TRACE ELEMENT CONTROL ON APATITE FISSION-TRACK ANNEALING AND ITS IMPACT ON BASIN PALEOTEMPERATURE ESTIMATION

Apatite fission-track is a low-temperature thermochronometer with a commonly assumed partial annealing zone of 110 – 70 ± 10 °C making it useful for tectonic, geomorphic, and sedimentary questions. However, apatite geochemistry has been demonstrated to exert a primary control, with chlorine-rich apatites (chlorapatite) found to be far more resistive to annealing. A similar trend between apatite annealing and geochemistry has been observed in rare earth element (REE) concentration, as apatites with elevated light REEs are far more susceptible to annealing at lower partial annealing zone temperatures. Since apatites have been shown to have highly variable REE concentrations there is an opportunity to refine apatite partial annealing zone for a given rock-type or even sample.

In this study, we explore the relationship between higher light REE concentrations in apatite and greater annealing of fission-tracks by targeting sedimentary borehole samples collected from the tectonically stable Anadarko Basin, Oklahoma. We present apatite major, trace, and rare earth element data via electron microprobe and laser ablation inductively coupled mass spectrometry combined with kinetic parameters through optical microscopy measurements (i.e. etch-pit diameters and confined track lengths) from ten sedimentary rock samples at increasing depth, from 500 to 6000 meters, and temperature intervals, from 10 to 120 °C. The variable source lithologies of the Anadarko Basin provide apatites derived from metamorphic and igneous rocks. Thus, we will correlate detailed apatite geochemistry to single-grain annealing parameters such as confined track length to resolve the role of trace elements on apatite annealing. Further, precise annealing data from this study will be integrated with well-constrained stratigraphic thicknesses from the Anadarko basin to provide a revised basin paleotemperature evolution. This analysis would allow further investigations to build enhanced thermal history and exhumation/burial timing models for different geological settings.