Petrogenesis and Tectonic Significance of the Late Paleoproterozoic to Early Mesoproterozoic (~1.80–1.53 Ga) A-Type Granites in the Southern Margin of the North China Craton

Abstract

A-type granites are extremely rare before middle Paleoproterozoic but more frequent since late Paleoproterozoic globally, probably indicating a causal change of tectonics and deep geodynamic mechanism of the continents. The late Paleoproterozoic to early Mesoproterozoic tectonic transition is witnessed by the occurrence of the A-type granites in the southern margin of the North China Craton (NCC), including the 1.80 Ga Guijiayu and Motianzhai granites, 1.74 Ga Shicheng granite, 1.60 Ga Longwangzhuang and Maping granites, and 1.53 Ga Zhangjiaping granite. Most of the granites contain perthite, annite, and calcic amphibole but are lack of alkali mafic minerals. All of the granitic rocks show characteristics of typical A-type granites, with high silicon and total alkali, and HFSEs (i.e., Zr, Nb, Ce, Y) and low MgO, CaO, and P2O5; with negative Eu, Sr, and Ti anomalies and high FeOt/(FeOt + MgO) and Ga/Al ratios. Their geochemical characteristics, along with the negative zircon e Hf(t) and whole-rock e Nd(t) values, indicate that those A-type granites were derived from partial melting of ancient continental crust. Integrated with regional data, the late Paleoproterozoic to early Mesoproterozoic A-type granites in the southern margin of the NCC are most likely formed under post-collisional (1.80–1.78 Ga) to rifting regimes (1.78–1.53 Ga, or even younger), as Zhai and Peng (Acta Petrol Sinica, 23: 2665–2682, 2007) and Zhai et al. (Earth Sci Frontiers 21: 100–119, 2014, Tectonophysics, in press, 2015) proposed.