NEOGENE TOPOGRAPHIC EVOLUTION OF THE CENTRAL BASIN AND RANGE PROVINCE

Determining the effects of crust-mantle dynamics on the topography of elevated regions is an important problem in the earth sciences. However, the topographic response of elevated regions to post-collisional changes in lithospheric structure is not well known. For example, the topographic response to crustal thinning beneath the Sierra Nevada and adjacent Basin and Range province is debated in the scientific literature, with one view holding that crustal thinning ultimately led to uplift of the mountain range during the late Cenozoic, and another view holding that crustal thinning led to topographic lowering of the range. To address this problem, we applied stable isotope paleotopographic methods to Neogene lacustrine deposits located throughout the central Basin and Range Province and adjacent regions. Authigenic mineral stable isotope records for six stratigraphic sections located throughout the central Basin and Range Province all exhibit an increasing trend in δ¹⁸O values with decreasing age since the early Miocene. This finding suggests that crustal thinning related to regional crustal extension resulted in ~1-2km of topographic lowering of the southern Sierra Nevada and central Basin and Range since the early Miocene. Furthermore, an authigenic calcite stable isotopic record from the Lake Mead area suggests the region experienced ~1.5km of surface uplift in the early Miocene, contemporaneous with regional magmatic activity.