The 2.45–2.20 Ga period during the early Paleoproterozoic era is considered to have witnessed a global “Tectono-Magmatic Lull (TML)” and thus marks a relatively quiescent period. Our study unveils a 2.45–2.20 Ga magmatic suite from the Xiong’ershan area in the southern North China Craton, offering some key constraints on localized active tectonics during the TML. Zircon U-Pb dating shows Paleoproterozoic ages for the meta-basalt (2.31, 2.28 Ga), Na-rich meta-andesite (~2.33 Ga), tonalite-trondhjemite-granodiorite (TTG) gneisses (2.36, 2.30 Ga), K-rich granodiorite (~2.29 Ga), and monzogranite (2.33, 2.27 Ga). The meta-basalts geochemically and petrographically belong to calc-alkaline basalts and show distinctive Nb, Ta, and Ti contents and primitive mantle normalized patterns from different places in the Xiong’ershan area. Combined with their enriched εHf(t) values, the magmas were derived from subduction-related enriched mantle sources within a convergent plate boundary. The meta-andesites display high MgO content (average 4.5 wt%) and Mg# (44–57), strongly fractionated rare-earth pattern, calc-alkaline affinity, and negative Nb, Ta, and Ti anomalies. The TTG gneisses are of high SiO2 type (>62 wt%), high (La/Yb)N (17.5, 39.2), and Sr/Y (50.2, 104.3) and mostly display positive Eu anomalies and high-pressure type. Zircons from these rocks show a relatively narrow range of δ18O isotope values (5.35‰, 6.79‰) with εHf(t) isotope characteristics (−9.3, −3.3), suggesting derivation from partial melting of a thickened mafic lower crust. The youngest K-rich granodiorite and monzogranite show high K2O/Na2O ratios (0.65, 2.45). Variable molar ratio Al2O3/(CaO+Na2O+K2O) (A/CNK) and low zircon εHf(t) values suggest that the K-rich granitoids formed from the partial melting of different levels of crust. The presence of meta-basalt to andesite assemblages and diverse intermediate to felsic magmatic rocks implies magmatic activity within a convergent plate boundary tectonic environment with potential influence from plume-triggered extensional processes, supported by evidence of slab rollback and upwelling of mantle material.

After 2.5 Ga, the globe has witnessed a relatively quiescent period for over 200 million years in terms of active plate tectonics, referred to as the “Tectono-Magmatic Lull (TML, 2.45–2.20 Ga),” with no significant continental crust growth or major orogenesis [1-6]. In this regard of the geological processes of TML, Silver and Behn [7] suggested stagnation of the global subduction system leading to a decrease in volcanic activity and continental growth, Condie et al. [1] referred to unusual period as a crustal age gap, while Spencer et al. [8] referred to it as a TML. At the Archean/Proterozoic boundary (2.50 Ga), the Earth underwent significant episodic evolution and transformation in the early Paleoproterozoic period [1, 9, 10].

There are controversial opinions about the tectonic evolution of the Precambrian era. Cawood et al. [11], Palin and Santosh [12], and Tang et al. [4] have suggested that the global plate tectonic regime began operating during the Meso- to Neoarchean. Furthermore, Campbell and Griffiths [13] proposed that the mantle potential temperatures significantly decreased during TML. The distributions of U-Pb zircon ages from both granitoids and detrital sediments demonstrate an exceptionally strong minimum during the TML (2.365, 2.235 Ma), although no recognized age gap was identified [2]. However, several studies have reported igneous rocks and detrital zircons that fall within the TML window, such as those found in the Minas Orogen in Brazil, the Arrowsmith Orogen in Canada, and the southern North China Craton (NCC) [14]. Notably, the intriguing period of ca. 2.45–2.20 Ga appears to have played pivotal roles in facilitating the transition from Archean to the Paleoproterozoic supercontinent. This transition is marked by fundamental changes in tectonic styles [15-18].

Several studies have identified tectonic magmatic activities occurring between 2.45 and 2.20 Ga in at least twenty-four cratons or cratonic blocks, including orogenic events, passive margins, and magmatism such as greenstone belts and tonalite–trondhjemite–granodiorite (TTG) rocks. These magmatic events must have been crucial in the transformation from the scattered cratons of the Archean tectonic system to the modern-style plate tectonic system [8]. Previous research suggests that plate tectonics, analogous to modern high-angle deep subduction, had already begun at around 3.0 Ga and became prevalent globally during the Neoarchean to the early Paleoproterozoic period [18, 19] as evidenced by global metallogenic events [6]. Condie et al. [1] compiled global zircon U-Pb ages from clastic sedimentary rocks and magmatic suites, providing evidence for global magmatism at 2.45 Ga that lasted for approximately 200–250 Ma. The occurrence of subduction and rift zones has served as a distinctive feature of plate tectonics [16]. The compressional and extensional events that occurred from 2.45 to 2.20 Ga, along with their associated settings, overlapped both temporally and spatially. As a result, the tectonic and geodynamic processes during this transitional period remain challenging to fully understand [20]. The primary source of contention in TML research comes from the limited magmatism at the onset of the TML—immediately before and shortly after—which has hindered the accumulation of sufficient data to validate a model of tectonic evolution [20, 21].

As one of the world’s oldest cratons, the NCC has undergone extensive examination regarding the presence of magmatic rocks and terranes associated with the TML [3, 22, 23]. This allows the NCC as an exceptional focus for exploring the processes involved in the formation and expansion of continental crust during the TML. In the Xiong’ershan area of the NCC, magmatism occurred during the TML, which is significantly different from other regions within this craton, as well as most other cratons in the world. To better understand the formation and evolution of the continental crust and associated magmatism during the TML, we have investigated the meta-basaltic and intermediate-felsic rocks including whole-rock geochemical, zircon geochronological, and zircon Hf-O isotopic studies. This study has a dual purpose: (1) to enhance comprehension of the tectonic setting in the Xiong’ershan area and its connections to the NCC and (2) to contribute additional constraints on the potential mechanisms that initiated the TML.

