Early Paleozoic Adakitic Granitoids from the Xingshuping Gold Deposit of East Qinling, China: Petrogenesis and Tectonic Significance

This study discussed the pertrological classification, geochronology, petrogenesis and tectonic evolution of early Paleozoic granites from the Xingshuping gold deposit in the East Qinling orogenic belt. In order to achieve this target, we carried out an integrated study of zircon U–Pb age, whole-rock major and trace elements, as well as Sr–Nd–Hf isotope compositions for the Xingshuping granites (part of the Wuduoshan pluton) from the Erlangping unit. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb dating constrains the emplacement age of the Xingshuping granites at 446.2 ± 1.2 Ma. The rocks at Xingshuping can be divided into two types: mainly biotite granite and monzonitic granite. The biotite granites are typical adakitic rocks, while the monzonitic granites show characteristics similar to normal arc volcanic rocks. The geochemical compositions reveal that they were derived from a clay-rich, plagioclase-rich and biotite-rich psammitic lower continental crust source, with contributions of mantle-derived magmas. The distinction is that the biotite granites were primarily derived from partial melting in a syn-collision extension setting, whereas the monzonitic granite went through a fractional crystallization process in an intraplate anorogenic setting.


Introduction
The East Qinling orogenic belt (EQOB) is part of the Central China orogenic belt (CCOB), where the North China Craton (NCC) is adjacent to the north and South China Craton (SCC) to the south [1,2] ( Figure 1A). The EQOB records complex geological and tectonic history, including continental rifting, ocean basins opening and closure along convergent margins, continental growth and recycling, continental collision and intraplate tectonics [3][4][5][6][7]. It is formed by multiple stages (Neoproterozoic, Paleozoic and Mesozoic) of tectonism since Neoproterozoic and finally formed by collision of the NCC and SCC during the Early Mesozoic; most granitoid magmatism or plutons have been intensively studied [8][9][10][11].  [12]. (B) Simplified geological map of the Wuduoshan pluton and distribution of the Au deposit, modified following [13].
This region hosts the largest molybdenum (Mo) belt in the world [14,15] and the second largest orogenic gold province in China [16][17][18]. It is well known that most of the Mo and Au reserves are associated with late Mesozoic (Late Jurassic to Middle Cretaceous) granites at the southern margin of the NCC [16][17][18][19][20], and only a few deposits are located within the neighbor terranes of the EQOB [20,21] or associated with other orogenic processes [13,22]. The unequal distribution of mineralization and their associated granites in the EQOB remains to be explained.
One of these gold deposits is the Xingshuping gold deposit, which is located in the west of Wuduoshan pluton (one of the biggest plutons in the EQOB with an exposed area of about 1420 km 2 ). This gold deposit was discovered in during the recent decade, and previous research only investigated the stratigraphy. There is currently no consensus on the source and evolution of the granitoids in this deposit, and detailed geochro-nology, geochemical characteristics and isotopic compositions of these granitic rocks are also unclear. In order to clarify these problems and to provide a basis for further study, in this paper, we report the pertrological classification, geochronology and petrogenesis of granites from the Xingshuping gold deposit combined with the amount of geochronological, geochemical and isotopic data that have been obtained for the Wuduoshan pluton in order to systematically study orogeny-related magmatic events and tectonic evolution.

