Crust and mantle structure across the Basin and Range-Colorado Plateau boundary at 37{degrees}N latitude and implications for Cenozoic extensional mechanism

Journal Article · Sat Jun 10 04:00:00 EDT 1995 · Journal of Geophysical Research

DOI:https://doi.org/10.1029/94JB03063· OSTI ID:245149

Zandt, G; Myers, S C; Wallace, T C ^[1]

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1. Univ. of Arizona, Tucson, AZ (United States)

The authors present new evidence on the seismic velocity and density of the crust and upper mantle along a 200-km-long transect across the eastern Basin and Range and western Colorado Plateau at 37{degrees}N latitude. Receiver functions computed from the P waveforms recorded with 10 portable broadband stations deployed along the transect were used to estimate crustal thickness variations. The timing of crustal multiples within the receiver functions were used to estimate the V{sub p}/V{sub s} of the crust along the profile, and the authors found that the western Colorado Plateau crust is characterized by a high Poisson`s ratio (0.28-0.29) indicative of a crust with an average mafic composition. They estimated the upper mantle lid thickness along their profile based on teleseismic P wave travel times and constraints provided by gravity data. This data and available geophysical constraints are most consistent with a lithosphere that thickens from an average thickness of 60 km beneath the Basin and Range to 100 km beneath the western Colorado Plateau, although the Basin and Range lithosphere may have significant thickness variations. The thick, strong mafic crust and thicker mantle lid under the Colorado Plateau can account for the relative geologic stability and subdued magmatism of the plateau during Laramide compression and Cenozoic extension compared to surrounding regions. The crustal and lithospheric thinning across the tectonic boundary occurs over a short distance ({approximately} 100 km), suggesting it is a geologically young feature produced by a predominantly mechanical response to late Cenozoic extension. The authors new lithosphere model at 37{degrees}N latitude is consistent with the existence, in early Cenozoic time, of a flat subducted slab at 100 km depth and a relict Sevier-Laramide 50-60 km thick crustal welt, and 60-100% pure shear extension ({beta} values of 1.6-2.0) during the late Cenozoic. 87 refs., 10 figs., 7 tabs.

• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 245149
• Journal Information: Journal of Geophysical Research, Journal Name: Journal of Geophysical Research Journal Issue: B6 Vol. 100; ISSN JGREA2; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
COLORADO PLATEAU
DENSITY
EARTH CRUST
EARTH MANTLE
SEISMIC P WAVES
THICKNESS
VARIATIONS
VELOCITY