Analysis Of Stratum And Structural Setting Of Meifeng Formation Volcanic Rocks In Wuyiling Area

This dissertation is object on the volcanic rock of Cretaceous Meifeng formation in Wuyiling area of Yichun city in Heilongjiang. Researching on the the features of the stratum, the characters of volcanic rocks and volcanic facies, volcanic structure, volcanic rhythm, isotopic geochronology and so on. At last, in combination with the features of rock assemblage, Geochemistry and the evolution of the regional structure, we do the Preliminary approach on the structural setting of Meifeng formation.According to the geological section, we clarified the stratum Parasequence of Meifeng formation. Also, on the basis of its lithology characters, rock assemblage, we divide it into two members:the up member and the low member. The rocks of the low member are trachyte, trachyandesite and shoshonite; The rocks of the up member are andesite, basalt-andesite and olivine basalt. In this area, the bottom of Meifeng formation is overlapping on the granite and the diorite formed in late Triassic Period. The top of Meifeng formation is unconformitied by rhyolite and dacite belonging to Fuminhe formation.We do some division on volcanic facies, also have some analysis of typical volcanic edifice. On the base of the study of lithology characters and petrography, we divide this volcanic rock into two volcanic eruption rhythms. Moreover, Some samples in the low member of Meifeng formation are age-dated by SHRIMP zircon U-Pb.The result show the age of the volcanic is 105.74±1.5Ma. It belongs to the late of Lower Cretaceous.The geochemical characteristics indicate that Meifeng formation volcanic rocks belong to calc-alkaline series. The main of it are High K calc-alkaline series and shoshonite series. And it also imply that the Meifeng formation volcanic rocks is forming in post-collisio, one unit of orogen evolution. It is tallies with the extending setting of post-collisio during the evolution of the regional structure. The subduction of the earth crust and the hybridization, metasomatism caused by it make great significance in the formation of the Meifeng formation volcanic rocks.