Fault zone damage and chemical reactions at depth in the San Andreas Fault Zone: A study of SAFOD drill core samples

第一个资助期的结果，特别是在四个SAFOD岩心样品的断层泥中运行的几种弱化和硬化机制的证明（例如，非晶材料，纳米级孔隙空间，溶解-沉淀过程，晶内塑性）激发了对微观结构的更详细研究，以确定圣安德烈亚斯断层（SAF）机械弱点的原因。因此，我们申请并接收了4个额外的岩心样本，分别来自不同深度和距离断层触点的不同距离。我们将特别关注：•分析新的SAFOD样品中的主要微观结构。根据我们以前的经验，我们将主要使用透射电子显微镜（TEM）。这些研究已被证明是分析微观结构最有力的工具。用聚焦离子束技术（FIB）切割箔，可以在不损坏的情况下识别纳米级的微结构。•观察到的微观结构将根据其对断层弱化机制的含义进行解释，并结合第一个资助期岩心样品的先前结果。•在之前的样品中观察到絮凝粘土颗粒的团聚要求对粘土矿物进行进一步详细的TEM研究。•一些脉状方解石显示出强烈的晶内塑性（变形孪晶和位错蠕变）。我们将在新的样品集中测量方解石脉中的位错和孪晶密度。结果将用于基于古压力测量关系的应力估计。•脉状方解石稳定同位素分析的初步结果表明，这些流体主要来自较深的来源。我们将进一步分析稳定同位素，以确定穿透断层泥的流体的来源。•汞孔隙度法和BET气体吸附法将用于测量我们新样品的连通岩石孔隙度、孔隙体积和孔表面积。孔隙度数据将用于粗略估计渗透率。•safod显微结构将与最近从台湾车隆堡断层钻探项目（TCDP）获得的样品进行比较。

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).