关键词: 华北, 古元古代, A型花岗岩, 小河岩体, 岩石成因

Abstract: Paleoproterozoic granitoids in the southern margin of the North China Craton are important carriers for studying the crustal evolution in Precambrian. In this study, we report zircon U-Pb ages and whole-rock geochemical compositions of the Xiaohe pluton exposed along the southern margin of the North China Craton in order to discuss its petrogenesis and significance for Precambrian crustal evolution. The Xiaohe pluton is composed of biotite-bearing monzogranite, geochemically, which can be divided into two categories according to its rare earth element characteristics. Type I shows the right dip distribution mode of light rare earth elements enrichment and heavy rare earth elements depletion, which has the characteristics of medium differentiation. Type II has a distribution pattern of rare earth elements with low total rare earth elements, insignificant fractionation of light and heavy rare earth elements, and depletion of middle rare earth elements, which has the characteristics of high differentiation. The zircon U-Pb dating on these two types of granite yielded ~1.80 Ga ages for the emplacement time of the magmas, indicating both of them emplaced in single magmatic period. All the analyzed rocks are rich in silica and alkaline and weakly peraluminous, having high-K alkali-calcareous and calc-alkaline characteristics. They are enriched in Rb, Th, U, K, etc., but depleted in Ba, Sr, P, and Ti. Both types granites have similar Nd-Hf isotopic compositions and their magmas should originate from partial melting of the Late Archean basement rocks along the southern margin of the North China Craton. The magmatism of A-type granite probably represents the tectonicsthermal event closely related to extension, implying a post-collisional/post-orogenic extensional setting along the southern margin of the North China Craton at ca. 1.80 Ga. 

Key words: North China, Paleoproterozoic, A-type granite, Xiaohe pluton, petrogenesis