Geochemistry And Petrogenesis Of Quartz Porphyry And Granite Porphyry In Dubi,Inner Mongolia

Taking the quartz porphyry and granite porphyry in Dubi area as the research object,this paper carried out detailed field geological survey,and systematically studied the petrology,zircon U-Pb chronology,zircon Hf isotope and geochemistry of the quartz porphyry and granite porphyry,determined their diagenetic age,analyzed their geochemical characteristics,and then discussed the petrogenesis and tectonic background,It provides a theoretical basis for the regional Mesozoic tectonic evolution.1.Diagenetic ageUsing the LA-ICP-MS zircon U-Pb dating method,the diagenetic ages of the quartz porphyry and granite porphyry of the area are determined to be 127.8±2.1 Ma(MSWD=0.05)and 128.8±0.68 Ma(MSWD=0.25),respectively.Both are the products of Early Cretaceous magmatic activity.2.Rock geochemical characteristicsQuartz porphyry is rich in silicon(Si O₂content 76.06%?77.2%),rich potassium(K₂O content 4.66%?6.48%),high Fe O^T(1.22%?1.43%),high Fe O^T/Mg O(10.42?12.55),Low Ca O(0.58%?0.70%),higher Al₂O₃(11.63%?12.67%),high10000Ga/Al ratio(2.71?3.27),aluminum saturation index(A/CNK)1.08?1.15;granite porphyry is rich in silicon(Si O₂content 70.67%?71.88%),Rich potassium(K₂O content 5.83%?6.45%),high Fe O^T(2.27%?2.63%),high Fe O^T/Mg O(10.91?12.10),Low Ca O(0.33%?0.44%),high Al₂O₃(14.47%?15.14%),high10000Ga/Al ratio(2.64?3.03),aluminum saturation index(A/CNK)1.14?1.16;rare earth element distribution curve has obvious negative europium anomaly and“seagull”right-leaning mode;trace elements are relatively enriched in Rb,Th,K,etc,Relatively depleted Sr,Ba,Ti,P,etc.The two rocks show the characteristics of aluminous A-type granite.3.Magma source areaThe main elements,trace elements,and zircon Hf isotopic characteristics of quartz porphyry and granite porphyry indicate that the magma is mainly derived from the remelting of the ancient crust,and there are residual facies of amphibole and plagioclase during the period.4.Structure backgroundQuartz porphyry and granite porphyry have the characteristics of A₁type granite,formed in the intraplate extensional environment,and are the products of lithospheric thinning in the early Cretaceous in the northern margin of North China plate.