Middle Silurian–Middle Devonian Magmatic Rocks in the Eastern Segment of the Northern Margin of the North China Craton: Implications for Regional Tectonics

: This paper presents a detailed study including LA-ICP-MS zircon U-Pb dating, geochemical, zircon Hf isotope, and whole rock Sr-Nd isotope analysis of magmatic rocks from the Yitong County, Jilin Province, NE China. These data are used to be tt er constrain the Middle Silurian–Middle Devonian tectonic evolution in the eastern segment of the northern margin of the North China Craton (NCC). Zircon U-Pb dating results show that the Ximangzhang tonalite formed in the Late Silurian (425 ± 6 Ma); the basalt, andesite, and metamorphic olivine-bearing basalt in the Fangniugou volcanic rocks formed in the Middle Silurian (428 ± 6.6 Ma) and Middle Devonian (388.4 ± 3.9 Ma, and 384.1 ± 4.9 Ma). The Late Silurian tonalites are characterized by high SiO 2 and Na 2 O and low K 2 O, MgO, FeOT, and TiO 2 , with an A/CNK ratio of 0.91–1.00, characteristic of calc-alkaline I-type granite. They are enriched in Rb, Ba, Th, U, and K, and depleted in Nb, Sr, P, and Ti, with positive ε Nd ( t ) (+0.35) and ε Hf ( t ) (+0.44 to +6.31) values, suggesting that they mainly originated from the partial melting of Meso–Neoproterozoic accretionary lower crustal material (basalt). The Middle Silurian basalts are characterized by low SiO 2 , P 2 O 5 , TiO 2 , and Na 2 O and high Al 2 O 3 , FeOT, and K 2 O, enriched in Rb, Ba, Th, U, and K and depleted in Nb, Ta, Sr, P, and Ti, indicative of shoshonitic basalt. The Late Silurian tonalites have positive ε Nd ( t ) (+4.91 to +6.18) values and primarily originated from depleted mantle magmas metasomatized by subduction ﬂ uids, supplemented by a small amount of subducted sediments and crustal materials. The Middle Devonian volcanic rocks exhibit low SiO 2 , TiO 2 , and Na 2 O and high K 2 O, and MgO, enriched in Rb, K, and LREEs and depleted in Nb, Ta, Sr, and HREEs, characteristic of shoshonitic volcanic rocks. Their ε Nd ( t ) (+2.11 to +3.77) and ε Hf ( t ) (+5.90 to +11.73) values are positive. These characteristics indicate that the Middle Devonian volcanic rocks primarily originated from depleted mantle magmas metasomatized by subduction ﬂ uids, with the addition of crustal materials or subducted sediments during their formation. Based on regional geological data, it is believed that the study area underwent the following evolutionary stages during the Silurian–Devonian period: (1) active continental margin stage of southward sub-duction of the Paleo–Asian Ocean (PAO) (443 ‒ 419 Ma); (2) arc-continent collision stage (419 ‒ 405 Ma); (3) post-collision extension stage (404 ‒ 375 Ma); (4) active continental margin stage, with the PAO plate subducting southward once again (375 ‒ 360 Ma).

Previous research was predominantly focused on the central and western regions of Inner Mongolia, while the northern margin of the NCC from northern Liaoning Province to central Jilin Province has received less attention [32,43,45,56,57].Moreover, the northern Liaoning Province to central Jilin Province region, which was originally classified as Early Paleozoic, has now been classified as Late Paleozoic or Early Mesozoic [12,19,51,[58][59][60][61][62][63][64][65][66].Therefore, it remains uncertain whether the Bainaimiao arc belt can extend over the Songliao Basin into northeastern China [12,58,59,67].With the deepening of research, some Ordovician-Devonian rocks have been discovered in recent years in northern Liaoning Province and central to eastern Jilin Province [43, 44,48,56,64,[68][69][70][71], providing valuable information for further understanding of tectonic evolution.The Silurian-Devonian rocks in Yitong County, Jilin Province, which document a continuous evolutionary history from the Silurian to the Permian, are particularly crucial for exploring the tectonic framework and accretionary processes along the eastern segment of the northern margin of the NCC.In this study, zircon U-Pb chronological, petrographical, geochemical, zircon Hf-isotope, and whole-rock Sr-Nd isotope analyses were conducted (Table 1), and the properties and tectonic setting of the source area of the Silurian-Devonian magmatic rocks in Yitong area are discussed.These data provide new evidence for the magmatic-tectonic evolution of the northern margin of the NCC in the Silurian-Devonian.[44], and 375.5 ± 4.6Ma [29] from the Fangniugou volcanic rocks, suggesting that they were formed during the Late Silurian to Late Devonian period.
In the northeast of the Taoshan Formation, the Fangniugou volcanic rocks are exposed with a suite of metamorphic carbonates, clastic rocks, and volcanic rocks, which formed during the Carboniferous to Permian [32,45] (Figure 1c).The Paleozoic geological units in the study area are composed of a series of tectonic slices, which were formed during the Silurian to Permian, and gradually became younger from southwest to northeast.Reflected in the process of oceanic crust subduction, various geological bodies of different ages and environments were, in turn, collaged laterally, and then transformed by later tectonic events.

Whole-Rock Composition Analyses
Geochemical analyses of the rock samples were conducted at the Northeast China Supervision Inspection Center of Mineral Resources, Ministry of Natural Resources, Shenyang Center of Geological Survey, China Geological Survey, Shenyang, China, using contamination-free equipment.Major elements were quantified via X-ray fluorescence

Whole-Rock Composition Analyses
Geochemical analyses of the rock samples were conducted at the Northeast China Supervision Inspection Center of Mineral Resources, Ministry of Natural Resources, Shenyang Center of Geological Survey, China Geological Survey, Shenyang, China, using contamination-free equipment.Major elements were quantified via X-ray fluorescence spectrometry (XRF), with errors in precision and accuracy of +/-5%.Trace elements were measured using Inductively Coupled Plasma Mass Spectrometry (ICP-MS), with errors in precision and accuracy of less than 10%.

