Late Mesoarchean crust growth event: evidence from the ca. 2.8Â Ga granodioritic gneisses of the Xiaoqinling area, southern North China Craton

Recently, more attention has been paid to Precambrian magma events and crustal growth of the North China Craton (NCC), accompanying with controversy in activity stages and dynamic mechanism. In this study, we report the Archean (2802 ± 13 Ma) granodioritic gneisses in the Taihua Complex from the Xiaoqinling area, located in the southern margin of the NCC. The zircon Lu-Hf isotope analysis of the rocks showed 176Hf/177Hf ratios of 0.280977-0.281228, corresponding to εHf(t) values ranging from −3.5 to +6.6, and two-stage Hf model ages varying from 2836 to 3409 Ma. It was confirmed that late Mesoarchean (2.9-2.8 Ga) juvenile crust made contribution to the source material of these ca. 2.8 Ga granodioritic gneisses in the Xiaoqinling area. The whole rock geochemical data indicate that the granodioritic gneisses are high-K calc-alkaline series, probably generated at relatively high pressure and temperature, and formed under the continental arc setting. Statistically, we conclude that the magmatic activities during 2.9-2.7 Ga may represent the most intense crustal growth events in the NCC and these Archean rocks at different locations in southern NCC underwent a similar crustal evolution history.