Water, besides being obviously present on the Earth?s surface, is also an integral part of the deep continental crust. In the crust, water is bound-up structurally in minerals and occurs in pore spaces of rocks, even many kilometers below the Earth's surface. During tectonic events, such as plate subductions and continental collisions, water is released from minerals during metamorphic reactions, and together with pore water can serve as a medium for heat transport and can promote weakening of rocks that are undergoing deformation. In this project, the Principal Investigator and students will study fluid flow that has occurred during the Mesozoic era in the White-Inyo Range of eastern California. During this era, the White-Inyo Range was buried deep within the western margin of North American crust that was experiencing metamorphism, magmatism, and volcanism as the oceanic Farallon tectonic plate was subducting beneath the continent. Geologic evidence in the range suggests that deep-crustal fluids promoted the emplacement of granitic plutons, by enhancing deformation of their host rocks, and were responsible for hydrothermal alteration of the crust within the range. The PI and students will study the Mesozoic hydrothermal system by analyzing the thermodynamic equilibrium relationships among preserved metamorphic minerals in collected rocks, by analyzing fluid-induced shifts in the ratios of carbon and oxygen in carbonate minerals, and by computer simulations. It is expected that the key factor that influenced the geometry of fluid flow and potential advective heat transport was variable permeability of rocks within the White-Inyo range. The expected outcome of the project will be a better understanding of the influence that deep-crustal fluids have on the geologic development of continental margins.
The White-Inyo Range is an excellent example of an exhumed continental magmatic arc. Magmatism in the arc occurred during two time periods, 180-165 Ma and 102-83 Ma ago, and it overlapped in time with magmatism in the Sierra Nevada Range. Previous structural and metamorphic studies have established that the plutons intruded a regional anticline that contains greenschist-facies shales, limestones, calcareous argillites, and sandstones. Intrusion of the plutons generated heterogeneous hydrodynamic systems, with heterogeneous fluid flow stemming from variable permeabilities and foliations of the rocks. In the project, mineral equilibria, metamorphic reactions, and C and O isotope ratios in carbonate minerals will be used to determine which rocks experienced syn-metamorphic fluid flow. These petrologic and geochemical portions of the project will be the foundation for computer simulations of reactive fluid flow, on both contact-aureole and regional scales, within the magmatic arc. The computer simulations will couple fluid flow with heat transport and metamorphic reactions, and they will include provisions for latent heat of crystallization of melts, heats of metamorphic reactions, and for fluids generated by the reactions and plutons. The project will have an impact on understanding conductive and advective heat transport within magmatic arcs and on the role that fluids have on promoting deformation and recrystallization of rocks in the deep continental crust.
