This project involves multidisciplinary (seismic, magnetotelluric) transects along and across the Sierra Nevada in order to examine the crust and upper mantle beneath these mountains. The principal investigators hope to resolve the cause of uplift of the Sierra Nevada and its relation to the adjoining Death Valley extensional province and the southern San Joaquin basin. Currently, two end-member models for uplift of the range have been presented. These are: (a) isostatic compensation of a deep crustal root and (b) upwelling of the asthenosphere associated with extension to the east. These two models have fundamentally different consequences for the dynamic behavior of the continents, particularly in the manner in which crustal sections are either (a) underplated by materials from the upper mantle or (b) weakened and extruded to fill in extensional voids. In addition to the uplift and related extension of comparable mountain ranges worldwide, examples of globally significant features that will be better understood by resolution of the Sierran root question include: factors controlling the manner in which sialic basement nappes detach; how collision zones collapse under their own burden; and how intracontinental transform faults partition strain to and beyond the Moho.
