UC Santa Barbara

Directly dating deformation is a critical, unresolved challenge in tectonics. The mineral titanite (CaTiSiO5) is one of the best candidates for a “deformation chronometer”—a way to interpret dates in their microstructural context to directly date deformation. The purpose of this dissertation is to assess the utility of dating deformation with titanite (“titanite deformation chronometry”). In the following three chapters, I integrate in situ titanite U-Pb geochronology with microstructures, zoning, and trace-element compositions of titanite from three ductile shear zones to (1) develop titanite deformation chronometry by assessing titanite recrystallization mechanisms in the Coast shear zone, British Columbia; (2) apply titanite deformation chronometry to directly date amphibolite-facies deformation in the Anita Shear Zone, New Zealand; and (3) evaluate the applicability of titanite deformation chronometry to constraining the temperature and fluid compositions during ductile deformation using an example from cm-scale, Cretaceous shear zones in the Eastern Transverse Ranges, CA. Work from the Coast shear zone, British Columbia illustrates that interface-coupled dissolution¬–reprecipitation and lattice bending were coupled grain-scale processes that together variably reset titanite U-Pb dates, demonstrating the feasibility of titanite deformation chronometry. The application of titanite deformation chronometry to the Anita Shear Zone revealed that amphibolite-facies deformation ended at ~11 Ma, unequivocally linking these fabrics to high-temperature deformation within the Alpine Fault system. The example from the Eastern Transverse Ranges illustrates that titanite deformation chronometry is not only a powerful tool to date events in ductile shear zones, but also to document the degree to which temperature and fluid compositions evolve during ongoing deformation.