AfricaArray Geophysical Field School – Day 1, Vredefort Dome

I am currently attending the AfricaArray field school, hosted by [http://wits.ac.za](Wits University). The first day was a relaxed one to allow for the international students to recover from jetlag. Accordingly, we wandered off to visit the Vredefort Dome.

This is one of the largest, and the oldest impact structures in the world, so we are very lucky that we can wander around it. It is also a UNESCO world heritage site. This is a world famous site and it was good to get an over view of the area.

We started by getting an overview of the area, and the basic geology.
Lew Ashford explains the general geology.

Sue going over the area.

Some of the most significant evidence is the presence of pseudotachylite within the basement granites of the Witwatersrand Basin. These formed under frictional melting due to the impact causing nearby rocks to move extremely rapidly. These are spectacularly exposed in some of the quarries in the area:
Pseudotachylite breccia

Pseudotachylite in an abandoned quarry.

These quarries are abandoned now, since the current fashion is for the use of very fine-grained, black facing stone, rather than textured rock.

After that, we stopped next to the Vaal River for lunch, which was pretty idyllic. The work did not stop, since we worked out that the quartzite rocks we were sitting on were slightly overturned. Heading further up the sequence, we found a metamorphosed shale.
Lunch at the Vaal River.

Investigating the metapelite.

Following lunch we went off to hunt shattercones. These are conical features which are caused by a shockwave moving through the rock, which only happens in fine-grained rocks. So shattercones are only found in shales and marbles, not the coarser granites.

A shattercone.

We then wandered our way back to Wits, where some entertainment was found, at least by some of us.

Playing chess.

Uno game in progress.

Tomorrow we start with more serious work, which I am looking forward to. Probably not many photos though, since it will be mostly theory.

There are a few more photos available on Facebook, if people want to see them. This album will be updated as the trip goes on.