Geochronology, geochemistry and petrogenesis of the Laozhaishan dolerite sills in the southeastern margin of the North China Craton and their geological implication

Abstract

Abstract The configuration of the North China craton (NCC) in the Rodinia supercontinent still remains controversial due to few reliable Neoproterozoic magmatism records. Here we report early Neoproterozoic dolerite sill swarms in the Laozhaishan region in the southeastern margin of the NCC. These sills intrude the Neoproterozoic sedimentary rocks (Wangshan, Gouhou and Shijia Formations), and are up to several hundred meters in thickness and >30\u202fkm in length. Baddeleyites separated from several representative dolerite samples show SIMS 207Pb-206Pb ages varying from 912\u202f±\u202f4\u202fMa to 916\u202f±\u202f4\u202fMa, which are consistent with concordant zircons U-Pb age of 913\u202f±\u202f10\u202fMa. Geochemically, the Neoproterozoic dolerite samples have relatively low rare earth elements (REEs) contents and show weak positive Eu anomalies. Moreover, these dolerite rocks are enriched in light rare earth elements (LREEs), large ion lithophile elements (LILEs; e.g., Rb and Ba) and some high field strength elements (HFSEs; e.g., Nb, U, Nd, Ti, Gd) and depleted in heavy rare earth elements (HREEs) and several HFSEs (e.g., Zr, Th), with geochemical affinities to within-plate tholeiitic basalts. The REE patterns, whole-rock eNd(t) (t\u202f=\u202f913\u202fMa) values varying from −0.60 to +3.12, and in-situ eHf (t) (t\u202f=\u202f913\u202fMa) values between +4.50 to +12.85 suggest that these dolerites were generated by mantle plumes, in which some enriched components were involved. In the context of assembly, growth and breakup of the Rodinia supercontinent, together with the recognition of ~913\u202fMa dolerite swarms in the NCC as well as nearly coeval rift-related magmatism recorded elsewhere on the globe such as the Congo craton and the Sao Francisco craton, we conclude that the NCC has involved in the evolution of Rodinia and the widespread dolerite swarms indicate the breakup of Rodinia.