title: Lithospheric structure of the Rio Grande rift.
abstract: A high-resolution, regional passive seismic experiment in the Rio Grande rift region of the southwestern United States has produced new images of upper-mantle velocity structure and crust-mantle topography. Synthesizing these results with geochemical and other geophysical evidence reveals highly symmetric lower-crustal and upper-mantle lithosphere extensional deformation, suggesting a pure-shear rifting mechanism for the Rio Grande rift. Extension in the lower crust is distributed over a region four times the width of the rift's surface expression. Here we propose that the laterally distributed, pure shear extension is a combined effect of low strain rate and a regionally elevated geotherm, possibly abetted by pre-existing lithospheric structures, at the time of rift initiation. Distributed extension in the lower crust and mantle has induced less concentrated vertical mantle upwelling and less vigorous small-scale convection than would have arisen from more localized deformation. This lack of highly focused mantle upwelling may explain a deficit of rift-related volcanics in the Rio Grande rift compared to other major rift systems such as the Kenya rift.
authors.affiliation: Department of Earth and Environmental Science and Geophysical Research Center, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801, USA. davew@ees.nmt.edu
authors.forename: David
authors.initials: D
authors.lastname: Wilson
authors.forename: Richard
authors.initials: R
authors.lastname: Aster
authors.forename: Michael
authors.initials: M
authors.lastname: West
authors.forename: James
authors.initials: J
authors.lastname: Ni
authors.forename: Steve
authors.initials: S
authors.lastname: Grand
authors.forename: Wei
authors.initials: W
authors.lastname: Gao
authors.forename: W Scott
authors.initials: WS
authors.lastname: Baldridge
authors.forename: Steve
authors.initials: S
authors.lastname: Semken
authors.forename: Paresh
authors.initials: P
authors.lastname: Patel