The Createous Volcanic Facies And Magma Evolution In North Lesser Khingan Range, Heilongjiang Province

A set of Mesozoic volcanic rock formation is widely exposed in Lesser Khingan Range in Heilongjiang province. Stratigraphy,petrology, the petro-graphic and geochemical of this formation is well studied in this paper. According to these studies, we clarifiedy the basic stratum Parasequence of this area, do some division on volcanic facies, also have some analysis of typical volcanic edifice. The process of the Magma Evolution is discussesd at last.Through the field and indoor study,divided the volcanic rock stratigraphic exposed in this area into Meifeng Formation and Fuminhe Formation.The rock assemblage of Meifeng Formation are basic, intermediate-basic to intermediate rocks. The main types of it are Olivine basalt, Basalt, Basalt andesite, Andesite, Trachyandesite, Andesite alloclastic breccia and Tuff. Connecting to the isotope age (105±1.5Ma),it belongs to the late of Lower Cretaceous. The rock assemblage of Fuminhe Formation are intermediate-acid to acid rocks. The main types of it are rhyolite, alkaline rhyolite, Dacite, Perlite, Suevite and Alloclastic breccia. Combining with the isotope age (77Ma), it belongs to the late Cretaceous.On the base study of stratigraphy, detailed mark out the volcanic rocks in the study area, the Meifeng Formation volcanic rocks are divided into four volcanic facies, five sub-volcanic facies; Fuminhe Formation volcanic rocks are divided into five volcanic facies, three sub-volcanic facies. meanwhile, Meifeng Formation volcatic rocks are mainly extrusive facies, a small amount of explosive facies, and Fuminhe Formation, mainly as extrusive facies-Volcanic sedimentary facies; and the Outbreak empty fell facies-extrusive facies. Measured profiles of exposed volcanic bodies (crater) a detailed description.On the base study of the geochemical characteristics in the area of volcanic rocks (including the characteristics of major elements, rare elements and trace elements characteristics and isotopic elements features), discussed the magmatic evolution of the area, will be divided into the late Early Cretaceous magmatic evolution, Meifeng Formation stage and the Late Cretaceous magmatic evolution Fuminhe Formation stage. Meifeng Formation of which stage of magma evolution, magma derived from the account by the subduction of the enriched mantle evolution,dominated by Crystallization differentiation,by the late of the evolution,the magma had been modified by the crustal materials' contamination visibly;Fuminhe Formation evolution mainly from magmatic contamination,result from the different degrees of melting in the crust,fractional crystallization less,mainly for the fractional crystallization of plagioclase.