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The Sedimentation and Tectonic Evolution of Late Paleozoic at the Southern Margin of Qinling Rift-Limited Ocean Basin
... The tectonic discrimination diagrams show that the Early Paleozoic alkaline magmatic rocks in the northern SCB are related to a within-plate setting (Fig. 17a, b, c and d). The different sedimentary successions in the two sides of the Chengkou-Fangxian Fault which was primarily a north-dipping normal fault in the Early Paleozoic indicate the extension to the north of the fault (Meng et al., 1996). To the south of the fault, shelf sediments occur, whereas deep-water carbonates, turbidites and bedded cherts dominate the northern domain of the fault (Meng et al., 1996). ...
... The different sedimentary successions in the two sides of the Chengkou-Fangxian Fault which was primarily a north-dipping normal fault in the Early Paleozoic indicate the extension to the north of the fault (Meng et al., 1996). To the south of the fault, shelf sediments occur, whereas deep-water carbonates, turbidites and bedded cherts dominate the northern domain of the fault (Meng et al., 1996). The sedimentary sequence changes northward into thick platform carbonates in the Zhenan-Xichuan area (Mei et al., 1995). ...
... Such magma sources are generally attributed to the rise of mantle plumes or asthenosphere upwelling (Eby, 1992). The vertical uplift in the Early Paleozoic may be the result of the rise of mantle plumes or asthenosphere upwelling (Meng et al., 1996;Mei et al., 1999). However, the mantle plume model is not plausible due to the lack of radial dike swarms or any massive magma eruption (Choudhuri and Nemčok, 2017). ...
The characteristic and tectonic implications of the Early Paleozoic alkaline magmatic belt in the South Qinling Belt, which was originally part of the northern Yangtze Block prior the Devonian, have remained elusive. Whether this magmatic belt is related to rifting of the passive continental margin, to back-arc extension in the active continental margin, or mantle plume activity is debated. Understanding the origin and geodynamic significance of this magmatic belt can provide new constraints on the Early Paleozoic tectonic evolution of the northern Yangtze Block. Here we present zircon U-Pb data from a suite of nepheline syenite, quartz syenite, diabase, and gabbro from the northern margin of the Yangtze Block which show an age range of ca. 435–440 Ma. The εHf(t) values of the intermediate rocks up to 16.59 suggesting magma generation from depleted mantle sources and new crustal growth. Geochemically, the syenites showing high total alkali contents and are enriched in LREE, LILE (Rb, Ba, and K), and HFSE (Th, U, Nb, Ta, Zr, and Hf), with depletion in Sr, P, and Ti. The intermediate and mafic magmatic rocks were generated through magmas sourced from the subcontinental lithospheric mantle metasomatized by asthenospheric mantle and underwent fractional crystallization without significant crustal contamination. The magmatic suite represents a significant phase of crustal extension in the northern margin of the Yangtze Block.
... The South Qinling belt subsequently rifted off the Yangtze plate and migrated northward as a micro-continental block during Late Silurian to Late Devonian time (e.g., Meng and Zhang, 1999;Zhang et al., 2001;Dong et al., 2011Dong et al., , 2013Dong et al., , 2015. In this model, Devonian rocks are interpreted to have accumulated either in a rift (e.g., Meng et al., 1996;Zhang et al., 2001 and references therein) or in a foreland basin formed by collision between the North Qinling belt and South Qinling micro-continental block (e.g., Dong et al., 2011, 2013 andreferences therein). ...
... Strongly deformed amphibolite-facies mafic-ultramafic and felsic metavolcanic rocks with MORB or arc geochemical affinities (Li et al., 1996;Lai and Yang, 1997;Lai et al., 2002Lai et al., , 2004Xu et al., 1998Xu et al., , 2000aXu et al., , 2000bXu et al., , 2002Xu et al., , 2008 occur in fault contact with the siliciclastic rocks. Sedimentary rocks were interpreted as turbidites and debris-flows in a rifted basin, development of which represented the initial opening of the Mianlue Ocean basin (Du, 1995;Meng et al., 1996;Dong et al., 2011 and references therein). Based on radiolarians from cherts associated with mafic blocks, Feng et al. (1996) proposed that this ocean opened prior to the Early Carboniferous. ...
