Paleomagnetism - using fossilised magnetic compasses to track continental motion

Igneous rocks in particular can act as very good fossilised magnetic compasses, because when the volcanic magma cools, tiny magnetic mineral grains within the rock line up with the earth's magnetic field. This ancient magnetic field preserved in the igneous rock can then be measured in the lab and used to work out the latitude on the earth's surface at which the rock formed. These types of studies have enabled geologists to understand the rates and direction of continental motion throughout earth history. In our drill core from the Barberton Mountain land we are especially interested to find out at what latitudes and hence what sort of climatic zones our rocks formed in.

To investigate the paleomagnetic properties of our drill core scientists need to precisely know the orientation of the core. A special tool was used during the drilling operations to a mark a continuous line on the core, this means that even after packing, transport and handling of the rock in the lab, all of which will cause rotation of sections of the cylindrical core, we can still determine the original orientation of the core beneath the ground.

Photo: Nicola McLoughlin inspecting and marking rock core in the core shed area. Each piece of core was carefully marked with orietation lines, cutting lines and way up indicator arrows to produce a continuous jig-saw fit type puzzle between the core boxes. Photo Credit: Eugene Grosch