Sr-Nd-Pb-Ca isotopic compositions of the Cenozoic volcanic rocks in Manila,Philippines:Implication to deep carbon cycle during the subduction of South China Sea
The deep carbon cycle is an important part of the global carbon cycle.Studying the deep carbon cycle process is helpful in understanding the balance of CO_2 in the atmosphere,which is a key factor that affects climate change.This study aims to explore the source of the volcanic rocks and trace the deep carbon cycle by using major and trace elements and Sr-Nd-Pb-Ca isotopic compositions of the Cenozoic high K calc-alkaline arc volcanic rocks in Manila,Philippines.These volcanic rocks are characterized by:(1) enriched LREE and LILE and depleted HREE and HFSE;(2) high ~(207)Pb/~(204)Pb and ~(208)Pb/~(204)Pb ratios,which can be best explained by the incorporation of continent-derived sediments;and (3) lighter Ca isotopic compositions as compared to the upper mantle with an average delta~(44/40)Ca of 0.74 0.03 (2sigma,n = 8),suggesting the possible involvement of marine sedimentary carbonates with low delta~(44/40)Ca into the source of the volcanic rocks.Our model calculation shows that about 4%~5% of the marine sedimentary carbonates were added to the mantle source.Combining with the regional tectonic history,we propose that the source region of Manila volcanic rocks was metasomatized by the subducted fluids derived from the South China Sea plate,which contained high amounts of Eurasian terrigenous sediments and marine carbonates.Thereafter,a partial melting of the metasomatized mantle wedge formed the Manila volcanic rocks.