Petrogenesis and Tectonic Signiﬁcance of Early Permian Intermediate–Felsic Rocks in the Southern Beishan Orogen, Northwest China: Geochronological and Geochemical Constraints

: Permian intermediate–felsic igneous rocks, widely distributed in the southern Beishan orogen, provide crucial constraints on the geodynamic process of the late Paleozoic Paleo-Asian Ocean. New zircon U–Pb dating using LA–ICP–MS determines the age of the northern Qingshan diorites, the Heishantou quartz diorites, and the southern Qingshan biotite granodiorites at 300 Ma, 294 Ma, and 291–286 Ma, respectively. Their whole-rock compositions exhibit arc-like geochemical features. Moreover, their zircon trace elements show the characteristics of continental arc zircons. The diorites, characterized by low SiO 2 , high MgO with Mg# (50–52), and low Cr, Co, and Ni, display enrichment in Sr-Nd-Hf isotopes ( 87 Sr/ 86 Sr = 0.7060 to 0.7061; E Nd (t) = − 1.4 to − 1.7; E Hf (t) = − 4.7 to − 0.6), originating from the fractionation process of magma derived from the enriched mantle. The quartz diorites show moderate SiO 2 and variable MgO (2.75–3.84 wt%) and exhibit enrichment in Sr-Nd ( 87 Sr/ 86 Sr = 0.7048–0.7050; E Nd (t) = − 1.5–+0.9) and depletion in zircon Hf isotopes ( E Hf (t) = 3.8 to 7.8). Combined with their high Y (20.0–21.0 ppm) and low (La/Yb) N (6.0 to 17.2), we conclude that they originated from the juvenile lower crust previously inﬂuenced by oceanic sediments, with the input of enriched mantle-derived materials. The biotite granodiorites display low A/CNK (0.91–0.97), 10000*Ga/Al (1.8–1.9), and Ti-in-zircon temperatures (average 711 ◦ C), indicating that they are I-type granitoids. These rocks show enrichment in Sr-Nd isotopes ( 87 Sr/ 86 Sr = 0.7054 to 0.7061; E Nd (t) = − 2.0 to − 1.6) and many variable zircon Hf isotopes ( E Hf (t) = − 2.3 to +4.5). Geochemical studies indicate that they originate from the mixing of magmas derived from the enriched mantle and preexisting juvenile lower crust. All these data imply the existence of oceanic subduction in southern Beishan during the early Permian. Integrating these results with previous studies, it is inferred that the retreating subduction of the Liuyuan Ocean contributed to early Permian intermediate–felsic rocks becoming widespread in the Shibanshan unit, the southernmost part of the Beishan orogen, and also why the Paleo-Asian Ocean in southern Beishan did not close during the early Permian.


Introduction
The Central Asian Orogenic Belt (CAOB), one of the largest accretionary orogenic belts in the world, is situated along the Siberian Craton and the North China and Tarim Cratons (Figure 1(1)).The CAOB formed through multi-stage accretionary-collisional processes of the Paleo-Asian Ocean (PAO) during the Neoproterozoic and Phanerozoic periods and consists primarily of microcontinental blocks, ophiolites, sea mountains, subductionaccretion complexes, magmatic arcs, and related basins [1][2][3].Recently, the Nd isotope mapping results of intermediate-felsic magmatic rocks in the CAOB revealed that the areal ods and consists primarily of microcontinental blocks, ophiolites, sea mountains, subduction-accretion complexes, magmatic arcs, and related basins [1][2][3].Recently, the Nd isotope mapping results of intermediate-felsic magmatic rocks in the CAOB revealed that the areal proportion of the juvenile crust is approximately 58% [4], supporting substantial continental growth within the CAOB.Moreover, the CAOB hosts a diverse range of world-class ore deposits, including porphyry Cu-(Au)-(Mo) deposits and numerous other polymetallic magmatic-hydrothermal deposits, showing significant mineral resource potential.The comprehension of the subduction-accretion history of the PAO is crucial for revealing the continental growth mechanisms and metallogenic significance of the CAOB [5][6][7].
The Beishan orogen, linking the Southern Tian Shan suture and the Solonker suture, occupies a vital region of the central part of the southern CAOB (Figure 1(1)) [8].Moreover, it acts as a crucial junction point connecting the CAOB and Tethys orogenic belt (Figure 1(1)) [9,10].The Beishan orogen thus offers an ideal place for investigating the geodynamic interactions between these two orogenic belts.Regarding the geodynamic evolution of this orogen during the Paleozoic, many works have focused on intrusive rocks, volcanic-sedimentary rocks, and structural geology, and much progress has been achieved [11][12][13][14][15][16].For instance, several ophiolitic mélanges and regional faults have been recognized in the Beishan region (Figure 1(2)) [8].They likely represent the different branches of the PAO and segment the Beishan orogen into different tectonic units (Figure 1(2)) [11,12].It is generally accepted that the early Paleozoic magmatism, which is widespread in the different units of the Beishan orogen, forms in an arc-related setting [12,14].However, the late Paleozoic geodynamic process and the timing of the termination of the Beishan orogen are controversial.In particular, the Permian tectonic setting in this orogen (1) Simplified tectonic map showing the CAOB, Tethysides, and Tarim and North China Cratons (modified after [1]); (2) Tectonic map of the Beishan orogen (modified after [8]).
The Beishan orogen, linking the Southern Tian Shan suture and the Solonker suture, occupies a vital region of the central part of the southern CAOB (Figure 1(1)) [8].Moreover, it acts as a crucial junction point connecting the CAOB and Tethys orogenic belt (Figure 1(1)) [9,10].The Beishan orogen thus offers an ideal place for investigating the geodynamic interactions between these two orogenic belts.Regarding the geodynamic evolution of this orogen during the Paleozoic, many works have focused on intrusive rocks, volcanic-sedimentary rocks, and structural geology, and much progress has been achieved [11][12][13][14][15][16].For instance, several ophiolitic mélanges and regional faults have been recognized in the Beishan region (Figure 1(2)) [8].They likely represent the different branches of the PAO and segment the Beishan orogen into different tectonic units (Figure 1(2)) [11,12].It is generally accepted that the early Paleozoic magmatism, which is widespread in the different units of the Beishan orogen, forms in an arc-related setting [12,14].However, the late Paleozoic geodynamic process and the timing of the termination of the Beishan orogen are controversial.In particular, the Permian tectonic setting in this orogen remains under debate.Different tectonic models, including a subduction-related arc setting [16,17], a mantle plume-related setting [18], and a post-collisional extensional setting [19,20], have been suggested.These controversies hamper our understanding of the evolutionary history of the PAO and the accretionary-collisional processes of the Beishan orogen.Permian magmatism, which is widely distributed in southern Beishan, offers a promising means to Minerals 2024, 14, 114 3 of 23 resolve the above disputes.Variations in magmatic compositions can be formed either in an ideal closed magmatic system through the partial melting and fractionation processes of different source materials under various conditions [21,22] or in an open magmatic system through the mixing process between different magmas and the wall-rock assimilationfractional crystallization process (AFC) [23,24].Other magmatic processes, such as liquid immiscibility and vapor-phase leaching [25,26], are also proposed to explain magmatic compositional changes.However, no evidence suggests that they perform a crucial role in producing chemical variations in igneous rocks [27].The compositional changes in natural igneous rocks can be influenced by multiple magmatic processes, with some being dominant while others are secondary [27,28].Generally, rock associations and geochemical compositions of magmatic rocks reflect the characteristics of their magma sources and formation conditions [29,30], thus offering insights into geodynamic settings.
This study presents new LA-ICP-MS zircon U-Pb dating and trace elements, wholerock geochemical data, and Sr-Nd-Hf isotopes for early Permian intermediate-felsic igneous rocks from southern Beishan (Figures 1(2) and 2).Combined with previous regional studies, our new data constrain the petrogenesis of these igneous rocks and provide a strong basis for understanding the early Permian geodynamic evolution in southern Beishan.
remains under debate.Different tectonic models, including a subduction-related arc setting [16,17], a mantle plume-related setting [18], and a post-collisional extensional setting [19,20], have been suggested.These controversies hamper our understanding of the evolutionary history of the PAO and the accretionary-collisional processes of the Beishan orogen.Permian magmatism, which is widely distributed in southern Beishan, offers a promising means to resolve the above disputes.Variations in magmatic compositions can be formed either in an ideal closed magmatic system through the partial melting and fractionation processes of different source materials under various conditions [21,22] or in an open magmatic system through the mixing process between different magmas and the wall-rock assimilation-fractional crystallization process (AFC) [23,24].Other magmatic processes, such as liquid immiscibility and vapor-phase leaching [25,26], are also proposed to explain magmatic compositional changes.However, no evidence suggests that they perform a crucial role in producing chemical variations in igneous rocks [27].The compositional changes in natural igneous rocks can be influenced by multiple magmatic processes, with some being dominant while others are secondary [27,28].Generally, rock associations and geochemical compositions of magmatic rocks reflect the characteristics of their magma sources and formation conditions [29,30], thus offering insights into geodynamic settings.
This study presents new LA-ICP-MS zircon U-Pb dating and trace elements, wholerock geochemical data, and Sr-Nd-Hf isotopes for early Permian intermediate-felsic igneous rocks from southern Beishan (Figures 1(2) and 2).Combined with previous regional studies, our new data constrain the petrogenesis of these igneous rocks and provide a strong basis for understanding the early Permian geodynamic evolution in southern Beishan.S1.The inserted histogram shows the compiled zircon U-Pb ages in the study area.Only 51 of the total 62 age data are included.

