Origin and implication of two newly identified peraluminous A-type granites in the early Paleozoic orogeny, Southeast Asia

Abstract: The amalgamation of the Yangtze and the Cathaysia Block in Neoproterozoic time led to the formation of the South China Block (SCB) and generated the Jiangnan Orogen with the occurrences of juvenile magmatic rocks. After this orogeny, a typical collisional orogen formed during the early Paleozoic period in Southeast Asia which is mainly distributed in the Wuyi-Nanling-Yunkai area in the SCB. However, the transitional time from syn-collisional compression to post-collisional extension is debatable. Here, we present new data on zircon U-Pb zircon ages, Lu-Hf isotopes, and geochemistry for the Guzhang and Shadi granites from the Nanling area, South China. Both plutons have similar zircon 238U/206Pb ages of ca. 430 Ma. Petrographic and geochemical characteristics (e.g., FeOt/(FeOt+MgO) = 0.82–0.95) indicate that both granites are peraluminous A-type, with high Ga/Al ratios (2.43–2.91) as well as high concentrations of Zr, Nb, Ce, Y (sum values from 327 to 527 ppm), and formation temperature (820°C–845°C). Shadi granite exhibit high positive εHf(t) values (clustering within 0 to +6) while Guzhang granite show relatively lower εHf(t) values (−8.7 to −2.9). Their mildly negative to positive zircon εHf(t) values are higher than that of many coeval granites and can be derived from anhydrous melting of tonalitic genesis in the middle crustal depth, with the Shadi pluton having more orthometamorphite in the source. The ages and Hf isotopic compositions of inherited zircons (εHf(t = 960 Ma) = 9.2, εHf(t = 950 Ma) = 7.3) suggest that the Neoproterozoic juvenile magmatic rocks in the Jiangnan Orogen were a significant source for these granites. We interpret these A-type granites derived at the post-collisional stage. Their occurrence indicates that the geological setting of this Paleozoic orogen shifted from compression to extension no later than 430 Ma.


Introduction
A nearly 2000 km long and 450 km wide orogen formed in Southeast Asia during the Ordovician to Silurian periods ( Figure 1; Charvet et al., 2010;Li et al., 2010;Zhao et al., 2022). This collisional belt was characterized by widely distributed regional metamorphic rocks (greenschist, amphibolites, and minor granulites) in the Wuyi-Nanling-Yukai area with ages ranging from 460 to 436 Ma (e.g., Shu et al., 2008;Charvet et al., 2010;Yu et al., 2014). The orogeny also caused angular unconformity between the Devonian and pre-Devonian strata.
