Geology of the Solitario Dome, Trans-Pecos Texas

RI0240. Geology of the Solitario Dome, Trans-Pecos Texas: Paleozoic, Mesozoic, and Cenozoic Sedimentation, Tectonism, and Magmatism. C. D. Henry and W. R. Muehlberger, Editors. 182 p., 73 figs., 2 tables, 1 appendix, 2 oversize color plates, 1996. ISSN: 0082-335X. Print.


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About This Publication
This report comprises 12 chapters that describe the structural, sedimentologic, volcanologic, petrographic, and geochronologic features of the Solitario.

ABSTRACT
The Solitario is a circular, 14- to 16-krn-diameter, mid-Tertiary laccolithic dome and caldera in southern Trans-Pecos Texas; it is among the world's largest laccoliths. Rocks ranging in age from Cambrian through Quaternary crop out in and around the dome. The oldest rocks, exposed in the core of the dome, are Cambrian through Pennsylvanian clastic, carbonate, and silicic sedimentary rocks, deposited in the ocean basin that lay south of the Paleozoic North American continent. A relatively thin sequence of Cambrian through Mississippian shale, sandstone, chert, novaculite, and limestone was deposited slowly in a passive-margin setting. Cambrian-Ordovician shale commonly contains blocks of the other rocks that are either olistoliths or highly boudinaged beds. A much thicker sequence of Upper Mississippian-Lower Pennsylvanian shale and sandstone was deposited rapidly in the Ouachita foreland basin. All these rocks were folded and thrust northwestward during late Paleozoic Ouachita-Marathon deformation. Individual folds in well-exposed areas that are held up by resistant novaculite and chert beds are asymmetric to overturned and verge northwestward. A complex, folded thrust in the eastern part of the Solitario is cut by numerous northwest-striking cross faults that parallel the direction of transport. The northern part of the Paleozoic outcrop consists mostly of poorly exposed but, where observed, intricately folded Ordovician shale.

Cretaceous sedimentary rocks were deposited over the region following a long hiatus during which the Paleozoic foldbelt eroded. The basal Cretaceous conglomerate is a terrestrial deposit (alluvial fans) that developed on a surface cut in the Paleozoic rocks. Overlying Cretaceous clastic and carbonate rocks are shallow-marine deposits that accumulated on the eastern flank of the Chihuahua trough, a deep basin related to rifting that formed the Gulf of Mexico. Alternation of massive limestone with marl or shale indicates deposition in intertidal to subtidal environments with varying contributions of fine terrigenous material.
 

The Solitario lies at the eastern edge of Laramide (early Tertiary) deformation and is superposed upon the Laramide Terlingua uplift and Fresno-Terlingua monocline. The monocline probably overlies a high-angle reverse fault in basement, and both the monocline and uplift are cut by numerous east-northeast-striking strike-slip faults. The southwestern rim of the Solitario aligns with the northern end of the northwest-striking Fresno monocline. Cretaceous rocks within the Solitario were largely flatlying before doming but show evidence of Laramide deformation, including east-northeast-striking strike-slip faults, calcite-filled veins and fractures, and tectonic stylolites.
 

During the late Eocene, the Solitario underwent a complex sequence of laccolith, sill, and dike injection; doming; ash-flow eruption; caldera collapse; and intracaldera volcanism and sedimentation. 40~r/39ag~ers demonstrate that Solitario magmatism occurred in three pulses at 36.0, 35.4, and 35.0 Ma. During the first pulse, abundant rhyolitic to trachytic sills, dikes, and small laccoliths were emplaced into both the relatively undefonned Cretaceous sequence and into the structurally complex Paleozoic rocks. The main laccolith that uplifted the dome was emplaced during the second, most voluminous pulse. The laccolith probably intruded Paleozoic rocks along the sole thrust of the Ouachita-Marathon system at a depth of 3 to 4 km. The dome is generally doubly hinged, resembling the geometry of many laccoliths worldwide. Cretaceous rocks dip15 degrees to 50 degrees radially outward in a continuous rim; however, the southwestern rim of the Solitario is substantially steeper than other sides, probably because doming was superposed upon the Laramide monocline. Cretaceous rocks flatten away from the dome along a concave-upward hinge. Steep dips were maintained well into the interior of the dome; probably only an area 2 to 3 krn wide in the center of the dome was flat. Radial faults and fractures developed over the dome as it rose, commonly reactivating east-northeast-striking Laramide faults. Quartz-phyric dikes intruded along these fractures on the north and west flanks of the dome. Ash-flow eruption along faults over the roof led to collapse of a 6- x 2-km, north-trending caldera over the south and central parts of the dome. Collapse was greater in the southern part of the caldera, where ponded ash-flow tuff buries older rocks, than in the northern part, where exposed Paleozoic and Cretaceous rocks dip steeply southward. 40Ar/39Ar ages averaging 35.4 Ma on the quartz-phyric, radial dikes and the ash-flow tuff probably indicate the age of the laccolith and doming. The caldera was filled by a complex sequence of debris-flow and debris-avalanche deposits, megabreccia blocks as much as 200 m in diameter, trachyte lava, and small-volume ash-flow tuff. Late subsidence within the caldera produced a north-striking syncline. The final pulse, at 35.0 Ma, consisted of several small laccoliths or stocks and numerous dikes in caldera fill and along the ring fracture.
 