Geological Background
The Beishan orogen extends across the Xinjiang-Gansu Inner Mongolia region, connecting the Dunhuang block and the Alxa block (Figure 1(1)).It is divided into five tectonic units by four east-west-oriented ophiolitic mélange belts (Figure 1(2)) [8].The Shibanshan unit, the southernmost tectonic unit, is situated to the south of the Liuyuan mélange belt and to the north of the Dunhuang block (Figure 1(2)).The Liuyuan mélange belt intermittently stretches for about 300 km along both sides of the Liuyuan-Daqishan-Zhangfangshan fault and is mainly exposed in the regions of Huitongshan, Liuyuan, and Zhangfangshan (Figure 1(2)) [31,32].Notably, the Liuyuan complex has been extensively studied [17,33,34].Zircon U-Pb dating results for the Liuyuan ophiolitic mélange belt span from 504 to 270 Ma [33][34][35].Moreover, geochemical analyses indicate that the basalts and gabbros from this ophiolitic mélange belt exhibit signatures typical of mid-ocean ridge  S1.The inserted histogram shows the compiled zircon U-Pb ages in the study area.Only 51 of the total 62 age data are included.
The Shibanshan unit is predominantly composed of the Beishan complex, upper Paleozoic, and Paleozoic intermediate-felsic intrusive rocks (Figure 2) [8].The Beishan complex mainly consists of felsic gneiss, biotite-plagioclase gneiss, and metamorphic sedimentary rocks [36].The origins and tectonic implications of the Beishan complex remain controversial.Some propose that the Beishan complex developed in an arc setting during the Paleozoic [36].However, other studies argue that it represents the Precambrian microcontinent in southern Beishan [37,38].The strata of the Carboniferous-Permian are widely distributed (Figure 2).The Carboniferous strata primarily consist of clastic rocks, slates, phyllites, limestones, and intermediate-felsic volcanic rocks.The Permian strata are mainly composed of clastic sedimentary rocks, pyroclastic rocks, and mafic-intermediate and felsic volcanic rocks [8,20].Paleozoic magmatism, dominantly intermediate-felsic intrusive rock, is widespread in the Shibanshan unit, mainly as Carboniferous-Permian granitoids and minor diorites (Figure 2 and Table S1).These rocks show different mineral assemblages and geochemical and Sr-Nd-Hf isotope compositions, which likely record the history of the geodynamic evolution in southern Beishan during the Paleozoic [12,16].

