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RI0262. Structure and Evolution of Upheaval Dome...

RI0262

RI0262. Structure and Evolution of Upheaval Dome: Pinched-Off Salt Diapir or Meteoritic Impact Structure?, by M.P.A. Jackson, D. D. Schultz-Ela, M. R. Hudec, I. A. Watson, and M. L. Porter. 93 p., 42 figs., 1 table, 1 appendix, 2001.  Print. To purchase this publication as a downloadable PDF, please order RI0262D.

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RI0262. Structure and Evolution of Upheaval Dome: Pinched-Off Salt Diapir or Meteoritic Impact Structure?, by M.P.A. Jackson, D. D. Schultz-Ela, M. R. Hudec, I. A. Watson, and M. L. Porter. 93 p., 42 figs., 1 table, 1 appendix, 2001. Print.

To purchase this publication as a downloadable PDF, please order RI0262D.



ABOUT THIS PUBLICATION
Upheaval Dome remains one of the most enigmatic structures in North America. Ongoing debate continues about whether the structure is a deeply eroded meteor-impact structure or a pinched-off salt dome. This report presents the case for the salt-dome hypothesis and critically evaluates the arguments on both sides of the debate.

 

ABSTRACT
Upheaval Dome (Canyonlands National Park, Utah, is an enigmatic structure previously attributed to underlying salt doming, cryptovolcanic explosion, fluid escape, or meteoritic  impact. We instead propose that an overhanging diapir of partly extrusive salt was pinched off from its stem and subsequently eroded. Many features support this inference, especially synsedimentary structures that indicate Jurassic growth of the dome over at least 20 m.y. Conversely, evidence favoring other hypotheses is sparse and equivocal.

In the rim syncline, strata were thinned by circumferentially striking, low-angle extensional faults verging both inward (toward the center of the dome) and outward. Near the dome's core, radial shortening produced constrictional bulk strain, forming an inward-verging thrust duplex and tight to isoclinal, circumferentially trending folds. Farther inward, circumferential shortening predominated: radially trending growth folds and imbricate thrusts pass inward into steep clastic dikes in the dome's core.

We infer that abortive salt glaciers spread from a passive salt stock during the Late Triassic and Early Jurassic. Later, during the Middle Jurassic, the allochthonous salt spread into a pancake-shaped glacier inferred to be 3 km in diameter. Diapiric pinch-off may have involved inward gravitational collapse of the country rocks, which intensely constricted the center of the dome. Sediments in the axial shear zone beneath the glacier steepened to near vertical. The central uplift is inferred to be the toe of the convergent gravity-spreading system.

 

Keywords: extrusive salt, meteoritic impact, necked diapir, salt diapir, syndepositional deformation, Upheaval Dome, Utah, Paradox Basin


CONTENTS
ABSTRACT

 

INTRODUCTION

 

            Hypotheses for Origin of Upheaval Dome

 

            Tectonic Setting

 

            Stratigraphic Setting

 

            Field Mapping and Methodology

 

CIRCUMFERENTIAL FOLD SYSTEM

 

SYNSEDIMENTARY STRUCTURES

 

            Syn-Chinle Deformation

 

            Syn-Wingate Deformation

 

                        Wingate Internal Diastems

 

                        Wingate Growth Folds

 

            Syn-Kayenta Deformation

 

                        Basal Kayenta Channels

 

                        Kayenta Internal Diastems and Inferred Shifting Rim Synclines

 

                        Kayenta Growth Faults

 

OUTER EXTENSIONAL SYSTEMS

 

INNER CONTRACTIONAL SYSTEMS

 

            Kayenta Fold and Thrust Belt

 

            Wingate Structures

 

            Chinle Deformation in Central Depression

 

            Central Moenkopi Constriction

 

            Dome Center and Clastic Dikes

 

COMPARISON OF EVIDENCE FOR IMPACT VERSUS PINCH-OFF

 

            Positive Evidence Compatible with Both Pinch-Off and Impact

 

                        Circularity

 

                        Central Uplift

 

                        Clastic Dikes

 

                        Crushed Quartz Grains

 

                        Inner Constrictional Zone

 

                        Outer Extensional Zone

 

                        Radial Lobes (Dog Tongues)

 

                        Underlying Salt

 

                        Gravity and Magnetic Anomalies

 

                        Contiguous Anticline

 

                        Nearby Salt Structures

 

                        Presence of Rim Syncline

 

            Positive Evidence Compatible with Pinch-Off but not with Impact

 

                        Synsedimentary Structures

 

                        Volume Imbalance. Indicating Salt Loss and Primary Thickness Changes

 

                        Multiple Episodes of Fracturing and Cementation

 

                        Presence of Steep Zones in Inner Limb of Rim Syncline

 

                        Presence of Outward-Verging Extension

 

                        Presence of Rim Monocline

 

                        Positive Evidence Compatible with Impact but not with Pinch-Off

 

                        Shatter Cones

 

                        Salt below Rim Syncline

 

            Negative Evidence Compatible with Impact and Pinch-Off

 

                        Absence of Rock Salt at the Surface

 

                        Paucity of Nearby Piercement Diapirs

 

                        Negative Evidence Compatible with Pinch-Off but not with Impact

 

                        Absence of Meteoritic Material

 

                        Absence of Melt

 

                        Paucity of Planar-Deformation Structures in Quartz

 

                        Absence of Ejecta Breccia

 

                        Absence of Shock-Metamorphic Minerals
                        Absence of In Situ Breccia

 