LA-ICP-MS Zircon U-Pb Dating
LA-ICP-MS Zircon U-Pb dating was performed at the Key Laboratory of Mineral Resources Evaluation in Northeast Asia, Ministry of Natural Resources, Jilin University, Changchun, China.The process utilized a COMPEx Pro type ArF excimer laser ablation system from the Coherent Company (Saxonburg, PA, USA) and an Agilent 7900 type ICP-MS (Agilent Technologies, Inc., Santa Clara, CA, USA).The laser spot diameter was set at 32 µm.High-purity helium served as the carrier gas, and argon was used as the auxiliary gas.Isotopic ratio corrections employed standard zircons 91500 and PLE, while the international standard NIST610 corrected the contents of Th, U, Pb, and other elements [73].The procedures followed for these analyses are elaborated in Yuan et al. [74].Age determinations were conducted using Isoplot software (version 3.0).

Zircon Lu-Hf Isotopic Analyses
Zircon Lu-Hf isotopic analyses were carried out at the Tianjin Institute of Geology and Mineral Resources.This process utilized a Thermo Fisher Neptune type Multi-Collector Inductively Coupled Plasma Mass Spectrometer (MC-ICPMS) and a 193 nm laser ablation system (NEW WAVE193nm FX), with a laser spot size of 50 µm (Thermo Fisher Scientific, Waltham, MA, USA).The methodologies applied, including isotopic fractionation corrections, are based on the techniques described by Geng Jianzhen et al. [75] and Wu Fuyuan et al. [17].

Whole-Rock Sr-Nd Isotopic Analyses
Whole-rock Sr-Nd isotopic analyses were conducted at the Analytical and Testing Research Center of the Beijing Research Institute of Uranium Geology.These analyses utilized an ISOPROBE-T thermal ionization mass spectrometer (Isotopx LTD., Cheshire, UK).The isotopic ratios for Sr and Nd were standardized using the values 86 Sr/ 88 Sr = 0.1194 and 146 Nd/ 144 Nd = 0.7219.

Zircon U-Pb Geochronology
The zircon U-Pb dating results are shown in Supplementary Table S1.Sample D11 is a tonalite from the Ximangzhang pluton.Twenty-five zircon grains from this sample were dated, with most results lying on or near the concordia line.These zircons are mostly granular and short columnar, with grain sizes of 100-200 µm and length/width ratios of 1:1 to 3:2.The cathodoluminescence (CL) images (Figure 3a) show that these zircon grains have typical zonal textures and Th/U ratios of 0.36-0.77,suggesting a magmatic origin.Of these, 17 zircon grains have 206 Pb/ 238 U ages of 420-437 Ma, with a weighted mean 206 Pb/ 238 U age of 425 ± 6 Ma (mean squared weighted deviation (MSWD) = 0.12) (Figure 4a), representing the best estimate for emplacement time of the tonalite.Another 8 zircon grains have 206 Pb/ 238 U ages of 445-459Ma, with a weighted mean 206 Pb/ 238 U age of 451 ± 10 Ma (MSWD = 0.08).
Sample DG075 is a basalt from the Fangniugou volcanic rocks.These zircons are short columnar, with grain sizes of 50-100 µm and length/width ratios of 2:1 to 3:2.The CL images (Figure 3b) show that these zircon grains have typical zonal textures and Th/U ratios of 0.41-0.75,suggesting magmatic zircons.Twenty zircon grains were analyzed in this study.Most results deviated from the concordia line, but all data could fit a line, showing a lower intercept age of 428 ± 6.6 Ma (MSWD = 0.77) (Figure 4b), which represents the best estimate for the eruption time of the basalt.
cons.Eighteen zircon grains in this sample were dated, with all results lying on or near the concordia line.Of these, 13 zircon grains have 206 Pb/ 238 U ages of 372-389Ma, with a weighted mean 206 Pb/ 238 U age of 384.1 ± 4.9 Ma (MSWD = 0.33) (Figure 4d   Sample J1917 is an andesite from the Fangniugou volcanic rocks.These zircons are tabular and short columnar, with grain sizes of 50-100 µm and length/width ratios of 1:1 to 2:1.The CL images (Figure 3c) show that these zircon grains have typical zonal textures and Th/U ratios of 0.56-1.47,suggesting magmatic zircons.Twenty-nine zircon grains in this sample were dated, with all results lying on or near the concordia line.The analyses give a weighted mean 206 Pb/ 238 U age of 388.4 ± 3.9 Ma (MSWD = 0.23) (Figure 4c), representing the best estimate for the eruption time of the andesite.
Sample PM07-12 is a metamorphic olivine-bearing basalt, from the Fangniugou volcanic rocks.These zircons are tabular and short columnar (Figure 3d), with grain sizes of 50-120 µm and length/width ratios of 1:1 to 3:1.The CL images show that these zircon grains have typical zonal textures and Th/U ratios of 0.45-1.35,suggesting magmatic zircons.Eighteen zircon grains in this sample were dated, with all results lying on or near the concordia line.Of these, 13 zircon grains have 206 Pb/ 238 U ages of 372-389Ma, with a weighted mean 206 Pb/ 238 U age of 384.1 ± 4.9 Ma (MSWD = 0.33) (Figure 4d

Whole-Rock Major and Trace Elements Analysis
The whole-rock major and trace elements analysis results are shown in Supplementary Table S2.
The K2O/Na2O ratios of Late Silurian tonalite (D11) samples are 0.44-0.59,indicating that they are relatively enriched in Na and depleted in K. Their A/CNK ratios range from 0.91 to 1.00, showing metaluminous signatures.In the An-Ab-Or classification diagram (Figure 5a), data for the samples are located within the field of tonalite.As revealed by the rock series discrimination diagram (Figure 5d), the samples all fall into the calc-alkaline zone.The samples have relatively higher ΣREE contents (167.38-180.81ppm), exhibiting LREE enrichment (LaN/YbN = 2.40-3.32)with slightly negative Eu anomalies (Eu/Eu* = 0.77-0.84)(Figure 6a).According to the parameters proposed by Irber [76] and Monecke [77], CeN/Ce* and PrN/Pr* of the tonalites are slightly less than 1, T1 is slightly greater than 0, and t1 is slightly less than 1 (Table S2), indicating that the first group of rare earth elements (La, Ce, Pr, and Nd) show a weak W-type tetrad effect.TbN/Tb*, DyN/Dy*, TmN/Tm*, and YbN/Yb* are significantly greater than 1, T3 is greater than 0, t3 and t4 are greater than 1 (Table S2), all indicating that the third group (Ga, Tb, Dy, and Ho) and the fourth group (Er, Tm, Yb, and Lu) of rare earth elements show a significant M-type tetrad

