Geological Characteristics And Tectonic Environment Of Cretaceous Volcanic Rocks In Shengzhou,Zhejiang Province

The cretaceous volcanic rocks in Shengzhou of Zhejiang province belong to the Cenozoic volcanic rocks in the southeast coast of China.In this thesis,from the chemical characteristics of the volcanic rocks and geochemical characteristics,tectonic setting and aspects of the earth,of Shengzhou Cretaceous volcanic geological features and tectonic environment for discussion.According to the field geological survey data and age,the Cretaceous volcanic-sedimentary strata are divided into two sets of volcanic rocks.From bottom to top,Dashuang Formation,Gaowu Formation,Xishantou Formation,Chawan Formation and Jiuliping Formation of lower volcanic rock series,Guantou Formation,Chaochuang Formation and Fangyan Formation of upper volcanic rock series.There is a unconformity between the upper and lower volcanic systems,and the groups in the volcanic system are integrated contact relationships.Meanwhile it is determined that the volcanic rocks belong Moshishan Group Early Cretaceous,not part of the previous Jurassic predetermined period.The volcanic rocks in this area are mainly composed of acidic pyroclastic rocks,rhyolite and rhyolitic pyroclastic rocks.The volcanic rocks in the Dashuang Formation are composed of a single fluidic texture,rhyolite-insitu pyroclastic rocks and a small number of rhyolite assemblages.The Xishantou Formation of fluxion fused tufted tuff and the thick layer of yinganyan multilayer sedimentary rock;The volcanic rocks in the Chawan Formation are mainly composed of high-potassium rhyolitic pyroclastic rocks.The volcanic rock in jiuliping Formation is a single high-potassium rhyolite-rhyolitic pyroclastic assemblage.Hall on volcanic series,Guantou Formation of grey purple-purple conglomerate,tuffaceous glutenite of pyroclastic rocks,rhyolite and basalt,the Ann and rhyolitic ignimbrite and crystal tuff and bi-model combination;The Chaochuang Formation of the red and red continental sedimentary rocks in the chaochuan group;The Fangyan Formation is a set of sedimentary rocks.It has a relatively complete volcanic facies.Geochemical analysis shows that over the Cretaceous volcanic rocks belong to high-K calc-alkaline series aluminum,rich LREE and LILE elements K,Th and Rb,significantly depleted in high field strength elements Ta,Nb,Ti and P elements;Th higher abundance,greater than 10.With the evolution of magma,rare earth elements are enriched and the degree of enrichment is mainly related to lithology;the fractionation degree of light rare earth elements in acidic rocks is obviously higher than that of heavy rare earths;in the process of magmatic action,crystallization differentiation is occurred,and the crystalline separation of feldspar minerals in the lower volcanic system is stronger than that of upper volcanic rocks The magma evolution degree of the lower volcanic system is higher than that of the upper volcanic system.Combined Cretaceous volcanic geological features Shengzhou,tectonic setting and geochemical analysis show Shengzhou Cretaceous volcanic Rocks were formed in the active continental marginal environment,mainly from the mantle-derived magma continental crust of the basement partially fused,from the Early Cretaceous to Late Cretaceous from the Paleo-Pacific plate from the subduction compressional effect gradually weakened,extensional tensile effect of the tectonic environment gradually enhanced.