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The habilitation thesis presented here includes results from several studies dealing with fluid-rock interactions and rock deformation processes in active fault zones. The focus in all of these studies is on the influence of clay minerals on the geochemical and the hydro-mechanical behavior of the fault rocks. The research was conducted on rock cores and cuttings from four scientific drilling projects at the San Andreas Fault (USA), the Nankai Trough subduction zone and the Japan Trench subduction zone (Japan), as well as the Alpine Fault in New Zealand. These ICDP (International Continental Scientific Drilling Program) and IODP (International Ocean Discovery Program) funded projects were all conducted with the aim to monitor and better understand earthquakes.
Chapter 1 contains a short introduction to the topic with basic principles and objectives regarding the research approach. Chapter 2 describes the state of the art in clay mineral and fault zone science, gives a short description of the individual drilling projects and their locations on which the research was based, and summarizes the most important analytical methods used. Chapter 3 comprises ten peer-reviewed publications that are connected thematically and methodologically. The papers were published in the years 2006-2015, and additional related publications including myself as co-author are given in the literature list. The ten publications address different questions concerning the formation of clay minerals and processes of fluid-rock interaction in active fault zones. Six papers contain results from the SAFOD drilling project, USA (San Andreas Fault Observatory at Depth), with the main focus on fluid-rock interaction processes in fault rocks and the formation and location of clay minerals. Three publications report on research from the NanTroSEIZE drilling project (Nankai Trough Seismogenic Zone Experiment) and the JFAST drilling project (Japan Trench Fast Drilling Project). Both projects are situated in Japan. Here, the swelling behavior of smectite clay minerals in relation to changing environmental conditions (e.g. temperature and/or humidity) was investigated. The last publication included here concerns a study from the DFDP project (Deep Fault Drilling Project) in New Zealand, where I investigated the deformation of clay minerals on the context of the hydro-mechanical behavior of the fault zone rocks. I was first author in nine of the publications and in charge of the project preparation, measurements and data analyses, and the completion of the manuscript. As co-author on the other publication I was responsible for electronmicroscopy analyses (SEM and TEM) and their interpretation.
The key results from the publications in Chapter 3 are discussed in Chapter 4 with additional considerations from more recent papers. Following the major theses in Chapter 5, Chapter 6 highlights a future research project in clay mineralogy research at the GFZ. An appendix includes more detailed descriptions of the laboratory equipment and lists of all publications, conference contributions and teaching courses and modules.
This study investigated the slope carbonates of two Miocene carbonate systems: the Maltese Islands (in the Central Mediterranean) and the Marion Plateau (Northeastern Australia, drilled during ODP Leg 194). The aim of the study was to trace the impact of the Miocene cooling steps (events Mi1-Mi6) in these carbonate systems, especially the Mi3 event, which took place around 13.6 Ma and deeply impacted the marine oxygen isotope record. This event also profoundly impacted oceanographic and climatic patterns, eventually leading to the establishment of the modern ice-house world. In particular, East Antarctica became ice covered at that period. The rational behind the present study was to investigate the impact that this event had on shallow water systems in order to complement the deep-sea record and hence acquire a more global perspective on Miocene climate change. The Maltese Islands were investigated for trends in bulk-rock carbon and oxygen isotopes, as well as bulk-rock mineralogy, clay minerals analysis and organic geochemisty. Results showed that the mid Miocene cooling event deeply impacted sedimentation at that location by changing sedimentation from carbonate to clay-rich sediments. Moreover, it was discovered that each phase of Antarctic glaciation, not just the major mid Miocene event, resulted in higher terrigenous input on Malta. Mass accumulation rates revealed that this was linked to increased runoff during periods when Antarctica was glaciated, and thus that the carbonate sediments were “diluted” by clay-rich sediments. The model subsequently developed to explain this implies feedback from Antarctic glaciations creating cold, dense air masses that push the ITCZ Northward, thus increasing precipitation on the North African subcontinent. Increased precipitation (or stronger African monsoon) accelerated continental weathering and runoff, thus bringing more terrigenous sediment to the paleo-location of the slope sediments of Malta. Spectral analysis of carbonate content and organic matter geochemical analysis furthermore suggest that the clay-rich intervals are similar to sapropelic deposits. On the Marion Plateau, trends in oxygen and carbon isotopes were obtained by measuring Cibicidoides spp foraminifers. Moreover, carbonate content was reconstructed using a chemical method (coulometer). Results show that the mid Miocene cooling step profoundly affected this system: a major drop in accumulation rates of carbonates occurs precisely at 13.8 Ma, around the time of the East Antarctic ice sheet formation. Moreover, sedimentation changes occurred at that time, carbonate fragments coming from neritic environments becoming less abundant, planktonic foraminifer content increasing and quartz and reworked glauconite being deposited. Conversely, a surprising result is that the major N12-N14 sea-level fall occurring around 11.5 Ma did not impact the accumulation of carbonates on the slope. This was unexpected since carbonate platform are very sensitive to sea-level changes. The model developed to explain that mass accumulation rates of carbonates diminished around 13.6 Ma (Mi3 Event) instead of 11.5 Ma (N12-N14 event), suggests that oceanic currents were controlling slope carbonate deposition on the Marion Plateau prior to the mid-Miocene, and that the mid Miocene event considerably increase their strength, hence reducing the amount of carbonate being deposited on slope sites. Moreover, by combining results from deep-sea oxygen isotopes with sea-level estimates based on coastal onlaps made during Leg 194, we constrain the amplitude of the N12-N14 sea-level fall to 90 meters. When integrating isotopic results from this study, this amplitude is lowered to 70 meters. A general conclusion of this work is that the mid Miocene climatic shift did impact carbonate systems, at least at the two locations studied. However, the nature of this response was highly dependant on the regional settings, in particular the presence of land mass (Malta) and the absence of a barrier to shelter from the effects of open ocean (Marion Plateau).