Newly acquired Sr, Nd, and Pb isotope data, combined with other recently available data in the literature, clearly show that Philippine arc volcanic rocks do not have a true Dupal isotopic anomaly. Instead, most of the volcanic rocks must have come from a mantle source with a “Dupal-like” Indian Ocean– to enriched ocean-island-basalt composition. This mantle source is present beneath the Philippine Sea plate and the South China Sea plate on either side of the Philippine arc systems. The isotopic signature of Philippine arc volcanics is most probably inherited from the previous southern locations of the different geologic terranes that compose the modern Philippine island arcs. The new data also show that the isotopic signature of Philippine arc volcanics, similar to volcanic rocks from other western Pacific island-arc–back-arc settings, is mainly a function of the mantle source and was only recently modified by a component from subducted sediments and crust.

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