Abstract

Pseudotachylyte is present in the Shimanto accretionary complex in Shikoku, Japan. The pseudotachylyte occurs as a vein in a fault zone and displays flow structure, TiO2 microlites, and other melting-related textures. The mineral assemblage of the pseudotachylyte suggests that the temperature was raised at least 450 °C above the background levels in the host rocks. This is the first direct evidence of seismogenic fault rock from an accretionary complex. The pseudotachylyte-bearing fault is a roof thrust above underthrusted mélange, which is overlain by an offscraped package of coherent units. The geologic setting of the pseudotachylyte is consistent with melt generation during seismic slip along the master décollement in the subduction zone.

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