滇西澜沧江构造带景谷地区团梁子岩组的时代与构造属性
Timing and Tectonic Affinity of the Tuanliangzi Formation in the Lancangjiang Tectonic Belt in the Western Yunnan Province, China

前人关于南澜沧江构造带团梁子岩组的时代和构造属性有不同的认识.对景谷地区的团梁子岩组的物质组成、锆石年代学和地球化学进行了系统研究.团梁子岩组是一套强变形、弱变质的构造地层，主要由深海洋盆泥质岩和近岛弧碎屑岩构成，夹杂有洋中脊型玄武岩、硅质岩等岩块.2件变沉积岩样品的锆石U-Pb年龄结果显示其原岩时代分别不早于272±2 Ma和259±1 Ma.侵入团梁子岩组的安山玢岩锆石U-Pb年龄为244±1 Ma.团梁子岩组的变玄武岩岩块属于低钾拉斑玄武岩系列，具有典型的N-MORB地球化学特征.综合团梁子岩组的岩石组合特征和原岩性质，认为其很可能是一套晚古生代俯冲增生杂岩.团梁子岩组和南澜沧江构造带内其他洋盆相残余物质指示南澜沧江构造带是一条古特提斯结合带，代表存在于晚古生代的弧后小洋盆，而非宽阔的大洋.
There are always different understandings about the age and tectonic affinity of the Tuanliangzi Formation in the Lancangjiang tectonic belt.In this paper,petrological investigation,zircon U-Pb geochronology and geochemical compositions of the Tuanliangzi Formation in the Jinggu area are studied in detail in order to constrain its timing and tectonic affinity.The Tuanliangzi Formation in the Jinggu area is a set of tectonic strata overprinted by strong deformation and weak metamorphism,which is mainly composed of marine argillaceous rocks in the deep ocean and clastic rocks near island arc and is interlayered by some mid-ocean ridge basalt and chert.The minimum detrital zircon U-Pb ages obtained from two metasedimentay rocks reveal that the protolith deposition ages are younger than 272±2 Ma and 259±1 Ma,respectively.Furthermore,an andesitic porphyrite occurred as intrusion in the Tuanliangzi Formation yields a zircon concordia U-Pb age of 244±1 Ma.Metabasalts in the Tuanliangzi Formation are classified into low-K tholeiitic magma series and are characterized by the typical trace element compositions of the normal mid-ocean ridge basalt (N-MORB).Thus,we suggest that the Tuanliangzi Formation could be represented by a set of the Late Paleozoic oceanic subduction-related accretionary complex,which is similar to other relict oceanic basins in the southern Lanchangjiang tectonic belt.The southern Lanchangjiang tectonic belt can be considered as a Paleo-Tethys suture zone resulted from the closure of the small Late Paleozoic back-arc oceanic basin instead of the wide ocean