Regional Geology
The EQOB located in Central-Eastern China, is one of the most important collision orogens due to the convergence between the NCC and SCC [1,2]. This orogen is bounded at the north by the Lingbao-Lushan Fault and on the south by the Mianlue-Bashan Fault [23], separated into the southern margin of the NCC (S-NCC), Northern Qinling belt (NQB) and the Southern Qinling belt (SQB) by the Luonan-Luanchuan Fault (LLF) and the Shangnan-Danfeng suture (SDS), respectively [24][25][26][27]. The SDS underwent a Middle Paleozoic subduction collision event and Mesozoic-Cenozoic intraplate strike-slip faulting [8,23,26].
The Wuduoshan pluton is an Early Paleozoic intrusive in the eastern part of the NQB, with complex granite types and multi-stage emplacement. Most part of the intrusion is located in the basic volcanic rocks of Erlangping group, and the southeast part comprises local intrusions into the Qinling complex above Erlangping group [29] ( Figure  1B). The rock types mainly comprise medium fine grain biotite monzogranite, medium fine grain two mica monzogranite and porphyric biotite monzogranite. Available data show that granitoid emplacement of Wuduoshan pluton took place during a long time span from 468.5 ± 4.1 Ma [30] to 414.5 ± 2.3Ma [31] concentrate mainly in the 441~428 Ma range [13,29,30,32,33]; the crystallization age, petrogenesis and related geodynamic background are still controversial. More than ten Au deposits or orebodies occur in the pluton or the inner-contact and outer-contact zones, most of which are distributed in the western part of the pluton [34] ( Figure 1B). The Xingshuping Au deposit is one of the deposits located in the inner-contact zone.

Deposit Geology and Samples
The Xingshuping deposit is located ~15 km east of Xiaguan town in Southern Henan Province, north of the ZXF. The deposit is still in the exploration stage, and its reserves and grade are unknown. Within the ore district, Au mineralization is closely related to magmatism, and the auriferous quartz veins are hosted mainly in medium fine grain biotite granite, as well as in the contact zone between the biotite granite and quartz-micaceous schist of the Yanlinggou formation, Qinling group. The ore-forming age, origin, genesis, evolution of the magmatic activity and the relationship between the magma and fluids are also unknown.
The stratigraphic sequence in the district mainly comprised the Xiaozhai formation of the lower Paleozoic Erlangping group in the north, Yanlinggou formation of the Paleoproterozoic Qinling group in the central to south and upper Cretaceous Gaogou formation in the south ( Figure 2). The Xiaozhai Formation consists of fine-grained metaclastic rocks, quartz-micaceous schist, quartz-biotite schist and phyllosilicate plagioclase schist, with flysch protoliths and interbed marbles [35]. The Yanlinggou formation consists mainly of biotite plagioclase gneiss, dolomitic marble and biotite-quartz schist, with metamorphic overprint greenschist facies [36]. The deposit is controlled strictly by the secondary faults of the NNW-trending ZXF. The exposed magmatic rocks in the mining area include biotite granite and monzonitic granite. The biotite granites are widespread, and monzonitic granites occur more in the drilling cores. Following detailed field investigations and sample collection, we selected representative biotite granite and monzonitic granite samples from field outcrop and drilled holes for detailed studies, respectively. The biotite granite is yellow/grey and composed of K-feldspar, quartz, biotite and plagioclase ( Figure 3) and accessory apatite, zircon, sphene, magnetite and allanite. The biotite monzonitic granite consists of K-feldspar, plagioclase, quartz, biotite, hornblende and a small quantity of accessory apatite, zircon and sphene. The Au orebodies, predominantly the auriferous quartz vein, are hosted in the fractures of the biotite granite intrusion or in the contact area between the biotite granite and the quartz-micaceous schist of the Yanlinggou formation. The ore-bearing wall rocks are mainly dolomitic marble that underwent silicification with pyrite and chlorite.

Whole Rock Major and Trace Element Analyses
Major and trace element analyses of the rocks at Xingshuping were conducted by ALS Chemex (Guangzhou) Co. Ltd. Approximately ~0.9 g of sample was added to ~9.0 g lithium borate flux (50-50% Li2B4O7-LiBO2), mixed well and fused in an autofluxer between 1050 °C and 1100 °C. A flat glass disk was prepared from the resulting melt. This disk was then analyzed by X-ray fluorescence spectrometry (XRF) for major elements, with an analytical precision better than ±1-2%. For trace elements, 0.2 g of sample was added to lithium metaborate flux (~0.9 g), mixed well and fused in a furnace at 1000 °C. The resulting melt was then cooled and dissolved in 100 mL of 4% nitric acid. This solution was analyzed by inductively coupled plasma mass spectrometry (ICP-MS) for trace elements with analytical precision better than ±5% for most trace elements. Two standards (plagioclase amphibolite GSR-15 and granitic gneiss GSR-14) were simultaneously analyzed in order to monitor analytical quality. A loss-on-ignition (LOI) measurement was undertaken on samples of dried rock powder by heating in a preignition silica crucible to 1000 °C for 1 h and recording the percentage weight loss [37]. The major and trace element compositions are reported in Table 1.