... Some Precambrian grains of the Lower Devonian sandstone samples (Duan, 2010) in the east of the Xiqingshan Mountains are also closely similar to the age population of the South Qinling belt and the Yangtze plate (Fig. 12). Paleocurrent data from the Xiqingshan Mountains and other areas (Du, 1995;Meng et al., 1996;Yan et al., 2006aYan et al., , 2006bYan et al., , 2007b document a southerly source for Devonian sedimentary rocks of the South Qinling belt. This demonstrates that the Devonian sediments on both sides of the DFS fault should have been deposited in different tectonic settings with distinct sources. ...
The Qinling Orogen between the North China and Yangtze plates comprises various accreted and collisional terranes, recording the evolution of the Proto-Tethyan Ocean and the formation of east Asia. Knowledge of the provenance and tectonic setting of a thick succession of E-W striking Devonian sedimentary rocks sandwiched tectonically between the Shangdan and Mianlue ophiolitic suture zones in this belt is essential to understanding the evolution of the Qinling Orogen and the assembly of the North China and Yangtze plates during the Late Paleozoic. Systematic studies of the Devonian sedimentary facies in the Xiqingshan Mountains indicate the northern margin of the South Qinling belt was uplifted prior to the Early Devonian. Lower Devonian sandstones are dominated by feldspathic litharenite (Q12-31F18-37L40–65), indicative of a continental arc derivation. Detrital zircon U–Pb data demonstrate that the Lower and Middle Devonian sandstones were derived respectively from ca. 770 Ma and ca. 400 Ma felsic arc-related magmatic sources. Devonian sedimentation in the Xiqingshan Mountains is interpreted to have occurred in a foreland basin between the Yangtze plate and the North Qinling continental arc.
... The fault plane is characterized by smoothly polished steep slickensides planes with horizontal slickenlines and striae showing a brittle sinistral strike–slip sense of motion. This fault zone separates the Late Paleozoic accretionary complex to the north from the Late Paleozoic initial rift and passive continental margin formations to the south (Meng et al., 1996). The boulders in the conglomerate have no ophiolitic materials nor island-arc-derived materials in their grains or matrices, but are made of continentalderived materials from the South China craton. ...
... Many more-coherent slices and blocks are enclosed within mélange defined by the thrust faults, ductile shear zones and the penetratively-deformed mélange matrix described above, forming an anastomosing structural slice shear system (Fig. 4) (Li et al., 2001a,b,c,d). The obvious diversity in structural orientation and style, stratigraphy, magmatism and metamorphism between these slices and blocks is consistent with other recent research on different tectonic lithofacies, structural analysis and volcanic geochemistry of the suture (Meng et al., 1996; Lai and Zhang, 1996; Lai et al., 1997 Lai et al., , 1999 Lai et al., , 2000 Lai et al., , 2003 Li et al., 2003). Tectono-stratigraphic units in this study area can be divided into four first-order units: the Qinling–Dabie microblock (or the South Qinling block), the Mianlue suture, the Bikou block and the South China craton (Li et al., 2001a,b,c, d). ...
... The oceanic volcanic rocks in the Mianlue ocean were being subducted and metamorphosed to produce metamorphic distinctive subduction-related HP/LT metamorphic minerals along S 1 before pre- Early Triassic, dated by Li et al. (1996). On the southern continental margin of the ocean, in the Gaochuan range, the carbonates make an upward transition to calcalaceous mudstone, black mudstone and cherts recording the evolution from the Devonian gentle slope, transitional upwards to the Carboniferous marginal plateau and the Permian stable deep-water platform (Meng et al., 1996). However, in the Qinling–Dabie microblock north of the Mianlue ocean, intrusion of Permian subduction-type granites at 285 Ma suggests that subducted had begun by the Permian (Zhang et al., 1996). ...
