Major-trace element and Sr–Nd isotopic geochemistry of Paleoproterozoic gneisses from the Taihua Complex within the Xiaoqinling terrane: Insights into the evolution of the southern margin of the Trans-North China Orogen

Abstract

Although the early Paleoproterozoic global magmatism appears to be rare, the Taihua Complex within the Xiaoqinling terrane of the southern Trans-North China Orogen (TNCO) contains abundant evidence for magmatic and tectonic activities during this period. In this contribution, we present whole-rock geochemical and Sr-Nd isotopic data for the gneisses from the Taihua Complex within the Xiaoqinling terrane to investigate their petrogenetic processes, geodynamic setting, and provide a better understanding of the tectonic evolution in the southern margin of the TNCO. Based on their patterns of geochemical characteristics, the studied samples can be broadly subdivided into three groups. The Group-1 and −3 gneisses have relatively low Sr/Y ratios, and negative Eu anomalies, indicating plagioclase was a residual phase during partial melting, which requires relatively low pressure conditions. The majority of the samples in these groups have negative whole-rock εNd(t) values, indicating the magma source was mainly ancient crust. However, these Group-2 gneisses have moderate to high Sr/Y ratios, and high Mg#, which may related to mantle-melt interactions. This study shows that the protoliths of studied gneisses from the Taihua Complex within the Xiaoqinling terrane were probably formed by either partial melting of pre-existing arc lower crust or partial melting of the delaminated thickened lower crust and then interacted with the mantle components in a post-collisional extension tectonic regime, which is consistent with the global tectonic regime at this time.