摘要
滇西腾冲地块高黎贡群变质沉积岩时代和构造背景的厘定对正确认识原特提斯构造域演化过程及腾冲地块与冈瓦纳大陆之间的关系十分关键。岩石学、岩石地球化学结果表明,高黎贡群变质岩由变质沉积岩和变质岩浆岩组成,前者以片岩和副片麻岩为主,夹少量大理岩和石英岩,其原岩由一套杂砂岩、泥岩夹少量灰岩、硅质岩岩石组合,为深海-半深海相沉积物,形成于活动大陆边缘环境。碎屑锆石LA-ICP-MS U-Pb定年结果表明高黎贡群变质沉积岩中的锆石主要来源于与罗迪尼亚、冈瓦纳超大陆拼合及原特提斯洋俯冲有关的岩浆岩(900~1000Ma和500~600Ma),少量来源于中元古代地层(1500~1600Ma和2300~2400Ma)。4件样品中最年轻碎屑锆石群的加权平均年龄(507~510Ma)及没有出现有意义的小于470Ma碎屑锆石,表明高黎贡群变质沉积岩原岩形成于510~470Ma,是晚寒武世-早奥陶世早期原特提斯洋壳向冈瓦纳大陆下俯冲过程中,在俯冲带上盘沉积的含有大量该期火成岩碎屑的斜坡相沉积物。
Identification on the sedimentary age of metamorphic rocks of Gaoligong Group in Tengchong block,western Yunnan and its tectonic setting is a key to study the evolution of the Prototethy tectonic zone and the relationship between Tengchong block and Gondwana.Petrological and geochemical data show that the metamorphic rocks in Gaoligong Group are composed of meta-sedimentary and-igneous rocks.The metasedimentary rocks are mainly comprise of schist and Para gneisses with a little of marble and quartzite,which is metamorphosed from greywacke and mudstone with a little limestone and siliceous rocks deposited in abyssal-bathyal environment in active continental margin.Detrital zircon LA-ICP-MS U-Pb dating show that the zircons in the meta-sedimentary rocks derived mainly from the igneous rocks related to the amalgamation of Rodina and Gondwana supercontinents as well as the subduction of the Prototethys(900～1000 Ma and 500～600 Ma).Weighted mean age of the youngest detrital zircon groups in four samples ranged from 507 to 510 Ma,and without any significant ages less than 470 Ma,show the protolith of metasedimentary rocks in Gaoligong group was depositing from 510 to 470 Ma.These sedimentary rocks were deposited with some igneous sediment on the hanging side between ocean trench and island arc during the subduction of prototethys oceanic crust toward the Gondwana continent in late Cambrian-early Ordovician.