Late Paleozoic Tectonic Evolution of the Northern Great Xing’an Range, Northeast China: Constraints from Carboniferous Magmatic Rocks in the Wunuer Area

Northeast China composes the main part of the Central Asian Orogenic Belt. Traditionally, Northeast China has been considered a collage of several microcontinental blocks. However, the tectonic evolution of these blocks remains uncertain. Igneous rocks can be used to infer the magmatic histories of the blocks and thus help reconstruct their evolution. In this study, we present new zircon U–Pb and whole-rock geochemical data for Carboniferous igneous rocks from the Wunuer area, northern Great Xing’an Range, Northeast China, to constrain the Carboniferous amalgamation of the united Xing’an–Erguna and Songnen–Zhangguangcai Range massifs. On the basis of zircon U–Pb dating results, we identify two main stages of magmatism, i.e., early Carboniferous (332–329 Ma) and late Carboniferous (312–310 Ma). The early Carboniferous igneous rocks include diorites and granodiorites, with the former being classified as calc-alkaline to tholeiitic and the latter as tholeiitic. Both rock types are enriched in Th and U and depleted in Nb and Ti. The rocks display slightly fractionated rare earth element (REE) patterns, with an enrichment in light REEs and a depletion in heavy (H)REEs. The geochemical characteristics of the early Carboniferous rocks indicate that they formed in a subduction-related continental-arc setting. The late Carboniferous igneous rocks include monzogranites and syenogranites, both of which are classified as high-K calc-alkaline rocks and show enrichment in Th, U, and Rb and depletion in Nb and Ti. The rocks display strongly fractionated REE patterns, with an enrichment in light REEs and a depletion in HREEs. The geochemical characteristics of the late Carboniferous rocks indicate that they formed in a syn-collisional tectonic setting. Combining the new geochronological and geochemical results and inferred tectonic settings with regional magmatic data, we propose a new three-stage model to interpret the late Paleozoic tectonic evolution of the united Xing’an–Erguna and Songnen–Zhangguangcai Range massifs of Northeast China: (1) early Carboniferous (360–340 Ma) subduction of the Paleo-Asian oceanic plate beneath the united Xing’an–Erguna Massif and formation of the Wunuer oceanic basin in the Yakeshi area; (2) early to late Carboniferous (340–310 Ma) sustained subduction of the Paleo-Asian oceanic plate beneath the united Xing’an–Erguna Massif and initiation of subduction of the Wunuer oceanic basin; and (3) late Carboniferous–early Permian (310–275 Ma) syn-collisional to post-collisional tectonic transition between the united Xing’an–Erguna Massif and the Songnen–Zhangguangcai


