Seismic Detection of the α -β Quartz Transition Provides Precise Temperature Estimation in the Tibetan Crust

In the deep crust, temperature, which is among the key parameters controlling lithospheric dynamics, is inferred by extrapolation from the surface using several assumptions that may well fail in regions of active tectonics and fluid migration. In the rare case that temperatures of 700° C or higher are exceeded in the upper/middle continental crust composed of quartz-rich felsic rocks, the α -β quartz transition (ABQT) will occur, generating a measurable seismic signature and offering the possibility for precisely estimating temperature from the known ABQT phase diagram. Here it is shown that all expected seismic features of the ABQT are met by the boundary at 18-32 km depth below the INDEPTH III profile in central Tibet. Thus, this seismic boundary more probably represents the signature of (recent) geological processes rather than a lithological boundary.