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

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Abstract
Starting with the Laramide orogeny and continuing through the Cenozoic, the U.S. Cordilleran orogen is unusual for its width, nature of uplift, and style of tectonic and magmatic activity. We present teleseismic tomography evidence for a thickness of modified North America lithosphere 100 km beneath New Mexico. Existing explanations for uplift or magmatism cannot accommodate lithosphere this thick. Imaged mantle structure is low in seismic velocity roughly beneath the Rocky Mountains of Colorado and New Mexico, and high in velocity to the east and west, beneath the tectonically intact Great Plains and Colorado Plateau. Structure internal to the low-velocity volume has a NE grain suggestive of influence by inherited Precambrian sutures. We conclude that the high-velocity upper mantle is Precambrian lithosphere, and the lowvelocity volume is partially molten Precambrian North America mantle. We suggest, as others have, that the Farallon slab was in contact with the lithosphere ...