Introduction
The Central Asian Orogenic Belt (CAOB) is one of the largest Phanerozoic accretionary orogens in the world (Figure 1). This belt is bounded by the Siberian Craton to the north
Uncertainty remains regarding the subduction of paleo-oceanic plates in Northeast China and how and when the amalgamation between the abovementioned blocks/ microcontinents took place, especially in regard to the evolution of the Xinlin-Xiguitu suture zone. This suture zone contains the Xinlin ophiolites, Tayuan metagabbros, Jifeng ophiolites, and Yimin blueschists [43][44][45][46][47][48][49][50][51]. Geochronological data for these units include a K-Ar phlogopite age for the Xinlin ophiolite of 539 Ma [43], a U-Pb zircon age for the Gaxian pyroxenite of 628.4 ± 9.7 Ma [52], a U-Pb zircon age for meta-gabbro from the Huanerku area of 696.8 ± 2.9 Ma [51], a U-Pb zircon age for gabbro from the Jifeng area of 647 ± 5 Ma, and a U-Pb zircon age of greenschist from the Toudaoqiao area of 511 ± 2 Ma.
Early Paleozoic post-orogenic A-type granites reported from the Tahe area are regarded as a product of the closure of the Xinlin-Xiguitu suture zone caused by the collision of the Erguna and Xing'an blocks [24]. The Wunuer ophiolitic mélange occurs in the southwest of the Xinlin-Xiguitu suture zone. This ophiolitic mélange comprises gabbro, diabase, metabasalt, and radiolarian bedded chert with serpentinized amphibole-pyroxene peridotites. Zircon U-Pb dating of the gabbro and diabase has yielded ages of 341 ± 6 and 346 ± 6 Ma, respectively, which suggest that the ophiolite formed during the early Carboniferous. The ophiolite is classified as SSZ type according to geochemical characteristics and may be a late product of a mature back-arc basin tectonic setting [53]. The Xinlin-Xiguitu oceanic basin is generally considered to have closed during the late Cambrian [5][6][7][8]24,33,41,50,54]. However, the recent discovery of the early Carboniferous Wunuer ophiolite suggests that the Xinlin-Xiguitu oceanic basin may have closed later than previously thought and that the late Paleozoic tectonic evolution of Northeast China needs to be reassessed.
In this study, we present zircon U-Pb and whole-rock geochemical data for Carboniferous igneous rocks from the Wunuer area, northern Great Xing'an Range, Northeast China, to reconstruct the tectonic evolution of this area during the late Paleozoic, including the opening (by subduction initiation) and closure (by collision) of the Wunuer Ocean. The integration of the new results with previous data allows us to reconstruct the late Paleozoic tectonic evolution of Northeast China. Jifeng area of 647 ± 5 Ma, and a U-Pb zircon age of greenschist from the Toudaoqiao area of 511 ± 2 Ma. Early Paleozoic post-orogenic A-type granites reported from the Tahe area are regarded as a product of the closure of the Xinlin-Xiguitu suture zone caused by the collision of the Erguna and Xing'an blocks [24]. The Wunuer ophiolitic mélange occurs in the southwest of the Xinlin-Xiguitu suture zone. This ophiolitic mélange comprises gabbro, diabase, metabasalt, and radiolarian bedded chert with serpentinized amphibole-pyroxene peridotites. Zircon U-Pb dating of the gabbro and diabase has yielded ages of 341 ± 6 and 346 ± 6 Ma, respectively, which suggest that the ophiolite formed during the early Carboniferous. The ophiolite is classified as SSZ type according to geochemical characteristics and may be a late product of a mature back-arc basin tectonic setting [53]. The Xinlin-Xiguitu oceanic basin is generally considered to have closed during the late Cambrian [5][6][7][8]24,33,41,50,54]. However, the recent discovery of the early Carboniferous Wunuer ophiolite suggests that the Xinlin-Xiguitu oceanic basin may have closed later than previously thought and that the late Paleozoic tectonic evolution of Northeast China needs to be reassessed.
In this study, we present zircon U-Pb and whole-rock geochemical data for Carboniferous igneous rocks from the Wunuer area, northern Great Xing'an Range, Northeast China, to reconstruct the tectonic evolution of this area during the late Paleozoic, including the opening (by subduction initiation) and closure (by collision) of the Wunuer Ocean. The integration of the new results with previous data allows us to reconstruct the late Paleozoic tectonic evolution of Northeast China.  [50]). Date from [33,43,[50][51][52][53]].

Geological Setting and Sample Descriptions
The study area is in the vicinity of Wunuer town, Yakeshi City, in the northern Great Xing'an Range of Inner Mongolia. Tectonically, the study area is located in the Xinlin-Xiguitu suture zone ( Figure 2). Ordovician outcrops in the area are composed mainly of the Duobaoshan and Luohe formations. The Duobaoshan Formation comprises a set of intermediate-felsic volcanic rocks with island-arc characteristics [54,55], whereas the  [50]). Date from [33,43,[50][51][52][53]].

Geological Setting and Sample Descriptions
The study area is in the vicinity of Wunuer town, Yakeshi City, in the northern Great Xing'an Range of Inner Mongolia. Tectonically, the study area is located in the Xinlin-Xiguitu suture zone ( Figure 2). Ordovician outcrops in the area are composed mainly of the Duobaoshan and Luohe formations. The Duobaoshan Formation comprises a set of intermediate-felsic volcanic rocks with island-arc characteristics [54,55], whereas the Luohe Formation is a set of clastic rocks that formed in an active-continental-margin setting [56,57].
Silurian strata are absent from the study area. Exposed Devonian strata are mainly the Niqiuhe and Daminshan formations, with the former comprising a set of continentalmargin clastic rocks [58] and the latter a set of intermediate-felsic volcanic rocks with island-arc characteristics [59]. A large number of late Paleozoic intrusive rocks occur in the study area, including diorite, granodiorite, monzogranite, and syenogranite [60,61], which are emplaced into Ordovician or Devonian strata and overlain by Mesozoic volcanic rocks and Quaternary cover ( Figure 3). accessory minerals (~3 vol.%) including magnetite, zircon, and apatite.

