Abstract: Field studies established that seismicity in the lower crust is linked to brittle failure of dry, strong rocks. This implies build-up of differential stresses to gigapascal (GPa) levels, but this requirement contrasts with the current models of continental lithosphere deformation, which typically favour a distributed flow of weak viscous lower crust. Thus, the magnitude of and the mechanisms capable of generating transiently high stresses in the continental lower crust are fundamental unknowns in structural geology and geodynamics. Recent advancements in micro-analytical techniques (i.e., high-angular resolution electron backscatter diffraction, HR-EBSD) have proven successful at measuring the residual stress resulting from elastic strain retained in mineral grains and have opened up new avenues in the research of crustal rheology.
The talk will present results from the study of pseudotachylytes (quenched frictional melt produced during seismic slip) from two exhumed lower-crustal terranes: Lofoten (Norway) and Musgrave Ranges (Central Australia). Field and microstructural observations, along with HR-EBSD measurements, will be used to discuss (1) mechanisms capable of generating transient high stresses required to nucleate earthquakes in the lower crust, and (2) the origin and significance of high residual stresses preserved in the crystal lattice of minerals that were seismically shocked in the lower crust. The results of our study have implications for the calculation of the energy balance of lower-crustal earthquakes, as well as for the bulk rheology and mechanical properties of the lower crust.
You will find the schedule for Njord Seminar Series Fall 2023 here.
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