EBSD and the Alpine Fault

Transcript

Professor Dave Prior

Electron back scatter diffraction, in the case of quartz in the Alpine Fault zone, it enables me to measure the orientation of every crystal in a sample. So a rock which is strongly deformed will tend to have all of the crystals lined up, and the way they’re aligned tells me which way it was pulled when it was deformed in the ground and what was the temperature conditions. So by measuring those kinds of things, I can forensically extract that information from a rock which finished deforming a million years ago. We haven’t as yet applied this to the drill sample but we have hand samples from the Alpine Fault zone, and one of the things we’ve been able to establish with the electron back scatter diffraction is what the movement direction was at depth in the Alpine Fault in a way that was difficult by other means. So one of the things we’ve been able to establish quite well is that, on this fault where we know at the surface the movement is like this – so that you could draw a line on the fault and the fault plane is moving like that – that the movement at depth for the most part is exactly the same, and that’s cool because that means that we can link the deformation at depth, the squidgy deformation at depth, with the earthquake-generating deformation higher up.

Acknowledgements Professor David Prior and Allan Mitchell, University of Otago. Stills of drilling rig and the Deep Fault Drilling Project site, courtesy of The Deep Fault Drilling Project – a multinational collaboration lead by GNS Science, the University of Otago and Victoria University of Wellington with researchers from the University of Auckland, the University of Canterbury, Liverpool University and the University of Bremen in Germany. Scientists from the United States and Canada are also participating.