Morphology and chemical composition of ash layer of about 8 Ma old from ODP-758 site, Bay of Bengal

Glass shards from an ash layer of about 8 Ma old extracted from a core drilled at an ODP-758 site in the Bay of Bengal (BOB) were studied for morphology and chemical composition in order to trace their possible source. Glass shards are of bubble wall, platy and pumice shard type indicating magmatic type of eruption. Electron probe micro analysis (EPMA) of glass shards suggesta rhyolite composition and high K cal-alkaline series. FeO (1.23%) and TiO2 (0.1%) contents of these glass shards are distinctly higher compared to the earlier known Youngest (~74 ka), Middle (~0.54 Ma) and Oldest (~0.84 Ma) Toba Tuffs. Tectonomagmatic, triangular (Ti-Zr-Y) plot and chondritenormalized REE pattern, are all indicative of volcanic arc source most probably from the nearby Indonesian arc volcanism.

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