Recent work has indicated that the role of fluids in rock deformation is greater than previously recognized, however the extent of the influence of fluids is not well constrained. This project will use oxygen isotopic techniques to document the spatial and temporal distribution of fluids in a well constrained structural sections by using oxygen isotopes as tracers. The work will focus on several thrust sheets of different compositions in the Ruby Gap duplex of Australia, which has recently been extensively studied structurally. Results are expected to provide an estimate of the influence of fluids and deformation mechanisms and the rock volume affected by isotopic exchange.