K-Ar ages of the Akan-Shiretoko volcanic chain lying oblique to the Kuriletrench: Implications for tectonic control of volcanism

The Akan-Shiretoko volcanic chain, situated in the Southwestern Kurile arc, consists mainly of nine subaerial andesitic stratovolcanoes and three cald eras. The chain extends in a SW-NE direction for 200 km, situated oblique t o the Kurile trench at an angle of 25 degrees. Thirty-seven new K-Ar ages, plus previous data, suggest that volcanic activity along the Akan-Shiretoko volcanic chain began at ca 4 Ma at Akan, at the southwestern end of the ch ain, and systematically progressed northeastward, resulting in the southwes t-northeast-trending volcanic chain. This spatial and temporal distribution of volcanoes call be explained by anticline development advancing northeas tward from the Akan area, accompanied by magma rising through northeast-tre nding fractures that developed along the anticlinal axis. The northeastward development of the anticline caused uplifting of the Akan-Shiretoko area a nd changed the area from submarine to subaerial conditions. Anticline forma tion was likely due to deformation of the southwestern Kurile arc, with sou thwestward migration of the Kurile forearc sliver caused by oblique subduct ion of the Pacific plate. The echelon topographic arrangement of the Shiret oko, Kunashiri, Etorofu and Urup was formed at ca 1 Ma.