Whole-Rock Major and Trace Elements Analysis
The whole-rock major and trace elements analysis results are shown in Supplementary Table S2.
The K 2 O/Na 2 O ratios of Late Silurian tonalite (D11) samples are 0.44-0.59,indicating that they are relatively enriched in Na and depleted in K. Their A/CNK ratios range from 0.91 to 1.00, showing metaluminous signatures.In the An-Ab-Or classification diagram (Figure 5a), data for the samples are located within the field of tonalite.As revealed by the rock series discrimination diagram (Figure 5d), the samples all fall into the calcalkaline zone.The samples have relatively higher ΣREE contents (167.38-180.81ppm), exhibiting LREE enrichment (La N /Yb N = 2.40-3.32)with slightly negative Eu anomalies (Eu/Eu* = 0.77-0.84)(Figure 6a).According to the parameters proposed by Irber [76] and Monecke [77], Ce N /Ce* and Pr N /Pr* of the tonalites are slightly less than 1, T1 is slightly greater than 0, and t1 is slightly less than 1 (Table S2), indicating that the first group of rare earth elements (La, Ce, Pr, and Nd) show a weak W-type tetrad effect.Tb N /Tb*, Dy N /Dy*, Tm N /Tm*, and Yb N /Yb* are significantly greater than 1, T3 is greater than 0, t3 and t4 are greater than 1 (Table S2), all indicating that the third group (Ga, Tb, Dy, and Ho) and the fourth group (Er, Tm, Yb, and Lu) of rare earth elements show a significant M-type tetrad effect.The trace element spider plot illustrates that the samples are relatively enriched in Rb, Ba, Th, U, and K (LILEs), and depleted in Nb, Sr, P, and Ti (HFSEs) (Figure 6b).
Minerals 2024, 14, 641 9 of 27 effect.The trace element spider plot illustrates that the samples are relatively enriched in Rb, Ba, Th, U, and K (LILEs), and depleted in Nb, Sr, P, and Ti (HFSEs) (Figure 6b).5f), the samples predominantly classify within the regions of basalt and basaltic andesite volcanic rocks, suggesting that the protolith was an intermediate to mafic volcanic rock.Their A/CNK ratios range from 0.84 to 1.07, showing metaluminous-weakly peraluminous signatures.The andesite samples plot in the shoshonite series field (Figure 5d) and in the sub-alkaline basalt and andesite regions on the SiO 2 vs. Nb/Y and Zr/TiO 2 vs. Nb/Y diagrams (Figure 5b,c).The samples have relatively lower REE contents (93.52-106.89ppm), exhibiting LREE enrichment (La N /Yb N = 9.77-10.23)with positive Eu anomalies (Eu/Eu* = 1.12-2.12)and no Ce anomalies (Ce/Ce* = 0.92-1.02)(Figure 6c).The trace element spider plot illustrates that the samples are relatively enriched in Rb and K and depleted in Ba, Th, U, Nb, Ta, Sr, P, Ti, and HREEs (Figure 6d).

Zircon Lu-Hf Isotopes
Based on LA-ICP-MS zircon U-Pb dating of Late Silurian tonalite and Middle Devonian andesite in the Yitong area, this study conducted in situ zircon Hf isotope analysis of some zircons from the dated samples (Figure 7a).The analytical results are shown in Supplementary Table S3.

Whole-Rock Sr-Nd Isotopes
Measured and age-corrected initial isotopic ratios of Sr and Nd are presented in Supplementary Table S4.The Sm, Nd, Rb, and Sr contents of these rocks are given in Supplementary Table S2.

Silurian to Devonian Magmatism in the Eastern Section of the Northern Margin of the NCC
Previous studies [29,32,43,44,48,68], indicate that the 424 ± 6 Ma Ximangzhang pluton underwent multiple episodes of magmatism during the Late Ordovician to Early Silurian (448-438 Ma), Late Silurian (425-419 Ma), and Early Devonian (414 Ma), forming a magmatic complex.The Fangniugou volcanic rocks emerged in the Middle Silurian to the Late Devonian, which was marked by multiple volcanic episodes at 428-425 Ma, 419 Ma, 404-400 Ma, 390-384 Ma, and 375 Ma.In recent years, Cambrian-Devonian geological bodies have been reported successively from the eastern section of the northern margin of the NCC in Faku-Kaiyuan, Liaoning Province, and Gongzhuling-Liaoyuan-Zhangjiatun-Yanbian, Jilin Province (Figure 8) [29,43,44,48,56,64,[68][69][70].The Early Paleozoic magmatism in this region extended from the Late Cambrian to the Late Silurian, with peaks observed at 494 Ma, 486 Ma, 475 Ma, 467 Ma, 459 Ma, 438 Ma, and 422 Ma.These peaks resemble those of the Early Paleozoic Bainaimiao arc belt magmatic rocks [32], suggesting that the subduction-accretionary complex belt in the Faku-Yanji area is an extension of the Bainaimiao arc belt in the east.Combined with previous data, the Silurian magmatism in the northern margin of the NCC ranges from 443 to 419 Ma, and the Devonian magmatism ranges from 414 to 375 Ma (Table 2).The Silurian (443~419Ma) magmatism is frequent and distributed along the north margin of the NCC in an east-west direction, mainly exposed in the Faku,

