Zircons are long and columnar with length-to-width ratios close to 2∶1. The sizes of zircons are between 100 and 150 µm. The edges of the zircons were obviously corroded. The U contents range from 446.6 to 1,515.8 ppm. Th contents range from 340.1 to 3,675.8 ppm. Th/U ratios varied from 0.4 to 1.7 (Table 1). The ²⁰⁶Pb/²³⁸U ages of sample HNGDM-2 are between 212.0 and 229.6 Ma, and yield the concordia age and mean age (n = 24) are 225.9 ± 1.28 Ma (MSWD = 0.49) and 225.9 ± 0.7 Ma (MSWD = 0.29), respectively (Figures 3A,B). The ²⁰⁶Pb/²³⁸U ages of Sample HNGDM-4 range from 236.1 to 207.6 Ma, and the concordia age and mean age (n = 19) of the zircon grains are 223.6 ± 1.3 Ma (MSWD = 1.5) and 223.7 ± 1.3 Ma (MSWD = 2.35), respectively (Figures 3C,D).

Zircons exhibit length-to-width ratios between 1:1 and 2:1 and sizes of 100–200 μm. Most zircon grains developed obvious oscillatory zoning (Figure 4). The U contents range from 53.3 to 4,703.3 ppm (except for one spot value up to 9,301.8 ppm), Th contents range from 54.3 to 4,333.7 ppm (except for one spot value up to 6,293.6.8 ppm), and the Th/U ratios range from 0.5 to 1.9, suggesting an igneous origin (Rubatto, 2002; Wu and Zhen, 2004). Out of 30 spots in sample HNGDM-1, 14 analyses yield ²⁰⁶Pb/²³⁸U ages of 221.2–233.2 Ma, with a concordia U-Pb age of 227.4 ± 1.86 Ma (MSWD = 0.97) and a mean age of 227.41 ± 0.95 Ma (MSWD = 1.06) (Figures 4A,B). The ²⁰⁶Pb/²³⁸U ages of Sample HNGDM5-1 range from 217.3 to 228.7 Ma, with a concordia U-Pb age of 225.19 ± 1.61 Ma (MSWD = 0.72) and a mean age of 225.20 ± 0.82 Ma (MSWD = 0.99, n = 16) (Figures 4C,D).

Zircons developed obvious oscillatory zoning. They exhibit length-to-width ratios from 1:1 to 2:1 with sizes from 100 to 200 μm (Figure 5B). U contents range from 516 to 3,309.6 ppm, Th contents range from 127.1 to 6,116.0 ppm, and Th/U ratios range from 0.1 to 2.2. Thirty spot analyses yield ²⁰⁶Pb/²³⁸U ages of 189.7–234.4 Ma. Two groups of ²⁰⁶Pb/²³⁸U ages can be identified. The first group is from 219.5 to 234.4 Ma with a concordia U-Pb age of 229.37 ± 0.71 Ma (MSWD = 2.6) (Figure 5A). The ²⁰⁶Pb/²³⁸U ages of the second group range from 189.7 to 211.4 Ma (Figure 5A).

Two distinct groups of zircons were identified. The first group of zircon grains are complex and exhibits length-to-width ratios from 1:1 to 2:1 and sizes from 50 to 200 μm, Most of them developed obvious oscillatory zoning and are generally incomplete in shape, wheras a small amount is smaller in size (50–100 μm) and round in shape. The second group exhibits length-to-width ratios from 3:1 to 4:1 and sizes of approximately 100–150 μm with U contents from 249.8 to 1,195.2 ppm, Th contents from 324.4 to 1,348.3 ppm, and Th/U ratios from 1.0 to 1.3. Out of 61 spot analyses of L4, 4 analysis points yield ²⁰⁶Pb/²³⁸U ages of 106.0–133.8 Ma, with a concordia U-Pb age of 121.22 ± 1.16 Ma (MSWD = 7) (Figures 5C,D). The first group of zircons exhibits a long-term span and contains at least nine stages of magmatism 1) 217.7–227.8 Ma; 2) 240.6–268.0 Ma; 3) 295.9–379.6 Ma; 4) 405.3–466.8 Ma; 5) 539.1–615.4 Ma; 6) 769.7–842.8 Ma; 7) 972.4–1,135.0 Ma; 8) 1,625.9–1931.6 Ma, and 9) 2,114.4–2,573.1 Ma, which could reveal the long chronological evolutionary history of South China.

