海南岛二叠纪—三叠纪构造演化:源自岩浆岩和变质岩同位素年代学和地球化学的约束  

Permian-Triassic tectonic evolution of Hainan Island:Constraints from geochronology and geochemistry of magmatic and metamorphic rocks

作　　者：吕方 辛宇佳 李建华[1,2] 王金铭 LÜFang;XIN Yujia;LI Jianhua;WANG Jinming(Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing 100081,China;Key Laboratory of Paleomagnetism and Tectonic Reconstruction,Ministry of Natural Resources,Beijing 100081,China)

机构地区：[1]中国地质科学院地质力学研究所,北京100081 [2]自然资源部古地磁与古构造重建重点实验室,北京100081

出　　处：《地质学报》2023年第1期30-51,共22页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号42072239,41822205,42102274);中国地质科学院地质力学研究所基本科研业务费项目(编号DZLXJK202005)联合资助的成果。

摘　　要：本文对海南岛广泛出露的中-酸性花岗质岩体和中—高级变质岩开展了系统的岩石学、年代学、地球化学及Lu-Hf同位素研究,识别出270~259 Ma和242 Ma两期岩浆事件和251~248 Ma变质-深熔事件。270~259 Ma岩浆岩包括花岗(石英)闪长岩和含石榴子石花岗岩。花岗(石英)闪长岩为准铝质I型花岗岩,锆石εHf(t)值变化较大,Mg#和CaO/Na_(2)O比值较高,Rb/Sr比值较低,起源于玄武质下地壳,并存在少量幔源岩浆的混入;含石榴子石花岗岩为典型的强过铝质S型花岗岩,锆石εHf(t)值为负,CaO/Na_(2)O比值较高,源岩主要为壳源贫黏土的碎屑岩。它们均富集LREEs(轻稀土元素)和LILEs(大离子亲石元素),明显亏损HFSEs(高场强元素),显示出与洋壳俯冲相关的岛弧岩浆岩的地球化学特征,形成于大陆弧背景下。251~248 Ma变质-深熔事件与区域上广泛分布的壳源S型花岗岩和韧性剪切变形同期,推测为一期弧-陆碰撞造山事件。242 Ma花岗岩为A_(2)型花岗岩,具正的锆石εHf(t)值,其源岩为新生的玄武质下地壳物质,标志造山已进入伸展垮塌阶段。海南岛在二叠纪末期到三叠纪初期完成了由洋壳俯冲向弧-陆碰撞造山的转换,该时期构造演化主要受古特提斯构造域控制。This paper presents a combined petrologic,geochemical and geochronological study and Lu-Hf isotopic analysis of granitic plutons and metamorphic rocks in Hainan Island.Two-stage(270~259 Ma and 242 Ma)magmatic events and a 251~248 Ma tectonothermal event are identified.The 270~259 Ma magmatic rocks include quartz diorites,granodiorites and garnet-bearing granites.Quartz diorites and granodiorites are metaluminous I-type granitoids with variable zirconεHf(t)values,high Mg#and CaO/Na_(2)O ratios,and low Rb/Sr ratios.They are interpreted to form by partial melting of basaltic lower crust with minor involvement of mantle-derived melts.The garnet-bearing granites are strongly peraluminous S-type granites.They display negative zirconεHf(t)values and high CaO/Na_(2)O ratios,indicating a crustal clay-poor,plagioclase-rich,psammitic source.All 270~259 Ma magmatic rocks are enriched in LREEs and LILEs,and depleted in HFSEs,sharing the common features of arc-related magmatic rocks.They are interpreted to be formed in the continental arc setting associated with the subduction of oceanic plate.The 251~248 Ma tectonothermal event,combined with coeval crust-derived S-type granites and ductile shearing deformation,is interpreted to be caused by arc-continent collision.The~242 Ma granites are A_(2)-type granites with positive zirconεHf(t)values.They were generated by partial melting of juvenile basaltic crustal material at high-temperature conditions in the post-orogenic setting.During late Permian to early Triassic,the Hainan Island experienced a tectonic transition from oceanic subduction to arc-continent collision,which was closely associated with the evolution of the Paleo-Tethys Ocean.

关 键 词：海南岛 晚二叠世—早三叠世 花岗岩 洋壳俯冲 弧-陆碰撞 锆石U-Pb同位素 LU-HF同位素 

分 类 号：P588.3[天文地球—岩石学] P597.3[天文地球—地质学]