Thick-Structured Proterozoic Lithosphere of the Rocky Mountain Region

Abstract

the base of an imbricated Moho, directly under the Cheyenne suture. We suggest this slab was trapped against the edge of the thick, Archean-age Wyoming lithosphere after the subduction polarity flipped from south-to north-directed after and/or during accretion of the first Proterozoic arc along Wyoming's southern margin 1.78-1.75 Ga. Such a tectonic model for the evolution of the Cheyenne belt is consistent with observations along many other Archean-Proterozoic sutures worldwide. Overall, our results demonstrate that Proterozoic crustal sutures in the Rocky Mountain region extend throughout a thick chemical lithosphere and that young lithospheric melting has been focused along old suture zones. The coincidence of old deep structure and young tectonism supports the hypothesis that the lithospheric structure created during Proterozoic assembly provides a first-order control on the complex history of exhumation, deformation, sedimentation, and magmatism of this fascinating, tectonically active region.