Abstract
Determining the petrogenesis and tectonic environment of the 2.18–2.14 Ga Liaoji granites is important to understand the Paleoproterozoic tectonic evolution of the Liao-Ji belt in the North China Craton. The Muniuhe granitic pluton is one representative of the Liaoji granites; it is located in the northwestern part of the Liao-Ji belt and is composed of syenogranite and granodiorite that intruded at ~2.18 Ga and were metamorphosed at ~1.88 Ga. Geochemically, the Muniuhe granitic pluton shows a magnesian and weakly peraluminous character, with low REEs, 10,000 × Ga/Al and Zr + Nb + Ce + Y values, and negative Nb and Ta anomalies, typical of arc-related I-type granite. It was formed by partial melting of Archean crustal material at low temperatures in oxygenated and hydrous conditions and then underwent crystallization differentiation of feldspar.The results of this study, together with those of previous studies investigating the Liaoji granites, indicate that the formation of the 2.18–2.14 Ga Liaoji granites (including the Muniuhe granitic pluton) can be subdivided into three stages: 1) the formation of ~2.18 Ga granites with A2-type characteristics (the Mafeng-Longchang, Jiguanshan, and Laoheishan-Yongdian granitic plutons), and ~2.18 Ga granites with arc-related I-type characteristics (the Muniuhe granitic pluton) in the northwestern and southeastern parts of the Liao-Ji belt; 2) the formation of ~2.16 Ga granites with arc-related I- and A2-type characteristics (Hupiyu-Hadabei, Simenzi-Gujiabao, and Qianzhuogou granitic plutons) in the central part with a NE-trending distribution; and 3) the formation of ~2.14 Ga granites (the Dafangshen granitic pluton) with A2-type characteristics in the central part. The intrusion ages show a trend to become younger from the margins to the center and the geochemical characteristics of these plutons indicate that they formed during the extension of a back-arc basin related to partial melting of the Archean continental crust. Together with the Liaohe Group and 2.13–2.11 Ga mafic intrusions, the Liaoji granites indicate that the existence of a back-arc basin extension during 2.18–2.11 Ga in the Liao-Ji belt.
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