The Solitario is nearly surrounded by Tertiary volcanic, volcaniclastic, and intrusive rocks that are representative of magmatism in Trans-Pecos Texas. These rocks erupted from numerous local and distant sources between 47 and at least 24 Ma ago. Most postdate 36- to 35-Ma Solitario magmatism, but a group of peralkaline rhyolite lava domes erupted north and west of the Solitario 35.4 Ma ago, contemporaneous with the main pulse of magmatism in the Solitario. A thick, coarse conglomerate shed from the Solitario dome is interbedded with the volcanic and volcaniclastic rocks. Igneous rocks emplaced before about 30 Ma ago are part of a subduction-related volcanic arc related to convergence off the west coast of North America. Igneous rocks emplaced after that time are related to Basin and Range extension, including distinctive alkali basalts emplaced contemporaneously with initial faulting about 25 Ma ago. The Solitario lies in the eastern part of the Basin and Range province. It occupies a relatively unfaulted block surrounded by Basin and Range normal and strike-slip faults.

 

Keywords:  ash-flow tuff, basin and range, Bee Mountain Basalt, Big Bend, Black Mesa, Bofecillos Mountains, Boquillas Formation, Buda Limestone, Caballos Novaculite, caldera, Chisos, Cretaceous, Dagger Flat Sandstone, Del Carmen Limestone, Del Rio Clay, dike, dome, foldbelt, Fort Peña Formation, Fresno Formation, Glen Rose Limestone, K-Ar, karst, laccolith, Laramide, magmatism, Marathon Formation, Maravillas Formation, Mitchell Mesa Rhyolite, monocline, Mule Ear Spring Tuff, novaculite, ore deposits, Ouachita, Paleozoic, Pen Formation, Rawls Formation, rhyolite, Santa Elena Limestone, shutup, sill, Solitario, Sue Peaks Formation, Tascotal Formation, Terlingua uplift, Tertiary, Tesnus Formation, trachyte, Trans-Pecos Texas, Tule Mountain Trachyandesite, Woods Hollow, Yucca Formation

CONTENTS

Abstract

Introduction

Regional Setting

Geomorphology

Previous Work

Access

Paleozoic Stratigraphy, by William R. Muehlberger and Christopher D. Henry

     Introduction and Regional Setting

     Dagger Flat Sandstone

     Marathon Formation

          White Shale Member (Informal)

          Undifferentiated Marathon Formation

          Rodrigues Tank Sandstone Member

          Complexities of the Marathon Formation

    Fort Peña Formation

    Woods Hollow Shale

    Maravillas Formation

    Caballos Novaculite

    Tesnus Formation

Paleozoic Structure, by William R. Muehlberger

Regional Setting

Tesnus Homocline

Righthand Shutup Folded Area

Northern Folded Area

Tres Papalotes Folded Area

Structure North of the Solitario Fault

Solitario Fault

Structure of the Marathon Formation

Cretaceous Stratigraphy, by C. Larry McCormick, Charles I. Smith. and Christopher D. Henry

Introduction and Regional Setting

Lower Cretaceous Rocks

Shutup Conglomerate

Correlation and Terminology

Description, Interpretation, and Age

Yucca Formation

Correlation and Terminology

Description, Interpretation, and Age

Glen Rose Limestone

Correlation and Terminology

Description, Interpretation, and Age

Del Carmen Limestone

Correlation and Terminology Description, Interpretation, and Age

Sue Peaks Formation

Correlation and Terminology

Description, Interpretation, and Age

Santa Elena Limestone

Correlation and Terminology

Description, Interpretation, and Age

Upper Cretaceous Rocks

Del Rio Clay

Buda Limestone

Boquillas Formation

Pen Formation

Laramide Deformation of the Solitario Area, by Richard J. Erdlac, Jr.

