菲律宾马尼拉新生代火山岩的Sr-Nd-Pb-Ca同位素特征:对南海俯冲过程中深部碳循环的制约  

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

作　　者：马东东 刘芳[1,2] 祝红丽 张兆峰[1] 邓江洪[3,4] MA Dong-dong;LIU Fang;ZHU Hong-li;ZHANG Zhao-feng;DENG Jiang-hong(State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Guangzhou 510640, China;University of Chinese Academy of Sciences, Beijing 100049, China;CAS Key Laboratory of Crust-Mantle Material and Environments, University of Science and Technology of China, Hefei 230026, China;Center of Deep Sea Research, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China)

机构地区：[1]中国科学院广州地球化学研究所同位素地球化学国家重点实验室,广东广州510640 [2]中国科学院大学,北京100049 [3]中国科学技术大学中国科学院壳幔物质与环境重点实验室,安徽合肥230026 [4]中国科学院海洋研究所深海研究中心,山东青岛266071

出　　处：《地球化学》2018年第6期593-603,共11页Geochimica

基　　金：国家自然科学基金(41773009;41373007;41673040);中国地质大学地质过程与矿产资源国家重点实验室科学基金(GPMR201708);中国博士后科学基金(2015M582003)

摘　　要：对菲律宾马尼拉新生代高钾钙碱性岛弧火山岩的主元素、微量元素和Sr-Nd-Pb-Ca同位素组成进行了研究,探讨了其源区组成并尝试示踪深部碳循环这一全球碳循环的重要组成部分。研究表明,马尼拉火山岩具有以下地球化学特征:(1)富集轻稀土元素(LREE)和大离子亲石元素(LILE),亏损高场强元素(HFSE,如Nb, Ta和Ti等),具岛弧火山岩的地球化学特征;(2)高207Pb/204Pb和208Pb/204Pb比值,暗示其源区有陆源沉积物的加入;(3)δ44/40Ca从0.70‰变化至0.85‰,平均值是0.74‰±0.03‰(2σ,n=8),低于原始地幔值(0.94‰±0.05‰)。这些特征暗示其源区中可能加入了低δ44/40Ca组成的海相沉积碳酸盐岩。二端元模拟计算结果显示:其源区中加入了约4%～5%的海相沉积碳盐岩。结合区域构造背景,认为该火山岩可能是上覆欧亚大陆陆源沉积物和海洋沉积碳酸盐岩的南海板块沿马尼拉海沟俯冲过程中交代上覆地幔楔,使得地幔楔发生部分熔融的产物。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 CO2in 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)high207Pb/204Pb and208Pb/204Pb 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 averageδ^44/40Ca of0.74‰±0.03‰(2σ,n=8),suggesting the possible involvement of marine sedimentary carbonates with lowδ^44/40Ca into the source of the volcanic rocks.Our model calculation shows that about4%-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.

关 键 词：岛弧火山岩 Sr-Nd-Pb-Ca同位素组成 深部碳循环 马尼拉 

分 类 号：P597[天文地球—地球化学]