Analytical Methods
One sample for zircon geochronological analysis (U-Pb2071001) and eight samples for geochemical analysis were collected from the diorite pluton. One sample for zircon geochronological analysis (U-Pb2071003) and four samples for geochemical analysis were obtained from the granodiorite pluton. One sample for zircon geochronological analysis (U-Pb2072001) and two samples for geochemical analysis were collected from the monzogranite pluton. One sample for zircon geochronological analysis (U-Pb2071005) and seven samples for geochemical analysis were obtained from the syenogranite pluton.

Zircon U-Pb Dating
Zircons were separated from samples using conventional heavy liquid and magnetic techniques. Zircon grains were then randomly handpicked in alcohol under a binocular microscope, mounted in epoxy along with zircon standards, and polished to expose grain centers for cathodoluminescence (CL) imaging and U-Pb analysis. CL images were obtained at Beijing Geoanalysis Co., Ltd., Beijing, China. U-Pb analysis was performed by laser-ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) at Beijing Createch Testing Technology Co., Ltd., Beijing, China. The analytical instruments used for the dating were a ThermoFisher Neptune multi-receiver ICP-MS instrument and an SIUP193FXArF LA system. The operating conditions during analyses included a laser denudation spot diameter of 35 µm, a laser energy density of 10-13 J/cm 2 , and a frequency of 8-10 Hz. Age data were plotted using Isoplot [62].

Major and Trace Elements
Whole-rock geochemical analyses were performed at the Analytical Laboratory of Beijing Research Institute of Uranium Geology, Beijing, China. Major elements (SiO2,

Analytical Methods
One sample for zircon geochronological analysis (U-Pb2071001) and eight samples for geochemical analysis were collected from the diorite pluton. One sample for zircon geochronological analysis (U-Pb2071003) and four samples for geochemical analysis were obtained from the granodiorite pluton. One sample for zircon geochronological analysis (U-Pb2072001) and two samples for geochemical analysis were collected from the monzogranite pluton. One sample for zircon geochronological analysis (U-Pb2071005) and seven samples for geochemical analysis were obtained from the syenogranite pluton.

Zircon U-Pb Dating
Zircons were separated from samples using conventional heavy liquid and magnetic techniques. Zircon grains were then randomly handpicked in alcohol under a binocular microscope, mounted in epoxy along with zircon standards, and polished to expose grain centers for cathodoluminescence (CL) imaging and U-Pb analysis. CL images were obtained at Beijing Geoanalysis Co., Ltd., Beijing, China. U-Pb analysis was performed by laser-ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) at Beijing Createch Testing Technology Co., Ltd., Beijing, China. The analytical instruments used for the dating were a ThermoFisher Neptune multi-receiver ICP-MS instrument and an SIUP193FXArF LA system. The operating conditions during analyses included a laser denudation spot diameter of 35 µm, a laser energy density of 10-13 J/cm 2 , and a frequency of 8-10 Hz. Age data were plotted using Isoplot [62].

Major and Trace Elements
Whole-rock geochemical analyses were performed at the Analytical Laboratory of Beijing Research Institute of Uranium Geology, Beijing, China. Major elements (SiO 2 , FeO, TiO 2 , Al 2 O 3 , Fe 2 O 3 , MgO, MnO, CaO, Na 2 O, K 2 O, and P 2 O 5 ) were analyzed using an AxiosmAX X-ray fluorescence spectrometer, with an analytical precision of approximately ±5%. Trace elements and rare earth elements (REEs) were analyzed using a NexION300D ICP-MS instrument, with an accuracy better than 10%.  Table S1 and Figure 6a), which is interpreted as the crystallization age of the zircons. The emplacement age of the diorite pluton is therefore inferred to be early Carboniferous.