Whole-Rock Sr-Nd Isotopes
Measured and age-corrected initial isotopic ratios of Sr and Nd are presented in Supplementary Table S4.The Sm, Nd, Rb, and Sr contents of these rocks are given in Supplementary Table S2.
The Late Silurian tonalites have high contents of SiO 2 and Na 2 O, and low contents of K 2 O, MgO, FeOT, and TiO 2 , with an A/CNK ratio of 0.91-1.00,indicative of I-type granites.In the Na 2 O vs. K 2 O diagram (Figure 9a), the tonalite samples fall within the zone of the I-type granite.Additionally, in the petrogenetic discrimination diagrams (Figure 9b), all tonalite samples fall within the zone of unfractionated granitoids.These characteristics are consistent with those of metaluminous calc-alkaline I-type granitoids.They exhibit enrichment in Rb, Ba, Th, U, and K (LILEs) and depletion in Nb, Sr, P, and Ti (HFSEs), displaying magmatic arc features [19,92,93].The explanations for the tetrad effect of rocks include mineral crystallization [94,95], late-stage magma-fluid interactions [76,96,97], or inheritance from the parental magma [76,97].According to published papers [29,43], the Ximangzhang tonalites do not exhibit tetrad effects, indicating that this characteristic is not a feature of its primary magma.The low Zr/Hf (12.81-14.99)and Y/Ho (15.41-18.83)ratios in tonalites cannot be explained by mineral crystallization [98,99].Crust-derived magmas that have undergone significant magma-hydrothermal exchange typically exhibit lower Zr/Hf ratios (<20) [76].The Nb/Ta ratio (4.11-12.49,average 7.38) in tonalite is similar to the differentiated continental crust (11) [100].Therefore, the REE anomalies may be caused by magma-fluid interactions.Increasing La concentrations correspond with a rise in the La/Sm ratio, indicative of partial melting processes during their formation.The absence of pronounced Sr and Eu anomalies further supports the partial melting of plagioclase in the source material.The tonalites have low Cr (24.70-30.82ppm) and Ni (5.34-6.56ppm) content and Mg# (39.26-43.79)values, indicating a crustal source.Their La/Sm ratios between 3.72 and 4.34 (average 3.98) suggest a moderate degree of crustal contamination, given that ratios above 4.5 typically indicate strong contamination, while those below 2 suggest primary compositions [101].Additionally, the tonalites display high Ba/Th (48.35-196.86,average 117.57) and Ba/La (14.27-24.49,average 19.79) ratios, but low Th content (3.63-9.13ppm) and Th/Yb ratios (0.56-1.05), implying that slab-derived fluids primarily influenced the source of these Late Silurian magmatic rocks [102], with lesser contributions from sediments or melts.The Rb/Ba vs. Rb/Sr diagram (Figure 9c) shows that the source material for the tonalite is predominantly basalt   The Middle Silurian basalts have low contents of SiO 2 , P 2 O 5 , TiO 2 , and Na 2 O and high contents of Al 2 O 3 , FeOT, CaO, and K 2 O, with a K 2 O/Na 2 O ratio of 1.24-1.57.Notably, these basalts contain primarily K-feldspar phenocrysts, with σ values ranging from 9.70 to 11.75, and CIPW norm calculations indicating the presence of nepheline (Ne = 7.41-10.69),but alkaline minerals are absent in thin section observations.Positioned within the subalkaline basalt region in the SiO 2 vs. Nb/Y and Zr/TiO 2 vs. Nb/Y diagrams (Figure 5b,c), these samples are identified as shoshonitic rocks rather than typical alkaline rocks.The ratios of incompatible elements, largely unchanged by fractional crystallization, remain constant during the partial melting of the mantle, thereby serving as indicators of magma source characteristics [106].Geochemical analysis reveals an average Lu/Yb ratio of 0.15-0.16,closely aligned with the typical mantle-derived magmatic value of 0.14-0.15[107], and an average Nb/Ta ratio of 19.80, approaching the mantle standard of 17.5 [84,106], affirming their mantle-derived magmatic nature.Positive ε Nd (t) values ranging from +4.91 to +6.18 further affirm a mantle origin.Additionally, high ratios of La/Ta (37.94-60.22 > 22) and La/Nb (2.27-2.47> 1.7), alongside low Zr/Ba (0.12-0.16) and La/Ba (0.03-0.04) ratios, point to a genesis within the lithospheric mantle, modified by subduction processes [108][109][110][111][112].These basalts also exhibit high Ba/Th (128.08-177.84)and Ba/La (27.88-36.84)ratios and lower La/Sm (4.78-5.03)and Th/Yb (1.69-1.97)ratios, indicative of a mantle-derived magmatic source predominantly influenced by slab dehydration [102].They are enriched in Rb, Ba, Th, U, K, and LREE, yet depleted in Nb, Ta, Sr, P, and Ti, characteristic of island arc magmatic rocks [19], suggesting an origin from the lithospheric mantle that has been metasomatized by subduction fluids [113].Furthermore, relatively low Cr (67.60-70.51ppm), Ni (38.95-40.13 ppm), and Co (17.96-19.97ppm) contents and Mg# (32.15-34.95)values suggest a significant evolutionary process during its formation [114], such as fractional crystallization of olivine or pyroxene, or crustal contamination.Their average Rb/Sr ratio of 0.16 distinctly reflects a mixed mantle-crust source, consistent with the typical mantle-crust mixed source magmatic Rb/Sr ratio range of 0.05-0.50[106].Island arc volcanic rocks often exhibit a characteristic negative anomaly in Ce concentrations [115].The samples have negative Ce anomaly (0.68-0.74) and low Ce/Th ratios (6.97-7.89),further suggesting the incorporation of subducted sediment melts into the source.The ε Nd (t) vs.I sr diagram (Figure 9d) indicates that the magma mainly originated from a depleted mantle with some crustal material addition.The Nd isotope single-stage model age (T DM1 ) ranges from 647 to 758 Ma, which represents the mixed age of juvenile crust and older crust, suggesting the presence of a Proterozoic crystalline basement in the study area.Collectively, these features indicate that the Middle Silurian basalts primarily originated from depleted mantle magmas metasomatized by subduction fluids, supplemented by a small amount of subducted sediments and crustal materials.