2.1. Tectonic Framework of the NCC

The NCC is one of the oldest cratons on Earth with a basement comprising Archean and Paleoproterozoic rocks and is also a prominent example of widespread craton destruction during the Mesozoic era, with world-class metallogeny along its margins [6, 24, 25]. The NCC is divided into the Western Block, Eastern Block, and Trans-North China Orogen (TNCO) by Zhao et al. [26], who suggest that the craton was formed through the collision of the eastern and western blocks along the TNCO, leading to final cratonization at 1.85 Ga (Figure 1(a)). The Paleoproterozoic assembly of the NCC with the global events led to the formation of the supercontinent Columbia [15-18, 27, 28]. The TNCO includes fragments of oceanic crust-related substances and experiences a prolonged and consecutive subduction (Figure 1(a)) [26, 29]. According to Zhai and Santosh [30], the NCC is composed of several Archean microblocks that were assembled along oceanic sutures represented by greenstone belts in the Neoarchean. The formation of the NCC occurred through the collision and amalgamation of seven microblocks (Xuhuai, Xuchang, Jining, Ordos, Jiaoliao, Qianhuai, and Alashan blocks) along the greenstone belts at approximately 2.7 and 2.5 Ga [31]. Following the Archean/Proterozoic boundary, intricate rock associations and episodic tectonothermal events allow for a model featuring “three mobile belts”: Jiao-Liao-Ji, Jinyu, and Fengzhen Mobile Belt. These belts are associated with tectonic phases of rift extension (2.35, 2.00 Ga) and subduction-accretion-collision (2.00, 1.80 Ga) to form a cohesive block. Other models propose the opening of the Taihang and Lüliang oceans in a proto-NCC from 2.30 to 2.00 Ga [32] and back-arc extension from 2.35 to 2.00 Ga on an Archean basement in the Hengshan-Wutai-Fuping region, inducing that the formation of bimodal magmatism and sedimentary rocks suggest a model of the Jiao-Liao-Ji Mobile Belt in the Eastern Block and the Inner Mongolia-Northern Hebei Orogen in the north [33-35]. Peng et al. [36, 37] propose two magmatic belts representing different magmatic systems in the eastern and western blocks of the NCC. The terminal collision possibly resulted from ridge subduction between the two blocks, leading to the exhumation of igneous rocks in the two belts from different crustal levels, distinguishable by their varying grades of metamorphism.

2.2. Taihua Complex in Southern NCC

The Taihua Complex is an Archean-Paleoproterozoic metamorphic complex with a large exposed area within the TNCO in the southern margin of the NCC. It is generally distributed in the NW-SE direction and is mainly exposed in Xiaoqinling, Gushan, Xiong’ershan, Lushan, and Wuyang (Figure 1(b)). The Taihua Complex is composed of a set of regional metamorphic rocks and minor migmatites [38, 39].

Recent investigation on the metamorphic crystalline basement distributed across different regions of the Taihua Complex has demonstrated a nonuniform distribution pattern [39-41]. The Taihua Complex, which is broadly distributed across regions such as the Xiaoqinling, Lushan, and Xiong’ershan areas, displays three periods of significant magmatic activity, comprising Mesoarchean (~2.8 Ga) and Neoarchean (~2.5 Ga) TTG gneiss, and Paleoproterozoic (2.3, 2.1 Ga) TTG gneiss, potassic granite, and amphibolite [6, 42-45]. The most predominant group is Paleoproterozoic, encompassing 2.3 Ga TTG gneiss and 2.1 Ga potassic granites [20, 44, 46-48]. In the Lushan region, Mesoarchean (2.9, 2.7 Ga) TTG gneiss and amphibolite, as well as 2.5 and 2.2–2.1 Ga potassic granite, are observed [49-51]. The Taihua Complex found in the Xiong’ershan area is primarily composed of Paleoproterozoic rocks, including ~2.3 Ga TTG gneisses, ~2.2 Ga TTG gneisses, and high-potassic granites [3, 23, 48, 52]. The study area is located within the Taihua Complex in the Xiong’ershan area, which forms a part of the Archean-Paleoproterozoic basement of the NCC.

2.3. Xiong’ershan Area in the Taihua Complex

The Xiong’ershan terrane located on the southern margin of the NCC is a part of the continental thrust fold belt of the Qinling orogenic belt. The area is bounded by the Machaoying fault to the south and the Luoning fault to the north.

This area has undergone long-term evolution under different tectonic regimes (Table 1) [53]. Based on significant Varieties in Zircon Hf isotopes and whole-rock εNd(t) values, the rocks in this region are mainly composed of 2.318–2.305 Ma TTG gneiss. In addition, the protolith of gneiss is formed by the combination of preexisting continental crust and juvenile materials, which are formed by the varied mixing of older continental crust with juvenile elements in an Andean-type continental arc or island arc setting [3, 43]. Wang et al. [6] suggested Paleoproterozoic oceanic slab subduction in the TNCO of Xiong’ershan area. Amphibolite and granite exposed in this area, including TTG gneisses and high potassic calc-alkaline granites, have been studied by Huang et al. [23, 43], who reported ages of ca. 2.3 and 2.19–2.07 Ga for the meta-basaltic rocks and intermediate-felsic rocks [23, 43, 46]. Huang et al. [23, 43] obtained magmatic ages of 2.2–2.0 Ga from potassic gneisses in Ganshugou and ages of 2169 ± 6 and 2188 ± 26 Ma for tonalite gneiss from Ganshugou and Longmendian in the Xiong’ershan area. The granite intrusions of 2.19–2.07 Ga were identified in the Taihua Complex in the Xiong’ershan area, whose emplacement age is consistent with the extensive magmatic and thermal event of 2.2–2.1 Ga in the NCC [54]. Chen et al. [45] analyzed the Secondary Ion Mass Spectrometry (SIMS) zircon U-Pb ages of the garnet felsic gneisses found in the eastern part of the Xiong’ershan area which yielded ages of 2177 ± 22 Ma. Based on the metamorphic mineral assemblages, two magmatic events (2.32, 2.33, and 2.18 Ga) were identified [46].

In this study, magmatic suites in the Xiong’ershan area have peak ages of ca. 2.160 and 2.310 Ma (Figure 2(a)). We obtained ages of 2.147 ± 13 to 2.336 ± 10, 2.168 ± 15 to 2.334 ± 10, 2.316 ± 16 to 2.336 ± 13, and 2.163 ± 12 to 2.318 ± 3 Ma for basic rocks, diorite, TTG gneiss, and potassic granite, respectively (Table 1, Figure 2(b)). The crystallization ages of basic rocks, diorites, and potassic granites are similar and formed after the TTGs [3, 6, 44-46, 48, 55-57] (Table 1, Figure 2(b)).

The aim of this study is to investigate the rock assemblages dated at 2.35–2.29 Ga in the Xiong’ershan area for understanding the global TML including meta-basaltic rocks, meta-andesite, TTG, and potassium-rich granitic rocks (Figures 3 and 4). Six representative calc-alkaline meta-basaltic rock samples were collected from the Xiaonangou area, as well as two drill core samples obtained in Huanggou area of Luoning City (Figures 3 and 4). The lithology of the rocks is primarily composed of plagioclase amphibolite and biotite plagioclase amphibolite, with mafic enclaves such as plagioclase amphibolite of varying dimensions observed in these rocks. Potassic granite veins are also commonly observed, which are similar to those found in early Paleoproterozoic meta-andesite or potassium-rich granitic rocks intruded by undeformed quartz veins or potassic granite veins (Figure 4(a) and (b)). Furthermore, anatectic felsic veins have developed in the metamorphosed igneous rocks in some areas, which are parallel to the gneissic foliation in strong strain areas (Figure 4(a) and (b)). The TTG gneisses in the Xiaonangou area display gentle wavy and lenticular shapes and are distributed along the strike (Figure 4(a) and (c)).

The drill core samples contained granodiorite and monzogranite, which exhibit an unconformable contact relationship from Huanggou area (Figure 4(g)). There are some small granite porphyry bodies, mostly elliptical in distribution (Figure 4(h) and (i)). The granodiorite shows porphyritic nature with megacrysts of K-feldspar (Figure 4(i)).