The origin of this early Paleozoic orogen was long timely debated from the early 1990s to the present (e.g., Ren et al., 1997;Lin et al., 2018;Wang et al., 2018). The main point of contention is whether the orogen formed with or without oceanic crust subduction. The lack of early Paleozoic ophiolites, magmatic volcanic rocks, subduction complexes, and high-pressure metamorphism was cited as evidence for intracontinental origin (Charvetet al., 2010;Li et al., 2010;Shu et al., 2014;Wang et al., 2013;Yao et al., 2012;Kong et al., 2021;Zhao et al., 2022). While the oceanic crust subduction model is supported by a few newly discovered arclike rocks with ages from 445 to 430 Ma (Peng et al., 2006;Peng et al., 2016;Zhang et al., 2016;Lin et al., 2018). To our opinion, the lack of abundant volcanic rocks and detrital zircons with ages ranging from 520 to 460 Ma in the adjacent strata and river sands of South China (Xu et al., 2007) may further support the intra-continent model.
Despite this debate, the geological processes related to syncollisional crustal thickening and post-collisional thinning were documented in this orogen. The time scale of the collisional events could be constrained by the ages of regional amphibolitefacies metamorphic rocks and gneissic S-type granites (e.g., 460-440 Ma, Li et al., 2010). While the approximate time when the region began to shift into an extensional geological setting is still under debate (e.g., Huang and Wang, 2019;Xin et al., 2020). Some previous studies suggested the hornblende bearing I-type granites and associated mafic rocks  were produced in an extensional setting caused by lithospheric delamination (e.g., Zhong et al., 2012;Zhang et al., 2015). For instance, Zhang et al. (2015) suggest an extensional tectonic regime has developed from the beginning of the Silurian (442 Ma) with the occurrence of Guiyang I-type granites and associated Dakang mafic-felsic intrusion. Others regarded the occurrence of the A-type granites (Figures 1,(400)(401)(402)(403)(404)(405)(406)(407)(408)(409)(410)(411)(412)(413)(414)(415) as the mark of the extensional setting (Feng et al., 2014;Li et al., 2016b;Cai et al., 2017;Xin et al., 2020). The transitional time defined by the A-type granites (ca. 415 Ma) is incompatible with the timing defined by the I-type granites and the Age distribution map of early Paleozoic granitic rocks in South China Block. Most of the metamorphic and magmatic rocks are distributed in the WuYi-Nanling-Yukai area. The A-type granites (marked with ①~④) are uncommon and have ages from 415 to 400 Ma. The Jiangshan-Shaoxing fault is thought to be the boundary between the Yangtze and the Cathaysia block at the Neoproterozoic time while the westward extension of the boundary is unclear(marked as the dotted lines in Figure 1A. Frontiers in Earth Science frontiersin.org 02 contemporaneous mafic rocks (ca. 435 Ma), which require urgent constraint.
In this study, we identified two new A-type granites with ages of 430 Ma in the Nanling region. This new finding, which is in agreement with the presence of I-type granites and contemporaneous mafic-felsic complex, suggests that the Wuyi-Nanling-Yunkai orogeny had changed from compressional setting to an extensional setting at least from 430 Ma.

