Fluid-rock-deformation interaction and strain localization in detachment systems
During the extension that accompanies orogenic collapse, the upper crust thins by brittle faulting, while the lower crust flows laterally. Localization of the deformation in the upper crust eventually leads to the formation of a metamorphic core complex (MCC). In a MCC, a ten to hundred meters thick detachment shear zone (DSZ) separates the brittlely deformed hanging wall from the footwall. DSZs commonly record the transition from brittle to ductile deformation, and are associated with high metamorphic gradients. Several stable isotope studies from hydrous minerals have revealed the presence of surface-derived fluids in the deforming mylonite. Pervasive fluid flow is enhanced by brittle faulting in the upper crust. Fluids reach the brittle-ductile transition and the ductile shear zone below, therefore helping to refrigerate the detachment shear zone, leading to high transient geothermal gradient.
Large-scale fluid flow occurs along fault zones and fractures, and accommodates large fluid fluxes. Such channelized fluid flow is effective at transporting heat and significant quantities of dissolved chemical components, but interaction between the fluid and rocks is limited to a narrow channel zone. In most geological settings, it is the pervasive grain-scale transport that governs isotope and chemical exchange among minerals and between minerals and fluids, growth of minerals by metamorphic reactions and deformation by mechanisms such as diffusion creep and pressure solution. Pervasive fluid transport is controlled by diffusional processes along grain boundaries.
Objective And Goals Of The Project: The proposed project aims at understanding the processes of oxygen isotopic exchange between fluid and rock during deformation, using an approach that combines fieldwork and high-resolution analytical techniques. Ultimately, we wish to understand the role of fluids during deformation, from the grain to the crustal scale. This project focuses on several MCC of southern Arizona.