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Insights into the kinematic Cenozoic evolution of the Basin and Range-Colorado Plateau transition from coincident seismic refraction and reflection data

Jill McCarthy and Tom Parsons
Insights into the kinematic Cenozoic evolution of the Basin and Range-Colorado Plateau transition from coincident seismic refraction and reflection data
Geological Society of America Bulletin (June 1994) 106 (6): 747-759

Abstract

Estimates of surface extension in the southern Basin and Range province and transition into the Colorado Plateau range from a few percent to several hundred percent locally, yet the crustal thickness varies perhaps only 10 - 15 km across these provinces. Within the southern Basin and Range and the metamorphic core complex belt, extremely extended crust is directly juxtaposed against equally thick (or thinner) crust that underwent far milder extension. Unless preextension crustal thickness varied dramatically over a short distance, the crust must have maintained its thickness during extension, through mechanisms that involve crustal flow and magmatism. We employ a 300-km-long profile of seismic refraction and coincident vertical-incidence reflection data to investigate the geophysical signature of these processes from the extended southern Basin and Range province to the unextended Colorado Plateau. By integrating the seismic velocity with the pattern of reflectivity along the profile, we estimate the amounts of Tertiary magmatism and flow that have occurred. We estimate an upper bound of 8 km of mafic material intruded beneath the metamorphic core complex belt and 4 and 5 km of intruded material beneath the Transition Zone and southern Basin and Range province, respectively. We emphasize that this 8-km estimate is strictly an upper bound, and that the actual amount of magmatism was probably less (3 to 4 km). We further speculate that several kilometers of silicic rock was added to the metamorphic core complex belt via ductile flow. As suggested by numerous numerical models of crustal extension, we conclude that a mobile, felsic midcrustal layer accommodated most of this crustal flow. This ductile midcrustal layer appears to be thickest beneath the most extended terranes and thinnest beneath the less extended Transition Zone and Colorado Plateau. In contrast, the lowermost crust appears to have thinned passively in an amount that corresponds more directly to the regional surface extension.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 106
Serial Issue: 6
Title: Insights into the kinematic Cenozoic evolution of the Basin and Range-Colorado Plateau transition from coincident seismic refraction and reflection data
Affiliation: U. S. Geological Survey, Menlo Park, CA, United States
Pages: 747-759
Published: 199406
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 88
Accession Number: 1994-032692
Categories: Structural geologyApplied geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: sects., sketch maps
N31°15'00" - N37°00'00", W115°00'00" - W109°00'00"
N29°00'00" - N43°30'00", W122°00'00" - W102°30'00"
N33°40'00" - N40°30'00", W114°00'00" - W106°19'60"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 199415
Program Name: USGSOPNon-USGS publications with USGS authors
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