CONSTRAINING THE PHANEROZOIC TIME-TEMPERATURE HISTORY OF THE ILLINOIS BASIN USING DETRITAL APATITE U-TH/HE THERMOCHRONOLOGY

The intracratonic Illinois Basin, in the North American continental interior, has an enigmatic thermal history. Past work has drawn upon authigenic minerals, ore deposits, and vitrinite reflectance data to support the hypothesis that the Illinois Basin was exposed to temperatures from ~90 – 140 °C between 400 – 300 Ma. This hypothesis suggests thermal modification of the Illinois Basin occurred in tandem with tectonic activity associated with Appalachian orogenesis. In contrast, a recent investigation based upon kimberlite trends and geophysical surveys suggest the North American Midcontinent traveled over a hot spot between 100 – 50 Ma. In an effort to better constrain the time-temperature history of the Illinois Basin and test if thermal modification occurred due to Paleozoic tectonics and/or late Cretaceous hot spot activity, we utilize detrital apatite U-Th/He thermochronology. The U-Th/He system in apatite has a closure temperature between 40 – 100 °C, making it an ideal thermochronometer for testing these hypotheses. U-Th/He ages of apatite sampled from a core of Cambrian Mount Simon Sandstone taken at 2.6 km confirm that the Illinois Basin was thermally modified at least once in Phanerozoic time. Preliminary inverse and forward modeling utilizing these ages suggest that thermal modification of the Illinois Basin between 100 – 50 Ma is plausible. This provides further evidence for the Midcontinent passing over a hot spot during the Late Cretaceous. Future work will investigate the spatial and along-depth variability of apatite U-Th/He ages in order to better constrain the Illinois Basin time-temperature history.