Faulting processes in active faults - Microstructural, mineralogical and geochemical characterization of drill core samples from international drilling projects

第一个资助期的研究侧重于应用我们的综合实地和分析方法来研究DGLab(希腊)和SAFOD(美国)以及DFDP-2，(新西兰)的断层岩石样品。然而，由于DFDP-2的钻探提前结束，项目计划不得不修改。在修改后的项目框架内，我们开始对DFDP-1A岩心和四个不同位置的粘土、泥和碎裂岩样品进行分析，以了解断层的地质力学行为。除了ICDP的这些研究外，JFAST(日本)和SATREPS(南非)项目的钻芯样本也包括在我们的研究中。我们的研究已经完成，但阿尔卑斯断层样本除外。这些结果，特别是首次证明DGLab样品的断层泥材料中存在强大的粘土组构，以及流体辅助的断层弱化机制的明显优势，激发了对微观结构的更详细研究，以阐明断裂带关键特征的证据，控制断层的物理和化学条件。2016年初，对阿尔卑斯山断层进行了采样，以研究其断层核心内的应变局部化。样品覆盖了10厘米的悬挂物-以及下壁单元和长达3米的悬挂墙。此外，我们还获得了DFDP-1A钻孔的断层泥和碎裂岩样品。首先，观察表明，沿阿尔卑斯山断层的应变局部化要么与厚(10s Cm)没有任何宏观组构的单元有关，要么与薄(&lt；1 cm-&lt；7 cm)层状结构有关。基于这些发现，阿尔卑斯断裂似乎统一了现有的两种上地壳应变局部化和断裂动力学的端元模型(中等变形的破坏带和狭窄的断核区与具有网状剪切带的宽带区)，但这一解释还需要更详细的检验和验证。对获得的样品进行详细分析将有助于我们在当前资金周期的剩余时间内了解阿尔卑斯山断层。为了全面了解阿尔卑斯山断层，我们需要进一步获得高质量、高分辨率的样品，特别是从露头的高特溪获得样品，它距离已经钻探的DFDP-1A和B孔只有几百米。将重点研究样品的微观结构(光学显微镜、扫描电子显微镜、透射电子显微镜)、地球化学(XRF、EDS、电感耦合等离子体质谱、化学发光)和岩石物理(汞孔探、BET气体吸附)。距断层核不同距离的粘土矿物组成(X射线衍射)和结构(XTG，同步辐射X射线)将进一步揭示断层的力学和水文行为。所有结果都将与以往钻探项目的结果进行比较。将特别关注主要断层内的应变局部化、相关的弱化和/或硬化过程以及断层作用的物理和化学条件。

The research of the first funding period focused on the application of our integrated field and analytical approach for the study of fault rock samples from DGLab (Greece) and SAFOD (USA) as well as DFDP-2, (New Zealand). However, the project plan had to be modified due to the premature end of drilling of DFDP-2. In the frame of the modified project we started to analyse clay gouge and cataclasite samples from DFDP-1A cores and four different locations to understand the geomechanical behavior of the fault. Beyond these ICDP studies, drill core samples from the projects JFAST (Japan) and SATREPS (South Africa) have been included in our studies.Our studies have been completed with exception of Alpine Fault samples. The results, particularly the first proof of a strong clay fabric in the fault gouge material of DGLab samples and the clear dominance of fluid-assisted fault weakening mechanisms, inspired a more detailed study of microstructures to elucidate evidence for the key features of fault zones, controlling physical and chemical conditions of faulting.In early 2016 the Alpine Fault was sampled in order to investigate strain localization within its fault core. Samples cover 10 cm of hanging- as well as footwall units and up to 3 m of the hanging wall. Additionally, we were provided with fault gouge and cataclasite samples from the DFDP-1A drill hole.First, observations indicate that strain localization along the Alpine Fault is either associated with thick (10s cm) units without any macroscopic fabric or with thin (< 1cm - < 7 cm) layered structures. Based on these findings, it seems that the Alpine Fault unites the two existing end-member models of strain localization and fault dynamics in the upper crust (fault with a moderately deformed damage zone and a narrow fault core vs. a wide zone with anastomosing shear zones).However, this interpretation has to be examined and verified in more detail. Detailed analysis of the obtained samples will contribute to our understanding of the Alpine Fault within the remaining time of the current funding period.To understanding the Alpine Fault comprehensively, we need to gain further high-quality, high-resolution samples, especially from the outcrop Gaunt Creek, which is located only a few hundred meters from the already drilled DFDP-1A and B holes. Samples will be studied with focus on microstructures (optical microscopy, SEM, TEM), geochemistry (XRF, EDS, ICP-MS, CL) and petrophysics (Hg porosimetry, BET gas adsorption). Clay mineral composition (XRD) and texture (XTG, synchrotron X-ray) with varying distance to the fault core will provide further implications for the mechanical and the hydrological behavior of the fault.All results will be compared with results from previous drilling projects. Special focus will be on strain localization within major faults, associated weakening and / or hardening processes as well as on physical and chemical conditions of faulting.