滇西漕涧地区崇山变质杂岩中崇山岩群的时代与构造属性

滇西崇山变质杂岩带位于三江造山带"峰腰"的北段，带内构造挤压变质作用强烈，主体由一套中-深变质岩系（崇山岩群）和晚期花岗岩组成.其中崇山岩群历来被认为是元古代的结晶基底，但至今无精确的年龄依据，其形成时代和构造属性存在较大争议，严重制约了对区域构造演化的认识.对滇西漕涧地区崇山岩群中的岩石组分开展了碎屑锆石U-Pb年代学及岩石地球化学研究，结果显示副变质岩中的锆石均具明显的磨圆特征和较大的岩浆核，其中3件样品的最小一组碎屑锆石年龄分别为366~412 Ma（平均值为395 Ma）、435~508 Ma（平均值为473 Ma）和673~704 Ma（平均值为689 Ma），指示了其原始沉积时代应不早于395 Ma；岩石地球化学表明，副变质岩是一套活动大陆边缘或被动大陆边缘构造背景有关的大陆岛弧碎屑岩，变质基性岩和变质中性岩为同源异相，均具活动大陆边缘的弧火山岩特征.结合副变质岩和两类正变质岩的构造属性相同以及普遍具相互伴生关系的特点，该3类岩石应属同一套地层系统的不同物质组分，崇山岩群主体为一套成岩于晚古生代（236~395 Ma）和形成于陆缘弧环境的火山-沉积地层单元；并与南东侧澜沧增生杂岩的志留纪弧火山岩组合成原-古特提斯洋盆东侧不同时代多岛弧的构造格局.综合研究认为，崇山变质杂岩带内的中-深变质岩系（崇山岩群）不（全）是前人认为的元古代结晶基底建造，应为原-古特提斯洋盆向东俯冲在兰坪-思茅地块西缘形成的一套火山-沉积地层系统；崇山岩群主要由年轻的（晚古生代）地层岩石组成，由于后期遭受中生代和新生代变质变形作用后形成了现今所见的"古老"岩石面貌的中-深变质系. 

Age and Tectonic Attributes of Chongshan Group in Chongshan Metamorphic Complex in Caojian Area,West Yunnan

The Chongshan metamorphic complex belt in West Yunnan is located in the northern part of "peak waist" of Sanjiang orogenic belt. The tectonic compression metamorphism in the belt is strong, and the main body is composed of a suite of medium-deep grade metamorphic rocks (Chongshan Group) and late granite.Among them, Chongshan Group has always been regarded as the crystalline basement of Proterozoic, but so far there is no accurate age basis, and its formation time and tectonic attributes are controversial, which seriously restricts the understanding of regional tectonic evolution.In this paper, the detrital zircon U-Pb geochronology and petrogeochemistry of the rock components in Chongshan Group in Caojian area, West Yunnan Province were studied. The results show that the zircons in the parametamorphic rocks have obvious rounded features and large magmatic nuclei.The smallest group of detrital zircon ages of the three samples are 366-412 Ma (mean value 395 Ma), 435-508 Ma (mean value 473 Ma) and 673-704 Ma (mean value 689 Ma), respectively, indicating that their original sedimentary age should be no earlier than 395 Ma. Rock geochemistry shows that the meta-metamorphic rocks are a set of continental island arc clastic rocks related to the tectonic setting of active continental margin or passive continental margin, and the metamorphic mafic rocks and metamorphic intermediate rocks are homologous and heterogeneous and have the characteristics of arc volcanic rocks of active continental margin.Retrogeochemistry shows that the meta-metamorphic rocks are a set of continental island arc clastic rocks related to the tectonic setting of active continental margin or passive continental margin, and the metamorphic basic rocks and metamorphic intermediate rock are homologous and heterogeneous and have the characteristics of arc volcanic rocks of active continental margin.The main body of Chongshan Group is a set of volcanic-sedimentary stratigraphic units which were diagenetic in the Late Paleozoic (236- 395 Ma) and formed in the marginal arc environment. It is combined with Silurian arc volcanic rocks of Lancang River accretion complex in the south east side to form the structural pattern of multi-island arcs in different times on the east side of the Proto- Paleo-Tethys ocean basin. According to comprehensive research, the medium-deep grade metamorphic rocks(Chongshan Group) in Chongshan metamorphic complex belt is not (all) a Proterozoic crystalline basement, but a volcanic-sedimentary stratigraphic system formed by the subduction of the original-Paleo-Tethys ocean basin eastward on the western edge of Lanping-Simao block.Chongshan Group is mainly composed of young (Late Paleozoic) stratigraphic rocks, which formed the medium-deep grade metamorphic rocks with "old" rock features after being subjected to Mesozoic and Cenozoic metamorphism and deformation in the later period.