Zircon U-Pb Age and Hf-O Isotope Evidence of the Taihua Complex on the Southern Margin of the North China Craton: Implications for Its Magmatic Process During the Early Paleoproterozoic

1. Introduction

A global-scale continental magmatism decreased during the Tectono-Magmatic Lull (TML, 2365–2235 Ma) (Condie et al., 2022) has attracted considerable attention. Although there were a few magmatic activities during this period, there is a relative scarcity in terms of silicic magmatism (SiO₂ > 65 wt%) (Partin et al., 2014; Scaillet et al., 2016; Teixeira et al., 2015). The North China Craton (NCC) (fig. 1) is one of the ancient cratons in the world, preserving older crustal remnants that date back to circa (ca.) 3.8 Ga in the eastern part of the craton (D. Y. Liu et al., 1992). It is noteworthy that the NCC witnessed early Paleoproterozoic silicic magmatism at ca. 2.3 Ga, and the tonalite-trondhjemite-granodiorite (TTG) suits formed in the Taihua complex of the southern margin of the Trans-North China Orogen (TNCO) (fig. 1) (Diwu et al., 2014; Huang et al., 2012; X.-L. Jia et al., 2019; G.-D. Wang et al., 2017; Yu et al., 2013). Geologists have carried out extensive field-based structural, petrological, geochemical, geochronological and geophysical investigations on the southern TNCO, and produced large amounts of data and competing interpretations. However, most of these investigations have focused on ages, structural, and tectonic evolution (Diwu et al., 2014; Huang et al., 2012; X.-L. Jia et al., 2019; Y. Li et al., 2018; X. Wang et al., 2019; Yu et al., 2013; Y. Zhou et al., 2016). Comparatively, less attention has been paid to magmatic processes that had been operative on the southern part of the TNCO. Oxygen isotopes have been extensively adopted in combination with petrological and geochemical data to determine magmatic processes, such as crystallization, evolution, and generation of magma (Taylor & Sheppard, 1986). Only a few oxygen isotope data have been reported for early Precambrian rocks in the southern NCC (Sun et al., 2023; X. Wang et al., 2021; Y. Zhou et al., 2021). The Xiaoqinling is the largest terrane of the Taihua Complex and records Paleoproterozoic magmatism (Diwu et al., 2014; Yu et al., 2013), which is one of the most potential regions for understanding of secular changes in tectonic processes during the ~2.3 Ga magmatic lull.

Figure 1.Geological sketch map of the North China Craton (NCC) (after Chen & Zhao, 2023). A square indicates the study area. Abbreviations: CD—Chengde; DF—Dengfeng; EH—Eastern Hebei; FP—Fuping; HA—Huai’an; HS—Hengshan; JD—Jiaodong; LL—Lvliang; NH—Northern Hebei; NL—Northern Liaoning; SJ—Southern Jilin; SL—Southern Liaoning; TH—Taihua; WL—Western Liaoning; WT—Wutai; WS—Western Shandong; XH—Xuanhua; ZH—Zanhuang; ZT—Zhongtiao. I to V refer to terranes in the Taihua complex: I. Xiaoqinling; II. Xiaoshan; III. Xiong’rshan; IV. Lushan; V. Wuyang.

In this contribution, we report zircon U-Pb, Lu-Hf and O isotopic compositions for the granitic gneiss, tonalitic gneisses, and migmatitized tonalitic gneiss from the Taihua Complex within the Xiaoqinling terrane. This study aims to constrain the timing and magmatic processes of the Taihua Complex within the Xiaoqinling area, and through an integrated data of the Paleoproterozoic silicic magmatism (ca. 2.3–2.2 Ga) from across the craton to provide further insights into the Great Oxidation Event (GOE) and the global Huronian Glaciation Event (HGE).