Middle Devonian Volcanic Rocks
The Middle Devonian volcanic rocks have undergone weak metamorphism and deformation with a slightly higher loss on ignition (LOI = 2. 94-4.78).Therefore, to discern the rock origins and source characteristics, less mobile lithogenic elements along with rare earth elements and high field strength elements, which are less affected by metamorphism and alteration, are primarily utilized [116].
The Middle Devonian volcanic rocks have low SiO 2 , TiO 2 , and Na 2 O content and high K 2 O content, and a high K 2 O/Na 2 O ratio with a wide range of variation in Al 2 O 3 content (ranging from 13.65 to 17.50 wt%).In the SiO 2 vs. Nb/Y and Zr/TiO 2 vs. Nb/Y diagrams (Figure 5b,c), these volcanic rocks primarily fall into the subalkaline basalt and andesite zones, indicating that the K-rich and Na-poor characteristics of the samples are a result of alteration.The samples are enriched in LILEs such as Rb, K, and LREEs and are depleted in Nb, Ta, Sr, and HREEs, showing geochemical characteristics similar to those of arc volcanics [117][118][119][120][121].
In the ε Hf (t) vs. t and ε Nd (t) vs. t diagrams (Figure 7a,b), the Middle Devonian volcanic rock samples fall within the ε Hf (t) and ε Nd (t) ranges of the Bainaimiao arc.The volcanic rocks have ε Nd (t) values of +2.11 to +3.77 and zircon ε Hf (t) values of +5.90 to +11.73, falling between the chondritic and depleted mantle evolution lines (Figure 7a,b), suggesting that their source mainly originated from depleted mantle; the decoupling of ε Nd (t) and ε Hf (t) indicates crustal contamination.The Nd isotope T DM2 ranges from 823 to 956 Ma, and the Hf isotope T DM2 ranges from 636.0 to 1001. 4 Ma, representing the mixing ages of juvenile crust and Proterozoic crust, indicating the presence of a Proterozoic crystalline basement in the study area.These characteristics indicate that the Middle Devonian volcanic rocks primarily originated from depleted mantle magmas metasomatized by subduction fluids, with the addition of crustal materials or subducted sediments during their formation.

Tectonic Setting
In the study area, the Middle-Late Silurian magmatic rocks are mainly composed of basalt, andesite, tonalite, granodiorite, dacite, and rhyolite, which is similar to a typical island arc magmatic rocks assemblage.These rocks are enriched in Rb, Ba, Th, U, and K, while being depleted in Nb, Ta, Sr, P, and Ti, a signature suggesting formation in a subduction zone environment [92,129].In the Sr/Y vs. Y and La/Yb vs. Th/Yb diagrams (Figure 10a,c), the tonalite and basalt samples fall within the zone of a typical island arc.Additionally, in the Rb vs. (Y + Nb) diagram (Figure 10d), the tonalite samples fall within the zone of a volcanic-arc granite.In the Th/Yb vs. Ta/Yb diagram (Figure 10d), the basalt samples fall within the active continental margin field.These Middle-Late Silurian magmatic rocks (428-419 Ma) share isotopic and geochemical traits with the earlier Late Ordovician to Early Silurian tonalite and quartz diorite (446 Ma, 438 Ma) [29,32].Notably, the tonalite, characterized by low Sr and high Yb, formed at a depth similar to standard crustal thickness of about 30-40 km [130], suggesting that no arc-continent collision occurred during this period.Therefore, this study suggests that the Middle-Late Silurian magmatic rocks formed in an active continental margin environment.
The Middle Devonian volcanic rocks are marked by low SiO 2 , Na 2 O, MgO, Sr, and Y but are rich in K 2 O.In the Sr/Y vs. Y diagram (Figure 10a), these samples fall within the zone of the typical island arc.In the Th/Yb vs. Ta/Yb diagram (Figure 10d), the samples fall within the active continental margin field, exhibiting characteristics of the calc-alkaline to shoshonitic series.The La/Yb vs. Th/Yb diagram (Figure 10c) further underscores their affinity with a mature continental arc.Furthermore, the Early Devonian rhyolitic tuff (404 ± 4.5 Ma) in the study area, showing the features of typical A2-type granite, formed in a post-collisional extension setting [29].In the La/Sm vs. Sm/Yb diagram (Figure 11), the Middle Silurian and Middle Devonian volcanic rock samples can be derived from spinel-garnet lherzolite (Figure 11), with degrees of partial melting ranging from 1 to 5%, and magma source depths estimated between 60 and 80 km [131].The Middle Silurian volcanic rocks can be derived from spinel lherzolite, whereas the Middle Devonian rocks are more likely derived from spinel-garnet lherzolite (spinel:garnet = 1:1), suggesting an increase in crustal thickness during the Middle Devonian.The collision of the Late Silurian Bainaimiao arc with the NCC led to the subsequent formation of a series of alkaline series magmatic rocks [31,86,[132][133][134][135][136][137][138].Combined with the Middle Devonian magmatic rocks in the northern Liaoning Province to central Jiling Province having characteristics of I-and A-type granites [43], this suggests that the study area was an extensional environment after the arc-continent collision during the Middle Devonian period.

