INTERACTIONS AMONG METAMORPHISM, DEFORMATION, AND CHEMICAL TRANSPORT PROCESSES IN HIGH STRAIN CRUSTAL ROCKS

INTERACTIONS AMONG METAMORPHISM, DEFORMATION, AND

CHEMICAL TRANSPORT PROCESSES IN HIGH STRAIN CRUSTAL ROCKS

By Jeffrey H. Marsh

Thesis Advisors: Drs. Scott E. Johnson and Christopher C. Gerbi

An Abstract of the Dissertation Presented

 in Partial Fulfillment of the Requirements for the

Degree of Doctor of Philosophy

(in Earth Sciences)

August, 2010

            The relative motions of Earth’s tectonic plates commonly results in deformation of rocks at or near Earth’s surface. In continental crust, deformation manifests as seismicity along fault zones, the building of mountain ranges (orogenesis), and the formation of large rift basins. The mechanical behavior of the middle parts of Earth’s crust plays a major role in controlling the intensity and distribution of these features. Thus, a more complete understanding of the nature of deformation and the mechanical behavior of mid-crustal rocks is of primary importance.

            This thesis investigates the interaction of micro-scale chemical and mechanical processes that occur during localized deformation of middle to lower crustal rocks, and evaluates the potential effects of grain-scale weakening processes on orogenesis. Structural and petrologic data from two kilometer-scale ductile shear zone systems (and their adjacent wall rocks) from exhumed orogenic belts provide useful information on mechanisms associated with the weakening of discrete crustal volumes. Additionally, crustal-scale computer models are presented that investigate how the structural and topographic evolution of a generic model orogen is affected by the presence of low-viscosity mid-crustal shear zones. The models also test the relative influence, and combined effect, of shear zone depth/geometry and surface erosion. Related petrological and geochronological investigations help constrain the tectono-metamorphic evolution of the investigated areas.