Holocene eruptions of Mt. Popa, Myanmar: volcanological evidence of the ongoing subduction of Indian Plate along Arakan Trench

In the western part of Myanmar the geodetic and seismic data indicate the ongoing highly oblique subduction of Indian Plate under Eurasian Plate. Volcanoes of Burma arc, however, did not produce eruptions in the recorded history and are considered extinct. Such perception questions the ongoing subduction, as well as keeping local officials unaware of possibility of future volcanic eruptions in the country. We have investigated the youngest lava flows and pyroclasts of Mt. Popa, which is the best-preserved polygenetic volcanic edifice in Myanmar. The Ar/Ar dating of the youngest products of the volcano provided very young radiometric ages which were unable to be measured accurately. The radiocarbon dating of paleosols intercalated with the most recent ash layers of the volcano has shown that Mt. Popa produced several eruptions in the beginning of Holocene. The youngest eruption occurred ~8000 BP and included the 1.3 km³ gravitational collapse of the volcanic cone with deposition of the 11-km-long debris avalanche, immediately followed by emplacement of 0.1 km³ of pyroclastic flow of calc-alkaline basaltic andesite composition. The collapse direction as well as complex morphology of the resulted crater were prearranged by geometry of the listric fault, which was formed during the pre-collapse asymmetric gravitational spreading of the volcanic cone. The recently erupted products are geochemically similar to products of young monogenetic volcanoes of Monywa area located 150 km north Mt. Popa, and both display patterns consistent with magma generation at an active subduction system. Low magma production rate of Mt. Popa (3 × 10−⁵ km³/year averaged for the 1 Ma of the volcano history) is in agreement with the highly oblique angle and slow rate of the subduction. The fact of the Holocene eruptions of calc-alkaline composition in Burma arc represents volcanological evidence of the ongoing subduction in this part of the collision zone between India and Asia.