BASIN TO MOUNTAINS: CARBONIFEROUS INVERSION OF THE OUACHITA TROUGH, ARKANSAS AND OKLAHOMA U.S.A

The Ouachita Mountains in Oklahoma and Arkansas expose late Paleozoic, lower greenschist facies metasedimentary rocks that represent the structurally inverted remnants of a major Paleozoic deep-water sedimentary basin. Basin evolution, driven by the collision between Laurentia and a microcontinent (volcanic arc) outboard of the leading edge of the South American segment of Gondwana, is marked by several major regional-scale tectonic events. The relative timing of sediment deposition is known from stratigraphic/paleontological studies, and a small number of volcanic ash beds. Most intervening events, including timing of basin inversion and orogenic evolution, are not constrained. Thermochronology, analytical methods that yield temperature-time data, provide an age constraint of the cooling of rocks from depth. Zircon fission track and (U-Th)/He are useful thermochronometers in the more thermally mature parts of the orogen, recording the time rocks cooled through ~ 265°C to ~165°C, respectively. Published apatite and titanite fission track ages, along with bulk-mica and whole-rock ⁴⁰Ar/³⁹Ar ages, indicate greenschist rocks of the eastern metamorphic core have reset thermochronometers because of intrusive bodies emplaced during a Cretaceous event. There are no reset (Cretaceous) cooling ages in the western, less thermally overprinted, parts of the orogen.

Zircon fission track ages from surface rock samples range from 307 ± 19 Ma to 333.4 ± 39 Ma within and along the flanks of the Benton uplift, Arkansas. Eleven new zircon fission track ages range from 268.7 ± 22 Ma to 379.0 ± 32 Ma and one new apatite fission track age of 193.4 ± 19.2 Ma are along a North-South traverse in easternmost Oklahoma, extending from the Arkoma Basin to the Broken Bow uplift. These cooling ages indicate progressive cooling to the southwest and are consistent with published vitrinite reflectance values. Twenty-seven aliquots from these same rocks for (U-Th)/He dating range from 181.6 ± 14.5 Ma (reset) to 916.0 ± 73.28 Ma (partially reset). Recent (U-Th)/He results from rocks within the Arkoma Basin are similar to (U-Th)/He dates of the Broken Bow uplift. These ages are consistent with derivation of Arkoma Basin sediments from the syn-tectonic rocks of the Ouachitas without heating above the (U-Th)/He reset temperature.