.,

2010). Thus, all GPS acquired data must match (or be converted to match) this projection and

datum or risk positional inaccuracy. If the batch vertical position extraction method described

from our methods is used, additional conversion of the Google earth points to a NAD83

geographic coordinate system to match the NED (United State Geological Survey, 2006) is

required. Use of improper geographic coordinate systems can result in assignment of slightly to

significantly different coordinates for a designated location on Earth’s surface (Google Inc.,

2010). Vertical datums should also be matched when comparing positional data. The NED

utilizes the North American Vertical Datum 1988 (NAVD88) datum (United State Geological

Survey, 2006). Lastly, positional inaccuracies can result if data points utilized are referenced

from height above ellipsoid (HAE) rather than height above mean sea level (MSL) and vice

versa. In this investigation we found height above MSL to be consistent with NED and Google

Earth measurements.

Poor image georectification can also result in horizontal position inaccuracy. Potere

(2008) provided numerous examples of merged Google Earth imagery with noticeable offsets

and inconsistencies that could be resultant of poor georectification. Additionally, various (un-

reviewed) internet forums also note instances such as road mismatches or GPS coordinates that

contrast with those listed on screen in Google Earth. While we acknowledge the shear difficulty

in minding georectification issues while attempting to merge an image set covering the entire

Earth, such issues do affect any horizontal position accuracy calculated.

Each factor that can potentially influence horizontal position accuracy can also directly affect the vertical position accuracy. If horizontal position accuracy is large, this can lead to display of an inappropriate vertical position in Google Earth (or any GIS program). For

example, in our batch vertical position data extraction method the cell size of the digital terrain

model from which vertical positions are acquired is at present 10 meters (United States

Geological Survey, 2009), if horizontal position accuracy is > 10 meters then vertical position data could be collected from a neighboring cell. The worse the horizontal position accuracy is the further the distance a point will be from the cell containing the proper vertical position measurement.

Additionally, the positioning of individual remotely sensed cells in a digital terrain model may affect vertical position accuracy. If a cell value reported is derived via averaging multiple elevations collected in a cell-sized area, inaccuracies might result based on percent of cell coverage over steep, sharp elevation dropping sub-regions, such as cliffs or ridges. Cells predominantly covering cliff and ridge tops may display values more reflective of higher elevations although significantly lower elevations, representing cliff or ridge bottom, exist in the same cell. Similarly, cells covering the majority of cliff and ridge bottoms might also bias values reported in a cell. A simplified illustration of this concept is provided in Figure 13.

10.2 Post-Laramide Surface of Easternmost Big Bend Ranch State Park

Paleo-valleys and modeled paleo-surface relief indicate topographic highs existed in the southeastern Bofecillos Mountains and Lajitas Mesa areas by the late Eocene. Similar paleo- topographic highs were formed at this time by intrusions associated with laccocalderas forming further west in the Bofecillos Mountains (Henry, 1998), at The Solitario (Henry and

Muehlberger, 1996, and references therein, Henry et al., 1996a; Henry, 1998) and in the Chisos

Mountains area in adjacent Big Bend Ranch State Park (Maxwell et al., 1967; Ogley, 1979;

Miggins, 2004, 2007). However, the nearest magmatism in the Bofecillos Mountains was centered 5 to 10 km northwest and produced features smaller than the topographic high shown in the model (Henry et al., 1998). Additionally, contours associated with high paleo-elevations modeled are more linear than would be expected by doming. Therefore, we suggest three possibilities for the high paleo-topographic features modeled. First, the paleo-topographic highs modeled from the unconformity could represent gentle folding around deep seated and much larger intrusives, perhaps similar in size to The Solitario. Second, relief demonstrated by the paleo-surface modeled from the unconformity could represent a paleo-drainage pattern and exhibit remnant Larmide features in the region that were more resistant to erosion. In either of these scenarios Laramide deformation (i.e. faulting, monoclinal folding, etc.) could have been masked by subsequent regional volcanism. Third, the entire area modeled could have alternatively been uplifted and dissected during the Laramide Orogeny.

We favor the second scenario. As noted, it seems the modeled area is perhaps too distal to be related to magmatic activity centered to the west in the central Bofecillos Mountains as suggested by the first scenario. Furthermore, we feel presence of the Fresno-Terlingua

Monocline would facilitate erosion of Laramide topography. If paleo-drainage flowing away from the Fresno-Terlingua monocline merged it may well form a channel bisecting the topography in a shape similar to that observed in our model. While the course of the Rio Grande may have altered with time, this idea is relatively consistent with the present day drainage pattern of tributaries, such as Contrabando and Fresno creeks, in the study area adjacent the Fresno-

Terlingua Monocline. Due to the overprinting of Basin & Range extensional features in easternmost Big Bend Ranch State Park, we feel there is too little evidence to support the third scenario. 48

All three scenarios imply formation of a topographic low in northern Chihuahua, south of the Big Bend region, prior to the Oligocene. This is important because as this area was the heart of the Laramide Chihuahuan fold and thrust belt. Thus, the topographic low through which the

Rio Grande flows at present may have formed very soon after the end of the Laramide Orogeny.

Establishment of this southern drainage direction may be roughly coincident with deposition of early Tertiary units such as the Jeff Conglomerate.

11. CONCLUSIONS

The initial portion of this investigation was dedicated to determining current accuracy of

Google Earth due to lack of information provided by program developers, increases in remote

sensing technologies, and aging of benchmark studies which provided initial constraints on

horizontal and vertical position accuracy. Our results show increased accuracy in Google Earth

since initial investigations by Potere (2008) and Jain and Ravibabu (2008). We determined a horizontal position accuracy of 2.64 meters RMSEr by comparing 268 Google Earth data points with in-field positions collected via high precision GPS unit. Using a workaround solution to solve certain program difficulties, we were also determined a current vertical position accuracy of 1.63 meters RMSEz by comparing 268 Google Earth data points with the NED.

The later portion of this investigation was dedicated toward application of Google Earth

(and NED) data collected along an early Tertiary unconformity to develop methods for and

preliminarily construct a post-Laramide paleo-surface model for easternmost Big Bend Ranch

State Park. Despite facing numerous complications due to the area’s complex geologic history

(i.e. surface inflation due to regional magmatism, burial of Laramide topography by subsequent

volcanism and sedimentation, difficulties in resolving structural features derivative of Laramide

compressional versus Basin & Range extensional stresses, etc.), a post-Laramide paleo-surface

model was produced with the ability to resolve paleo-topographic highs in the southeastern

Bofecillos Mountains and at Lajitas Mesa. Based on the amount of surface relief depicted,

inconsistency with subsequent deformation, and distance from magmatic features capable of

surface doming or inflation, we believe paleo-topography modeled legitimately reflects the post-

Laramide surface for this area. We interpret the model to reflect an eroded post-Laramide 50

surface where noted paleo-topographic highs represent remnant Laramide topography that was

more resistant to erosion. The model also implies a southern paleo-drainage direction for the area and suggests that the present day topographic low through which the Rio Grande flows may

have formed very soon after the Laramide Orogeny.

The paleo-surface model for easternmost Big Bend Ranch State Park derived from

Google Earth data collected along the early Tertiary unconformity was able to illustrate post-

Laramide features despite complications mentioned. Because these data proved successful in

preliminary modeling test in the rugged and geologically complex Big Bend region, we believe use of these techniques and Google Earth data will prove equally—if not more successful—in

other regions of the United States. Despite our results, we recommend and emphasize caution

when using Google Earth data for scientific investigation due to the limited amount of

information disclosed by developers regarding the program and its accuracy.

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FIGURES

Figure 1: Google Maps terrain image of central to western Big Bend National Park. Numbers indicate approximate locations of South Rim Formation vents: 1) Pulliam Peak; 2) Lost Mine Peak; 3) Casa Grande; 4) Crown Mountain; 5) Emory Peak; 6) South Rim; 7) Burro Mesa; 8) Kit Mountain; 9) Goat Mountain; 10) Brazos de Maria; 11) El Fuego de Ricardo; 12) Trap Mountain; 13) Round Mountain; 14) Horseshoe Canyon; 15) Cerro Castellan. Dashed circle in Chisos Mountains approximately delineates Pine Canyon caldera. Inset map shows extent of mid- to late Tertiary basins of the Rio Grande Rift (from Dickerson and Muehlberger, 1994; Chapin et al., 2004; White et al., 2006). Image bounding coordinates 29.400° through 29.003° N and -103.661° through -103.051°W. 77

Figure 2: Alkali feldspar chemical variation plot for the South Rim Formation (lower) and the peralkaline Greater Olkaria Volcanic Complex (upper). Compositions of experimentally crystallized alkali feldspar are from Scaillet and Macdonald (2003) and naturally crystallized alkali feldspar are from Macdonald et al. (1987). All experimental feldspar plotted were crystallized at temperatures from 661 to 758 °C and fugacities from -1.1 to -3.2 ΔNNO.

Figure 3: Clinopyroxene chemical variation plot for the South Rim Formation (lower) and the peralkaline Greater Olkaria Volcanic Complex (upper). Compositions of experimentally crystallized clinopyroxene are from Scaillet and Macdonald (2003) and naturally crystallized clinopyroxene are from Macdonald et al. (1987). All experimental clinopyroxene plotted were crystallized at temperatures from 738 to 790 °C and fugacities from -1.1 to -2.1 ΔNNO.

Figure 4: Amphibole cationic variation plot (after Gualda and Vlach, 2007) for the South Rim Formation rocks and those of other igneous peralkaline systems. Outlined regions and plotted points illustrate cationic distribution in A, B, and T sites per amphibole. Unfilled outlined field, the Greater the Olkaria Volcanic Complex (Macdonald et al., 1987); light grey field, the island of Pantelleria (Avanzinelli et al., 2004); dark grey field, the Eburru Volcanic Complex (Ren et al., 2006). Data for one Pine Canyon Suite amphibole (uppermost plotted) from White et al. (2006). Triangles and corresponding oxygen fugacity values (ΔNNO) for experimentally crystallized amphibole from the Greater Olkaria Volcanic Complex (Scaillet and Macdonald, 2003); temperatures range from 678 to 693 °C. 80

Figure 5: TiO2-FeO-Fe2O3 ternary composition diagram showing compositions of Fe-Ti oxides in South Rim Formation rocks. Lines denote solid solution series.

Figure 6: Alkaline magma series variation diagram showing relative abundances of K2O and Na2O in Pine Canyon Suite and Emory Peak Suite rocks (from White et al., 2006) and associated alkali feldspar phenocrysts (after Middlemost, 1975). 82

Figure 7: Area map illustrating the Big Bend region of West Texas (from White et al., 2006). Boundaries of Big Bend National Park and Big Bend Ranch State Park are shown. Transparent blue boxes denote areas investigated and approximate areas where unconformities were traced for paleo-surface model construction. CH = Chisos Mountains; CG = Castolon Graben.

Figure 8: Generalized stratigraphic sections featuring geologic unconformities investigated for areas in Big Bend National Park and Big Bend Ranch State Park from Maxwell et al. (1967), Henry et al. (1996b), and McCormick et al. (1996). Approximate timing of Laramide Orogeny is depicted for reference (see in text citations).

Tornillo Flat

Chisos Mountains

Figure 9: A) Shaded relief image (from NED data) of Big Bend National Park showing large-scale distribution of virtually collected Google Earth-NED data points along the Hannold Hill Formation-Canoe Formation unconformity. Dashed line approximates boundary of Tornillo Flat. Scale is approximately 1:62,500. Image is north oriented.

Figure 9 (continued): B) Partial geologic map of eastern Big Bend National Park (from Maxwell et al., 1967) illustrating stratigraphic units creating unconformities (map key located in Appendix A). Map is north oriented.

Dogie Mountain

Chisos Mountains

Castolon Graben

Figure 9 (continued): C) Shaded relief image (from NED data) of Big Bend National Park showing distribution of virtually collected Google Earth-NED data points along the Javelina Formation-Chisos Group/Burro Mesa Formation unconformity. Dashed lines approximates boundary of the Castolon Graben. Scale is approximately 1:62,500. Image is north oriented.

