THERMAL HISTORY OF THE TISHOMINGO GRANITE AT TEN ACRE ROCK, SOUTHERN OKLAHOMA

The thermal history of Ten Acre Rock, southern Oklahoma was determined with multiple thermochronometers and thermal modeling in order to determine the cooling history of basement rocks on the flank of the Arbuckle Mountains. The Tishomingo anticline exposes Precambrian rocks of the Oklahoma aulocogen that are nonconformably overlain by the Cambrian Reagan Fm. and other Paleozoic sedimentary rocks. Titanite, zircon, and apatite (U-Th)/He dating (THe, ZHe, AHe) was conducted on the Tishomingo Granite (1364 ± 2 Ma) (Thomas et al., 2012) at the Capital quarry site. Titanite (U-Th)/He dating using interior shards (n=4) yielded a mean THe age of 605.8 ± 105.5 Ma. Mean zircon and apatite (U-Th)/He ages are 456.4 ± 13.0 Ma (n=4) and 188.2 ± 48.8 Ma (n=6), respectively. Titanite and zircon ages show no correlation between (U-Th)/He age and the effective uranium concentration [eU], whereas AHe ages are strongly correlated with eU. Inverse thermal modeling of (U-Th)/He ages conducted with HeFTy provides a thermal history of Ten Acre Rock. Thermo-geochronologic ages, along with their respective closure temperatures (Tc), and sedimentary relationships constrain basement cooling for the inverse thermal model. Cambrian deposition of the Reagan sandstone and Cretaceous sedimentary onlap indicate surface temperatures during these respective periods. Titanite (U-Th)/He ages likely represent pre-rift basement cooling. Deposition of the Reagan Fm. indicates surface conditions followed by reburial sufficient to completely reset ZHe ages by ~456 ± 13 Ma. Large deviations in THe ages may be the result of partial resetting during burial. The large spread in aliquot ages and [eU] correlation are both expected results of long residence times in the PRZ. (U-Th)/He data constrains burial to at least ZHe Tc (~180° C) but not deep enough to fully reset titanite (Tc ~210° C). Assuming a geothermal gradient of 20-30° C/km and a max temperature of 200° C, a maximum burial depth of ~6-10 km is interpreted for Ten Acre Rock. This study provides new exhumation constraints for rocks on the northern flank of the Oklahoma aulocogen, adjacent to the southern Washita Valley fault (WVF).