Moho can be petrologically imaged for the Japan arcs and the ocean floor through xenoliths, and drilled or dredged rocks from the current ocean floor and ophiolites, respectively. Beneath the NE Japan arc, the lower crust composed of amphibolites and granulites grades downward to the upper mantle through pyroxene-hornblende rocks (= Moho transition zone; MTZ). Beneath the SW Japan arc, the granulitic lower crust grades downward to the peridotitic upper mantle through spinel websterites (= MTZ). This structure has been modified by young cumulates to various degrees. The sub-oceanic uppermost mantle, mainly composed of harzburgite, grades upward to the layered gabbro (= lower crust) through MTZ composed of dunite + wehrlite + gabbro bands. The sub-oceanic structure has been possibly modified by so-called late-intrusive rocks.