Figure 9 (continued): D) Partial geologic map of eastern Big Bend National Park (from Maxwell et al., 1967) illustrating stratigraphic units creating unconformities (map key located in Appendix A). Map is north oriented. 88

Terlingua Uplift

Bofecillos

Mountains

Fresno-Terlingua Monocline

Contrabando

Lowlands

Lajitas

Mesa

Figure 10: A) Shaded relief image of Big Bend National Park showing large-scale distribution of virtually collected Google Earth-NED data points along the Javelina Formation-Chisos Group/Burro Mesa Formation unconformity. Scale is approximately 1:24,500. Image is north oriented.

Figure 10 (continued): B) Partial geologic map of easternmost Big Bend Ranch State Park (from Henry et al., 1996) illustrating stratigraphic units creating unconformities (map key located in Appendix B). Map is north oriented.

Figure 11: All images are north oriented. A) Distribution of field truthed data points collected along the Javelina Formation-Chisos Group/Burro Mesa Formation unconformity along two ridges in the Castolon Graben of western Big Bend National Park—trace bb8a. B) Distribution of field truthed data points collected along the Hannold Hill Formation-Canoe Formation unconformity along a cliff in Tornillo Flat area of eastern Big Bend National Park— trace unc1g. All images acquired in Google Earth.

Figure 11 (continued): C) Distribution of another set of field truthed data points collected along the Hannold Hill Formation-Canoe Formation unconformity along cliffs in the Tornillo Flat area—trace unc1i. D) Distribution of another set of field truthed data points collected along the Pen Formation-Jeff Conglomerate unconformity along a ridge in the Contrabando Lowlands of easternmost Big Bend Ranch State Park—trace unc4. All images acquired in Google Earth.

Figure 11 (continued): E) Distribution of field truthed data points collected along the Pen Formation-Jeff Conglomerate unconformity along a steep cliff in the Contrabando Lowlands of easternmost Big Bend Ranch State Park—trace unc17. All images acquired in Google Earth.

Bofecillos Terlingua Uplift Mountains

Fresno-Terlingua Monocline

Lajitas

Mesa

Figure 12: A) Paleo-surface model and data points and distribution of data points (black circles) from which the model was interpolated. Major subsequent normal faulting is also illustrated. Letters A-D illustrate model paleo-valleys. The model is north oriented with 20 meter contour intervals.

Figure 12 (continued): B) Paleo-surface model with generalized geology superimposed (adapted from Henry et al. (1996) and Texas Water Development Board (1999)). Major subsequent normal faulting is also illustrated. Letters A-D illustrate modeled paleo-valleys. The model is north oriented with 20 meter contour intervals. Color key: green = Cretaceous clays and limestones, brown = mid- to late Eocene Chisos Group volcanics, grey = post- Oligocene volcanics, yellow = Quaternary sediments, pink = mid-Eocene Jeff Conglomerate, red = Tertiary igneous intursions, black lines = faulting.

Figure 13: Simplistic example illustrating the potential effects of different cell positioning on the value reported by the cell itself, assuming cell reports the mean elevation value of an area. In this example, the position of the cell can result in up to 15 meters difference in actual versus reported elevation.

TABLES

Table 1: South Rim Formation Mineral Assemblage by Suite

Mineals Pine Canyon Suite Emory Peak Suite

Major phases (up to 10 vol. %) sanidine, quartz sanidine, quartz

ferroaugite ferroaugite arfvedsonite/ferrorichterite arfvedsonite Fe-Ti oxides Fe-Ti oxides aenigmatite fayalite/hortonolite Minor phases (<1 vol. %) monazite annite apatite apatite zircon zircon pyrrhotite chevkinite bastnasite

Trace fluorite fluorite

Table 2A: Pine Canyon Suite: Pine Canyon Rhyolite Mineral Compositions

Alkali feldspar

Sample SiO2 TiO2 Al2O3 FeO* CaO Na2OK2O Total An Ab Or

PC-01 fs1 66.67 18.85 0.04 7.73 5.98 99.28 0.00 64.94 35.06 fs2 66.86 18.83 7.61 6.16 99.46 0.00 63.90 36.10 fs4 67.97 19.14 8.12 5.35 100.59 0.00 64.94 35.06

U04-02 fs1 67.14 19.33 0.25 11.14 0.69 98.56 1.27 94.64 4.09 fs2 63.47 18.44 0.07 0.78 15.65 98.40 0.00 6.66 93.34

Clinopyroxene

Sample SiO2 TiO2 Al2O3 FeO* M nO MgO CaO Na2O Total Wo En Fs

99802 cpx1 46.65 0.33 0.22 30.03 0.90 0.10 18.75 1.02 98.01 43.83 0.33 55.84 cpx2 46.05 0.36 0.22 29.68 0.94 0.62 18.08 1.32 97.26 42.57 2.03 55.40

Aenigmatite

Sample SiO2 TiO2 Al2O3 FeO* M nO MgO CaO Na2OK2O Total

99802 aenig1 38.98 8.04 1.06 39.26 1.13 0.08 0.44 6.32 0.26 95.30

PC-01 aenig1 38.99 6.61 0.51 41.34 0.75 0.02 0.68 6.94 95.85

Zircon

Sample SiO2 TiO2 Al2O3 FeO* M nO ZrO2 ThO2 HfO2 Total

BC-01 zirc1 30.25 0.02 0.01 0.05 0.05 66.13 0.02 0.98 97.52 zirc3 30.62 0.06 0.01 0.09 0.05 66.10 0.00 1.00 97.92

Pyrrhotite Sample Fe S Zr Total

BC-01 py 58.98 37.96 2.16 99.09

Bastnasite SampleF CeLaNdCaP SiFeO total

U04-02 bst1 5.79 21.06 11.04 7.24 11.25 0.61 0.39 0.40 10.69 68.46

Tanle 2B: Pine Canyon Suite: Boot Rock Member Mineral Compositions

Alkali feldspar

Sample SiO2 TiO2 Al2O3 FeO* CaO Na2OK2O Total An Ab Or

BC-01 fs1 65.75 0.24 19.34 7.19 6.24 98.76 2.64 60.62 36.73 fs3 65.94 19.66 6.90 6.73 99.23 1.66 58.48 39.86

PC-06 fs1 66.84 19.54 0.49 7.31 6.43 100.61 2.36 60.48 37.16 fs2 66.67 19.40 0.24 6.84 7.17 100.32 0.97 56.48 42.55 fs3 65.81 18.45 0.35 5.58 8.64 98.84 0.00 48.06 51.94 fs4 65.95 18.14 0.29 5.20 9.58 99.16 0.00 43.73 56.27 fs5 68.09 19.31 0.27 7.38 6.54 101.60 0.00 61.77 38.23

PJ-01 fs1 67.32 0.00 19.62 0.00 0.00 10.79 0.18 97.91 0.00 98.85 1.15 fs3 67.12 0.00 19.89 0.00 0.00 10.85 0.26 98.12 0.00 98.34 1.66

Clinopyroxene

Sample SiO2 TiO2 Al2O3 FeO* MnO MgO CaO Na2O Total Wo En Fs

PC-06 cpx1 48.13 0.11 0.43 28.88 0.87 1.29 19.92 0.43 100.06 44.44 4.01 51.55 cpx2 47.55 0.17 0.47 29.91 0.86 0.45 20.11 0.47 100.00 45.10 1.39 53.51 cpx3 47.56 0.16 0.51 29.67 0.89 0.44 19.66 0.50 99.39 44.67 1.39 53.94 cpx4 46.45 0.26 0.70 29.56 0.97 0.29 19.45 0.59 98.27 44.73 0.92 54.35

Zircon

Sample SiO2 TiO2 Al2O3 FeO* MnO ZrO2 ThO2 HfO2 Total

BC-01 zirc1 30.25 0.02 0.01 0.05 0.05 66.13 0.02 0.98 97.66 zirc2 30.85 0.06 0.02 0.19 0.03 64.73 0.02 1.00 97.08 zirc3 30.62 0.06 0.01 0.09 0.05 66.10 0.00 1.00 98.13

Table 2C: Emory Peak Suite: Emory Peak Rhyolite Mineral Compositions

Alkali feldspar

Sample SiO2 TiO2 Al2O3 FeO* CaO Na2OK2O Total An Ab Or

CO-01 fs1 65.31 0.00 18.36 0.06 0.02 6.79 6.85 97.39 0.12 58.58 41.30 fs2 65.77 0.00 18.65 0.01 0.00 6.76 7.06 98.25 0.01 57.84 42.15

CO-06 fs1 65.96 0.00 18.66 0.18 0.02 6.15 7.66 98.63 0.10 53.42 46.49 fs2 65.63 0.00 18.65 0.19 0.03 6.13 7.40 98.02 0.13 54.21 45.67

Crown-Vit fs1 66.10 0.02 19.12 0.25 0.14 6.42 7.23 99.28 0.73 55.55 43.72 fs2 66.75 0.03 18.57 0.43 0.18 6.41 6.62 98.99 0.95 57.55 41.50 fs3 66.27 0.01 18.78 0.27 0.12 6.28 7.43 99.15 0.58 54.45 44.97 fs4 66.11 0.02 18.97 0.29 0.19 6.36 7.27 99.22 0.99 55.03 43.98 fs5 66.90 0.02 18.94 0.25 0.11 6.55 7.27 100.04 0.55 56.04 43.41 fs6 66.98 0.04 18.62 0.41 0.15 6.76 6.44 99.40 0.79 59.58 39.62 fs7 66.38 0.02 19.18 0.25 0.13 6.63 7.08 99.68 0.68 56.87 42.45 fs8 66.73 0.02 19.04 0.24 0.13 6.44 7.39 99.98 0.65 55.14 44.21

LA-01 fs1 66.84 0.00 19.39 0.22 0.01 6.43 7.42 100.31 0.07 55.34 44.60 fs2 66.75 0.00 19.46 0.21 0.01 6.40 7.31 100.15 0.06 55.60 44.34 fs3 66.78 0.00 19.35 0.20 0.01 6.32 7.63 100.29 0.05 54.22 45.73 fs4 66.49 0.00 19.29 0.22 0.02 6.42 7.56 99.99 0.08 54.82 45.09

SR-05 fs1 66.06 0.03 19.36 0.11 0.39 6.62 7.14 99.71 1.95 55.91 42.15

U04-04 fs1 67.57 0.04 19.47 0.26 0.02 6.26 7.70 101.31 0.09 53.75 46.16 fs2 67.95 0.07 19.49 0.27 0.08 5.64 7.43 100.94 0.44 51.87 47.69 fs3 67.26 0.06 18.78 0.70 0.02 5.95 7.39 100.15 0.12 52.41 47.47 fs4 67.95 0.05 19.42 0.28 0.02 5.75 7.46 100.94 0.11 53.49 46.40 fs5 67.79 0.02 17.75 1.77 0.00 5.30 8.07 100.69 0.01 48.47 51.52 fs6 66.64 0.05 17.39 1.20 0.04 4.01 9.01 98.34 0.23 38.83 60.94 fs7 67.29 0.06 18.21 1.37 0.01 6.13 7.64 100.71 0.07 53.44 46.50 fs8 67.84 0.12 18.16 1.48 0.01 5.28 7.78 100.68 0.04 49.25 50.71 fs9 67.65 0.06 19.44 0.32 0.30 5.97 7.29 101.04 1.58 53.12 45.30

AP-01 fs1 66.55 0.05 18.60 0.36 0.03 6.49 7.70 99.78 0.16 54.58 45.25 fs2 66.83 0.04 18.75 0.35 0.04 6.48 7.59 100.09 0.20 54.90 44.90 fs3 66.59 0.05 17.52 0.73 0.03 5.55 8.18 98.65 0.16 49.18 50.66

BC-02 fs1 67.23 0.12 17.80 0.65 0.25 6.66 6.46 99.19 1.30 58.85 39.85

Clinopyroxene

Sample SiO2 TiO2 Al2O3 FeO* MnO MgO CaO Na2O Total Wo En Fs

LA-01 cpx1 47.59 0.00 0.19 31.39 0.62 0.08 19.10 0.60 99.57 43.38 0.26 56.36 cpx2 47.56 0.00 0.16 31.33 0.61 0.08 19.18 0.63 99.56 43.42 0.24 56.33

