缅甸密支那、抹谷地区地幔橄榄岩岩石和矿物化学组成研究及其构造意义  

Petrological and mineralogical chemistry of mantle peridotites from the Myitkyina-Mogok ophiolitic belt(Myanmar) and its tectonic significance

作　　者：魏超 彭头平[1,3] 范蔚茗 张靖祎[1,2] 高剑峰 董晓涵[1,2] 梁细荣 陈林丽[1] WEI Chao;PENG Tou-ping;FAN Wei-ming;ZHANG Jing-yi;GAO Jian-feng;DONG Xiao-han;LIANG Xi-rong;CHEN Lin-li(State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou510640, 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》2018年第6期612-626,共15页Geochimica

基　　金：国家自然科学基金(41490613;41672058)

摘　　要：蛇绿岩作为古老大洋消亡的产物,隐含了重要的关于古大洋形成和演化的信息。缅甸地区作为我国藏东东构造结的南延,两条重要的蛇绿岩带(东带和西带)被证实,其中东带密支那-抹谷蛇绿岩带形成于中侏罗世,西带形成于早白垩世。针对缅甸东带蛇绿岩中的地幔橄榄岩开展了系统的岩石(相)学和矿物化学的研究。岩石(相)学的研究显示,东带密支那和抹谷地区的地幔橄榄岩组成相同,主要由尖晶石方辉橄榄岩和纯橄岩组成。进一步矿物化学组成分析表明,密支那地区尖晶石方辉橄榄岩(Fo=90.4～90.9)与纯橄岩(Fo=90.8)具有相同的橄榄石Fo值,前者的尖晶石Cr#值(0.36～0.47)明显低于纯橄岩角砾中的尖晶石Cr#值(Cr#=0.61);抹谷地区尖晶石方辉橄榄岩(Fo=91.32～92.01)具有比纯橄岩(Fo=91.93～93.69)略窄的橄榄石Fo值变化范围,以及略低的尖晶石Cr#值(前者为0.66～0.71,后者为0.68～0.80)。两个地区地幔橄榄岩矿物化学组成的差别反映了其源区部分熔融程度的差别,即密支那地区地幔橄榄岩的部分熔融程度要低于抹谷地区橄榄岩。而两地橄榄岩矿物化学组成均表明它们具有SSZ型蛇绿岩地幔橄榄岩的特征。结合前人对密支那地区地幔橄榄岩和相关岩石组合的研究结果,暗示缅甸东带蛇绿岩带形成于中侏罗世的俯冲背景。考虑到我国境内滇西地区并未证实与西藏地区相似的班公-怒江洋演化的岩浆产物,我们认为密支那-抹谷蛇绿岩带代表的是西藏班公-怒江洋(中特提斯洋)的南延,而不是新特提斯洋演化的产物。An ophiolite is a section of the Earth’s oceanic crust and the underlying upper mantle that has been emplaced onto continental crustal rocks.The origin and formation of ophiolites are very important to constrain the formation and evolution of the extinct ocean.Two ophiolitic belts have been identified in Myanmar,namely the Eastern Belt and Western Belt.The Myitkyina-Mogok ophiolites within the Eastern Belt were formed during the Middle Jurassic,whereas the ophiolites in the Western Belt were generated during the Early Cretaceous.This paper presents a new petrological investigation and mineralogical data for the mantle peridotites from the Eastern Belt.Both the Myitkyina and Mogok mantle peridotites from the Eastern Belt are composed of spinel harzburgites and dunite.In the case of the mantle peridotite in the Myitkyina mantle,the olivines in the spinel harzburgites(Fo=90.35-90.94)had similar Fo values to those in the dunite(Fo=90.79),whereas the spinels in the former(Cr^#=0.36-0.47)showed lower Cr^#values than those in the latter(Cr^#=0.61).For the Mogok mantle peridotite,the Fo values of the olivines and Cr^#values of the spinels from the spinel harzburgites were lower relative to those from the dunites.Collectively,the higher Fo values and Cr#values of the Mogok mantle peridotites compared with those of the Myitkyina mantle peridotites indicated a higher degree of partial melting for the former.Nonetheless,the chemical compositions of the minerals in the Myitkyina and Mogok mantle peridotites were commonly similar to those generated in a subduction-related tectonic setting.Combined with previous data,it is likely that the east ophiolites in Myanmar were generated in a subduction regime.Based on the fact that no Jurassic ophiolites similar to those in the Tibetan Plateau were identified in the western Yunnan Province,it is likely that the Myitkyina-Mogok ophiolites in the Eastern Belt of Myanmar are the southern continuation of the Bangong-Nujiang suture in the Tibetan Plateau,which represents relics of the Me

关 键 词：地幔橄榄岩 SSZ型蛇绿岩 密支那 抹谷 缅甸 

分 类 号：P595[天文地球—地球化学] P594[天文地球—地质学]