Neoproterozoic Magmatic Records in the North Beishan Orogenic Belt: Evidence of the Gneissic Granites from the Hazhu Area, Inner Mongolia

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The Beishan orogenic belt is located in the middle of the Central Asian orogenic belt (CAOB) and the tectonic history of its Precambrian basement rocks is the key to understand the formation and evolution of the Beishan orogenic belt. In this study, we select the gneissic granites in the North Beishan orogenic belt (NBOB) for zircon U-Pb chronology and geochemical analysis. The results show that the gneissic granites formed in the 885±4 Ma, which reveals the Neoproterozoic magmatic events in the NBOB for the first time. The gneissic granites belong to the peraluminous, high-K, calc-alkaline series and are characterized by high SiO 2 and K 2 O+Na 2 O, low CaO. The gneissic granites show an enrichment of light rare earth elements (LREE) with Europium negative anomaly and are characterized by enrichment of large ion lithophile elements (LILE) such as Rb, K, Th, U, but depletion in high field strength elements (HFSE) such as Nb, Sr, P, Ti. The petrography and geochemical signatures reveal a possible S-type granite affinity and are derived from the partial melting of metamorphic complex sandstone of source area with initial melt temperature (777-798 ℃). The gneissic granites were likely generated in a continental collision tectonic setting. By comparing our new data with previous results from the Precambrian basement in the South Beishan orogenic belt and the Tianshan block (microcontinent in the Chinese Tianshan), we suggest that the Precambrian microcontinents in the northern Beishan have similar crustal evolutionary history to the South Beishan orogenic belt (SBOB) and Central Tianshan block. They participated in the Rodinia supercontinent aggregation together and formed a part of Rodinia during the Neoproterozoic period. The Neoproterozoic magmatic events in the Beishan area are the response of the Rodinia supercontinent aggregation. © 2019, Editorial Department of Earth Science. All right reserved.

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... Neoproterozoic granitic gneisses (1024-867 Ma) mostly occur in the southern portion of the Beishan orogen (e.g., Liu, et al., 2015;Yuan et al., 2015;Wang et al., 2017a;Soldner et al., 2020a;Wang et al., 2021b), whereas a ca. 885 Ma granitic gneiss is documented in the Hazhu area in the northern portion of the Beishan orogen (Figs. 2 and 14B; Table S3) (Niu et al., 2019). Here, according to the distribution of Proterozoic granitoids Table S3 (see text footnote 1). ...
... in the Beishan orogen (Fig. 14B), we divide the Beishan orogen into southern and northern parts along the Hongliuhe-Xichangjing tectonic zone. The geochemical composition of Neoproterozoic granitoids in the Beishan orogen suggest petrogenesis from reworked ancient crust during the assembly of Rodinia (Niu et al., 2019;Soldner et al., 2020a;Wang et al., 2021b). Cambrian-Silurian arc magmatic rocks (525-430 Ma) (e.g., Song et al., 2013b;Hu et al., 2015;Xiu et al., 2018;Yuan et al., 2018;Zhuan et al., 2018;Li et al., 2020a;Lv et al., 2021) and Silurian-Devonian syn/postorogenic granitoids (430-395 Ma) (e.g., Zheng et al., 2012;Ding et al., 2015;Wang et al., 2018b;Zhang et al., 2018a;Bai et al., 2020;Li et al., 2020a) only occur north of the Hongliuhe-Xichangjing tectonic zone, suggesting the existence of a north-dipping early Paleozoic subduction zone along the Hongliuhe-Xichangjing tectonic zone (Figs. ...
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The Beishan orogen is part of the Neoproterozoic to early Mesozoic Central Asian Orogenic System in central Asia that exposes ophiolitic complexes, passive-margin strata, arc assemblages, and Precambrian basement rocks. To better constrain the tectonic evolution of the Beishan orogen, we conducted field mapping, U-Pb zircon dating, whole-rock geochemical analysis, and Sr-Nd isotopic analysis. The new results, when interpreted in the context of the known geological setting, show that the Beishan region had experienced five phases of arc magmatism at ca. 1450–1395 Ma, ca. 1071–867 Ma, ca. 542–395 Ma, ca. 468–212 Ma, and ca. 307–212 Ma. In order to explain the geological, geochemical, and geochronological data from the Beishan region, we present a tectonic model that involves the following five phases of deformation: (1) Proterozoic rifting that separated the North Beishan block from the Greater North China craton that led to the opening of the Beishan Ocean, (2) early Paleozoic north-dipping subduction (ca. 530–430 Ma) of the Beishan oceanic plate associated with back-arc extension followed by collision between the North and South Beishan microcontinental blocks, (3) northward slab rollback of the south-dipping subducting Paleo-Asian oceanic plate at ca. 450-440 Ma along the northern margin of the North Beishan block that led to the formation of a northward-younging extensional continental arc (ca. 470–280 Ma) associated with bimodal igneous activity, which indicates that the westward extension of the Solonker suture is located north of the Hongshishan-Pengboshan tectonic zone, (4) Late Carboniferous opening and Permian north-dipping subduction of the Liuyuan Ocean in the southern Beishan orogen, and (5) Mesozoic-Cenozoic intracontinental deformation induced by the final closure of the Paleo-Asian Ocean system in the north and the Tethyan Ocean system in the south.
