Western Northern Luzon Isotopic Evidence of Transition From Proto-South China Sea to South China Sea Fossil Ridge Subduction

Abstract

© 2019. American Geophysical Union. All Rights Reserved. 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 (~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 (<~9 Ma) exhibit consistent 87Sr/86Sr ratios with variable εNd 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 (>~9 Ma) magmatism exhibit intraoceanic arc isotopic signatures, suggestive of a chemical imprint from subducted pelagic sediments. The Mio-Pleistocene (<~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 ~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.

Source or Periodical Title

Tectonics

ISSN

2787407

Document Type

Article

Subject

Arc-continent collision, Luzon Arc, Proto-South China Sea, Ridge subduction, Scarborough Seamount Chain, South China Sea

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