The S- and I-type scheme was initially proposed by Chappell and White (1974); Chappell and White (1992), and this letter scheme classification has been widely developed in later studies (Loiselle and Wones, 1979; Whalen et al., 1987; Eby, 1990; Eby, 1992; King et al., 1997; Bonin, 2007; etc.). The mineral assemblage, with the absence of typical alkaline mafic minerals, indicates I- and S-type granitic characteristics for Guandimiao granitoids. In addition, G1 and G2-1 of the Guandimiao batholith have low SiO2 and high FeOT contents and K/Na and FeO^T/MgO ratios; G2-2 and G3 are enriched in SiO₂ contents, Al₂O₃ contents, and K/Na ratios but depleted in MgO and CaO contents. The values of (Zr + Nb + Ce + Y) for the Guandimiao granitoids range from 138 to 295.7 ppm. The ΣREEs are 96.2–193 ppm, and 10,000 × Ga/Al ratios are 2.09–3.02. These values are significantly lower than the lowest values observed in A-type granite (Whalen et al., 1987). Whole-rock Zr saturation temperatures suggest that crystallization temperatures (714–785°C) are consistent with crystallization temperatures < 800°C of I- and S-type granite rather than crystallization temperatures (>8 00°C, even possibly > 1,000°C) of A-type granite (Clemens et al., 1986). All samples plot in the S- and I-type granite fields on the FeO^T/MgO versus Zr + Nb + Ce + Y (Figure 9A).

On the ACF classification diagram, G2-2 and G3 plot in the S-type granite field, whereas G1 and G2-1 plot within the I-type granite field (Figure 9B).

The Pb isotope compositions of the Guandimiao granitoids present higher radiogenic Pb isotope compositions than syntectic granite and plot in the remelting granite of the South China field on the (²⁰⁷Pb/²⁰⁴Pb)_i versus (²⁰⁸Pb/²⁰⁴Pb)_i diagram and ²⁰⁷Pb/²⁰⁴Pb versus ²⁰⁶Pb/²⁰⁴Pb diagram. It is also above the mantle evolution line proposed by Hart (1984) (Figures 10A,B). This suggests that the Pb was mainly derived from the upper crust.

However, the existence of different genetic types (I- and S-type) and lithological compositions of intrusive rocks indicates diverse sources for the Guandimiao batholith (Chappell and White, 1974; Chappell et al., 1988). Zhou (2003) noted that the Indosinian granitoids are scattered across South China. Because of the uneven thickness of the Earth’s crust, the granitoids are characterized by multiple sources and are dominated by thickened continental crust. G1 and G2-1 of the Guandimiao batholith enclosed mafic microgranular enclave, which might have been formed by the rapid crystallization of mafic minerals upon chilling and reduction in viscosity instead of by the mixing of mantle-derived components (Vernon, 1984; Sparks and Marshall, 1986; Zhao et al., 2017).