Crown-Vit cpx1 47.18 0.31 0.39 31.11 0.69 0.00 18.58 0.51 98.76 42.91 0.00 57.09 cpx2 47.08 0.31 0.36 31.61 0.70 18.96 0.47 99.49 43.06 0.00 56.94

Olivine

Sample SiO2 TiO2 Al2O3 FeO MnO MgO CaO Total Fa

Crown-Vit olv1 30.09 0.04 0.26 66.69 1.46 0.00 0.23 98.95 97.95 olv2 29.14 0.00 0.03 69.46 1.72 0.01 0.30 100.66 97.54 hort1 36.06 0.03 1.64 59.86 1.25 0.00 0.17 99.57 97.93

Biotite

Sample SiO2 TiO2 Al2O3 FeO M nO M gO CaO Na2OK2OCr2O3 ZrO2 Nb2O3 FClTotal

CO-02 bt1 41.94 3.02 6.85 28.43 0.47 0.12 0.16 0.08 7.22 0.02 0.00 0.95 2.48 0.14 91.88 bt2 42.12 2.89 7.29 27.79 0.07 0.17 0.18 0.07 0.00 2.21 7.07 0.84 0.00 0.54 91.25

Chevkinite

Sample SiO2 TiO2 FeO CaO La2O3 Ce2O3 Nd2O3 Pr2O3 Bi2O3 Nb2O3 ThO2 ZrO2 Gd2O3 Y2O3 Total

LA-01 chvk1 18.42 18.50 10.84 2.74 12.49 20.71 6.84 2.10 1.70 1.14 0.88 0.71 0.54 0.53 98.14 chvk2 18.63 17.81 10.83 2.82 12.86 21.26 6.90 2.32 1.64 1.34 0.90 0.74 0.54 0.44 99.04 chvk3 18.60 18.11 10.93 2.86 12.61 21.48 7.16 2.56 1.66 1.03 0.89 0.67 0.55 0.46 99.55 chvk4 18.66 18.46 11.07 2.91 12.91 21.03 6.70 2.36 1.69 1.12 0.75 0.75 0.68 0.44 99.54 chvk5 18.62 18.29 10.84 2.75 12.72 21.30 7.11 2.27 1.55 1.13 0.81 0.66 0.66 0.43 99.13 chvk6 18.85 18.25 11.10 2.85 13.25 21.29 6.63 2.14 1.50 1.29 0.67 0.73 0.49 0.44 99.48 chvk7 18.96 18.32 10.79 3.16 12.98 20.31 6.75 2.25 1.46 1.01 0.81 1.00 0.48 0.48 98.75 100

Table 2C: Emory Peak Suite: Emory Peak Rhyolite Mineral Compositions (continued )

Zircon

Sample SiO2 TiO2 Al2O3 FeO* MnO ZrO2 ThO2 HfO2 Total

CO-01 zirc1 30.78 0.04 0.00 0.30 60.57 1.18 3.59 96.46 zirc2 30.89 0.00 0.00 0.23 60.18 1.16 3.55 96.02

CO-06 zirc1 31.19 0.02 0.00 0.33 65.29 0.05 2.14 99.02

LA -01 zirc1 31.55 0.00 0.04 0.51 65.96 0.00 1.15 99.21 zirc2 31.51 0.00 0.07 0.12 65.95 0.02 1.17 98.84 zirc3 31.31 0.00 0.03 0.10 65.56 0.02 1.16 98.18 zirc4 31.00 0.00 0.03 0.00 65.97 0.00 1.17 98.17

101

Table 2D: South Rim Formation Sodic Amphibole

Suite Pine Canyon Suite Pine Canyon Suite Pine Canyon Suite Pine Canyon Suite Emory Peak Suite Emory Peak Suite Emory Peak Suite Member Boot Rock Member Boot Rock Member Pine Canyon Rhyolite Pine Canyon Rhyolite Emory Peak Rhyolite Emory Peak Rhyolite Emory Peak Rhyolite Sample PC-06 PC-01 PC-02 99802 CO-01 CO-01 BC-02 Grain amph1 amph1 amph2 amph1 amph1 amph2 amph1

SiO2 48.59 49.30 50.38 48.85 48.36 48.75 49.79

TiO2 0.12 0.12 0.01 1.42 0.63 0.58 0.15

Al2O3 0.28 0.33 0.20 0.22 0.71 0.50 0.14 FeO* 34.78 33.56 28.72 34.07 36.17 34.89 35.25 M nO 1.06 0.80 0.43 0.79 0.56 0.71 1.24 M gO 0.03 0.30 0.01 0.04 0.05 0.02 0.04 CaO 1.81 2.86 7.67 1.64 0.67 0.73 3.24 Na2O 7.55 7.35 8.79 7.83 7.50 8.36 5.56

K 2O 1.36 1.42 1.47 0.93 1.09 1.50 Total 95.58 96.04 96.22 96.32 95.58 95.63 96.91

Si 7.977 8.016 7.991 7.958 7.985 7.952 8.154 Al (iv) 0.023 -0.016 0.009 0.042 0.015 0.048 -0.154 T 8.000 8.000 8.000 8.000 8.000 8.000 8.000

Al (vi) 0.031 0.080 0.028 0.001 0.122 0.048 0.181 Ti 0.015 0.014 0.001 0.174 0.078 0.071 0.018 Cr 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Fe(iii) 0.610 0.384 0.495 0.473 0.334 0.685 0.000 Fe(ii) 4.164 4.178 3.315 4.168 4.660 4.073 4.826 M n 0.148 0.110 0.058 0.109 0.079 0.098 0.172 M g 0.006 0.073 0.003 0.010 0.012 0.006 0.009 C 4.974 4.839 3.900 4.935 5.285 4.981 5.206

C-5 0.000 0.000 0.000 0.000 0.285 0.000 0.206 Ca 0.318 0.497 1.304 0.286 0.118 0.127 0.569 Na 1.682 1.503 0.696 1.714 1.597 1.873 1.225 B 2.000 2.000 2.000 2.000 2.000 2.000 2.000

Na 0.721 0.814 2.006 0.761 0.804 0.771 0.541 K 0.285 0.295 0.000 0.305 0.196 0.227 0.312 A 1.006 1.109 2.006 1.065 1.000 0.998 0.854

class arf arf frcht arf arf arf arf

102

Table 2E: South Rim Formation Fe- Ti Oxides

Pine Canyon Suite Sample SiO2 TiO2 Al2O3 FeO MnO MgO CaO Total N-Ti N-Mg N-Mn Calculat Calculat Adjusted Ilm Hem Gkl Pyf ed ed FeO Total Boot Rock Member BC-01 ilm1 0.00 52.58 0.00 41.99 1.22 0.00 0.19 95.98 0.97 0.00 0.00 0.03 0.00 -- -- ilm2 0.02 49.50 0.00 40.61 1.62 0.00 0.06 91.81 0.96 0.00 0.00 0.04 0.00 -- -- ilm4 0.00 53.26 0.00 39.86 1.53 0.00 0.09 94.75 0.96 0.00 0.00 0.04 0.00 -- -- mt1 4.32 0.00 0.02 83.62 0.42 0.00 0.17 88.55 0.03 0.04 0.03 54.77 34.34 94.04 mt2 3.53 0.63 0.36 83.33 0.25 0.00 0.12 88.21 0.00 0.00 0.01 54.77 34.05 93.70 mt3 4.06 0.37 0.32 83.22 0.29 0.00 0.15 88.41 0.01 0.00 0.01 54.15 34.49 93.83 mt4 4.17 1.66 0.62 78.64 0.31 0.01 1.02 86.42 0.06 0.00 0.01 49.55 34.05 91.38 mt5 3.64 1.43 0.39 81.66 0.26 0.00 0.21 87.60 0.05 0.00 0.01 52.33 34.57 92.84 uvsp1 0.07 18.58 0.07 69.60 2.51 0.01 0.04 90.88 0.56 0.00 0.09 28.58 43.88 93.74 uvsp2 0.08 19.01 0.10 68.01 2.50 0.02 0.06 89.77 0.58 0.00 0.09 27.55 43.22 92.53 uvsp3 0.39 19.88 0.10 65.85 2.80 0.01 0.21 89.25 0.61 0.00 0.10 26.67 41.85 91.92

PC-06 uvsp1 0.07 18.58 0.07 69.60 2.51 0.01 0.04 90.88 0.56 0.00 0.09 28.58 43.88 93.74 uvsp2 0.08 19.01 0.10 68.01 2.50 0.02 0.06 89.77 0.58 0.00 0.09 26.83 43.86 92.46 uvsp3 0.39 19.88 0.10 65.85 2.80 0.01 0.21 89.25 0.06 0.00 0.10 23.90 44.34 91.64

PJ-01 ilm1 2.65 49.33 0.14 40.27 0.05 0.00 0.02 92.47 1.00 0.00 0.00 0.00 0.00 -- -- ilm3 0.37 57.01 0.18 34.41 0.03 0.01 0.03 92.03 1.00 0.00 0.00 0.00 0.00 -- -- mt1 0.09 3.45 0.05 86.69 0.00 0.00 0.00 90.29 0.10 0.00 0.00 59.46 33.19 96.25 mt2 0.12 5.78 0.03 85.50 0.01 0.00 0.00 91.45 0.17 0.00 0.00 55.42 35.63 97.00 mt3 0.97 1.28 0.29 86.11 0.00 0.00 0.01 88.66 0.04 0.00 0.00 60.23 31.91 94.69 mt4 0.77 0.26 0.17 87.75 0.03 0.00 0.01 88.98 0.01 0.00 0.00 63.25 30.84 95.31 mt5 0.14 3.64 0.08 86.83 0.01 0.00 0.01 90.70 0.11 0.00 0.00 59.21 33.55 96.63 uvsp1 0.15 15.09 0.03 76.50 0.00 0.00 0.03 91.79 0.45 0.00 0.00 36.25 43.88 95.42 psd1 0.37 57.01 0.18 34.41 0.03 0.01 0.03 92.03 13.94 21.86 93.43

Pine Canyon Rhyolite U04-02 mt1 2.46 3.99 0.18 81.19 0.49 0.01 0.13 88.45 0.13 0.00 0.02 50.87 35.41 93.54 mt2 2.76 5.00 0.15 81.80 0.64 0.00 0.18 90.52 0.15 0.00 0.02 49.63 37.14 95.49

Emory Peak Suite

Sample SiO2 TiO2 Al2O3 FeO MnO MgO CaO Total N-Ti N-Mg N-Mn Calculat Calculat Adjusted Ilm Hem Gkl Pyf ed ed FeO Total Emory Peak Rhyolite CO-01 uvsp4 0.10 19.58 0.09 69.33 0.35 0.01 0.02 89.48 0.60 0.00 0.01 28.08 44.06 92.29

CO-06 mt1 2.95 1.67 1.32 80.48 0.26 0.02 0.18 86.88 0.05 0.00 0.01 51.88 33.80 92.08 mt2 3.52 2.26 0.89 79.62 0.00 0.00 0.24 86.53 0.07 0.00 0.00 49.50 35.07 91.48 mt4 2.80 1.81 0.91 79.06 0.39 0.01 0.22 85.20 0.08 0.00 0.01 51.23 32.96 90.33 mt5 4.77 1.44 1.11 77.82 0.23 0.03 0.15 85.55 0.05 0.00 0.01 47.04 35.48 90.26 mt6 2.44 2.19 0.98 79.95 0.41 0.03 0.24 86.24 0.07 0.00 0.01 52.06 33.10 91.46

Crown-Vit ilm1 0.01 47.62 0.02 49.58 0.97 0.00 0.01 98.21 0.90 0.08 0.00 0.02 20.08 31.51 100.22 ilm2 0.01 49.16 0.04 47.94 0.78 0.00 0.01 97.94 0.93 0.05 0.00 0.02 19.42 30.47 99.89 ilm3 0.10 47.70 0.02 47.19 0.83 0.01 0.08 95.93 0.92 0.06 0.00 0.02 19.11 29.99 97.85 ilm4 0.02 48.32 0.00 47.65 0.85 0.00 0.02 96.86 0.92 0.06 0.00 0.02 19.30 30.28 98.79

