Geophysics and Tectonics Seminar spring-2019

Friction-generated heat exerts a fundamental control on fault strength and fault rock rheological evolution during the seismic cycle. Hematite fault mirrors in exhumed fault zones record these transient thermal and mechanical processes during earthquakes. Novel nanoscale textural and chemical tools can document evidence for dynamic weakening and potential re-strengthening of fault surface hematite. Hematite is also amenable to (U-Th)/He thermochronometry and the kinetics of this system responds to short-duration, high-temperature thermal pulses from flash heating of asperities to serve as paleotemperature proxy. Accurate interpretation of hematite (U-Th)/He data requires hematite textural characterization, grain-size (closure temperature) distribution data, and constraints on ambient thermal conditions during and after hematite formation from apatite He thermochronometry. This talk explores innovative applications of nanotextural and nanochemical data and hematite (U-Th)/He thermochronometry to recover transient heat signatures in fault rocks, with implications for dynamic weakening and re-strengthening mechanisms during seismic slip.