2. Geological Settings and Samples

2.1. North China Craton

The North China Craton (NCC) is an important tectonic unit, bordered by the globe’s largest Phanerozoic accretionary orogen, the Central Asian Orogenic Belt to the north, and Central China Orogen to the south. Tectonically, the NCC can be divided into two major blocks named the Eastern and Western Blocks, separated by the Trans-North China Orogen (TNCO) which represents a ca. 1.85 Ga collision zone between the two blocks (fig. 1) (G. Zhao et al., 2001). The Western Block formed by amalgamation of the Yinshan Block in the north and the Ordos Block in the south along the Khondalite Belt at ca. 1.95 Ga (fig. 1) (G. Zhao et al., 2005). The Eastern Block underwent Paleoproterozoic (2.2–1.9Ga) rifting along its eastern continental margin, and the final closure of this rift system at ca.⁠1.9 Ga led to the formation of the Jiao-Liao-Ji Belt (fig. 1) (G. Zhao et al., 2005). The basement of the NCC consists of variably exposed Archean to Paleoproterozoic rocks, including TTG gneiss, granite, charnockite, migmatite, amphibolite, ultramafite, mica schist, greenschist, Al-rich gneiss (khondalite), calcsilicate rock, banded iron formation (BIF), meta-arkose and marble, with a Mesoproterozoic to Phanerozoic cover (Jahn et al., 1987; Jahn & Zhang, 1984; Zhai, 2004).

2.2. Taihua Complex

The Taihua Complex, also termed the Taihua Group, is scattered along the southern margin of the TNCO from the Xiaoqinling, Xiaoshan, Xiong’ershan, Lushan, to Wuyang terranes (fig. 1). These five terranes may be part of the Qinling Orogen and hosted metalliferous deposits (Mao et al., 2002; Zhang et al., 2000).

2.3. Lithologies of the study area and sampling

The Taihua Complex within the Xiaoqinling terrane is the largest outcrop of Archean-Paleoproterozoic basement in the southern TNCO (fig. 1), which can be further subdivided into the lower and upper parts of the Taihua Complex. The lower part of the Taihua Complex mainly consists of tholeiite and tonalite-trondhjemite-granodiorite (TTG) suites metamorphosed into amphibolite and TTG gneiss, whereas the upper part of the Taihua Complex comprises quartzite, metapelitic gneiss and schist, marble and iron formation (Qi, 1992). According to earlier studies, the lithology of the Taihua Complex in the Xiaoqinling area can be further divided into four units: the ca. 2.8–2.2 Ga crystalline basement rocks that belong to the lower Taihua subgroup (X. Jia et al., 2016; Yu et al., 2013); the ca. 2.0–1.8 Ga metamorphic supracrustal rocks of the upper Taihua subgroup (Wan et al., 2006); the ca. 1.8–1.6 Ga sedimentary rocks covered above the Taihua Complex (Diwu et al., 2013); and the ca. 160 Ma–110 Ma granite, which intrude into the Precambrian Complex in the region (Xu et al., 2009).

In this study, we collected representative granitic gneiss, tonalitic gneisses, and migmatitized tonalitic gneiss samples for geochronological and Lu-Hf and O isotopic analyses. The sampling locations are shown in figure 2, and their key information, including the coordinates, rock types, and mineral compositions, is listed in Supplementary Table S1. In the field, the grayish-white granitic gneiss (sample 22TH-06) (fig. 3A), collected from the Yushiyu section, Tongguan county, in the eastern part of the Xiaoqinling terrane, shows a granular granoblastic texture and a distinct gneissic structure, with nearly vertical foliation and oriented minerals such as quartz and feldspar. Most of the plagioclase grains are euhedral to subhedral in shape. The average quartz grains are larger than the feldspar grains. Samples 22TH-12 and 22TH-21 are two tonalitic gneisses collected some 0.9 km apart. These rocks are composed predominantly of quartz, feldspar, and biotite. The tonalitic gneiss (sample 22TH-12), collected from the Shaohuashan section in the central segment of the Xiaoqinling terrane, outcrops as river channel bedrock and is generally gray in color, showing a distinct gneissic structure with visible quartz, feldspar and biotite (fig. 3B). The tonalitic gneiss (sample 22TH-21), obtained from the Bayuan section in the western segment of the Xiaoqinling terrane, shows a pronounced orientation of quartz, feldspar and biotite in the field, with a gneissic foliation striking 175° and dipping 20° (fig. 3C). The tonalitic gneiss (sample 22TH-14), also collected from the Shaohuashan section in the central segment of the Xiaoqinling terrane, encloses blocks of amphibolite and exhibits local migmatization in the field, with small late-stage granitic veins intruding both the gneiss and the amphibolites (fig. 3D).

Figure 2.Simplified geological map of the Taihua Complex in the Xiaoqinling terrane, showing the sampling locations of U-Pb zircon dating and Hf-O isotopic study. (modified after the Geological Bureau of Shaanxi Province, 1966).

