滇西大理地区存在泛非期构造-热事件记录

Pan-African tectonic-thermal events recorded in Dali area, western Yunnan

大理地区存在较完整的新元古代泛非期构造-热事件记录,海东挖色花岗闪长岩、花岗岩中获得黑云母K-Ar年龄799Ma、锆石U-Pb年龄667Ma,苍山云弄峰黑云母二长花岗岩中获得锆石U-Pb年龄748Ma,大沟箐角闪辉长岩中获得K-Ar年龄892.3Ma。新元古代挖色花岗岩和云弄峰花岗岩与奥陶系大成村组沉积接触。大成村组粉砂岩中产腕足类、腹足类化石,顶部与中志留统阴阳山组假整合接触,缺失下志留统。向阳村奥陶系—志留系发育较好,产丰富的三叶虫、笔石化石,其中不乏早奥陶世的标准分子。大理地区的地层构造与丽江地区差异较大,不能对比,但可以同青海南部及藏东对比。古中元界苍山群相当于宁多群,新元古界罗平山岩组相当于草曲群,缺失震旦系—寒武系。下奥陶统向阳组、迎凤村组相当于青泥洞组和曾子顶组。因此,大理地区板坱构造划分应归属西藏-三江造山系中的扬子西缘多岛-弧-盆系。西藏-三江造山系与扬子-华南陆块区的界线应移至红河-程海断裂上。

There are relatively complete Late Paleoproterozoic Pan-African tectonic-thermal events in Dali area, the isotopic ages of the biotite K-Ar and zircon U-Pb obtained from Haidong Wase granodiorite and granite are 799 Ma and 667 Ma, Cangshan Yunnongfeng biotite monzogranite yields the U-Pb age of 748 Ma, and isotopic age of K-Ar obtained from Zhoucheng Bojite is 892.3Ma.Late Paleoproterozoic Wase granite and Yunnongfeng granite are in sedimentary contact with the Ordovician Dachengcun Formation. Dachengcun Formation siltstone produced brachiopods and gastropods fossils. There is an unconformable contact between the top and Middle Silurian Yinyangshan Formation,with the lack of Lower Silurian strata. Ordovician-Silurian strata of Xiangyang Village are developed well and contain abundant trilobites, graptolite fossils, with lots of standard molecules of Early Ordovician. The stratigraphic structure in Dali area is different from that of Lijiang area and hence cannot be compared, but it can be compared with things of southern Qinghai and eastern Tibet. The Paleoproterozoic Cangshan Group is equivalent to Ningduo Formation, and the Late Proterozoic Luopingshanyan Group is equivalent to Caoqu Formation, with the lack of the Sinian-Cambrian strata. The Lower Ordovician Xiangyang and Yingfengcun formations are equivalent to the Qingniudong Formation and Zengziding Formation. Therefore, the Dali plate structure should be assigned to the multi-island-arc-basin system on the western margin of the Yangtze of the Ti-bet-Sanjiang orogenic system. The boundary between the Tibet-Sanjiang orogenic system and the Yangtze-Southern China block should be transferred to the Honghe-Chenghai fault.