Revisiting the high temperature metamorphic field gradient of the Ryoke Belt (SW Japan): New constraints from the Iwakuni-Yanai area

We conclude that the exposed metamorphic field gradient is an apparent, but fortuitous, alignment of P-T data resulting from spatially and temporally distinct thermal events. Peak temperature conditions in the relatively shallow schist zone were attained during a first, pre-tectonic, contact metamorphic event. A second, regional metamorphic overprint arose from the syn-tectonic intrusion of granitoids in the deeper gneiss zone. A younger contact metamorphic event locally affected the eastern part of the schist zone. The revised tectono-thermal history highlights the composite and diachronous character of the Ryoke metamorphic field gradient.