Meta-basaltic rocks from Xiaonangou are medium- to coarse-grained with massive gneissic structure including amphibole (45%–55%) and plagioclase (42%–50%; Figure 4(d)), whereas the samples in the Huanggou area contain a small amount of biotite (Figure 4(j)). Zircon, epidote, and opaque minerals are present as accessory minerals. The meta-andesite is composed of phenocrysts and matrix. The phenocrysts are composed of plagioclase that is weakly oriented and interwoven with a volcanic matrix with a grain size of 0.1–0.3 mm (Figure 4(e)). The TTG gneisses vary from medium- to coarse-grained textures. Those with coarse characteristics consist of plagioclase (60%–65%), quartz (25%–30%), and biotite (5%–10%; Figure 4(f)), whereas the more leucocratic varieties are mainly composed of plagioclase (52%–60%) and quartz (25%–32%), with less volume of biotite (8%–10%). Accessory minerals in the TTG gneisses are zircon, apatite, and opaque oxide minerals.

The granodioritic and monzogranitic gneisses contain a significant volume of K-feldspar. The granitic gneisses are mainly potassic monzogranite–alkali granite–syenite. Most granodioritic gneisses assemblage of the monzogranite has equal amounts of plagioclase and alkali-feldspar (total of 40%–60%) with subordinate quartz (25%–35%), minor hornblende, and biotite (~10%; Figure 4(k)). Monzogranite is mainly composed of microcline (35%–40%), quartz (35%–40%), and plagioclase (10%–20%). The alkali-granite is composed of alkali-feldspar (40%–60%), quartz (25%–30%), plagioclase (~5%), and minor hornblende and biotite (~5%; Figure 4(l)).

4.1. In Situ Zircon U-Pb Dating and Lu-Hf Isotope

4.1.1. In Situ Zircon U-Pb Dating

Zircon grains from a total of eight samples, including two meta-basalt samples (XNG09-2 and XNG10-2), one meta-andesite sample (XNG11-2), two tonalite gneisses samples (XNG7-2 and XNG20-2), one granodiorite sample (HG40), and two monzogranite samples (HG37 and HG43), were analyzed for U-Pb dating using LA-ICP-MS online Supplementary Material 1. The obtained U-Pb data are presented in online supplementary Table S1 and are plotted in Figure 5.

The zircon grains from the meta-basalt samples are characterized by euhedral to subhedral morphology with prismatic and columnar shapes, ranging in length from 150 to 300 µm. The cathodoluminescence (CL) images of the zircons from XNG09-2 to XNG10-2 show good oscillatory zoning and low luminescence, indicating the absence of inherited cores (Figure 5(a) and (b). B). The Th and U contents of the zircons from XNG09-2 vary from 28 to 320 and 98 to 333 ppm, respectively with high Th/U ratios of 0.19–0.96. Zircons from XNG10-2 exhibit smaller Th (most show 14–18 ppm) and U contents (35, 54 ppm) and high Th/U ratios of 0.29–0.42, related to magmatic zircon similarity (online supplementary Table S2). The concordia diagrams show that the magmatic zircons from the two meta-basalt have similar weighted mean ages of 2.281 ± 16 [Mean Square Weighted Deviation (MSWD) = 0.95] and 2.313 ± 26 Ma (MSWD = 0.22), respectively, and these ages are interpreted as the crystallization age of the rocks (Figure 5(a) and (b)).

The meta-andesite samples (XNG11-2) contained stubby to elongate zircon grains showing generally oscillatory or banded zoning on CL images, with some enveloped by dark structureless rims (Figure 5(c)). Ten analyzed spots were found within the homogeneous zircons and cores, with Th and U contents ranging from 142 to 551 ppm and 339 to 613 ppm, respectively, and Th/U ratios of 0.42–0.77, suggesting a magmatic origin. In conventional concordia diagrams, except for spot 11-2-5 with the youngest 207Pb/206Pb age of 2.205 ± 53 Ma, and high Th and U content, the other nine spots were concentrated on concordia and defined a weighted mean 207Pb/206Pb age of 2.328 ± 36 Ma (MSWD = 0.12; Figure 5(c)), which was interpreted as the crystallization age of the protolith of Xiaonangou meta-andesite.

The zircon grains from two tonalite gneiss samples of XNG7-2 and XNG20-2 were found to be euhedral to subhedral with prismatic and columnar shapes, ranging in length from 100 to 200 µm. On CL images, they displayed good oscillatory zoning and low luminescence without inherited cores (Figure 5(d) and (e). They also showed variable Th (41, 1127 ppm) and U contents (98, 1252 ppm) and high Th/U ratios (0.12, 1.32; online supplementary Table S2). In conventional concordia diagrams, magmatic zircons from the XNG7-2 and XNG20-2 were found to be discordant with upper intercept ages of 2.309 ± 9 and 2.350 ± 10 Ma (MSWD = 1.7 and 1.5, with most of the plots falling below the Concordia line; Figure 5D). However, they had a different weighted mean age of 2.299 ±11 (MSWD = 0.94) and 2.365 ± 31 Ma (MSWD = 0.01), respectively, and these ages are interpreted as the crystallization age of the rocks.

One sample of granodioritic gneiss from HG40 was obtained in the vicinity of Huanggou, with the objective of ascertaining its age of formation. Zircon grains from this sample display anhedral to subhedral shapes with lengths ranging from 100 to 180 µm and exhibit core-rim structures in the CL images (Figure 5(f)). Ten spots were analyzed within the homogeneous zircons and cores, with Th and U contents ranging from 60 to 336 ppm and 106 to 464 ppm, respectively with Th/U ratios of 0.4–1.0. The concordia diagrams and the results show strong discordance with an upper intercept age of 2.277 ± 41 Ma (MSWD = 0.24; Figure 5(f)) and a weighted mean 207Pb/206Pb age of 2.289 ± 41 Ma (MSWD = 0.44), which is interpreted as the crystallization age of the protolith of Huanggou granodioritic gneisses.

Two monzogranite samples of HG37 and HG43 were also analyzed, with twenty and ten spots, respectively, from the homogeneous zircons and cores. These zircon grains exhibit oscillatory or banded zoning, with some displaying dark structureless rims (Figure 5(g) and (h)). Variable Th and U contents were observed (62–809 and 123–1403 ppm, respectively) with relatively variable Th/U ratios of 0.2–0.7 (online supplementary Table S2). The upper intercept ages of the two samples are 2.319 ± 32 (MSWD = 1.6) and 2.254 ± 50 Ma (MSWD = 0.25), respectively, with weighted mean ages close to the upper intercept ages of 2.332 ± 32 (MSWD = 0.26) and 2.268 ± 54 Ma (MSWD = 0.17), respectively (Figure 5(g) and (h)). The crystallization age of the monzogranite is interpreted to be 2.268–2.332 Ma, which is similar to those of the other rocks in the study area.

