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 2.18–2.13 Ga. Metamorphic zircon U–Pb data obtained from these rocks show two distinct metamorphic ages of 2.49–2.52 and 1.84 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±3.38 ppm) and growth temperatures (718±44 °C) for the zircons aged 2.13–2.17 Ga and an increase in zircon U/Yb ratios from 2.93 Ga (0.34±0.12) through 2.73 Ga (0.96±0.42) to 2.53 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 negativeɛHf(t) values, late Mesoarchean magmatic zircons with juvenile Hf isotopic features, early Neoarchean magmatic zircons with model ages of 2.9–3.0 Ga, and two regional metamorphic events at 2.52–2.48 and 1.88–1.80 Ga in the Bengbu and Jiaobei areas indicate a Palaeoarchean–Mesoarchean micro-continent entrained in the Jiao-Liao-Ji Belt at the southeastern NCC.

Petrogenesis and tectonic significance of Neoarchean (~2.6 Ga) alkaline ultrapotassic granitic gneisses from the southeastern margin of the North China Craton: Constraints from U-Pb dating, Hf isotope and petrogeochemistry

“…2.9 Ga, 2.7 Ga and 2.5 Ga events are widely preserved in Bengbu and Huoqiu areas (Fig. 8; Liu et al, 2019;Wang et al, 2014). These data indicate that the main magmatic events in the southeastern margin of the NCC occurred at ~2.9 Ga, ~2.7 Ga and ~ 2.5 Ga, and represent three significant crustal growth and reworking episodes.…”

“…The first one is represented by the Mesoarchean TTG gneisses mainly distributed at Hongxin Town. A zircon U-Pb age of 2.9 Ga was obtained in these lithologies by Liu et al (2019). These magmatic zircon ages suggest the existence of late Mesoarchean crust in the southeastern portion of the NCC.…”

“…U-Pb analyses of the metamorphic mantle domains from two gneiss samples (1504MS2 and 1410MS6) yield nearly identical late Neoarchean ages of 2498 ± 12 Ma and 2456 ± 13 Ma, suggesting a major late Neoarchean metamorphic event. Previous workers have reported major metamorphic events at ~2.5 Ga in the southeastern margin of the NCC (Liu et al, 2009a(Liu et al, , 2013b(Liu et al, , 2019Wang et al, 2012) as shown in Fig. 8.…”

“…The second phase of granitic intrusion is marked by the widespread occurrence of Neoarchean TTG gneisses outcropping continuously in the Wuhe County. Liu et al (2019) obtained in these lithologies conventional zircon U-Pb ages of 2.7 Ga, which are in accordance with published zircon ages of 2.7 Ga from the TTG gneiss, syenogranite, potassic granite and amphibolite in the Huoqiu complex (Liu et al, 2015;Wang et al, 2014;Xie et al, 2014). The third phase of granitic intrusion is represented by TTG gneisses and potassic granite, and give late-Neoarchean zircon ages of 2.5 Ga, which are in agreement with previously published zircon U-Pb ages of 2.5 Ga from a garnet-bearing mafic gneiss xenolith in the Jiagou Mesozoic intrusion and from marbles at Fengyang (Liu et al, 2017;Wang et al, 2012).…”

“…The last major early Precambrian episode of magmatism occurred at ca. 2.1 Ga and is represented by potassic granites well exposed in the Huaiyuan County, Shimenshan and Zhuangzili (Yang et al, 2009;Liu et al, 2019;Wang et al, 2017); nearly same ages are reported in the 2.13 Ga amphibolite of the Wuhe Group (Liu et al, 2018) and in the 2.1 Ga garnet-bearing felsic gneiss xenoliths of the Jiagou Mesozoic intrusion (Liu et al, 2013b). Therefore, this wide set of geochronological data from the Precambrian basement rocks and lowercrustal xenoliths in the Bengbu and neighboring areas suggest multistage magmatic events during the late Mesoarchean-middle Palaeoproterozoic period, with felsic magmatism occurring at ca.…”