Petrological And Geochemical Characteristics Of Late Jurassic Volcanic Rocks In Chaihe Area

In this thesis,the research of petrology and geochemistry have been carried out on the volcanic rocks in the Manitu Formation and Baiyingaolao Formation in Chaihe,central Great Xing' an Range.Detailed studies of the petrology and geochemical characteristics of the volcanic rocks in the Manitu and Baiyingaolao Formations in order to reveal tectonic setting and the lithospheric evolution of Chaihe in the late Jurassic.They have SiO2 contents of 55.10%-75.94%,as in the acid-acidic volcanic rock;Al2O3 contents of 12.55%-17.81%;and are characterized by poverty in magnesium and iron,TFe2O3 contents of 1.8%-9.1%,MgO contents of 0.2%-3.7%,Mg#=13.6-49;TiO2 contents of 0.17%-1.68%;The alkali(Na20+K20=4.74-9.51%):and sodium(Na2O/K2O=0.12-1.53).Their C60 values range from 2.30 to 4.53.Plots of SiO2 against other major oxides show broadly negative corrdations with TiO2,MgO,TFe2O3,CaO and P2O5,positive correlations with K:0,and without correlations with Na2O while Al2O3 increase firstly and then decrease with the increase of SiO2 contents.They belong to subalkaline series and show a calc-alkaline evolutionary trend,most of them are plotted within(high-K)calc-alkaline series in SiO2 vs.K2O diagram.All the samples of the volcanic rocks are characterized by the enrichment of LREE and LILE,depletion of HREE and HFSE like Nb,Ta,Ti.Geochemically,these Late Jurassic volcanic rocks are similar to those from the active contmental margin setting,and their primary magma could been derived frem the lithospheric mantle wedge modified by fluid from a subducted slab.Magmatic evolution dominated by Crystallization differentiation,by the late of the evolution,the crustal materials'contamination enhanced gradually.The volcanic rocks display the geochemical characteristics of arc volcanic rocks and its genesis should be related to the subduction of Izanagi-Kula plate.