Composition and volatile (sulfur and chlorine) contents of lavas and tephras from Mayon Volcano, Philippines

Mayon Volcano is one of the most active volcanoes in the Philippine archipelago. This stratovolcano has erupted 49 times since its first recorded eruption in 1616. Mayon eruptions exhibit a wide range of eruptive styles and are often explosive, bringing various hazards to almost 900,000 people living around the volcano. Combined major and volatile compositions of olivine-hosted melt inclusions indicate that Mayon could have produced central vent basaltic andesites from basaltic parents by fractional crystallization. The melt inclusions contain 900--3300 +/- 200 ppm and 500--1300 +/- 200 ppm of S and Cl respectively, consistent with their arc origin. Melt inclusions from the central vent have consistently higher S and Cl contents than those from the parasitic cinder cones. The S and Cl contents of melt inclusions from the 1897 eruption are high, which may explain the eruption's unusual explosivity. Trace element characteristics of Mayon magmas are diagnostic of subduction setting worldwide; i.e., enriched large ion lithophile elements (LILE) relative to low abundances of high field strength elements (HFSE) compared to mid-ocean ridge basalt (MORB). The high Th/Nb ratios of Mayon lavas suggest a strong influence of subducting sediments.