Arc-type and intraplate-type ridge basalts formed at the trench-trench-ridge tripIe junction: Implication for the extensive sub-ridge mantle heterogeneity |
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| Authors: | Soichi Osozawa Takeyoshi Yoshida |
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| Institution: | Institute of Geology and Paleontology, Faculty of Science, Tohoku University, Sendai, 980 Japan;Institute of Mineralogy, Petrology and Economic Geology, Faculty of Science, Tohoku University, Sendai, 980 Japan |
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| Abstract: | Abstract ' In situ basalts' represent the ridge magmatism at and close to the ancient trench-trench-ridge triple junction. Such basalts in the Amami, Mugi, and Setogawa accretionary complexes, Southwest Japan, were described and analysed. The geochemical data show that the ' in situ basalts' include all the types of basalts, ranging from alkali basalts and high-alumina basalts to tholeiites, and the compositions tend towards intermediate and silicic rocks. The data also reveal that the ridge basalts are indistinguishable both from the island arc and intraplate basalts, no affinities with mid-ocean-ridge basalts. The sub-ridge mantle adjacent to the triple junction had a component of sub-arc mantle, and this mantle heterogeneity can be generated by the formation of a slab window. |
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| Keywords: | arc-type and intraplate-type basalts in situ basalt mantle heterogeneity ridge subduction slab window |
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