Microstructural evolution of pseudotachylyte-bearing rocks during increasing temperatures: Evidence from rock-heating experiments

摘要

Pseudotachylyte are solidified melts that form from frictional heating on a fault plane during earthquakes and play an important role in the mechanism of faulting. Pseudotachylytes interact with mineralizing fluids and their textures are altered over long periods of time; consequently, determining seismic parameters by characterizing pseudotachylytes in the field remains challenging. In this study, we performed heating experiments on faulted pseudotachylyte-bearing cataclasites recovered from the Wenchuan Earthquake Fault Scientific Drilling Project-2 (WFSD-2) to constrain the formation of temperatures and microstructural evolution of the pseudotachylytes. These experiments revealed that melting occurred at 1100 degrees C, while microlites formed at 1100 degrees C and disappeared at 1500 degrees C, and metallic iron spherulites formed at 1300 degrees C. Fractures and cracks occurred in the pseudotachylytes after rapid cooling, implying an increase in pore volume that allowed for fluid infiltration and subsequent alteration. Because natural pseudotachylyte of the WFSD-2 shows the lack of microlite and the presence of metallic iron spherulites, our results imply that its formation was at temperature of 1300-1500 degrees C under water-deficient conditions.