Igneous history based on temporospatial changes and petrogenesis: Example of large-scaled volcanism in the Toyama basin during back-arc spreading in the Sea of Japan

Back-arc spreading, rifting event in subduction zones, is an important geotectonic event to study magmatism through Earth’s history. Magmatism during back-arc spreading displays both geochemical features of convergent and divergent plate boundaries. In the Toyama Basin, which is one of the Cenozoic sedimentary basins on the side of the Sea of Japan, andesites and rhyolites related to the back-arc spreading in the Sea of Japan are widely distributed with large volumes (>1000 km3). I have studied them to reveal when, how, and why such large scaled volcanism had occurred in the basin during the back-arc spreading event. Firstly, I overviewed geology, chronology, and geochemistry of Cenozoic igneous rocks in and around the Toyama basin to know temporospatial changes of magmatism. Secondly, I examined detailed lithostratigraphy of the large volumed andesites to reveal eruption style of large scaled andesitic volcanism in the Toyama basin. Thirdly, I studied petrology and geochemistry of andesites and rhyolites to understand their magmatic processes and interactions in the crust. The geological and petrological studies in the Toyama basin will throw an arrow to geotectonic studies on magmatism in back-arc basin regions.