The geologic framework of the Phanerozoic Qinling–Dabie orogen was built up through two major suturing events of three blocks. From north to south these include the North China craton (including the north Qinling block), the Qinling–Dabie microblock, and the South China craton (including the Bikou block), separated by the Shangdan and Mianlue sutures. The Mianlue suture zone contains evidence for Mesozoic extrusion tectonics in the form of major strike–slip border faults surrounding basement blocks, a Late Paleozoic ophiolite and a ca. 240–200 Ma thrust belt that reformed by 200–150 Ma thrusts during A-type (intracontinental) subduction. The regional map pattern shows that the blocks are surrounded by complexly deformed Devonian to Early Triassic metasandstones and metapelites, forming a regional-scale block-in-matrix mélange fabric. Five distinct tectonic units have been recognized in the belt: (1) basement blocks including two types of Precambrian basement, crystalline and transitional; (2) continental margin slices including Early Paleozoic strata, and Late Paleozoic fluviodeltaic sedimentary rocks, proximal and distal fan clastics, reflecting the development of a north-facing rift margin on the edge of the South China plate; (3) out of sequence oceanic crustal slices including strongly deformed postrift, deep-water sedimentary rocks, sheeted dikes, basalts, and mafic–ultramafic cumulates of a Late Paleozoic ophiolite suite, developing independent of the rift margin in a separate basin; (4) out-of-sequence island-arc slices; (5) accretionary wedge slices. All the tectonic units were deformed during three geometrically distinct deformation episodes (D1, D2 and D3 during 240–200 Ma). Units 2–4 involved southward thrusting and vertical then southward extrusion of about 20 km of horizontal displacement above the autochthonous basement during the D1 episode. Thrust slices 20 km south of the Mianlue suture are related to this vertical extrusion due to the same rock assemblages, ages and kinematics. The D2 and D3 episodes folded all the units in a thick-skinned style about east–west (D2) and west–northwest (D3) axes in the Mianlue suture zone. An early foreland propagating sequence of accretion of Late Paleozoic rocks deposited above the Yangtze craton is not involved in D1 deformation but is temporally equivalent to the D2 and D3 deformation in the Mianlue suture. Two stages of strike–slip faulting mainly occurred at the end of D2 and D3, respectively. During D2 deformation, the Bikou block was obliquely indented to the ESE into the Mianlue suture, rather than being thrust over the Mianlue suture from the north as a part of the Qinling–Dabie microblock. During D3 deformation, however, the Bikou block was bounded by the south boundary fault of the Mianlue suture, and the Yangpingguan fault on the south. These faults are coeval strike–slip faults, but of opposite senses, and accommodated minor southwestward extrusion of the Bikou block into Songpan–Ganze orogen. The other basement blocks north of the Mianlue suture were extruded eastward by about 20 km of lateral displacement, based on the offset of the Wudang dome, during the D3 episode due to the northeastward indentation of the Hannan complex of the South China craton. Post-D3 emplacement of granite, cutting across the strike–slip faults such as the Mianlue suture, provides a minimum age of 200 Ma for D3 deformation. Therefore, based on insights from the evolution of the Mianlue suture, the D2 and D3 episodes in the Mianlue suture and its neighbors are not responsible for and associated with the two-stage extrusion of the Dabie UHP-HP terranes from the Foping dome to the present erosional surface (more than 350 km).
... The V/(V + Ni) ratios indicate that the sedimentation conditions were slighlty oxidative, which should reflect intermingling with terrigenous substances. In previous studies [102][103][104], it has been suggested that the ocean basin of the COB was width-limited and narrow, which strongly supports the input of terrigenous materials during the hydrothermal precipitation. In agreement with the previous studies [102,104], a deposition of siliceous rocks in relatively shallow seawater, is also supported by the fact that these rocks are located on top of carbonate rocks of Gudaoling Formation. ...
... Under this situation, the organisms which were involved in the sedimentation process exhibit also terrigenous characteristics, and their dead bodies and catabolites have been deposited together with hydrothermal sediments according to [106]. Both terrigenous material and biological activities partly contributed to the formation of the siliceous rocks, as may be expected to be the case in a geological setting of a limited ocean basin [102][103][104]. By expanding previous studies that the COB was neritic facies during the Middle Permian [28], this work suggests that the whole COB was a limited ocean basin with deep to shallower seawater neritic facies since the Middle Paleozoic. ...