Silurian-Devonian Tectonic-Magmatic Evolution in the Eastern Section of the Northern Margin of the NCC
Based on previous studies and the division of tectonic evolution, the magmatic and tectonic progression of the eastern section of the northern margin of the NCC from the Silurian to Devonian can be delineated into four primary stages: Early Paleozoic magmatism along the eastern segment of the northern margin of the NCC commenced in the Late Cambrian and persisted through the Late Silurian.The rock assemblages and peak ages of this Early Paleozoic magmatism align closely with those observed in the central-western segment of the northern margin of the NCC, indicating that the eastern magmatism is a continuation of the Bainaimiao arc [29,32].Between the Late Cambrian and Middle Ordovician (493-458 Ma), the magmatic rocks are mainly composed of peridotite, pyroxenite, gabbro, high-Mg andesite, pyroxene andesite, quartz diorites, etc., representing the initial stages of subduction [43] within an intra-oceanic arc environment [57], and can be compared with the Ondor Sum subduction-accretionary complex.These early magmatic rocks are primarily located around areas such as Xiaosuhe, Zhangjiatun, Toudaogou, and Huadian, positioned northeastern of the study area, closer to the Changchun Yanji suture zone.Subsequent magmatism (446-419 Ma) is mainly composed of adakitic diorite, andesite, quartz diorites, granodiorites, tonalites, rhyolitic dacites, granites, and rhyolites.These rocks are similar to active continental margin rock assemblages and belong to the calc-alkaline to high-K calc-alkaline series, displaying mature island arc rock characteristics [43].Silurian magmatic rocks are enriched in LREEs and LILEs, yet are depleted in HFSEs such as Nb, Ta, and Ti, mirroring the geochemistry of arc volcanic rocks.Discrimination diagrams suggest that these Silurian magmatic rocks were produced within an active continental margin setting.Due to subsequent strong modification, rocks from the Late Cambrian and Middle Ordovician are limited and scattered in exposure.Therefore, the position of the immature arc of the Late Cambrian and Middle Ordovician is not very clear.In general, the immature arc of the Late Cambrian and Middle Ordovician is located on the northeast side of the volcanic arc with an age of 446-419 Ma.They can be compared with the Bainaimiao Arc and Ondor Sum subduction-accretionary complex.Early Paleozoic magmatism along the eastern segment of the northern margin of the NCC commenced in the Late Cambrian and persisted through the Late Silurian.The rock assemblages and peak ages of this Early Paleozoic magmatism align closely with those observed in the central-western segment of the northern margin of the NCC, indicating that the eastern magmatism is a continuation of the Bainaimiao arc [29,32].Between the Late Cambrian and Middle Ordovician (493-458 Ma), the magmatic rocks are mainly composed of peridotite, pyroxenite, gabbro, high-Mg andesite, pyroxene andesite, quartz diorites, etc., representing the initial stages of subduction [43] within an intra-oceanic arc environment [57], and can be compared with the Ondor Sum subduction-accretionary complex.These early magmatic rocks are primarily located around areas such as Xiaosuhe, Zhangjiatun, Toudaogou, and Huadian, positioned northeastern of the study area, closer to the Changchun Yanji suture zone.Subsequent magmatism (446-419 Ma) is mainly composed of adakitic diorite, andesite, quartz diorites, granodiorites, tonalites, rhyolitic dacites, granites, and rhyolites.These rocks are similar to active continental margin rock assemblages and belong to the calc-alkaline to high-K calc-alkaline series, displaying mature island arc rock characteristics [43].Silurian magmatic rocks are enriched in LREEs and LILEs, yet are depleted in HFSEs such as Nb, Ta, and Ti, mirroring the geochemistry of arc volcanic rocks.Discrimination diagrams suggest that these Silurian magmatic rocks were produced within an active continental margin setting.Due to subsequent strong modification, rocks from the Late Cambrian and Middle Ordovician are limited and scattered in exposure.Therefore, the position of the immature arc of the Late Cambrian and Middle Ordovician is not very clear.In general, the immature arc of the Late Cambrian and Middle Ordovician is located on the northeast side of the volcanic arc with an age of 446-419 Ma.They can be compared with the Bainaimiao Arc and Ondor Sum subductionaccretionary complex.
South of the Changchun-Yanji Suture zone, the study area records a continuous evolution process from the Late Ordovician to the Permian period.From southwest to northeast, Late Ordovician to Late Silurian intrusive rocks, Silurian to Devonian volcanic and clastic rocks, Late Carboniferous to Early Permian carbonate and clastic rocks, and Permian metamorphic volcanic rocks are exposed sequentially.Based on rock assemblages, protolith formation, and geochemical characteristics, they can be divided into a Late Ordovician to Late Devonian arc-basin system and a Late Carboniferous to Late Permian arc-basin system.The Paleozoic geological bodies in the area are generally distributed in a northwest direction, and geological bodies of different ages are mostly in tectonic contact, reflecting the process of transpression during the southward subduction of the PAO.In summary, we suggest that the Silurian magmatic rocks in the area formed in an active continental margin environment during the southward subduction of the PAO.

Arc-Continent Collision (419-405 Ma)
The northern margin of the NCC and the Bainaimiao arc show different evolutionary histories and basement properties during the Early Paleozoic era [86].Currently, many workers believe that the NCC and the Bainaimiao arc underwent an arc-continent collision at the end of the Early Paleozoic and the beginning of the Late Paleozoic [32,[42][43][44][45][46][47][48].The Xibiehe Formation and Zhangjiatun Formation, exposed in central Inner Mongolia to central Jilin Province, are considered to be post-collision molasse, unconformably overlying Early Paleozoic units [143].The Xibiehe Formation in the Jiefangyingzi area of Chifeng City was deposited in the Early (with tuff interlayer ages of 405 ± 2 Ma); the Zhangjiatun Formation in central Jilin Province was deposited after 404 ± 14 Ma and 409 ± 8 Ma [43].Detrital zircon geochronology from the Xibiehe Formation indicates that the arc-continent collision occurred during the Late Silurian to the Early Devonian [86].Moreover, along the Chifeng-Kaiyuan fault, syn-collisional magmatic rocks have been dated to between 419 and 411 Ma [13,15,144,145].Therefore, the arc-continent collision should have occurred in the Early Devonian (419-405 Ma).

Post-Collisional Extension (404-375 Ma)
During the Devonian period, the northern margin of the NCC and the central to the western section of the Bainaimiao arc show the development of an alkaline magmatic belt from 400 to 380 Ma [31], comprising mafic-ultramafic rocks, alkaline rocks, A-type granites, and bimodal volcanic rocks [31,62,133,135,137,146,147].These features suggest that this region was in an extensional tectonic environment during the Devonian period.Devonian magmatism in the eastern section of the northern margin of the NCC (414-375 Ma) is mainly composed of basalt, basaltic andesite, andesite, granodiorite, monzonite, dacite, rhyolite, and rhyolite tuff, with notable magmatic peaks at 411 Ma, 400 Ma, 387 Ma, and 377 Ma (Figure 8).Age peaks correspond closely to those in the northern margin of NCC and the Bainaimiao arc (400 Ma, 392 Ma, 379 Ma) [31], suggesting a similar evolutionary history from the eastern to western sections of the northern margin of the NCC during the Devonian period.
In the study area, the Early Devonian rhyolitic tuff (404 Ma) shows A2-type granite geochemical characteristics and was formed in a post-collisional extensional tectonic setting [29].The Early Devonian monzogranite (400 Ma) and Middle Devonian rhyolite (390 Ma) display adakitic geochemical characteristics, reflecting the thickening of the crust after collision [43,44].In the Chifeng area, the Middle Devonian syenogranite (392 Ma), granite (385 Ma), and granitic porphyry (377 Ma) [132,148] are classified as A2-type granites, formed in a post-collisional or post-orogenic environment, indicating that the Middle Devonian setting was post-collisional.The intermediate and mafic volcanic rocks from the Middle Devonian (388-384 Ma) in the study area are rich in alkali elements and belong to the shoshonitic series, formed in an extensional setting.In summary, the northern margin of the NCC appears to have been in a post-collisional extensional environment during the Early to Middle Devonian (404-375 Ma).