Zircon U-Pb
Zircons from the sampled granodiorite are predominantly dark and subhedral, and some display oscillatory zoning in CL images (Figure 5b). The Th/U ratios of the zircons range from 1.04 to 2.68, consistent with a magmatic origin. Analyses of zircons from sample U-Pb2071003 yielded 206Pb/238U ages of 350-322 Ma, with a weighted mean age of 332.6 ± 6.9 Ma (MSWD = 3.1, N = 11; Table S1 and Figure 6b), which is interpreted as the crystallization age of the zircons. The emplacement age of the granodiorite pluton is therefore inferred to be early Carboniferous.

Late Carboniferous Intrusive Rocks
Most zircon grains from the sampled monzogranite are subhedral and display oscillatory zoning in CL images (Figure 5c) with Th/U ratios of 0.63-1.24, indicating a magmatic origin. Analyses of zircons from sample U-Pb2072001 yielded 206Pb/238U ages of 321-308 Ma, with a weighted mean age of 310.8 ± 4.7 Ma (MSWD = 0.26, N = 10; Table S1 and Figure  6c), which is interpreted as the crystallization age of the zircons. The emplacement age of the monzogranite pluton is therefore inferred to be late Carboniferous.
Zircons from the sampled syenogranite are predominantly subhedral, display oscillatory zoning in CL images (Figure 5d), and have Th/U ratios of 0.63-1.19, indicating a magmatic origin. Analyses of zircons from sample U-Pb2071005 yielded 206Pb/238U ages of 331-293 Ma, with a weighted mean age of 312.1 ± 9.4 Ma (MSWD = 4.2, N = 8; Table S1 and Figure 6d), which is interpreted as the crystallization age of the zircons. The emplacement age of the syenogranite pluton is therefore inferred to be late Carboniferous.   Zircons from the sampled granodiorite are predominantly dark and subhedral, and some display oscillatory zoning in CL images (Figure 5b). The Th/U ratios of the zircons range from 1.04 to 2.68, consistent with a magmatic origin. Analyses of zircons from sample U-Pb2071003 yielded 206Pb/238U ages of 350-322 Ma, with a weighted mean age of 332.6 ± 6.9 Ma (MSWD = 3.1, N = 11; Table S1 and Figure 6b), which is interpreted as the crystallization age of the zircons. The emplacement age of the granodiorite pluton is therefore inferred to be early Carboniferous.

Late Carboniferous Intrusive Rocks
Most zircon grains from the sampled monzogranite are subhedral and display oscillatory zoning in CL images (Figure 5c) with Th/U ratios of 0.63-1.24, indicating a magmatic origin. Analyses of zircons from sample U-Pb2072001 yielded 206Pb/238U ages of 321-308 Ma, with a weighted mean age of 310.8 ± 4.7 Ma (MSWD = 0.26, N = 10; Table S1 and Figure 6c), which is interpreted as the crystallization age of the zircons. The emplacement age of the monzogranite pluton is therefore inferred to be late Carboniferous.
Zircons from the sampled syenogranite are predominantly subhedral, display oscillatory zoning in CL images (  Table S1 and Figure 6d), which is interpreted as the crystallization age of the zircons. The emplacement age of the syenogranite pluton is therefore inferred to be late Carboniferous.

Trace Element Compositions
The sampled diorites are relatively enriched in Th and U and depleted in so high-field-strength elements (HFSEs; e.g., Nb and Ti). The rocks display slightly fr tionated REE patterns between light REEs (LREEs) and heavy REEs    (Table 1). These samples are classified as granites in a TAS diagram (Figure 7a), are peraluminous with A/CNK values of 1.14-1. 16 (Table 1 and Table 1). These samples are classified as granites in a TAS diagram (Figure 7a), are peraluminous with A/CNK values of 1.03-1.12 (Table 1 and Figure 7b), and are classified as high-K calc-alkaline in a K 2 O vs. SiO 2 diagram (Figure 7c).
The sampled granodiorites are relatively enriched in Th and U and depleted in some HFSEs (e.g., Nb and Ti).

Carboniferous Intrusive Rocks in the Great Xing'an Range
According to our geochronological analyses, the studied diorite and granodiorite were emplaced during the early Carboniferous, and the syenogranite and monzogranite were emplaced during the late Carboniferous. There are widespread occurrences of coeval magmatic rocks in the Great Xing'an Range. Most of the early Carboniferous intrusive rocks are distributed in a strip along the Xinlin-Xiguitu and Hegenshan suture zones ( Figure 9). The late Carboniferous intrusive rocks have a wider distribution, occurring mainly in the Yakeshi, Duobaoshan, Zhalantun, Heihe, and Wudalianchi areas.

