The Redefinition And Tectonic Significance Of Wuligou Formation, Ordovician, Shule River Area, Qinghai

The study area is located in the Qinghai-Tibet plateau northeastern margin of the Qilian mountains, whose main body belongs to the Qilian block. This paper`s main work is researching Ordovician Wuligou formation exposed in Shule river area. In order to further explore central south Qilian structural properties and geological evolution process materials provide new constraints. I have set characteristics and structural properties of Wuyligou formation, through field route survey, the measured profile, thin section identification, rock geochemistry analysis and indoor comprehensive study. Paper's main understanding is as follows:1. There are a set of early Paleozoic stratigraphic in Shule river area. From the oldest to the youngest, they are Ordovician Wuligou formation(O1w), Yanchiwan formation(O2y), Silurian Balonggonggaer formation(Sb).2. There are mainly ocean silicon deposition of mud and fine flysch deposits. folder underwater fan conglomerate and basaltic pyroclastic rock. vertical consists of two sedimentary- eruption cycle, siliceous rocks and purple silicon pelite development mainly in the lower the bottom of the cycle. It is the flysch sedimentary clip subaqueous fan conglomerate in middle of the two cycle; The top of the cycle are basalt, volcanic breccia, volcanic clastic rock and limestone, marbleized limestone.3. According to the position, rock assemblage and regional comparative analysis of Wuligou formation, concluded that Wuligou formation belongs to a basin background, in which stability and activity appear alternately. It indicates a turbulent environment.4. Through the rock geochemical analysis, it is concluded that Wuligou formation basic volcanic rocks belongs to calc-alkaline series and high in potassium calc-alkaline series. Distribution curves of REE chondrite standardized the whole change law is consistent, light and heavy rare earth fractionation characteristic is obvious; the total REE of basic volcanic rock is higher than volcanic rocks' s. LREE is more enrichment than HREE in both of them,which show that the right curve of light rare earth element enrichment, no obvious Eu anomaly.5. Based on the volcanic tectonic environment discrimination of Wuligou formation, concluded that forming environment of Wuligou formation is the oceanic island environment.