Archive for June, 2015

AfricaArray Field School – Day 3

Today started with a short lecture about the petrology and geochemistry of the Bushveld Complex. I was a bit out of my depth, since the last time I used a petrographic microscope in anger was in about 2010. Luckily the bit of prac tutoring that I did last year helped me at least remember what plagioclase and pyroxenite looked like. There are some seriously cool rocks in the BC, and it is absolutely massive. One million cubic kilometres of mafic magma, between seven and nine kilometres thick. And the age dates suggest that it emplaced and cooled within a million years or so. I mean, that is a lot of magma, in a very short space of time. This made me wonder why it never made to surface, like other large igneous provinces, such as the Deccan and Siberian Traps. Answers on a postcard (or a journal article cover), please. As a side-note, the Wits Petrology Lab is seriously cool. I think it only opened last year, and it looks like a great place to teach and learn petrology: great microscopes, an easy way for the lecturer to show specific examples of thin sections. I was slightly jealous, I will […]

Continue...

AfricaArray Field School – Day 2

This morning we got visitors’ cards, which led to a large amount of laughter, especially regarding the photos that people were having taken. Unfortunately, this took longer than planned, so we were running a bit behind for the rest of the day. After getting cards, we had a basic introduction, before some sneaky geochemists who have tagged along split off to do geochemistry stuff. The rest of us got a quick overview of the considerations that go into planning a geophysical survey, which brought back memories of Ground Africa days planning geotech investigations. We then spent the time until lunch productively by getting a short familiarisation session with the methods that we will need to use next week, in the field. Usually the fieldwork happens on the Bushveld Complex‘s eastern limb, but there are currently some concerns regarding safety, so this year we are going to be working in the Vredefort Dome, near Parys. The methods we will be playing around with include magnetic, gravity, resistivity, seismic, and electromagnetic. For my part, I am most interested in the magnetic survey, even if the ground-based nature of this survey will be quite different to my own dataset. The session today looked […]

Continue...

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. 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: 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 […]

Continue...