Figure 3.Photographs of metamorphic rocks outcropping in the study area: (A) granitic gneiss, site 22TH-06; (B) tonalitic gneiss, site 22TH-12; (C) tonalitic gneiss, sample 22TH-21; (D) migmatitized tonalitic gneiss, site 22TH-14.

3. Analytical methods

Zircon cathodoluminescence (CL) images were obtained to reveal the internal texture of the grains, preparing for further zircon U-Pb age analyses and Hf-O isotopes. Cathodoluminescence (CL) images were taken by using a Scanning Electron Microscope (TESCAN MIRA 3) connected to a TESCAN MIRA 3 system, for examination of zircon internal structures and for selection of analytical spots.

Zircon U-Pb isotopic analysis was performed using a GeoLas HD laser ablation system combined with an Agilent 7900 quadrupole ICPMS (inductively coupled plasma mass spectrometer). A spot size of 32 μm with a laser repetition rate of 5 Hz was used, and the laser energy density was 5.5 J/cm². Zircon 91500 (Wiedenbeck et al., 1995) and synthetic silicate glass NIST610 (Jochum et al., 2011) were used as external standards for U-Pb dating and trace element calibration, respectively. Whereas zircons GJ-1 (Jackson et al., 2004), Tanz (Hu et al., 2021) and Plešovice (Sláma et al., 2008) were used for data quality control. Raw data were processed by using software ICPMSDataCal (Y. Liu et al., 2010). Detailed analytical results are presented in Supplementary Table S2. Concordia diagrams and ²⁰⁷Pb/²⁰⁶Pb age histograms were plotted using Isoplot/Ex_ver3 software (Ludwig, 2003).

In situ Lu-Hf isotopic analysis of zircon was performed using a 193 nm GeoLas HD excimer ArF laser ablation system (Coherent, Göttingen, Germany), attached to a Neptune Plus MC-ICP-MS (Thermo Fisher Scientific, Bremen, Germany). All analyses were carried out with a beam diameter of 44 μm, an 8 Hz repetition rate, and energy of 10 J/cm². Zircon standards Plešovice, GJ-1, and 91500 were analyzed after analysis every ten sample spots to ensure instrument stability and for data calibration (Morel et al., 2008). Detailed analytical results are presented in Supplementary Table S3. Initial Hf isotopic ratios are recalculated to the determined ages, using the ¹⁷⁶Lu-¹⁷⁶Hf decay constant of 1.867 × 10⁻¹¹ yr⁻¹ (Söderlund et al., 2004). The values of εHf(t) are calculated relative to the chondritic reservoir with a ¹⁷⁶Hf/¹⁷⁷Hf ratio of 0.282772 and ¹⁷⁶Lu/¹⁷⁷Hf ratio of 0.0332 (Blichert-Toft & Albarède, 1997). Single-stage Hf mode ages (T_DM1) are calculated relative to the depleted mantle with a present-day value of ¹⁷⁶Hf/¹⁷⁷Hf = 0.28325, similar to that of average MORB (Nowell et al., 1998) and ¹⁷⁶Lu/¹⁷⁷Hf = 0.0384 (Griffin et al., 2000). Two-stage Hf model ages (T_DM2) are calculated by assuming a mean ¹⁷⁶Lu/¹⁷⁷Hf value of 0.015 for the average continental crust (Griffin et al., 2002).

Zircon oxygen isotope analysis was conducted using a CAMECA IMS 1300-HR³ instrument. A primary 133Cs⁺ ion beam (2.4–2.5 nA current and 20 keV total impact energy) was focused on the sample surface. A 5 μm × 5 μm raster was used in this study, and a normal-incidence electron gun was used for charge compensation. An NMR field sensor was applied to stabilize the magnetic field. The signals of ¹⁶O and ¹⁸O were collected simultaneously using two Faraday cups at positions L’2 and H’2, respectively. The L’2 and H’2 positions were configured with a resistor circuit of 10¹⁰ Ω and 10¹¹ Ω, respectively. The mass resolving power (MRP, M/ΔM), measured at 50% peak height, was set at ~2500 to minimise isobaric interferences. The total analytical time was about 5 min per pit: 100 s pre-sputtering (to remove the Au coating); ~ 60 s automatic centering of the secondary ions in the field aperture, and a total of 80 s integration of secondary ions (twenty cycles × 4 s). To evaluate the reliability of the analytical protocols in this study, well-characterized zircon reference materials Penglai (X.-H. Li et al., 2010) and Qinghu (X. Li et al., 2013) were also analyzed. Detailed analytical results are presented in Supplementary Table S4.

