滇西澜沧江构造带中段中生代岩浆岩的年代学、地球化学特征及其地质意义  

Geochronology,Geochemistry and Geological Significance oft he Mesozoic Magmatic Rocks in the Middle Segment of the Lancangjiang Tectonic Belt,SW China

作　　者：张菁菁 李大鹏[1] 康欢 耿建珍[3] 陈静[1] ZHANG Jingjing;LI Dapeng;KANG Huan;GENG Jianzhen;CHEN Jing(School of Earth Sciences and Resources,China University of Geosciences,Beijing 100083,China;Institute of Geology,China Earthquake Administration,Beijing 100029,China;Tianjin Institute of Geology and Mineral Resources,China Geological Survey,Tianjin 300170,China)

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083 [2]中国地震局地质研究所,北京100029 [3]中国地质调查局天津地质矿产研究所,天津300170

出　　处：《现代地质》2021年第6期1733-1751,共19页Geoscience

基　　金：国家自然科学基金项目(41502212);中央高校基本科研业务费拔尖青年教师创新能力培养项目(2652019056)。

摘　　要：滇西澜沧江构造带被认为是古特提斯洋的闭合位置,该带南段完好地保存了蛇绿岩及与俯冲消减和闭合相关的大量岩浆记录。然而这些记录在澜沧江构造带中段鲜有报道,导致区域构造格架的划分产生了分歧,严重影响了对青藏高原发展演化的认识。我们最近在澜沧江构造带中段崇山变质带内发现了印支期岩浆记录。通过开展系统的锆石U-Pb年代学和Lu-Hf同位素以及全岩主微量元素和Sr-Nd同位素的研究,结合区域上已有的研究资料,得到如下主要认识。锆石U-Pb定年揭示澜沧江构造带中段崇山变质带闪长岩、花岗岩样品的结晶年龄为印支期(228~210 Ma)。区域印支期岩浆记录主要可以分为闪长岩、I型花岗岩以及S型花岗岩,这些岩浆岩均具有Nb、Ta和Ti等元素的亏损。闪长岩及I型花岗岩均表现出高MgO含量、Mg^(#)值(42~52)及较高的Cr含量,二者具有相似的全岩Nd同位素和锆石Hf同位素组成。S型花岗岩具有更高的K_(2)O含量以及更富集的同位素组成。不同类型岩石的空间接触关系、矿物学、捕获锆石年龄及主要地球化学特征揭示区域闪长质岩石为少量幔源物质与不同类型地壳物质混合的复杂产物,I型花岗岩为闪长质岩浆分异产物,S型花岗岩为壳源碎屑沉积岩的部分熔融产物。澜沧江构造带中段崇山变质带内印支期岩浆记录的岩性组合、主要地球化学特征及不同岩石成因均可与南段代表古特提斯主洋末期演化的岩浆记录类比,是古特提斯洋闭合阶段的响应。The Lancangjiang tectonic belt(LTB)in the western Yunnan is considered as the closure position of the Paleo⁃Tethyan ocean.Many ophiolitic rocks and magmatic rocks related to the subduction and closure of the Paleo⁃Tethyan ocean were well preserved in the southern segment of the LTB.However,such records have been rarely reported in the middle part of the LTB.As a result,regional tectonic framework has been debated,which seriously hampered the understanding of the development and evolution of the Tibetan Plateau.Recently,the Indosinian magmatic records has been discovered in the Chongshan metamorphic belt(CMB)in the middle segment of the LTB.Systematic analyses including zircon U⁃Pb and Lu⁃Hf isotopes,and whole⁃rock elements and Sr⁃Nd isotopes have been carried out on these rocks.Together with previous studies,we reached several main conclusions as follows.Zircon U⁃Pb dating indicates the Indosinian crystallization ages(228-210 Ma)of these dioritic and granitic rocks in the CMB in the middle part of the LTB.These magmatic records can be divided into the dioritic,I⁃type granitic,and S⁃type granitic rocks.All these magmatic rocks are depleted in Nb,Ta and Ti contents.Both the dioritic and I⁃type granitic rocks show high MgO contents,Mg^(#)values(42-52)and high Cr concentrations.The dioritic and I⁃type granitic rocks share similar whole rock ε_(Nd) and zircon ε_(Hf) values.The S⁃type granites have higher K_(2)O contents and more enriched Hf isotopic compositions.Their field occurrence,mineral assemblages,xenocrystic zircon ages,and geochemical characteristics of different types of rocks reveal that the dioritic rocks were products of a small amount of mantle⁃derived materials mixed with different types of crustal materials.The I⁃type granites differentiated from the dioritic magma.In contrast,the S⁃type granites were generated by partial melting of crustal derived clastic sedimentary rocks.Therefore,these Indosinian magmatic records in the CMB in the middle segment of the LTB show compa

关 键 词：青藏高原 澜沧江构造带 锆石U-PB定年 古特提斯洋 地球化学 

分 类 号：P597[天文地球—地球化学] P588.12[天文地球—地质学]