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

The paper presents 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°N latitude. The 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. The crustal and lithospheric thinning across the tectonic boundary occurs over a short distance, suggesting it is a geologically young feature produced by a predominantly mechanical response to late Cenozoic extension. The new lithosphere model 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 (β values of 1.6-2.0) during the late Cenozoic. -from Authors