MELT-PRODUCTS AT THE FLYNN CREEK IMPACT STRUCTURE, TENNESSEE

During core and petrographic description of selected drill cores from Flynn Creek impact structure, Jackson County, Tennessee, silica melt particles were discovered, which occurred as rare clasts ranging from a few millimeters to 3 cm. These melt clasts are situated within breccias from both the central uplift and the crater moat. Prior to the work of Adrian et al. (2017), no melt products of any kind had previously been described at Flynn Creek. Flynn Creek melt particles are typically almost white in drill core and cut slabs, and thus are quite distinctive from the majority grey carbonate clasts and grey breccia matrix. In thin section, Flynn Creek melt clasts commonly display flow texture and some of the larger clasts have chalcedony rims. The melt clasts have an exceedingly fine groundmass that has a bimodal population of carbonate clasts. Despite the apparent isotropism of the groundmass, it is not in fact amorphous. Rather, it is minute, cryptocrystalline quartz as determined by both micro-Raman and micro-FTIR spectroscopy. We interpret this Flynn Creek melt as forming by rapid cooling, but over a time sufficiently long enough so that it did not quench to form a glass. Major and trace element geochemistry obtained via LA-ICP-MS is consistent with both quartz groundmass and high-Mg calcite clasts. The quartz is enriched in Al and Ti, both of which are consistent with high-temperature crystallization from an impact melt. Initial U-Pb concentrations are not favorable for age-dating, but we are continuing to explore samples of the melt with regard to other isotopic systems.