Carboniferous Intrusive Rocks in the Great Xing'an Range
According to our geochronological analyses, the studied diorite and granodiorite were emplaced during the early Carboniferous, and the syenogranite and monzogranite were emplaced during the late Carboniferous. There are widespread occurrences of coeval magmatic rocks in the Great Xing'an Range. Most of the early Carboniferous intrusive rocks are distributed in a strip along the Xinlin-Xiguitu and Hegenshan suture zones (Figure 9). The late Carboniferous intrusive rocks have a wider distribution, occurring mainly in the Yakeshi, Duobaoshan, Zhalantun, Heihe, and Wudalianchi areas.  Early Carboniferous igneous rocks in the Wunuer area comprise diorite and granodiorite. These rocks contain hornblende and biotite but no primary muscovite. The

Petrogenesis of the Wunuer Early Carboniferous Igneous Rocks
Early Carboniferous igneous rocks in the Wunuer area comprise diorite and granodiorite. These rocks contain hornblende and biotite but no primary muscovite. The mineral assemblages are consistent with those of I-type granites [74][75][76][77][78][79]. A/CNK values (0.75-0.95) classify the diorites and granodiorites as metaluminous rocks. The rocks are characterized by relatively high Al 2 O 3 , Fe, Mg, and Sr and low Si and K contents, the enrichment in LILEs and LREEs, and the depletion in HREEs. The granodiorites plot in the I-type and S-type granite fields in the Nb-(10,000 Ga/Al), Ce-(10,000 Ga/Al), and Y-(10,000 Ga/Al) diagrams (Figure 10a-c) and mainly in the I-type granite field in an ACF diagram (Figure 10d).
The average value of Rb/Sr for the diorite and granodiorite is 0.04, which is close to the primitive mantle (0.03), E-MORB (0.033), and OIB (0.047) [80], but lower than the crustal ratio (0.15). These geochemical characteristics suggest that the diorite and granodiorite are sourced from partial malting of the mantle.

Inferred Tectonic Settings
The geochemical characteristics of the diorites and granodiorites (Section 4.2) are consistent with formation in a subduction-related continental-arc setting, and those of the monzogranites and syenogranites suggest formation in a syn-collisional tectonic setting. The granodiorites plot in the volcanic arc fields in Rb-(Y + Nb) and Rb-(Yb + Ta) diagrams (Figure 11a,b) and mostly in the volcanic arc fields in Rb/10-Hf-3Ta and Rb/30-Hf-3Ta diagrams (Figure 11c,d). The syenogranites and monzogranites fall predominantly in the syn-collisional fields in Rb-(Y + Nb) and Rb-(Yb + Ta) diagrams ( Figure  11a,b) and in the syn-collisional fields in Rb/10-Hf-3Ta and Rb/30-Hf-3Ta diagrams (Figure 11c,d).

Petrogenesis of the Wunuer Late Carboniferous Igneous Rocks
Late Carboniferous igneous rocks in the Wunuer area comprise monzogranite and syenogranite. These rocks are composed predominantly of quartz, K-feldspar, and plagioclase. A/CNK values (1.03-1.16) classify the monzogranites and syenogranites as peraluminous rocks. The rocks are characterized by relatively high SiO 2 and K 2 O and low P 2 O 5 contents, the enrichment in Rb, Th, and U, and the depletion in Ba, Nb, Ta, Sr, P, and Ti. These characteristics are consistent with those of S-type granites. The monzogranites and syenogranites plot in the I-type and S-type granite fields in Nb-(10,000 Ga/Al), Ce-(10,000 Ga/Al), and Y-(10,000 Ga/Al) diagrams (Figure 10a-c) and mostly in the S-type granite field in an ACF diagram (Figure 10d).
The average value of Rb/Sr for the monzogranite and syenogranite is 2.53, which is close to the crustal ratio (0.15) but higher than the primitive mantle (0.03), E-MORB (0.033), and OIB (0.047) [80]. These geochemical characteristics suggest that the monzogranite and syenogranite are sourced from partial melting of the crust.

