Project Details
Projekt
Fault zone damage and chemical reactions at depth in the San Andreas Fault Zone: A study of SAFOD drill core samples
Applicant
Dr. Christoph Janssen
Subject Area
Mineralogy, Petrology and Geochemistry
Term
from 2009 to 2014
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 116858641
The results of the first funding period, particularly the proof of several weakening and hardening mechanisms operating in the fault gouge of four SAFOD core samples (e.g. amorphous material, nano-scale pore spaces, dissolution-precipitation processes, intracrystalline plasticity) inspired a more detailed study of microstructures in order to specify the cause of mechanical weakness along the San Andreas Fault (SAF). Therefore we applied for and received four additional core samples from different depths and different distances to the fault contact. In particular, we will focus on: • The analysis of dominant microstructures in the new SAFOD samples. Based on our previous experience we will predominantly use the transmission electron microscopy (TEM). These studies have proven to be the most powerful tool for analyzing microstructures. The cutting of foils with the focused ion beam technique (FIB) allows identifying microstructures down to the nm scale without damage. • The observed microstructures will be interpreted in view of their implication for fault weakening mechanisms integrating previous results of the core samples from the first funding period. • The observed agglomeration of flocculated clay particles in previous samples calls for further detailed TEM investigations of clay minerals. • Some vein-calcites show evidence for intense intracrystalline plasticity (deformation twins and dislocation creep). We will measure dislocation and twin densities in calcite veins in the new sample set. The results will be used for stress estimations based on paleo-piezometric relationships. • First results of stable isotope analyses of vein calcites provide indications that the fluids were dominantly derived from deeper sources. We will further analyze stable isotopes with the aim to characterize the origin of fluids penetrating the fault gouge. • Mercury porosimetry and the BET gas adsorption methods will be used to measure the connected rock porosity pore volume and pore surface areas of our new samples. Porosity data will be used to roughly estimate permeability. • SAFOD microstructures will be compared to samples recently obtained from the Taiwan Chelungpu fault Drilling Project (TCDP).
DFG Programme
Infrastructure Priority Programmes
International Connection
USA
Participating Persons
Professor Dr. Georg Dresen; Professor Dr. Hans-Rudolf Wenk
