Initiation and propagation of subduction along the Philippine Trench: evidence from the temporal and spatial distribution of volcanoes

K–Ar ages of 37 samples collected from the Bicol peninsula, the Luzon island, Philippines, were determined by the unspiked sensitivity method in order to constrain the timing of initiation of subduction along the Philippine Trench. The measured K–Ar ages range from 0 to 7 Ma with two old outliers of 27 and 43 Ma. Together with K–Ar ages previously reported on volcanics in Leyte and eastern Mindanao, subduction volcanism has likely propagated from north to south: ∼6.6 Ma in Bicol and ∼3.5 Ma in Leyte and its vicinity. The temporal and spatial distribution suggests that the subduction volcanism started earlier in the north than in the south. This is consistent with the southern propagation of subduction along the Philippine Trench from ∼8 Ma.