Constraining the Origin of Primary Magma in Barren Island and Narcondam of Andaman Subduction Zone, <scp>NE</scp> Indian Ocean Using Arc Basalt Simulator 5 ( <scp>ABS5</scp> )

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 87 Sr/ 86 Sr– 143 Nd/ 144 Nd 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 &lt; 0.5%–1.5%. Barren Island shows lower β % (fraction of slab liquid in the partial melt) than Narcondam. The H 2 O 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 87 Sr/ 86 Sr‐ 143 Nd/ 144 Nd, while the mantle melts contributed HFSE, MREE, HREE, Y 143 Nd/ 144 Nd in Barren Island and Narcondam. ABS5 indicates that the total melt production (%), H 2 O content in slab liquid and mantle wedge were higher in post‐caldera than in pre‐caldera rocks.