A minimum age for the active Barren Island volcano, Andaman Sea

Barren Island of Andaman Sea is the only active volcano in the Indian subcontinent. While the volcano has erupted sporadically many times over the last similar to 70 ka, it is not known when it formed and breached the sea surface. To provide estimates for the timing of these events, we dated two tephra (ash) layers older than 42 ka and generated by this volcanism in a previously studied marine sediment core collected similar to 32 km southeast of the island using the newly established modern 40Ar-39Ar facility in India. The 40Ar-39Ar plateau ages of plagioclase separates from successive tephra layers at 310 and 375 cm are 1.8 +/- 0.4 (2 sigma) Ma and 1.5 +/- 1.8 (2 sigma) Ma respectively. We interpret the more robust age of 1.8 Ma as the time of crystallization of plagioclase grains. As this age is very much older than the depositional age of the tephra layer (similar to 61 ka), we infer that it represents the age of older rocks present in the plumbing system of the volcano that were blown out with later pyroclastic eruptions and therefore, sets a strict younger limit to the time of formation of the volcano.