三江南段勐海布朗山地区早古生代变火成岩岩石成因及其大地构造意义  

Petrogenesis and Tectonic Implication of the Early Paleozoic Metaigeneous Rocks in the Bulangshan Area,Menghai County,Southern Sanjiang Tectonic Zone

作　　者：孙载波 周坤 周家喜 刘桂春 赵江泰 吴嘉林 胡绍斌 浦涛 李小军 赵枫[4] 刘梦琼 SUN Zaibo;ZHOU Kun;ZHOU Jiaxi;LIU Guichun;ZHAO Jiangtai;WU Jialin;HU Shaobin;PU Tao;LI Xiaojun;ZHAO Feng;LIU Mengqiong(Yunnan Institute of Geological Survey,Kunming 650216,Yunnan,China;Yunnan Geological Survey,Key Laboratory of Sanjiang Metallogeny and Resources Exploration and Utilization,Ministry of Natural Resources,Kunming 650061,Yunnan,China;School of Earth Sciences,Yunnan University,Kunming 650500,Yunnan,China;State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Beijing 100083,China;Yunnan Archtectural Engineering Design Company Limited,Kunming 650217,Yunnan,China)

机构地区：[1]云南省地质调查院,云南昆明650216 [2]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650061 [3]云南大学地球科学学院,云南昆明650500 [4]中国地质大学地质过程与矿产资源国家重点实验室,北京100083 [5]云南省建筑工程设计院有限公司,云南昆明650217

出　　处：《大地构造与成矿学》2021年第3期586-607,共22页Geotectonica et Metallogenia

基　　金：国家自然科学基金地区基金项目(420602005);国家自然科学基金特提斯重大研究计划重点项目(92055207);云南省自然资源厅地质勘查基金项目(D2017014);中国地质调查局项目(121201010000150007、DD20160345-02);云南大学引进人才科研启动项目(YJRC4201804)联合资助。

摘　　要：滇西昌宁‒孟连蛇绿混杂岩带保存了晚古生代古特提斯洋演化的记录,近年来在该带内还识别了一套早古生代的SSZ型蛇绿岩以及早古生代洋岛型高压变质岩原岩,证实了带内具有与青藏高原内部龙木措‒双湖蛇绿混杂岩带相对应的原特提斯演化的记录。通过对昌宁‒孟连蛇绿混杂岩带东南部布朗山地区澜沧岩群中变火山岩和变辉长岩岩石学、岩石地球化学、锆石U-Pb年代学及锆石原位Hf同位素研究,年代学结果显示,变辉长岩年龄为480.2±1.8 Ma,变火山岩年龄分别为465.5±1.2 Ma和472.5±2.9 Ma,代表了变辉长岩和变火山岩原岩形成时代。地球化学特征显示,变辉长岩具有典型的E-MORB微量、稀土元素特征,亏损锆石Hf同位素组成(εHf(t)=12.8~13.6),为洋中脊玄武岩(N-MORB)和洋岛玄武岩(OIB)混合的产物,代表了早古生代原特提斯洋演化的洋壳残片;变火山岩由高镁安山岩和高镁玄武岩组成,具有典型的岛弧岩浆岩亏损高场强元素(Nb、Ta和Ti)的特征,指示它们来源于俯冲交代富集的岩石圈地幔部分熔融,代表的是早古代原特提斯洋俯冲消减过程的产物。因此,昌宁‒孟连原特提斯洋在早古生代早期就具有现今太平洋多岛洋的格局,这一研究为深入理解昌宁‒孟连蛇绿混杂岩带原‒古特提斯发展和演化提供了新的、重要的信息。The Changning-Menglian ophiolitic complex zone(CMOCZ)preserves the records of the Late Paleozoic Palaeo-Tethyan evolution in the western Yunnan province.In recent years,a set of Early Paleozoic SSZ-type ophiolites and oceanic island-type high-pressure metamorphic rocks has been recognized in this zone,which confirms a record of Proto-Tethyan evolution corresponding to the Longmucuo-Shuanghu ophiolites zone in the Tibetan Plateau.In this study,the petrology,petrogeochemistry,zircon U-Pb chronology and in situ zircon Hf isotopes of the metavolcanics and metagabbro within the Lancang Group in the Bulangshan area have been analyzed.The chronological results show that the protolith of the metagabbro was formed at 480.2±1.8 Ma,while those of the metavolcanic rocks were formed at 465.5±1.2 Ma and 472.5±2.9 Ma.The metagabbros have trace element features typical for the E-MORB,and the depleted zircon Hf isotopic compositions(εHf(t)=12.8–13.6)that may arise from mixing of the mid-ocean ridge basalt(N-MORB)and ocean island basalt(OIB),and therefore,may represent the fragments of the Early Paleozoic oceanic crust of the Proto-Tethys.The metavolcanic rocks consist of high-Mg andesite and high-Mg basalt.They have characteristics typical for island arc magmatic rocks such as depletion of high-field elements(Nb,Ta,and Ti).It is thus can be inferred that the metavolcanic rocks were derived from partial melting of the enriched lithospheric mantle by subduction metasomatism,and represent the products of the subduction of the Early Paleozoic Proto-Tethyan Ocean.Therefore,the Changning-Menglian Proto-Tethyan Ocean in the Early Paleozoic had a pattern which is roughly analoguous to that of the current Pacific multi-island.This study provides new and important information for the in-depth understanding of the development and evolution of the Proto-and Palaeo-Tethys in the CMOCZ.

关 键 词：锆石U-Pb定年 变辉长岩 变火山岩 原特提斯洋 昌宁‒孟连蛇绿混杂岩带 

分 类 号：P612[天文地球—矿床学]