Age and geochemistry of the early Mesoproterozoic A-type granites in the southern margin of the North China Craton: Constraints on their petrogenesis and tectonic implications

• The Zhangjiaping pluton in the southern margin of the NCC was emplaced at ca. 1.53 Ga.
• These granites show an affinity to fractionated aluminous A-type granites.
• They originated from partial melting of the Archean calc-alkaline granitoids.
• They were the products of anorogenic magmatism.
• Their generation was related to the breakup of the Columbia supercontinent.

A-type granites are a spectrum of especial felsic rocks that are produced commonly within an extensional environment. They are rare before middle Paleoproterozoic but present abundantly since the late Paleoproterozoic, probably indicating a causal change of tectonics and geodynamic mechanism in the continental evolution of the Earth. An early Mesoproterozoic A-type granite belt was recognized in the southern margin of the North China Craton (NCC) in recent decades. The occurrence of this type of rocks indicates a possible spatial–temporal link between the tectonic evolution of the NCC and the breakup of the Columbia supercontinent during the Mesoproterozoic. The Zhangjiaping granitic pluton is located in the southern margin of the NCC and one part of the A-type granite belt. It can be divided into three zones according to their textural and compositional differences of the rocks with a gradually increasing degree of evolution inwards: wall zone, intermediate zone and core zone. LA-ICP-MS zircon U–Pb dating shows that it was emplaced at ca. 1.53 Ga. Petrologically, the Zhangjiaping granites contain perthite and calcic amphibole but are lack of alkali mafic minerals. Geochemically, all the Zhangjiaping granitic rocks show an affinity to fractionated aluminous A-type granites, with enrichment in silicon and total alkali, and depletion in MgO, CaO and P2O5 with negative Eu, Sr and Ti anomalies, as well as high FeOt/MgO, TiO2/MgO and Ga/Al ratios and high HFSEs (i.e., Zr, Nb, Ce, Y) concentrations. Such signatures, along with their low εHf(t) values (−12.5 to −4.0) of all the granites from the Zhangjiaping pluton, obviously indicate that the Zhangjiaping aluminous A-type granites were derived from partial melting of the crustal calc-alkaline granitoids (i.e., the granodiorites of the Taihua Complex in the study area) and experienced fractional crystallization during magmatic evolution. Their generation would be related to the underplating of mafic magmas in an extensional regime. Integrated with regional data, the Zhangjiaping aluminous A-type granites were the products of anorogenic magmatism likely corresponding to the breakup of the Columbia supercontinent.