Petrogenesis of the late Early Palaeozoic adakitic granitoids in the southern margin of the Songliao Basin, NE China: Implications for the subduction of the Palaeo‐Asian Ocean

Abstract

Many data have been reported from the Early Palaeozoic subduction complex belt and accretionary arc to the south of the Solonker‐Xar Moron‐Changchun‐Yanji Suture (SXCYS) zone. However, as the suture is covered to the east by the Mesozoic–Cenozoic Songliao Basin, there have yet been no related reports about the Early Palaeozoic igneous rocks in this area. The authors discovered an Early Palaeozoic granitoid intrusion in the Fangjiatun area, northern Liaoning, and performed petrologic, geochemical, zircon U–Pb dating and Hf isotopic analyses on it. Zircon SHRIMP U–Pb dating results show that the intrusion formed at 437–432 Ma, that is, in the late stage of the Early Silurian. Petrogeochemical analysis indicates that the intrusion records 63.14%–66.45% SiO2, with Na2O/K2O ratios of 1.01–6.12 and magnesian index (Mg#) values of 32.42–40.82. The REEs show a certain degree of LREE/HREE fractionation and slightly lower ΣREE contents. The trace elements are relatively enriched in Rb, Ba, Th, K, and Sr (large‐ion lithophile elements [LILEs]) and depleted in Nb, Ta, P, and Ti (high‐field‐strength elements [HFSEs]), displaying continental magmatic arc characteristics. The rocks have high Sr mass fractions, low Y and Yb mass fractions, and high Sr/Y ratios, which are consistent with the geochemical signatures of typical adakites. Zircon Hf isotopic analyses indicate that their εHf(t) values range from 0.29–6.56, reflecting the relatively depleted signatures of the source area. Based on its occurrence location and emplacement time, the intrusion is interpreted to have been produced by tectonic thermal events during the subduction of the Palaeo‐Asian oceanic crust beneath the northern margin of the North China Craton (NCC), thus reflecting the existence of an Early Palaeozoic continental marginal accretionary arc in the eastern segment of the NCC along the south of the SXCYS and provide new evidence for the tectonic evolution of the northern margin of the NCC in the Early Palaeozoic.