Date of Award
Doctor of Philosophy
Micah J. Jessup
Anna Szynkiewicz, Nicholas Dygert, Dennis L. Newell, Christopher M. Fedo
The Cordillera Blanca in central Peru, is an example of synconvergent extension following increased exhumation, enhanced weathering and erosion, and development of high, potentially unstable, terrane. The western edge of the range is being exhumed along a normal fault extending parallel to the subduction zone. Normal faulting has exposed a young ductile shear zone capping coeval granodiorite. Preservation of a mid-crustal detachment along an active structure provides an opportunity to explore the causes of trench-parallel synconvergent extension. In chapter one, I report δ2H [hydrogen isotope] values from micas within the detachment-associated Cordillera Blanca shear zone to proxy paleoelevation and explore the role of meteoric fluid infiltration and topographic evolution in the formation of this fault system. In chapter two, I use existing δ2H [hydrogen isotope] and δ18O [delta 18-O] values from surface and thermal waters in the Upper Rio Santa River catchment to explore the most appropriate stable isotope-based lapse rate for reconstruction of historic elevation in the Cordillera Blanca. In chapter three, I deploy zircon 206Pb*/238U [uranium lead] ages and trace and rare earth element chemistry from granites in the Cordillera Blanca and Cordillera Huayhuash to explore magmatism during slab shallowing and connections between timing of igneous activity, fluctuations in crustal thickness, and initiation of the Cordillera Blanca detachment. In chapter four, I apply 40Ar/39Ar [forty-argon-thirty-nine argon] thermochronology of micas and feldspar from across the range to constrain the timing of exhumation and cooling of the Cordillera Blanca shear zone and batholith. These approaches dictate that magmatism progressed from south to north across the central Peruvian Andes during a period of crustal thickening and thinning. Magmatism aids localized weakness in the upper and middle crust. This weakening is associated with intrusion of the youngest magmatic rocks in the region, which aid local stress switching and extension. Meteoric water that is introduced during early stages of detachment development was derived from high elevations that were 500 – 700 m below the modern mean elevation. The interplay of magmatism and meteoric water infiltration result in a period of rapid, fault-driven exhumation that migrated south to north between 5.2 to 3.7 Ma.
Grambling, Tyler A., "CHRONOLOGICAL AND GEOCHEMICAL FRAMEWORK FOR OVERLAPPING MAGMATISM, DUCTILE DEFORMATION, AND HYDROTHERMAL CIRCULATION IN THE CORDILLERA BLANCA, PERU. " PhD diss., University of Tennessee, 2022.
Available for download on Tuesday, August 15, 2028