Constraining the Origin of Primary Magma in Barren Island and Narcondam of Andaman Subduction Zone, NE Indian Ocean Using Arc Basalt Simulator 5 (ABS5)
Abstract
This review presents new insights on the origin of primary arc magma and its geochemical signatures in the Barren Island and Narcondam using Arc Basalt Simulator 5 (ABS5). Barren Island rocks are basalt to basaltic andesite showing tholeiitic composition, while Narcondam is mostly andesite showing calc-alkaline composition. ABS5 indicates that slab dehydration and P T conditions were similar, and slab liquid uptake was highest from the altered oceanic crust, followed by sediment and mantle wedge coupled to slab top. Unlike trace elements, the 87Sr/86Sr 143Nd/144Nd ratios of the slab liquid show a depleted signature in Barren Island compared with Narcondam, due to R% (reactivity between solid and liquid in the slab). The initial mantle composition in the Barren Island and Narcondam indicates prior melt extraction of <?0.5% 1.5%. Barren Island shows lower ?% (fraction of slab liquid in the partial melt) than Narcondam. The H2O content in slab liquid was slightly higher in Barren Island (7.3 8.6?wt%) than Narcondam (5.5 6.8?wt%). Accordingly, the degree of partial melting (F?=?10.9% 20.20% in Barren Island, F?=?5.3% 10.5% in Narcondam) and total melt productivity (%) were higher in Barren Island compared with Narcondam. ABS5 indicates that the slab liquid contributed LILE, LREE, Th, U and 87Sr/86Sr-143Nd/144Nd, while the mantle melts contributed HFSE, MREE, HREE, Y143Nd/144Nd in Barren Island and Narcondam. ABS5 indicates that the total melt production (%), H2O content in slab liquid and mantle wedge were higher in post-caldera than in pre-caldera rocks.
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