Description of Samples
In this study, we investigated three intermediate-felsic intrusive plutons, including the Heishankou, southern Qingshan, and northern Qingshan plutons (Figure 2), in the Shibanshan unit.The northern Qingshan pluton is composed of early granitoids and later intruding diorites (Figure 3(1)).The early granitoids, covering an area of about 150 km 2 , intrude into the Precambrian strata (Figure 2).The diorites, forming as a stock, show an exposed area of approximately 6 km 2 (Figure 2).The diorites sampled in this study are dark gray and medium-grained (Figure 3(1)), primarily consisting of plagioclases (50 vol%), quartzes (5-10 vol%), amphiboles (35-40 vol%), and biotites (~5 vol%).Euhedral to subhedral plagioclases present a zoning texture and polysynthetic twinning (Figure 3(4)).Their interiors generally show a slight alteration, appearing blurred compared to their edges (Figure 3(4)).Dark green amphiboles are anhedral, whereas biotites are subhedral to euhedral.Quartzes are anhedral as interstitial crystals (Figure 3(4)).Furthermore, the presence of amphiboles with residual pyroxene (Figure 3(4)) implies that the preexisting pyroxene reacted with the surrounding magma [39].Three rock samples were collected from the diorite pluton.All were determined for whole-rock major and trace element contents; one sample was selected for the analyses of zircon U-Pb dating and Lu-Hf isotopes, and two rocks were used for the whole-rock Sr-Nd isotope measurement.The Heishankou pluton extends nearly east-west for approximately 90 km and covers an area of approximately 350 km 2 (Figure 2).Here, we focused on the eastern section of this pluton, which consists mainly of the quartz diorites sampled in this study and minor granodiorites with less mafic minerals (amphibole and biotite).The quartz diorites are light gray and medium-grained (Figure 3(2)) and are mainly composed of plagioclases (~60 vol%), quartzes (15 vol%), amphiboles (10-15 vol%), biotites (10 vol%), as well as minor K-feldspars (~1 vol%) (Figure 3(5)).Plagioclases are euhedral to subhedral, generally displaying polysynthetic twinning, with some Carlsbad-albite twins observed (Fig- The Heishankou pluton extends nearly east-west for approximately 90 km and covers an area of approximately 350 km 2 (Figure 2).Here, we focused on the eastern section of this pluton, which consists mainly of the quartz diorites sampled in this study and minor granodiorites with less mafic minerals (amphibole and biotite).The quartz diorites are light gray and medium-grained (Figure 3(2)) and are mainly composed of plagioclases (~60 vol%), quartzes (15 vol%), amphiboles (10-15 vol%), biotites (10 vol%), as well as minor K-feldspars (~1 vol%) (Figure 3(5)).Plagioclases are euhedral to subhedral, generally displaying polysynthetic twinning, with some Carlsbad-albite twins observed (Figure 3(5)).Greenish-brown amphiboles are subhedral to anhedral, while biotites appear subhedral as interstitial minerals (Figure 3(5)).Four rocks were collected from the quartz diorite pluton.All rock samples were measured for whole-rock major and trace element compositions, with one rock chosen for the measurement of zircon U-Pb dating and Lu-Hf isotopes and two rocks selected for the determination of whole-rock Sr-Nd isotopes.

Zircon U-Pb and Lu-Hf Isotopic Analyses
Conventional heavy liquid and magnetic techniques were employed to extract zircons.Subsequently, these grains were mounted in epoxy resin and polished to roughly half-thickness at the Shougang Geological Exploration Institute, China.Grains showing euhedral to subhedral shapes, distinct zoning textures, and no fractures and inclusions under cathodoluminescence (CL), transmission, and reflection images were selected as potential zircon specimens for U-Pb dating and Lu-Hf isotopes.
Zircon U-Pb dating was performed using laser ablation (LA)-ICP-MS in the Mineral and Fluid Inclusion Microanalysis lab, Institute of Geology, Chinese Academy of Geological Sciences, Beijing, China.Zircon 91500 and SA01 were analyzed twice and once, respectively, for every 12 sample points analyzed.Detailed analytical methods are described in [40,41].The Iolite software (ver.3.7) was used for the reduction in analyzed data [42].The exponential function was used to calibrate the downhole fractionation [42].No corrections for common lead were implemented, and the reported errors in Table S2 represent 2 sigma values.NIST610 and 91Zr served as external and internal standards for calibrating the zircon trace element contents, respectively.Concordia diagrams and weighted mean calculations of U-Pb age were constructed using Isoplot (ver.3.0) [43].
The determination of in situ zircon Lu-Hf isotopes was completed using a Resolution S155 laser ablation microprobe attached to a Neptune multicollector ICP-MS (LA-MC-ICP-MS) at the MNR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing.The instrumental conditions and data collection were thoroughly described by [44,45].The reference standard during our measurement was zircon GJ-1.Analytical data were processed offline (including sample and blank signal selection and mass bias calibrations) using the software ICPMSDataCal (ver.11.4).The E Hf (t) values and Hf model ages (T DM Hf) were calculated using the 176 Lu-177 Hf decay constant of 1.867 × 10-11 yr −1 [46], chondrite ratios of 176 Hf/ 177 Hf = 0.282772 and 176 Lu/ 177 Hf = 0.0332 [47], and DM parameters of 176 Hf/ 177 Hf = 0.28325 and 176 Lu/ 177 Hf = 0.0384 [48].

Whole-Rock Major and Trace Elements
The measurement of whole-rock major and trace elements was carried out at the Wuhan SampleSolution Analytical Technology Co., Ltd., Wuhan, China.The sample pretreatment for the analysis of whole-rock major elements was made using the melting method.The flux is a mixture of Li 2 B 4 O 7 , LiBO 2 , and LiF (45:10:5).NH 4 NO 3 and LiBr were employed as oxidant and release agents, respectively.The melting temperature was 1050 • C, and the melting time was 15 min.Zsx Primus II wavelength dispersive X-ray fluorescence spectrometer (XRF) produced by RIGAKU, Japan, was adopted for the determination of whole-rock major elements.The relative standard deviation (RSD) was less than 2%.The measurement of whole-rock trace elements was performed on an Agilent 7700e ICP-MS, and the analytical precision was better than 10%.The standards BHVO-2, BCR-2, RGM-1, and JA-2 were used to monitor the data quality.Detailed sample preparation methods, as well as analytical precision and accuracy for the analysis of whole-rock trace elements, are described in [49].

