Fluid flow commonly results in mineral precipitation in fractures which can yield a chemical archive of the physico-chemical conditions during tectonic deformation. However, interpreting subsurface conditions from traditional geochemical proxies can be ambiguous. Here we test clumped isotope thermometry as a tool to provide better understanding of the relationship between deformational structures and diagenetic processes.
Three main questions are addressed by this PhD thesis. The first question regards the reliability of clumped isotope compared to fluid inclusions in fractures within granites. We selected calcite veins resulting from deep-biosphere activity in oligotrophic fractures environment in Sweden. The clumped isotope results demonstrate that the optimal habitat to support microbial activity was below the detection limit of fluid inclusion. Hence, carbonate clumped isotope in this case is a valuable tool complementary to fluid inclusions that offers tighter constraints on the temperature and origin of diagenetic fluid.
The second objective was to investigate potential kinetic fractionation effects due to precipitation rates in fractures filled with meteoric cements. To address this objective, we apply clumped isotopes and trace element analysis along a detailed transect of single minerals of calcite in faults. The strong correlation between the ratio of Mn/Fe with clumped isotope temperature lead us to argue that this is indicative of variable crystal precipitation rates and in some cases kinetic fractionation. Thus for the first time we can independently show potential kinetic fractionation within ancient natural calcite samples that resulted in clumped isotopes temperature higher than ambient.
The third and final objective of the thesis was to apply clumped isotopes within an integrated study aiming at understanding the relationship between paleo-temperature, fluid flow and salt-doming in Jebel Madar, Oman. The results lead us to re-interpret the structural diagenesis of Jebel Madar, and demonstrate the value of clumped isotopes in structural diagenesis studies in general.