Whole Rock Sr-Nd Isotope Analyses
Whole rock Sr and Nd isotopic compositions were measured on a Triton thermal ionization mass spectrometer (TIMS) and Neptune Plus Multi-Collector (MC)-ICP-MS, respectively, at the State Key Laboratory of Geological Processes and Mineral Resources (GPMR), China University of Geosciences (CUG), Wuhan. The sample powders were digested in Teflon bombs with mixed agents of double distilled HNO3 and HF acids at 190 °C for 48 h. Subsequently, the samples were completely dissolved in 1 mL of 2.5 M HCl solution. Procedural Sr and Nd blanks were <4 ng and <1 ng, respectively [38].

LA-ICP-MS Zircon U-Pb Dating and Lu-Hf Isotope Analyses
Zircon grains for LA-ICP-MS U-Pb dating were separated using conventional heavy liquid and magnetic separation methods. Representative zircon grains were hand picked under a binocular microscope, mounted on an epoxy resin disk and polished down to nearly half the section to expose their internal structures for LA-ICP-MS analysis. Zircons were documented with transmitted and reflected light micrographs as well as with cathodeluminescence (CL) images to reveal their internal structures, and the mount was vacuum coated with high-purity gold. CL images were then taken with the scanning electron microscope at the State Key Laboratory of Geological Processes and Mineral Resources (GPMR), China University of Geosciences (CUG), Wuhan.
Zircon U-Pb dating was performed by using the laser ablation (LA) inductively coupled plasma mass spectrometry (ICPMS) at GPRM, CUG. A pulse Geolas of 193 nm ArF Excimer laser with 50 mJ/pulse energy at a repetition ratio of 10Hz coupled to an Agilent 7500a quadrupole ICP-MS was used for ablation. The sizes of laser spot were 32 μm in diameter. The detailed analytical procedures used followed those described by Liu et al. [39]. Harvard zircon 91500 was used as an external standard to normalize isotopic fractionation during analysis. Zircon standard GJ-1 was analyzed as a controlled standard for four times each sample. Lead isotopic data, U-Pb ages and trace element contents were processed using the ICPMSDataCal software [40]. The external errors of the standard 91500 were propagated to the ultimate results of each analytical spot [39]. Uncertainties on individual analysis are reported at 1σ level, and the weighted mean ages for pooled U/Pb analyses are quoted at 95% confidence interval [41]. The U-Pb re-sults were conducted with the ISOPLOT program of Ludwig [42]. The results are shown in Table 3.
Trace-element analysis was performed on zircon using the same LA-ICPMS. Oxide production rate was tuned to <0.5% ThO/Th. The NIST610 glass was used as an external standard to calculate the trace element concentrations of unknowns, with working values recommended by Pearce [43]. Mineral inclusions were monitored by 29 Si and 49 Ti signatures during analysis. A detailed compilation of instrument and data acquisition parameters was given by Liu [39]. The formation temperatures of zircons were calculated by using the Ti-in-zircon thermometer [44,45]. Quartz is present in all the studied samples. Thus, the activity of SiO2 is considered as one for all samples. Due to the absence of rutile in all the samples, but the existence of ilmenite, the activity of TiO2 was set to be 0.7, as suggested by Watson [45]. Zircon Lu-Hf isotope compositions for the samples were determined using a Neptune plus multi-collector (MC)-ICPMS system, in combination with a Geolas 2005 system at the GPMR, CUG. Zircons were ablated by a 193 nm excimer ArF laser-ablation systems with spot size of 44 μm and a laser repetition rate of 10 Hz at 100 mJ/pulse. Measurements of Lu-Hf isotopic compositions were made on the same spot or domain formerly analyzed for U-Pb isotopes. Offline selection and integration of analytical signals and mass bias calibrations were performed by using ICPMSDataCal [37]. During the Hf isotopic analysis, raw count rates for 172 Yb, 173 Yb, 175 Lu, 176 (Hf + Yb + Lu), 177 Hf, 178 Hf, 179 Hf, 180 Hf and 182 W were collected, and isobaric interference corrections for 176 Lu and 176 Yb on 176 Hf were determined precisely. Zircon standards 91500 and GJ-1 were used as references during analysis. 176 Lu/ 177 Hf and 176 Hf/ 177 Hf ratios of 0.0336 and 0.282785 for the chondritic uniform reservoir (CHUR) and a decay constant of 1.867 × 10 −11 /year for 176 Lu [46] were adopted for calculating the εHf(t) values. Two-stage Hf model ages (TDM2) are calculated by assuming a mean 176 Lu/ 177 Hf value of 0.015 for the average continental crust [47]. We adopted TDM2 for all samples, for they were not directly derived from the Depleted Mantle. The notations of εHf(t), ƒLu/Hf, TDM1 and TDM2 are defined as in Wu [48]. Figure 4 shows the CL images of representative zircon grains from biotite granite (XSP17-12 sample), along with 206 Pb/ 238 U ages and εHf(t) values. Figure 5 shows the zircon U-Pb concordia diagrams and the zircon chondrite-normalized Rare Earth Elements (REE).  The zircon grains from sample XSP17-12 are euhedral to subhedral, transparent and pale yellow to dark grey in color. Their lengths range from 40 to 150 μm with ratios of 1:1-4:1. They exhibited clear core structure and dark oscillatory zoned rims in CL and BSE images (Figure 4), suggesting magmatic crystallization.

