Petrology of tremolite rocks in the high-pressure metamorphic terranes

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The Franciscan Complex, California, and the Kamuikotan metamorphic belt, Japan, are accompanied by serpentinite melange with deeper high-grade metamorphic rocks, whereas the Sanbagawa metamorphic belt, Japan, contains less amounts of serpentinite and is not accompanied by any serpentinite melange. The former were probably formed under a tensional stress regime, and the latter under a compressional one. The restricted occurrence of serpentinite to the high-grade pelitic schist in the Sanbagawa belt suggests that the serpentinites had been supplied from wedge mantle into pelagic sediments on the top of subducting plate at the initiation of accretion. Tremolite rocks and phengite-chlorite schists near serpentinite in the Sanbagawa belt and from Chamorro Seamount, Mariana forearc, may suggest the widespread metasomatism along the boundary between wedge mantle serpentinite and pelagic sediments. Further research on the mechanical and physico-chemical behaviors of these metasomatic rocks are important to understand the phenomena along the subduction boundary between oceanic and land-ward plates.