Marine siliceous rocks are widely distributed in the central orogenic belt (COB) of China and have a close connection to the geological evolution and metallogenesis. They display periodic distributions from Mesoproterozoic to Jurassic with positive peaks in the Mesoproterozoic, Cambrian—Ordovician, and Carboniferous—Permian and their deposition is enhanced by the tensional geological settings. The compressional regimes during the Jinning, Caledonian, Hercynian, Indosinian, and Yanshanian orogenies resulted in sudden descent in their distribution. The siliceous rocks of the Bafangshan-Erlihe ore deposit include authigenic quartz, syn-depositional metal sulphides, and scattered carbonate minerals. Their SiO2 content (71.08–95.30%), Ba (42.45–503.0 ppm), and ΣREE (3.28–19.75 ppm) suggest a hydrothermal sedimentation origin. As evidenced by the Al/(Al + Fe + Mn), Sc/Th, , and ratios and δCe values, the studied siliceous rocks were deposited in a marginal sea basin of a limited ocean. We suggest that the Bafangshan-Erlihe area experienced high- and low-temperature stages of hydrothermal activities. The hydrothermal sediments of the former stage include metal sulphides and silica, while the latter was mainly composed of silica. Despite the hydrothermal sedimentation of the siliceous rocks, minor terrigenous input, magmatism, and biological activity partly contributed to geochemical features deviating from the typical hydrothermal characteristics.
... The Qinling-Dabie-Sulu orogen marks the suture zone between the North and South China cratons Lai and Zhang, 1996;Meng et al., 1996;Wang et al., 2001Wang et al., , 2003Wang et al., , 2005aXu et al., 2002aXu et al., ,b, 2008Sun et al., 2002a,b,c;Zheng et al., 2003;Ratschbacher et al., 2003;Liu et al., 2003Liu et al., , 2005Dong et al., 2004Dong et al., , 2005Dong et al., , 2008Zhai et al., 2007;Li et al., 2007;Rogers and Bernosky, 2008). The HP-UHP metamorphic rocks in this orogen extend from eastern Qinling southeastwards to Tongbai and Dabie, and then across the Tanlu fault northeastwards to the Sulu region (inset of Fig. 1) and the Hongseong-Odesan fold belt of Korea (Oh, 2006;Oh and Kusky, 2007;Li et al., 2007). ...
... The western Dabie orogen, usually called the Hong'an block in Chinese literature, is separated from the eastern Dabie orogen by the Shangma fault, from the North China craton by the Shancheng-Shucheng fault (an eastern segment of the Shangdan suture), and from the South China block by the Xiang-Guang fault (an eastern segment of the Mianlue suture). The Dawu fault in the west separated the western Dabie from the Tongbai orogen (Fig. 1, Yu and Meng, 1995;Zhang et al., 1996Zhang et al., , 2002Zhang et al., , 2004Zhang et al., , 2005Lai and Zhang, 1996;Lai et al., 1997Lai et al., , 1999Lai et al., , 2000Lai et al., , 2003Lai et al., , 2004Li et al., 1999Li et al., , 2000Li et al., , 2001aLi et al., ,b,c,d,e, 2002Li et al., , 2003Li et al., , 2007Li et al., , 2009aLiu et al., 2001Liu et al., , 2003Liu et al., , 2004Liu et al., , 2005Meng et al., 1996Meng et al., , 2005Meng and Zhang, 2000;Wang et al., 2001Wang et al., , 2003Wang et al., , 2005aXu et al., 2000,b, Dong et al., 2004Sun et al., 2002a,b,c;Zhou et al., 2008a,b,c;Liu and Li, 2008). In this area, various HP and UHP metamorphic rocks and structures are well preserved due to the weak Cretaceous tectonic and thermal overprint (Webb et al., 1999). ...