LA-01 psd1 0.86 54.79 0.07 36.43 1.20 0.01 0.01 93.36 14.76 23.15 94.84 psd2 1.16 53.93 0.11 37.87 0.90 0.01 0.03 94.01 15.34 24.07 95.55 psd3 1.33 54.73 0.14 35.29 1.94 0.01 0.04 93.49 14.30 22.43 94.92

U04-04 mt1 0.59 4.90 0.02 83.55 0.44 0.00 0.10 89.59 0.15 0.00 0.02 54.75 34.28 95.08 mt2 0.98 4.44 0.12 85.29 0.22 0.00 0.03 91.07 0.13 0.00 0.01 55.68 35.19 96.65 uvsp1 1.33 13.61 0.28 74.93 0.34 0.01 0.11 90.61 0.42 0.00 0.01 35.25 43.21 94.14 uvsp2 1.05 12.79 0.22 76.29 0.38 0.00 0.07 90.81 0.39 0.00 0.01 37.87 42.22 94.60

BC-02 mt1 4.28 1.04 0.49 78.99 0.50 0.04 0.24 85.57 0.03 0.00 0.02 53.41 35.93 95.92 ilm1 3.06 44.35 1.33 42.77 1.17 0.03 0.05 92.76 0.92 0.05 0.00 0.03 17.32 27.18 94.49

AP-01 ilm1 0.12 51.46 0.06 41.01 2.98 0.02 0.02 95.67 0.93 0.00 0.00 0.07 0.00 -- --

1) End member compositions of ilmenite, magnetite, and ulvospinel calculated with QUILF95 v. 6.42 (Anderson et al., 1993) and are reported in mol. %.

103 Table 3: Pre-31 Ma Alternative Tectonic Stress Regime Considerations

Age Location and Evidence for Potential Alternative Stress Suggestive Paleostress Petrologic Notes References (Ma)

Structural and Magmatic Evidence in Trans-Pecos Texas

Considerable dike and vein orientation scatter suggests small magnitude Delaney et al., 1986; Henry et difference between σ1 and σ3 48-32 neutral -- al., 1991

Cameron et al., 1986; Henry et Intrusions in the Christmas Mountains area 44-40 some degree of extension peralkaline al., 1989

Infiernito tuffs north of the Chinati Mountains ~37 some degree of extension peralkaline Henry et al., 1992

Bracks Rhyolite, Star Mountain Formation, and Crossen Trachyte in the Davis near-neutral, neutral, some degree of Mountains 36.8 extension A-type, mildly peralkaline Henry et al., 1993

36.8- Parker, 1983; Parker and Gomez tuff and other volcanism in the Davis Mountains 35 some degree of extension peralkaline-very peralkaline White, 2008

Domes north and west of the Solitario laccocaldera ~35.4 some degree of extension peralkaline Henry et al., 1997

32.2- near-neutral, neutral, some degree of Benker, 2005; White et al., South Rim Formation in central Big Bend National Park 32 extension A-type, peralkaline 2006

Alternative σ1 interpretation of dike and vein orientation (disregarded as faulting pre- σ1 = east-northeast to vertical; some degree was negligable) 32 of extension -- Henry et al., 1991

Structural and Magmatic Evidence in Adjacent Regions

Emplacement of porphyry copper system near the Jarilla Mountains (NM) 48-42 near-neutral -- Beane et al., 1975

Regional stress field characterization for New Mexico and Colorado (NM, CO) 45-36 near-neutral -- Chapin et al., 2004

Intercalation of half graben deposited conglomerate and Bell Top Formation (NM) ~36 some degree of extension -- McMillan et al., 2000

Geochemical signature of Rubio Peak Formation basalts and Bell Top ~38- same protolith as extensional Formation (NM) 36 -- Uvas lavas McMillan et al., 2000

Villa Ahumada carbonatite complex in northern Chihuahua ~37 near-neutral, neutral likely A-type Nandigam, 2000

35- Creation of Goodsight-Cedar Hills half graben (NM) 28.5 some degree of extension -- Mack, 2001; Mack et al., 1994

Dikes striking N40°W in the Organ batholith (NM) 32.5 some degree of northeast extension -- Newcomer et al., 1983

7 km long dike generally striking northerly near San Carlos-Santana caldera complex (MEX) 32 some degree of extension -- Chuchla, 1981; Gregory, 1981

104

Table 4: Horizontal position offset distances and accuracy calculations between Google Earth and field truthed positions of 268 points in the Big

Bend region. X are latitudinal measurements whereas Y are longitudinal measurements. All measurements are in meters.

offset x2 offset y2 Trace Point # GE x GPS x offset x (1) GE y GPS y offset y (2) (1)+(2) sqrt[(1)+(2)] bb8a 1 3226571.38 3226569.91 1.46 2.15 650557.51 650560.75 -3.24 10.49 12.64 3.56 bb8a 2 3226561.05 3226559.98 1.07 1.15 650550.05 650554.37 -4.32 18.70 19.85 4.45 bb8a 3 3226557.09 3226556.17 0.92 0.85 650548.23 650554.32 -6.09 37.12 37.97 6.16 bb8a 4 3226553.09 3226552.03 1.06 1.13 650548.07 650554.80 -6.73 45.25 46.37 6.81 bb8a 5 3226551.57 3226548.28 3.30 10.86 650547.60 650554.52 -6.91 47.77 58.64 7.66 bb8a 6 3226550.46 3226542.16 8.30 68.96 650545.17 650550.41 -5.25 27.52 96.49 9.82 bb8a 7 3226538.85 3226540.73 -1.88 3.53 650540.11 650543.10 -2.99 8.95 12.48 3.53 bb8a 8 3226536.02 3226538.41 -2.39 5.72 650541.20 650544.06 -2.86 8.17 13.89 3.73 bb8a 9 3226534.39 3226535.55 -1.16 1.35 650540.52 650543.04 -2.51 6.32 7.67 2.77 bb8a 10 3226533.19 3226532.44 0.75 0.57 650540.04 650542.19 -2.15 4.62 5.19 2.28 bb8a 11 3226528.60 3226530.05 -1.45 2.10 650540.70 650542.97 -2.28 5.18 7.28 2.70 bb8a 12 3226527.53 3226528.49 -0.96 0.92 650540.10 650546.01 -5.91 34.95 35.87 5.99 bb8a 13 3226525.94 3226525.37 0.57 0.33 650540.55 650546.24 -5.69 32.37 32.69 5.72 bb8a 14 3226524.45 3226522.71 1.74 3.04 650539.77 650548.19 -8.42 70.88 73.92 8.60 bb8a 15 3226646.15 3226645.60 0.55 0.30 650394.43 650394.40 0.03 0.00 0.30 0.55 bb8a 16 3226645.10 3226644.19 0.91 0.83 650394.07 650394.79 -0.72 0.52 1.35 1.16 bb8a 17 3226643.63 3226642.95 0.68 0.46 650392.67 650394.74 -2.07 4.29 4.75 2.18 bb8a 18 3226641.14 3226640.05 1.09 1.19 650391.20 650393.37 -2.17 4.73 5.91 2.43 bb8a 19 3226638.38 3226638.38 0.00 0.00 650390.22 650391.29 -1.07 1.15 1.15 1.07 bb8a 20 3226635.77 3226635.67 0.09 0.01 650388.65 650390.16 -1.51 2.28 2.29 1.51 bb8a 21 3226633.15 3226632.66 0.49 0.24 650388.12 650389.43 -1.31 1.72 1.96 1.40 bb8a 22 3226630.57 3226629.91 0.66 0.43 650387.33 650387.08 0.24 0.06 0.49 0.70 bb8a 23 3226626.97 3226626.69 0.28 0.08 650385.83 650386.22 -0.39 0.15 0.23 0.48 bb8a 24 3226624.42 3226623.68 0.74 0.55 650383.48 650384.23 -0.75 0.56 1.11 1.06

105 Table 4 (continued) bb8a 25 3226623.51 3226620.43 3.09 9.52 650382.73 650383.53 -0.80 0.64 10.16 3.19 bb8a 26 3226620.84 3226617.92 2.92 8.52 650378.52 650380.54 -2.01 4.05 12.58 3.55 bb8a 27 3226612.11 3226611.49 0.62 0.38 650375.00 650376.41 -1.41 1.99 2.37 1.54 bb8a 28 3226611.40 3226608.68 2.72 7.39 650373.73 650374.15 -0.42 0.18 7.57 2.75 bb8a 29 3226608.29 3226605.55 2.74 7.51 650367.35 650370.75 -3.39 11.51 19.01 4.36 bb8a 30 3226605.66 3226604.07 1.59 2.53 650365.52 650367.52 -2.00 3.98 6.52 2.55 bb8a 31 3226604.91 3226604.63 0.28 0.08 650365.00 650364.49 0.50 0.25 0.33 0.57 bb8a 32 3226602.23 3226602.37 -0.14 0.02 650362.49 650362.47 0.02 0.00 0.02 0.14 bb8a 33 3226601.39 3226602.02 -0.63 0.40 650361.89 650360.73 1.16 1.34 1.73 1.32 bb8a 34 3226599.47 3226600.47 -0.99 0.99 650360.42 650358.70 1.72 2.94 3.93 1.98 bb8a 35 3226598.47 3226599.71 -1.24 1.55 650358.94 650357.40 1.54 2.38 3.93 1.98 bb8a 36 3226597.26 3226598.63 -1.37 1.87 650358.03 650355.26 2.77 7.68 9.55 3.09 bb8a 37 3226593.52 3226596.53 -3.01 9.07 650355.15 650353.33 1.81 3.28 12.35 3.51 bb8a 38 3226592.91 3226594.83 -1.91 3.66 650353.97 650351.56 2.41 5.80 9.46 3.08 bb8a 39 3226589.59 3226592.90 -3.30 10.92 650350.45 650349.41 1.04 1.07 11.99 3.46 bb8a 40 3226589.59 3226591.94 -2.35 5.52 650350.45 650347.55 2.90 8.41 13.93 3.73 bb8a 41 3226588.33 3226591.21 -2.88 8.31 650348.90 650344.88 4.02 16.14 24.44 4.94 bb8a 42 3226584.36 3226588.09 -3.73 13.91 650346.59 650342.50 4.09 16.70 30.60 5.53 bb8a 43 3226583.12 3226585.78 -2.66 7.09 650345.98 650341.53 4.45 19.82 26.91 5.19 bb8a 44 3226581.04 3226584.24 -3.20 10.23 650344.68 650339.96 4.71 22.20 32.43 5.70 bb8a 45 3226579.24 3226582.13 -2.90 8.40 650343.57 650338.47 5.10 25.98 34.38 5.86 bb8a 46 3226576.90 3226579.07 -2.16 4.69 650342.48 650337.77 4.72 22.26 26.94 5.19 bb8a 47 3226574.34 3226575.88 -1.54 2.36 650341.77 650336.41 5.36 28.74 31.10 5.58 bb8a 48 3226569.38 3226573.19 -3.82 14.55 650337.95 650334.85 3.10 9.64 24.20 4.92 bb8a 49 3226567.39 3226570.03 -2.65 7.00 650335.31 650332.83 2.48 6.13 13.14 3.62 bb8a 50 3226565.73 3226566.04 -0.31 0.09 650334.42 650331.30 3.12 9.72 9.81 3.13 bb8a 51 3226561.24 3226562.90 -1.66 2.75 650332.00 650328.78 3.21 10.32 13.07 3.62 bb8a 52 3226556.76 3226559.53 -2.77 7.68 650323.80 650325.12 -1.33 1.76 9.44 3.07

