Japan and the Korean Peninsula

The geology of the Korean Peninsula is dominated by Precambrian gneiss and metasedimentary sequences overlain by Paleozoic sediments. Granite intrusions are also common with the main formation stage in the Jurassic. The boundary between the North and South China continental blocks probably passes through the Korean Peninsula, but its location is disputed. The main geological history of Japan starts in the Paleozoic with fragments of continental shelf units associated with ophiolites formed in arc settings. Accretionary complexes are widespread with formation ages of Carboniferous to Recent and consisting of basalt and chert overlain by trench-fill mud- and sandstone commonly with blocks of limestone. Domains of high P/T metamorphism record conditions in the deeper parts of subducted units. Eroded remnants of ancient volcanic arcs are represented by areas of high T/P metamorphism and granitic plutons in both Korea and Japan. Most active volcanism and seismicity are related to subduction beneath Japan. Where the arcs are underlain by continental crust this volcanism is dominantly andesitic and large calderas are locally present. In the oceanic arcs, volcanism is mainly basaltic. Intraplate volcanism occurs in North Korea. Rapid subduction of the Pacific plate is associated with strong seismicity including rare mega-earthquakes every 500-1000years. Slower subduction of the Philippine Sea Plate beneath SW Japan is associated with less seismicity but more frequent large earthquakes. Tectonic forces not relieved by the subduction seismicity cause intraplate earthquakes and creep within both Japan and Korea. Large tsunamis are caused by both volcanic eruptions and subduction earthquakes.