Whole-Rock Sr-Nd Isotopic Analyses
Sr-Nd isotopes and Rb, Sr, Sm, and Nd concentrations for the Heishantou quartz diorites and southern Qingshan biotite granodiorites were completed at the Institute of Precambrian Geology and Geochronology, Russian Academy of Sciences.The Sr-Nd isotopes were analyzed using a Triton TI (Finnigan MAT, Bremen, Germany) multicollector solid-phase mass spectrometer in the static mode.The method of isotopic dilution was used to determine the concentrations of Rb, Sr, Sm, and Nd trace elements.Detailed processes are similar to those described in [50].The 87 Sr/ 86 Sr and 143 Nd/ 144 Nd ratios were normalized to 0.1194 and 0.7219, respectively.During data collection, repeated measurements of the NBS987 and JNdi-1 standard solutions provided average values for 87 Sr/ 86 Sr and 143 Nd/ 144 Nd, at 0.710262 ± 0.000005 (2σ, n = 6) and 0.512103 ± 0.000003 (2σ, n = 5), respectively.Sr-Nd isotope analyses for the northern Qingshan diorites were carried out at the University of Science and Technology of China, Hefei, China.The Sr-Nd isotopes were analyzed using a Finnigan MAT 262 mass spectrometer.The 87 Sr/ 86 Sr and 143 Nd/ 144 Nd ratios were normalized to 0.1194 and 0.7219, respectively.Detailed analysis processes were similar to those described in [51,52].During data collection, repeated measurements of the NBS987 and JNdi-1 standard solutions provided average values for 87 Sr/ 86 Sr and 143 Nd/ 144 Nd at 0.710245 ± 0.000012 (2σ, n = 3) and 0.512116 ± 0.000008 (2σ, n = 3), respectively.The values of ( 147 Sm/ 144 Nd) CHUR (0.1967), ( 143 Nd/ 144 Nd) CHUR (0.512638), ( 147 Sm/ 144 Nd) DM (0.2136), and ( 147 Nd/ 144 Nd) DM (0.513151) were employed to calculate all the E Nd (t) values and model ages in this study [53,54].

Zircon U-Pb Ages and Lu-Hf Isotope Compositions
Zircon U-Pb dating and Lu-Hf isotope results are shown in Supplementary Tables S2 and S3, respectively.Zircons from the four rock samples in the Shibanshan unit generally appear light to dark gray in the cathodoluminescence (CL) images (Figure 4).These zircon grains typically exhibit euhedral to subhedral and prismatic shapes, with lengths varying from ∼60 to 120 µm and widths from ∼30 to 70 µm.Zircons from the northern Qingshan diorite (G22924-11.1)display relatively high aspect ratios of 2:1 to 5:1, while those from the other three samples (G22917-2.1,G22919-5.1,and G22923-2.1)have low aspects ratios of 2:1 to 3:1 (Figure 4).All analyzed zircon spots exhibit clear rhythmic zoning in the CL images (Figure 4).With the exception of one zircon from the biotite granodiorite (G22923-2) that shows a high, flat rare earth element (REE) pattern indicative of chemical alteration [55], all analyzed zircons demonstrate steeply rising REE distribution patterns from La to Lu and exhibit positive Ce and negative Eu anomalies (Figure S1), suggesting their magmatic origins [55,56].Furthermore, in the (Sm/La) N vs. La and Th vs. U diagrams (Figure 5), they are plotted within the magmatic zircon field, providing additional evidence for their igneous origins [57,58].[55].The broader magmatic zircon fields (light gray shaded area) in (1,2) are from [58].Fourteen zircons from the northern Qingshan diorite (G22924-11.1)yielded 206 Pb/ 238 U ages of 310 to 291 Ma, with a weighted mean age of 300 ± 2 Ma (n = 14, MSWD = 1.2) (Figure 6(1)).Eleven zircons were chosen for the analysis of Lu-Hf isotopes.They exhibited E Hf (t) values ranging from −4.7 to −0.6 and relatively old two-stage Hf model aged (T DM2 Hf) between 1614 Ma and 1355 Ma.Eighteen zircons from the Heishantou quartz diorite (G22917-2.1)yielded 206 Pb/ 238 U ages ranging from 301 to 284 Ma, with a weighted mean age of 294 ± 2 Ma (n = 18, MSWD = 0.94) (Figure 6(2)).Fifteen dated zircon grains were selected for the determination of Lu-Hf isotopes.Their ℇHf(t) values varied from 3.8 to 7.8, with young TDM2Hf between 1059 and 813 Ma.

Whole-Rock Major and Trace Element Geochemistry
Whole-rock major and trace element compositions are shown in Supplementary Table S4.All analyzed rocks exhibited a low loss on ignition (LOI) content ranging from 0.58 Additionally, fourteen zircon grains were analyzed for Lu-Hf isotope compositions.Their E Hf (t) values varied from −0.9 to 2.9 with T DM2 Hf from 1364 to 1113 Ma.