106 Table 4 (continued) bb8a 53 3226557.16 3226559.63 -2.47 6.10 650321.24 650321.17 0.07 0.01 6.11 2.47 bb8a 54 3226558.69 3226559.44 -0.74 0.55 650316.16 650316.93 -0.77 0.59 1.14 1.07 bb8a 55 3226560.15 3226560.12 0.03 0.00 650312.92 650313.33 -0.41 0.17 0.17 0.41 bb8a 56 3226560.42 3226559.72 0.69 0.48 650308.28 650309.90 -1.62 2.64 3.12 1.77 bb8a 57 3226559.55 3226559.48 0.07 0.00 650307.34 650307.03 0.31 0.10 0.10 0.32 bb8a 58 3226555.35 3226558.30 -2.95 8.71 650302.82 650301.09 1.73 3.00 11.71 3.42 bb8a 59 3226546.98 3226552.47 -5.50 30.22 650294.00 650296.41 -2.41 5.80 36.02 6.00 bb8a 60 3226547.54 3226550.93 -3.39 11.48 650290.80 650292.12 -1.32 1.74 13.21 3.63 unc1g 61 3254180.50 3254175.23 5.27 27.76 676501.51 676492.42 9.09 82.64 110.40 10.51 unc1g 62 3254208.68 3254208.24 0.44 0.19 676498.70 676486.14 12.56 157.84 158.03 12.57 unc1g 63 3254243.87 3254242.44 1.43 2.06 676493.43 676481.26 12.17 148.09 150.15 12.25 unc1g 64 3254269.53 3254265.42 4.11 16.93 676483.64 676469.34 14.30 204.54 221.46 14.88 unc1g 65 3254283.41 3254279.12 4.30 18.48 676471.66 676463.63 8.03 64.45 82.93 9.11 unc1g 66 3254302.04 3254305.11 -3.07 9.41 676459.53 676460.74 -1.20 1.45 10.87 3.30 unc1g 67 3254318.37 3254319.54 -1.17 1.37 676452.20 676455.71 -3.51 12.29 13.65 3.69 unc1g 68 3254334.49 3254343.40 -8.90 79.28 676435.50 676446.04 -10.54 111.06 190.34 13.80 unc1g 69 3254360.07 3254363.01 -2.93 8.60 676430.59 676441.09 -10.51 110.36 118.96 10.91 unc1g 70 3254392.42 3254399.93 -7.51 56.44 676411.45 676418.84 -7.40 54.70 111.14 10.54 unc1g 71 3254410.80 3254419.69 -8.89 78.98 676394.79 676410.34 -15.56 242.02 321.00 17.92 unc1g 72 3254426.83 3254442.65 -15.82 250.13 676375.76 676388.99 -13.23 174.93 425.06 20.62 unc1g 73 3254445.19 3254468.46 -23.27 541.41 676349.54 676348.61 0.94 0.87 542.28 23.29 unc1g 74 3254465.90 3254469.14 -3.24 10.47 676335.26 676336.99 -1.73 2.98 13.45 3.67 unc1g 75 3254483.46 3254477.48 5.98 35.72 676331.41 676326.01 5.39 29.06 64.79 8.05 unc1g 76 3254502.13 3254502.37 -0.24 0.06 676319.21 676317.92 1.29 1.68 1.73 1.32 unc1g 77 3254516.12 3254510.68 5.44 29.60 676328.59 676316.36 12.22 149.40 179.00 13.38 unc1g 78 3254538.78 3254530.58 8.20 67.22 676324.13 676310.06 14.07 198.04 265.26 16.29 unc1g 79 3254555.27 3254555.98 -0.71 0.50 676316.59 676301.64 14.95 223.48 223.98 14.97 unc1g 80 3254581.01 3254569.06 11.95 142.84 676313.77 676304.30 9.47 89.71 232.55 15.25

107 Table 4 (continued) unc1g 81 3254599.70 3254595.34 4.36 19.04 676320.63 676295.93 24.69 609.74 628.78 25.08 unc1i 82 3252561.65 3252565.60 -3.95 15.59 680850.36 680850.45 -0.09 0.01 15.60 3.95 unc1i 83 3252560.53 3252565.31 -4.79 22.91 680847.06 680847.14 -0.09 0.01 22.91 4.79 unc1i 84 3252555.28 3252563.56 -8.28 68.64 680837.48 680838.90 -1.42 2.02 70.66 8.41 unc1i 85 3252554.56 3252563.05 -8.49 72.17 680835.16 680830.37 4.79 22.91 95.07 9.75 unc1i 86 3252552.32 3252557.56 -5.24 27.48 680829.49 680825.26 4.23 17.89 45.37 6.74 unc1i 87 3252549.51 3252556.12 -6.61 43.75 680827.00 680822.16 4.83 23.36 67.11 8.19 unc1i 88 3252552.83 3252556.15 -3.32 11.02 680811.50 680814.96 -3.46 11.98 23.00 4.80 unc1i 89 3252555.14 3252557.21 -2.08 4.31 680810.10 680810.19 -0.08 0.01 4.31 2.08 unc1i 90 3252556.72 3252559.34 -2.62 6.87 680806.79 680807.10 -0.32 0.10 6.97 2.64 unc1i 91 3252559.40 3252560.73 -1.33 1.77 680802.13 680801.37 0.76 0.58 2.35 1.53 unc1i 92 3252561.89 3252562.78 -0.89 0.79 680799.38 680798.34 1.04 1.09 1.88 1.37 unc1i 93 3252564.08 3252566.20 -2.11 4.47 680796.79 680796.65 0.14 0.02 4.49 2.12 unc1i 94 3252562.94 3252566.44 -3.50 12.23 680793.48 680792.66 0.82 0.68 12.91 3.59 unc1i 95 3252560.05 3252564.60 -4.55 20.69 680790.96 680788.36 2.60 6.74 27.44 5.24 unc1i 96 3252551.27 3252557.28 -6.01 36.09 680775.33 680774.86 0.47 0.23 36.32 6.03 unc1i 97 3252552.12 3252556.79 -4.67 21.82 680769.41 680771.59 -2.19 4.79 26.60 5.16 unc1i 98 3252552.57 3252557.55 -4.98 24.83 680766.82 680767.40 -0.58 0.34 25.17 5.02 unc1i 99 3252552.13 3252557.53 -5.41 29.22 680764.67 680763.44 1.23 1.52 30.74 5.54 unc1i 100 3252552.84 3252557.21 -4.37 19.11 680756.39 680759.58 -3.18 10.13 29.24 5.41 unc1i 101 3252552.45 3252554.26 -1.81 3.28 680754.04 680749.81 4.23 17.92 21.19 4.60 unc1i 102 3252546.18 3252551.47 -5.30 28.05 680747.82 680747.14 0.68 0.46 28.50 5.34 unc1i 103 3252547.06 3252555.49 -8.43 71.00 680744.51 680743.19 1.32 1.74 72.74 8.53 unc1i 104 3252561.25 3252562.72 -1.47 2.15 680718.57 680733.76 -15.19 230.73 232.87 15.26 unc1i 105 3252569.33 3252572.56 -3.23 10.46 680717.55 680723.73 -6.18 38.21 48.67 6.98 unc1i 106 3252572.66 3252575.42 -2.76 7.60 680715.59 680715.75 -0.16 0.03 7.63 2.76 unc1i 107 3252573.17 3252576.71 -3.54 12.53 680712.61 680713.05 -0.45 0.20 12.73 3.57 unc1i 108 3252571.16 3252579.17 -8.01 64.15 680710.48 680704.70 5.78 33.39 97.53 9.88

108 Table 4 (continued) unc1i 109 3252580.76 3252585.43 -4.67 21.83 680688.87 680700.55 -11.67 136.25 158.08 12.57 unc1i 110 3252584.64 3252589.71 -5.07 25.72 680687.63 680698.23 -10.60 112.32 138.04 11.75 unc1i 111 3252591.42 3252594.90 -3.48 12.12 680686.14 680693.04 -6.90 47.55 59.67 7.72 unc1i 112 3252593.42 3252597.77 -4.35 18.93 680685.40 680688.76 -3.36 11.27 30.20 5.50 unc1i 113 3252599.07 3252604.80 -5.73 32.81 680673.21 680675.35 -2.14 4.59 37.39 6.12 unc1i 114 3252600.93 3252605.34 -4.41 19.46 680669.91 680671.88 -1.97 3.87 23.33 4.83 unc1i 115 3252602.20 3252604.45 -2.25 5.04 680667.97 680668.75 -0.78 0.61 5.65 2.38 unc1i 116 3252603.05 3252604.64 -1.59 2.52 680665.67 680667.26 -1.59 2.52 5.04 2.24 unc1i 117 3252602.32 3252604.66 -2.34 5.46 680662.28 680661.51 0.77 0.59 6.04 2.46 unc1i 118 3252604.51 3252605.21 -0.70 0.49 680657.81 680657.94 -0.13 0.02 0.50 0.71 unc1i 119 3252608.09 3252607.12 0.97 0.94 680658.13 680653.84 4.29 18.36 19.30 4.39 unc1i 120 3252611.60 3252609.59 2.01 4.03 680657.92 680652.08 5.83 34.01 38.04 6.17 unc1i 121 3252614.06 3252610.64 3.42 11.68 680656.70 680650.79 5.92 35.00 46.68 6.83 unc1i 122 3252616.77 3252613.16 3.61 13.02 680654.32 680648.93 5.39 29.04 42.06 6.49 unc1i 123 3252620.51 3252616.26 4.25 18.10 680651.95 680645.55 6.40 40.93 59.04 7.68 unc1i 124 3252624.56 3252616.27 8.29 68.77 680645.95 680642.73 3.23 10.41 79.18 8.90 unc1i 125 3252624.12 3252617.78 6.34 40.20 680637.89 680640.30 -2.41 5.82 46.01 6.78 unc1i 126 3252622.44 3252616.26 6.18 38.14 680635.25 680637.32 -2.07 4.28 42.43 6.51 unc1i 127 3252622.03 3252615.84 6.18 38.22 680632.87 680633.35 -0.49 0.24 38.46 6.20 unc1i 128 3252621.25 3252616.44 4.80 23.06 680629.90 680630.40 -0.50 0.25 23.31 4.83 unc1i 129 3252620.92 3252616.13 4.79 22.98 680627.25 680625.59 1.66 2.76 25.74 5.07 unc1i 130 3252620.92 3252615.54 5.38 28.91 680623.42 680622.90 0.52 0.27 29.18 5.40 unc1i 131 3252620.90 3252622.09 -1.19 1.42 680618.78 680617.64 1.14 1.29 2.71 1.65 unc1i 132 3252621.66 3252623.84 -2.17 4.73 680614.07 680614.09 -0.02 0.00 4.73 2.17 unc1i 133 3252628.86 3252637.88 -9.02 81.38 680601.34 680612.43 -11.09 122.96 204.34 14.29 unc1i 134 3252643.80 3252657.67 -13.87 192.31 680583.26 680586.78 -3.52 12.37 204.68 14.31 unc1i 135 3252645.58 3252662.55 -16.97 288.08 680576.58 680579.13 -2.54 6.48 294.55 17.16 unc1i 136 3252646.88 3252656.19 -9.31 86.71 680569.79 680571.16 -1.37 1.87 88.57 9.41