Zircon U-Pb Ages
Nineteen spot analyses were performed on 19 zircon grains from sample XSP17-12. They yielded a weighted mean 206 Pb/ 238 U age of 445.46 ± 0.96 Ma (MSWD = 0.59) ( Figure  5A). One of them has a low Th/U ratio of 0.09 (<0.1), others have Th/U ratios of 0.16 to 1.05, which also suggests that these zircons have a magmatic origin [50].

Zircon Lu-Hf Isotopic Compositions
Zircon grains from samples XSP17-12 were analyzed for Lu-Hf isotopes on the same dated spots or morphologically similar domains; the results are listed in Table 5. The initial 176 Hf/ 177 Hf ratios denoted by εHf(t) values and Hf model ages for the zircons were by calculated using the U-Pb crystallization ages (t = 446.2 Ma). Histograms of the εHf(t) values for these samples are shown in Figure 6. Ten zircon grains from sample XSP17-12 display initial 176 Hf/ 177 Hf ratios varying from 0.282356 to 0.282481. Their corresponding εHf (t) values vary within a narrow range from −5.2 to −0.7, with a weighted mean of −3.7 ( Figure 6A). Correspondingly, their single-stage Hf model ages vary from 1.09 to 1.26 Ga, and their two-stage Hf model ages (TDM2) are 1.34-1.59 Ga (mean 1.51 Ga) ( Figure 6B, Table 5).

Whole-Rock Major and Trace Elements
The six biotite granite samples plotted in the granite field, two monzonitic granite samples are plotted in syenite and quartz monzonite granite field, respectively, in the SiO2 vs. Na2O + K2O (TAS) diagram ( Figure 7A). Previously available data with respect to the Wuduoshan pluton are also shown in Figure 7 for comparison.  [57]). Literature data are from [13,29,30,32,33]).