4. Results

4.1. Zircons from Granitic gneiss

Zircons from granitic gneiss 22TH-06 are colorless or dark gray, transparent to translucent, and oval or sub-rounded in shape. Grain length ranges from 80 to 220 μm, with length/width ratios of 1.5:1 to 3:1. Most of the zircons have sector or fir-tree zoning (fig. 4A), which is typical for metamorphic zircon (Corfu et al., 2003). Zircon U-Pb dating yields nearly concordant apparent U-Pb ages of 1894 ± 39 to 1781 ± 38 Ma (1SE) (Supplementary Table S2 and fig. 5A) with a weighted mean ²⁰⁷Pb/²⁰⁶Pb age of 1838 ± 18 Ma (2SE, n = 16, MSWD = 0.93), representing the metamorphic age. Ten analyses yield ¹⁷⁶Hf/¹⁷⁷Hf ratios vary from 0.281463–0.281498 (2SE), with corresponding negative εHf(t) values (−6.1 to −3.3), and Hf isotopic T_DM2 model ages from 2883–2748 Ma (Supplementary Table S3). Fifteen O isotope analyses yield δ¹⁸O values varying from 7.28 to 7.68‰ (2SE) (Supplementary Table S4).

Figure 4.Representative Cathodoluminescence (CL) images of zircon grains from (A) granitic gneiss, (B) tonalitic gneiss, (C) tonalitic gneiss, (D) migmatitized tonalitic gneiss from the Taihua Complex within the Xiaoqinling terrane. Yellow circles indicate the Lu-Hf spots, red circles indicate the U-Pb spots, and blue circles denote the O isotope analysis spots.

Figure 5.U-Pb concordia diagrams for metamorphic rock samples in this study. (A) granitic gneiss, sample 22TH-06; (B) tonalitic gneiss, sample 22TH-12; (C) tonalitic gneiss, sample 22TH-21; (D) migmatitized tonalitic gneiss, sample 22TH-14. Data-point error ellipses are 2SE and data-point error symbols are 2SE. Abbreviations: MSWD—mean square weighted deviation.

4.2. Zircons from Tonalitic gneisses

Zircons from tonalitic gneiss 22TH-12 are generally dull gray to black, transparent to translucent, and oval or irregular in shape. Grain length ranges from 80 to 250 μm, with length/width ratios of 1.5:1 to 3:1. Zircon grains from this sample are subhedral to elliptical with clear core-rim structures (fig. 4B), which is characteristic of metamorphic zircon. The cores have euhedral to irregular shapes with oscillatory zones, while the broad rims are banded, or no zones (fig. 4B). Two concordant analyses yield concordia ages of ca. 1976–1902 Ma (1SE) (²⁰⁷Pb/²⁰⁶Pb ages), indicating zircon recrystallization/regrowth during metamorphism. Zircon U-Pb dating yields nearly concordant apparent U-Pb ages of 2372 ± 28 to 2279 ± 33 Ma (1SE) (Supplementary Table S2 and fig. 5B) with a weighted mean ²⁰⁷Pb/²⁰⁶Pb age of 2328 ± 17 Ma (2SE, n = 13, MSWD = 0.8), representing its protolith age. Th/U ratios for the zircons vary from 0.19 to 0.72 consistent with igneous origin. In this sample, nine analyses of oscillatory zoned zircon cores have δ¹⁸O values of 2.71–7.87‰ (2SE). These zircons have ¹⁷⁶Hf/¹⁷⁷Hf ratios between 0.281345 and 0.281405 (2SE), slightly negative to positive initial εHf(t) values (−0.8 to +2.1), and Hf isotopic T_DM2 model ages from 2884–2739 Ma (Supplementary Table S3). Three metamorphic zircons (1976–1902 Ma) (1SE) have slightly lower δ¹⁸O values of 4.30–4.54‰ (2SE) (Supplementary Table S4).

