关键词: 大囫囵花岗岩, 古元古代, 锆石UPb年代学, 地球化学, 冀北 ,  

Abstract:  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 UPb geochronology, geochemistry, and SrNdPb 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) (0.740.80), and 10000×Ga/Al ratios (3.363.55) and high zircon saturation temperature (840873 ℃), 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 00.716 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 (206Pb/204Pb)t, (207Pb/204Pb)t and (208Pb/204Pb)t ratios were 14.97615.178, 15.19215.228 and 35.41336.626, 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.

Key words: Dahulun granite, paleoproterozoic, zircon UPb geochronology, geochemistry, northern Hebei Province