2024-03-29T13:56:01Zhttps://eprints.lib.hokudai.ac.jp/dspace-oai/requestoai:eprints.lib.hokudai.ac.jp:2115/367532022-11-17T02:08:08Zhdl_2115_34989hdl_2115_34816hdl_2115_116Origin of Lateral Variations in 87Sr/86Sr Ratios of Quaternary Volcanic Rocks from the Kurile Arc in Hokkaido, JapanIkeda, YasuoKatsui, YoshioKurasawa, Hajime45087Sr/86Sr ratios were examined for volcanic rocks from Quaternary volcanoes in the Kurile arc in Hokkaido, Japan. The results show that the ratios decrease immediately away from the volcanic front, then increase in the middle part of the arc, but decrease again toward the back-arc side. The complex lateral variations of the ratios can be ascribed to breakdown of different minerals in the mantic wedge, i.e. amphibole decomposes beneath the volcanic front, whereas phlogopite breaks down beneath the middle part of the arc. Geochemical characters of the rocks from Rishiri volcano, located furthest away from the volcanic front arc quite different from those commonly observed in the trench-arc systems. The characters are similar to those of lavas from Deception island, located in Bransfield Strait formed by bad-arc spreading. This suggests that the Rishiri volcanism is independent of the arc magmatism.北海道大学Departmental Bulletin Paperapplication/pdfhttp://hdl.handle.net/2115/36753https://eprints.lib.hokudai.ac.jp/dspace/bitstream/2115/36753/1/22_2_p325-335.pdf0018-3474北海道大学理学部紀要2223253351987-08engpublisher