The western Dabie orogen (also known as the Hong'an block) forms the western part of the Dabie–Sulu HP–UHP belt, central China. Rocks of this orogen have been subjected to pervasive ductile deformation, and include numerous quartz schists and felsic mylonites cropping out in ductile shear zones. Quartz textures in these mylonites contain important clues for understanding the movement sense of late-collisional extrusion and exhumation of high-pressure–ultrahigh-pressure (HP–UHP) rocks from the lower crustal level to the upper crustal level during Middle Triassic and Early Jurassic. The orientation and distribution of quartz crystallographic axes were used to confirm the regional shear sense across the orogen. The asymmetry of c-axis patterns consistently indicates top-to-the-southeast thrusting across the orogen in early structural stages. Later stages of deformation show different senses of movement in northern and southern parts of the orogen, with top-to-the-northwest sinistral shearing recorded in rocks north of the Xinxian HP–UHP eclogite-facies belt, and top-to-the-southeast dextral shearing south of the same unit.
... Cao et al., 1979;Guo et al., 1996;Huang et al., 2011;Korsch et al., 1991;Zhang et al., 1979). Thereafter, it developed as a foreland basin to orogenic belts forming to the west, north and east, and was infilled by terrestrial sediments (Figure 1b,c;Chen et al., 1994;Meng et al., 1996;Yong et al., 2003). However, the late Neoproterozoic to early Palaeozoic development of the Sichuan Basin remains poorly understood. ...
The Upper Ediacaran to Lower Cambrian of the Sichuan Basin in South China has long been considered to be dominated by shallow‐water deposition. Hydrocarbon exploration, however, has revealed that a NW‐SE trending intraplatform trough formed in the basin during the same period. Although different models have been proposed, the formation and evolution of the trough are still not fully understood. In this study, we investigate both the origin of the intraplatform trough and the formation of the Sichuan Basin by integrating seismic interpretation, well correlation, and tectonic subsidence analysis. The seismic and well data clearly show three stages of development of the trough. The first stage, in the early Late Ediacaran, is characterized by considerable thinning of the lower two members of the Upper Ediacaran from the platform margins to the trough. In the second stage, in the late Late Ediacaran, the platform margins backstepped and the extent of the trough expanded significantly to a width of ~400 km. The third stage, in the early Early Cambrian, was dominated by gradual filling of the trough and onlapping of the platform margins. Backstripped tectonic subsidence curves show one, or two closely spaced episodes of linear subsidence starting at ~550 Ma and then decreasing exponentially until ~450 Ma. The shape of the subsidence curves is consistent with formation of the Sichuan Basin by low, and slow amounts of lithospheric stretching of thickened cratonic lithosphere. The tectonic subsidence increases from the centre to the NW of the basin. Interestingly the margins of the trough do not correlate with contoured values of increased tectonic subsidence and we infer that the trough was a palaeogeographic embayment in a large carbonate platform that developed in a broad, ramp‐like area of slow and low subsidence tilting down to the proto‐Tethyan ocean located to the NW of the basin.
... Some argue that the Shangdan Ocean was closed during early Paleozoic (e.g., Chen & Liu, 2011;Chen et al., 2004Chen et al., , 2015Cheng et al., 2011Cheng et al., , 2012Li et al., 2012Li et al., , 2014Liao et al., 2016;Liu et al., 2003Liu et al., , 2010Liu et al., , 2013Liu et al., , 2016Qian et al., 2013;Su et al., 2004;Tang et al., 2016;Wang et al., 2011Wang et al., , 2014Wang et al., , 2016Yang et al., 2003Yang et al., , 2005Yu et al., 2016;Zhang et al., 2013) or Early Devonian (Dong et al., 2013;Gao et al., 1995;Zhang et al., 1997), while others suggest that NCB and SCB collided during Late Triassic (Ames et al., 1996;Enkin et al., 1992;Hacker et al., 1998;Hsü et al., 1987;Li, 1994;Li et al., 1993;Okay et al., 1993) or Early Triassic to Middle Jurassic (Gilder et al., 1999;Gilder & Courtillot, 1997; Van der Voo et al., 2015;Yang & Besse, 2001;Zhao & Coe, 1987, 1989. collision between the SQB and the SCB along the Mianlue Suture (Dong et al., 1999Meng et al., 1996;Meng & Zhang, 1999;Zhang et al., 1995Zhang et al., , 2001. This two-stage collision model seems to reconcile the disputes over the collision timing between the NCB and SCB. ...