Whole-Rock Sr-Nd Isotopes
Initial Sr isotope ratios and εNd (t) values are calculated at t = 446 Ma. The five biotite granite samples exhibit low initial Sr isotopic ratios of 0.701201 to 0.709437 and negative εNd (t) values of −7.12 to −4.31, two monzonitic granite samples show similar initial Sr isotopic ratios of 0.707542 to 0.708316 and negative εNd (t) values of −11.17 to −12.92, ( Table 5). The biotite granites have two-stage Nd model ages (TMD2) vary between 1.37 Ga and 1.56 Ga, which are comparable with previous studies on the Wuduoshan biotite granites [13], and they are younger than the Paleoproterozoic to Mesoproterozoic basement material in NQ as well as the Mesoproterozoic to Neoproterozoic supracrustal units of the Qinling Group [60]. On the other hand, the monzonitic granites have older TMD2 varying between 1.84Ga and 1.96 Ga, which are comparable with those of gneissic rocks from the NQ unit (TMD2 = 1.90 to 2.07 Ga [61]). These Sr-Nd isotopic compositions of the biotite granites and monzonitic granites plot around or along the extension of the mantle array. The ranges of different rocks from the NQ are shown for comparation [60].

Age of the Intrusion
Previous studies have reported the intrusion ages of different positions of the Wuduoshan pluton ( Figure 1B). The older group of ages are quartz diorite (468.5 ± 4.1 Ma) from the southern part of Wuduoshan and porphyritoid biotite granite (464.1 ± 4.6) from Sikeshu [31] in the northeast, represent the early stage intrusion age of the pluton. The middle group of ages are widespread in the pluton and concentrate mainly from 452 Ma to 428.3 ± 2.1 Ma [13,28,31,32,34]; biotite granite and biotite monzonitic granites are the major rock types [28,32]. The younger group of ages are 414.5 ± 2.3Ma [33], and they are biotite monzonitic granite from the south part of the pluton [33]. This is consistent with the viewpoint that has been pointed out by Wang [23] about the division of emplacement stages of Paleozoic granites in the NQ: 507-470 Ma, 460-422 Ma and ~415-400 Ma.
The age of granites in Xingshuping deposit has not been studied before. The zircon grains extracted from the biotite granite samples show morphological and geochemical features of a magmatic origin [62]. LA-ICP-MS U-Pb zircon ages suggest the 206 Pb/ 238 U age of 445.46 ± 0.96 Ma represent the emplacement timing of biotite granites.

