VREDEFORT IMPACT BRECCIA (FINE POLISHED SLAB) - South Africa

VREDEFORT IMPACT BRECCIA

Two billion year old pseudotachylite breccia of Vredefort in South Africa

Located about 150 kilometres south west of Johannesburg, the Vredefort impact structure is the largest known impact structure on Earth. The crater, which has since been eroded away, was around 180–300 km across when it was formed. The impact occurred about 2 billion years ago.

A considerable amount of the crust, and indeed the meteorite itself, would have vapourised on impact. The remaining structure, the ‘Vredefort Dome’, consists of a partial ring of hills created by the rebound of deeply buried rocks below the impact site.

The Vredefort impact structure now exposes shattered pink granitic gneiss uplifted in the centre, cut by veins of a dark, glassy rock known as pseudotachylite. A pseudotachylite is a rapidly-cooled ‘impact melt’, formed as a direct result of the impact. It was probably the result of shock-melting, associated with the extremely rapid movement of faults but the precisely how it was formed is not understood.

This example is a small slab, partially polished on both sides.

Click on a picture for a larger image