The paleoposition of the South Qinling Belt is a crucial key to understanding the collisional process between the North and South China blocks. In order to identify the paleogeography of the South Qinling Belt during the Early Triassic and its correlation to the North and the South China blocks, combined paleomagnetic studies have been conducted on the Lower Triassic sedimentary rocks in the South Qinling Belt. After systematic thermal demagnetization, a high‐temperature characteristic remanence was isolated from 133 specimen embracing 22 sites with a mean direction of D = 330.5°, I = 27.7° (α95 = 2.5°). The positive fold and reversal tests suggest that the characteristic remanence was acquired during deposition. This characteristic remanence corresponds to a mean paleopole at φp = 7.2°E, λp = 62.5°N (A95 = 2.4°), indicating a paleolatitude of ~23.6°N for the South Qinling Belt. These new data are in concordance with the coeval paleomagnetic pole of the North China Block but are distinctly different from that of the South China Block with ~10.0° paleolatitude and ~73.6°declination differences. Together with the regional geology, our new data suggest that the South Qinling Belt had amalgamated with the North China Block along the Shangdan Suture by the Early Triassic times; however, it was still separated from the South China Block by the Mianlue Ocean up to the Early Triassic. The final collision between the North and South China blocks resulted from a ~73.6° clockwise rotation of the South China Block relative to the South Qinling Belt along the Mianlue Suture during the Late Triassic.
... The CFF has a multi-stage evolutional history and served as the master extensional fault in the Early Paleozoic. The Early Paleozoic alkaline magmatism and rift-related sedimentation occurred in the NDB Meng et al., 1996), but were absent in the SDB. The CFF is thereby no younger than the Early Paleozoic. ...
... Nevertheless, radiolarians in the cherts in association with the ultramafic and mafic volcanic rocks give an age of Carboniferous (Feng et al., 1996), suggesting that the ocean basin probably came into existence during the Carboniferous. This deduction is further supported by the occurrence of an inferred breakup unconformity, usually regarded to coincide with the transition from rifting to drifting, between the Devonian and the Carboniferous-Permian strata on the southern side of the Mianlue suture zone (Meng, 1994;Meng et al., 1996). These facts prove that the Mianlue suture zone was the product of the closure of a paleoocean between the South Qinling orogen and the South China block in Late Triassic time. ...
The Qinling orogen was formed by the joining of the North and South China blocks, but the timing of their integration has been debated for more than a decade. The controversies obviously stem from different approaches to reconstruction of the integration history. Two contrasting lines of evidence yield two different ages for collision of the North and South China blocks---middle Paleozoic and Late Triassic. The Shangdan suture within the Qinling was regarded in previous studies as the trace along which the North and South China blocks collided. Our studies, however, demonstrate that there are two sutures within the Qinling: the well-documented Shangdan suture and the newly discovered Mianlue suture. We show in this paper that the Late Proterozoic to early Mesozoic evolution of the Qinling involved interactions between the North China block, the North and South Qinling orogens, and the South China block. The middle Paleozoic collision along the Shangdan suture, as constrained by some evidence, accreted only the South Qinling orogen to the southern part (i.e., the North Qinling) of the North China block. Contemporaneous rifting of the South China block and subsequent drifting separated the South Qinling from the South China block during the middle to late Paleozoic. The separation of the South from the North China blocks is supported by other evidence, in particular, geomagnetic data. Evidently it was the Late Triassic collision of the South China block with the South Qinling orogen along the Mianlue suture that led to final integration of the North and South China blocks.
... The Devonian system consists of turbidites, carbonates, argillite, quartzite, and quartzose sandstone, whereas the Carboniferous rocks comprise mainly carbonates and shale. In contrast, there are virtually no Ordovician and Silurian sediments within the Mianlue suture (e.g., Meng et al., 1996;Meng and Zhang, 1999). ...
