黎府构造带北部南莫溪蛇绿混杂岩的发现及其地质意义

东南亚特提斯构造格架复杂，特别是印支板块西缘琅勃拉邦-黎府构造带构造演化及区域构造线连接更是争议不断. 通过老挝西北部填图工作，首次在黎府构造带北部南莫溪地区发现保存完整的蛇绿混杂岩，为探讨黎府构造带的属性以及区域古地理格局，选取了蛇绿混杂岩中的含放射虫硅质岩、辉长岩以及洋岛海山中的礁灰岩，开展了岩相学、古生物学、锆石LA?ICP?MS U?Pb年代学、岩石地球化学研究. 结果表明，该蛇绿混杂岩出露端元包括蛇纹岩、蛇纹石化橄榄岩、辉长岩、辉绿岩、玄武岩和硅质岩，蛇绿岩套层序特征完整；辉长岩LA?ICP?MS锆石U?Pb年龄为350.4±3.3 Ma，成岩为早石炭世；洋岛海山中珊瑚种属为Thamnopora sp.和Paracravenia sp.，所属时代为中二叠世；硅质岩岩石地球化学元素特征指示其为生物成因，沉积环境为洋盆或开阔的盆地环境，放射虫共鉴定出9属30种，所属时代为中泥盆世-早石炭世. 综合本次研究，反映出南莫溪蛇绿混杂岩所代表的洋盆具有长期的演化历史，从晚泥盆世开始，一直持续到中二叠世还未结束，演化时间至少超过135 Ma，指示了该蛇绿混杂岩代表残留的古特提斯洋盆，而非弧后盆地. 认为黎府构造带向北应与琅勃拉邦构造带相连，且该区域从晚泥盆世开始一直存在古特提斯洋. 

The Discovery of Ophiolitic Complex in Namhonr,Northern Loei Tectonic Belt and Its Geological Significance

The Tethyan tectonic framework in Southeast Asia is complex, especially the tectonic evolution history and tectonic belt connection of Luang Prabang?Loei tectonic belt on the western margin of the Indo china block is more controversial. Basing on the geological mapping work, we discovered for the first time a well?preserved ophiolitic complex in the Namhonr area, northern Loei tectonic belt. In order to explore the attributes of the Loei tectonic belt and the regional paleogeographic pattern, the lithology identification for the ophiolitic complex, zircon LA?ICP?MS U?Pb dating forthe gabbro, paleobiology and major and trace elements for the radiolarian chert and reef limestone are presented in this paper. The results show that the outcroped end members of the ophiolitic complex include serpentinite, serpentinized peridotite, gabbro, diorite, basalt and siliceous rock, which display a complete sequence of ophiolitic complex. The LA?ICP?MS U?Pb ages of gabbro is 350.4±3.3 Ma, indicating the gabbro was formed in the Early Carboniferous. The coral species in the oceanic island?seamount are Thamnopora sp. and Paracravenia sp. which belong to the Middle Permian. The geochemical characteristics of the siliceous rock indicate that it is of biological origin and the sedimentary environment is an ocean basin or an open basin environment. A total of 30 species of radiolarians have been identified in 9 genera, which belong to the Middle Devonian?Early Carboniferous. The results of this research reflect that the ocean basin represented by the ophiolitic complex in the Namhonr area has a long?term evolution history, starting from the Late Devonian and continuing to the Middle Permian, the evolution duration is at least 135 Ma, indicating that the ophiolitic complex represents the residual Paleo?Tethys ocean basin, not the back?arc basin. We believe that the Loei tectonic belt should be connected to the Luang Prabang tectonic belt to the north, the Paleo?Tethys Ocean has existed in this area since the Late Devonian.