Crustal reworking in the North China Craton at ∼2.5Ga: Evidence from zircon U-Pb ages, Hf isotopes and whole-rock geochemistry of the TTG gneisses in the Zhongtiao Mountain

The Sushui Complex in the Zhongtiao Mountain, located in the central NCC, is one of the reprehensive TTG gneisses in Late Archaean of North China Craton. In order to study the tectono-magmatic thermal event of the North China Craton during Late Archaean and the formation and evolution of the Early Precambrian continental crust, we choose the TTG gneisses of Sushui complex as the research object. The results show that the TTG gneisses are characterized by high Na, Al and Sr contents, but low Y, Cr, Ni contents. The TTG rocks are rich in LREE, and chondrite normalized REE patterns are characterized by right inclining type. And their trace elements display the features of enrichment of large ion lithophile elements (such as Rb and Ba) and strongly depleted in high field strength elements (Nb and Ta). LA-ICP-MS zircon U-Pb age data indicate that the rocks formed within the range of 2553 similar to 2561Ma, so their formation age is restricted at Late Archaean. In-situ zircon Lu-Hf isotopic analyses show that they have positive epsilon(Hf)(t) values and the corresponding two-stage model age are mainly between 2.7Ga and 2.8Ga. According to geochemical characteristics of TTG gneisses in Sushui Complex, we can conjecture that their magmatic origin was mainly related to the partial melting of 2.7 similar to 2.8Ga basaltic lower crust at the end of Neoarchaean, and contaminated by a few mantle sourced materials. With the fact of the widely distributed granitic rocks in the NCC, we hold that there was no proof of large-scale subduction process in the central NCC and the North China Craton should have been formed in Late Archaean. Based on the zircon Lu-Hf isotopic analyses in this article and previous research results, we consider that the magmatic event in similar to 2.5Ga in the Zhongtiao Mountain represents a major event of crustal reworking.