Dr. Arran Murch

A magmas original volatile content determines the final composition of a lava erupted at the surface through influencing the onset of crystallization and fractionation during ascent. Dissolved volatiles additionally provide the fuel for volcanism at the surface, with eruption style largely a function of the magma composition and the abundance of dissolved volatiles. An understanding of original magma volatile content is therefore vital in attempting to understand magmatism on both tectonic scales (i.e. volatile cycles, magma generation, and ponding depths) as well as for single volcanic centers (i.e. possible eruption processes and associated hazards).

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The Ryukyu subduction zone is a trench-arc-back arc system that stretches ~1200 km from Taiwan in the south to Kyushu, Japan in the north, composed of the Ryukyu Trench, Ryukyu Arc, and Okinawa Trough. It is formed by subduction of the Philippine Sea Plate beneath the east Asian continental margin at ~5-7 cm/yr (Shinjo, 1999; Shinjo et al., 2000, 1999; Shinjo and Kato, 2000). The Okinawa Trough is an incipient continental rift formed by back-arc extension. Recent volcanism is focused on extensional en echelon grabens in the south and middle Okinawa Trough producing a bimodal basaltic–rhyolitic magma suite characteristic of continental rifting. Chemical signatures in Okinawa Trough basalts display spatially variable input sources with mantle, and slab derived fluids in the middle, while in the south a more chemically heterogeneous mantle source is indicated.