A DEPLETED, DESTABILIZED CONTINENTAL LITHOSPHERE NEAR THE RIO GRANDE RIFT

Abstract

Seismic waveform diffraction patterns reveal a 120 km thick slab-like anomaly with about 4% increases in both compressional and shear wave speed, extending down to nearly 600 km between the Rio Grande Rift and the western Great Plains in the southwestern United States. Monte Carlo simulations suggest that the most probable interpretation is a temperature anomaly of about - 400 K with additions of olivine (11%), orthopyroxene (12%) and losses of clinopyroxene (- 14%), garnet (- 9%) relative to the adjoining mantle asthenosphere beneath the Rio Grande Rift. This sesimic anomaly, probably continental lithosphere, is cold and is as depleted as the Archean continental lithosphere. It was likely formed in the Proterozoic age but destabilized during the Cenozoic rifting of the Rio Grande Rift. © 2007 Elsevier B.V. All rights reserved.