Petrology and geochemistry of Camiguin Island, southern Philippines: insights to the source of adakites and other lavas in a complex arc setting

Camiguin is a small volcanic island located 12 km north of Mindanao Island in southern Philippines. The island consists of four volcanic centers which have erupted basaltic to rhyolitic calcalkaline lavas during the last simi lar to 400 ka. Major element, trace element and Sr, Nd and Pb isotopic data indicate that the volcanic centers have produced a single lava series from a common mantle source. Modeling results indicate that Camiguin lavas were produced by periodic injection of a parental magma into shallow magma cham bers allowing assimilation and fractional crystallization (AFC) processes t o take place. The chemical and isotopic composition of Camiguin lavas bears strong resemblance to the majority of lavas from the central Mindanao volc anic field confirming that Camiguin is an extension of the tectonically com plex Central Mindanao Are (CMA). The most likely source of Camiguin and mos t CMA magmas is the mantle wedge metasomatized by fluids dehydrated from a subducted slab. Some Camiguin high-silica lavas are similar to high-silica lavas from Mindanao, which have been identified as "adakites" derived from direct melting of a subducted basaltic crust. More detailed comparison of C amiguin and Mindanao adakites with silicic slab-derived melts and magnesian andesites from the western Aleutians, southernmost Chile and Batan Island in northern Philippines indicates that the Mindanao adakites are not pure s lab melts. Rather, the CMA adakites are similar to Camiguin high-silica lav as which are products of an AFC process and have negligible connection to m elting of subducted basaltic crust.