Cenozoic thermal evolution of the central Sierra Nevada, California, from (UTh)/He thermochronometry

摘要: Apatite(U-Th)/He cooling ages are reported for igneous apatite samples from the central Sierra Nevada and compared to published fission track length data same mineral separates. Helium youngest at low elevations increase systematically toward higher elevations, ranging 43 84 Ma Yosemite Valley, 32 74 Kings River Canyon, 23 75 Mt. Whitney. high elevation generally concordant with corresponding ages, while lower helium substantially younger. Cooling histories inferred present laboratory derived annealing diffusion models do not match well, suggesting that either rates or miscalibrated temperatures below about 60°C geologic exposure periods. Unlike results, indicate a very geothermal gradient in during early middle Tertiary time.