Geological And Geochemical Characteristics Of The Huogeqi Granodiorite In Inner Mongolia And Its Geological Significance

The Huogeqi mining area is located in the central and western part of the Inner Mongolia Autonomous Region and in the western part of the northern margin of the North China Block.Magmatic rocks are well developed in the area,of which the Warwick-Indosinian magmatic activity is the most intense,mainly developed granite and granodiorite.Taking the biotite granodiorite outcropped in the southwestern part of the mining area as the research object,a systematic study was carried out based on previous studies.Through field investigation and in-depth analysis of petrography,mineral chemistry,U-Pb chronology and element geochemistry of the rocks,the petrogenesis and material sources of the biotite granodiorite were further discussed,and the extinction of the Paleo-Asian Ocean Plate and the Siberian Plate and the Siberian Plate were also discussed.The collisional assemblage of the North China Block provides time constraints.The Huogeqi biotite granodiorite in Inner Mongolia is light gray,medium-fine-grained semi-automorphic-it-shaped granular structure and massive structure.It is mainly composed of plagioclase,quartz,potassium feldspar and dark rock-forming mineral biotite.The plagioclase ring structure is of medium-longer rock,biotite is of primary magmatic origin and ferrous biotite.According to the formula for calculating the crystallization pressure of Al,the consolidation pressure of the magma ranges from 177 MPa to 264 MPa,and the emplacement depth is 6.71 to 9.98 km.The crystallization temperature of biotite Ti is between 640 and 690?,and logf O₂=-18.5-16.8 is known from the formula of oxygen fugacity,which indicates that oxygen fugacity is low in the process of diagenesis.Zircon U-Pb dating results show that biotite granodiorite was formed in the Middle Permian(271 Ma)and belongs to the product of Variscan-Indosinian magmatism.In addition,the samples have geochemical characteristics of high silicon(67.89%?69.48%),alkali-rich(ALK=6.23%?6.85%)and low titanium(0.36%?0.42%),low magnesium(1.24%?1.45%)and low phosphorus(0.10%?0.12%).At the same time,Rb,K and,light rare earth elements are enriched,Ba,Ta,Nb,P,Ti and heavy rare earth elements are relatively deficient,(La/Yb)N=10.23?37.01,which indicates that the fractionation of light rare earth elements is obvious,with slight negative Eu anomaly.(delta Eu=0.72?1.02)belongs to type I granite of high potassium calc-alkaline weak peraluminous(A/CNK=1.05?1.09).Zircon Lu-Hf isotope measurements show that the biotite granodiorite epsilon?_Hf(t)=-7.49-5.99,and its second-stage model age T_DM2=1671-1757 Ma,indicating that its magma originated from the Paleoproterozoic ancient crustal material.Based on the analysis of its regional geological background and geochemical characteristics,it is considered that it was formed in the compressive tectonic background of the Paleo-Asian Ocean plate subducting southward under the North China block.