4.1.2. In Situ Zircon Lu-Hf-O Isotope

The initial Hf isotope ratios were computed at both the mean crystallization age (t) and 207Pb/206Pb age of the same domain (online supplementary Table S3). The Hf model ages (TDM) refer to the extraction from a depleted mantle.

Ten analyses of the amphibolite sample of XNG09-2 reveal a moderate range of 176Hf/177Hf ratios of 0.281224–0.281338, corresponding to εHf(t) values of 4.5–0.5, respectively (Figure 6) online Supplementary Material 1. Their TDM1 values vary from 2.62 to 2.82 Ga.

Zircons grain from the ten analyses of TTG gneisses of XNG7-2 exhibits 176Hf/177Hf ratios in a narrow range of 0.281054–0.281223. The εHf(t) values calculated using their corresponding 207Pb/206Pb ages (Figure 6) range from –9.3 to –3.3 and are generally below the chondrite. The depleted mantle model ages (TDM1) range from 2.76 to 2.99 Ga.

For the two monzogranite samples, ten HG37 and seven HG43 analyses reveal a moderate range of 176Hf/177Hf ratios of 0.281142–0.281276 and 0.281254–0.281278, respectively, corresponding to εHf(t) values ranging from –5.4 to –0.6 and –2.9 to –2.1, respectively (Figure 6) which generally fall below the chondritic line. Their TDM1 values range from 2.69 to 2.89 and 2.70 to 2.73 Ga.

Amphibolite zircons samples from XNG09-2 were analyzed at twenty points, resulting in δ18O values ranging from 2.21‰ ± 0.2‰ to 5.93‰ ± 0.3‰ with an average of 5.15‰ ± 0.21‰. Similarly, Zircon δ18O values from TTG gneisses samples XNG7-2 vary from 5.35‰ ± 0.09‰ to 6.79‰ ± 0.29‰ with an average of 5.92‰ ± 0.12‰ (online supplementary Table S4) online Supplementary Material . In the Huanggou area, zircon oxygen isotope analysis was conducted on two samples, HG37-1 and HG43-1. HG37-1 yielded δ18O values ranging from 2.59‰ ± 0.18‰ to 5.11‰ ± 0.17‰ with an average of 4.06‰ ± 0.17‰. Similarly, zircon samples from HG43-1 showed a range of δ18O values from 1.96‰ ± 0.14‰ to 3.28‰ ± 0.14‰, with an average of 2.83‰ ± 0.16‰. By comparing with the oxygen isotope data from the two regions, the samples from the Xiaonangou area δ18O value are significantly higher than that of the Huanggou area. This difference in oxygen isotopes between the two regions may be attributed to influences originating from the source area or the occurrence of water-rock reactions (lower or higher temperatures; Figure 7).

4.2. Whole-Rock Geochemical Characteristics

The Taihua Complex in the Xiong’ershan area features a diverse range of rocks, including eight meta-basaltic rocks, seven intermediate meta-andesitic rocks, two tonalite gneisses, and eleven K-rich granitoids online Supplementary Material . The data are listed in online supplementary Table S1 and plotted in Figures 8 and 9. Potassic granitoids with similar ages have previous literature studies from Huang et al. [23, 43]. The meta-basaltic rocks are generally calc-alkaline and exhibit variable SiO2 contents of 46.02–52.97 wt%. Meanwhile, the meta-andesitic rocks are commonly presented in calc-alkaline and display moderate SiO2 contents of 52.34–55.55 wt%. The TTG gneisses and K-rich granites have SiO2 contents of 62.20–67.74 and 53.34–74.92 wt%, respectively (Figure 9(a)). Among these, the granodiorite includes intermediate-felsic potassium-rich rock types, with the largest variation in SiO2 (53.34, 69.65 wt%). On the An-Ab-Or diagram (Figure 9(b)), the samples are projected in the areas of four tonalite, one trondhjemite, sixteen granodiorite, and thirteen monzogranite. Notably, the K2O/Na2O ratio of the granodiorite and monzogranite is greater than 0.6 (0.65, 1.53, and 0.72–2.45), and they do not belong to the TTG rock units. The geochemical characteristics of these meta-basaltic rocks and intermediate felsic rock samples are of interest.

4.2.1. Meta-Basaltic Rocks and Meta-Andesitic Rocks

online supplementary Table S1 lists the major and trace element analysis of nine meta-basaltic rocks and nine intermediate meta-andesitic rocks. Based on the mineral assemblages and geochemical characteristics on plots such as Zr versus MgO, it can be inferred that almost all the samples are metamorphosed volcanic rocks, rather than paragneiss (Figure 8(a)). The SiO2 content is low, whereas the Na2O and K2O contents are high. The samples in this study are plotted in the subalkaline basalt and andesite field in the Ni/Y versus SiO2 discrimination diagram (Figure 8(b)) and plotted calc-alkaline series region in the diagram of Yb-La (Figure 8(c)). The Rittman index (σ = [Na2O + K2O]2/[SiO2 − 43]) is below 3.3, and the rock resembles the calc-alkaline suite.

The rocks exhibit high MgO (3.32, 5.79 wt%), Fe2O3 (8.8, 17.32 wt%), and CaO (1.15, 7.58 wt%) contents and a wide range of Al2O3 (12.54, 17.53 wt%) and TiO2 contents (mostly of 0.79–1.68 wt%, but THX05-42 and THX08-39 have up to 3.73–4.40 wt% at Ganshugou area; Figures 8 (d) and 10(a) and 10(b)). The MnO and P2O5 values fall within 0.13–0.29 and 0.17–0.58 wt%, respectively, which are higher than tonalite gneisses and monzogranite. In the rare earth element (REE) diagram, the rocks show moderate moderately fractionated REE patterns with slightly negative Eu anomalies and Light Rare Earth Elements (LREE) enrichment. The primitive mantle normalized display negative anomalies of Nb, Ta, P, and Ti and slightly positive and/or negative anomalies of Sr. Based on the collected meta-basaltic rocks data, Huanggou and Xiaonangou have negative Nb and Ta anomalies, whereas contents of Nb and Ta are higher in Ganshugou area (Figure 10). Furthermore, it appears that meta-basaltic rocks exhibit greater similarities to Ocean Island Basalt (OIB) and Oceanic Arc Basalts (OAB) as opposed to Mid-Ocean Ridge Basalt (MORB).