Petrological Classification and Magmatic Evolution
The biotite granite samples from the Xingshuping deposit have high SiO2 = 70.65-80.72 wt% and are typical of high-K calc-alkaline to shoshonitic series on the basis of its slightly peraluminous nature, which is similar but not identical to available granite data from other part of the Wuduoshan pluton. Abundant K-feldspar, plagioclase, quartz and biotite occur in biotite granite rocks, in conjunction with decreasing Al2O3, MgO, TFe2O3, CaO, TiO2 and P2O5 with increasing SiO2 contents ( Figure 8) and depletion in HFSE (Nb, Ta, Zr, Hf, P and Ti), with obviously negative Eu anomalies. They have lower MgO content, which means mafic minerals have been separated during magmatic fractionation. Previous studies show that most granites of the Wuduoshan pluton have I-type to S-type characteristics with few of A-type ( Figure 7G), which were considered to be derived from the lower crust with involvement of mantle-derived magma in a collisional setting [23]. Whereas the biotite granites from Xingshuping have relatively high Ce + Nb + Zr + Y (>300 ppm) and low (K2O + Na2O)/CaO values, most are plotted in the typical A-type granites field ( Figure 7G) [57], different from the I-type to S-type granites proposed by predecessors. The high Zr + Ce + Y values and Rb/Ba ratios are also plotted in the A-type granites field in Figure 7H. In addition, in the Sr/Y vs. Y ( Figure 7E) [63] discrimination diagram, the biotite granites have high Y but lower Sr/Y ratios than the typical adakite rocks, but most of the previous data display strong similarities with adakite rocks for their low Y and high Sr/Y ratios, and few of them are plotted in the normal arc vocanic rocks. In the (La/Yb)N vs. (Yb)N ( Figure 7F) [56] diagram, the biotite granites and most of the previous data display strong similarities with typical adakite rocks for their low YbN and high (La/Yb)N ratios. Thus, biotite granites from Xingshuping have characteristics of adakite rocks but are mixed with other materials.
Extensive fractionation of plagioclase and/or K-feldspar would result in significant Eu negative anomalies. The negative Sr-Eu anomalies suggest fractionation of plagioclase, and Eu-Ba anomalies require fractionation of K-feldspar; thus, both plagioclase and K-feldspar were the fractionating phases ( Figure 9). Ti depletion is thought to be associated with fractionation of a Ti-bearing phase such as ilmenite and titanite. The P depletion likely resulted from apatite fractionation. Trends on the Rb vs. Sr plot ( Figure  10A) suggest garnet/amphibole, plagioclase and K-feldspar fractionation, without muscovite and biotite fractionation, whereas the predecessors mainly show plagioclase, K-feldspar, muscovite and biotite fractionation, and no garnet or amphibole fractionation occurred. As shown on the Ba vs. Sr diagram ( Figure 10B), garnet/amphibole, plagioclase and K-feldspar are the main fractionation phases, with few muscovite and bio-tite fractionation. Trends on the Dy/Yb vs. SiO2 diagram ( Figure 10C) suggest garnet and amphibole fractionation.  [13,29,30,32,33].
These geochemical characteristics suggest that biotite granites from Xingshuping are A-type granites [64,65], have some adakite rocks characteristics, and plagioclase, K-feldspar, garnet, amphibole and biotite, apatite and Fe-Ti oxides were the major fractionating phases.
Compared to the biotite granites, the monzonitic granites show lower SiO2, Na2O and MgO but higher K2O, TiO2, CaO, TFe2O3 and P2O5 contents and mainly consist of K-feldspar, plagioclase and quartz with a minor amount of biotite. The variable A/CNK values result in different falling plots of metaluminous and strong peraluminous granites ( Figure 7C). The low MgO content also suggests separation of mafic minerals. Al2O3, MgO, TFe2O3, CaO, TiO2 and P2O5 decrease with increasing SiO2 contents (Figure 8), and they also deplete in Ba, Nb, Ta, Zr, Hf, P and Ti, with obviously "V" type negative Eu anomalies, suggesting partial melting and/or fractional crystallization. Different from the A-type biotite granites, the monzonitic granites are plotted in fractionated granites to unfractionated I-type or S-type granite field in Figure 7G The significant "V" type negative anomalies in the REE diagram require extensive fractionation of plagioclase and K-feldspar ( Figure 9). The Ti and P depletions are likely the result of ilmenite, titanite and apatite fractionation, respectively. Trends on the Rb vs. Sr plot ( Figure 10A) and Ba vs. Sr diagram ( Figure 10B) suggest plagioclase and K-feldspar fractionation and minor muscovite and biotite fractionation but no garnet/amphibole fractionation. As shown on the Dy/Yb vs. SiO2 diagram ( Figure 10C), further proof of no garnet or amphibole fractionation is displayed.
In conjunction with previous studies on the Wuduoshan pluton, both the biotite granites and monzonitic granites exhibit a positive correlation between La and La/Sm ( Figure 11A), suggesting that partial melting or source characteristics were major controlling factors. A positive relationship between Tb/Yb versus Yb ( Figure 11B) and La/Yb versus Yb ( Figure 11C), both suggesting partial melting, was a major controlling factor for the biotite granites. On the other hand, the relationships between Tb/Yb versus Yb ( Figure 11B) and La/Yb versus Yb ( Figure 11C) suggest that fractional crystallization was the controlling factor for the monzonitic granites with minor or no partial melting. In summary, the geochemical and isotopic variations of the intrusions at Xingshuping were controlled by partial melting for the biotite granites and fractional crystallization for the monzonitic granites, respectively.  [13,29,30,32,33].

