Evidence of dmisteinbergite (hexagonal form of CaAl2Si2O8) in pseudotachylyte: A tool to constrain the thermal history of a seismic event

The determination of the maximum temperatuer achieved by friction melt (T(melt)) in pseudotachylyte bearing faults is crucial to estimate earthquake source parameters (e.g., earthquake energy budgets, co-seismic fault strength) on a geological fault strength) oil a geological basis. Here we investigated the mineralogy of a pseudotachylyte from the Gole Larghe Fault (Italian Alps) by using X-ray powder diffraction, micro-Raman spectroscopy, and EDS-equipped scanning dectron microscopy. In particular, we report the presence of the hexagonal polymorph of CaAl(2)Si(2)O(8) (dmisteinbergite) in a pseudotachylyte. Published experimental work shows dmisteinbergite call crystallize at 1200-1400 degrees C by rapid quencing Therefore, the presence of dmisteinbergite in pseudotachylyte could be a reliable geothemometer for friction melts for which T(melt) has only as yet been estimaied.