4.2.2. TTG Gneisses

The major and trace elements analysis of five TTG samples is provided in online supplementary Table S1. The TTGs samples exhibit high SiO2 (62.20, 67.74 wt%), Al2O3 (15.67, 16.99 wt%), and Na2O (3.45, 6.48 wt%) but low MgO (0.93, 1.98 wt%), TiO2 (0.30, 0.59 wt%), K2O (1.11, 2.24 wt%), and Fe2O3 (3.51, 5.77 wt%). The contents of MnO, CaO, and P2O5 range from 0.03–0.08, 1.86–4.86, and 0.10–0.15 wt%, respectively (online supplementary Table S1 and Figure 9). With the low Na2O/K2O (0.17, 0.51, avg. = 0.44) and low Na2O + K2O (5.15, 7.59 wt%, avg. = 6.23 wt%) content, the rocks have a medium-K calc-alkaline affinity (Figure 9(a) and (c)). The TTG samples, which include tonalite and trondhjemite, demonstrate a pronounced sodium-rich trend when depicted on the K2O–Na2O–CaO ternary diagram (Figure 9(b) and (d)). Moreover, the samples have similar characteristics of high SiO2 and low Mg# to high-silica adakites (Figure 10(e)). On the A/CNK versus A/NK plot, all samples fall between peraluminous and metaluminous (Figure 9(f)). The TTG samples from Xiaonangou show strongly fractionated REE patterns ([La/Yb]N = 17.49–39.20; Figure 11(a); online supplementary Table S1). On the primitive mantle-normalized multielement diagram (Figure 11(b)), the samples display moderate fractionation patterns with weak negative Nb, Ta, P, and Ti anomalies but positive Zr and Hf anomalies.

4.2.3. Granodioritic and Monzogranitic Rocks

The present study analyzed sixteen granodioritic and thirteen monzogranitic rock samples from an area of interest. The samples displayed varying Na2O (1.84, 4.32 wt%) and K2O (2.16, 5.94 wt%) contents, resulting in moderate to high K2O/Na2O ratios of 0.65–2.45 (Figure 9(a) and (b)). All samples were classified as the high-K calc-alkaline rocks and shoshonite, with the latter being more K-rich than the former and yielding a K-rich trend on the K2O–Na2O–CaO ternary diagram (Figure 9(c) and (d)). The granodioritic gneiss samples exhibited medium to high SiO2 (53.34, 69.65 wt%) and Fe2O3 (2.68, 14.1 wt%) but high MgO (1.11, 3.89 wt%) and Mg# (26–52) contents. In contrast, monzogranite displayed variable SiO2 (64.69, 74.92 wt%), low Fe2O3 (1.97, 6.74 wt%), MgO (0.1, 1.37 wt%), and Mg# (8–49) (Figure 9(e)). The samples were located in the field of experimental melts derived from meta-basaltic rocks [55]. In A/CNK versus the A/NK plot (Figure 9(f)), granodioritic gneiss samples were observed to be metaluminous, while monzogranite samples were more peraluminous.

The granodioritic gneiss samples exhibited high total REE contents and showed fractionated REE patterns, with moderate to high (La/Yb)N (7.98, 61.46) ratios, without significant Eu anomalies (Figure 11(c)). The monzogranite samples showed variable REE patterns with negative Eu anomalies (Figure 11(e)). On the primitive mantle-normalized multielement diagram, they exhibited negative Nb, Ta, P, and Ti anomalies and positive Zr and Hf anomalies (Figure 11(d) and (f)).

5.1. Evaluation of Element Mobility

The Paleoproterozoic basement rocks in the Xiong’ershan area have undergone amphibolite to granulite facies metamorphism [39]. For the interpretation of petrogenetic processes, the element mobility must be considered [58].

Polat et al. [59] proposed that intermediate-felsic rock samples with minimal late metamorphic alteration have a low loss on ignition (LOI) values (˂6 wt%) and weak Ce anomalies [Ce/Ce* = CeN/Sqrt[LaN × PrN] ranging from 0.90 to 1.10. The majority of the meta-basaltic and intermediate-felsic rocks samples in this study possess low LOI values (0.21, 4.71 wt%) and insignificant Ce anomalies (Ce/Ce*= 0.93–1.06). In contrast, large ion lithophile elements (LILEs) such as Ba, Rb, Th, and K are more dispersed, indicating they have undergone various degrees of modification. Furthermore, Zr’s stability during metamorphism has been demonstrated. Linear correlations with Zr are frequently used for both the REEs, including La, Sm, Yb, and Y, as well as high-field strength elements (HFSEs; e.g., Nb and Ti), while LILEs (e.g., Ba, Rb, and Th) are more dispersed and the linear trend is not evident [60].

5.2. Magma Sources of Meta-Basaltic Rocks and Meta-Andesitic Rocks

5.2.1. Meta-Basaltic Rocks

Seven samples from Xiaonangou and Huanggou areas are calc-alkaline basalts that show strong fractionation of light and heavy REEs and negative anomalies of Nb, Ta, and Ti (Figure 10(a) and (b)). Due to differences in water content, two magma evolution trends may develop during mineral crystallization [61]: the calc-alkaline series and the tholeiitic series. These geochemical characteristics are similar to most convergent margin basalts and typical island arc calc-alkaline basalts [62]. Calc-alkaline magmas predominantly originate at the periphery of convergent plate boundaries, such as island arcs, and are notable for their elevated water content [63]. Previous studies have suggested that the geochemical imprint of subduction-related basalts, including negative anomalies of Nb and Ta, can result from a variety of genetic mechanisms. It can reflect partial melting from the mantle source area that has been metasomatized by subduction materials or the mixing process of shallow crust [64]. On the other hand, the LILE enrichment and HFSE depletion of the meta-basaltic rocks show an affinity to OAB (Figure 10(a) and (b)). This suggests that the mode of formation is in harmony with the outcomes attributed to hotspot interactions in conventional models [62]. The Ta versus Ta/Sm plots suggest that the samples analyzed in this study are primarily controlled by partial melting (Figure 12(a)), and the Hf isotopic versus Mg# of zircon indicates no trend of any contamination (Figure 12(b)). Notably, high Nb content in (THX05-42 and THX08-39) indicates that the mantle source is subjected to subduction melt metasomatism. This is consistent with the significant increase in the Nb content of mantle-derived magma observed in other studies (e.g., Nb-rich basalts with Nb content as high as 7 and 20 ppm) [65]. The positive anomalies of Nb, Ta, and Ti observed in the Ganshugou area suggest that the samples might have been influenced by the mantle source area (Figure 10(b)). Furthermore, the conversion of the mantle latent temperature model suggests that the basalt in the Ganshugou area has a higher TiO2 content than Xiaonangou area, which is reflective of a higher mantle temperature [21, 23]. In contrast, the basalts in study areas exhibit lower TiO2 contents that indicate lower mantle temperatures.