In addition, G1 and G2-1 have obvious I-type granite affinities and are characterized by relatively high εN_d(t) values (−6.17 to −10.54), low initial ⁸⁷Sr/⁸⁶Sr ratios (0.712005–0.71758) and T_DM2 values (1.52 Ga for G1 and 1.85 to 1.76 Ga for G2-1). G2-2 and G3 show S-type granite affinities and have high initial ⁸⁷Sr/⁸⁶Sr ratios (0.7344) and T_DM2 values (1.73 Ga for G2-2 and 1.93 Ga for G3) but lower ε_Nd(t) values (−8.96 to −12.14). All samples show characteristics of crustal sources on the T versus ε_Nd(t) diagram (Figure 11A). The AMF [molar Al₂O₃/(FeO^T + MgO)] values of G1 and G2-1 range from 1.36 to 1.65, much lower than the values of G2-2 and G3 (3.59–4.63). The CMF [molar CaO/(FeO^T + MgO)] values of G1 and G2-1 are between 0.47 and 0.62, whereas the G2-2 and G3 values range from 0.24 to 0.27. On the diagram of AFM versus CFM, G1 and G2-1 are derived from metabasaltic to metatonalitic source fields, which is consistent with the Jingtou granite, which was derived from a high-K calc-alkaline amphibolite source with metabasaltic to metatonalitic compositions (Figure 11B; Altherr et al., 2000; Zhao et al., 2017). In contrast, G2-2 and G3 plot near the Shizhuqiao granite field, indicating a source similar to the para-metamorphic basement of the Cathaysia Block (Shen et al., 1993; Altherr et al., 2000; Zhao et al., 2015; Zhao et al., 2017).

Moreover, the variation features of two stages of Sm-Nd isotope model ages show an inhomogeneous source. The T_DM2 of G1 is much younger than those of metamorphosed basement in the Cathaysia block (1.8–2.2 Ga) and might be derived from the remelting of meta-juvenile crust in the Mesoproterozoic. The T_DM2 values of G2-1, G2-2 and G3 range from 1.74 to 1.93 Ga, which is consistent with the Paleoproterozoic metamorphosed basement of the Cathaysia block. These results amply justify their geological affiliation. L4 of the Guandimiao batholith has low ε_Nd(t) values (−10.18 to −9.62) but high I _sr (0.71449–0.71784) and T_DM2 values (1.75–1.70 Ga), which represents significant deviation from the Mesozoic EM II-type OIB in the SCB (6.8–10.8; Meng et al., 2012; Qin et al., 2020). The ²⁰⁷Pb/²⁰⁴Pb versus ²⁰⁷Pb/²⁰⁴Pb and ¹⁴³Nd/¹⁴⁴Nd versus ⁸⁷Sr/⁸⁶Sr diagrams show that L4 was derived from a Mesoproterozoic pelagic and/or terrigenous sediment source (Figures 10C,D).

Garnet and spinel were mainly La-, Sm-, and Yb-bearing minerals in the magma source. They are significantly insensitive and can be used as an indicator to trace the melt source and the degree of partial melting (Aldanmaz et al., 2000; Zhao and Zhou, 2008). As the partial melting of a garnet lherzolite occurred in the source, the Sm/Yb ratio decreased sharply, while the La/Sm ratio decreased gradually. The partial melting of garnet lherzolite produces higher Sm/Yb ratios than spinel lherzolite melting (Johnson, 1994; Aldanmaz et al., 2000). The La/Sm versus Sm/Yb and Sm/Yb versus Yb diagrams show that the lamprophyre samples plot near the garnet lherzolite melting curves. These results suggest that the lamprophyre was mainly formed by partial melting of garnet lherzolite. However, a wide degree of partial melting is also presented in Figures 11C,D, which indicates extensive crustal contamination. The same conclusion can also be drawn from the Nb/Y versus Zr/Y and ε_Nd(t) versus La/Nb diagrams. The lamprophyre samples deviate from the Iceland array and plot in the field of mixing trends between the OIB-like asthenosphere and South China SCLM. It shows strong crustal information (Condie, 2005; Meng et al., 2012; Figures 15E,F).

