Magma Genesis At Andaman Volcanic Arc Regime, North-Eastern Indian Ocean: Role Of Slab-Mantle Interaction

This study reports new petrological and geochemical data of submarine volcanic rocks dredged from the Andaman arc, northeastern Indian Ocean and evaluates their petrogenetic and tectonic implications. The studied samples exhibit wide range of compositions including basalts, andesites, dacites and rhyolites depicting BADR trend of magmatic differentiation. The basalts are porphyritic and composed of calcic plagioclase phenocrysts embedded in the groundmass consisting of plagioclase, clinopyroxene and volcanic glass. Andesite and dacites comprise clusters of plagioclase are phenocrysts embedded in glassy ground mass depicting glomeroporphyritic and vitrophyric textures. Plagioclase microlites in andesites show primary flow texture. Rhyolites from the study area porphyritic in nature predominantly consisting K-feldspar, quartz and plagioclase phenocrysts embedded in a silica rich merocrystalline groundmass of quartz, K-feldspar, biotite, opaque and glass. Plagioclase compositions in basalts and rhyolites correspond to An76-78 and An5-8 respectively. Geochemical and tectonic attributes marked by uniform LILE-LREE enriched, HFSE depleted trends corroborate (i) Mariana-type subduction of old, cold, thick and dense Indian Ocean lithosphere (ii) slabdehydration, variable slab-mantle interaction, metasomatism and flux melting of mantle wedge and (iii) magma underplating and melting of lower oceanic crust resulting into talc-alkaline magmatism of B-A-D-R compositional spectra.