Some samples of meta-basalts from the Xiaonangou area fall below the mantle trend composed of N-MORB, indicating that they have experienced variable degrees of crustal recycling. The samples from the Huanggou and Ganshugou areas fall between the mantle trend composed of N-MORB and the Archean upper continental crust (AUCC), indicating that their source area has been modified by a small amount of crustal material recycling (Figure 12(c)) [66]. This is consistent with the generally high (Nb/La)N ratios and chondrite-like (Hf/Sm)N ratios, further demonstrating that the mantle sources were affected by subduction-fluid-related or metasomatism. Furthermore, it is supported by high Al2O3 (13.22, 19.11 wt%) contents, which is not a type of carbonate rock metasomatism. The (Hf/Sm)N-(Nb/La)N diagram shows that these samples are slightly lower than the chondrite composition, further demonstrating that the mantle sources were unaffected by subduction-related or carbonate metasomatism (Figure 9(d)). Only three samples show the effects of metasomatism, and the majority of samples are near chondritic [67]. Their CaO/Al2O3 ratio decreases gradually with the increase of MgO content, the lack of both Eu anomalies, and the MgO content and Mg# number increase slightly, indicating the separation and crystallization of a small amount of clinopyroxene (Cpx) (Figure 12(e)) [68]. On the Ni versus Cr diagram, the meta-basalt samples in Ganshugou and Xiaonangou areas are mainly subjected to Cpx accumulation (Figure 12(f)). The high K2O content of 9.27 wt% of the samples in the Huanggou area is difficult to be explained by the model of fractional crystallization of low potassium alkaline basaltic rocks (mostly 0.70–3.42 wt%). Therefore, the involvement of an enriched lithospheric mantle (containing hydrous minerals such as phlogopite) possibly resulted in potassium enrichment in the Xiong’ershan area [69]. The low degree of partial melting of alkaline rocks also contributes to the potassium enrichment in the melt. In addition, the (Sm/Yb)N versus (La/Sm)N diagram shows that the geochemical characteristics of samples in the Xiaonangou and Huanggou areas are consistent with the partial melting products of spinel peridotite with 2%–4% garnet in residual phase [70], while the rock samples in the Ganshugou area are high-level partial melting products of garnet peridotite with 2%–4%, indicating that they are subjected to higher temperature and pressure conditions (Figure 12(g)) [70]. In the Th/Yb versus Nb/Yb diagram (Figure 12(h)), the meta-basaltic rocks show subduction signals falling above the MORB-OIB mantle trend mainly falling in the calc-alkaline series related to the continental arc. Compared with the Ganshugou samples belonging to the MORB-OIB setting, the normalized NbN-MORB and ThN-MORB values are 1.67–11.97 and 5.17–26.33. All Xiaonangou and Huanggou samples belong to the convergent plate setting (Figure 12(i)).

In summary, the data from meta-basaltic rocks in conjunction with those from intermediate felsic magmatic rocks, as well as the temporal and spatial distribution, suggested formation in an extensional setting and asthenosphere upwelling. Oxygen isotopes are typically situated below the magma source region, with a few data points exhibiting lower oxygen isotope values, potentially associated with zircon alteration caused by high-temperature hydrothermal fluids. According to Smithies et al. [71], TTG can host zircons akin to the mantle’s δ18O value, with the potential for relatively high zircon content δ18O values (approximately 5.9‰). Subsequently, these droplets traverse the lower crust and descend into the mantle, releasing fluids and melts with high δ18O. This process leads to metasomatism of the lithospheric mantle, creating a magma source region enriched in large-ion lithophile elements and water-bearing sanukite. These findings can be correlated with the phenomenon of slab rollback, which acts as a heat source, facilitating partial melting of the lower crust. The formation of a large number of metamorphic calc-alkaline basalts, andesites, and granitic gneiss protoliths is related to the subsequent active continental margin arc setting [68]. Highly evolved zircon εHf(t) values are likely to record a strong asthenosphere upwelling in the early Paleoproterozoic (~2.3 Ga) from the southern margin of the NCC (Figure 12(i)).

5.2.2. Meta-Andesitic Rocks

Based on the Ta and Ta/Sm (Figure 12(a)) and SiO2 versus Mg# diagram (Figure 10(b)), there is no evidence of a magma mixing process. However, the Mg# values of the samples fall within the range of high-Mg meta-andesites from the Archean or Paleoproterozoic, which exhibit geochemical characteristics similar to those of slab-derived adakites (Figure 12(b)) [68].

The (Nb/La)N ratios do not show a linear relationship with MgO or Mg#, indicating that the magma has not been significantly modified by crustal mixing (Figure 12(b) and (c)). Their low (La/Yb)N and Sr/Y ratios and high Y (13.2, 39 ppm) and Yb contents distinguish these meta-andesites from those originating from in the lower crust [72]. Contrarily, the Ti and Zr diagrams suggest that the source region for these meta-andesites is located between the AUCC and N-MORB, most likely originating from the partial melting of the metasomatized mantle (Figure 12(c)). The sample contents of (Nb/La)N and (Hf/Sm)N 0.09–0.13 and 0.81–0.96, respectively, can be distinguished in the (Nb/La)N-(Hf/Sm)N diagram, consistent with previous samples, indicating the influence of subduction-derived fluids (Figure 12(d)). La/Sm and Ba/Th ratios of the samples range from 4.9 to 7.4 and 98.1 to 432, respectively, suggesting a volcanic arc affinity with the contribution of sediment-derived melts [73]. Additionally, the high (La/Sm)N and (Sm/Yb)N ratios (range from 2.6 to 4.2 and 2.6 to 4.5, respectively) provide additional evidence that the parent magmas of meta-andesitic rocks originated in a stable garnet field. This indicates a relatively deeper mantle level, which is more conducive to the generation of melts from subducting slabs (Figure 12(g)) [70]. The Th/Yb versus Nb/Yb diagram Figure 12(h)) indicates that the samples are largely consistent with subduction signal form on continental lithosphere [74]. Moreover, the normalized NbN-MORB and ThN-MORB values range from 2.35 to 4.12 and 23.3 to 43.3, respectively, as shown in the discrimination plots, indicating that the samples all belong to the convergent plate setting (Figure 12(i)) [75]. Based on these findings, it can be inferred that the meta-andesite rocks originated from partial melting of fluid-metasomatized mantle sources.

5.3. TTG Gneisses

The TTG rocks in the Xiong’ershan area exhibit similar ages to the meta-basalts, meta-andesitic rocks, granodiorites, and monzogranites (Figure 5). The tonalite gneisses show a partial melting trend and have enriched εHf(t) characteristics with negative values, indicating an ancient and enriched Archean mantle source (Figure 6, Figure 13). Negative correlations are observed between their SiO2 and FeO, TiO2, and P2O5, suggesting a close genetic connection between the various rock types. On the Ta versus Ta/Sm plot (Figure 11(a)), the TTGs exhibit Ta and Ta/Sm ranging from 0.19 to 0.66 and 0.06 to 0.15 ppm, respectively, indicating that they formed by partial melting. They display low Yb (0.43, 1.44 ppm) and Y (5.1, 14.5 ppm) contents but high (La/Yb)N (17.4, 39.2) and Sr/Y (13.3, 104.3) ratios (Figure 13(b) and (c)). The Y versus Ce/Sr diagram indicates most have high-pressure characteristics, predominantly exhibiting positive Eu anomalies resembling those of high-pressure TTG gneisses (Figure 11(a); Figure 13(d)).