                        Absence of Outer Fault Terracing

 

                        Absence of Overturned Peripheral Flap

 

SUMMARY

 

SALT-TECTONIC HYPOTHESIS: A RECONSTRUCTION

 

            Initiation of Diapirism

 

            Stage 1: End Pennsylvanian

 

            Stage 2: End Chinle

 

            Stages 3and 4: End Wingate to End Kayenta

 

            Stage 5: End Navajo

 

                        Salt Extrusion

 

                        Diapir Pinch-off

 

            Stage 6: Present Day

 

CONCLUSIONS

 

ACKNOWLEDGMENTS

 

REFERENCES

 

APPENDIX 1. Volumetric Calculations

 

Figures

 

1. Location map of the northern Paradox Basin, showing Upheaval Dome, known salt structures, and Tertiary intrusions

2. Oblique air photograph, looking east up Upheaval Canyon

3. Panorama, looking generally southeast across the inner depression of Upheaval Dome

 

4. Oblique air photograph, looking approximately west across alcove D in Trail Canyon

 

5. Structure-contour map of Upheaval Dome and surroundings, showing the base of the Wingate Formation

 

6. Schematic illustrations of hypotheses supporting meteoritic impact and salt-dome pinch-off as explanations for the evolution of Upheaval Dome

 

7. Stratigraphic section near Upheaval Dome

 

8. Stratigraphy viewed from the rim monocline in an undeformed area immediately south of Upheaval Dome

 

9. Photograph illustrating our descent route down the Wingate Formation escarpment toward the inner depression

 

10. Geologic map of Upheaval Dome

 

11. Geologic maps of the central depression, showing stratigraphic units and faults and stratigraphic contacts, bedding attitudes, faults, fold axes, drainage network, and linear line of section B-B' shown in figure 13 and circular line of section C-C' shown in figure 14

 

12. Summary map of Upheaval Dome outer structures

 

13. Linear cross section of B-B' of Upheaval Dome and surroundings as inferred from surface exposures and projection from Buck Mesa well

 

14. Approximately circular cross section C-C' of the inner depression

 

15. Photograph illustrating view east from the valley that approximately follows the rim syncline on the southwest part of Upheaval Dome

 

16. Northwest-southeast cross section D-D' of Whale Rock, in the southeast part of dome, showing abrupt, anomalous steepening of Navajo dips on the inner limb of the withdrawal syncline

 

17. West-northeast cross section of panorama 9 traced from photographs of Holeman Spring alcove and adjoining exposures farther west on the south side of Upheaval Dome, photograph of similar view, and schematic reconstruction of synsedimentary deformation of Wingate Formation

 

18. Photograph illustrating northward view of radial growth folds in Lower Wingate sandstone in the northeast cliffs of the inner depression

 

19. Photograph illustrating southwestward view of a growth fault in cliff-forming Wingate Formation on the south wall of alcove A

 

20. Panoramas traced from photographs of outward-verging extensional-fault systems encircling Upheaval Dome

 

21. Photograph illustrating southwestward view across Upheaval Canyon, showing truncation surfaces of variable dip within the Kayenta Formation

22. East-west schematic restoration of intra-Kayenta geometries exposed in spurs south of Upheaval Canyon

23. Panoramas traced from photographs of inward-verging extensional-fault systems encircling Upheaval Dome

24. Oblique air photograph illustrating southwestward view of alcoves B and A

 

25. Panorama comprising three photographs along the east wall of the major valley adjacent to the syncline on the west to southwest side of Upheaval Dome

 

26. Closer view of left part of figure 25, interpreted as panorama 11 of figure 23

 

27. Photograph of outward-verging normal faults diagrammed in panorama 2 of figure 20

 

28. Photograph and west-east, wider, interpreted panorama 15 of a Kayenta thrust duplex and abrupt transition into the adjoining extensional system farther west

 

29. Geometry and inferred evolution of dog tongues

 

30. Views of dog tongues and intervening radial anticlines in southwest and west walls of inner depression

 

31. Photograph showing northward view of several circumferential. upright. tight to isoclinal folds in upper Wingate and lower Kayenta strata

 

32. Minor structures exposed in a folded thrust sheet in the southwest part of the inner depression

 

33. Photograph illustrating eastward view of radial thrusts stacking Moenkopi Formation in the western inner depression

 

34. Annotated photograph. looking north-northeast from the dome center at folds, imbricated thrust faults, and clastic dikes

 

35. Photograph, looking south at the center of Upheaval Dome

 

36. Branching of a clastic dike at its termination

 

37. Clastic dikes in the center of Upheaval Dome. showing both concordant and discordant relations with enclosing sedimentary layers

 

38. Clastic dike spires in the center of Upheaval Dome, looking northeast

 

39. Pinched-off diapir imaged by reflection seismic in the Gulf of Mexico

 

40. Microfractured quartz in White Rim clastic dikes from the core of Upheaval Dome

 

41. Air photograph of Dome 16 in the Great Kavir salt desert of Central Iran

 

42. Schematic reconstruction of the salt-tectonic evolution of Upheaval Dome

Table
1. Evidence supporting pinch-off and impact hypotheses


Citation
Jackson, M. P. A., Schultz-Ela, D. D., Hudec, M. R., Watson, I. A., and Porter, M. L., 2001, Structure and Evolution of Upheaval Dome: Pinched-Off Salt Diapir or Meteoritic Impact Structure?: The University of Texas at Austin, Bureau of Economic Geology, Report of Investigations No. 262, 93 p.