Regional Setting of Laramide Deformation

The Terlingua Uplift

Laramide Structures on the Southern Part of the Terlingua Uplift

Folds

Thrust and Contraction Faults

Northeast-Striking Fault Systems

Tectonic Stylolites

Laramide Structures in the Solitario

Northeast-Striking Faults

Veins and Fractures

Tectonic Stylolites

Timing and Origin of the Terlingua Uplift

Age of Uplift

Origin of Uplift

Summary

Igneous Geology of the Solitario, by Christopher D. Henry

Predoming Magmatism

Rim Sills and Related Volcanic Rocks

Intrusions (Tirl, Tir2, Titl)

Volcanic Equivalents (Tvrl, Tvrlt, Tvr2)

Central Intrusions

Porphyritic Syenite (Tis)

Rhyolite Breccia (Tirx)

Rhyolite (Tir3) and Intrusive Breccia (Tir3x) of Needle Peak

Intrusions Contemporaneous with Doming

Quartz-Phyric Rhyolite Dikes (Tir4)

Breccia Dikes (Tbd)

Caldera-Fill Ash-Flow Tuff, Debris Deposits (Breccia), and Lava

Tx 1

Ash-Flow Tuff of the Solitario (Tas)

Ash-Flow Tuff Vent (Tasv)

Tx2

Tvt

Tx6

Overall Sequence

The Solitario Laccolith

Late Intrusions

Biotite Quartz Trachyte (Tiq)

Porphyritic Trachyte Dome (Tit2)

Porphyritic Rhyolite (Tir5)

Trachyte(?) (Tit3)

Coarsely Porphyritic Rhyolite (Tir6)

Late(?) Basalt (Tib)

Tertiary Volcanic, Volcaniclastic, and Intrusive Rocks Adjacent to the Solitario, by Christopher D. Henry and Linda L. Davis

Introduction

Jeff Conglomerate (Tj)

Chisos Group

Regional Stratigraphy

Alamo Creek Basalt (Tcac) Sedimentary Strata of the Undifferentiated Chisos Group (Tc)

Bee Mountain Basalt (Tcbm)

Mule Ear Spring Tuff (Tcm)

Tule Mountain Trachyandesite (Tctm)

Devils Graveyard Formation (Tdg)

Solitario Conglomerate (Tsg and Tsl)

Terneros Creek Rhyolite

Mitchell Mesa Rhyolite (Tmm)

Fresno and Tascotal Formations (Tf and Tta)

Regional Stratigraphy

Fresno Formation (Tfr, Tft, Tftp, Tf)

Tascotal Formation (Tta)

Rawls Formation (Tr)

Regional Stratigraphy

Tuff of Fresno Canyon (Trla) of the Leyva Canyon Member

Basalt and Porphyritic Basalt (Trsb and Trsbp) of the Sauceda Lavas Member

Rancho Viejo Tuff (Trr)

Basalt and Trachyte Lavas (Trab and Trat) of the Alazan Lavas Member

Closed Canyon Formation and Related Dikes (Tmb, Tms, and Tim)

Intrusive Rocks

Rhyolite (Tir) of Contrabando Dome

Peralkaline Quartz Trachyte of Solitario Peak (Tiqt)

Syenogabbro or Hawaiite (Tig)

Trachyandesite (Tita)

Black Mesa Dome and Intrusion, by Christopher D. Henry and Richard J. Erdlac, Jr.

Geochronology of the Solitario and Adjacent Volcanic Rocks, by Christopher D. Henry and Michael J. Kunk

Introduction

Previous Work

Samples

Methodology

40Ar/39Ar and K-Ar Data and General Interpretation

Timing of Magmatism

47-Ma Alamo Creek Basalt

36- to 35-Ma Solitario

35.4.-Ma Terneros Creek Rhyolite

34- to 33-Ma Late Chisos Volcanism

Approximately 33- to 31- Ma Fresno Lavas

27.3. to 27.1 -Ma Rawls Volcanism

25- to 24-Ma Basalts of the Closed Canyon Formation

Comparison of 40Ar/39Ar and K-Ar Ages

Structure of the Solitario Dome and Caldera, by Christopher D. Henry and William R. Muehlberger

Structure of the Dome Cretaceous Rim

Central Basin

Amplitude of the Dome

Volume of the Main Laccolith

Amount of Extension over the Dome

Faults Related to Doming

Discussion

Depth and Horizon of Emplacement of the Main Laccolith

Structure of the Solitario Caldera

Geometry of the Caldera

The Collapse Block

Late Subsidence

Gravity and Aeromagnetic Data

Discussion

Basin and Range Fault System, by Christopher D. Henry and Richard J. Erdlac, Jr.

