Volcanics Geochemical Behavior Study In Xujiaweizi Faulted Depression, Yingcheng 1 Formation Of The Northern Songliao Basin

Based on a great quantity of petrographic thin section analysis , geochemical analysis and previous research results, this essay deals with the close classification of complex lithological rocks and concludes that there are all together 23 forms of rocks. Most of the test samples taken from Yingcheng formation are rhyolite and show some distinguishing features such as high silicon.For example,the primary components are alkali calcic rocks, what take the second place are calcic rocks, alkali rocks and strong caustic rocks;The quantity of K2O is positive proportion to that of SiO2;quantity of Na2O is inverse proportion to that of SiO2;Accessory elements in volcanics are also inverse proportion to quantity of SiO2. Meanwhile, rare-earth elements are very rich in these smples. Rhyolites have obvious Eu negative anomaly and troughs of high field strength elements--Nb,Ta,Zr,Hf,All the above mentioned features prove that the formation of volcanics are the results of crust-mantle intermingling.By the use of geochemical analysis, combining with rock core and logging materials, author studies the volcanic rock geochemical behavior and makes a systematical classification. In reference to prevenient research findings and the study, this essay establishes typical lithofacies denotations. According to the lithologic characters, volcanics lithofacies of Yingcheng formation can be divided into 5 facies and 16 subfacies. On the basis of outcrop materials , rock core materials, seismic data, log data and log information ,author sets up signs for volcanic eruption cycle and subdivides it to 4 eruption cycle phases- Cycleâ… , Cycleâ…¡,Cycleâ…¢,Cycleâ…£. From the view of Geochronology, geochemistry and lithogenesy, Songliao basin and the volcanics formed in Cretaceous Period around it belong to the same rock association.Geochemical behaviors and volcanics distribution classify that volcanics are formed at continental margin which is related with the closure of Mongolia-Okhotsk to northern Songliao basin at Mesozoic Era.