Project Details
Projekt
Faulting processes in active faults - Microstructural, mineralogical and geochemical characterization of drill core samples from international drilling projects
Applicant
Dr. Christoph Janssen
Subject Area
Palaeontology
Mineralogy, Petrology and Geochemistry
Mineralogy, Petrology and Geochemistry
Term
from 2015 to 2019
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 270673698
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.
DFG Programme
Infrastructure Priority Programmes
International Connection
New Zealand
Co-Investigator
Professor Dr. Georg Dresen
Cooperation Partner
Professorin Dr. Virginia Toy