Basin and Range Extensional Province of Western North America

Basin and Range Faulting of the Solitario-Bofecillos Block

Redford-Lajitas Fault Zone and Tascotal Mesa Fault in This Map Area

North-Northwest-Striking Normal Faults of the Terlingua Uplift Southeast of the Solitario

Origin of the Solitario-Bofecillos Block

Amount of Extension and Possible Quaternary Faulting

Solution-Collapse Features, by Christopher D. Henry

Economic Geology, by Christopher D. Henry

Base and Precious Metals in the Solitario

Molybdenum

Ag-Pb-Zn-Cu-Au Vein: The "Gold Mine"

Ag-Pb-Zn-Mn Vein: The "Manganese Mine"

Manganese Deposits in the Caballos Novaculite

Uranium and Copper(?) Prospect

Mercury Mineralization of the Terlingua District

Fresno and Whitroy Mines

Contrabando Dome

Pickens Oil (La Escondida) Prospect

Other Prospects

Areas of Silicification

Fluorspar

Synthesis and Directions for Further Research, by Christopher D. Henry, William R. Muehlberger, C. Larry McCormick, Richard J. Erdlac, Jr., Michael J. Kunk, Linda L. Davis, and Charles I. Smith

Precambrian North American Craton

Paleozoic Sedimentation

Paleozoic Deformation

Mesozoic Erosion, Rifting, and Marine Deposition

Laramide Deformation

Tertiary Magmatism

Pre-Solitario Activity

The Solitario

Terneros Creek Rhyolite

Black Mesa

Post-Solitario Activity

Basin and Range Faulting

Acknowledgments

References

Appendix

Figures

1. Location of the Solitario map area and the Big Bend Ranch State Park

2. Satellite image of the Solitario and adjacent parts of the Big Bend region

3, Oblique aerial view of the Solitario. looking northeastward across the dome

4. The Solitario, near the junction of six major tectonic provinces

5. Diagram of major geomorphic elements of the Solitario map area

6. Previous geologic maps that cover parts of the Solitario map area

7. Stratigraphy of Paleozoic rocks exposed in the Solitario

8. Regional setting and distribution of Ouachita-facies Paleozoic rocks, Ouachita-Marathon orogen, in Texas and adjacent areas

9. Geologic map between McGuirks Tanks and High Tank

10. View southwest across the Tesnus homocline and Lower Shutup to rim of Solitario

11. View southwest across the Tesnus homocline to Fresno Peak. capped by Del Carmen Limestone

12. View west in an approximate down-plunge view of the Maravillas-Caballos folds and thrust in the Righthand Shutup Folded Area

13. View north at syncline in lower Tesnus Formation about 300 m south-southwest of Tres Papalotes

14. View south to Lion Mountain

15. Recumbent fold hinges in limestone blocks encased in shale of the Marathon Formation

16. Shale-rich Marathon Formation with boudins of thin limestone beds

17. Black chert showing domino block tilting of Marathon Formation

18. View east at blue-gray limestone showing thrust(?) truncation dipping south

19. Late Paleozoic tectonic elements and early Mesozoic paleogeography

20. Early Cretaceous tectonic elements and paleogeography

21. Correlation chart of Lower Cretaceous formations, southern Trans-Pecos Texas

22. Shutup Conglomerate near entrance to Lefthand Shutup

23. Two massive limestones at the base of the Del Carmen Limestone in the northern rim of the Solitario

24. Small biohermal masses in Del Carmen Limestone in north wall of Lefthand Shutup

25. Middle part of Santa Elena Limestone. Lefthand Shutup

26. Outer edge of the western rim of the Solitario

27. Contact between thick, bedded, nodular Buda Limestone and overlying, thin-bedded Boquillas Formation

28. Laramide faults and folds within Trans-Pecos Texas and northeastern Mexico

29. Tectonic map of the western part of the Terlingua uplift

30. East along the Terlingua monocline

31. Westward along the Lowes Valley fault zone from the northwest flank of Black Mesa

32. Schematic diagram of the intersection of the Lowes Valley fault zone and the Fresno monocline

33. Histogram of tectonic stylolite teeth trends measured within the Cretaceous strata on the Terlingua uplift and in the rim of the Solitario

