Ultramafic Rocks from the Sanbagawa Belt: Records of Mantle Wedge Processes

Abstract

Mantle wedge domains beneath the forearc Moho are unique regions of Earth’s interior where mantle encounters subducting oceanic plates. Crystal-plastic deformation and fluid-induced reactions in the supra-subduction mantle control global material circulation, arc volcanism, and seismicity within subduction zones. The Sanbagawa metamorphic belt contains numerous ultramafic blocks in its higher-grade zones, some of which likely originated as lower crustal arc cumulates that were subsequently incorporated into the mantle wedge and transported to the slab–mantle interface by mantle flow. Properties of these ultramafic rocks provide a valuable opportunity to understand the dynamic processes of the mantle wedge up to 80 km depth, including mantle flow, hydration/dehydration, and fluid–rock interactions near the slab–mantle interface of a warm subduction zone.