A Palaeoarchean–Mesoarchean micro-continent entrained in the Jiao-Liao-Ji Belt at the southeastern North China Craton: evidence from the zircon record in the Bengbu area

Abstract

The Bengbu area in the southeastern North China Craton (NCC) consists predominantly of Archean-Palaeoproterozoic (gneissic) granitoids with minor supracrustal rocks (the Fengyang and Wuhe groups). This study presents new zircon laser ablation-inductively coupled plasma-mass spectrometry U-Pb and Lu-Hf isotopic data and trace-element contents for these granitoids, which improve understanding the Archean-Palaeoproterozoic crustal evolution of the NCC. Magmatic zircon U-Pb data reveal that zircons in the (gneissic) granitoids were generated by multi-stage events at 2.93, 2.73, 2.53-2.52 and 2.18-2.13Â Ga. Metamorphic zircon U-Pb data obtained from these rocks show two distinct metamorphic ages of 2.49-2.52 and 1.84Â Ga, suggesting that the Bengbu area experienced a regional metamorphic event at the end of the Neoarchean Era and encountered reworking by a tectonothermal event associated with the formation of the Palaeoproterozoic Jiao-Liao-Ji Belt. Trace-element compositions of magmatic zircons reveal the highest Ti concentrations (8.08±3.38Â ppm) and growth temperatures (718±44Â °C) for the zircons aged 2.13-2.17Â Ga and an increase in zircon U/Yb ratios from 2.93Â Ga (0.34±0.12) through 2.73Â Ga (0.96±0.42) to 2.53Â Ga (1.05±0.46), but an evident decrease at 2.17-2.13 Ga (0.61±0.40 ppm). Similar Palaeoarchean xenocrystic and detrital zircons with negative É Hf(t) values, late Mesoarchean magmatic zircons with juvenile Hf isotopic features, early Neoarchean magmatic zircons with model ages of 2.9-3.0Â Ga, and two regional metamorphic events at 2.52-2.48 and 1.88-1.80Â Ga in the Bengbu and Jiaobei areas indicate a Palaeoarchean-Mesoarchean micro-continent entrained in the Jiao-Liao-Ji Belt at the southeastern NCC. © Cambridge University Press 2019.