Deep-water sedimentary siliceous rocks and limestones, widely developed in Luodian, South Guizhou during Middle-Upper Devonian time, belong to a special formation type of siliceous rocks, because their formation type is distinctly different from siliceous rock developed within the island arc-type or accretionary environments.The petrological, mineralogical, and geochemical study was carried out for 42samples collected from the Middle-Upper Devonian siliceous sediments at Mengjiang and Guoshizhai in Luodian county, South Guizhou.The results reveal that the middle Devonian siliceous sedimentary rocks are high in Al2O3(0.62％～22.1％), TiO2(0.01％～0.84％),Fe2O3(0.41％～10.5％) and ∑REE content(7.87×10-6 ～319 × 10-6),and Ce/Ce* (0.51～0.96), and relatively low in Y/Ho(26.6～37.0, ave.30.8) and (La/Ce)N(1.06～1.99,ave.1.28);while the Mengjiang siliceous sediments of Upper Devonian are low in Al2O3(2.42％～10.6％), TiO2 (0.06％～0.43％), Fe2O3 (0.62％～2.65％), ∑ REE(28.7×10-6～163×10-6), Ce/Ce*(0.45～0.82), and relatively high inY/Ho(28.2～36.7,ave.34.2)and (La/Ce)N(1.34～2.34,ave.1.82).Except the effect of SiO2 dilution, the siliceous sediments in the study area have greatly variable REE contents and indicate multiple sources in origin, with large part from seawater from Middle to Upper Devonian and minor from terrigenous clastics.The discrimination diagrams of Al2O3/TiO2-Al(Al+Fe+Mn), Al-Fe-Mn and (∑REE-+-Y)-SiO2/Al2O3, and the major and rare earth element geochemical characteristics of the Middle-Upper Devonian siliceous sediments at Guoshizhai and Mengjiang in Luodian, indicate that these siliceous sediments formed in a normal marine sedimentary environment, with the depositional environment changing from restricted margin rift basin to an open-ocean rift basin during Middle to Upper Devonian.This study is of important value for further understanding the evolution for the Shuicheng-Ziyun-Nandan rift basin in the Late Paleozoic and Youjiang basin during Middle to Upper Devonian.%黔南罗甸地区中晚泥盆世广泛发育深水相沉积硅质岩、灰岩,其建造类型明显不同于增生型或岛弧型硅质岩,属于一种特殊的硅质岩建造类型.对罗甸蒙江(中、上泥盆统)和过石寨(中泥盆统)42件硅质岩类样品进行岩石学、矿物学以及主量和稀土元素地球化学研究,结果表明,中泥盆世硅质沉积物Al2O3 (0.62％～22.1％)、TiO2(0.01％～0.84％)、Fe2O3(0.41％～10.5％)、∑REE(7.87×10-6～319×10-6)、Ce/Ce*(0.51～0.96)值整体偏高,而Y/Ho值(26.6～37.0,平均30.8)和(La/Ce)N值(1.06～1.99,平均1.28)相对较低.晚泥盆世硅质沉积物的Al2O3(2.42％～10.6％)、TiO2(0.06％～0.43％)、Fe2O3 (0.62％～2.65％)、∑REE(28.7×10-6～163×10-6)、Ce/Ce*(0.45～0.82)值则相对偏低,而Y/Ho值(28.2～36.7,平均34.2)和(La/Ce)N值(1.34～2.34,平均1.82)相对升高.除去SiO2稀释作用影响,区内硅质沉积物稀土元素含量及来源变化均大,其中上泥盆统硅质沉积物中(∑REE+ Y)除部分来自陆源碎屑外,更多地从海水中获取.结合Al2O3/TiO2-Al(Al+ Fe+ Mn)、Al-Fe-Mn和(∑REE+ Y)-SiO2/Al2O3图解,以及主量和稀土元素地球化学特征,认为罗甸中晚泥盆世硅质沉积物为正常海相沉积,从中泥盆世到晚泥盆世,沉积环境已由较为局限的边缘裂谷盆地向开阔的边缘裂谷盆地转化.这对深刻认识水城紫云-南丹晚古生代裂陷盆地,以及右江盆地在中晚泥盆世的发展、演化过程均具有重要意义.
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