109 Table 4 (continued) unc1i 137 3252648.60 3252653.09 -4.49 20.14 680565.19 680566.78 -1.59 2.52 22.66 4.76 unc1i 138 3252650.74 3252651.35 -0.61 0.37 680557.15 680557.21 -0.06 0.00 0.38 0.61 unc1i 139 3252649.88 3252651.71 -1.83 3.35 680552.81 680552.67 0.15 0.02 3.37 1.84 unc1i 140 3252651.85 3252651.90 -0.06 0.00 680547.29 680550.05 -2.77 7.65 7.65 2.77 unc1i 141 3252652.03 3252653.88 -1.85 3.43 680542.79 680544.60 -1.81 3.26 6.69 2.59 unc1i 142 3252651.41 3252656.31 -4.90 24.00 680537.56 680539.12 -1.56 2.44 26.44 5.14 unc1i 143 3252651.70 3252659.68 -7.98 63.68 680532.60 680534.86 -2.26 5.11 68.79 8.29 unc1i 144 3252652.58 3252663.82 -11.24 126.26 680527.30 680531.05 -3.75 14.08 140.34 11.85 unc1i 145 3252654.06 3252667.60 -3.75 14.08 680521.63 680521.00 0.63 0.40 14.48 3.81 unc1i 146 3252662.46 3252662.37 0.09 0.01 680505.06 680502.56 2.50 6.27 6.27 2.50 unc1i 147 3252666.05 3252662.85 3.20 10.27 680502.97 680499.18 3.78 14.32 24.58 4.96 unc1i 148 3252670.00 3252664.76 5.24 27.49 680501.47 680493.38 8.09 65.46 92.95 9.64 unc1i 149 3252675.10 3252666.44 8.66 74.97 680495.67 680491.82 3.85 14.84 89.81 9.48 unc1i 150 3252677.18 3252666.12 11.06 122.43 680491.63 680488.22 3.42 11.67 134.10 11.58 unc1i 151 3252678.48 3252680.12 -1.64 2.70 680484.83 680481.87 2.96 8.75 11.45 3.38 unc1i 152 3252678.86 3252685.38 -6.52 42.52 680475.74 680476.78 -1.04 1.09 43.60 6.60 unc1i 153 3252676.85 3252691.33 -14.47 209.47 680466.07 680466.53 -0.46 0.21 209.68 14.48 unc1i 154 3252678.61 3252692.86 -14.25 203.02 680459.49 680462.48 -3.00 8.98 212.00 14.56 unc1i 155 3252680.59 3252695.84 -15.25 232.67 680453.96 680457.97 -4.01 16.07 248.74 15.77 unc1i 156 3252681.47 3252692.10 -10.63 112.94 680450.67 680453.20 -2.53 6.40 119.33 10.92 unc1i 157 3252689.72 3252696.56 -6.85 46.88 680438.63 680436.77 1.87 3.48 50.36 7.10 unc1i 158 3252689.46 3252697.43 -7.97 63.51 680432.00 680433.31 -1.31 1.72 65.23 8.08 unc1i 159 3252690.61 3252695.98 -5.37 28.85 680425.74 680426.36 -0.61 0.38 29.22 5.41 unc1i 160 3252688.89 3252697.95 -9.06 82.08 680420.82 680419.89 0.93 0.87 82.95 9.11 unc1i 161 3252688.72 3252697.72 -9.00 81.08 680413.95 680416.30 -2.35 5.53 86.61 9.31 unc1i 162 3252689.04 3252699.90 -10.86 117.98 680407.10 680408.79 -1.69 2.86 120.84 10.99 unc1i 163 3252613.65 3252649.25 -35.60 1267.40 680161.31 680165.78 -4.47 20.00 1287.41 35.88 unc1i 164 3252602.19 3252636.48 -34.29 1175.72 680137.61 680127.49 10.12 102.37 1278.09 35.75

110 Table 4 (continued) unc1i 165 3252599.62 3252633.48 -33.86 1146.62 680126.94 680117.31 9.64 92.84 1239.46 35.21 unc1i 166 3252597.67 3252627.49 -29.82 889.39 680119.43 680109.75 9.68 93.66 983.05 31.35 unc1i 167 3252588.51 3252624.70 -36.19 1309.57 680105.88 680086.86 19.02 361.81 1671.38 40.88 unc1i 168 3252578.33 3252618.49 -40.16 1612.97 680086.61 680072.37 14.24 202.78 1815.74 42.61 unc1i 169 3252576.43 3252602.78 -26.36 694.67 680082.59 680061.92 20.67 427.28 1121.94 33.50 unc1i 170 3252573.95 3252595.55 -21.61 466.85 680078.98 680064.19 14.80 219.02 685.86 26.19 unc1i 171 3252555.79 3252572.35 -16.56 274.22 680065.51 680051.70 13.81 190.62 464.84 21.56 unc1i 172 3252554.57 3252568.01 -13.44 180.54 680064.12 680051.20 12.92 166.97 347.51 18.64 unc1i 173 3252551.08 3252563.98 -12.90 166.48 680061.76 680045.81 15.94 254.16 420.64 20.51 unc1i 174 3252538.81 3252558.32 -19.52 380.92 680043.04 680037.31 5.73 32.80 413.72 20.34 unc1i 175 3252537.13 3252551.54 -14.41 207.65 680034.03 680025.51 8.52 72.59 280.24 16.74 unc1i 176 3252535.38 3252548.57 -13.19 174.02 680032.47 680019.36 13.11 171.93 345.95 18.60 unc1i 177 3252533.53 3252537.61 -4.08 16.65 680031.28 680013.75 17.53 307.31 323.96 18.00 unc1i 178 3252520.93 3252533.71 -12.78 163.21 680021.83 680011.46 10.37 107.49 270.70 16.45 unc1i 179 3252512.34 3252522.66 -10.32 106.53 680015.10 680000.07 15.03 225.83 332.36 18.23 unc1i 180 3252510.76 3252521.72 -10.96 120.11 680014.16 679996.54 17.62 310.47 430.58 20.75 unc1i 181 3252498.61 3252502.10 -3.48 12.14 680004.62 679988.26 16.37 267.83 279.97 16.73 unc1i 182 3252480.95 3252484.11 -3.16 9.97 679995.35 679985.01 10.34 106.94 116.91 10.81 unc1i 183 3252460.75 3252473.99 -13.24 175.40 679983.58 679976.68 6.90 47.60 223.01 14.93 unc1i 184 3252458.29 3252471.03 -12.73 162.14 679977.58 679973.91 3.68 13.53 175.66 13.25 unc1i 185 3252456.65 3252467.63 -10.98 120.61 679974.57 679970.17 4.40 19.34 139.95 11.83 unc1i 186 3252455.81 3252465.32 -9.51 90.46 679971.52 679966.68 4.84 23.43 113.89 10.67 unc1i 187 3252453.15 3252461.48 -8.33 69.45 679968.20 679963.72 4.48 20.09 89.54 9.46 unc1i 188 3252449.61 3252456.56 -6.95 48.24 679966.22 679954.89 11.32 128.22 176.47 13.28 unc1i 189 3252446.76 3252453.42 -6.65 44.24 679964.67 679951.99 12.68 160.74 204.98 14.32 unc1i 190 3252443.16 3252452.35 -9.19 84.51 679962.92 679938.97 23.95 573.66 658.17 25.65 unc1i 191 3252424.73 3252434.32 -9.59 91.91 679929.01 679926.73 2.28 5.19 97.11 9.85 unc1i 192 3252422.67 3252433.35 -10.68 114.02 679924.69 679921.30 3.38 11.45 125.47 11.20

111 Table 4 (continued) unc1i 193 3252418.43 3252434.94 -16.51 272.56 679893.44 679896.55 -3.11 9.65 282.21 16.80 unc1i 194 3252418.84 3252439.10 -20.25 410.12 679890.85 679892.81 -1.96 3.84 413.96 20.35 unc1i 195 3252416.30 3252463.44 -47.14 2222.12 679884.22 679868.46 15.77 248.62 2470.74 49.71 unc4 196 3241851.81 3241851.98 -0.17 0.03 609931.69 609933.71 -2.02 4.08 4.10 2.03 unc4 197 3241849.11 3241850.84 -1.73 3.00 609933.39 609935.08 -1.69 2.87 5.87 2.42 unc4 198 3241847.02 3241848.99 -1.97 3.89 609935.86 609937.94 -2.09 4.36 8.25 2.87 unc4 199 3241845.06 3241847.76 -2.69 7.25 609937.12 609940.32 -3.20 10.23 17.48 4.18 unc4 200 3241842.97 3241847.75 -4.78 22.81 609939.63 609941.56 -1.93 3.71 26.52 5.15 unc4 201 3241841.01 3241847.44 -6.43 41.37 609941.29 609944.17 -2.88 8.30 49.67 7.05 unc4 202 3241839.91 3241847.60 -7.69 59.19 609943.51 609947.66 -4.15 17.23 76.42 8.74 unc4 203 3241837.74 3241841.66 -3.92 15.39 609949.53 609950.71 -1.18 1.38 16.78 4.10 unc4 204 3241837.43 3241838.17 -0.74 0.54 609952.75 609951.57 1.18 1.40 1.94 1.39 unc4 205 3241835.60 3241835.52 0.07 0.01 609955.11 609954.83 0.28 0.08 0.08 0.29 unc4 206 3241834.65 3241834.32 0.34 0.11 609960.13 609959.29 0.84 0.71 0.82 0.91 unc4 207 3241835.25 3241832.08 3.17 10.03 609963.46 609962.77 0.69 0.47 10.50 3.24 unc4 208 3241835.23 3241830.55 4.68 21.91 609967.34 609966.83 0.52 0.27 22.17 4.71 unc4 209 3241833.02 3241829.39 3.63 13.19 609971.67 609970.76 0.91 0.82 14.01 3.74 unc4 210 3241829.24 3241827.73 1.51 2.28 609975.78 609974.19 1.59 2.52 4.81 2.19 unc4 211 3241827.39 3241825.79 1.60 2.56 609978.14 609977.07 1.07 1.15 3.71 1.93 unc4 212 3241826.96 3241824.22 2.74 7.52 609980.21 609979.05 1.16 1.34 8.86 2.98 unc4 213 3241822.77 3241824.21 -1.44 2.06 609983.32 609982.59 0.73 0.54 2.60 1.61 unc17 214 3239638.73 3239636.34 2.39 5.73 612297.46 612294.81 2.65 7.01 12.75 3.57 unc17 215 3239639.86 3239640.05 -0.19 0.04 612296.04 612293.86 2.18 4.74 4.78 2.19 unc17 216 3239641.47 3239640.71 0.76 0.58 612294.06 612293.62 0.44 0.19 0.78 0.88 unc17 217 3239643.39 3239643.14 0.24 0.06 612292.69 612292.80 -0.12 0.01 0.07 0.27 unc17 218 3239643.64 3239643.71 -0.07 0.00 612290.87 612291.21 -0.34 0.12 0.12 0.35 unc17 219 3239643.47 3239643.62 -0.15 0.02 612288.90 612289.84 -0.94 0.89 0.91 0.95 unc17 220 3239644.27 3239645.31 -1.04 1.08 612285.97 612286.69 -0.72 0.52 1.60 1.26

