Montalvo-Delgado, Stephanie D.

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    Detrital shocked zircons in the Orange River, South Africa
    (2015) Montalvo-Delgado, Stephanie D.; Cavosie, Aaron J.; College of Arts and Sciences - Sciences; Santos, Hernán; Gibbon, Ryan; Department of Geology; Cruzado, Ivette
    The study of detrital shocked minerals in fluvial systems has great potential for the identification of eroded impact structures, since the impact record on Earth is incomplete. This research describes searching for Vredefort-derived detrital shocked zircons in the Orange River (South Africa) to evaluate their limits of distance traveled beyond the Vaal River. It was previously established that shocked minerals could travel 759 km in the Vaal River and be identified. Here, I show that they can travel ~2,000 km from their source and retain their diagnostic shock microstructures. Fieldwork, SEM imaging, EBSD analysis, and SHRIMP U-Pb geochronology were performed on the shocked grains to document the microstructures and age of the grains to determine their provenance from the 2.02 Ga Vredefort impact structure. Two detrital shocked zircon grains were found out of 9,136 zircon grains investigated. One shocked zircon was located at the mouth of the Orange River on the Atlantic coast, and the other was found in a sandbar ~15 km upriver from the mouth of the Orange River. The crystallization ages for the two detrital shocked zircons are ~3.1 Ga, which correlates well with previously determined ages of granitoids in the core of the Vredefort impact structure. From the results of this research it can be concluded the abundance of detrital shocked zircons decreases the further they travel from their source, which indicates that a larger quantity of zircons needs to be investigated to find shocked grains that have travelled long distances in a fluvial system. This study confirms the existence of a sedimentary record at extreme distances that could be used to look for evidence of ancient impacts, with the purpose of reconstructing the missing impact record of Earth.