The Intra-oceanic Barren Island and Narcondam Arc Volcanoes, Andaman Sea: Implications for Subduction Inputs and Crustal Overprint of a Depleted Mantle Source

Abstract

The active Barren Island volcano and the Pleistocene Narcondam ­volcano, located ∼140 km to the North, are the only two subaerially exposed Andaman arc volcanoes, which rise from the 1,000 to 2,300 m deep seafloor of the Andaman Sea, and are associated with the subduction of the Indian plate beneath the Burma plate. Lavas at Barren Island range in composition from basalt to andesite while lavas from Narcondam volcano range from andesite to silicic andesite/dacite. Similarities in the geochemistry of both lava suites include strong and comparable depletions in Nb and Ta (K2O/Nb ∼0.7; Ba/Nb 130–250), low MORB-like Nb/Zr (0.01–0.03) and nearly constant U/Th (0.15–0.22). These characteristics suggest a genetic link between both magma suites, but there are geochemical differences such as elevated trace element abundances and ratios in Narcondam lavas compared to Barren Island lavas. These include elevated Ba, Rb, and U concentrations and higher Ba/Zr and Nb/Zr. Additionally, isotopic ratios of Barren Island lavas are 87Sr/86Sr ∼0.7039–0.7041, 143Nd/144Nd ∼0.51285–0.51296, and 206Pb/204Pb ∼18.063–18.309. For Narcondam, isotope ratios are 87Sr/86Sr > 0.705, 143Nd/144Nd ∼0.51270, and 206Pb/204Pb ∼18.565–18.617. Additional geochemical parameters (e.g., Sr/Y, Zr/Y, Th/La, U/La, Ba/La) of Narcondam lavas positively correlate with increasing SiO2 but are anchored at the mafic end within compositions observed at Barren Island volcano.