海南岛晚侏罗世沙心花岗岩的成因和地质意义:年代学、地球化学和Sr-Nd-Hf同位素制约  

Petrogenesis and geological significance of Late Jurassic Shaxin granite in northern Hainan:Constraints from chronology,geochemistry and Sr-Nd-Hf isotopes

作　　者：吕昭英 熊富浩[3,4] 胡在龙[1,2] 林义华 魏昌欣 袁勤敏[2] 吕嫦艳 LüZhaoying;Xiong Fuhao;Hu Zailong;Lin Yihua;Wei Changxin;Yuan Qinmin;LüChangyan(Hainan Key Laboratory of Marine Geological Resources and Environment,Haikou 570206;Hainan Provincial Geological Survey,Haikou 570206;College of Earth Science,Chengdu University of Technology,Chengdu 610059;State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Chengdu 610059)

机构地区：[1]海南省海洋地质资源与环境重点实验室,海口570206 [2]海南省地质调查院,海口570206 [3]成都理工大学地球科学学院,成都610059 [4]油气藏地质及开发工程全国重点实验室,成都610059

出　　处：《地质科学》2024年第5期1374-1390,共17页Chinese Journal of Geology(Scientia Geologica Sinica)

基　　金：海南省自然科学基金项目(编号:421QN368);中国地质调查局项目(编号:12120113065900);海南省财政项目(编号:HNDZDC-2020-2)资助。

摘　　要：海南岛侏罗纪岩浆岩属于华南晚中生代岩浆岩带的西南端组成部分,是探究华南晚中生代古太平洋板片俯冲动力学过程的重要探针。本文对海南岛北部侏罗纪沙心花岗岩开展系统的岩石学、年代学、岩石地球化学、全岩Sr-Nd同位素和锆石Hf同位素研究,探讨其岩石成因和地质意义。沙心花岗岩主要岩性为中细粒黑云母二长花岗岩。LA-ICP-MS锆石U-Pb定年表明,沙心花岗岩形成于161±1 Ma,属于晚侏罗世岩浆活动的产物。沙心岩体具有富硅(SiO_(2)=70.73%~75.15%)和富碱的特征((K_(2)O+Na_(2)O)=7.64%~8.31%)。岩石贫Ca、Mg和Fe,其铝饱和指数(A/CNK)的平均值为1.06,属高钾钙碱性和弱过铝质岩石系列。样品的轻稀土相对富集(75.35×10^(-6)~112.71×10^(-6)),重稀土相对亏损(6.40×10^(-6)~8.63×10^(-6)),其铕异常相对较弱(0.87~1.10)。岩石具有较低的高场强元素(Zr+Nb+Ce+Y)=123×10^(-6)~217×10^(-6)、^(T)FeO/MgO值(3.39~5.08)和锆石饱和温度(724℃~772℃),且岩石缺少典型过铝质矿物。沙心花岗岩具有较高的ε_(Nd)(t)值(-2.7~-1.9)和较低的二阶段Nd模式年龄(1.17~1.10 Ga)。岩石具有较高的锆石ε_(Hf)(t)(-1.71~+1.84)和较低的二阶段Hf模式年龄(1.32~1.09 Ga)。综合分析表明,沙心花岗岩属Ⅰ型花岗岩,是古太平洋板块俯冲后撤相关的陆缘弧环境下的中元古代变质砂岩熔融的产物,其岩浆源区存在一定地幔物质的贡献。Jurassic igneous rocks in Hainan Island are located in the southwest end of the Jurassic magmatic belt of South China,which are the key probes to constrain the Late Mesozoic magmatic dynamic settings in South China and the subduction dynamic processes of the Paleo-Pacific oceanic slab.This study presents systematic petrological,chronological,geochemical,whole rock Sr-Nd isotopic and zircon Lu-Hf isotopic studies on the Jurassic Shaxin granite pluton in northern Hainan Island,aiming to reasonably explore its petrogenesis and geological significance.The Shaxin pluton mainly comprises by medium to fine-grained biotite monzogranite.LA-ICP-MS zircon U-Pb dating reveals that the Shaxin pluton was formed at 161±1 Ma,belonging to the Late Jurassic magmatism.The Shaxin pluton has Sio_(2) contents of 70.73%~75.15%and total alkali contents of 7.64%~8.31%(K_(2)O+Na2O).The studied rocks have low contents of Ca,Mg,and Fe with an average A/CNK value of 1.06,belonging to the high potassium,calc-alkaline,and weakly peraluminous rocks.They are enriched in light rare earth elements(75.35×10^(-6)~112.71×10^(-6))but are depleted in heavy rare earth elements(6.40×10^(-6)~8.63×10^(-6))with insignificant europium anomaly(δEu=0.87~1.10).The Shaxin pluton has highε_(Nd)(t)values(-2.7~-1.9)and low two-stage Nd model ages(1.17~1.10 Ga).The studied rocks show high zirconεHf(t)ratios(-1.71~+1.84)and low two-stage Hf model ages(1.32~1.09 Ga).The rocks have low high-field-strength elements(Zr+Nb+Ce+Y)contents(123×10^(-6)~217×10^(-6)),^(T)FeO/MgO values(3.39~5.08)and zircon saturation temperatures(724℃~772℃),and lack the typical peraluminous minerals.Comprehensive study indicate that the Shaxin granites belong to theⅠ-type granite,and are derived by from the partial melting of late Mesoproterozoic metamorphic sandstone with the input of minor mantle-derived materials in a continental arc environment related to the rollback of the Paleo-Pacific Plate.

关 键 词：年代学 地球化学 晚侏罗世 Ⅰ型花岗岩 海南岛 

分 类 号：P597.3[天文地球—地球化学]