The Character And Geological Significance Of The Nianzishan Miarolitic Alkaline Granite In Qiqihar City,Heilongjiang Province

The genetic and genetic types of granites,which is rich in geodes,are still controversial,and the controversy mainly focus on A type and Most felsic I type granite.Because of the high similarity on the characteristics of rock and the characteristics of geochemical characteristics between them,there is a great challenge for the study of genetic type.However,it is especially important to determine the genesis type and the age accurately for determining the dynamic mechanism of tectonics.In this paper,petrology,mineral chemistry,LA-ICP-MS zircon U-Pb chronology,geochemistry were studied in alkaline miarolitic granite body of Nianzishan in NE China to Try to accurately determine the type of genesis,and to explore the genesis of rock and regional dynamics,and to provide new informations for regional granite research.The miarolitic alkaline granite body of Nianzishan is located at the junction of the Greater Xing'an Mountains and the Songliao Basin in the NE China,and the lithology is mainly alkaline granite.Mineralogy is characterized by the development of alkaline melanocratic mineral:arfvedsonite and aegirine.In geochemical characteristics,it is high silicon,high alkali,potassium,Fe/Mg ratio.In the trace elements,the contents of Ga,Zr,Nb and Y in granite are higher,and the content of Ba,Sr,P and Ti is lower,the value of Zr+Nb+Ce+Y is 1394-1631ppm,10⁴*Ga/Al ratio between(4.10-4.29),Rare earth elements show a typical right-leaning light rare earth enrichment model,Eu anomalies are obvious.Zircon saturation temperature between 900-1000?,belonging to the typical A-type granite.According to the classification scheme proposed by Eby,it belongs to A₁type granite.According to the classification scheme proposed by Hong Dawei,it belongs to AA type granite,which belongs to non-orogenic granite and non-orogenic granite.By LA-ICP-MS zircon U-Pb chronology test,The age of granite formation were 112.54±0.44Ma and 114.1±1.7Ma,and the age of formation of quartzitic porphyry was 118.77±0.43Ma.The isotopic characteristics are characterized by very low initial Sr values and positive?Nd(t)values,the two-stage model age is 600-800 Ma,indicate that the source of the material may be a Proterozoic residual oceanic crust,And be contaminated by mantle material.The origin of the granite is the derivative model of the positive magma formed by the new crustal remodeling formed by the subduction of the early oceanic crust.Through the tectonic environment analyzed,all the rocks in the miarolitic alkaline granite body of Nianzishan fall into the WPG environment,and the granitic genesis type is A₁and AA,which represent the non-orogenic extensional environment,According to the characteristics of regional igneous rock assemblage,the main developmental rocks in the northeastern China during the period of 140-120Ma are CA-A,and a small amount of C,and 120-100Ma are mainly AC,Therefore,it is believed that the alkaline granite in Nianzishan cave is the product of the late Cretaceous plate in the northeastern China.In the early Cretaceous period,the northeastern region of China had a large-scale regional extension under the subduction of the western Pacific Ocean,and the extension peak is about 120-100Ma.