Geological background and sample introduction
The South China Block has recorded two major orogenic events before the Carboniferous era: the Neoproterozoic Jiangnan orogeny and the Early Paleozoic Wuyi-Nanling-Yunkai orogeny (Zhao et al., 2022). The Jiangnan Orogen was formed at 1.0-0.82 Ga during the assemblage of the Yangtze and Cathaysia block (Yao et al., 2019) and is characterized by the occurrence of arc-related magmatic rocks with highly depleted Nd-Hf isotopes (Li et al., 2009). However, early Paleozoic mafic rocks in the Wuyi-Nanling-Yunkai orogeny have slightly enriched to moderately depleted Nd-Hf isotopes (Xu and Xu, 2017), and were suggested to be mainly derived from a lithospheric mantle that had been metasomatized by the Neoproterozoic subducted crustal materials (e.g., Wang et al., 2013). These rare mafic rocks have a total outcrop of ca. 50 Km 2 (gabbros, with minor basalt and hornblende, Shu et al., 2020), with the ages varying from 443 to 400 Ma.
More than 200 Ordovician-Devonian granitic plutons have been found in the South China Block, with large proportions of S-, a few Iand minor A-type granites. These granitic rocks have zircon 238 U/ 206 Pb ages ranging from 464 to 381 Ma (e.g., Zhang et al., 2010;Huang et al., 2013;Cai et al., 2017) and made up the vast majority proportion of the magmatic rocks during the orogeny. The S-type granites have zircon 238 U/ 206 Pb ages from 464 to 401 Ma (e.g., Huang and Wang, 2019), and the I-type granites have zircon 238 U/ 206 Pb ages from 442 to 381 Ma (e.g., Zhao et al., 2013;Xu and Xu, 2015). Only four A-type granitic plutons have been reported, with zircon 238 U/ 206 Pb ages from 415 to 400 Ma (Feng et al., 2014;Li et al., 2016b;Cai et al., 2017;Xin et al., 2020).
The newly identified A-type granites, including two plutons named Guzhang and Shadi, are located in the middle part of the early Paleozoic Wuyi-Nanling-Yukai orogeny ( Figure 2). The Guzhang granite has an outcrop of ca. 208 km 2 and Shadi granite has an outcrop of ca. 54 Km 2 . The Guzhang and Shadi granitic pluton intruded into the Cambrian and Neoproterozoic basement rocks. The Cambrian rocks are mainly composed of quartz greywacke and carbonaceous slates and the Precambrian rocks are composed of tuffaceous sandstone. Hornfels is found in the granites and basement rocks contact zone.

