【摘要】 滇东南老君山地区出露了一套穹隆状变形-变质岩系,新近完成的1:5万都龙幅、麻栗坡县幅区域地质矿产调查报告,将其分解为晚志留纪南温河花岗岩、新元古界新寨岩组和古元古界猛硐岩群。首次对猛硐岩群的石英角闪斜长片麻岩进行了SHRIMP锆石U-Pb定年,结合阴极发光图像分析,获得两组岩浆锆石的结晶年龄分别为761±12Ma和829±10Ma,指示滇东南老君山地区存在新元古代岩浆活动,同时从同位素年代学上,表明猛硐岩群是一套前寒武纪的变质沉积-岩浆杂岩。此外,还获得一些年龄为≈1．83Ga的残留锆石,表明该区存在古元古代的结晶基底。石英角闪斜长片麻岩及共存的斜长角闪岩,它们的原岩具有大陆裂谷背景下玄武质-玄武安山质岩浆系列的地球化学特征,可能与新元古代Rodinia超大陆聚合-裂解过程中的岩浆活动有关,本区在新元古代可能位于南华裂谷与康滇裂谷的交汇部位。更多还原

【Abstract】 The region includes southeastern Yunnan and North Vietnam,which locates among the Nanhua,Yangtze and Indio-China Blocks,is a key target to study the tectonic evolution of South China and Southeastern Asian.There is a deformed-metamorphic dome outcrops in the Laojunshana area,Southeastern Yunnan.It had been divided into the Later Silurian Nanwenhe granite, the Neoproterozoic Xinzhai Formation and the Paleoproterozoic Mengdong Group in the recently 1/50000 regional geological surveys. The SHRIMP zircon U-Pb dating have been done first on the quartz-hornblende-plagiogneiss from the Mengdong Group,and the ages of two magmatic zircon groups are 761±12Ma（N=11,MSWD=0.85）and 829±10Ma（N=10,MSWD=0.36）,respectively. Combined with the crystal features,CL images,concordant of U-Th-Pb ages（the D% are 2.6 and 4.8,respectively）and the correlation index（0.64 and 0.19,respectively）,761±12Ma should present the crystal age,and 829±10Ma should presented the age of an older magmatism.These ages suggested that there should have the Neoproterozoic magmatism in the area,and the Mengdong Group should be a Precambrian metamorphic sedimentary and magmatic complex.Besides these,the inherited zircons with≈1.83Ga U-Pb dating indicated that there should have the paleo-proterozoic basement rocks in this area.The coexist quartz-plagio-amphibolite have rare-earth element and trace element distribution characteristic of OIB,and the quartz-hornblende-plagiogneiss have similar geochemistry characteristics beside low TiO₂,P₂O₅,K₂O,Rb,Sr,Eu contents and moderate Nb-Ta negative anomaly,which should be attributed to crystal fraction and crust-contaminate.The geochemistry and tectonic setting identification of these samples suggested that their protolith should be basaltic to basaltic-andesitic magmatic series related to mantle-plume.Based on these mention above,the Laojunshan area,Southeastern Yunnan should located in the cross region of the Nanhua Rift and the Kangdian Rift during breaking-up of the Rodinian Super-continent in the Neoproterozoic.更多还原