The latest Cretaceous‐Early Paleogene rapid growth of accretionary complex and exhumation of high pressure series metamorphic rocks in northwestern Pacific margin

Episodic growth of accretionary complexes along the northwestern Pacific margin is well documented from detailed biostratigraphy and radiometric dating of metamorphic rocks. The latest Cretaceous to early Paleogene rapid growth of the accretionary complexes observed in Hokkaido and Sakhalin Islands was caused by the supply of a large amount of terrigenous sediments from an intracontinent collision zone: the Mongolia‐Okhotsk zone in the northern Asian continent. Rapid growth of the accretionary prism resulted in episodic tectonic events in the forearc and magmatic arc. Rapid underplating caused uplift and exhumation of previously accreted complexes along with high pressure series metamorphic rocks, now exposed as the Kamuikotan complex in Hokkaido and the Susunai complex in Sakhalin. The forearc basin shallowed as a result of the uplift. The uplift collapsed the old accretionary complex and supplied olistoliths onto the forearc region. Magmatic activity along the continental margin was also active at the same time. Subduction of a large amount of terrigenous sediments into the mantle may have contributed to active magmatism at that time. A large supply of water trapped in the subducted sediments entered the mantle and increased partial melting of the mantle wedge.