Zircon U-Pb dating
Zircon grains were isolated using density and magnetic separation techniques. Zircons were mounted into an epoxy resin disk and polished to expose their surfaces. After photographing in both reflected and transmitted light, CL (cathode luminescence) imaging was taken by a JSM6510 SEM attached to a Gatan CL detector. Zircon U-Pb isotopic analyses were carried out on the transparent zircons without fracture or mineral inclusion using a Thermo X2 ICP-MS housed at the Testing Center of Shandong Bureau of China Metallurgical Geology Bureau, Jinan, Shandong province. The mounted zircon grains were ablated using an attached Coherent Geolas Pro 193 nm laser ablation system with a spot diameter of 30 μm. Ablation occurred in intervals of ten sample zircons, directly preceded and followed by two 91,500 standard zircons and one artificial glass 610. The analyzed results of the 91,500 fall into the ranges of the long-term test values of the Lab, with the uncertainty of 1.5% (1 RSD) for most of the 206 Pb/ 238 U measurement and are listed in Supplementary Table S1. Detailed instrument conditions and data acquisition have been described by Li et al. (2016a). The ICPMSDataCal 8.0 (Liu et al., 2010) was used to select offline raw data, integrate background and analytical signals, and time drift correct and quantitative calibrate U-Pb isotopes. The common lead correction was made following the method of Anderson (2002). The age distributions are visually compared using probability density plots (PDPs; Ludwig, 2003). Weighted average age calculation was made using Isoplot 3.23 (Ludwig, 2003).

Whole rock major and trace element geochemistry
All samples were prepared by crushing them in an agate shatter box. Major elements were analyzed using an Axios 4.0 X-ray

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frontiersin.org fluorescence spectrometer (XRF) at the Testing Center of Shandong Bureau of China Metallurgical Geology Bureau, Jinan, Shandong province, following the procedures described by Franzini et al. (1972), with analytical precision better than 1%. Rare earth elements and other trace elements from the rocks were analyzed using ICP-MS (Thermo Fisher icap Q) techniques at the Testing Center of Shandong Bureau of China Metallurgical Geology Bureau, Jinan, Shandong province. The precisions for most elements are better than 5% (1SE).

Zircon Lu-Hf isotopic composition
Zircons Hf isotope analyses were carried out using a Neptune Plus MC-ICP-MS equipped with a GeoLas Pro193 nm laser at MiDeR, Nanjing University. The diameter is 44 μm with a pulse rate of 10 Hz, and beam energy of 5 J/cm 2 . Only zircon grains with concordant ages and suitable sites for Hf analyses were analyzed. The zircon standard 91,500 was analyzed during the analytical session, which yielded a 176 Hf/ 177 Hf ratio of 0.282310 ± 9  (Griffin et al., 2000). The average crustal 176 Lu/ 177 Hf value used for TDM calculations is 0.015 (Griffin et al., 2002).  Shu et al., 2011). Sixteen zircon grains were analyzed from sample 9653. Four of the results are discordant and one grain is inherited zircon. These zircons have low Th, U concentrations (<500 ppm), with Th/U ratios from 0.13 to 1.05, and are of magmatic origin (Hoskin and Schaltegger, 2003). Eleven zircon grains yield a weighted average   Xin et al., 2020. Because the mafic rocks generally lack zircons, the ε Hf (t) values of mafic rocks are recalculated from the data source in Shu et al., 2021 by assuming the Nd-Hf isotopes are coupled (εHf=1.36pεNd+3; Vervoort et al., 1999). The Nd-Hf relationship of early Paleozoic magmatic rocks was discussed by Xia et al., 2014. Frontiers in Earth Science frontiersin.org 06

