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Available data enable the recognition of three periods of back-arc crustal generation and three pulses of volcanic activity along the associated island arcs of the Philippine Sea. The geochemistry of the basalts from the back-arc basins of different ages indicates that in most cases they are identical to mid-ocean ridge basalts, and therefore should have similar sources and origins. In contrast, the island arc rock composition is variable in space and time, reflecting the different source and more complex nature of corresponding magmatism. Geomagnetic studies and recent Deep Sea Drilling Project results suggest an alternate sequence of back-arc and arc magmatic cycles. Both geochemical and geological observations provide important constraints on models of magmatism and extensions tectonics at convergent plate boundaries.

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