The Northern Qingshan Diorites
The northern Qingshan diorites exhibit low SiO 2 , high Al 2 O 3 , TFe 2 O 3 , and CaO, and moderate K 2 O and Na 2 O contents, resembling the characteristics of the Setouchi sanukitoid suite (Figures 7 and 8).Additionally, they demonstrate similar REE and trace element distribution patterns to the Setouchi and central Beishan sanukitoids (Figure 9).However, these rocks exhibit slightly low MgO (4.46-4.53wt%) contents with Mg# values of 50 to 52 and significantly low Cr (18.1-31.4ppm) and Ni (6.87-7.74ppm) contents when compared to these sanukitoids (Figure 11(1-3)).Consequently, the northern Qingshan diorites should be normal calc-alkaline series rocks (Figure 7(2)).Their potential origins include (1) a magma mixing process between mafic and felsic magmas [73], (2) the partial melting of mafic crustal rocks [74,75], and (3) the fractional crystallization of mantle-derived mafic magma [22].First, the absence of mafic enclaves in the diorites and their limited range of Sr-Nd-Hf isotopes (Figures 10 and 12) do not support the existence of a magma mixing process [23,76].Furthermore, experimental research has demonstrated that the partial melting of mafic rocks can generate calc-alkaline intermediate melts (SiO 2 < 58 wt%) [67,75,77].These intermediate melts coexist with granulite residues below approximately 1.0 GPa and with garnet-bearing granulite or eclogite residues at higher pressures [67].The studied diorites show high Y contents (17.8-19.1 ppm) and flat HREE patterns with low (La/Yb) N ratios of 5.9 to 6.2 (Figure 9(1)).If the diorites are formed through the partial melting process, these features preclude the involvement of garnet in the residues during partial melting, indicating a relatively low melting pressure (<1.0 GPa).At low pressures, the partial melting of metabasaltic rocks always yields intermediate melts with high Na 2 O (>4.38 wt%) and low Mg# values (<50) [67,75,78], which are not shown by the diorites from the northern Qingshan (Figures 8(5) and 11( 1)).Therefore, it is inferred that the partial melting of crustal rocks cannot account for the formation of the northern Qingshan diorites.Alternatively, the diorites likely formed through the fractional crystallization of mantle-derived magma.In the Mg# vs. SiO2 diagram (Figure 11(1)), they are plotted near the trend associated with the crustal assimilation-fractional crystallization (AFC) of mantlederived melts.Moreover, their significantly lower Cr and Ni contents and Mg# values compared to those of mantle-derived mafic magma (Ni > 150 ppm; Mg# > 65) [83] suggest the extensive fractionation of the mafic magma [22,84].Additionally, these rocks exhibit enrichments in LREEs relative to HREEs, positive anomalies in Rb, Th, U, K, and Pb, and  2) Zircon E Hf (t) vs. the whole-rock E Nd (t) diagram.The fields of oceanic sediments, including deep-sea clays and biogenic muds, Fe-Mn crusts and nodules, and sands, the seawater array, and the terrestrial array are from [81,82].
Alternatively, the diorites likely formed through the fractional crystallization of mantlederived magma.In the Mg# vs. SiO 2 diagram (Figure 11(1)), they are plotted near the trend associated with the crustal assimilation-fractional crystallization (AFC) of mantlederived melts.Moreover, their significantly lower Cr and Ni contents and Mg# values compared to those of mantle-derived mafic magma (Ni > 150 ppm; Mg# > 65) [83] suggest the extensive fractionation of the mafic magma [22,84].Additionally, these rocks exhibit enrichments in LREEs relative to HREEs, positive anomalies in Rb, Th, U, K, and Pb, and negative anomalies in Nb and Ta (Figure 9).Together with their enrichment in wholerock Sr-Nd isotopes ( 87 Sr/ 86 Sr = 0.7060-0.7061;E Nd (t) = −1.4-−1.7)and zircon Hf isotopes (E Hf (t) = −4.7 to −0.6) (Figures 10 and 12), we infer that they were sourced from an enriched mantle.The component with enriched compositions can be introduced to mantle-derived magma, either through slab-derived materials (source contamination) or through the overriding continental crust (path contamination) [85].Here, it is difficult to quantify the relative contributions of source and path contamination in the enriched mantle source proposed for the northern Qingshan diorites due to the lack of detailed knowledge of different end components.We prefer to suggest that the slab-derived fluids/melts likely play a crucial role in forming the enriched mantle source, as indicated by the absence of wall-rock xenoliths and the ancient inherited zircon in the studied diorites.Moreover, both Ba and Th elements are mobile and tend to show high contents in subduction-related fluids/melts [86].The diorites display high Th/Yb and low La/Ba ratios, implying the influence of slab-derived materials in their magma source.In summary, we infer that the northern Qingshan diorites likely originate from an enriched mantle modified by subduction-related components.

The Heishantou Quartz Diorites
The Heishantou quartz diorites are coeval with the northern Qingshan diorites discussed above, and they define curvilinear and/or linear compositional trends for major elements with increasing SiO 2 contents (Figure 8), which may suggest that the fractional crystallization process dominantly contributed to their generation [87].However, the quartz diorites show a slight depletion in whole-rock Sr-Nd ( 87 Sr/ 86 Sr = 0.7048-0.7050;E Nd (t) = −1.5-+0.9)and zircon Hf (E Hf (t) = 3.8-7.8)isotope compositions than those of the diorites (Figures 10 and 12).This precludes the possibility of a magma fractionation process.Moreover, geochemical modeling suggests that fractional crystallization would yield an almost horizontal line in plots of incompatible trace elements with different bulk partition coefficients, while partial melting and magma mixing would produce a straight line with a slope [88].In the Th/Nd vs. Th diagram (Figure 13(1)), the quartz diorites and diorites do not define such a trend, which is inconsistent with a magma fractionation process.ℇNd(t) = −1.5-+0.9)and zircon Hf (ℇHf(t) = 3.8-7.8)isotope compositions than those of the diorites (Figures 10 and 12).This precludes the possibility of a magma fractionation process.Moreover, geochemical modeling suggests that fractional crystallization would yield an almost horizontal line in plots of incompatible trace elements with different bulk partition coefficients, while partial melting and magma mixing would produce a straight line with a slope [88].In the Th/Nd vs. Th diagram (Figure 13(1)), the quartz diorites and diorites do not define such a trend, which is inconsistent with a magma fractionation process.The calc-alkaline quartz diorites have SiO2 contents of 58.79 to 63.08 wt% and MgO contents of 2.75 to 3.84 wt% (Figure 8).In the Mg# vs. SiO2 diagram (Figure 11(1)), these rocks are plotted near the area of experimental melts of crustal rocks and tend to have higher Mg# values with decreasing SiO2 contents.This observation indicates that quartz diorites likely represent crustal-derived magma with varying degrees of input from mantle-derived mafic melts.Among the quartz diorites, those with higher SiO2 (59.61 wt%) show an enrichment in the Nd isotope composition (ℇNd(t) = −1.5)compared to less mafic rocks (SiO2 = 62.57wt%; ℇNd(t) = 0.9) (Supplementary Table S5).Therefore, the mafic The calc-alkaline quartz diorites have SiO 2 contents of 58.79 to 63.08 wt% and MgO contents of 2.75 to 3.84 wt% (Figure 8).In the Mg# vs. SiO 2 diagram (Figure 11(1)), these rocks are plotted near the area of experimental melts of crustal rocks and tend to have higher Mg# values with decreasing SiO 2 contents.This observation indicates that quartz diorites likely represent crustal-derived magma with varying degrees of input from mantlederived mafic melts.Among the quartz diorites, those with higher SiO 2 (59.61 wt%) show an enrichment in the Nd isotope composition (E Nd (t) = −1.5)compared to less mafic rocks (SiO 2 = 62.57wt%; E Nd (t) = 0.9) (Supplementary Table S5).Therefore, the mafic magma that was involved in the formation of quartz diorites should be sourced from enriched mantle materials.Furthermore, the quartz diorites are all characterized by a slight depletion in Sr-Nd-Hf isotopes (Figures 10 and 12), indicating a juvenile lower crust.Additionally, they are enriched in LREEs relative to HREEs and display positive anomalies of Rb, Th, U, K, and Pb, as well as negative anomalies of Nb and Ta (Figure 9), showing the signatures of arc-like magmatism.
Generally, Nd and Hf isotopes of most crustal and mantle-derived rocks form the "Terrestrial Array" due to the similar fractionation of Sm/Nd and Lu/Hf ratios during magma evolution [82].However, oceanic sediments, such as Fe-Mn crusts and nodules, sea clays, and biogenic muds, are typically enriched in trace elements (e.g., Sm, Nd, and Lu) and tend to have higher Lu/Hf ratios, resulting in high E Hf values at given E Nd values (Figure 12(2)) [82].In the zircon E Hf (t) vs. the whole-rock E Nd (t) diagram (Figure 12(2)), the quartz diorites are plotted over the terrestrial array line, suggesting that oceanic sediments from a subducted slab probably modified the mantle source where partial melting occurred to form the juvenile lower crust mentioned above.Additionally, the breakdown of garnet during crustal melting under high pressures can yield melts with elevated HREE contents, leading to high Lu/Hf ratios and E Hf (t) values in derived melts [89].However, the quartz diorites show high Y contents (20.0-21.0ppm) and flat HREE patterns with (La/Yb) N ratios of 6.0 to 17.2, which do not support the existence of garnet during their formation.The mechanism of the disequilibrium melting of zircon during the crustal melting process is also utilized to explain Nd-Hf isotope decoupling, as residual zircon can retain 177 Hf and, thus, generate high 176 Hf/ 177 Hf in melts [90].However, the quartz diorites show positive Zr-Hf anomalies (Figure 9(2)) and high Zr contents (94.3-158 ppm).Together with the absence of inherited zircons, we infer that residual zircons do not substantially exist, precluding the possibility of zircon disequilibrium melting [91].In summary, the Heishantou quartz diorites were derived from the partial melting of the juvenile lower crust, previously influenced by oceanic sediments, with the involvement of enriched mantle-derived magma.