112 Table 4 (continued) unc17 221 3239645.73 3239646.01 -0.28 0.08 612283.05 612282.40 0.65 0.43 0.51 0.71 unc17 222 3239647.95 3239646.49 1.46 2.12 612280.42 612281.08 -0.67 0.44 2.57 1.60 unc17 223 3239648.91 3239647.06 1.84 3.39 612278.82 612277.39 1.43 2.04 5.43 2.33 unc17 224 3239649.42 3239647.66 1.75 3.07 612276.33 612275.97 0.36 0.13 3.21 1.79 unc17 225 3239650.17 3239649.02 1.15 1.33 612273.02 612274.49 -1.47 2.16 3.49 1.87 unc17 226 3239651.87 3239649.24 2.62 6.88 612270.51 612268.66 1.85 3.42 10.30 3.21 unc17 227 3239653.20 3239651.48 1.71 2.94 612267.77 612267.18 0.60 0.35 3.29 1.82 unc17 228 3239654.54 3239654.53 0.01 0.00 612265.15 612264.39 0.76 0.57 0.57 0.76 unc17 229 3239655.94 3239655.15 0.79 0.63 612262.49 612262.61 -0.11 0.01 0.64 0.80 unc17 230 3239657.31 3239657.05 0.26 0.07 612259.39 612259.02 0.37 0.13 0.20 0.45 unc17 231 3239660.10 3239658.15 1.95 3.79 612257.08 612256.42 0.66 0.44 4.23 2.06 unc17 232 3239662.42 3239658.28 4.15 17.19 612254.46 612254.48 -0.02 0.00 17.19 4.15 unc17 233 3239870.59 3239871.25 -0.66 0.43 612160.78 612156.47 4.31 18.58 19.01 4.36 unc17 234 3239868.03 3239868.82 -0.79 0.62 612158.88 612155.99 2.89 8.37 8.99 3.00 unc17 235 3239864.81 3239866.11 -1.30 1.69 612156.64 612155.20 1.44 2.08 3.76 1.94 unc17 236 3239861.60 3239861.50 0.10 0.01 612154.89 612154.96 -0.08 0.01 0.02 0.13 unc17 237 3239859.16 3239859.10 0.06 0.00 612153.47 612153.40 0.07 0.00 0.01 0.09 unc17 238 3239857.84 3239858.34 -0.51 0.26 612153.19 612152.63 0.56 0.31 0.57 0.75 unc17 239 3239855.92 3239855.74 0.18 0.03 612152.20 612152.21 -0.01 0.00 0.03 0.18 unc17 240 3239854.55 3239854.95 -0.40 0.16 612151.63 612152.20 -0.57 0.32 0.48 0.70 unc17 241 3239852.51 3239852.29 0.22 0.05 612153.22 612152.66 0.56 0.32 0.37 0.60 unc17 242 3239848.89 3239849.15 -0.27 0.07 612155.32 612155.48 -0.16 0.03 0.10 0.31 unc17 243 3239844.83 3239845.16 -0.33 0.11 612155.86 612158.09 -2.23 4.98 5.09 2.26 unc17 244 3239840.97 3239841.11 -0.14 0.02 612157.82 612159.30 -1.49 2.21 2.23 1.49 unc17 245 3239836.98 3239838.73 -1.76 3.10 612159.48 612161.56 -2.08 4.33 7.43 2.73 unc17 246 3239832.76 3239832.65 0.11 0.01 612162.47 612164.20 -1.73 2.99 3.01 1.73 unc17 247 3239829.89 3239832.38 -2.49 6.21 612166.49 612168.46 -1.98 3.91 10.12 3.18 unc17 248 3239828.36 3239830.23 -1.86 3.47 612171.19 612172.02 -0.84 0.70 4.17 2.04

113 Table 4 (continued) unc17 249 3239827.39 3239828.65 -1.26 1.60 612176.05 612176.35 -0.30 0.09 1.68 1.30 unc17 250 3239827.60 3239827.37 0.24 0.06 612178.69 612178.43 0.26 0.07 0.12 0.35 unc17 251 3239824.44 3239827.53 -3.09 9.53 612180.37 612180.50 -0.13 0.02 9.55 3.09 unc17 252 3239822.50 3239824.96 -2.46 6.07 612184.68 612186.07 -1.39 1.94 8.01 2.83 unc17 253 3239820.65 3239824.08 -3.43 11.77 612188.56 612188.04 0.53 0.28 12.05 3.47 unc17 254 3239819.06 3239820.82 -1.76 3.12 612192.90 612193.54 -0.63 0.40 3.52 1.88 unc17 255 3239818.03 3239818.53 -0.50 0.25 612197.69 612198.09 -0.39 0.15 0.40 0.63 unc17 256 3239815.24 3239815.65 -0.40 0.16 612201.54 612202.02 -0.48 0.23 0.40 0.63 unc17 257 3239812.03 3239812.12 -0.09 0.01 612204.90 612205.26 -0.36 0.13 0.14 0.37 unc17 258 3239807.86 3239806.91 0.95 0.91 612207.06 612206.44 0.62 0.39 1.29 1.14 unc17 259 3239804.98 3239804.47 0.51 0.26 612209.66 612208.39 1.27 1.61 1.87 1.37 unc17 260 3239802.02 3239801.69 0.34 0.11 612210.45 612210.33 0.12 0.02 0.13 0.36 unc17 261 3239799.82 3239798.94 0.88 0.78 612213.45 612211.75 1.70 2.89 3.68 1.92 unc17 262 3239796.72 3239795.20 1.52 2.31 612215.95 612214.54 1.40 1.97 4.28 2.07 unc17 263 3239794.74 3239793.58 1.17 1.36 612218.52 612217.26 1.26 1.59 2.95 1.72 unc17 264 3239792.57 3239791.75 0.82 0.66 612221.26 612220.83 0.43 0.18 0.85 0.92 unc17 265 3239790.61 3239789.87 0.75 0.56 612224.71 612223.89 0.82 0.67 1.22 1.11 unc17 266 3239789.60 3239789.33 0.27 0.07 612227.75 612227.59 0.16 0.03 0.10 0.31 unc17 267 3239787.94 3239788.93 -0.99 0.98 612229.34 612229.56 -0.21 0.05 1.03 1.01 unc17 268 3239786.15 3239788.30 -2.15 4.63 612229.32 612230.47 -1.14 1.31 5.94 2.44 sum 1864.24 average 6.96

RMSEr 2.64

114 Table 5: Vertical position offset distances and accuracy calculations between Google Earth and NED positions of 268 points in the Big Bend

region. Z denotes elevation measurements. All measurements are in meters.

offset z2 Trace Point # GE z NED z offset z (1) sqrt (1) bb8a 1 792.00 792.99 0.99 0.98 0.99 bb8a 2 792.00 793.06 1.06 1.12 1.06 bb8a 3 792.00 792.99 0.99 0.98 0.99 bb8a 4 792.00 792.94 0.94 0.88 0.94 bb8a 5 792.00 792.93 0.93 0.86 0.93 bb8a 6 792.00 792.96 0.96 0.92 0.96 bb8a 7 792.00 792.77 0.77 0.59 0.77 bb8a 8 792.00 792.71 0.71 0.50 0.71 bb8a 9 792.00 792.67 0.67 0.45 0.67 bb8a 10 792.00 792.64 0.64 0.41 0.64 bb8a 11 792.00 792.54 0.54 0.29 0.54 bb8a 12 792.00 792.51 0.51 0.26 0.51 bb8a 13 792.00 792.50 0.50 0.25 0.5 bb8a 14 792.00 792.50 0.50 0.25 0.5 bb8a 15 810.00 811.64 1.64 2.69 1.64 bb8a 16 810.00 811.47 1.47 2.16 1.47 bb8a 17 810.00 811.22 1.22 1.49 1.22 bb8a 18 809.00 810.83 1.83 3.35 1.83 bb8a 19 809.00 810.42 1.42 2.02 1.42 bb8a 20 808.00 810.04 2.04 4.16 2.04 bb8a 21 808.00 809.68 1.68 2.82 1.68 bb8a 22 808.00 809.33 1.33 1.77 1.33 bb8a 23 807.00 808.85 1.85 3.42 1.85 bb8a 24 807.00 808.54 1.54 2.37 1.54

115 Table 5 (continued) bb8a 25 807.00 808.43 1.43 2.04 1.43 bb8a 26 806.00 808.16 2.16 4.67 2.16 bb8a 27 806.00 807.11 1.11 1.23 1.11 bb8a 28 806.00 806.92 0.92 0.85 0.92 bb8a 29 805.00 806.09 1.09 1.19 1.09 bb8a 30 805.00 805.77 0.77 0.59 0.77 bb8a 31 805.00 805.69 0.69 0.48 0.69 bb8a 32 805.00 805.37 0.37 0.14 0.37 bb8a 33 805.00 805.29 0.29 0.08 0.29 bb8a 34 805.00 805.12 0.12 0.01 0.12 bb8a 35 804.00 805.01 1.01 1.02 1.01 bb8a 36 804.00 804.92 0.92 0.85 0.92 bb8a 37 804.00 804.71 0.71 0.50 0.71 bb8a 38 804.00 804.66 0.66 0.44 0.66 bb8a 39 803.00 804.55 1.55 2.40 1.55 bb8a 40 803.00 804.55 1.55 2.40 1.55 bb8a 41 803.00 804.46 1.46 2.13 1.46 bb8a 42 802.00 804.07 2.07 4.28 2.07 bb8a 43 802.00 803.87 1.87 3.50 1.87 bb8a 44 802.00 803.51 1.51 2.28 1.51 bb8a 45 802.00 803.20 1.20 1.44 1.2 bb8a 46 801.00 802.84 1.84 3.39 1.84 bb8a 47 801.00 802.49 1.49 2.22 1.49 bb8a 48 800.00 801.62 1.62 2.62 1.62 bb8a 49 799.00 801.19 2.19 4.80 2.19 bb8a 50 799.00 800.94 1.94 3.76 1.94 bb8a 51 799.00 800.29 1.29 1.66 1.29 bb8a 52 797.00 799.24 2.24 5.02 2.24

116 Table 5 (continued) bb8a 53 797.00 799.07 2.07 4.28 2.07 bb8a 54 797.00 798.75 1.75 3.06 1.75 bb8a 55 797.00 798.57 1.57 2.46 1.57 bb8a 56 797.00 798.16 1.16 1.35 1.16 bb8a 57 796.00 798.01 2.01 4.04 2.01 bb8a 58 796.00 797.35 1.35 1.82 1.35 bb8a 59 795.00 796.19 1.19 1.42 1.19 bb8a 60 794.00 795.99 1.99 3.96 1.99 unc1g 61 902.00 902.69 0.69 0.48 0.69 unc1g 62 902.00 902.85 0.85 0.72 0.85 unc1g 63 902.00 902.58 0.58 0.34 0.58 unc1g 64 902.00 902.70 0.70 0.49 0.7 unc1g 65 902.00 903.02 1.02 1.04 1.02 unc1g 66 903.00 903.62 0.62 0.38 0.62 unc1g 67 904.00 904.19 0.19 0.04 0.19 unc1g 68 905.00 905.36 0.36 0.13 0.36 unc1g 69 907.00 907.24 0.24 0.06 0.24 unc1g 70 909.00 908.49 -0.51 0.26 0.51 unc1g 71 909.00 908.85 -0.15 0.02 0.15 unc1g 72 909.00 909.01 0.01 0.00 0.01 unc1g 73 909.00 909.82 0.82 0.67 0.82 unc1g 74 912.00 912.47 0.47 0.22 0.47 unc1g 75 920.00 919.71 -0.29 0.08 0.29 unc1g 76 924.00 922.18 -1.82 3.31 1.82 unc1g 77 927.00 927.99 0.99 0.98 0.99 unc1g 78 928.00 928.10 0.10 0.01 0.1 unc1g 79 927.00 926.14 -0.86 0.74 0.86 unc1g 80 926.00 923.94 -2.06 4.24 2.06

117 Table 5 (continued) unc1g 81 928.00 927.05 -0.95 0.90 0.95 unc1i 82 878.00 877.85 -0.15 0.02 0.15 unc1i 83 884.00 880.73 -3.27 10.69 3.27 unc1i 84 882.00 878.68 -3.32 11.02 3.32 unc1i 85 880.00 878.72 -1.28 1.64 1.28 unc1i 86 879.00 880.40 1.40 1.96 1.4 unc1i 87 880.00 881.63 1.63 2.66 1.63 unc1i 88 876.00 883.31 7.31 53.44 7.31 unc1i 89 875.00 882.14 7.14 50.98 7.14 unc1i 90 875.00 879.58 4.58 20.98 4.58 unc1i 91 873.00 876.03 3.03 9.18 3.03 unc1i 92 872.00 874.96 2.96 8.76 2.96 unc1i 93 872.00 874.15 2.15 4.62 2.15 unc1i 94 872.00 874.04 2.04 4.16 2.04 unc1i 95 872.00 872.98 0.98 0.96 0.98 unc1i 96 875.00 872.46 -2.54 6.45 2.54 unc1i 97 874.00 873.40 -0.60 0.36 0.6 unc1i 98 873.00 873.95 0.95 0.90 0.95 unc1i 99 873.00 874.88 1.88 3.53 1.88 unc1i 100 871.00 875.58 4.58 20.98 4.58 unc1i 101 871.00 875.63 4.63 21.44 4.63 unc1i 102 870.00 875.64 5.64 31.81 5.64 unc1i 103 870.00 874.82 4.82 23.23 4.82 unc1i 104 870.00 873.03 3.03 9.18 3.03 unc1i 105 870.00 872.52 2.52 6.35 2.52 unc1i 106 870.00 871.53 1.53 2.34 1.53 unc1i 107 870.00 871.35 1.35 1.82 1.35 unc1i 108 871.00 870.49 -0.51 0.26 0.51