... In the Shuangyingshan-Huaniushan Terrane, current reported Precambrian rocks are the Gubaoquan granitic and mafic rocks (905-865 Ma; Mei et al., 1999;Ye et al., 2013;Liu et al., 2015;Yuan et al., 2015;Saktura et al., 2017;Soldner et al., 2019). In the Heiyingshan-Hanshan Terrane, the Xiaohuangshan gneissic granite (713 ± 6 Ma; Ao et al., 2016) and the Hazhu gneissic granite (885 ± 4 Ma; Niu et al., 2019) were reported. Instead, Song et al., 2013aSong et al., , 2013bSong et al., , 2013c reported new zircon U-Pb age data for orthogneisses and mylonitized granites of the Beishan complex in the Hongshishan and Mazongshan areas, indicative of crystallization ages of 525-300 Ma. ...
... In addition, the coeval Baidunzi orthogneiss also has Al-rich minerals (garnet and muscovite; Jiang et al., 2013), which suggests that its protolith is an S-type granite, and a coeval S-type origin of the Hazhu granitic gneiss was proposed by Niu et al. (2019) on the basis of bulkrock major-and trace-elements. A metamorphic event at ~ 900 Ma (Zong et al., 2017) with synchronous reworking of crust (He et al., 2018;Jiang et al., 2013;Liu et al., 2015;Ye et al., 2013;Yuan et al., 2015; this study) has been suggested, both of which would have generated the geological conditions necessary for the formation of S-type granites in the Beishan Orogenic Belt. ...
The distribution of Precambrian rocks and microcontinents is a key to understanding the architecture of the Beishan Orogenic Belt, southern Central Asian Orogenic Belt (CAOB). We present zircon U-Pb-Hf isotopic and whole-rock geochemical data for early Neoproterozoic granitic rocks from the eastern Shuangyingshan–Huaniushan Terrane in the Beishan Orogenic Belt. The zircon ages show that the granitic gneiss, the mylonitized granite, and the mylonitized monzonite formed at 895 Ma, 894 Ma, and 884 Ma, respectively. These ages confirm that the Shuangyingshan–Huaniushan Terrane is a microcontinental block and that Precambrian magmatic rocks are not restricted to the western Gubaoquan area. Both the gneiss and granite contain Al-rich muscovite, high SiO2 (69.59–78.10 wt%) contents, and show peraluminous features (molar Al2O3/(CaO + Na2O + K2O) values = 1.03–1.28), negative correlations of Th and Y with respect to Rb, typical features of S-type granites. The monzonite contains hornblende, and relatively low SiO2 (62.11–64.10 wt%), high CaO (5.33–5.41 wt%), Na2O (5.88–6.02 wt%), V and Cr contents, and low K2O/Na2O, Rb/Sr and Rb/Ba ratios, consistent with I-type granites. These studied granitic rocks are calc-alkaline to shoshonitic, and all exhibit similar LREE-enriched trace-element patterns, pronounced negative Eu anomalies, positive Rb, Th, U and K anomalies, negative Ba, Nb, Ta, Sr, P and Ti anomalies, evolved zircon εHf(t) values of −6.25 to + 1.09, and two-stage Hf model ages of 2.16–1.70 Ga. These characteristics suggest that they have mainly crustal sources, similar to coeval reported granitic rocks in the Beishan Orogenic Belt, and indicating an older crustal reworking event. The Precambrian basement of the Beishan Orogenic Belt shows evidence of Mesoproterozoic crustal growth and early Neoproterozoic crustal reworking, with zircon εHf(t) values plotting within the crustal evolution trend defined by 2.1–1.3 Ga crustal material, similar to the Yili, Central Tianshan and Northern Alxa blocks, and indicating an affinity with those blocks. Geochronological data from these blocks and terranes suggest that the southern CAOB contains an extensive assemblage of early Neoproterozoic magmatic rocks that are related to the assembly of Rodinia and can be trace over 2000 km as an east–west-trending belt.