Zircons in tonalitic gneiss 22TH-21 are oval and elongate round, colorless and translucent. Grain length ranges from 40 to 150 m, with length/width ratios of 1.5:1 to 3:1. The zircon crystals occur as subhedral to euhedral grains. Most grains from this sample display a well-developed core-rim structure (fig. 4C). The zircon cores generally display oscillatory zoning or patchy zoning and some grains show very dark cores. The oscillatory zoning and high Th/U ratios (0.35–0.76) of these dated zircon cores are indicative of igneous origin and the obtained ²⁰⁷Pb/²⁰⁶Pb age of 2271±17 Ma (2SE) is interpreted as dating the crystallization of the protolith of the tonalitic gneiss (fig. 5C). Ten analyses yield ¹⁷⁶Hf/¹⁷⁷Hf ratios vary from 0.281276 to 0.281348 (2SE), with corresponding negative εHf(t) values (−3.0 to −0.3), and Hf isotopic T_DM2 model ages from 2999–2870 Ma (Supplementary Table S3). Fifteen O isotope analyses yield δ¹⁸O values varying from 6.35 to 6.85‰ (2SE) (Supplementary Table S4).

4.3. Zircons from Migmatitized Tonalitic gneiss

Zircons in migmatitized tonalitic gneiss 22TH-14 are generally colorless and translucent, and oval to irregular in shape. Grain length ranges from 40 to 250 μm, with length/width ratios of 1.5:1 to 5:1. Most of the grains have patchy zoning (fig. 4D), which is typical for metamorphic zircon (Corfu et al., 2003). Notably, some zircon exhibit microcracks and pseudo-inclusion, which were often observed in metamictization of zircons (K. Zhou et al., 2023). One nearly concordant spot has an age of 1820 ± 31 Ma (1SE) (²⁰⁷Pb/²⁰⁶Pb age) (fig. 5D), which may be represented as the migmatization age. However, it is not likely to extract a reliable age of migmatitization from the data. Thirteen nearly concordant analyses yield ²⁰⁷Pb/²⁰⁶Pb ages of 2498–2287 Ma (1SE) (fig. 5D). The scatter is probably related to metamictization of the zircons and diffusional loss of radiogenic Pb. Collectively, the data suggest formation of the protolith from this sample at ca. 2498–2287 Ma (1SE), possible migmatitization and vein formation at ca. 1820 Ma (1SE). Ten analyses yield ¹⁷⁶Hf/¹⁷⁷Hf ratios vary from 0.281278 to 0.281449 (2SE), with εHf(t) values of −2.8 to +1.9, and Hf isotopic T_DM2 model ages from 3018 to 2758 Ma (Supplementary Table S3). Fifteen O isotope analyses yield δ¹⁸O values of 6.31 to 6.67‰ (2SE) (Supplementary Table S4).

5. Discussion

5.1. Paleoproterozoic crustal evolution of the study region revealed by U-Pb-Hf-O isotopes

In the following section, we discuss zircon Hf-O isotopic signatures of the two main age groups of ca. 2.3–2.2 Ga and 1.8 Ga samples in this study and assess the origin and evolution of the Taihua metamorphic complex along the southern margin of the North China Craton (NCC).

The ca. 2498–2287 Ma migmatitized tonalitic gneiss sample 22TH-14 of the Taihua metamorphic complex defines the oldest protolith age in this study. It has crust-like Hf-O isotopic compositions with negative to positive εHf(t) (−2.8 − +1.9) and moderately elevated δ¹⁸O values (6.31–6.67‰) (fig. 6), indicating the involvement of crustal components during magmatic crystallization. The δ¹⁸O range is also similar for the I-type granite zircon values of 5.5 to 7.0 permil (Wörner et al., 1987). Thus, they are not primary melts directly from the depleted mantle but most likely have a mixed origin of continental crust assimilated by mantle-derived magmas.

Figure 6.Composite plots of (A) Epsilon Hf(t) vs. U-Pb age for zircons from this study and comparative data from other regions of the NCC. Dashed lines show evolution of average continental crust, assuming ¹⁷⁶Lu/¹⁷⁷Hf = 0.015 (Griffin et al., 2002). Abbreviations: CHUR—chondrite uniform reservoir; DM—depleted mantle. (B) δ¹⁸O vs. U-Pb age for zircons from this study and comparative data from other regions of the NCC. Data sources: This study; Xiong’ershan (Y. Zhou et al., 2021); Xiaoqinling (X. Wang et al., 2021); Xiaoshan (Sun et al., 2023); Taiyue complex (X. Wang et al., 2022); Bayanwulashan (Dan et al., 2012). Error bars are 2 SE.