The Xichahe tonalite emplaced into the Proterozoic Foping metamorphic complex, south Qinling Mountains, central China, has been dated at 213.6 ± 2.2 Ma using the LA-ICP MS zircon U-Pb method, indicating that it is post-orogenic (≤242 ± 21 Ma). With the exception of higher Mg# (52.94-67.59) values, the tonalite has compositional similarities to high-silica adakites from suprasubduction-zone tectonic settings. Chondrite-normalized rare-earth element patterns of the tonalite are characterized by high (La/Yb)N ratios and concave-upward shapes of HREE, and without a significant Eu anomaly (δEu = 0.65-1.10). In conjunction with high Ba (877.13-1963.52 ppm) and Sr (820.76-1252.75 ppm), low Y (10.58-18.30 ppm) and HREE, e.g., Yb = 0.79-1.51 ppm), trace elements, and REE patterns suggest that the tonalite magma protolith was most likely a feldsparpoor, garnet ± amphibole-rich eclogite assemblage. Isotopic values of Sr/Sr = 0.7065-0.7069, Isr = 0.7054-0.7064, Nd/Nd = 0.5123-0.5124, εNd(t) = -1.52 to -3.62, Pb/Pb = 18.294-18.349, Pb/Pb = 15.993-15.997, and Pb/Pb =39.502-39.526, are similar to those of the Proterozoic Yaolinghe Group mafic volcanics in the south Qinling Mountains; the Nd isotopic model age of 1.15-1.38 Ga is close to the formation age (~1.1 Ga) for the Yaolinghe metabasalts. High Mg# and Nb/Ta ratios, and Cr and Ni contents of the Xichahe adakitic tonalitie indicate that the parental magma mixed with a mantle melt. Based on the geological setting, it is concluded that the Xichahe tonalite was unlikely to have been produced by partial melting of recycling lower continental crust, and that mixing of the parental adakite magma with mantle melts resulted from Triassic asthenospheric upwelling caused by breakoff of the subducting Mianlue oceanic slab during the postorogenic stage of the South Qinling orogenic belt.
... The Devonian System consists of turbidite, carbonates, argillite, quartzite, and quartzose sandstone, while the Carboniferous rocks consist mainly of carbonates with shales. In contrast, there are virtually no Ordovician and Silurian beds within the Mianlue tectonic zone (e.g., Meng et al. 1996;Meng and Zhang 1999). ...
The ca. 400-km-long granitoid belt in the South Qinling is believed to be a synorogenic product of the collision between the North and South China Blocks along the Qinling-Dabie orogenic belt in central China. Single and multigrain zircon U-Pb dating of six of these granitoid bodies indicate that the granitoids were formed between 220 +/- 1 and 205 +/- 1 Ma, supporting the idea that the collision between the North and South China Blocks happened in the Triassic. The formation of these synorogenic granitoids in the South Qinling is similar in time but slightly later than the rapid exhumation of the ultrahigh-pressure metamorphic rocks and their country rocks in the eastern part of the Qinling-Dabie orogen, suggesting a close relationship between the rapid exhumation of the ultrahigh-pressure metamorphic rocks in the Dabie Mountains and the formation of the South Qinling granitoids. According to regional geology, the breakoff of a subducted slab, if there was any, should have occurred at a shallower depth in the South Qinling compared with that in the Dabie Mountains and Sulu terrane. This shallow breakoff is likely to have disturbed the asthenosphere seriously, leading to the melting of the overlaying lithosphere as well as the formation of the granitoid belt.
... Okay et al., 1993;Kröner et al., 1993;Zhou et al., 2001;Ratschbacher et al., 2003Ratschbacher et al., , 2006Xu et al., 2005aXu et al., , 2005bLi et al., 2005;Zheng et al., 2005). Based on new structural data (see below) and our new field observations, we consider that the rocks of this unit were scraped off from the north Qinling arc and its forearc flysch during the subduction (Meng et al., 1996;Zhang et al., 2001), carried into the subduction zones and accreted on to the overriding plate without experiencing the Triassic ultrahigh-pressure metamorphism. The Lijiazhuang ductile shear zone (f 8 in Figure 1) to the south separates the Nanwan slice from the Xiaojiamiao mélange unit. ...
