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

Abstract

In the western part of Myanmar the geodetic and seismic data indicate the ongoing highly oblique subduction ofIndian Plate under Eurasian Plate. Volcanoes of Burma arc, however, did not produce eruptions in the recordedhistory and are considered extinct. Such perception questions the ongoing subduction, as well as keeping localofficials unaware of possibility of future volcanic eruptions in the country. We have investigated the youngestlavaflows 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 un-able to be measured accurately. The radiocarbon dating of paleosols intercalated with the most recent ash layersof the volcano has shown that Mt. Popa produced several eruptions in the beginning of Holocene. The youngesteruption occurred ~8000 BP and included the 1.3 km3gravitational collapse of the volcanic cone with depositionof the 11-km-long debris avalanche, immediately followed by emplacement of 0.1 km3of pyroclasticflow of calc-alkaline basaltic andesite composition. The collapse direction as well as complex morphology of the resulted cra-ter were prearranged by geometry of the listric fault, which was formed during the pre-collapse asymmetricgravitational spreading of the volcanic cone. The recently erupted products are geochemically similar to productsof young monogenetic volcanoes of Monywa area located 150 km north Mt. Popa, and both display patterns con-sistent withmagma generationatanactivesubductionsystem. Low magma productionrateofMt.Popa(3×10−-5km3/year averaged for the 1 Ma of the volcano history) is in agreement with the highly oblique angle and slowrate of the subduction. The fact of the Holocene eruptions of calc-alkaline composition in Burma arc representsvolcanological evidence of the ongoing subduction in this part of the collision zone between India and Asia.