Compared to the sample 22TH-14, the Hf isotopic compositions of ca. 2372–2279 Ma tonalitic gneiss (sample 22TH-12) from the bedrock of the river channel are more radiogenic with εHf(t) values of −0.8 to +2.1 (fig. 6A), indicating a juvenile input and a decrease crustal reworking. The zircons from this sample show a wide variation in δ¹⁸O value: 2.71 to 7.87 permil, and most of them have δ¹⁸O values lower than typical mantle zircon values of 5.3 ± 0.3 permil (1SD) (Valley et al., 2005).

Similar moderately elevated δ¹⁸O values (6.35–6.85‰) were also observed for the tonalitic gneiss sample 22TH-21 (fig. 6B). Its protolith age at ca. 2309–2209 Ma with negative εHf(t) values of −3.0 to −0.3, which reflects that crustal reworking was dominant during their genesis.

The metamorphic age at ca. 1976–1902 Ma tonalitic gneiss (sample 22TH-12) with slightly positive εHf(t) and low δ¹⁸O values (4.30–4.54‰) (fig. 6), which implies a hydrothermal alteration occurred. Based on theoretical calculations, high-T water-rock interaction is an important process to lower the oxygen isotope ratios of rocks and/or minerals (Z.-F. Zhao & Zheng, 2003). We may thus infer that this low δ¹⁸O tonalitic gneiss can be formed by high-temperature hydrothermal alteration of surface water (seawater or meteoric water) (Bindeman & Valley, 2001; Zheng et al., 2004, 2008).

The metamorphic age at ca. 1894–1781 Ma granitic gneiss (sample 22TH-06) have negative εHf(t) values of −6.1 to −4.5 and relatively high δ¹⁸O values (7.28–7.68‰) (fig. 6), which suggests that the recycled high δ¹⁸O crustal material (Valley et al., 2009). Some zircons have elevated δ¹⁸O (>7.5‰) due to melting of protoliths that were altered at low-temperature by hydrothermal reactions (Valley, 2003).

5.2. Comparison with Hf-O isotopic data of the Paleoproterozoic silicic magmatism at ca. 2.3–2.2 Ga in the NCC and further insights into the GOE and HGE

The Paleoproterozoic silicic magmatism occurred during the TML (ca. 2.3–2.2 Ga) (Condie et al., 2022). We compiled the Hf-O isotopic results of our samples with available published data from granites and gneisses (protoliths) across the craton in the Bayanwulashan Complex of the Western Block, Taiyue Complex, and Taihua Complex of the Trans-North China Orogen (TNCO) during this period (fig. 6) (Dan et al., 2012; Sun et al., 2023; X. Wang et al., 2021, 2022; Y. Zhou et al., 2021).

In this study, the protolith of the tonalitic gneisses have crust-like Hf-O isotopic compositions with slightly negative to positive εHf(t) (−3.0− +2.1) and low to moderately elevated δ¹⁸O values (2.71–7.87‰) (fig. 6), suggesting the involvement of crustal components during magmatic crystallization. Our results imply that they are not primary melts directly from the depleted mantle but most likely have a mixed origin of continental crust assimilated by mantle-derived magmas. Based on previous study (X. Wang et al., 2021), the gneisses in the Xiaoqinling terrane show a relatively wide range of Hf isotopic values from −6.4 to +1.9 (fig. 6), indicating various contributions from multiple mantle- and crust-derived components. Similar low to moderately elevated δ¹⁸O values (3.97–6.79‰) has also been observed, which may represent the high-temperature hydrothermal alteration. The quartzofeldspathic orthogneiss in the Bayanwulashan Complex (Dan et al., 2012) has slightly negative to positive εHf(t) (−0.7 to +1.0) and moderate δ¹⁸O value of 7.12–7.98‰ (fig. 6), which indicates that juvenile inputs during their genesis and low-temperature hydrothermal alteration might have occurred. The biotite granite in the Xiaoshan terrane (Sun et al., 2023) displays slightly negative to positive εHf(t) (−1.1 to +1.4) and low to moderately elevated δ¹⁸O values of 2.41–6.04‰ (fig. 6). Compared to the biotite granite in the Xiaoshan terrane, the granite in the Taiyue complex (X. Wang et al., 2022) has similar Hf-O isotopic compositions, with slightly negative to positive εHf(t) (−1.6 to +2.6) and low δ¹⁸O values of 3.29–5.53‰ (fig. 6). The high-K granites in the Xiong’ershan terrane (Y. Zhou et al., 2021) show negative εHf(t) (−9.3 to −1.1) and slightly negative to low δ¹⁸O values (−1.24–4.78‰), which indicating that crustal reworking was dominant during their genesis associated with high-temperature hydrothermal alteration of surface water.

