How Laramide-Age Hydration of North American Lithosphere by the Farallon Slab Controlled Subsequent Activity in the Western United States

摘要: Starting with the Laramide orogeny and continuing through Cenozoic, U.S. Cordilleran orogen is unusual for its width, nature of uplift, style tectonic magmatic activity. We present teleseismic tomography evidence a thickness modified North America lithosphere ≥200 km beneath Colorado >100 New Mexico. Existing explanations uplift or magmatism cannot accommodate this thick. Imaged mantle structure low in seismic velocity roughly Rocky Mountains Mexico, high to east west, tectonically intact Great Plains Plateau. Structure internal low-velocity volume has NE grain suggestive influence by inherited Precambrian sutures. conclude that high-velocity upper lithosphere, lowvelocity partially molten mantle. suggest, as others have, Farallon slab was contact most western during orogeny. further suggest de-watering under increasingly cool conditions hydrated base continental causing steady regional attributed hydration-induced lithospheric melting much southern Mountains. Laramide-age ascent heated weakened which turn allowed horizontal shortening occur region thrusting Subsequent removal resulted additional unloading. It also triggered vigorous magmatism, especially where asthenosphere made relatively thin fertile what now Basin Range. This dry, depleted basaltic components, hot, buoyant, weak.