Remobilization of Highly Crystalline Felsic Magma by Injection of Mafic Magma: Constraints from the Middle Sixth Century Eruption at Haruna Volcano, Honshu, Japan |
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| Authors: | Suzuki Yuki; Nakada Setsuya |
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| Institution: | 1Institute of Mineralogy, Petrology and Economic Geology, Graduate School of Science, Tohoku University, Aoba-Ku, Sendai, 980-8578, Japan
2Earthquake Research Institute, University of Tokyo, 1-1-1, Yayoi, Bunkyo-Ku, Tokyo, 113-0032, Japan |
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| Abstract: | The latest eruption of Haruna volcano at Futatsudake took placein the middle of the sixth century, starting with a Plinianfall, followed by pyroclastic flows, and ending with lava domeformation. Gray pumices found in the first Plinian phase (lowerfall) and the dome lavas are the products of mixing betweenfelsic (andesitic) magma having 50 vol. % phenocrysts and maficmagma. The mafic magma was aphyric in the initial phase, whereasit was relatively phyric during the final phase. The aphyricmagma is chemically equivalent to the melt part of the phyricmafic magma and probably resulted from the separation of phenocrystsat their storage depth of  15 km. The major part of the felsicmagma erupted as white pumice, without mixing and heating priorto the eruption, after the mixed magma (gray pumice) and heatedfelsic magma (white pumice) of the lower fall deposit. Althoughthe mafic magma was injected into the felsic magma reservoir(at 7 km depth), part of the product (lower fall ejecta) precedederuption of the felsic reservoir magma, as a consequence ofupward dragging by the convecting reservoir of felsic magma.The mafic magma injection made the nearly rigid felsic magmaerupt, letting low-viscosity mixed and heated magmas open theconduit and vent. Indeed the lower fall white pumices preservea record of syneruptive slow ascent of magma to 2 km depth,probably associated with conduit formation. KEY WORDS: high-crystallinity felsic magma; magma plumbing system; multistage magma mixing; upward dragging of injected magma; vent opening by low-viscosity magma |
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| Keywords: | : high-crystallinity felsic magma magma plumbing system multistage magma mixing upward dragging of injected magma vent opening by low-viscosity magma |
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