Precambrian rocks are necessary to understand the tectonic and crustal evolution of the Central Asian Orogenic Belt, especially the tectonic affinities of embedded microcontinents. We conducted a combined analysis of whole‐rock geochemistry, zircon U–Pb geochronology, and Hf isotope on the Mesoproterozoic igneous rocks from the Zhusileng–Hangwula Belt of the northern Alxa area to investigate its tectonic affinity. The zircon ages show that the gneissic granites, metagabbro, and amphibolite formed at 1,433–1,424 Ma, 1,383, and 1,373 Ma, respectively. Furthermore, zircon xenocrysts from the rhyolite in the Zhusileng area exhibit a 206Pb/238U ages cluster at about 1.4 Ga. Geochemically, the gneissic granites are high‐potassium calc‐alkaline granitoids and exhibit light rare earth element‐enriched pattern, pronounced significant negative Eu anomalies, negative Nb–Ta anomalies, positive εHf(t) values (3.2–11.3), and young two‐stage model ages (2.21–1.46 Ga), indicating that they were derived from a magma source of rapid reworking of juvenile mantle‐derived materials with a limited ancient crustal contamination. The FeOT, CaOm and MgO contents of mategabbros and amphibolite are high, but their total rare earth elements are relatively low (TREE = 31.45–32.74). They are characterized by relatively positive zircon εHf(t) values (5.3–11.0), and very young two‐stage model ages (1.98–1.49 Ga), indicating that they were generated from the depleted mantle. Our geochemical data suggest that these Mesoproterozoic rocks in the Zhusileng–Hangwula Belt are consistent with the formation period and tectonic environment of juvenile basement rocks from the Central Tianshan Arc and southern Beishan Orogenic Belt, whereas a Mesoproterozoic correlation with the Tarim Craton is highly unlikely. Thus, we believe that the Zhusileng–Hangwula Belt has an analogous tectonic evolution and a close affinity with the Central Tianshan Arc and southern Beishan Orogenic Belt during the Mesoproterozoic. The new geochemical and zircon U–Pb–Hf isotopic data of the Mesoproterozoic igneous rocks indicate that the Zhusileng–Hangwula Belt in the northern Alxa area has an analogous tectonic evolution and a close affinity with the Central Tianshan Arc and southern Beishan Orogenic Belt during the Mesoproterozoic.
A Mesoproterozoic granite covering about 5 km2 is firstly recognized in the Zhusileng area, which is located between the northern Alxa Block and the South Gobi microcontinent. New geochronological data from this area provide new insight for understanding the Precambrian crustal evolution of the middle segment of the southern Central Asian Orogenic Belt (CAOB). Based on the crystal shapes, internal textures, and high Th/U ratios, the zircons from this Mesoproterozoic granite are interpreted as magmatic origin. Meanwhile, LA‐ICP‐MS zircon U–Pb dating shows that it was emplaced at 1458 ± 7.5 Ma. Published geochronological data and Sr–Nd isotopic compositions of igneous rocks from the Zhusileng area and its vicinity are also compiled in this study. The Late Palaeozoic granitoids from the Zhusileng area have strongly negative εNd(t) values (−0.1 to −10.8), high (87Sr/86Sr)i (0.69657–0.73423) and old Nd model ages (0.9–1.8 Ga), suggesting the existence of Precambrian microcontinent in the Zhusileng area. Furthermore, the statistical analysis (or isotopic mapping) of Sr–Nd isotopic compositions of Palaeozoic granitoids from the middle segment of the southern CAOB also displays similar εNd(t) values and relatively old Nd model ages along the Hanshan Block, Zhusileng, Tsaggan Uul terrane, and Hutag Uul terrane. Therefore, we propose that those units may share a common basement during Mesoproterozoic to Early Neoproterozoic. Integrating the new zircon U–Pb ages of gneissic granites, published geochronological data and Nd isotopic compositions of igneous rocks from the northern Alxa Block and its vicinity, we propose that the ZHTZ, Hanshan Block, Tsaggan Uul terrane, and the Hutag Uul terrane may share a common Precambrian crystalline basement, which may constitute the Late Riphean South Gobi microcontinent.
