Contrasting lithospheric structure between the Colorado Plateau and Great Basin: Initial results from Colorado Plateau ‐ Great Basin PASSCAL Experiment

Sheehan, A. F.; Jones, Craig H.; Savage, M. K.; Ozalaybey, Serder; Schneider, Jeffrey M.

doi:10.1029/97gl02782

Cited by 32 publications

(28 citation statements)

References 25 publications

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“…McQuarrie and Chase (2000) argued that the present crustal thickness of the Colorado Plateau (42 ± 5 km; Sheehan et al, 1997) is too thick for the plateau to have been at sea level in the Late Cretaceous, and they noted that globally there are no areas of continental crust the breadth and thickness of the Colorado Plateau at sea level today. To explain this apparent discrepancy, McQuarrie and Chase (2000) invoked ~15 km thickening of 30-km-thick Colorado Plateau crust by Laramide mid-crustal fl ow eastward from the thickened Sevier hinterland, thus producing ~2 km of uplift in the Colorado Plateau.…”

Section: Laramidementioning

confidence: 97%

Diachronous episodes of Cenozoic erosion in southwestern North America and their relationship to surface uplift, paleoclimate, paleodrainage, and paleoaltimetry

2012

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The history of erosion of southwestern North America and its relationship to surface uplift is a long-standing topic of debate. We use geologic and thermochronometric data to reconstruct the erosion history of southwestern North America. We infer that erosion events occurred mostly in response to surface uplift by contemporaneous tectonism, and were not long-delayed responses to surface uplift caused by later climate change or drainage reorganization. Rock uplift in response to isostatic compensation of exhumation occurred during each erosion event, but has been quantifi ed only for parts of the late Miocene-Holocene erosion episode. We recognize four episodes of erosion and associated tectonic uplift: (1) the Laramide orogeny (ca. 75-45 Ma), during which individual uplifts were deeply eroded as a result of uplift by thrust faults, but Laramide basins and the Great Plains region remained near sea level, as shown by the lack of signifi cant Laramide exhumation in these areas; (2) late middle Eocene erosion (ca. 42-37 Ma) in Wyoming, Montana, and Colorado, which probably occurred in response to epeirogenic uplift from lithospheric rebound that followed the cessation of Laramide dynamic subsidence; (3) late Oligocene-early Miocene deep erosion (ca. 27-15 Ma) in a broad region of the southern Cordillera (including the southern Colorado Plateau, southern Great Plains, trans-Pecos Texas, and northeastern Mexico), which was uplifted in response to increased mantle buoyancy associated with major concurrent volcanism in the Sierra Madre Occidental of Mexico and in the Southern Rocky Mountains; (4) Late Miocene-Holocene erosion (ca. 6-0 Ma) in a broad area of southwestern North America, with loci of deep erosion in the western Colorado-eastern Utah region and in the western Sierra Madre Occidental. Erosion in western Colorado-eastern Utah refl ects mantle-related rock uplift as well as an important isostatic component caused by compensation of deep fl uvial erosion in the upper Colorado River drainage following its integration to the Gulf of California.Erosion in the western Sierra Madre Occidental occurred in response to rift-shoulder uplift and the proximity of oceanic base level following the late Miocene opening of the Gulf of California. We cannot estimate the amount of rock or surface uplift associated with each erosion episode, but the maximum depths of exhumation for each were broadly similar (typically ~1-3 km). Only the most recent erosion episode is temporally correlated with climate change.Paleoaltimetric studies, except for those based on leaf physiognomy, are generally compatible with the uplift chronology we propose here. Physiognomy-based paleo eleva tion data suggest that near-modern elevations were attained during the Paleogene, but are the only data that uniquely support such interpretations. High Paleogene elevations require a complex late Paleogene-Neogene uplift and subsidence history for the Front Range and western Great Plains of Colorado that is not compatible with the regional sedimentation and er...

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Section: Laramidementioning

confidence: 97%

Diachronous episodes of Cenozoic erosion in southwestern North America and their relationship to surface uplift, paleoclimate, paleodrainage, and paleoaltimetry

2012

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“…Little shear-wave splitting is observed for seismic recordings in the northern CP extending into northern Colorado, where upwelling asthenosphere and resultant vertical olivine a-axes alignment could be responsible. In the central GB, there is a circular pattern of anisotropic fast polarization direction of split SKS waves (Sheehan et al, 1997;Savage and Sheehan, 2000;Zandt and Humphreys, 2008). This pattern cannot be attributed to either preexisting lithospheric finite strain or to asthenospheric strain related to NA plate motion.…”

Section: Introductionmentioning

confidence: 85%

“…The NNE-SSW anisotropic fast axes are part of a remarkable circular pattern first noted by Sheehan et al (1997) and Savage and Sheehan (2000). Given that the GB is a region of very thin lithosphere (e.g., Wannamaker et al, 2008), underlying uppermost asthenospheric flow is likely responsible for this change.…”

Section: Discussionmentioning

confidence: 99%

“…A plume origin for GB azimuthal anisotropy was hypothesized by Savage and Sheehan (2000), but subsequent geophysical and geochemical evidence has been lacking (e.g., Zandt and Humphreys, 2008). Mantle flow around the edge of the Gorda-Juan de Fuca slab has most recently been proposed to account for the observed circular fast anisotropy pattern in the central GB (Sheehan et al, 1997;Badger et al, 2007;Zandt and Humphreys, 2008).…”