The Southern Qingshan Biotite Granodiorites
The southern Qingshan biotite granodiorites exhibit moderate SiO 2 contents (65.11-66.61wt%) and contain amphibole in their mineral assemblages (Figure 3(6)), together with their metaluminous characteristics (A/CNK = 0.91-0.97)(Figure 7(3)), which indicate I-type affinities for these rocks [92,93].The low 10,000×Ga/Al (1.8-1.9)ratios (Figure 11(4)) and Ti-in-zircon temperature (647-790 • C, average 711 • C) further confirm their classification as I-type granitoids [80,94,95].Additionally, these rocks show high K 2 O contents (2.88-3.70 wt%) with high K 2 O/Na 2 O ratios (0.9-1.3), belonging to the high-K calc-alkaline series (Figure 7(2)).High-K calc-alkaline I-type granitoid can form via the (1) fractional crystallization of mantle-derived alkaline mafic melts [96], (2) the partial melting of mafic-intermediate metaigneous rocks with transitional to high K calc-alkaline characteristics [97], and (3) magma mixing between crustal-and mantle-derived melts [98].The absence of coeval cogenetic mafic rocks and associated cumulates in the regional context precludes the possibility of the fractionation process.The biotite granodiorites show enrichment in whole-rock Sr-Nd isotope compositions ( 87 Sr/ 86 Sr = 0.7054-0.7061;E Nd (t) = −2.0-−1.6)(Figure 10), which may indicate a uniform crustal source.However, their zircon Hf isotopes are variable, with E Hf (t) values ranging from −2.3 to +4.5 (Figure 12(1)).Mafic enclaves are commonly present in the southern Qingshan pluton (Figure 3(3)).They exhibit an igneous texture and zircon U-Pb age (274 Ma), similar to the host biotite granodiorites [12].The mafic enclaves show lower SiO 2 (46.42 wt%) and high MgO contents (5.52 wt%), together with their arc geochemical signatures [12], implying that they originated from the enriched mantle.Moreover, the enclaves also present variable E Hf (t) values of −1.3 to 5.1 [12], indicating that they were modified by the host rocks.In the MgO and Mg# vs. SiO 2 diagrams, the biotite granodiorites plot in the area of experimental crustal melts, and some rocks exhibit a higher MgO and Mg# than those of these melts (Figures 8(3) and 11(1)), suggesting the involvement of mafic magma.All these data imply the key role of the magma mixing process in the formation of the biotite granodiorites [23,99].In the Th/Nd vs. Th diagram (Figure 13(1)), these rocks follow the geochemical trend of partial melting or magma mixing processes.Additionally, previous studies have shown that the magma mixing process tends to be expressed by an almost straight line in one compatible vs. one incompatible element diagram [88].In the 1/V vs. Rb/V diagram, the biotite granodiorites define a straight line with a slop, which is consistent with the magma mixing process.Therefore, the geochemical features of trace elements further support the inference of magma mixing.
The mafic enclaves likely approached the composition of the mafic end member, although they were influenced by the host biotite granodiorites.The felsic end member was probably sourced from the juvenile lower crust.In the zircon E Hf (t) vs. whole-rock E Nd (t) diagram (Figure 12(2)), the biotite granodiorites lie on or above the terrestrial array.As discussed in Section 5.1.2,several factors, including the effect of garnet, zircon, and oceanic sediments, can lead to higher E Hf (t) at given E Nd (t) values [100].First, the effect of garnet can be ruled out based on the high Y contents (14.0-19.6 ppm) and flat HREE patterns ((La/Yb) N = 3.7 to 11.2).Second, the effect of zircon is also improbable.These rocks have high Zr contents (106-142 ppm) and positive Zr-Hf anomalies, which do not indicate the substantial occurrence of residual zircons during the process of crustal partial melting.Therefore, we infer that the juvenile lower crust was probably sourced from oceanic sediment-modified mantle materials.In summary, the magma mixing process played a vital role in the formation of the southern Qingshan biotite granodiorites.Two end member magmas were involved as follows: one derived from an enriched mantle and the other from a preexisting juvenile lower crust.