Source Nature
The geochemical characteristics of the rocks from both of the biotite granites and monzonitic granites are characterized by low MgO; depleted Ti and Sr; low Mg# ratios (13.6-29.6 and 27.8-28.4)l; low Cr (9-18 ppm and 5-19 ppm) and Ni (0.4-2.8 ppm and 0.2-0.7 ppm) values; and high LREE and LILE with negative whole-rock εNd (t), sug-gesting a source enriched in LREE and LILE much closer to a lower continental crust (Mg# ratios 10-40, Cr 5-33 ppm and Ni 3-39 ppm).
The Nd and Hf isotope data are thought to be robust tracers of parental reservoirs of granites [66]. The Xingshuping biotite granite and monzonitic granite rocks have narrow ranges of initial 87 Sr/ 86 Sr ratios (0.701201-0.709437 and 0.707542-0.708316) and εNd (t) values (−7.12 to −4.31 and −11.17 to −12.92), with different old TMD2 age of 1.37-1.56 Ga and 1.84-1.96 Ga, which were plotted around or along the extension of the mantle array in ( 87 Sr/ 86 Sr)i vs. εNd (t) diagram ( Figure 12). Biotite granite zircon Hf isotopic compositions also have a narrow range of εHf (t) values (−5.2 to −0.7). Moyen [67] has documented that rocks generated from melting of the lower continental crust with garnet residue may have signatures similar to adakitic trace elements. However, their Sr-Nd isotopic compositions are significantly different from those of lower continental crust (LCC) and upper continental crust (UCC) [64] and Neoproterozoic gneisses and amphibolites of the Qinling Group, even though the biotite granites have some adakitic trace element characteristics and older TMD2 ages than their crystallization ages. Thus, the granites from Xingshuping do not simply form by an exclusive lower-crustal source; mantle-derived melts played an important role in the formation. The lower εNd (t) values and older TMD2 age of monzonitic granites suggest more continental crust and less mantle-derived materials in the formation.  [13]. Fields for the upper continental crust (UCC) and lower continental crust (LCC) are from Jahn et al. [64], and the mantle array is from Depaolo and Wasserburg [68]. Whole-rock Sr-Nd isotopic compositions of the Neoproterozoic Qinling Group and Fushui mafic complex are from Liu et al. [65] and references therein and Wang et al. [12], respectively. ( 87 Sr/ 86 Sr)i and εNd(t) values are based on t = 446.2 Ma.
The εHf(t) and 176 Hf/ 177 Hf values all fall around the line of the lower crust [69] (Figure 13A,B), indicating that the magma of the biotite granites was derived from either the partial melting of the ancient enrichment lithospheric mantle materials or depleted mantle-derived melts that mixed significantly with mature continental crustal materials [70]. However, the Hf isotope crustal model ages of TDM2 (1.34-1.59 Ga) agree with the εNd (t) TMD2 of 1.37-1. 56 Ga and indicate further that the granite may have resulted from the partial melting of Late Paleoproterozoic to Early Mesoproterozoic crustal materials, with contributions from mantle-derived magmas [71]. Partial melting of different source rocks such as amphibolite, metagreywacke and metapelite will produce various magma compositions under variable melting conditions [73,74]. The biotite granites and monzonitic granites from Xingshuping exhibit relatively high Rb/Ba (0.46-10.5) and Rb/Sr (1. 83-7.18) and are dominantly plotted in the clay-rich sources field, which are different from previous studies that show they are mainly from a clay-poor source Figure 14A. Combined with their relatively high CaO/Na2O (generally >0.3) (Figure 14B), we can conclude their derivation from clay-rich and plagioclase-rich psammitic sources. In summary, the granites from Xingshuping may have resulted from partial melting (minor fractional crystallization) of a clay-rich and plagioclase-rich psammitic lower continental crust source, with contributions from mantle-derived magmas at a relatively low temperature (~714.2 °C).