Active Continental Margin (375-360 Ma)
Previous research suggests that extension during this period may have continued until the end of the Devonian period [70,[147][148][149] or the Early Carboniferous period [150].
Studies on ophiolites and volcanic rocks indicate that southward subduction of the PAO commenced in the Late Devonian to Early Carboniferous.The discovery of Late Devonian calc-alkaline I-type rhyolite in the Yitong area (375.5 ± 4.6 Ma) [29] and high-K calc-alkaline I-type granite in the Changtu area (377 ± 2 Ma) [70] suggests that the PAO plate began to subduct southward during the Late Devonian.Late Devonian high-Mg andesite (370 Ma) in the Faku area, formed in a back-arc rift environment, that the PAO underwent southward subduction at this time, leading to the initiation of continental rifting in the Faku area and the development of a post-arc basin [71].Song et al. [151] based on ophiolites exposed in the CAOB, proposed the existence of two major oceanic expansion/subduction cycles between 500-410 Ma and 360-220 Ma.Xie et al. [152] suggested that the Heishan mafic-ultramafic intrusive rock (357 ± 4 Ma) along the northern margin of the Tarim Craton formed in an active continental margin setting.In summary, this paper posits that the PAO began southward subduction during the Late Devonian (377-360 Ma), leading to the formation of a post-arc basin.
(2) The Late Silurian tonalites are characterized by high SiO 2 and Na 2 O and low K 2 O, MgO, FeOT, and TiO 2 , with an A/CNK ratio of 0.91-1.00,and thus belong to the calcalkaline series, identified as I-type granite.They are enriched in Rb, Ba, Th, U, and K and depleted in Nb, Sr, P, and Ti, with positive ε Nd (t) (+0.35) and ε Hf (t) (+0.44 to +6.31) values, suggesting that they mainly originated from partial melting of Meso-Neoproterozoic era accretionary lower crustal material (basalt).The Middle Silurian basalts are characterized by low SiO 2 , P 2 O 5 , TiO 2, and Na 2 O and high Al 2 O 3 , FeOT, and K 2 O, enriched in Rb, Ba, Th, U, and K and depleted in Nb, Ta, Sr, P, and Ti, indicative of shoshonitic basalt.The Late Silurian tonalite has positive ε Nd (t) (+4.91 to +6.18) values and primarily originated from depleted mantle magmas metasomatized by subduction fluids, supplemented by a small amount of subducted sediments and crustal materials.The Middle-Late Silurian magmatic rocks formed in an active continental margin environment influenced by the southward subduction of the PAO.
(3) The Middle Devonian volcanic rocks exhibit low SiO 2 , TiO 2 , and Na 2 O and high K 2 O, and MgO and enriched in Rb, K, and LREEs and depleted in Nb, Ta, Sr, and HREEs, characteristic of shoshonitic volcanic rocks.ε Nd (t) (+2.11 to +3.77) and ε Hf (t) (+5.90 to +11.73) values are positive.These characteristics suggest that the Middle Devonian volcanic rocks primarily originated from depleted mantle magmas metasomatized by subduction fluids, with the addition of crustal materials or subducted sediments during their formation.The Middle Devonian magmatic rocks formed in an extensional environment after the arc-continent collision.

Supplementary Materials:
The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/min14070641/s1,Table S1.LA-ICP-MS zircon U-Pb data of samples from the Yitong Area; Table S2.Major element (wt.%), and trace elements (ppm) compositions of samples from the Yitong Area; Table S3.Lu-Hf isotopic compositions of zircons from the Yitong area; Table S4.Sr-Nd isotopic compositions of samples from the Yitong area.

Figure 1 .
Figure 1.(a) Tectonic division of the Central Asian Orogenic Belt and adjacent regions (modified after [22]), and the position of Figure 1b (black color square); (b) Tectonic division of NE China (modified from[12]); (c) Geological sketch map of the Yitong area in Jilin Province (modified from[29]).

Figure 1 .
Figure 1.(a) Tectonic division of the Central Asian Orogenic Belt and adjacent regions (modified after [22]), and the position of Figure 1b (black color square); (b) Tectonic division of NE China (modified from[12]); (c) Geological sketch map of the Yitong area in Jilin Province (modified from[29]).

Figure 3 .
Figure 3. Representative CL images of zircons from the Middle Silurian-Middle Devonian magmatic rocks in the Yitong area.(a) CL image of zircons from sample D11.(b) CL image of zircons from sample DG075.(c) CL image of zircons from sample J1917.(d) CL image of zircons from sample PM07-12.The solid line circle is the Hf isotope analysis point; the dotted line circle is the U-Pb age analysis point.The numbers show the ages of the zircons (Ma) and the εHf(t) values.

Figure 3 .
Figure 3. Representative CL images of zircons from the Middle Silurian-Middle Devonian magmatic rocks in the Yitong area.(a) CL image of zircons from sample D11.(b) CL image of zircons from sample DG075.(c) CL image of zircons from sample J1917.(d) CL image of zircons from sample PM07-12.The solid line circle is the Hf isotope analysis point; the dotted line circle is the U-Pb age analysis point.The numbers show the ages of the zircons (Ma) and the ε Hf (t) values.

Figure 4 .
Figure 4. Zircon U-Pb concordia diagrams from the Middle Silurian-Middle Devonian magmatic rocks in the Yitong area.(a) Zircon U-Pb concordia diagrams from sample D11.(b) Zircon U-Pb concordia diagrams from sample DG075.(c) Zircon U-Pb concordia diagrams from sample J1917.(d) Zircon U-Pb concordia diagrams from sample PM07-12.Data-point error ellipses are 1 sigma.Age errors are 95% confidence.