Section: Discussionmentioning

confidence: 99%

“…In the southern RGR and west Texas, a nearly north-south fast direction from split SKS phases is observed, where mantle flow may be affected by regional rift-parallel asthenospheric currents (Sandvol et al, 1992;Gok et al, 2003), asthenospheric flows between the GP and CP lithospheric roots, and/or fabric effects in the thicker lithosphere of the Great Plains. A dramatic change from the predominant northeast-trending fast directions (e.g., as measured from LR1 and LR1.5 SKS data in the central CP) to a north-south oriented fast direction in the CP-GB transition was first recognized from data recorded at both permanent and temporary CP-GB stations (Sheehan et al, 1997;Savage and Sheehan, 2000). The details of this transition have been especially densely sampled and are reported on here using LR1.5 data.…”

Section: Introductionmentioning

confidence: 99%

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Shear-Wave Splitting and Mantle Flow beneath the Colorado Plateau and Its Boundary with the Great Basin

Wang¹,

Ni²,

Aster³

et al. 2008

Bulletin of the Seismological Society of America

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Shear-wave splitting measurements from SKS and SKKS phases show fast polarization azimuths that are subparallel to North American absolute plate motion within the central Rio Grande Rift (RGR) and Colorado Plateau (CP) through to the western rim of the CP, with anisotropy beneath the CP and central RGR showing a remarkably consistent pattern with a mean fast azimuth of 40° 6°E of N. Approaching the rim from the southeast, fast anisotropic directions become northnortheast-south-southwest (NNE-SSW), rotate counter clockwise to north-south in the CP-GB transition, and then to NNW-SSE in the western Great Basin (GB). This change is coincident with uppermost mantle S-wave velocity perturbations that vary from 4% beneath the western CP and the eastern edge of the Marysvale volcanic field to about 8% beneath the GB. Corresponding delay times average 1.5 sec beneath the central CP, decrease to approximately 0.8 sec near the CP-GB transition, and increase to about 1.2 sec beneath the GB. For the central CP, we suggest anisotropy predominantly controlled by North American plate motion above the asthenosphere. The observed pattern of westward-rotating anisotropy from the western CP through the CP-GB transition may be influenced to asthenospheric flow around a CP lithospheric keel and/or by vertical flow arising from edge-driven small-scale convection. The anisotropic transition from the CP to the GB thus marks a first-order change from absolute plate motion dominated lithosphere-asthenosphere shear to a new regime controlled by regional flow processes. The NNW-SSE anisotropic fast directions of split SKS waves in the eastern GB area are part of a broad circular pattern of seismic anisotropic fast direction in the central GB that has recently been hypothesized to be due to toroidal flow around the sinking Juan de Fuca-Gorda slab.Online Material: SKS and SKKS splitting results from LA RISTRA 1.5.

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The meaning of midlithospheric discontinuities: A case study in the northern U.S. craton

Hopper

Fischer

2015

Geochem Geophys Geosyst

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Converted wave imaging has revealed significant negative velocity gradients, often termed midlithospheric discontinuities, within the thick, high‐velocity mantle beneath cratons. In this study, we investigate the origins and implications of these structures with high‐resolution imaging of mantle discontinuities beneath the Archean Wyoming, Superior and Medicine Hat, and Proterozoic Yavapai and Trans‐Hudson terranes. Sp phases from 872 temporary and permanent broadband stations, including the EarthScope Transportable Array, were migrated into three‐dimensional common conversion point stacks. Four classes of discontinuities were observed. (1) A widespread, near‐flat negative velocity gradient occurs largely at 70–90 km depth beneath both Archean and Proterozoic cratons. This structure is consistent with the top of a frozen‐in layer of volatile‐rich melt. (2) Dipping negative velocity gradients are observed between 85 and 200 km depth. The clearest examples occur at the suture zones between accreted Paleoproterozoic Yavapai arc terranes and the Wyoming and Superior cratons. These interfaces could represent remnant subducting slabs, and together with eclogite in xenoliths, indicate that subduction‐related processes likely contributed to cratonic mantle growth. (3) Sporadic positive velocity gradients exist near the base of the lithospheric mantle, perhaps due to laterally variable compositional layering. (4) In contrast to off‐craton regions, clear Sp phases are typically not seen at lithosphere‐asthenosphere boundary depths beneath Archean and Proterozoic terranes, consistent with a purely thermal contrast between cratonic mantle lithosphere and asthenosphere.

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Contrasting lithospheric structure between the Colorado Plateau and Great Basin: Initial results from Colorado Plateau ‐ Great Basin PASSCAL Experiment

Abstract: Abstract.The Colorado Plateau -Great Basin (CPGB) PASSCAL experiment provides broadband seismic data that allow us to determine crustal and upper mantle structure in the

Cited by 32 publications

References 25 publications

Diachronous episodes of Cenozoic erosion in southwestern North America and their relationship to surface uplift, paleoclimate, paleodrainage, and paleoaltimetry

Diachronous episodes of Cenozoic erosion in southwestern North America and their relationship to surface uplift, paleoclimate, paleodrainage, and paleoaltimetry

Shear-Wave Splitting and Mantle Flow beneath the Colorado Plateau and Its Boundary with the Great Basin

The meaning of midlithospheric discontinuities: A case study in the northern U.S. craton

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