Implications for the Early Permian Geodynamic Setting in the Southern Beishan
The Shibanshan unit, situated at the southernmost end of the Beishan orogen, occupies a key location for understanding the final amalgamation of this orogen [8].Permian igneous rocks are widely developed, and their compositions range from mafic to felsic (Figure 2) (Supplementary Table S1).Previous studies propose that the early Permian mafic-ultramafic rocks in the Beishan orogen formed in a rifting tectonic setting related to the early Permian Tarim mantle plume [18,101].However, the distribution pattern of early Permian mafic rocks in the Shibanshan unit, along the Liuyuan ophiolitic mélange belt (Figure 2), contradicts the planar distribution typically observed in mantle plume-associated igneous rocks [16,102].Furthermore, some authors argue that these rocks exhibit distinct whole-rock trace element characteristics from those in the Tarim Large Igneous Province (LIP) [16].Additionally, Permian (281-265 Ma) mafic igneous rocks in the Shibanshan unit were considered to be sourced from mantle materials influenced by subduction-related fluids/melts [103].Collectively, these data do not support the existence of a mantle plume during the early Permian in the Shibanshan unit.
Additionally, a post-collisional setting [20,31] or continental arc setting [16,33] was suggested to account for the formation of the early Permian igneous rocks in southern Beishan.We preclude the possibility of a post-collisional setting based on several reasons.First, the Liuyuan complex to the north of the Shibanshan unit developed a large volume of MORB-type ophiolitic blocks during the early Permian to Late Triassic, which means that the Liuyuan Ocean still existed in that period [17,33].Second, the high-Mg diorite and gabbro dikes showing arc-like geochemical features, along with adakitic-like granites, suggest the ongoing southward subduction of the Liuyuan Ocean during the middle Permian (269-267 Ma) [16].Third, our study reveals that the early Permian intermediatefelsic rocks in the Shibanshan unit exhibit geochemical signatures of arc igneous rocks, and subduction-related components were involved in their generation.Finally, zircon trace element-based diagrams were constructed to discriminate the mid-ocean ridge, plumeinfluenced ocean island, and subduction-related arc environments [58].All the analyzed zircons from the three plutons in the Shibanshan unit plot were within and/or near the continental arc-type zircon field (Figure 14).These findings suggest that a continental arc setting is more feasible for the early Permian magmatism in the Shibanshan unit.the continental arc-type zircon field (Figure 14).These findings suggest that a continental arc setting is more feasible for the early Permian magmatism in the Shibanshan unit.Furthermore, our study reveals the involvement of different magma components in the formation of early Permian intermediate-felsic rocks, indicating the interaction between crustal-and mantle-derived magma.Early-mid Permian (295-273 Ma) granitoids with A-type affinities were documented in the Shibanshan unit [19,72].The occurrence of A-type granitoids most likely indicates an extensional setting, where crustal source rocks experienced partial melting under relatively high temperatures and low pressures [94,104].These A-type granitoids show many variable whole-rock Sr-Nd and zircon Hf isotope compositions (Figures 10 and 12), suggesting strong interaction between the depleted mantle and/or juvenile lower crust and ancient crustal rocks.Here, we propose a retreating subduction zone developed in the Shibanshan unit during the early Permian period (Figure 15).Retreating subduction occurs where the rate of rollback of the subducted slab is greater than the rate of advance of the overriding plate, leading to crustal extension in the latter [105].The extensional regime within the overriding continental arc likely facilitated the generation of A-type granitoids in the Shibanshan unit (Figure 15) [106].Additionally, during retreating subduction, the upwelling hot asthenospheric mantle can cause the partial melting of overriding crustal rocks, in which mantle materials can be involved, producing the strong crust-mantle interaction discussed above.In summary, it is inferred that the retreating subduction of the Liuyuan Ocean produced the early Permian intermediate-felsic magmatism in the Shibanshan unit (Figure 15).
The Beishan orogen comprises five tectonic units separated by four east-west ori- Furthermore, our study reveals the involvement of different magma components in the formation of early Permian intermediate-felsic rocks, indicating the interaction between crustal-and mantle-derived magma.Early-mid Permian (295-273 Ma) granitoids with A-type affinities were documented in the Shibanshan unit [19,72].The occurrence of A-type granitoids most likely indicates an extensional setting, where crustal source rocks experienced partial melting under relatively high temperatures and low pressures [94,104].These A-type granitoids show many variable whole-rock Sr-Nd and zircon Hf isotope compositions (Figures 10 and 12), suggesting strong interaction between the depleted mantle and/or juvenile lower crust and ancient crustal rocks.Here, we propose a retreating subduction zone developed in the Shibanshan unit during the early Permian period (Figure 15).Retreating subduction occurs where the rate of rollback of the subducted slab is greater than the rate of advance of the overriding plate, leading to crustal extension in the latter [105].The extensional regime within the overriding continental arc likely facilitated the generation of A-type granitoids in the Shibanshan unit (Figure 15) [106].Additionally, during retreating subduction, the upwelling hot asthenospheric mantle can cause the partial melting of overriding crustal rocks, in which mantle materials can be involved, producing the strong crust-mantle interaction discussed above.In summary, it is inferred that the retreating subduction of the Liuyuan Ocean produced the early Permian intermediate-felsic magmatism in the Shibanshan unit (Figure 15).formed in a post-collisional setting [116], implying that the Hongshishan Ocean probably closed before the middle Permian [117,118].Furthermore, the oceanic blocks from the Liuyuan mélange belt, located in the southernmost part of the Beishan orogen, show zircon U-Pb ages spanning the Cambrian-Permian period (540-270 Ma) [17,33].Our study also demonstrates that the Liuyuan Ocean still existed during the early Permian.The final closure of this ocean may be later than 234 Ma, as indicated by the age of the sedimentary matrix from the Liuyuan complex [33].To summarize, the existence of the late Paleozoic ophiolitic mélanges and arc magmatism likely implies that the Beishan orogen formed through multiple accretionary-collisional processes during the Paleozoic.The Liuyuan ophiolitic mélange belts may represent the site of the final closure of the PAO in the Beishan orogen.[16].A-type granitoids are from [19,72].Abbreviations: SCLM-subcontinental lithospheric mantle.The Beishan orogen comprises five tectonic units separated by four east-west oriented ophiolitic mélange belts (Figure 1(2)).The nature and timing of these mélange belts remain under debate, and different tectonic models have been proposed to account for the formation of the Beishan orogen [35,107].Primarily based on studies of volcano-sedimentary successions, some authors argue that the Jijitaizi-Xiaohuangshan mélange belt may represent a major branch of the PAO and that the Beishan orogen evolved into a continental rift setting following the closure of this ocean around the Early Devonian [108,109].However, this mélange belt formed in the Ordovician-early Carboniferous period (480 to 321 Ma), as revealed by LA-ICP-MS zircon U-Pb dating results [35,110], and is thought to have formed in a back-arc setting [14,32].The Hongliuhe-Niujuanzi-Xichangjing mélange belt shows zircon U-Pb ages ranging from 536 to 426 Ma [35], and the ocean it represents is thought to have closed before the Early Devonian [111,112].The development of the Early Devonian S-and A-type granites in central Beishan orogen further supports this inference [113].Additionally, the Hongshishan mélange belt, situated in the northernmost part of the Beishan orogen, was formed in the Carboniferous-early Permian period (357-297 Ma) according to zircon U-Pb dating results [35].Coeval arc calc-alkaline magmatism in the Heiyingshan-Hanshan unit also indicates the existence of the southward subduction of the ocean represented by the Hongshishan mélange belt [114,115].The early Permian (289 Ma) alkali feldspar granites in the Hongshishan area are considered to have formed in a post-collisional setting [116], implying that the Hongshishan Ocean probably closed before the middle Permian [117,118].Furthermore, the oceanic blocks from the Liuyuan mélange belt, located in the southernmost part of the Beishan orogen, show zircon U-Pb ages spanning the Cambrian-Permian period (540-270 Ma) [17,33].Our study also demonstrates that the Liuyuan Ocean still existed during the early Permian.The final closure of this ocean may be later than 234 Ma, as indicated by the age of the sedimentary matrix from the Liuyuan complex [33].To summarize, the existence of the late Paleozoic ophiolitic mélanges and arc magmatism likely implies that the Beishan orogen formed through multiple accretionary-collisional processes during the Paleozoic.The Liuyuan ophiolitic mélange belts may represent the site of the final closure of the PAO in the Beishan orogen.

