Characterization of the Pleistocene Volcanic Chain of the Bicol Arc, Philippines: Implications for Geohazard Assessment

Several active volcanic arcs are present in the Philippine Mobile Belt, the region enclosed by the Philippine Trench and the Manila-Negros-Cotabato Trench systems. One of the most prominent among them is the Bicol Arc, a similar to 260 km long volcanic arc located in the central-eastern margin of the Philippine Mobile Belt. The Bicol Arc hosts three of the active volcanoes in the country, including the Mayon Volcano, which has erupted repeatedly within the last decade. Aside from the three active volcanoes, there are at least nine other Pleistocene major volcanic centers that make up the volcanic arc. Although the rocks from the arc range in composition from basalt to rhyolite, they are mostly basaltic andesites and andesites. Magma mixing and fractional crystallization accompanied the generation of these rocks. The rocks exhibit typical island arc geochemical signatures. In addition, the Sr and Y ratio plots suggest that the Bicol Arc is mainly composed of mantle-wedge derived magmas with some samples from Bacon-Manito and Culasi showing similarities to adakites. Along-arc geochemical variation may be related to the variation in crustal thickness of the volcanic arc. The petrological and geochemical characterizations of the rocks provide information on how the volcanic centers evolved. This is important in assessing the attendant geohazards related to this volcanic arc.