海南岛新生代玄武岩成因的PGE与Os同位素地球化学制约  

Origin of Cenozoic Basalts in Hainan Island:Constraints from Re-Os Isotops and PGE Geochemistry

作　　者：王国庆 郭锋[1,3] 赵亮[1,3] WANG Guoqing;GUO Feng;ZHAO Liang(State Key Laboratory of Isotope Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,Guangdong,China;College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China;CAS Center for Excellence in Deep Earth Science,Guangzhou 510640,Guangdong,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]中国科学院大学地球与行星科学学院,北京100049 [3]中国科学院深地科学卓越研究中心,广东广州510640

出　　处：《大地构造与成矿学》2022年第3期483-500,共18页Geotectonica et Metallogenia

基　　金：国家基金委NSFC-广东省联合基金项目(U1701641);国家自然科学基金项目(41525006,42073032,42021002)联合资助。

摘　　要：本文对海南岛新生代玄武岩开展了PGE和Re-Os同位素体系的系统研究,结合全岩主量、微量元素和Sr-Nd-Pb同位素数据,取得了如下认识:①海南岛新生代玄武岩根据PGE含量和配分模式可以划分为两类,第一类PGE总量为1.88×10^(−9)~4.54×10^(−9),配分模式为相对平坦型(Pd/Ir<3.5),高Os含量和低^(187)Os/^(188)Os值,代表了来自亏损软流圈地幔的熔体;第二类PGE总量为0.35×10^(−9)~2.67×10^(−9),配分模式为向右上倾型(Pd/Ir>5.0),低Os含量和高^(187)Os/^(188)Os值,反映其熔融地幔源区包含了大量的再循环洋壳;②海南岛新生代玄武岩PGE地球化学特征受控于岩浆演化过程中硫化物的熔离作用;③Os-Pb同位素模拟结果暗示海南岛新生代玄武岩再循环洋壳的年龄在100~300 Ma之间,为近期/同期俯冲的大洋板片。本次研究为进一步理解海南岛新生代玄武岩源区的再循环组分来源、硫化物在岩浆起源与演化的作用以及地幔柱演化动力学方面提供了新的依据。In this paper,we report PGE and Re-Os isotope compositions of the Cenozoic basalts in Hainan Island.In combination with the whole-rock major,trace element and Sr-Nd-Pb isotopic results,the following conclusions can be reached.(1)The Hainan basalts can be subdivided into two groups on the basis of chondrite-normalized PGE patterns.The high-Os(Os>40×10^(−12))basalts have PGE concentrations varying from 1.88×10^(−9) to 4.54×10^(−9) and show a relatively flat PGE pattern with Pd/Ir<3.5;whereas the low-Os(Os<40×10^(−12))basalts have PGE contents varying from 0.35×10^(−9) to 2.67×10^(−9) and demonstrate an upright-inclined PGE patterns with Pd/Ir>5.0.The high-Os basalts also have low ^(187)Os/^(188)Os ratios(0.1251-0.1554),representative of melt from the depleted asthenospheric mantle.By contrast,the low-Os basalts have higher ^(187)Os/^(188)Os ratios(0.1469-0.3018),suggestive of significant involvement of recycled crust either in the mantle source or during the magmatic differentiation.The samples with ^(187)Os/^(188)Os<0.20 show a positive correlation between Os and ^(187)Os/^(188)Os,which cannot be produced by crustal assimilation.The radiogenic Os compositions of the low-Os basalts might have primarily been derived from the recycled oceanic crust in the melting source.(2)The PGE geochemistry of the Cenozoic Hainan basalts might have been controlled by sulfide segregation during the magma differentiation.(3)The Os-Pb isotope modelling results imply that the age of recycled oceanic crust for the Cenozoic Hainan basalts varies between 100 and 300 Ma,which represents young or contemporaneous subducted oceanic slabs.The new geochemical results of Re-Os isotopes and PGE concentrations provide further insights into the recycled source mantle components and the role of sulfides in the origin and evolution of the primitive magma of the Cenozoic Hainan basalts,and the geodynamics of mantle plume activity.

关 键 词：再循环洋壳 PGE RE-OS同位素 新生代玄武岩 海南岛 

分 类 号：P581[天文地球—岩石学] P595[天文地球—地质学] P597