Fe mineralogy of rocks from the Vredefort impact structure investigated with Mössbauer spectroscopy

Abstract

The Vredefort impact structure in South Africa is the largest and oldest remnant impact structure on Earth. Observations from above the crater reveal lower than average magnetic field intensities, but the rocks in the crater have been shown to possess much higher magnetic intensities than the regional average that varies on a centimeter scale. Various mechanisms, including the presence of single domain magnetite structures, have been proposed for this anomaly. Mössbauer spectroscopy has been applied to study the Fe-mineralogy of samples from near the centre of the Vredefort crater. Transmission Mössbauer measurements on bulk and microtomics sections of samples showed that the magnetic minerals were magnetite and hematite, and we suggest that oxidation of olivine during the impact is responsible for the magnetic properties of the rocks.