海南岛北部中三叠世A型花岗岩的成因及其地质意义  

Formation of Middle-Triassic A-type granites in northern Hainan Island and its geological implications

作　　者：齐重向 温淑女 庞崇进[1] 梁航 王勇[2] 官军 余红霞[1] QI Zhongxiang;WEN Shunv;PANG Chongjin;LIANG Hang;WANG Yong;GUAN Jun;YU Hongxia(Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration,Collaborative Innovation Center for Exploration of Hidden Nonferrous Metal Deposits and Development of New Materials in Guangxi,Guilin University of Technology,Guilin 541004,Guangxi,China;School of Geosciences and Info-physics,Central South University,Changsha 410083,Hunan,China;Hainan Key Laboratory of Marine Geological Resources and Environment,Haikou 570206,Hainan,China;Hainan Geological Survey Institute,Haikou 570206,Hainan,China)

机构地区：[1]桂林理工大学广西隐伏金属矿产勘查重点实验室/广西有色金属隐伏矿床勘查及材料开发协同创新中心,广西桂林541004 [2]中南大学地球科学与信息物理学院,湖南长沙410083 [3]海南省海洋地质资源与环境重点实验室,海南海口570206 [4]海南省地质调查院,海南海口570206

出　　处：《地球化学》2023年第1期69-83,共15页Geochimica

基　　金：国家自然科学基金项目(41803020);广西自然科学基金项目(2015GXNSFBA139182、2018GXNSFAA050041);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开放基金项目(SKLIG-KF-14-06)联合资助。

摘　　要：海南岛北部儋州地区大面积出露三叠纪花岗岩体,其岩石成因与构造背景对揭示华南中生代构造演化具有重要意义。LA-ICP-MS锆石U-Pb定年结果显示儋州大王岭花岗岩体的侵位时间为243±1.8 Ma,表明该岩体形成于中三叠世早期。儋州大王岭花岗岩相对富铝(Al2O3=15.08%~15.49%)、钾(K2O=4.90%~5.63%)和稀土元素(∑REE=331~369μg/g),属钾玄质钙碱性系列;A/CNK值为0.93~0.95,属于准铝质。岩体相对富集轻稀土元素,轻重稀土元素分异明显(LaN/YbN=29.2~43.1),显示明显的Eu负异常(δEu=0.18~0.21)。样品具有相对高的Ga/Al值,结合(Nb+Zr+Ce+Y)含量指示其属于A型花岗岩。较低的锆石Hf同位素(εHf(t)=-13.9~-10.0)及较老的Hf同位素二阶段模式年龄(tDM2=1.54~1.73 Ga),反映其可能源自海南岛早–中元古代变质基底(如抱板群变沉积岩和变基性火山岩)部分熔融的产物。结合区域上同期岩浆岩组合以及其地球化学特征,指示中三叠世早期海南岛处于造山后陆内伸展拉张环境。Many Middle-Triassic granitic plutons crop out in the Danzhou region in northern Hainan Island,China.The petrogenesis and associated tectonic setting of these plutons can provide crucial information for understanding the Mesozoic tectonic evolution of the South China Block.Zircon U-Pb age dating using laser ablation inductively coupled plasma mass spectrometry show that the Danzhou Dawangling granitic pluton was emplaced during the early Middle-Triassic period (243±1.8 Ma).Samples collected from the Danzhou Dawangling granitic pluton have relatively high aluminum (Al2O3=15.08%–15.49%),potassium (K2O=4.90%–5.63%),and rare earth element (REE,331 to 369μg/g) levels,with metaluminous-type Al2O3/(CaO+Na2O+K2O) values (0.93 to 0.95),belonging to shoshonitic high-K calc-alkaline series.The enrichment of light REEs characterized the samples along with the depletion of heavy REEs (LaN/YbN=29.2–43.1) and obvious negative Eu anomalies (δEu=0.18–0.21).In addition,the samples had relatively high Ga/Al and (Nb+Zr+Ce+Y) values,indicating the geochemical features of A-type granite.Compared to the experimental melt compositions,the A-type granite samples were plotted in fields of partial melts of metagraywacke.In contrast,some samples were plotted in the overlapping area between metagraywacke and amphibole,indicating that they were derived from partial melting of a metamorphosed sandy sedimentary rock source.Zircon grains in the granite sample had very lowεHf(t) values (-13.9 to -10.0) and old two-stage model ages (tDM2=1.54–1.73 Ga),suggesting that parental magma of A-type granite was formed by the partial melting of the rocks in the Paleoproterozoic-Mesoproterozoic basement,which include the meta-sedimentary and meta-volcanic rocks in the Baoban Group in Hainan Island.Together with previously published data,the findings of this study suggest that Hainan Island underwent post-orogenic,intraplate extension during the early Middle-Triassic period.

关 键 词：中三叠世 A型花岗岩 壳源部分熔融 锆石HF同位素 海南岛 

分 类 号：P597[天文地球—地球化学]