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Coupline Between Fluid Flow, Deformation Processes and Reaction

Experimental, field-based, microstructural and numerical modelling approaches are being used to explore several aspects of coupling between deformation processes, fluid transport, chemical reactions and the strength of earth materials in crustal and subduction zone environments.

Experimental studies have focussed on measuring changes in permeability of serpentinites during dehydration reactions in isostatic stress regimes, as well as during deformation. Fluid generation and associated reaction-enhanced permeability in devolatilising serpentinite in subducting slabs is likely to be a key factor influencing nucleation of intermediate depth earthquakes, as well as metasomatism and melt generation in the overlying mantle wedge. Analysis of chemistry of fluids generated during serpentinite devolatilisation has provided surprising implications for boron budgets in the mantle.

A new project, funded by ARC and a consortium of minerals industry sponsors, is examining why fluid flow tends to be localised within particular parts of crustal-scale fault networks. This research is aimed at understanding controls on the distribution of lode gold systems in fault networks. New field and modelling studies of a major goldfield north-west of Kalgoorlie in WA have shown that the distribution of gold deposits is consistent with the deposits forming in low displacement faults that were repeatedly reactivated following mainshocks on a nearby large displacement fault. The distribution of gold deposits formed in aftershock networks is found to be predictable if mainshocks are repeatedly arrested at large scale fault jogs or bends. Ongoing research is testing these concepts elsewhere in the Eastern Goldfields province of the Yilgarn Craton.

Field-based studies have used C/O stable isotope studies of vein systems to explore growth of fracture-controlled fluid pathways during low temperature deformation of a limestone sequence. Systematic variations in d18O in veins and altered wall-rocks within the carbonate sequence indicate growth of fracture networks was driven by upwards invasion of pore fluids into the sequence. The work highlights the role that high pore fluid pressures, rather than stress states, can have in driving both the growth of fault systems, and repeated slip events on these structures.