Inferred Tectonic Settings
The geochemical characteristics of the diorites and granodiorites (Section 4.2) are consistent with formation in a subduction-related continental-arc setting, and those of the monzogranites and syenogranites suggest formation in a syn-collisional tectonic setting. The granodiorites plot in the volcanic arc fields in Rb-(Y + Nb) and Rb-(Yb + Ta) diagrams (Figure 11a,b) and mostly in the volcanic arc fields in Rb/10-Hf-3Ta and Rb/30-Hf-3Ta diagrams (Figure 11c,d). The syenogranites and monzogranites fall predominantly in the syn-collisional fields in Rb-(Y + Nb) and Rb-(Yb + Ta) diagrams (Figure 11a,b) and in the syn-collisional fields in Rb/10-Hf-3Ta and Rb/30-Hf-3Ta diagrams (Figure 11c,d).

Tectonic Implications
The integrated results of this study, combined with regional geological data, allow a new model to be proposed for the late Paleozoic tectonic evolution of the northern Great Xing'an Range (Figure 12), as follows. During the early Carboniferous (360-340 Ma), subduction of the Paleo-Asian oceanic plate beneath the united Xing'an-Erguna Massif occurred, with the associated development of a back-arc ocean basin (the Wunuer oceanic basin). The early Carboniferous igneous rocks (360-340 Ma) display markedly different rock associations and geochemical characteristics from east to west across the Xing'an block. Igneous rocks in the east of the Xing'an block (the Heihe, Nenjiang, Zhalantun, and Moguqi areas) are composed of gabbro, gabbro diorite, monzogranite, and syenogranite and are classified as calc-alkaline, consistent with formation in a subduction-related setting [41,[85][86][87][88]. In contrast, ophiolites and gabbros in the west of the Xing'an block (the Wunuer area) are consistent with a back-arc ocean basin setting, for example, the age of the Wunuer ophiolitic mélange is 341~346 Ma; the Wunuer ophiolitic mélange is classified as SSZ type according to geochemical characteristics and may be a late product of a mature back-arc basin tectonic setting [53]. We suggest that early Carboniferous igneous rocks formed as a result of northwest-directed subduction of the Paleo-Asian oceanic plate, which was initiated during the late Devonian [66,89]. The continuous subduction of the Paleo-Asian oceanic slab generated a magmatic arc en- Figure 11. (a) Rb versus Y+Nb diagram (after [83]), (b) Rb versus Yb+Ta diagram (after [83]), (c) Rb/10-Hf-3Ta diagram (after [84]), (d) Rb/30-Hf-3Ta diagram (after [84]). VAG = volcanic arc granites, WPG = within plate granites, COLG = collisional granites, and ORG = oceanic ridge granites.

