Petrogenesis and tectonic setting of late Paleoproterozoic diorites in the Trans-North China Orogen

Abstract. Unravelling the tectonic setting and evolution of cratons during the late Paleoproterozoic has long been a major focus of geological research. As one of Earth's major cratonic blocks, the North China Craton (NCC) preserves extensive magmatism during this period. Recent investigations have identified numerous 1.78 Ga dioritic intrusions along the southern margin and the center of the NCC. The NCC experienced widespread magmatism at ∼ 1.78 Ga, and the tectonic setting of this period remains unclear and needs better understanding. Diorites of the NCC can help to constrain the late Paleoproterozoic tectonic setting in this region. In this paper we report zircon U-Pb ages of ∼ 1.78 Ga and geochemical data of the Jiguanshan diorite. The diorites in the Trans-North China Orogen and the southern margin of the NCC, including the Jiguanshan diorite, have similar element and isotopic characteristics. The average initial 87Sr / 86Sr and εNd(t) values are 0.7052 ± 0.0003 and −6.5 ± 0.2, respectively. The initial Pb isotope compositions of the diorite samples do not show significant enrichment of radiogenic lead. In terms of Sr-Nd-Pb isotope compositions and Nb / Ta, Ba / Th, and Sr / Th ratios, the diorites differ from the coeval Xiong'er volcanic rocks and mafic dike swarms. Our results suggest that the diorites originated from basaltic lower crust, rather than from enriched subcontinental lithospheric mantle. Whole-rock and zircon trace element features indicate that the diorites formed in a rift-related environment. The formation of the diorites reveals a potential transition from late Paleoproterozoic orogenic-related magmatism towards intraplate magmatism.