Time‐Lapse Record of an Earthquake in the Dry Felsic Lower Continental Crust Preserved in a Pseudotachylyte‐Bearing Fault

The mechanisms of earthquake rupture in lower continental crust, below the usual frictional-viscous transition, remain uncertain. In addressing this problem, study pseudotachylyte (quenched frictional melt produced during seismic fault slip) and related structures from deeply exhumed rocks can provide direct observational constraints. A felsic granulite Musgrave Ranges (central Australia) exceptionally preserves pristine microstructures spatially to a pseudotachylyte. This sample remained dry, without introduction hydrous fluids, development subsequent exhumation. It was therefore unaffected by alteration metamorphic re-equilibration. Fractures damage zone developed asymmetrically either side are marked new, randomly oriented quartz, feldspar garnet grains. Pulverization occurred locally between intersecting fractures, with powder injected into dilatant fractures quartz inclusion within host. Injection pulverized material explain growth compositionally different minerals (quartz, feldspar, kyanite, ilmenite, magnetite, rutile) along short-lived event. contains only clasts suggesting an unusually high melting temperature. sequentially time-lapse record thermo-mechanical processes single event, including: initial propagation associated off-fault local pulverization very dynamic fluctuations stress field; heating eventual slip; flow injection melt; rapid solidification (quenching) crystallization new minerals. under crustal conditions ca. 650 °C 1.2 GPa about 550 Myrs ago.