海南加茂地区红峰队岩体锆石U-Pb年代学、Hf同位素及其对构造环境的指示  

Zircon U-Pb Geochronology,Hf Isotopic Composition of the Hongfengdui Granitic Intrusion in Jiamao Area of Hainan Island and Its Tectonic Setting Implications

作　　者：胡在龙 陈婕 黄武轩 魏昌欣 王超[1,2] 吕昭英 HU Zai-Long;CHEN Jie;HUANG Wu-Xuan;WEI Chang-Xin;WANG Chao;LYU Zhao-Ying(Hainan Key Laboratory of Marine Geological Resources and Environment,Haikou 570206,Hainan,China;Hainan Geological Survey Institute,Haikou 570206,Hainan,China;Hainan Geological Survey&Design Institute,Haikou 570206,Hainan,China)

机构地区：[1]海南省海洋地质资源与环境重点实验室,海南海口570206 [2]海南省地质调查院,海南海口570206 [3]海南地质综合勘察设计院,海南海口570206

出　　处：《华南地质》2022年第3期496-507,共12页South China Geology

基　　金：中国地质调查局项目(DD20160035);海南省自然科学基金(420RC744)。

摘　　要：本文在野外地质调查的基础上,对海南加茂地区红峰队细中粒黑云母正长花岗岩体进行锆石年代学、Hf同位素及地球化学等特征的深入研究,以揭示该岩体形成的构造环境。结果显示,红峰队花岗岩体锆石LA-ICP-MS U-Pb年龄为259.5±1.3 Ma,形成于晚二叠世;具有高硅(SiO_(2)=72.26%~75.69%)、富碱(K_(2)O+Na_(2)O=8.51%~9.18%),高钾(K_(2)O/Na_(2)O=1.13~1.7),贫CaO(0.38%~0.75%)和P_(2)O_(5)(0.01%~0.02%)等地球化学特征,A/CNK值为0.99~1.08,属于准铝质-弱过铝质花岗岩;富集Rb、Th、U、K、Pb、Nd、Zr、Hf、Sm和轻稀土,明显亏损Ba、Nb、Ta、Sr、P、Eu、Ti,具强烈的负Eu异常;锆石饱和温度也较低(767~796℃);显示该岩体属于高分异I型花岗岩;ε_(Hf)(t)值变化较小(+3.0~+7.3),反映了其岩浆来源较为均一。红峰队岩体来源于新生地壳的部分熔融,并且发生了较高程度的分离结晶,可能形成于华南与印支块体的碰撞后伸展环境。A large number of intrusive rocks are distributed in the Jiamao area of Hainan Island.Limited by the degree of research,the predecessors have changed the formation age of the Hongfengdui granitic intrusion mass many times.This article in-depth study zircon chronology,Hf isotopes and geochemistry of the Hongfengdui granitic intrusion on the basis of field geological surveys in order to reveal the tectonic setting of the Hongfengdui granitic formation.The results show that the LA-ICP-MS zircon U-Pb age is 259.5±1.3Ma,with high Si(SiO_(2)2=72.26-75.69 wt%),rich alkali(K_(2)O+Na_(2)O=8.51-9.18 wt%),high K(K_(2)O/Na_(2)O=1.13~1.7),low CaO(0.38%~0.75%)and P_(2)O_(5)(0.01%~0.02%),belonging to the subalkaline high-K calc-alkaline series.While the A/CNK value is 0.99~1.08,belonging to quasi-aluminous to weakly peraluminous granite.On trace and REE aspects,the rocks are enriched in Rb,Th,U,K,Pb,Nd,Zr,Hf,Sm and LREE,obviously depleted in Ba,Nb,Ta,Sr,P,Eu and Ti with strong negative Eu anomaly and lower zircon saturation temperatures(767~796℃).Integrated geological and geochemical data suggest that Hongfengdui granitic should be genetically ascribed to highly fractionated I-type granites.Zircon Hf isotopic compositions of the granites are lowly variable withε_(Hf)(t)values ranging from+3.0 to+7.3,showing that magma source is relatively uniform.Geochemical characteristics indicate that the Hongfengdui granitic was generated from partial melting of mafic crust,and a high degree of fractionation occurred during the magma’s evolution,the granitic intrusion may be formed in the collision of the South China and Indosinian blocks and belonged to the post-collision tectonic environment,combined with other Late Permian granite features in the region,which proposes the boundary between the tectonic setting of extrusion and the tectonic setting of extension is probably to be accurate to about 259Ma about Hercynian-Indosinian magmatic activity.

关 键 词：锆石U-PB测年 HF同位素 地球化学 红峰队岩体 海南岛 

分 类 号：P581[天文地球—岩石学]