118 Table 5 (continued) unc1i 109 875.00 870.40 -4.60 21.16 4.6 unc1i 110 875.00 869.91 -5.09 25.91 5.09 unc1i 111 873.00 870.83 -2.17 4.71 2.17 unc1i 112 873.00 871.45 -1.55 2.40 1.55 unc1i 113 874.00 874.40 0.40 0.16 0.4 unc1i 114 874.00 875.66 1.66 2.76 1.66 unc1i 115 876.00 876.15 0.15 0.02 0.15 unc1i 116 876.00 876.86 0.86 0.74 0.86 unc1i 117 876.00 876.23 0.23 0.05 0.23 unc1i 118 877.00 876.05 -0.95 0.90 0.95 unc1i 119 875.00 877.76 2.76 7.62 2.76 unc1i 120 874.00 879.04 5.04 25.40 5.04 unc1i 121 873.00 879.61 6.61 43.69 6.61 unc1i 122 873.00 877.49 4.49 20.16 4.49 unc1i 123 872.00 877.60 5.60 31.36 5.6 unc1i 124 871.00 878.44 7.44 55.35 7.44 unc1i 125 871.00 878.99 7.99 63.84 7.99 unc1i 126 871.00 878.35 7.35 54.02 7.35 unc1i 127 872.00 875.58 3.58 12.82 3.58 unc1i 128 872.00 874.74 2.74 7.51 2.74 unc1i 129 873.00 872.44 -0.56 0.31 0.56 unc1i 130 873.00 871.32 -1.68 2.82 1.68 unc1i 131 872.00 871.43 -0.57 0.32 0.57 unc1i 132 872.00 871.74 -0.26 0.07 0.26 unc1i 133 871.00 872.28 1.28 1.64 1.28 unc1i 134 874.00 873.27 -0.73 0.53 0.73 unc1i 135 873.00 874.25 1.25 1.56 1.25 unc1i 136 875.00 875.62 0.62 0.38 0.62

119 Table 5 (continued) unc1i 137 875.00 872.67 -2.33 5.43 2.33 unc1i 138 875.00 871.78 -3.22 10.37 3.22 unc1i 139 876.00 871.53 -4.47 19.98 4.47 unc1i 140 875.00 869.98 -5.02 25.20 5.02 unc1i 141 874.00 869.49 -4.51 20.34 4.51 unc1i 142 875.00 868.24 -6.76 45.70 6.76 unc1i 143 874.00 870.89 -3.11 9.67 3.11 unc1i 144 874.00 872.01 -1.99 3.96 1.99 unc1i 145 873.00 870.75 -2.25 5.06 2.25 unc1i 146 870.00 890.42 20.42 416.98 20.42 unc1i 147 869.00 891.83 22.83 521.21 22.83 unc1i 148 869.00 894.23 25.23 636.55 25.23 unc1i 149 868.00 895.11 27.11 734.95 27.11 unc1i 150 868.00 897.13 29.13 848.56 29.13 unc1i 151 868.00 895.27 27.27 743.65 27.27 unc1i 152 896.00 893.26 -2.74 7.51 2.74 unc1i 153 894.00 893.21 -0.79 0.62 0.79 unc1i 154 895.00 895.82 0.82 0.67 0.82 unc1i 155 895.00 894.69 -0.31 0.10 0.31 unc1i 156 893.00 892.44 -0.56 0.31 0.56 unc1i 157 894.00 894.25 0.25 0.06 0.25 unc1i 158 892.00 892.86 0.86 0.74 0.86 unc1i 159 894.00 893.82 -0.18 0.03 0.18 unc1i 160 893.00 892.52 -0.48 0.23 0.48 unc1i 161 892.00 891.11 -0.89 0.79 0.89 unc1i 162 891.00 890.47 -0.53 0.28 0.53 unc1i 163 894.00 894.00 0.00 0.00 0 unc1i 164 895.00 895.01 0.01 0.00 0.01

120 Table 5 (continued) unc1i 165 895.00 895.47 0.47 0.22 0.47 unc1i 166 895.00 894.59 -0.41 0.17 0.41 unc1i 167 892.00 891.22 -0.78 0.61 0.78 unc1i 168 888.00 888.21 0.21 0.04 0.21 unc1i 169 892.00 891.54 -0.46 0.21 0.46 unc1i 170 891.00 891.35 0.35 0.12 0.35 unc1i 171 891.00 888.47 -2.53 6.40 2.53 unc1i 172 892.00 889.28 -2.72 7.40 2.72 unc1i 173 892.00 889.17 -2.83 8.01 2.83 unc1i 174 890.00 887.80 -2.20 4.84 2.2 unc1i 175 894.00 891.35 -2.65 7.02 2.65 unc1i 176 892.00 889.96 -2.04 4.16 2.04 unc1i 177 890.00 888.77 -1.23 1.51 1.23 unc1i 178 889.00 888.51 -0.49 0.24 0.49 unc1i 179 892.00 890.03 -1.97 3.88 1.97 unc1i 180 892.00 890.36 -1.64 2.69 1.64 unc1i 181 893.00 892.02 -0.98 0.96 0.98 unc1i 182 888.00 888.56 0.56 0.31 0.56 unc1i 183 886.00 885.98 -0.02 0.00 0.02 unc1i 184 885.00 884.92 -0.08 0.01 0.08 unc1i 185 884.00 884.07 0.07 0.00 0.07 unc1i 186 883.00 883.16 0.16 0.03 0.16 unc1i 187 882.00 882.69 0.69 0.48 0.69 unc1i 188 882.00 882.17 0.17 0.03 0.17 unc1i 189 882.00 882.10 0.10 0.01 0.1 unc1i 190 884.00 884.25 0.25 0.06 0.25 unc1i 191 885.00 886.17 1.17 1.37 1.17 unc1i 192 886.00 886.69 0.69 0.48 0.69

121 Table 5 (continued) unc1i 193 888.00 888.24 0.24 0.06 0.24 unc1i 194 887.00 887.57 0.57 0.32 0.57 unc1i 195 897.00 897.01 0.01 0.00 0.01 unc4 196 770.00 773.55 3.55 12.60 3.55 unc4 197 770.00 773.38 3.38 11.42 3.38 unc4 198 770.00 773.01 3.01 9.06 3.01 unc4 199 770.00 772.97 2.97 8.82 2.97 unc4 200 771.00 772.70 1.70 2.89 1.7 unc4 201 771.00 772.67 1.67 2.79 1.67 unc4 202 771.00 772.40 1.40 1.96 1.4 unc4 203 771.00 771.59 0.59 0.35 0.59 unc4 204 771.00 771.02 0.02 0.00 0.02 unc4 205 772.00 770.91 -1.09 1.19 1.09 unc4 206 773.00 770.16 -2.84 8.07 2.84 unc4 207 773.00 769.41 -3.59 12.89 3.59 unc4 208 774.00 768.65 -5.35 28.62 5.35 unc4 209 774.00 768.13 -5.87 34.46 5.87 unc4 210 774.00 768.20 -5.80 33.64 5.8 unc4 211 775.00 768.23 -6.77 45.83 6.77 unc4 212 776.00 767.94 -8.06 64.96 8.06 unc4 213 777.00 768.65 -8.35 69.72 8.35 unc17 214 711.00 712.22 1.22 1.49 1.22 unc17 215 710.00 712.32 2.32 5.38 2.32 unc17 216 710.00 712.35 2.35 5.52 2.35 unc17 217 711.00 712.47 1.47 2.16 1.47 unc17 218 712.00 712.83 0.83 0.69 0.83 unc17 219 713.00 713.16 0.16 0.03 0.16 unc17 220 715.00 713.87 -1.13 1.28 1.13

122 Table 5 (continued) unc17 221 717.00 714.91 -2.09 4.37 2.09 unc17 222 717.00 715.21 -1.79 3.20 1.79 unc17 223 719.00 716.10 -2.90 8.41 2.9 unc17 224 719.00 716.41 -2.59 6.71 2.59 unc17 225 719.00 716.68 -2.32 5.38 2.32 unc17 226 720.00 718.05 -1.95 3.80 1.95 unc17 227 720.00 718.20 -1.80 3.24 1.8 unc17 228 720.00 718.55 -1.45 2.10 1.45 unc17 229 720.00 718.88 -1.12 1.25 1.12 unc17 230 720.00 719.51 -0.49 0.24 0.49 unc17 231 720.00 719.72 -0.28 0.08 0.28 unc17 232 720.00 719.84 -0.16 0.03 0.16 unc17 233 721.00 718.28 -2.72 7.40 2.72 unc17 234 722.00 718.89 -3.11 9.67 3.11 unc17 235 723.00 719.68 -3.32 11.02 3.32 unc17 236 724.00 720.90 -3.10 9.61 3.1 unc17 237 725.00 721.73 -3.27 10.69 3.27 unc17 238 726.00 722.04 -3.96 15.68 3.96 unc17 239 726.00 722.78 -3.22 10.37 3.22 unc17 240 726.00 722.99 -3.01 9.06 3.01 unc17 241 728.00 723.62 -4.38 19.18 4.38 unc17 242 729.00 723.99 -5.01 25.10 5.01 unc17 243 730.00 724.57 -5.43 29.48 5.43 unc17 244 731.00 725.38 -5.62 31.58 5.62 unc17 245 731.00 725.50 -5.50 30.25 5.5 unc17 246 732.00 726.35 -5.65 31.92 5.65 unc17 247 732.00 725.88 -6.12 37.45 6.12 unc17 248 732.00 726.02 -5.98 35.76 5.98

123 Table 5 (continued) unc17 249 732.00 725.93 -6.07 36.84 6.07 unc17 250 732.00 725.79 -6.21 38.56 6.21 unc17 251 732.00 725.21 -6.79 46.10 6.79 unc17 252 732.00 724.82 -7.18 51.55 7.18 unc17 253 732.00 724.74 -7.26 52.71 7.26 unc17 254 732.00 725.08 -6.92 47.89 6.92 unc17 255 731.00 725.42 -5.58 31.14 5.58 unc17 256 730.00 726.38 -3.62 13.10 3.62 unc17 257 728.00 726.64 -1.36 1.85 1.36 unc17 258 728.00 726.79 -1.21 1.46 1.21 unc17 259 726.00 725.27 -0.73 0.53 0.73 unc17 260 725.00 723.87 -1.13 1.28 1.13 unc17 261 724.00 722.92 -1.08 1.17 1.08 unc17 262 723.00 721.32 -1.68 2.82 1.68 unc17 263 723.00 719.95 -3.05 9.30 3.05 unc17 264 722.00 718.29 -3.71 13.76 3.71 unc17 265 721.00 717.06 -3.94 15.52 3.94 unc17 266 720.00 715.46 -4.54 20.61 4.54 unc17 267 719.00 714.66 -4.34 18.84 4.34 unc17 268 720.00 714.42 -5.58 31.14 5.58 sum 712.82 average 2.66

RMSEz 1.63

124 APPENDICES

Appendix A: Geologic map key and general descriptions from Maxwell et al. (1967) for Figure 8 B and D.

125

Appendix B: Geologic map key and general descriptions from Henry et al. (1996) for Figure 9B.

126 CURRICULUM VITA

Son of Stevan and Maryjane Benker, Stevan Christian Benker resided, and attended his

early years of education, in the state of Massachusetts. Beginning in the earliest days of his

education he excelled in science because the workings of everyday life peaked his interest.

During his studies at Bridgewater State College his original intention was to become a forest ranger under the United States Forest Service; however, after participating in several earth science courses a decision was made to pursue a graduate degree in geologic science. Soon after completion of his undergraduate degree he was accepted into graduate studies at Eastern

Kentucky University in Richmond, Kentucky. It was here where geologic studies on the Big

Bend area of Texas began. Upon completion of his Masters degree he was accepted into the doctoral program at the University of Texas, El Paso where he would continue his studies in the

Big Bend area of Texas, more specifically focusing on timing of magmatism likely associated with onset of the southern Rio Grande and GIS-based three-dimensional modeling of rock units and their application in better understanding features created during the Laramide Orogeny.

127