During granitic magmatism, the main Ti-bearing minerals (ilmenite, rutile, titanite, anatase, etc.) could lead to a significant depletion of Ti, Nb, Ta, etc. The fractional crystallization of apatite could significantly decrease the P concentration in the residual melt. Eu, Sr, and Ba could be depleted during fractional crystallization of feldspar, as they usually substitute K⁺ and Ca²⁺ sites into K-feldspar and/or plagioclase. In the Guandimiao batholith, there is significant depletion in Ba, Nb, Sr, and Ti for G2-2 and G3 but less depletion in Ba, Nb, Sr, P, and Ti for G1 and G2-1. This may suggest that the Guandimiao granitoids experienced obvious fractional crystallization of feldspar, Ti-bearing minerals and apatite at the early stages of magmatism. In addition, the negative correlations between Ba and Sr and between Rb and Sr suggest that the magmatic system underwent intense fractional crystallization of K-feldspar and plagioclase (Figures 12A,B). For the rare earth elements (La and Yb), carrier minerals include zircon, apatite, allanite, monazite, etc. The negative relationship between La and La/Yb suggests that the fractional crystallization of allanite and monazite also played an important role in the evolution of magmatism (Figure 12C). It is worth mentioning that G1 and G2-1 have higher K/Rb ratios and lower Rb/Sr ratios than G2-2 and G3. More proof is required that the late stage of magmatism was higher in the degree of fractionation than the early stage (Figure 12D). The granitoids of the Guandimiao batholith were the result of multistage differentiation of an identical long-term magma chamber.

Nine stages of lamprophyre (L4) fully reveal the episodic growth of the South China plate (Figure 13B). Similar evidence has been reported by Shu (2012) and Shu et al. (2020). Five time intervals of detrital zircons dating from the Jinggangshan–Nanling region (2.56–2.38 Ga; 1.93–1.52 Ga; 1.3–0.9 Ga; 0.85–0.73 Ga; and 0.68–0.55 Ga) have been identified. The 5 time intervals could also be identified by detrital zircons from Hubei Province (Gaojiabei Formation), Jiangxi (Huangdongkou Formation, Jueshangou Formation and Tiaomajian Formation), Guangdong Province (gneiss), Sichuan Province (Pingyipu Formation), and Guizhou Province (Dazhuyuan Formation; Shu, 2012; Zhao et al., 2013; Wang D. H. et al., 2014; Wang X. L. et al., 2014) (Figure 13A).

The Neoarchean to Paleoproterozoic ages (2,573.1–2,447.3 Ma) were extensively derived from xenolith crystals in mafic dikes and clastic zircons in Paleozoic strata (Zheng et al., 2008). They are obviously younger than the Kongling Group in the Yangtze block (3.3 Ga, Ma et al., 1997). They represent global continental nucleus growth events and mixing processes between Neoarchean mafic magma and more ancient crustal components.

The middle to late Paleoproterozoic data (2,232.7–2,114.4 Ma and 1931.6–1,625.9 Ma) is linked to the response of the convergence and breakup effect of the Columbia supercontinent. The convergence of the Columbia supercontinent began 2.1 Ga, which is represented by the formation of the Kora-Kareline conjunctive craton and West Australian craton and the outgrowth of the western Amazon ancient continental plate margin in South America (Hoffman, 1988). Correspondingly, significant tectonic magmatic events were also recorded in the North China craton (NCC) and Yangtze craton (Zhang et al., 2006; Yin et al., 2013). Subsequently, the tectonic regime transformed to breakup on a global scale 1.7–1.5 Ga. A large number of A-type granitoids and mafic dikes developed in the Yangtze craton, indicating the existence of intracontinental rifting (Rogers and Santosh, 2002; Zhao et al., 2002; Evans and Mitchell, 2011; Gibson et al., 2012; Geng et al., 2019).

