Detrital Zircon Records of the Banxi Group in the Western Jiangnan Orogen: Implications for Crustal Evolution of the South China Craton

Abstract

The Neoproterozoic evolution of the Jiangnan Orogen is important for understanding the tectonic history of South China. As a volcanic‐sedimentary sequence developed in the Nanhua rift, the Banxi Group preserves the records of important magmatic and tectonic events linked to the assembly and breakup of the Rodinia supercontinent. In this study, we report the results from whole‐rock major‐ and trace‐element concentrations, with zircon LA‐(MC)‐ICP‐MS U‐Pb ages, trace elements and Lu‐Hf isotopic compositions of sandstones from the Banxi Group. The rocks are characterized by high SiO2 (65.88%–82.76%, with an average of 75.50%) contents, moderate (Fe2O3T + MgO) (1.81%–7.78%, mean: 3.79%) and TiO2 (0.39%–0.54%, mean: 0.48%), low K2O/Na2O (0.03–0.40, mean: 0.10) ratios and low Al2O3/SiO2 (0.11–0.24, mean: 0.15) ratios. The sandstones have high ΣREE contents (mean: 179.1 ppm), with chondrite‐normalized REE patterns similar to the upper crust and PAAS, showing enriched LREE ((La/Yb)N mean: 14.85), sub‐horizontal HREE curves and mild Eu (Eu/Eu*: 0.75–0.89, mean: 0.81) negative anomalies. Their geochemical characteristics resemble those of passive continental margin sandstones. Most of the zircons are magmatic in origin and yield a U‐Pb age distribution with three peaks: a major age peak at 805 Ma and two subordinate age peaks at 1990 Ma and 2470 Ma, implying three major magmatic sources. The Neoproterozoic zircons have ɛHf(t) values ranging from –47.4 to 12.4 (mostly –20 to 0), suggesting a mixture of some juvenile arc‐derived material and middle Paleoproterozoic heterogeneous crustal sources. The Hf model ages of middle Paleoproterozoic zircons (∼1990 Ma) with negative ɛHf(t) values (–12.65 to –6.21, Ave. = –9.8) concentrated around the Meso‐Paleoarchean (mean TDMC = 3.3–3.1 Ga). For late Neoarchean detrital zircons (∼2470 Ma), ɛHf(t) values are divided into two groups, one with negative values (–9.16 to –0.6) with model ages of 3.5–2.9 Ga, the other featuring positive values (1.0 to 3.9) with model ages of 2.9–2.7 Ga, recording a crustal growth event at ∼2.5 Ga. Neoproterozoic zircons show volcanic arc affinities with partly intraplate magmatic features. We propose that the Banxi Group formed in a rift basin within a passive continental margin setting, which derived detritus from felsic to intermediate rocks from the Yangtze Block and a small amount of arc volcanic rocks. The middle Paleoproterozoic detrital zircon data suggest Columbia‐aged basement lies beneath the western Jiangnan orogen.

Apatite Fission Track Thermochronology of Granite from the Xiazhuang Uranium Ore Field, South China: Implications for Exhumation History and Ore Preservation

“…South China was formed by the amalgamation of the Yangtze and the Cathaysia blocks through the Jiangshao fault and experienced a long history of intra-plate tectonic deformation accompanied by multi-stage granitic magmatism and mineralization since the early Neoproterozoic (Fig. 1) (e.g., Wang et al, 2013Wang F et al, 2015;Zhu et al, 2022;Zhou et al, 2023). The NMB, generally referred to the E-W trending Nanling Range, is geographically located within the central part of the Cathaysia Block (Sun Y et al, 2021b;Bonnetti et al, 2023).…”

Extensive Resetting of Feldspar Pb Isotopic Composition in Archean–Paleoproterozoic Granitic Rocks from the Kongling Terrane, South China: Implications for Tracing Thermal Evolutionary History

“…Neoproterozoic magmatic events, which are widely distributed in the Yangtze Craton (Xu et al, 2016;Li et al, 2018;Huang et al, 2023;Zhou et al, 2023), are considered to be related to the assembly (at 1.1-0.9 Ga) and break-up (at 750-600 Ma) of the Rodinia supercontinent (McMenamin and MacMenamin, 1990;Dalziel, 1991Dalziel, , 1997Hoffman, 1991;Moores, 1991;Meert and Torsvik, 2003;Torsvik, 2003;Goodge et al, 2008;Li Z X et al, 2008;Zheng et al, 2008a, b). Following the final assembly of Rodinia (1.1-0.9 Ga), its margins underwent subduction-related accretion in the early Neoproterozoic, as evidenced by the presence of an arc/ forearc ophiolite suite with an age of ~1.1-0.9 Ga.…”

Early Triassic Silicic Volcanics of South China: Petrogenesis and Constraints on the Geodynamic Evolution of the Paleo‐Tethys Ocean Region

“…The South China Block was formed by collision of the Yangtze and Cathaysia blocks during the Neoproterozoic (Zheng et al, 2013;Zhou et al, 2023). The South China Block is surrounded by the Indochina Block to the southwest separated by the Song Ma suture zone, the North China Block to the north, and the Pacific plate to the east.…”