As the most significant event in the early Paleoproterozoic, the Great Oxidation Event (GOE), is known for the dramatic change in atmospheric composition where the free oxygen in the atmosphere increased by nearly five orders of magnitude, a likely response to biogeochemical feedbacks linked to the evolution of photosynthesizing bacteria (Kump, 2008). Extreme environmental changes greatly affected ocean and atmosphere chemistry. Tang and Chen (2013) proposed a two-stage oxygenation model for the GOE, which includes the early-stage hydrosphere oxidation (2.5–2.3 Ga) and the late-stage atmospheric oxygenation (2.3– 2.2 Ga). After 2.3 Ga, increasing O₂ and decreasing CH₄ and CO₂, the icehouse effect of O₂ cooled the climate and resulted in the global Huronian Glaciation Event (HGE, 2.29–2.25 Ga) (Hoffman, 2013; Tang & Chen, 2013).

Integration of our new U-Pb and Hf-O isotope data with available published data of the NCC of this period (ca. 2.3–2.2 Ga) (Supplementary Table S5), indicating that most of the magma source(s) at the Taiyue Complex, and Taihua Complex (e.g., Xiaoqinling, Xiaoshan, and Xiong’rshan areas) in the southern TNCO, which were likely formed by high-temperature hydrothermal alteration of surface water (at ca. 2.3 Ga). In contrast, the magma source(s) at the Bayanwulashan Complex of the Western Block experienced low-temperature hydrothermal reactions at roughly the same time. The protolith of the gneisses (2.32 to 2.21 Ga) were occurred in the Xiaoqinling area does appear in which temporal coincidence with the HGE. It is noteworthy that at ca. 2.2 Ga, the Taihua Complex within the Xiaoqinling area underwent low-temperature hydrothermal reactions during the magmatic crystallization, which might have affected by the HGE. However, further study will be needed to reveal the mechanisms.

6. Conclusions

Based on the new data presented in this study and in combination with previous studies, we can draw the following conclusions:

1. The protolith of the tonalitic gneisses in the study area have crust-like Hf-O isotopic compositions with slightly negative to positive εHf(t) (−3.0− +2.1) and low to moderately elevated δ¹⁸O values (2.71–7.87‰), indicating a mixed origin of continental crust assimilated by mantle-derived magmas.

2. Low δ¹⁸O values suggest that the protolith of the tonalitic gneisses in the Taihua Complex within the Xiaoqinling area was likely formed by high-temperature hydrothermal alteration of surface water. The granitic gneiss in the study area has elevated δ¹⁸O (>7.5‰), which underwent low-temperature hydrothermal reactions.

3. The study area underwent low-temperature hydrothermal reactions during the magmatic crystallization at ca. 2.2 Ga, which might have been affected by the HGE. However, further study will be needed to reveal the mechanisms.

Acknowledgments

This research was financially supported by the National Science and Technology Council (NSTC) in Taiwan, under Grant NSTC111-2636-M-006-019 and NSTC112-2116-M-006-005-MY2. We thank Xin Zhu, Rutao Zang, Fubao Chong, and Qingxing Luo for assistance in the field excursion. We also thank two anonymous reviewers for their suggestions in the revision process.

Author Contributions

Nancy Hui-Chun Chen: Writing – review & editing, Writing –original draft, Visualization, Validation, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization. Yunpeng Dong: Investigation. Bo Hui: Investigation.

Data and Supplementary Information

Supplementary Tables S1–S5 are available: https://doi.org/10.17632/zpyp4rmb43.1

Competing Interests

The authors declare no competing financial interests.

Editor: Mark Brandon, Associate Editor: Guochun Zhao