34. Example of pure shear of calcite veins within the Lefthand Shutup

35. Three-stage model for Laramide-age development of the Terlingua-Solitario push-up block

36. Sill of porphyritic rhyolite in Shutup Conglomerate at entrance of Lefthand Shutup

37. View to east-northeast of intrusion of quartz-phyric rhyolite in Del Carmen Limestone, Righthand Shutup

38. Extremely large blocks of the caldera wall slumped into the caldera immediately following ash-flow eruption and caldera collapse

39. Densely welded ash-flow tuff of the Solitario, showing distinctive thick, dark pumice

40. Low-level aeromagnetic map of the Solitario

41. Distribution of the Mule Ear Spring Tuff

42. Ash-flow tuff vent in the ridge of Caballos Novaculite west of Tres Papalotes and 1.5 km east of the caldera

43. Outcrop of ash-flow tuff vent

44. Coarse debris-flow deposit in unit Tx4

45. Coarse, massive debris-flow deposit in unit Tx6

46. Aeromagnetic map of southern Trans-Pecos Texas

47. Calderas and other volcanic centers of southern Trans-Pecos Texas and adjacent Chihuahua, Mexico

48. Diagrammatic stratigraphy of Tertiary rocks around the Solitario

49. Distribution of the Jeff Conglomerate in the Solitario map area

50. Jeff Conglomerate in Fresno Canyon southwest of the Solitario

51. Chisos Group in the west face of South Lajitas Mesa

52. Solitario Conglomerate north of Arroyo Segundo and west of Fresno Canyon

53. Intrusion of peralkaline quartz trachyte

54. Geologic map of the Black Mesa area southeast of the Solitario

55. Black Mesa dome southeast of the Solitario

56. Histogram of 40Ar/39Ar and K-Ar ages determined on rocks of the Solitario and volcanic rocks of the Bofecillos Mountains area; histogram of 40Ar/39Ar ages from the Solitario, Terneros Creek Rhyolite, and Black Mesa

57. Representative age spectra

58. Plot of 40Ar/39 Ar and K-Ar ages

59. View to the southeast of southwestern rim of Solitario. showing moderately steeply dipping Cretaceous rocks, mostly Glen Rose Formation

60. Southwestern part of Solitario, showing Cretaceous rocks in angular unconformity over Pennsylvanian Tesnus Formation

61. View to northeast of south rim of the Solitario, east of the Lower Shutup, showing monocline related to doming, mostly in Santa Elena Limestone

62. View to the northeast of the southwestern rim of the Solitario and the Fresno monocline where the two join

63. View southwest across the southeastern rim of the Solitario

64. Rose diagram of faults in the rim of the Solitario and along the Fresno monocline immediately south of the Solitario

65. Gravity map and profiles

66. Diagrammatic evolution of caldera collapse

67. Generalized map of Basin and Range faults, contemporaneous basalts, and basin-fill deposits of southern Trans-Pecos Texas and adjacent Chihuahua, Mexico

68. Surface of west-northwest-striking Basin and Range fault along Highway 170 approximately 4 km west of Lajitas

69. Geologic map of the Tascotal Mesa fault where it cuts 35.4-Ma Terneros Creek Rhyolite and 27.1-Ma Rawls Formation in the northern part of the map area

70. Shallow caves developed in massive Santa Elena Limestone in the western rim of the Solitario

71. Faults and folds formed during late Paleozoic Ouachita-Marathon deformation

72. Faults active during early Cenozoic Laramide deformation

73. Faults and hinges active during doming or caldera collapse

Tables

1. Revised stratigraphy of the Rawls Formation

2. ⁴⁰Ar/³⁹Ar and K-Ar data from the Solitario

Appendix Tables

A1. Fossils of the Marathon Formation

A2. Fossils in Cretaceous formations of the Solitario

A3. Petrography of Solitario igneous rocks

A4. Chemical analyses of igneous rocks, the Solitario and adjacent areas

A5. Petrographic data of Tertiary volcanic and intrusive rocks

Plates (in pocket of book)

1. Geologic map of the Solitario dome, Trans-Pecos Texas

2. Geologic cross sections of the Solitario dome, Trans-Pecos Texas

Citation
Henry, C. D., and Muehlberger, W. R., editors, 1996, Geology of the Solitario Dome, Trans-Pecos Texas: Paleozoic, Mesozoic, and Cenozoic Sedimentation, Tectonism, and Magmatism: The University of Texas at Austin, Bureau of Economic Geology, Report of Investigations No. 240, 182 p.