Tectonic Implications
The integrated results of this study, combined with regional geological data, allow a new model to be proposed for the late Paleozoic tectonic evolution of the northern Great Xing'an Range (Figure 12), as follows. During the early Carboniferous (360-340 Ma), subduction of the Paleo-Asian oceanic plate beneath the united Xing'an-Erguna Massif occurred, with the associated development of a back-arc ocean basin (the Wunuer oceanic basin). The early Carboniferous igneous rocks (360-340 Ma) display markedly different rock associations and geochemical characteristics from east to west across the Xing'an block. Igneous rocks in the east of the Xing'an block (the Heihe, Nenjiang, Zhalantun, and Moguqi areas) are composed of gabbro, gabbro diorite, monzogranite, and syenogranite and are classified as calc-alkaline, consistent with formation in a subduction-related setting [41,[85][86][87][88]. In contrast, ophiolites and gabbros in the west of the Xing'an block (the Wunuer area) are consistent with a back-arc ocean basin setting, for example, the age of the Wunuer ophiolitic mélange is 341~346 Ma; the Wunuer ophiolitic mélange is classified as SSZ type according to geochemical characteristics and may be a late product of a mature back-arc basin tectonic setting [53]. We suggest that early Carboniferous igneous rocks formed as a result of northwest-directed subduction of the Paleo-Asian oceanic plate, which was initiated during the late Devonian [66,89]. The continuous subduction of the Paleo-Asian oceanic slab generated a magmatic arc encompassing the Heihe, Nenjiang, Zhalantun, and Mogiqi areas, as well as the Wunuer back-arc oceanic basin in the Wunuer area [53,60,66,[90][91][92].
During the early-late Carboniferous (340-310 Ma), sustained subduction of the Paleo-Asian oceanic plate and subduction of the Wunuer oceanic basin occurred. Igneous rocks in the east of the Xing'an block (the Longzhen and Yaergenchu areas) are composed of granodiorite and monzogranite, which are classified as calc-alkaline series, implying formation in a subduction-related setting [93,94]. The diorite, granodiorite, monzogranite, and syenogranite in the west of the Xing'an block (Tahe, Taerqi, and Wunuer areas) formed in a subduction-related setting, indicating that the Wunuer oceanic basin had entered the subduction phase [28,52,95,96]. formed in a subduction-related setting, indicating that the Wunuer oceanic basin had entered the subduction phase [28,52,95,96]. The late Carboniferous-early Permian (310-275 Ma) was characterized by a syn-collisional to post-collisional tectonic setting between the united Xing'an-Erguna Massif and the Songnen-Zhangguangcai Range Massif. The widely distributed late early Carboniferous-early Permian igneous rocks in the northern Great Xing'an Range are composed mostly of syenogranite and monzogranite and signify a syn-collisional setting [61,67,96]. The occurrence of early Permian alkaline rocks implies a subsequent extensional tectonic environment in a post-collisional setting [52,67]. Therefore, we suggest that the late Carboniferous-early Permian igneous rocks formed in a syn-collisional to post-collisional transitional setting in the Wunuer and Taerqi areas [52,67,96] and in the Heihe, Duobaoshan, Nenjiang, and Zhalantun areas [28,67,68,97], implying that both the Wunuer Ocean and Paleo-Asian Ocean had closed.

Conclusions
We generated new zircon U-Pb and whole-rock geochemical data for Carboniferous igneous rocks from the Wunuer area, northern Great Xing'an Range, to reconstruct the late Paleozoic tectonic evolution of this area and, in combination with regional geological and geochronological data, to establish an integrated tectonic history of Northeast China. The main conclusions of this study are as follows: (1) Intrusive rocks in the Wunuer area include diorite, granodiorite, monzogranite, and syenogranite. The zircon U-Pb mean ages of the diorite and granodiorite are 329.7 ± 5.0 and 332.6 ± 6.9 Ma, respectively, indicating early Carboniferous emplacement of these The late Carboniferous-early Permian (310-275 Ma) was characterized by a syncollisional to post-collisional tectonic setting between the united Xing'an-Erguna Massif and the Songnen-Zhangguangcai Range Massif. The widely distributed late early Carboniferous-early Permian igneous rocks in the northern Great Xing'an Range are composed mostly of syenogranite and monzogranite and signify a syn-collisional setting [61,67,96]. The occurrence of early Permian alkaline rocks implies a subsequent extensional tectonic environment in a post-collisional setting [52,67]. Therefore, we suggest that the late Carboniferous-early Permian igneous rocks formed in a syn-collisional to post-collisional transitional setting in the Wunuer and Taerqi areas [52,67,96] and in the Heihe, Duobaoshan, Nenjiang, and Zhalantun areas [28,67,68,97], implying that both the Wunuer Ocean and Paleo-Asian Ocean had closed.

Conclusions
We generated new zircon U-Pb and whole-rock geochemical data for Carboniferous igneous rocks from the Wunuer area, northern Great Xing'an Range, to reconstruct the late Paleozoic tectonic evolution of this area and, in combination with regional geological and geochronological data, to establish an integrated tectonic history of Northeast China. The main conclusions of this study are as follows: (1) Intrusive rocks in the Wunuer area include diorite, granodiorite, monzogranite, and syenogranite. The zircon U-Pb mean ages of the diorite and granodiorite are 329.7 ± 5.0 and 332.6 ± 6.9 Ma, respectively, indicating early Carboniferous emplacement of these rocks. The zircon U-Pb mean ages of the monzogranite and syenogranite are 310.8 ± 4.7 and 312.1 ± 9.4 Ma, respectively, indicating late Carboniferous emplacement.
(2) The geochemical signatures of the Wunuer rocks indicate that the diorite and granodiorite formed in a subduction-related continental-arc setting and that the syenogranite and monzogranite formed in a syn-collisional tectonic setting. (