Timing and formation mechanism of fault-related calcite precipitates: implications for tectonic studies

Perach Nuriel (2011). Timing and formation mechanism of fault-related calcite precipitates: implications for tectonic studies PhD Thesis, School of Earth Sciences, The University of Queensland.

       
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Author Perach Nuriel
Thesis Title Timing and formation mechanism of fault-related calcite precipitates: implications for tectonic studies
School, Centre or Institute School of Earth Sciences
Institution The University of Queensland
Publication date 2011-03
Thesis type PhD Thesis
Supervisor Dr Gideon Rosenbaum
Prof Sue Golding
Prof Jian-xin Zhao
Total pages 210
Total colour pages 36
Total black and white pages 174
Subjects 04 Earth Sciences
Abstract/Summary Dating of brittle deformation has remained a major challenge. This challenge arises from a lack of information on the timing and formation mechanism of newly grown (authigenic) syn-tectonic minerals within the fault zone. Seismological studies have shown that earthquake-mobilised fluids are common processes in the seismic cycle and that such fluids are commonly associated with the formation of syn-tectonic calcite minerals in co-seismic veins and fissures. Calcite precipitation may also occur by karst processes within opening-mode fractures during periods in which fault is inactive. Thus, constraining the timing and formation mechanism of fault-related calcite precipitates can provide valuable information on the seismic and inter-seismic fault activity, with important implications for various tectonic studies. The first aim of the thesis is to demonstrate and discus the formation mechanism of the different types of calcite precipitates within fault zones and to identify post-formation deformation and recrystallisation processes. The second aim of the thesis is to constrain the timing of calcite precipitation by applying U-Th age dating to various types of fault-related calcite precipitates, and to implement their ages in the context of the local and regional deformation evolution. The study involves structural, isotopic, geochemical and geochronological investigations. The structural geology component consists of field observations, microstructural analyses on oriented thin-sections and cathodoluminescence. This was complemented by isotopic investigations including δ13C, δ18O and 87Sr/86Sr, and trace and major element geochemical analyses. Geochronological constraints were obtained by the U-Th dating technique. These methods have been applied to five different types of fault-related calcite precipitates: calcite-filled dilation veins, calcite coating fault planes, calcite injection veins, calcite filling dilation breccias and calcite fault striae. Samples have been taken from different segments along the East Anatolian (SE Turkey) and Dead Sea (Israel) fault zones. A large research component was done on one particular site in northern Israel, the Kefar Giladi quarry, where an ~E-W striking calcite-filled vein system is emplaced orthogonal to major ~N-S trending vertical fault planes, offering an ideal opportunity to study faulting and veining processes both spatially and temporally. The results show major differences in the nature of calcite precipitates and precipitation mechanisms within the different segments along the East Anatolian and Dead Sea fault zones. Calcite within hydraulic fractures, injection vein structures, and within syn-tectonic veins and tension gashes structures precipitated either co-seismically or syn-tectonically during the faulting events. In contrast, calcite-filled dilation veins, and calcite coating precipitated by karst processes following the formation of opening-mode structures. The ages obtained for these samples are at the limit of U-Th dating method. However the results indicate that active tectonics in both strike-slip systems occurred between 550 and 405 ka. The study of calcite-filled dilation veins in the Kefar Giladi quarry indicates a prolonged history (>500 ka) of vein growth. It is shown that brecciation and initial fracturing were followed by calcite precipitation in an opening-mode fracture by karst processes. A minimum age of ~500 ka marks the timing of vein initiation and increasing plate convergence along this sector of the Dead Sea Fault Zone. An additional high-resolution study on selected veins reveals that vein development was episodic and sealing-hiatuses during vein growth were followed by additional opening events. Once opened, the veins-fractures acted as rainwater flow paths, functionally similar to those developed by karst processes. When combined with high-resolution stable isotope analyses, these calcite precipitates may provide a reliable palaeoenvironmental proxy. The study of calcite cement and calcite striae in the Kefar Giladi quarry indicates precipitation by host-rock buffered fluids, and involving dissolution-recrystallisation processes during deformation. U-series systematics within these calcite precipitates indicates an increase in the magnitude of fracturing and enhanced fluid-rock interactions with time due to accumulating deformation in the fault zone. Fault activity is constrained to be dominant in the period between 220 and 60 ka. The combined time constraint on periods of faulting and veining in the Kefar Giladi quarry indicates that deformation style switched from a dominant N-S dextral strike-slip style to a dominant N-S extensional deformation style a few times during the deformation history. The results offer a unique approach towards the understanding of calcite precipitation mechanisms and fluid-rock interaction in brittle deformation zones. It demonstrates that geochemical and structural analyses, combined with U-Th geochronology, can shed light on co-seismic and inter-seismic fault activity, and can provide constraints on the timing, the style, and the extent of brittle deformation.
Keyword calcite veins
U-Th dating
oxygen isotopes
carbon isotopes
Sr isotopes
Dead Sea Fault
East Anatolian Fault
fault striae
calcite cement
Additional Notes Colour pages : 15, 23, 37, 39, 55, 62, 67-69, 71, 85, 94-96, 100, 106-107, 111, 113, 123-126, 128-130, 153, 181, 185, 187, 189, 193, 195, 197, 199, 201

 
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Created: Mon, 12 Sep 2011, 10:50:04 EST by Ms Perach Nuriel on behalf of Library - Information Access Service