In addition, the TTG rocks exhibit relatively low A/CNK values and high (La/Yb)N ratios, indicating their affinity toward adakites and the classic island arc domain. The combination of high Rb/Sr ratios and Mg# with low Cr and Ni values suggests that magma generation could be linked to the partial melting of the thickened basaltic lower crust. The samples were analyzed using discrimination diagrams such as 3*CaO–Al2O3/(FeOt + MgO)–5*K2O/Na2O and [(Calcium Oxide) / (MgO+FeOt) (Molar ratio)] CFM versus [ Al2O3 (Aluminum Oxide) / (MgO+FeOt) (Molar ratio)] AFM. The results indicate that they fall in the low K mafic source rocks area and fall in the partial melting from meta-basaltic to meta-tonalitic sources area, which is consistent with the generally accepted TTG source (Figure 13(e) and (f)) [76]. The higher SiO2 content and less mafic minerals in the TTG rocks suggest that they originated from the partial melting of a basaltic source.

The low εHf(t) values of tonalite gneisses (–9.3 to –3.3; Figure 6) indicate that the magma sources for the TTG rocks are primarily ancient crust. Smithies et al. [71] observed that TTG rocks with mantle-like δ18O values can also exhibit relatively high zircon δ18O values (about 5.9‰). They proposed that the TTG magma sources area with slightly enriched δ18O are hydrated partial melts formed from the source lithospheric mantle, leading to the formation of sanukitoids [6, 71]. Based on zircon Hf-O isotope data, it is suggested that ancient crust may have been the source of these rocks. Therefore, it can be concluded that high-degree partial melting of ancient thickened basaltic subcrust generated the tonalite gneisses.

5.4. K-Rich Granodioritic and Monzogranitic Rocks

The potassium-rich granitic rocks and TTG gneisses exhibit differences in their geochemical and zircon Lu-Hf-O isotopic signatures, suggesting that they have different petrogenetic mechanisms (Figure 7). Based on their SiO2 and MgO contents, these rocks can be classified into two groups: the high MgO group (1.11, 3.89 wt%, granodiorite) and the low MgO group (0.10, 1.37 wt%, monzogranite). The granodiorites typically have higher MgO content compared with the monzogranites. However, both rock types exhibit a broadly similar range of FeOt + MgO (Figure 14(c) and (d)).

In the FeOt/(FeOt + MgO) versus SiO2 diagram, most of the monzogranites fall in the A-type granites field (Figure 14(a)), with some of them exhibiting the characteristics of A-type granite. Moreover, there is a correlation between the Dy/Yb versus SiO2 diagrams (Figure 14(b)). Among the LaN versus (FeOt + MgO) and (Nb + Zr + Y) versus (FeOt + MgO) diagrams, granodiorites fall in the mantle source field and monzogranites in the crustal melting field (Figure 14(c) and (d)) [77]. Therefore, it is inferred that the K-rich granites may have experienced metasomatism through mantle input and, to a lesser extent, products of intracrustal reworking. In the 3*CaO–Al2O3/(FeOt + MgO)–5*K2O/Na2O discrimination diagram (Figure 14(e)), the potassium-rich granodiorites are located in the high K mafic rocks field and generally preserve the primary magma compositions. While the granitic rocks are distributed in the meta-sedimentary rock region. This conclusion is consistent with the consistently low A/CNK ratio (<1.14) and zircon εHf(t) values, which mostly fall below the chondrite values for these samples. Therefore, it is deduced that the granodiorites may have originated from mantle-derived magmas. The granodiorite samples have higher (La/Yb)N values (mostly at 7.98–61.46) than typical adakitic rocks and higher TiO2 content (generally >0.68) than the global low-Ti sanukitoid rocks (<0.64). These samples have lower (Hf/Sm)N values (mostly 1–1.65), indicating that they came from mantle-derived origin. The rocks have higher CaO + FeOt + MgO + TiO2 contents (6.9, 22.5), reflecting their parent magma mainly originated from the partial melting of amphibolite. Additionally, they display strongly fractionated light REE patterns (Figure 14(f)) [78]. The A/CNK values are generally less than 1.1, demonstrating metaluminous characteristics and suggesting an origin from high K mafic rocks. In the Xiong’ershan area, supracrustal rocks of Paleoproterozoic age (ca. 2.3–2.1 Ga) with similarly high K2O contents are common, which (or the chemical equivalents) could potentially serve as the source lithologies for the granodioritic gneisses.

In contrast, the monzogranites exhibit negative anomalies of Nb, Ta, P, and Ti. They generally have low Sr/Y ratios (mostly <20.1) and a limited range in A/CNK values of 0.96–1.10, consistent with experimental melts derived from the partial melting of tonalites [79]. They do not display any distinct correlation in the Dy/Yb and SiO2 diagram. The rocks have high K2O and LILE contents in combination with Eu abnormal, and consistent with zircon εHf(t) (−5.4, −0.6), the rocks display the greatest degree recycling of older crust and the least contribution from new mantle material. Low-δ18O (δ18O = 1.96 to 5.11, 3.55 on average) in high-K granites implies that the remelting of hydrothermally altered crustal materials at upper crustal levels likely occurred, possibly driven by an extensional tectonic environment in which the continental crust was subjected to elevated temperatures.

In summary, the granodiorites and monzogranites may have originated from various depths, with either garnet and hornblende (at the base of a thickened crust) or plagioclase (at a shallow crustal level) present in the residue.

5.5. Geochronological Framework

Magmatism occurs in various tectonic settings, such as subduction-related island arcs, postcollisional extension, or anorogenic rifting. In the global context, Paleoproterozoic magmatism is linked to both subduction and rift-related settings [7, 80]. Sun et al. [81] have related the formation of Neoarchean TTG gneisses in the eastern NCC to changes in continental crust thickness and geothermal gradient. Cui et al. [47] proposed subduction-related magmatism in the southern margin of the NCC. Diwu et al. [3] mentioned global TML in the southern margin of the NCC at 2.45–2.20 Ga. Based on Hf and whole-rock Nd-Hf isotopic data, they suggested an Andean-type continental margin arc or island arc tectonic setting [3].

Based on studies on the TTG gneisses and potassic granites, Huang et al. [43] and Diwu et al. [3] suggested a transition from accretionary orogeny to an extensional regime in the southern part of the TNCO at ~2.1 Ga, which is consistent with the result of this study. They suggest that the TTG gneisses were produced by multiple mixing of preexisting continental crust and juvenile material. Therefore, the temporal change from low-K magmatic rocks (TTG) to high-K magmatic rocks in the southern segment of the TNCO indicates that the tectonic transformation can be divided into two phases in the Early Paleoproterozoic of an accretionary orogeny at 2.32–2.30 Ga and a postcollisional uplift to extensional regime at 2.19–2.08 Ga [43]. Zhou et al. [48] reported a low O isotopic signature of zircons and suggested that an oceanic plate existed beneath the basement of the Xiong’ershan area. It is concluded that the Taihua Group TTG gneisses in this area were formed in an Andean-type continental arc or island arc environment. Before 2.332 ± 32 Ma, the majority of εHf(t) values reside below the chondrite line, suggesting their origin from ancient intraplate basaltic crust, potentially triggered by processes such as underplating of upwelling mantle material or intrusion of mantle-derived magma. Chen et al. [46] identified a clockwise P-T path with isothermal decompression from amphibole in the Luoning terrane and dated the protolith magmatism at 2.32 Ga, followed by metamorphism at 1.97–1.94 Ga, corresponding to subduction, collision, and extension in the Paleoproterozoic.

