PALEOZOIC BURIAL AND EXHUMATION OF THE AMARILLO-WICHITA UPLIFT: INSIGHTS FROM ZIRCON (U-TH)/HE THERMOCHRONOLOGY

The Amarillo-Wichita Uplift of northern Texas and southern Oklahoma is the easternmost major uplift in the Pennsylvanian-Permian Ancestral Rocky Mountains (ARM) system. Key evidence for the timing of uplift comes from the adjacent Anadarko Basin, which is the deepest basin on the North American craton and preserves a record of accelerated subsidence and accumulation of sediment shed from the rising block beginning at ~325 Ma. Here, we present an independent and complementary record of ARM tectonism, utilizing the zircon (U-Th)/He system to reconstruct the thermal history of basement rocks exposed in the uplift. Crystalline rocks of the Wichita Igneous province include rhyolites and sheet granites emplaced in the uppermost 1.5 km of the crust during rifting in the Cambrian (530-539 Ma). These rocks were buried during early to middle Paleozoic subsidence before experiencing exhumation during ARM tectonism.

Igneous grains with a large variation in effective uranium concentrations yield zircon (U-Th)/He dates that range from 46 to 499 Ma, indicating a variable degree of resetting as the rocks passed through the zircon (U-Th)/He partial retention zone (~125-175°C). We explore the range of thermal histories compatible with these data by creating both forward and inverse models using the software HeFTy. Initial analyses reveal thermal histories consistent with geologic constraints, including slow heating to 160-170°C by ~325-310 Ma followed by rapid cooling to near-surface temperatures at rates of 5-10°C/Ma. These data also provide information about subsequent reheating during post-ARM burial. Modeled time-temperature paths suggest temperatures reached 80-100°C by 100 Ma before Cenozoic exhumation.