This project aims at detailed structural examination of fault damage zone samples (cataclasite, fault breccia) combined with mineralogical and geochemical analysis of the same fault rocks taken during phase 3 drilling at SAFOD. Our study is complementary and coordinated with the research of R. Wenk (University of California) who proposed microstructural investigations of corresponding samples.

The SAFOD drill core contains a succession from undeformed host rock to fault gouges. By correlating mineralogical and geochemical fault rock variations with deformation mechanisms, we hope to establish new insights into the nature of fault rock evolution. In more detail, our observations and data from core material will be used to investigate the questions listed below:

• How to correlate the suggested change in deformation mechanisms between cataclasites and gouge layers with mineralogical and geochemical alteration processes in these fault rocks?
• What are the dominant deformation mechanisms producing the observed fault rock micro¬structures? What is the relation between fracturing and other deformation mechanisms operating in the damaged sequence?
• How is fault zone strength affected by chemical reactions and mineral transformations?
• What are the differences in timing, and mechanisms of fault sealing (veins, cement) between cataclasites and gouge samples?
• Which processes control fault healing? What are the chemical signatures of the fluids? Were the fluids derived from local or distant sources?

We aim at investigating core samples that represent different stages of faulting (e.g. fault gouge, cataclasites). The applied methods include microstructural, mineralogical and geochemical analysis using Microprobe (JEOL Hyperprobe JXA-8500F), Ion microprobe (SIMS, Cameca ims 6f), Micro-laser Raman spectrometer (Dilor XY-Triple 800), Micro X-ray fluorescence spectrometer (EAGLE III XL), X-ray microdiffractometer (D8 DISCOVER with GADDS), mass spectrometer and ICP-MS (Thermo Element 2 XR). To study deformation mechanisms at high resolution we will use optical mi¬croscopy (including cathoduliminescence microscopy), scanning and transmission electron microscope techniques (TEM/FEI TecnaiTMG2 F20 X-Twin).

Im Rahmen des SAFOD (San Andreas Fault Observatory at Depth) Projektes werden an ausgewähltem Bohrkernen Gesteinszusammensetzung und Deformationsmechanismen untersucht.

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