FIGURE 6
Harker diagrams for representative major (A-E) and trace elements (F-H) from the Shadi and Guzhang plutons.The coeval magmatic rock samples from the Nanling area are also plotted for comparison and the detailed data are listed in the appendix in Shu et al., 2021. Frontiers in Earth Science frontiersin.org 07 depleted mantle) are from 1.63 to 1.95 Ga. The inherited zircon from 9605 has ε Hf (t = 654 Ma) value of −0.2 ± 0.6. The zircon ε Hf (t) values from sample 9653 have more narrow ranges, varying from −6.7 to −3.0 (n = 15), with a peak value close to −4, corresponding to the T DM2 ages from 1.60 to 1.81 Ga. The inherited zircon from 9653 has ε Hf (t = 950 Ma) value of 7.3 ± 0.5.

Trace elements and REEs
Samples from Guzhang have higher concentrations of highfield-strength elements (HFSEs, e.g., Nb, Zr, Figures 6F,G) when compared with other coeval granites in the Nanling area (Xu and Xu, 2015). Primitive mantle normalized spider diagrams exhibit strong enrichment in Rb, Th, U, and Nd as well as clear negative anomalies in Ba, Nb, Sr, P, Eu, and Ti. The Rare earth element (REE) abundances vary from 152 to 212 ppm with light REE enrichment, significant negative Eu anomalies, and flat-sloping heavy REE patterns ( Figures 8A, B). Samples from the Shadi have similar trace element features with the Guzhang granite, which are featured by the enrichment of HFSEs and depletion of Ba, Nb, Sr, Eu, and Ti. The total REEs of Shadi granites have larger variations than that of Guzhang granites, from 67 to 254 ppm. It also shows strong negative Eu abnormally on the chondrite normalized REEs patterns ( Figures 8C, D). The heavy depletion of Eu, Ba, and Sr in both plutons indicates that the feldspars played a significant role during the magma generation, either as residuals in the source or as fractionated minerals.

Genesis type
The majority of granites can commonly be classified as I-, S-, or A-types based on mineral combinations and geochemical characteristics (Bonin, 2007). Chappell and white (1974) divided the granites in the Lachlan fold belt into I-and S-type. The I-type granites are characteristic of low SiO 2 contents, ASI values (normally <1.1), depleted isotopes (e.g., Sr, Nd, Hf), and the appearance of hornblendes, derived from mainly meta-igneous rock sources. The S-type granites are featured by high ASI values (normally >1.1), enriched isotopes with the appearance of garnet and/or cordierite, and are suggested to be mainly derived from metasedimentary rocks. It is worth noting that the mineralogical and geochemical characteristics mentioned above are not solid standards for the classification of granite types. For example, aluminum-rich minerals such as primary garnet can also be found in weak peraluminous and even meta-aluminous granites (Chappell, 1999). The geochemical characteristics of A-type granites differ from those of I-and S-type granites (e.g., high contents of HFSEs and Ga/Al ratios), and the geochemical parameters used to define A-type granite are unambiguous. (Loiselle and wones, 1979;Eby, 1990;Creaser et al., 1991;Bonin, 2007).
Even the high ASI values and the existence of biotite and minor muscovite are similar to the future of some typical S-type granites (Bonin, 2007), the high formation temperatures, FeO tot / (FeO tot +MgO) ratios, and limited inherited zircons (3 inherited zircons of 76 grains) and other features that will be discussed next preclude the S-type origin. The most noticeable characteristics of Guzhang and Shadi plutons are as follows: 1) high FeO tot /(FeO tot +MgO) ratios and ASI values (Figures 6, 7); 2) low contents of Al 2 O 3 , CaO, MgO ( Figure 6); 3) mildly negative to positive Zircon Hf isotopic composition ( Figure 5B); 4) high HFSEs concentrations and Ga/Al ratios; 5) the occurrences of interstitial biotites and perthitic microcline; 6) lack of inherited zircons. The FeO t /(FeO t +MgO) ratios of samples from both plutons are plotted in the ferroan A-type granites field ( Figure 7C, defined by 175 A-type granites worldwide; Frost et al., 2001) and are distinguishable compared with the magmatic rocks that formed during 460-400 Ma in Nanling area ( Figure 6B). Most of the samples were plotted near or in the field of A-type granites on different chemical diagrams because of the high HFSEs concentrations and 10,000*Ga/Al ratios (Figure 9).
Besides the distinct A-type granite geochemical features, these two plutons also have high Zr saturation temperatures. The Guzhang granite has whole rock Zr saturation temperatures from 820°C to 840°C (Supplementary Table S1, M[(Na + K + 2*Ca)/ (Al*Si)]=1.1-1.2; Watson and Harrison, 2005) and four of six samples from the Shadi granite (M=1.2-1.4) have temperatures from 813°C to 845°C ( Figure 10A). The other two low-  Sun and McDonough (1989).