During the early Neoproterozoic (1,135.0–769.7 Ma), the region experienced the suture of the Paleo-Huanan Ocean along the Jiangnan–Shaoxing large fault zone, and the collision between the Yangtze block and Cathaysia block created the initial appearance of the ancient SCB. This was completely documented by abundant ophiolites and associated pyroclastic rocks developed along the Dexin–Dongxiang and Zhuji–Lishui–Wuyi–Meixi belts in the southeastern Cathaysia block from 1.0–0.9 Ga. The I-type granite and mafic rocks of the southern Jiangnan orogenic belt, which formed 0.9–0.8 Ga, indicates the subduction of pristine oceanic crust (Ye et al., 2007; Shu et al., 2012; Zhou et al., 2018). The subsequent break-up of the supercontinent and extension events occurred along the paleo-suture and formed the Nanhua continental rift basin and three main tectonic domains (Nanling, Wuyi, and Yunkai) 825–760 Ma (Wang et al., 2017; Yang et al., 2018). The eventual Phanerozoic collage of the SCB (early Paleozoic, 466.8–405.3 Ma) and multistage intracontinental orogenic events (late Paleozoic, 268.0–258.8 Ma; 379.6–295.9 Ma) constituted the basic tectonic appearance in the Paleozoic (Liu et al., 1990; Shu et al., 2006; Shu et al., 2012).

The Guandimiao batholith is the central part of the SCB. The G1, G2-1 and G2-2 phases were emplaced 239–203 Ma and were dominant in the period from 230 to 220 Ma. The structural discriminant diagram shows that these rocks formed in a postcollisional environment (Figure 14A; post-COLG field; Pearce, 1996). The lamprophyre plots near the WPG field and Ⅵ₃ field on the Rb versus Y + Nb diagram (intraplate basalt) (Figure 14B), which indicates an intracontinental extensional setting.

During the early Indosinian (250–240 Ma), the forceful collision and extensive metamorphism between the Indo-China block and the Sibumas-Qingtang block occurred in the Early-Middle Triassic and exerted a profound impact on the southeastern Eurasian continent (Chen et al., 2002; Li et al., 2006). Meanwhile, the closure of the Paleo-Tethys Ocean caused southeastward subduction and collision between the NCC and the SCB. The SCB underwent multidirectional compression and massive shortening, accompanied by an approximately 50 km thickening of the continental lithosphere (Tapponnier et al., 1982; Gilder et al., 1995; Carter et al., 2001; Wang et al., 2002; Li et al., 2017) (Figure 15A). The collisional orogenic events immensely shortened the crust and resulted in a series of thrust faults and uplift structures. There was an approximately 10 Myr. Interval before granitoids melted following the end of crustal thickening (Patio Dounce et al., 1990), and Sylvester (1998) proposed a possible relaxation and thinning of the thickened crust with a time interval of 10–20 Myr. The Guandimiao dome developed at the center of the SCB. The main part of the Guandimiao batholith was formed in a postcollision setting after the Indosinian crustal thickening events in the SCB. The thermal stress from crustal extension caused decompression and melting of thickened crust, along with continuous emplacement of mantle-derived magma (Pape et al., 2012). It induced extensive melting of Paleoproterozoic metamorphic basement in the SCB (Zhou et al., 2006; Guo et al., 2012; Qin et al., 2022) (Figure 15B).

Approximately 200–180 Ma, the transformation of the tectonic regime occurred from NE-directed paleo-Tethys ocean dominance to NE-directed paleo-Pacific ocean dominance. The continued subduction of the paleo-Pacific plate beneath the Eurasian plate affected more than 1,000 kilometers. Due to the stable structure and the shortage of transcrustal faults, there was a significant deficiency in magmatic rocks, and the volume and scale of magmatism were far less than those developed either in the early Insinian or late Mesozoic and have been confirmed as the break-in period (200–180 Ma) of igneous rocks in South China (Mao et al., 2004; Zhang et al., 2009) (Figure 15C). Scattershot intrusions occurred as stocks and dikes exposed in the interior batholith with limited scope.

In the Middle Jurassic, subduction of the paleo-Pacific oceanic plate converted to rollback steep subduction and caused large-scale extensional events in the back-arc basin. The uplift of asthenospheric mantle melted the ancient metamorphic basement and formed a large granitic melt 135–118 Ma (Zhou et al., 2006; Jiang et al., 2015; Yang, 2018; Li et al., 2019). Moreover, mafic magma rapidly intruded along the deeply penetrating faults and extensively contaminated the upper crustal materials. This made it possible for the formation of lamprophyre with intense crustal information (L4) (Figure 15D).