滇东南八布蛇绿岩的SHRIMP锆石U-Pb年代学研究  

SHRIMP Zircon U-Pb Chronology of the Babu Ophiolite in Southeastern Yunnan Province

作　　者：张斌辉[1] 丁俊[1] 张林奎[1] 张彬[1] 陈敏华[1] 

机构地区：[1]中国地质调查局成都地质调查中心,成都610081

出　　处：《地质学报》2013年第10期1498-1509,共12页Acta Geologica Sinica

基　　金：中国地质调查局"越北古陆北缘地质构造演化及其成矿效应研究"项目(1212010911065);"云南麻栗坡地区矿产远景调查"项目(1212010880402)资助的成果

摘　　要：滇东南地区是扬子、华夏、印支地块的汇聚部位。本区的八布蛇绿岩被认为是古特提斯洋分支右汀洋盆的残留洋壳。对八布蛇绿岩进行的地质填图、岩石组合、地球化学和年代学综合研究表明，八布蛇绿岩具有较完整的组合，包括地幔橄榄岩、堆晶辉长岩、辉绿岩墙群、枕状玄武岩和放射虫硅质岩，但其是外来系统推覆在原地系统三叠系兰木组浊流沉积之上。其中地幔橄榄岩以方辉橄榄岩为主，熔岩和辉绿岩为低钾拉斑系列。稀土死素和微量元素具有类似NMORB的特征，Ti／V比值为20～50之间，Nb／Yb～Th／Yb比值落在亏损地幔源区，应为MOR型蛇绿岩。斜长角闪岩SHRIMP锆石U—Pb年龄为272±8Ma（n—1]，MSWD=0．54），表明其时代为早二叠世晚期。综合扬子西南缘晚古生代火山岩分布和沉积演化特征，我们认为八布蛇绿岩代表了二叠纪早期右江洋盆剧烈扩张期的残留洋壳。The southeastern Yunnan area is the convergent plaace of Yantze, Cathaysia, Indo-China blocks, lhe Babu opholite is considered a remnant of the Youjiang oceanic crust, one branch of Paleo-Tethys. This study conducted an investigation using geological mapping, rock association, geochemistry and geochronology. Results shows that the Babu ophiolite has a relatively complete association： mantle peridotite, cumulate gabbro, diabase wall groups, pillow lava and radiolarian silicalite. But the Babu ophiolite is an allochthonousnappe superimposed onto Triassic turbidite deposit. Mantle peridotites consist mainly of harzburgite, and lavas and dikes are low-K tholeiitic basaltic rocks, with REE and trace elements similar to N-MORB. The typical trace element ratios such as Ti/V = 20-50, Nb/Yb-Th/Yb show that they were likely derived from DMM source. The observations suggest a MOR-type ophiolite. SHRIMP U- Pb age of zircons from amphibolites is 272iSMa（n=11, MSWD = 0.54）, indicating a late Early Permian epoch. Considering late Paleozoic basic magmatism and sedimentary evolution of southwest Yangtze block, we proposed that the Babu ophiolite represents the residual oceanic crust of Youliang basin during strong spreading in early Permian.

关 键 词：蛇绿岩 SHRIMP锆石U-Pb 古特提斯洋 右江盆地 滇东南 

分 类 号：P597.3[天文地球—地球化学]