滇西陇川地区早古生代火山岩年代学、地球化学特征及其对原特提斯洋俯冲的指示  

Chronology and Geochemical Characteristics of the Early Paleozoic Volcanic Rocks in Longchuan Area,Western Yunnan Province,and Their Significance to the Proto-Thehyan Ocean Subduction

作　　者：吴嘉林 浦涛 柏杨 刘军平 何世军[6] 李序贵 何兆荣 WU Jialin;PU Tao;BAI Yang;LIU Junping;HE Shijun;LI Xugui;HE Zhaorong(Yunnan Institute of Geological Survey,Kunming,Yunnan 650216;School of Earth Sciences,Yunnan University,Kunming,Yunnan 650504;Key Laboratory of Sanjiang Metallogeny and Resources Exploration and Utilization,Ministry of Natural Resources,Kunming,Yunnan 650051;School of Earth Sciences and Resources,China University of Geosciences(Beijing),Beijing 100083;The 12th Geological Brigade of Sichuan,Yibin,Sichuan 644600;The Second Geological Institute of China Metallurgical Geology Bureau,Fuzhou,Fujian 350108)

机构地区：[1]云南省地质调查院,云南昆明650216 [2]云南大学地球科学学院,云南昆明650504 [3]自然资源部三江成矿作用及资源勘查利用重点实验室,云南昆明650051 [4]中国地质大学(北京)地球科学与资源学院,北京100083 [5]四川省第十二地质大队,四川宜宾644600 [6]中国冶金地质总局第二地质勘查院,福建福州350108

出　　处：《地球学报》2024年第4期450-464,共15页Acta Geoscientica Sinica

基　　金：云南省科技计划项目(编号:202305AD160031,202401AT070012);云南省自然资源厅基金项目“云南省1:5万铜壁关幅弄璋街幅芒东幅平山幅陇川幅清平街幅区域地质调查”(编号:D2017015)和“云南省1:5万驾车湾幅菱角塘幅功山幅寻甸县幅区域地质调查”(编号:SJ[2024]QD002)联合资助。

摘　　要：为探讨滇西地区原特提斯的构造演化特征,选择滇西陇川地区高黎贡山岩群中识别出的一套角闪斜长变粒岩夹二长浅粒岩的岩石组合进行研究,其原岩恢复分别为玄武安山岩和流纹岩。对其进行年代学研究,分别获得(486.8±4.5)Ma和(486.6±4.2)Ma的锆石U-Pb年龄,喷发时代为早奥陶世。角闪斜长变粒岩具全碱含量低(alk=2.75%~4.58%)、富钠(Na_(2)O/K_(2)O=2.32~4.79)、低钛(TiO_(2)=0.70%~1.12%)的特点,稀土配分曲线显示具MORB稀土地球化学特征,相对富集Rb、Th、K、Nd和轻稀土元素,相对亏损Nb、Sr、Ba、P、Ti,Sr-Nd-Pb同位素特征显示角闪斜长变粒岩具有EMII地幔特征,在La-La/Nb图解中具有岛弧玄武岩特征,地球化学和同位素特征表明角闪斜长变粒岩(安山玄武岩)是由洋壳俯冲析出流体交代的富集地幔楔部分熔融形成。二长浅粒岩具有全碱含量中等(alk=6.09%~7.59%)、富钾(Na_(2)O/K_(2)O=0.4~0.9)、低钛(TiO_(2)=0.10%~0.21%)的特点,稀土配分曲线为右倾型,相对富集Rb、Th、K、Nd和轻稀土元素,强烈亏损Sr、P、Ti,轻微亏损Ba、U、Nb、Ta,类似于岛弧花岗岩特征,在Rb/30-Hf-3Ta图解中具有火山弧特征,地球化学特征表明,二长浅粒岩(流纹岩)是由地壳部分熔融形成。综合研究认为本次发现的早古生代火山岩组合形成的构造背景为活动大陆边缘,是由原特提斯洋向冈瓦纳大陆北缘俯冲的产物。To explore the structural evolution characteristics of the Proto-Tethyan in western Yunnan,we selected a rock combination consisting of hornblende plagioclase granulite and monzonite leptite,identified from the Gaoligongshan Group in the Longchuan area of western Yunnan,for research.The protolith of the hornblende plagioclase granulite was basaltic andesite,while that of the monzonite leptite was rhyolite.Using LA-ICP-MS zircon U-Pb dating,we determined the zircon U-Pb ages of the hornblende plagioclase granulite and monzonite leptite to be(486.8±4.5)Ma and(486.6±4.2)Ma,respectively,indicating that the rocks formed in the early Ordovician period.The hornblende plagioclase granulite exhibits characteristics of low alkali(alk=2.75%–4.58%),high potassium(Na2O/K_(2)O=2.32–4.79),and low titanium(TiO_(2)=0.70%–1.12%).Chondrite-normalized REE patterns of the hornblende plagioclase granulite resemble those of MORB.Trace elements show enrichment in Rb,Th,K,Nd,and light rare earth elements,and depletion in Nb,Sr,P,and Ti.Sr-Nd-Pb isotopic characteristics indicate that the rocks originated from EMⅡmantle,suggesting that hornblende plagioclase granulite(basaltic andesite)is a product of ocean crust subduction.The La-La/Nb diagram suggests that the hornblende plagioclase granulite exhibits geochemical features of island-arc basalts.The monzonite leptite has the characteristics of medium alkali(alk=6.09%–7.59%),high natrium(Na2O/K_(2)O=0.4–0.9),and low titanium(TiO_(2)=0.10%–0.21%).Chondrite-normalized REE patterns are inclined to the right.Trace elements show enrichment in Rb,Th,K,Nd,and light rare earth elements,heavy depletion in Sr,P,and Ti,and low depletion in Ba,U,Nb,and Ta,similar to the characteristics of island-arc granite.The Rb/30-Hf-3Ta diagram indicates that the monzonite leptite exhibits geochemical features of island-arc granite.The monzonite leptite(rhyolite)is formed by the intrusion of basic magma into the crust,providing sufficient heat to partially melt it.Geochemical characteristics indicat

关 键 词：早古生代火山岩 地球化学 SR-ND-PB同位素 陇川地区 原特提斯洋 

分 类 号：P595[天文地球—地球化学]