Figure 4 .
Figure 4. Zircon U-Pb concordia diagrams from the Middle Silurian-Middle Devonian magmatic rocks in the Yitong area.(a) Zircon U-Pb concordia diagrams from sample D11.(b) Zircon U-Pb concordia diagrams from sample DG075.(c) Zircon U-Pb concordia diagrams from sample J1917.(d) Zircon U-Pb concordia diagrams from sample PM07-12.Data-point error ellipses are 1 sigma.Age errors are 95% confidence.

Figure 6 .
Figure 6.Chondrite-normalized REE patterns (a,c) (normalizing values after Boynton [83]), and primitive-mantle-normalized trace element spider diagrams (b,d) (normalizing values after Sun and Mc Donough [84]) for the Middle Silurian-Middle Devonian magmatic rocks in the Yitong area.The K 2 O/Na 2 O ratios of the Middle Devonian metamorphic olivine-bearing basalt (PM07-12) samples are 13.25-24.14,indicating that they are enriched in K and depleted in Na.According to the (Al + Fe + Ti) vs. (Ca + Mg) diagram (Figure5f), the samples predominantly classify within the regions of basalt and basaltic andesite volcanic rocks, suggesting that the protolith was an intermediate to mafic volcanic rock.Their A/CNK ratios range from 0.84 to 1.07, showing metaluminous-weakly peraluminous signatures.The andesite samples plot in the shoshonite series field (Figure5d) and in the sub-alkaline basalt and andesite regions on the SiO 2 vs. Nb/Y and Zr/TiO 2 vs. Nb/Y diagrams (Figure5b,c).The samples have relatively lower REE contents (93.52-106.89ppm), exhibiting LREE enrichment (La N /Yb N = 9.77-10.23)with positive Eu anomalies (Eu/Eu* = 1.12-2.12)and no Ce anomalies (Ce/Ce* = 0.92-1.02)(Figure6c).The trace element spider plot illustrates that the samples are relatively enriched in Rb and K and depleted in Ba, Th, U, Nb, Ta, Sr, P, Ti, and HREEs (Figure6d).

Figure 8 .
Figure 8. Distribution of Paleozoic magmatic rocks and strata from the Faku-Yanji area in the eastern segment of the northern margin of the NCC [17,29,89-91].
. The ε Nd (t) vs.I sr diagram (Figure 9d) indicates that the magmas are composed of approximately 70-75% basalt and 25-30% lower continental crust.The ε Nd (t) value of tonalite is +0.35, with a two-stage model age of 1138 Ma, and zircon ε Hf (t) values ranging from +0.44 to +6.31, with a two-stage model age ranging from 1005.0 to 1379.5 Ma.These characteristics indicate that the tonalite predominantly originated from partial melting of Mesoproterozoic accreted lower crustal material (basalt), and magma ascent was accompanied by contamination with lower crustal material.Minerals 2024, 14, 641 14 of 27 Th content (3.63-9.13ppm) and Th/Yb ratios (0.56-1.05), implying that slab-derived fluids primarily influenced the source of these Late Silurian magmatic rocks [102], with lesser contributions from sediments or melts.The Rb/Ba vs. Rb/Sr diagram (Figure 9c) shows that the source material for the tonalite is predominantly basalt.The εNd(t) vs. Isr diagram (Figure 9d) indicates that the magmas are composed of approximately 70-75% basalt and 25-30% lower continental crust.The εNd(t) value of tonalite is +0.35, with a two-stage model age of 1138 Ma, and zircon εHf(t) values ranging from +0.44 to +6.31, with a twostage model age ranging from 1005.0 to 1379.5 Ma.These characteristics indicate that the tonalite predominantly originated from partial melting of Mesoproterozoic accreted lower crustal material (basalt), and magma ascent was accompanied by contamination with lower crustal material.

Minerals 2024 ,
14, 641 17 of 27affinity with a mature continental arc.Furthermore, the Early Devonian rhyolitic tuff (404 ± 4.5 Ma) in the study area, showing the features of typical A2-type granite, formed in a post-collisional extension setting[29].In the La/Sm vs. Sm/Yb diagram (Figure11), the Middle Silurian and Middle Devonian volcanic rock samples can be derived from spinelgarnet lherzolite (Figure11), with degrees of partial melting ranging from 1 to 5%, and magma source depths estimated between 60 and 80 km[131].The Middle Silurian volcanic rocks can be derived from spinel lherzolite, whereas the Middle Devonian rocks are more likely derived from spinel-garnet lherzolite (spinel:garnet = 1:1), suggesting an increase in crustal thickness during the Middle Devonian.The collision of the Late Silurian Bainaimiao arc with the NCC led to the subsequent formation of a series of alkaline series magmatic rocks[31,86,[132][133][134][135][136][137][138].Combined with the Middle Devonian magmatic rocks in the northern Liaoning Province to central Jiling Province having characteristics of I-and A-type granites[43], this suggests that the study area was an extensional environment after the arc-continent collision during the Middle Devonian period.

Figure 11 .
Figure 11.La/Sm-Sm/Yb diagram [141,142] for the Middle Silurian and Middle Devonian magmatic rocks in the Yitong area.

Figure 11 .
Figure 11.La/Sm-Sm/Yb diagram [141,142] for the Middle Silurian and Middle Devonian magmatic rocks in the Yitong area.

5. 4 .
Silurian-Devonian Tectonic-Magmatic Evolution in the Eastern Section of the Northern Margin of the NCC Based on previous studies and the division of tectonic evolution, the magmatic and tectonic progression of the eastern section of the northern margin of the NCC from the Silurian to Devonian can be delineated into four primary stages: 5.4.1.Active Continental Margin (443-419 Ma)

Author Contributions:
Methodology, B.L.; Investigation, B.L., F.Y., M.L., Y.Z. and C.Z.; Data curation, B.L.; Writing-original draft, B.L. and J.C., Writing-review & editing, B.L. and J.C.All authors have read and agreed to the published version of the manuscript.Funding: This research was funded by the China Geological Survey (Grants DD20242929, DD20230210, and DD20190042-04) and the funding project of Northeast Geological S&T Innovation Center of China Geological Survey (NO.QCJJ2022-42).

Table 2 .
Geochronological data for the Silurian-Devonian magmatic rocks in the eastern segment of the northern margin of the NCC.

Table 2 .
Geochronological data for the Silurian-Devonian magmatic rocks in the eastern segment of the northern margin of the NCC.