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frontiersin.org temperature samples (ca. 750°C) from the Shadi pluton have the highest SiO 2 and lowest Zr (68 and 80 ppm) and Ti contents, which may cause by fractional crystallization. The zircon Ti thermometry is also used to calculate the zircon crystallization temperature. A new correction of Ti in zircon temperature calculation was made by Schiller and Finger (2019), and they suggest the zircon temperatures in most A-type granites were underestimated. The zircons from Guzhang and Shadi granite have saturation temperatures from 700°C to 1000°C and 700°C-950°C, respectively ( Figure 10B). Combined with the occurrences of interstitial biotites and  Frontiers in Earth Science frontiersin.org perthitic microcline, it may be concluded that both plutons evolved under anhydrous conditions at high temperatures. All of the aforementioned characteristics suggest that these two granitic plutons are ferroan A-type.
The granulite model with pre-extraction of I-type granitic melt was argued by some scholars for such melts would have low Fe/Mg and (Na 2 O+K 2 O)/Al 2 O 3 ratios that differ from typical A-type granites (e.g., Creaser et al., 1991;Frost and Frost, 2011;Jiang et al., 2022). However, some studies suggested that the early Paleozoic A-type granites in the Wuyi-Nanling-Yunkai orogen were derived from mainly granulitic rock sources, such as granulitic meta-igneous rocks (Cai et al., 2017), granulitic metasedimentary rocks (Feng et al., 2014) or granulite that had extracted S-type granitic magma (Xin et al., 2020). The main reason is due to the low water affinity of the granulite which seems as a suitable source for the anhydrous A-type magmas. We are not intended to connect the Guzhang and Shadi plutons with the granulite source, since it is not a necessary factor to generate the A-type granites (Creaser et al., 1991;Skjerlie and Johnston, 1993).
The Guzhang granite has negative zircon ε Hf (t) values (−8.7-−3.0) that are unlikely derived from a coeval mantlederived mafic magma ( Figure 5B). The Shadi granite has higher ε Hf (t) values that overlap with the ranges of coeval mafic rocks, which can be derived from the differentiation of the basaltic rocks isotopically ( Figure 5B). However, A-type granites that derived from differentiation of the basaltic magma are generally metaluminous and commonly found in association with mafic intrusions (Mccurry et al., 2008). Both Guzhang and Shadi plutons are peraluminous and not found to be associated with mafic intrusion or mafic enclaves. Thus, they are not likely derived from the direct fractionation of mafic magmas. Besides, zircon ε Hf (t) values from both plutons have large ranges, up to 10 ε units. The large ranges in zircon ε Hf (t) are either caused by magma mixing (Griffin et al., 2002) or by disequilibrium melting during the crustal anataxis (Tong et al., 2021). The magma mixing model is not favored here because mafic magmas mostly have low ASI values (<0.8) and the magma produced by pure mixing can hardly achieve the strong peraluminous affinity of our samples, while source mixing is more plausible.
Partial melting of mainly quartzofeldspathic rocks during crustal anataxis is a possible way to generate the A-type granites (Frost and frost, 2011). For instance, dehydration melting of F-rich tonalitic gneiss at mid-crustal pressures can generate strong peraluminous A-type granites (Figure 7; Skjerlie and Johnston, 1993). The Guzhang granite has mildly negative ε Hf (t) values (−8.7-−3.0), which are higher than most coeval granitic plutons, especially the typical S-type granites (ε Hf (t) = −34.2-−0.2; n=963, median = −8.4; Xin et al., 2020) and also the Neoproterozoic basement rocks in the west Wuyishan area. (Figure 11). Thus, it is unlikely derived from a source that is dominated by old metasedimentary rock. Zircon from the Shadi pluton has positive ε Hf (t) values up to +6.3, indicating that it originated from the partial melting of more immature source rocks rather than sedimentary source rocks.
The Neoproterozoic juvenile rocks in the Jiangnan Orogen, like the tonalitic to rhyolitic magmatic rocks from Shuangxiwu and Pingshui area, seem a good candidate as the source of these A-type granites (Chen et al., 2009;Li et al., 2009). Neoproterozoic inherited zircons with depleted Hf isotopic characteristics were found in the Shadi (ε Hf (t=960 Ma) = 9.2 ± 0.6) and the Guzhang pluton (ε Hf (t=950 Ma) = 7.3 ± 0.5), both of which occur within the ranges of zircons from the tonalitic rocks at the eastern Jiangnan Orogen (Figure 11; Li et al., 2009). Besides, the Beiwu volcanic rocks with tonalitic composition (See Supplementary Table S2 in Li et al., 2009) have major elements similar to the starting materials used in the dehydration melting experiment in Skjerlie and Johnston, 1993. Thus, the dehydration melting of source rocks that are similar to the juvenile tonalitic rocks from the east Jiangnan Orogen can generate peraluminous Shadi A-type granite, geochemically and isotopically. Therefore, we suggest these two peraluminous granitic plutons were most likely formed by the dehydration melting of Neoproterozoic ε Hf (t) vs ages (Ma) diagrams. The Neoproterozoic data is from Li et al., 2009;Chen et al., 2009. The ranges of Neoproterozoic basement rocks in the west Wuyishan area are from Xin et al. (2020). Both plutons are not likely derived from the old basement rocks for the higher ε Hf (t) values. The Shadi granites can be mainly derived from a source similar to the Neoproterozoic juvenile tonalitic rocks in the eastern Jiangnan Orogen while the Guzhang granites have a mixed source with more old crustal materials.

