Abstract Title: Great Basin activity in the context of North America dynamics 
since the Laramide

Abstract Author(s):   Humphreys, Gene, University of Oregon 

Abstract: Gravitational collapse of the high-PE Great Basin is enabled by (1) 
cratonic root drag, which shields the western U.S. from ridge push-derived 
plate compression, (2) a lack of confinement of North America at southern 
Cascadia ("trench suction"), which provides space for Basin and Range extension 
to occur, and (3) thermal weakening of the Great Basin lithosphere, caused by 
post-Laramide partial melting of the fertile lithosphere west of the ~600 Ma 
hingeline ("Wasatch Line") that was hydrated by the "flat" Farallon slab before 
being withdrawn 45-20 Ma. In addition to being entrained with the Pacific Plate 
motion, the strong Sierra Nevada block is forced westward by the buoyant Great 
Basin upper mantle pushing on the Sierra Nevada mantle "keel". The Yellowstone 
hotspot, whose origin may or may not be a classical plume, initiated ~16 Ma 
beneath NE Oregon and propagated across southern Idaho, leaving buoyant mantle 
and densified crust in its wake. The NE Oregon initiation associated with the 
Columbia River Basalt eruptions is evidenced by ~2 km of post-eruption uplift 
of the Willowa Mtns in an absence of much extension and which are underlain by 
an imaged large volume of relatively high-velocity depleted mantle residuum; 
i.e., the main basalt eruptions were derived from the mantle beneath NE Oregon, 
not the north-central Nevada region. The Newberry hotspot initiated from the 
same ~16 Ma activity that preceded Yellowstone, but Newberry propagated WNW 
across what now is the southern Oregon Basin and Range.