Fluid penetration through carbonate fault rocks

Faults play a key role in the geochemical cycle, where volatiles from the hydrosphere are transferred to rocks as carbonate and hydroxyl minerals. Furthermore, faulting may lower kinetic barriers to low-temperature (greater than 100°C) mineral reactions. The consequences of these changes are predominantely manifested in the microfabric characteristics, as well as in geochemical and geochronologic properties of clay gouge. Additionally, dissolution and precipitation reactions, particulary in carbonates, may continue during faulting. If mineral reactions intimately interact with mechanical processes in shallow-crustal faults, then our current understanding of the mechanical and hydraulic properties of fault zones may be incomplete. Syndeformational mineral reactions and associated fabric changes could make faults much weaker than would be expected from evaluation of the static mineral assemblage of gouge and single crystal propertiesand may contribute to fault localization. In combining a series of techniques, experimental work and field sampling at selected sites this project will provide new insights in the controlling factors of the structural evolution of fault zones and the underlying mechanisms. These studies include: Microstructural studies (deformation mechanisms and rheology) Comparative chemical analysis of host- and fault-rocks, and of hydrothermally formed veins. Balancing of particular element ratios and chemical trends to calculate mass and volume changes during deformation. Analysis of stable isotopes by mass spectrometry.