Conclusions
(1) Intermediate-felsic igneous rocks are widespread in the Shibanshan unit, the southernmost end of the Beishan orogen.New LA-ICP-MS zircon U-Pb results reveal

Figure 2 .
Figure 2. Geological map of the Shibanshan unit showing the sampling location in the Shibanshan unit.The ages of igneous rocks are presented in Supplementary TableS1.The inserted histogram shows the compiled zircon U-Pb ages in the study area.Only 51 of the total 62 age data are included.

Figure 2 .
Figure 2. Geological map of the Shibanshan unit showing the sampling location in the Shibanshan unit.The ages of igneous rocks are presented in Supplementary TableS1.The inserted histogram shows the compiled zircon U-Pb ages in the study area.Only 51 of the total 62 age data are included.

Figure 4 .
Figure 4. Cathodoluminescence (CL) images of the analyzed zircons.The red and yellow circles on zircons show the positions for U-Pb dating and Lu-Hf isotope analysis, respectively.The numbers below zircons represent 206 Pb/ 238 U ages and ℇHf(t) values, respectively.

Figure 4 .
Figure 4. Cathodoluminescence (CL) images of the analyzed zircons.The red and yellow circles on zircons show the positions for U-Pb dating and Lu-Hf isotope analysis, respectively.The numbers below zircons represent 206 Pb/ 238 U ages and E Hf (t) values, respectively.

Figure 4 .
Figure 4. Cathodoluminescence (CL) images of the analyzed zircons.The red and yellow circles on zircons show the positions for U-Pb dating and Lu-Hf isotope analysis, respectively.The numbers below zircons represent 206 Pb/ 238 U ages and ℇHf(t) values, respectively.

Figure 9 .
Figure 9. (1) Chondrite-normalized REE patterns; (2) Primitive-mantle-normalized trace element spiderdiagrams.Data for the Setouchi and central Beishan sanukitoids are from the same source as those in Figure 8. Data for the chondrite and primitive mantle are from [71].

Figure 9 .
Figure 9. (1) Chondrite-normalized REE patterns; (2) Primitive-mantle-normalized trace element spiderdiagrams.Data for the Setouchi and central Beishan sanukitoids are from the same source as those in Figure 8. Data for the chondrite and primitive mantle are from [71].

Figure 12 .
Figure 12. (1) Zircon E Hf (t) vs. age (Ma) diagram.Data for A-type granitoids (295-273 Ma) are from the same source as those in Figure 10.(2) Zircon E Hf (t) vs. the whole-rock E Nd (t) diagram.The fields of oceanic sediments, including deep-sea clays and biogenic muds, Fe-Mn crusts and nodules, and sands, the seawater array, and the terrestrial array are from[81,82].

( 1 )
Intermediate-felsic igneous rocks are widespread in the Shibanshan unit, the southernmost end of the Beishan orogen.New LA-ICP-MS zircon U-Pb results reveal ages of 300 Ma for the northern Qingshan diorites, 294 Ma for the Heishantou quartz diorites, and 291-286 Ma for the southern Qingshan biotite granodiorites.The diorites were likely sourced from an enriched mantle influenced by subduction fluids and/or melts.The quartz diorites originated from the partial melting of the juvenile lower crustal rocks with input from the enriched mantle.The biotite granodiorites are Itype granitoids and originated from a mixing process between the enriched mantlederived and preexisting juvenile lower crust-derived magmas.(2) The early Permian intermediate-felsic rocks exhibit geochemical signatures of arc magmatism, and their generation involved subduction-related materials.Different magma components, including the enriched mantle and juvenile lower crust, participated in the generation of these rocks, implying a strong interaction between crustaland mantle-derived magmas.Additionally, all analyzed zircons in this study exhibit trace element characteristics typical of continental arc-type zircons.In conjunction with previous studies, we infer that an early Permian retreating subduction of the Liuyuan Ocean developed in the Shibanshan unit, the southernmost part of the Beishan orogen.Moreover, the Beishan orogen likely experienced multiple accretionary-collisional processes during the Paleozoic.Supplementary Materials:The following supporting information can be downloaded at: www.mdpi.com/xxx/s1,FigureS1: Chondrite-normalized REE patterns of analyzed zircons in this