Simultaneous boninitic and arc-tholeiitic volcanisms in the Izu forearc region during early arc volcanism, based on ODP Leg 125 Site 786 |
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| Authors: | Satoru Haraguchi Teruaki Ishii |
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| Institution: | (1) Ocean Research Institute, University of Tokyo, Nakano 164-8639, Japan |
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| Abstract: | Early arc volcanism during Eocene to Oligocene in the Izu forearc region was investigated during ODP Legs 125 and 126 in 1989,
and effusive and intrusive volcanics were recovered from Leg 125 Site 786. These rocks were all classified into boninites
and associated rocks by Leg 125 Shipboard Scientific Party, and they concluded that boninitic volcanism had occurred before
40 Ma, and arc tholeiitic volcanism began after 40 Ma. In this study, lava flows and breccias that classified into boninite
series are divided into two groups, tholeiite and boninite, based on petrographical and petrological properties. Both series
are also distinguished by bulk rock composition. It is considered that the sources of both rock types have similar depleted
compositions because of their similar, very low bulk HFSE concentrations. We suggest that boninitic and tholeiitic volcanism
occurred closely in time and space, and reflected different temperature and water condition. |
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| Keywords: | Boninite Tholeiite Early arc volcanism Two-pyroxene geothermometry Water condition |
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