The Precambrian metasedimentary rocks that are extensively distributed in the Beishan Orogenic Belt (BOB) can provide crucial geological information to constrain its tectonic affinity and geological evolution. Field investigation, zircon U–Pb dating and Lu–Hf isotopic analyses were conducted in combination for investigating them. Detrital zircon U–Pb dating shows that a quartzite sample of the Beishan Complex yields the youngest age at ca. 1710 Ma, with a major age peak at 1828–1778 Ma. Five quartzite samples from the Gudongjing Group and Pingtoushan Formation exhibit similar detrital zircon age distributions mainly from the late Paleoproterozoic to Mesoproterozoic, with the youngest ages at ca. 953 Ma, ca. 1000 Ma, ca. 978 Ma, ca. 960 Ma and ca. 985 Ma. Considering the 1.4 Ga granitoids and age peak of the early Neoproterozoic metasedimentary rocks, the supracrustal rocks within the Beishan Complex were probably deposited during the late Paleoproterozoic to early Mesoproterozoic (ca. 1.7–1.4 Ga). Moreover, owing to the presence of ca. 933–871 Ma granitoids, the deposition ages of the Gudongjing Group and Pingtoushan Formation can be constrained during the early Neoproterozoic (ca. 953–933 Ma). The metasedimentary rocks, the same as the Meso-Neoproterozoic granitic magmatism, support the existence of a Precambrian microcontinent in the BOB. The early Neoproterozoic metasedimentary rocks have continuous detrital zircon ages during the Mesoproterozoic, mainly with positive εHf(t) values. Integrated with the magmatic records of ca. 0.9 Ga and ca. 1.4 Ga, we believe that the Precambrian basement of the BOB could be a fragment drifted from the Fennoscandia of the Baltica Craton. Field investigation revealed that carbonate rocks, mature sandstones and siltstones primarily comprise the protoliths of the early Neoproterozoic metasedimentary rocks, implying the sedimentation in a passive continental margin. However, an almost contemporaneous granitic magmatism was formed in a continental arc setting associated with the assembly of Rodinia. Therefore, it can be inferred that the BOB could be located in the periphery of the Rodinia supercontinent, where the sedimentation of the passive continental margin occurred at its outboard position.
The Beishan orogenic belt, located in the southern Central Asian Orogenic Belt, includes several discrete arc terranes. Here, we report on a newly discovered Early Neoproterozoic volcano‐sedimentary sequence in the eastern Beishan orogenic belt in order to constrain the composition and origin of the Shuangyingshan‐Huaniushan Terrane. The ~766‐m‐thick volcano‐sedimentary sequence is very low‐grade metamorphosed, and characterized by muddy and silty slate with the well‐developed parallel laminations and minor thinly‐bedded limestone in its lower and upper sections, and thick packages of sandstone‐conglomerate and basaltic rocks in the middle section. Lava flow units in the basalt are very common, and the sandstone‐conglomerate exhibits sedimentary structures typical of gravity currents, including erosional and slump features, and Bouma sequences. These features suggest that syn‐sedimentary volcanism occurred and the sequence formed in an active, deep marine environment. The basalt has a zircon U–Pb age of 901 ± 10 Ma, indicating that this sequence formed during the Early Neoproterozoic. Basalt samples have moderate SiO2 (45.33–49.18%), and high TiO2 (1.27–4.04%) contents, Mg# values of 25–48, and plot in the alkali basalt field in the Nb/Y versus Zr/TiO2 diagram, indicative of an evolved alkali basalt magma. They show inclined chondrite‐normalized REE patterns with (La/Yb)N ratios of 4.74–6.53, no pronounced negative Eu anomalies (Eu/Eu* = 0.87–1.22), no obvious negative Zr, Hf, Nb, and Ta anomalies in the primitive‐mantle‐normalized trace‐element diagram, consistent with oceanic island basalts. Considered together, these lithologies resemble those of an oceanic seamount. Our results, and the presence of the previously reported Gubaoquan granitic and mafic rocks (905–865 Ma) that formed in an active continental margin setting and underwent an amphibolite‐facies metamorphism, suggest that the Shuangyingshan‐Huaniushan Terrane may be an accreted terrane that consists of different lithologies with various origins that formed during the Neoproterozoic. A newly discovered Early Neoproterozoic volcano‐sedimentary sequence occurs in the eastern Shuangyingshan–Huaniushan Terrane. Lithostratigraphic features indicate an active, deep marine environment. Together with the alkali basalt showing geochemical features of OIB‐type basalts, the lithologies similar to those of an oceanic seamount were suggested.
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