Provenance and geotectonic setting of the Palaeoproterozoic Zhongtiao Group and implications for assembly of the North China Craton: Whole-rock geochemistry and detrital zircon data

摘要

Geochemical data reveal the contrasting geochemical characteristics of the metasediments in the Jiepailiang and Bizigou formations of the Palaeoproterozoic Zhongtiao Group, North China Craton. High Zr/Sc and SiO_2/Al_2O_3 values and especially the evolved and uniform nature of εNd(t) values plus detrital zircon U-Pb ages and Hf isotopic signatures for the former are consistent with derivation from an evolved felsic source with sedimentary recycling signs. However, lower values of SiO_2/Al_2O_3 and Zr/Sc, and higher contents of Fe_2O_3* and MgO for the latter indicate input of more mafic components. These geochemical characteristics, combined with the wide range of εNd(t) values, suggest that these rocks were derived in part from old continental material, dominated by felsic rocks of magmatic origin, and in part from a continental island arc, which accounts for the variable mixture of mafic components. These results suggest that the Zhongtiao Group was deposited after c. 2110 Ma, in a back-arc basin, behind an eastward-directed subduction system. Subsequent deformation and metamorphism reflect closure of the oceanic basin between the Eastern and Western blocks of the North China Craton, along the Trans-North China Orogen, contributing to amalgamation of the supercontinental Columbia.