Huang et al. [23] proposed that the Taihua Complex, with an age of ~2.31 Ga, represents the initial north-south subduction in the southern margin of the NCC, which is related to the convergence of the global Columbia supercontinent. The 2.2–2.0 Ga period is characterized by significant crustal recycling with major mafic magmatism occurring in the southern margin of the NCC. Intermediate and felsic rock types dominate, thereby ruling out intraplate rift and bimodal magmatism.

Recently, Wang et al. [6] reported TTG gneisses from Bayuan that are primarily derived from partial melting of the lower crust. Zircons from these gneisses exhibit high thermal conductivity δ18O values of about 6.14‰ ± 0.38‰. These features suggest that the source rocks underwent varying degrees of water–rock interaction at relatively low temperatures, followed by recycling into the lower crust. The δ18O value characteristics of tonalities gneisses in this paper have more enriched Hf isotope characteristics than TTG in the Bayuan area and are more likely to represent the reworked preexisted crustal materials, suggesting possible crustal thickening.

Asthenosphere upwelling and the partial melting of basaltic rocks at the bottom can lead to the thickening of the lower crust and the generation of TTG. However, these processes result in only a small amount of meta-basaltic rocks entering the lower continent crust, most of which are formed in mantle magma and do not typically form a high δ18O rock. Alternatively, the subduction process can effectively generate TTGs by partial melting that inherit different degrees of high-temperature characteristics and δ18O values. The potassic granites from Xiong’ershan from Ganshugou show average δ18O isotopes of 3.98‰ ± 0.39‰ and 3.32‰ ± 0.41‰, respectively (Figure 7) [48, 82], suggesting that high-temperature water–rock reaction can cause rock’s δ18O value to decrease rapidly [82]. Zhou et al. [48] identified high-T water–rock interaction in the ancient crust before or during partial melting, and the genesis occurrence of potassic rocks and spatially related gabbro, diorite, and TTG was correlated to an extensional tectonic environment with asthenosphere upwelling and crustal thinning (Figure 14).

In summary, the high zircon oxygen isotope values and enriched Hf isotope characteristics of the ~2.3 Ga TTG gneiss suggest that it was not formed in the intraplate rift (Figures 13 and 14). Elevated Sr/Y and La/Yb ratios are characteristic traits of TTGs and adakites, which can be attributed to the melting of source materials with high Sr/Y composition [65]. TTGs are likely products of partial melting of the basaltic lower crust, as indicated by their generally low zircon εHf(t) values. It is usually accompanied by a large volume of mafic rocks and alkaline rocks. The southern margin of the NCC is dominated by intermediate felsic magma, with only a small amount of basic magma exposed, which is not in line with the characteristics of intraplate rift and bimodal magmatism. Moreover, the crust on the southern margin of NCC is generally compressed and thickened, so it is unlikely to be formed in the continental rift at the ~2.3 Ga.

Geochronological data indicate that the Huanggou and Xiaonangou areas in the Xiong’ershan have similar ages, suggesting that partial melting of thickened crust in a rift setting could plausibly account for the intermediate-felsic composition of the continental crust in the region (Figure 15) [23, 43, 47, 83]. A-type granites, such as the granodiorite and monzogranite found in the area, are typically formed through the melting of preexisting crustal rocks. In general, the K-rich granitoid rocks formed in a short period (0.02, 0.15 Ga) following a long period (0.2, 0.5 Ga) of TTG magmatism [77]. Metamorphic rocks distributed along convergent plate boundaries reflect the reworking of crustal rocks through dehydration and melting at lithospheric depths [16]. During the TML, igneous rocks and orogens tend to occur around the margins of Archean cratons in eastern South America, west Africa, and northwestern Canada [2]. Ancient-style plate tectonics likely developed since the Archean when plate margins were ductile enough for warm subduction [16]. Meanwhile, the Xiong’ershan area was surrounded by subduction zone, such as Xiaonangou, and high-angle subduction associated with crustal thickening also led to an extension in the region [84]. Additionally, the calc-alkaline meta-basalts were formed under varying temperature and pressure conditions, and the extension-related collapse of the orogen resulted in the formation of Na- and K-rich intermediate-felsic intrusive rocks in the late stage.

  1. Early Paleoproterozoic meta-basalts and intermediate-felsic rocks in the Xiong’ershan area along the southern margin of the NCC are dated at 2368−2265 Ma.

  2. The calc-alkaline meta-basalts exhibit varying Nb, Ta, and Ti contents in different locations within the Xiong’ershan area. The meta-andesites are primarily the result of partial melting caused by fluids and melts released from subducted slabs.

  3. TTG gneisses are formed through the partial melting of low-K mafic sources within thickened crust levels. Their distinctive high oxygen isotope values and enriched Hf-O isotope values differ from those of K-rich granites, which indicate high-temperature water–rock interactions.

  4. The protoliths of the granodiorite originate from high-K source regions, experiencing partial melting and melt-related metasomatism, and the monzogranites have their source in shallower crustal levels. Both rock types exhibit distinct A-type granite characteristics, associated with extensional tectonic processes.

  5. The Taihua Complex rocks in the Xiong’ershan area formed in a convergent plate margin environment, marked by an initial subduction phase followed by the extension of the thickened continental crust, accompanied by upwelling of the asthenosphere.

The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy restrictions.

The authors declare that they have no conflicts of interest.

Heng Liu: Writing - Original Draft, Investigation, Supervision; Lei Liu: Conceptualization, Funding acquisition, Investigation, Supervision; Dexian Zhang: Funding acquisition, Investigation; Inkyeong Moon: Editing; M. Santosh: Writing - Review & Editing; Yanyan Zhou: Supervision, Validation; Tianyang Hu: Validation; Shisheng Kang: Investigation.

The authors are grateful to anonymous reviewer and associate editor Dr. Bo Hui for their helpful comments and suggestions that helped to improve an earlier manuscript version. We are grateful to first geological brigade of Henan Nonferrous Metals Geology and Mineral Resources Bureau for their assistance during the fieldwork and data collection of the drill core. This research was supported by the National Natural Science Foundation of China (No. 41972198), the National Natural Science Foundation of Hunan province (No. 2022JJ30702), Central South University Graduate Student Independent Exploration and Innovation Project (No. 2023ZZTS0439), and China Scholarship Council (CSC202306370128).

Supp. Table 1. Major (wt%) and trace (ppm) element compositions and related parameters of early Paleoproterozoic Meta-basaltic rocks, Meta-andesitic rocks, Tonalite gneiss, and K-rich granitoids in the Xiong’ershan area in the southern of North China Craton. Supp. Table 2. LA-ICP-MS zircon U-Pb isotopic dating data for representative granitoid gneisses in the Xiong’ershan area in the southern of North China Craton. Supp. Table 3. Zircon Lu-Hf isotopic data for nine dated granitoid gneisses in the Xiong’ershan area in the southern of North China Craton. Supp. Table 4. In situ zircon O isotope of Xiong’ershan area.

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Supplementary data