A Tibetan model for the early Tertiary Western United States

A detailed examination of the post-orogenic geological evolution of the western US Cordillera in comparison to the collisional tectonics of the Tibetan and Turkish-Iranian plateaux in the Alpine-Himalayan mountain system, suggests that overthickened continental crust in these three regions share a common tectonomagmatic history. Both the Tibetan and Turkish-Iranian plateaux have high mean elevations above sea-level (> 5 km and 2.0-2.5 km, respectively), have experienced fast uplift and widespread unroofing during the last 10-8 m.y., and are undergoing extension nearly perpendicular to the direction of plate convergence. A two-stage magmatism, characterized by widespread calc-alkaline volcanism followed and/or overlapped by bimodal (basaltic to rhyolitic) volcanism, occurs synchronously with crustal extension and thinning. In the early Tertiary western US Cordillera, an early stage of orogenic collapse was followed by the Basin and Range extension, characterized by block faulting and bimodal volcanism, starting approximately 18-16 m.y. ago, and resulted in the development of the Great Basin with a mean elevation of 1.5 km above sea-level and a crustal thickness of 30 km. Similarities in the post-orogenic paths of these three regions indicate that continental lithosphere reacts to overthickening in a consistent way through large-scale crustal remobilization and extensional collapse, regardless of the mode of orogenic build-up.