What can hematite textures and (U-Th)/He thermochronometry tell us about fault mechanics in the shallow crust?
Alexis Ault
Utah State University
- Date & Time
- Location
- Online-only seminar via Microsoft Teams
- Summary
Above the seismogenic zone, earthquake ruptures may propagate to the surface along discrete fault planes or earthquake energy is attenuated in fault damage zones. Forecasting seismic hazards requires knowledge of the slip distribution and mechanical behavior of the shallow crust. Iron is the 4th most abundant element in Earth’s crust and hematite grows in a range of shallow fault rocks due to the redox potential of diverse Fe-bearing minerals. Hematite in fault rocks exhibits grain morphologies and nano- to microscale textures that preserve evidence for different slip rates and deformation conditions. Hematite is also amenable to (U-Th)/He thermochronometry, a powerful tool that, when combined with textural observations, informs the timing and temperatures (and thus rates) of fault slip. Hematite deformation experiments at ambient conditions and seismic and subseismic slip rates show low coefficients of quasi-static and dynamic friction, as well as generally velocity neutral behavior. In this talk, I share examples of how we fuse textures and thermochronometry data patterns from natural and experimental surfaces to inform fault mechanics. Investigation of hematite in shallowly exhumed, seismogenic faults, such as parts of the southern San Andreas fault (CA), eastern Denali fault zone (Yukon), and Intermountain Seismic Zone (UT) zone imply a broad range of hematite rheology, variable slip rates, and evolving mechanical properties that may promote or inhibit rupture propagation in the shallow crust.
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