SAFOD: Mineral Transformations and Fabrics

矿物转变和组构，特别是涉及层状硅酸盐的矿物转变和组构，可以严重影响浅层断层的力学行为。断裂岩中组构的发育也可能显著影响断裂带中流体的渗透率/孔隙度和作用。因此，详细的矿物学、矿物转化史和组构发育对研究断裂岩和理解断裂力学是至关重要的。地镜计划的SAFOD孔提供了研究未变形原岩到断层岩的原地变化的机会，从而为表征隐伏断裂带的变化类型和大小建立了参考。SAFOD孔样本还允许与附近出土的原岩和断层岩(例如，PunchBowl断层)进行直接比较，这些岩石被用作深部断层过程的代表。SAFOD孔洞样品的研究方法包括X射线衍射法(用于矿物鉴定、定量和结晶度)、X射线织构测角法(用于定量层状硅酸盐组构)、扫描电子显微镜(微米到毫米尺度的矿物分布、显微结构和定性化学)、透射电子显微镜(纳米级微结构和半定量化学)和电感耦合等离子体光电子能谱(量化元素组成和物质输运)。SAFOD孔样品的结果(1)提供了解释断裂带转换的矿物学框架，特别是在地震活跃的环境中；(2)检验了从研究折返的断层岩中推断出的过程的相关性；(3)提供了对发震断层的热机械行为的约束。这项工作补充了其他地质和地球物理团队对EarthScope的SAFOD洞的研究，并允许与附近和其他地方挖掘出的断层带的结果进行比较。

Mineral transformations and fabrics, particularly involving phyllosilicates, can critically affect the mechanical behavior of shallow faults. Fabric development in fault rocks may also significantly influence the permeability/porosity and role of fluids in fault zones. Thus, detailed mineralogy, mineral transformation history and fabric development are central to the study of fault rocks and our understanding of fault mechanics. The SAFOD Hole of the Earthscope Program provides the opportunity to study the in situ change from undeformed protolith to fault rock, thereby establishing a reference for the characterization of the type and magnitude of changes in buried fault zones. The SAFOD hole samples also allow for direct comparison with nearby exhumed protolith and fault rocks (e.g., the Punchbowl Fault), which have been used as representative for fault processes at depth. The research approach on SAFOD hole samples consists of X-ray diffraction (for mineral identification, quantification and crystallinity), X-ray texture goniometry (to quantify phyllosilicate fabrics), scanning electron microscopy (micron to millimeter scale mineral distribution, microstructure and qualitative chemistry), transmission electron microscopy (nanometer-scale microstructure and semi-quantitative chemistry), and ICP-OES (to quantify elemental composition and material transport). These complementary techniques provide a thorough characterization of the physico-chemical changes from protolith and fault rock.The results from SAFOD Hole samples (1) offer the mineralogic framework for interpreting fault zone transformation, particularly in seismically active settings, (2) test the relevance of the processes inferred from the study of exhumed fault rocks, and (3) provide constraints on the thermo-mechanical behavior of seismogenic faults. The work complements studies by other geologic and geophysical teams on Earthscope's SAFOD hole, and allows comparison with results from exhumed fault zones nearby and elsewhere.