Cenozoic tectonism in the central Basin and Range; magnitude, rate, and distribution of upper crustal strain

A wealth of pre-Cenozoic geologic markers across the central Basin and province, defined mainly by thrust faults developed within a miogeoclinal , makes it one of the best areas on Earth to reconstruct large-scale continental . We use this ~100,000 km^2 region, bounded by the southern Sierra Nevada the west and the Colorado Plateau on the east, to illustrate the concepts of and misalignment for regional strain markers and of strain compatibility kinematic viability in palinspastic reconstructions. The results indicate ~250 to 300 km of west-northwest motion of the Sierra away from the Plateau, accommodated both crustal thinning and north-south shortening. Tertiary intermontane basin and mineral cooling ages of deeply exhumed rocks constrain the overall of motion. Most of the westward motion occurred between 16 and 5 Ma, at near 2 cm/yr, slowing to 1 to 1.5 cm/yr in the last 5 Ma. We have quantified the of strain between vertical crustal thinning (via normal faults) and map-view strain (via conjugate strike-slip faults) by placing a grid of 10 x 10 km on a retrodeformed map of the region and measuring the increase in area of elements between the undeformed and present-day grids. This analysis yields a finite elongation of the Basin and Range at 36°N to 37°N of 3.4, oriented 73°W. Map-view area balance shows that 20 percent of this elongation is compensated ~north-south shortening, and 80 percent by crustal thinning. This yields an thinning factor for the upper crust of 2.7 between the Sierra and Plateau, with the hypothesis that Neogene deformation in the central Basin and is predominantly dextral-shear plane strain. These results, in concert with the that the southern Sierra Nevada has similar crustal thickness to the central and Range, support the hypothesis of large-scale eastward flow of Sierran deep during extension.