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frontiersin.org juvenile tonalitic rocks with minor metasedimentary rocks at medium crust pressure, with the source of Guzhang granite containing more old metasedimentary rocks ( Figure 12).

Tectonic implication
The orogeny of this early Paleozoic belt was first recognized by the mass distributions of the regional metamorphic rocks (greenschist, amphiboles, and minor granulites, Figure 1). Systematic geochronology studies of those metamorphic rocks were formed at 460-436 Ma (Yu et al., 2005;Yu et al., 2014;Li et al., 2010;Tong et al., 2021). The occurrence of high-pressure metamorphic rocks revealed crustal thickening events in the belt (Li et al., 2010;Yu et al., 2014;Tong et al., 2021). The crustal thickening events were mainly suggested to be triggered by continental collision (Charvet et al., 2010;Li et al., 2010;Yao et al., 2012;Wang et al., 2013;Shu et al., 2014;Kong et al., 2021;Zhao et al., 2022). The youngest metamorphic zircon U-Pb ages from the Yiyang granulite are at ca. 435 Ma (Yu et al., 2014) and this age may mark the end of the collision event since no metamorphic rocks with younger ages have been reported. However, the accurate transformational age of this belt from compression to extension is still debated.
A-type granites had long been recognized as derived at extensional settings (e.g., Collins et al., 1982;Forst and Forst, 2011). In collisional orogens, syn-collisional crustal thickening has been followed by delamination of substantial amounts of mantle lithosphere at the post-collisional stage (Davies and von Blanckenburg, 1995). The post-collisional extension provides a suitable environment for hot mafic magma upwelling and also the heat for melting the source rocks of A-type granites (Jiang et al., 2022). Thus, the formation ages of A-type granites are often suggested to be the time that the region changes into a strongly extensional geological background. A-type granites in SCB have previously been dated between 415 and 400 Ma, hence it was hypothesized that the Wuyi-Nanling-Yunkai orogeny transitioned from syn-orogenic crustal thickening to a postorogenic thinning at 415 Ma. (e.g., Xin et al., 2020).
However, most studies considered the hornblende bearing I-type granites (e.g., Guiyang granite formed at 442 Ma, Zhang et al., 2015) and coeval mafic rocks (e.g., Chayuanshan high Mg basalts formed at 435 Ma, Yao et al., 2012) were produced in an extensional setting that caused by lithospheric delamination. Huang and Wang (2019) also suggested that the occurrence of massive high-K calc-alkaline I-type granites in the Xuefengshan area can exemplify the transitional period from compression to extension, with the ages of ca. 430 Ma. Besides, the gneissic S-type granites in the belt mainly have a peak age of 440 Ma, and massive S-type granites have a peak age of 430 Ma. Those massive S-type granites were also suggested to be derived during the orogenic collapse stage (Feng et al. (2014). The ages of Shadi and Guzhang A-type granites in this study are consistent with the conclusion from the S-, I-type granites and the coeval mafic rocks. Thus, we suggest that the setting of Wuyi-Nanling-Yunkai orogen had changed from compression to extensional at least at ca. 430 Ma, which is 15 Ma earlier than the previous conclusion from A-type granites.

FIGURE 12
The schematic cartoons showing the tectonic evolution of SCB and the generation of the A-type granites in this study. The amalgamation of the Yangtze and the Cathaysia Block in Neoproterozoic time generated intermediate to felsic magmatic rocks with depleted Nd-Hf isotopic features (A). This amalgamation was followed by a post-orogenic extension which is recorded by A-type granites and other rift-related mafic rocks (B), Yao et al., 2019). However, after 760 Ma, the magmatism in SCB was limited (C). Some magmatic rocks and metamorphic rocks were identified in SCB with the ages from 470 to 445 Ma and regarded as products of the continental collisional stage (D). Large volumes of magmatic rocks were formed at the extensional stage (430-400 Ma) after the delamination of the thickened crust and upper lithospheric mantle (E).b Frontiers in Earth Science frontiersin.org 6 Conclusion 1) We identified two new peraluminous granites in the Wuyi-Nanling-Yunkai orogen, South China. These two plutons have high FeO t /(FeO t + MgO), Ga/Al ratios, and HFSEs concentrations with low CaO and MgO contents as well as high formation temperature, and are fitted with the affinities of A-type granites. 2) LA-ICP-MS zircon U-Pb dating results indicate the Shadi granite and the Guzhang granite were formed at 430 ± 5 Ma. Both granites can be formed by partial melting of mainly Neoproterozoic juvenile meta-tonalitic rocks at medium crust pressure while the source of Guzhang granite contains more old crustal materials. The Neoproterozoic juvenile tonalitic rocks in Jiangnan Orogen might be a significant source for the A-type granites. 3) This new finding suggests the geological setting of the Nanling area in the Wuyi-Nanling-Yunkai orogeny changed from collision to post-collisional extension no later than 430 Ma.

Data Availability Statement
The original contributions presented in the study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding author.