Tectonic Setting and Geodynamic Mechanisms
The granites at Xingshuping and most previous granite data from the Wuduoshan pluton are mainly plotted in the common area between the compression and extension field ( Figure 15A), but the trends suggest that, with the evolution of magma, the crust gradually transited from compression to extension. In the R1 versus R2 tectonic discrimination diagram ( Figure 15B), the samples mainly fall within the fields of syn-collision, minor samples plot in anorogenic to post orogenic domains. The biotite granites and most literature data are mainly plotted in the syn-collision granites (Syn-COLG) and volcanic arc granite (VAG) domains and minorly plotted in the within plate granite (WPG) domain, whereas the monzonitic granites mainly fall in the WPG domain on tectonic discrimination diagrams ( Figure 15C-E). This is consistent with magma that originated from partial melting of continental crust in an extensional setting [76]. Moreover, the trends exhibited from VAG to Syn-COLG and then to WPG domains are consistent with the trend of increasing extension. In the Nb-Y-Ce diagram [77] (Figure 15F), all the samples have a trend plot from the post-orogenic A-type granite (A2) domain to the anorogenic A-type granite (A1) domain. To summarize, the biotite granites from Xingshuping were mainly formed in a Syn-COLG extension setting, whereas the monzonitic granites mainly formed in an intraplate transformed from compression to extension setting. The geochemical and isotopic differences between the two kind granites at Xingshuping were likely caused not only by the variable composition of the mixed source and evolution processes but also by the transformation tectonic environment.  [78]); (B) R1 vs. R2 (after [79]); (C) Nb vs. Y (after [80]) and (D) Ta vs. Yb (after [80]). (E) Rb vs. (Y + Nb) (after [81]) and (F) Nb-Y-Ce (after [77]) diagram of the granite rocks from Xingshuping. 1: Mantle fractionates; 2: pre-plate collision; 3: post-collision up lift; 4: late orogenic; 5: anorogenic; 6: syn-collision; 7: post-orogenic; WPG: within plate granites; VAG: volcanic arc granites; ORG: ocean ridge granites; Syn-COLG: syn-collision; A1: anorogenic A-type granite; A2: post-orogenic A-type granite. Literature data are from [13,28,29,32,33].
The ongoing subduction of the Prototethyan Shangdan oceanic crust resulted in the formation of arc magmatism events in Late Ordovician to Early Silurian at ca. 450-420 [82][83][84]. As the oceanic slab continuously subducted, slab steepening and rollback occurred in response to progressive eclogitization at the tip of the slab, subsequently giving rise to corner flow within the asthenosphere, upper-plate transited from compression to extension and incipient back-arc rifting [85,86]. The slab rollback of the Prototethyan oceanic crust would result in asthenosphere mantle upwelling accompanied by partial melting of the mantle wedge in an extension setting and production of adakite magmas with high LILEs, LREE and mantle-like isotope signatures [82][83][84].

Conclusions
Geochronological, geochemical and isotopic investigations from the Xingshuping deposit in the Erlangping unit result in the following conclusions: 1. LA-ICP-MS zircon U-Pb dating indicates that the biotite granite was formed at ca.

The petrographic and geochemical data indicate that biotite granites from
Xingshuping are A-type granites and exhibit adakite rock affinities; the monzonitic granites are fractioned arc volcanic rocks. 3. The biotite granites are formed by partial melting of a clay-rich and plagioclase-rich psammitic lower continental crust source, with contributions of mantle-derived magmas, whereas the monzonitic granites share the same source with the biotite granites but are mainly formed by fractional crystallization. 4. The biotite granites were mainly formed in a Syn-COLG extension setting, whereas the monzonitic granites mainly formed in an intraplate transformed from compression to extension setting.