海南岛晨星早石炭世高度亏损N-MORB型玄武岩及其地质意义  

Extremely Depleted Carbonferous N-MORB Metabasite at the Chenxing Area(Hainan)and Its Geological Significance

作　　者：何慧莹[1,2] 王岳军[1,2] 张玉芝[1,2] 陈新跃[3] 周永智 

机构地区：[1]中山大学地球科学与地质工程学院,广东广州510275 [2]广东省地质过程与矿产资源探查重点实验室,广东广州510275 [3]湖南科技大学地质系,湖南湘潭411201

出　　处：《地球科学（中国地质大学学报）》2016年第8期1361-1375,共15页Earth Science-Journal of China University of Geosciences

基　　金：国家自然科学基金项目(No.41190073);国家重点基础研究发展计划(973计划)(No.2014CB440901);中山大学中央高校基本业务费项目

摘　　要：海南岛地处印支陆块和华南陆块的交界地带,具有复杂的构造演化史,其拼合机制及精细时代一直备受争议.在海南岛昌江-琼海断裂以北的晨星地区识别出一套具高ε_(Nd)(t)值的火山岩,对其进行了全岩40 Ar-39 Ar年代学及主、微量元素和同位素地球化学研究.结果表明,该火山岩的全岩^(40) Ar^(_39) Ar坪年龄为328.1±2.6Ma,代表了其喷发年龄;该变基性岩SiO_2含量为46.92%~52.58%,具有低TiO_2、低K_2O、高Al_2O_3的特征;稀土元素丰度为15.1×10^(-6)~28.7×10^(-6),呈现N-MORB型微量元素配分曲线,ε_(Nd)(t)高至9.02~9.85,显示出高度亏损的地球化学特征;其成因被解释为源于受流体交代作用改造的MORB型地幔源区.综合分析表明晨星地区变基性岩的形成可能与古特提斯洋陆俯冲格局下华南与印支陆块间的弧后盆地或有限洋演变有关.Hainan Island,located between the Indochina and South China Blocks,has undergone compound structural overprinting and complex tectonic evolution.However,the Late Paleozoic tectonic regime and amalgamation history of the South China with Indochina Blocks are still on debate.Our investigation identified the highly-depleted greenschist-facies basalt at the Chenxing area in the north of the Changjiang-Qionghai fault,Central Hainan Island.This paper presents a set of new geochronological and geochemical data for these metabasites.The representative sample for Chenxing metabasites gave the plateau age of328.1±2.6Ma,representing the eruption age.They have SiO_2 ranging from 46.92 % to 52.58 %,TiO_2 from 0.48 % to1.12% and Al_2O_3 from 12.34 %to 17.45%,and could be classified as basalt.These samples show lower K_2 O contents,and HFSEs and REEs contents relative to N-MORB.They are characterized by the left-sloping REE pattern and multi-elemental pattern with a geochemical affinity to N-MORB.These samples show extremely highε_（Nd）（t）values ranging from 9.02 to 9.85.Such geochemical characteristics for the Chenxing metabasites show the derivation of the MORB source modified by slab-related fluid.In combination with other available data,the Chenxing metabasites in Central Hainan are formed in the back-arc basin or a restricted ocean basin between the South China and Indochina blocks during the Carboniferous in response to the subduction ofthe Paleotethyan main ocean.

关 键 词：变基性岩 ND同位素 N-MORB 石炭纪 东古特提斯演化 地球化学 岩石学 

分 类 号：P581[天文地球—岩石学]