Temporal geochemical comparisons are conducted for representative magmatism from western Northern Luzon to reconstruct the Cenozoic tectonics. Oligo-Pleistocene magmas from western Northern Luzon display elemental and Sr-Nd-Hf-Pb-O isotope geochemistry similar to intraoceanic arc magmatism, consistent with derivation from the mantle wedge, coupled with fractional crystallization. Specifically, the Oligo-Miocene (similar to 26.8-15.6 Ma) Central Cordillera diorite complex samples exhibit a negative correlation between Sr-Nd isotopes, consistent with mantle metasomatism by fluids/melts released from pelagic sediments. The Mio-Pleistocene samples (<similar to 9 Ma) exhibit consistent Sr-87/Sr-86 ratios with variable epsilon(Nd) and partially overlap with those of Scarborough seamount basalts, consistent with mantle metasomatism by fluids/melts released from the Scarborough seamount basalts, which are being subducted beneath Northern Luzon with the South China Sea fossil ridge. Temporal changes in Sr-Nd-Hf-Pb isotopes are also observed for the Taiwan-Luzon arc magmatism. The Oligo-Miocene (>similar to 9 Ma) magmatism exhibit intraoceanic arc isotopic signatures, suggestive of a chemical imprint from subducted pelagic sediments. The Mio-Pleistocene (<similar to 9 Ma) lavas display enriched mantle-type isotope compositions, consistent with an input of terrigenous sediment in the mantle. The temporal variations in Sr-Nd-Hf-Pb isotopes for the Taiwan-Luzon magmatism, combined with paleomagnetic evidence, mirror a transition from the Proto-South China Sea to the South China Sea fossil ridge subduction beneath western Northern Luzon at similar to 9 Ma. In addition, this study also highlights the importance of relatively enriched components in the lower plate in the maturation of overriding juvenile oceanic crust in an arc-continent collision system.