Expanding Frontiers of Detrital Shocked Mineral Research

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

Meteorite impacts on Earth have caused rapid and dramatic changes in surface conditions, including rapid climate change and biological extinctions. Understanding the terrestrial impact history is thus crucial for a variety of scientific and social reasons that affect modern society, including informing policy decisions to study the hazard potential of future impacts. However, the geologic record of past impact events is fragmentary, as many craters have been removed by erosion over time. The true number of impact events Earth has experienced is underestimated based on the number of preserved craters, which makes predicting impacts in the future a challenging science. This project is focused on identifying evidence of eroded impact craters in the form of uniquely impact-deformed sand grains that collect in sedimentary environments. Sedimentary rocks throughout the geologic time scale may preserve the record of Earth's missing impacts, and thus allow a more accurate determination of the history of terrestrial impacts. Learning where to look for and how to identify this 'sedimentary record of impact' is the focus of this proposal. Detrital shocked minerals, including quartz (SiO2), monazite (CePO4), and zircon (ZrSiO4), have recently been documented in fluvial sediments eroding from the two largest impact basins on Earth, the 2.0 Gyr Vredefort Dome in South Africa and the 1.85 Gyr Sudbury impact in Canada. Shocked sand has been found in rivers >750 km downstream from the impact site. Shocked minerals have also been found in distal (>750 km) fluvial deposits in Miocene age sediments in South Africa. The shocked sand grains can be used to determine the age of the source terrane, in the age of impact, and set constraints on crater size. These findings imply that shocked minerals survive the erosion and transport process, and record structural and isotopic information about the impact event as they are dispersed to continental scales over long geologic time periods. This project will test the limit for the detection of detrital shocked minerals in diverse sedimentary environments in the geologic record in both time and space. We will search for shocked minerals eroded from Vredefort Dome impact in the Orange River basin, at distances up to ~2000 km from the crater. We will also search for shocked minerals in sediments transported during Paleozoic glaciations in southern Africa, 300 Myr ago. Other projects will further test the applicability of this approach to younger and small impact structures in North America. The results of this project will also provide insight during analysis of materials from future sample return missions to both the Moon and Mars, where heavily impacted early planetary crusts are preserved and targeted for future sampling campaigns.