Geochemistry,Petrogenesis and Tectonic Significance of the Paleoproterozoic Granites in Dahulun,North Hebei Province
Paleoproterozoic granites were discovered in localized areas of the northeastern margin of the landmass in the western part of north Hebei Province.However,systematically studies on their geochemical characteristics and geological significance are still unclear.Zircon U-Pb geochronology,geochemistry,and Sr-Nd-Pb isotopes analysis on the Paleoproterozoic granites in the Dahulun area,north Hebei Province,have been systematically studied.Two granite samples have been dated to(1 855±7)Ma and(1 844±8)Ma,and are rich in silicon(w(SiO2)=71.58％-74.01％)and potassium(w(K2O)=6.44％-7.07％),with K2O/Na2O ratios from 3.68 to 4.20 and A/CNK values from 1.12 to 1.27,displaying characteristics of strongly peraluminous,relatively potassic granites.They are enriched in light rare earth elements and large ion lithophilic elements,depletion in heavy rare earth elements and high field strength elements.Additionally,they show high TFeO/(TFeO+MgO)(0.74-0.80),and 10000XGa/Al ratios(3.36-3.55)and high zircon saturation temperature(840-873 ℃),which are typical characteristics of A2-type granite in a post-collisional extensional setting.All sample have high initial 87Sr/86Sr values of 0.713 0-0.716 2 and negative εNd(t)values of-8.0 to-7.6,with two-stage model ages(TDM2)ranging from 2.96 to 2.94 Ga.The(206 Pb/204 Pb)t,(207 Pb/204 Pb)t and(208 Pb/204 Pb)t ratios were 14.976-15.178,15.192-15.228 and 35.413-36.626,respectively.The comprehensive study shows that the Dahulun granitic magma originated from the partial melting of the～2.95 Ga Mesoarchean lower crust and was produced in an extensional tectonic setting following the collision between the Eastern and Western blocks of the North China Craton.
Dahulun granitepaleoproterozoiczircon U-Pb geochronologygeochemistrynorthern Hebei Province
万方数据
维普
