义敦地块中-晚三叠世中酸性侵入岩起源及其地质意义探讨  

Origin of the Middle-Late Triassic intermediate-acid intrusive rocks in the Yidun terrane and its geological significance

作　　者：方小玉 彭头平[1,3] 范蔚茗[3,4] 高剑峰[5] 刘兵兵 张靖祎 FANG Xiao-yu;PENG Tou-ping;FAN Wei-ming;GAO Jian-feng;LIU Bing-bing;ZHANG Jing-yi(State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;University of Chinese Academy of Sciences, Beijing 100049, China;CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China;Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China;State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China)

机构地区：[1]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,广东广州510640 [2]中国科学院大学,北京100049 [3]中国科学院青藏高原地球科学卓越创新中心,北京100101 [4]中国科学院青藏高原研究所,北京100101 [5]中国科学院地球化学研究所矿床地球化学国家重点实验室,贵州贵阳550081

出　　处：《地球化学》2017年第5期413-434,共22页Geochimica

基　　金：国家重点基础研究发展计划项目(2014CB440901)

摘　　要：地处青藏高原东部的义敦地块不仅发育特征显著的中生代构造-岩浆活动,而且也是重要的多金属成矿区。然而,对于区域上的构造-岩浆-成矿的时空格架及其深部动力学机制目前还未得到很好的约束。综合分析了近年来发表的该区中-晚三叠世中酸性侵入岩的研究资料和数据,进一步探讨了它们的起源、成因和构造意义。高精度的年代学结果显示,区内闪长斑岩和花岗岩的形成年龄为225~215 Ma,其峰值为~216 Ma。其中出露于义敦南部的闪长质岩石具有高的Mg~#值、Cr、Ni、Sr含量和Sr/Y比值,低Y、Yb含量及极弱的负Eu异常和正Sr异常等特征,显示出埃达克质岩的地球化学特征。结合其高K_2O/Na_2O比值和壳源型的Sr-Nd-Hf同位素组成特征,以及与缝合带东侧九龙地区同时代相同特征的钾质埃达克质花岗岩的对比,认为这些闪长质岩石并非前人认为的起源于俯冲洋壳板片或者交代富集的岩石圈地幔楔,而是下地壳部分熔融的产物。而巨大规模出露于该区中北部地区的花岗岩则比闪长质岩石具有更高的SiO_2(67.33%~78.01%)和K_2O(2.38%~6.41%)含量,以及明显的Eu和Sr负异常,略微弱的轻重稀土元素分馏以及更富集的全岩Sr-Nd和锆石Hf同位素组成的特征,表明这些花岗质岩石并非来自闪长质岩石的分离结晶作用,而是来源于更浅的中上地壳的部分熔融,为中上地壳不均一的中元古代地壳物质重熔的产物。结合甘孜-理塘缝合带两侧岩浆-沉积作用的特征,认为义敦地块中-晚三叠世岩浆作用形成于后碰撞的构造环境,是造山作用晚期岩石圈地幔拆沉作用的结果。因此,区域上中-晚三叠世中酸性侵入岩的综合分析表明,弧/陆-陆碰撞(义敦地块和松潘-甘孜地块),即甘孜-理塘洋盆的闭合在中-晚三叠世已经完成;义敦南部与铜多金属矿床密切相关的闪长质斑岩的源区并不具有成矿所需的高氧逸度和高水The Yidun terrane,located in the eastern part of the Tibetan Plateau,is not only a characteristic intrusive magmatic tectonic belt,but also a very important poly-metallic metallogenic belt.In this paper,we have integratedall published geochronological,element geochemical,Sr-Nd-Hf isotope data for the Middle to Late Triassicintermediate-felsic intrusive rocks in the Yidun terrane,along with the reported data from the Songpan-Ganziterrane,in order to further decipher their origin,petrogenesis and rock-forming tectonic setting.All preciselydating results of zircons from the Middle to Late Triassic diotitic and granitic rocks in the Yidun terrane show thatthe magmatism developed during225?215Ma,with a peak age of^216Ma.Dioritic porphyries from southernYidun terrane characterized by high Mg#,Cr,Ni and Sr contents and Sr/Y ratios,but low Y and Yb contents,together with weak Eu anomalies and positive Sr anomalies,are geochemically similar to adakities.Inconsideration of their high K2O/Na2O ratios,and crustal-type Sr-Nd-Hf isotopic compositions,and in comparisonof the chemical compositions of coeval potassic adakitic rocks in the Jiulong area(on the eastern side of the suturezone),it is clearly seen that these dioritic intrusive rocks were derived from remelting of the thickened lower crustrather than from the subducting of oceanic slab or sub-arc metasomatized lithospheric mantle as suggested before.Different from the coeval dioritic rocks,the granites show higher SiO2(67.33%?78.01%)and K2O(2.38%?6.41%)contents,and strongly negative Sr-Eu anomalies,along with their more enriched whole-rock Sr-Nd and zircon Hfisotopic compositions,indicating the granites are not a product of crystallization differentiation of dioritic magma.In combination with the unpublished data for the basalts in this region,we propose that these granites should bederived from partial melting of the mid-Proterozoic rocks at a middle to upper crustal level.In comparison withthe elemental and geochemical natures coupled with the pace-time patterns of co

关 键 词：中-晚三叠世 中酸性侵入岩 起源和成因 构造背景 义敦地块 

分 类 号：P59[天文地球—地球化学] P597[天文地球—地质学]