The Tongbai Collisional Orogen and associated units, located between the Qinling and Dabie orogens, can be divided into nine lithotectonic units. From north to south, these are the southern tectonic unit of the North China Plate—the Maoji Group, the Erlangping tectonic unit, the Qinling Complex unit, the Guishan and Nanwan slice, the Xiaojiamiao mélange unit, the northern high-pressure (HP) unit, the Tongbai high-grade Complex, the southern HP unit and the Suizhou tectonic belt. Based on structural analysis and available geochronological data, five principal episodes of deformation (D1-D5) are distinguished in this area following the Mesozoic HP metamorphism. The first two episodes of deformation developed in various tectonic units to the south of the Xiaojiamiao mélange unit, and the subsequent episodes of deformation developed in all the units of this area. The D1 deformation is correlated to ca. 255–238 Ma generating regional penetrative foliation and WNW-trending stretching lineation, and leading to the initial stage of eastward oblique extrusion of the HP rocks. The D2 event is characterized by top-to-the-SSW thrusting which contributed to the further vertical uplift of the HP rocks sometime around 230–215 Ma. The D3 event is defined by WNW-trending open folds, and must have taken place earlier than Lower Jurassic. The D4 event is characterized by ductile strike-slip shearing, and during this episode the Tongbai high-grade Complex was extruded to the east at ca. 131–119 Ma. The D5 event probably took place at ca. 100–80 Ma, and is marked by the NW and NE trending brittle faults which overprint all of the above mentioned structures. The exhumation of the Tongbai HP rocks illustrates the process of gradual extrusion and uplift, controlled by several episodes of deformation. Copyright © 2010 John Wiley & Sons, Ltd.
... There also occur Upper Permian-Lower Triassic deep-marine facies assemblages along the northernmost edges of both the northwest SCB and the SG terrane, consisting of thin-bedded chert, lime mudstone, carbonate turbidite, submarine debris-fl ow conglomerate, and slump intervals. These deep-marine sediments are in part involved into the Mianlue ophiolitic complex (Meng et al., 1996). A measured sedimentary section is tabulated in Table DR2 (see footnote 1) to show the typical facies associations of Upper Permian-Middle Triassic strata. ...
We present new sedimentary data integrated into a regional Mesozoic stratigraphic framework to provide a detailed picture of spatio-temporal variations in deposition and depocenter migration of the northwest Sichuan basin. The Mesozoic sedimentary evolution is utilized to interpret basin subsidence history and to unravel coeval basin-margin tectonics. The northwest Sichuan basin, together with the Songpan-Ganzi terrane, behaved as a passive margin south of the Qinling Paleo-Tethys from late Paleozoic to early Middle Triassic times and then evolved into a peripheral foreland basin in response to collision of the North and South China blocks since the late Middle Triassic. Coeval with strong north-south contraction of the Songpan-Ganzi terrane in the Late Triassic, sinistral transpressional deformation of the Longmen Shan belt led to flexural subsidence of the adjacent western Sichuan basin. Renewed basin-margin fold-thrust activity triggered recurrence of flexural subsidence of the northwest Sichuan basin since the Middle Jurassic, with the depocenter eventually shifting to the northwestern corner of the basin in the Early Cretaceous. Sedimentary evolution of the northwest Sichuan basin and the basin-margin deformation imply that the South China block had been rotating clockwise relative to the North China block throughout the Mesozoic with an interim period of Early Jurassic tectonic quiescence. A model is advanced that invokes clockwise rotation of the South China block as a driver for tectonic evolution of both the basin and adjoining structural belts and provides an explanation for several salient features that are otherwise puzzling.
Rare earth element and yttrium (REY) deposits are important strategic resources widely used in high-tech applications, such as solar cells and wind turbines. This paper summarises the temporal-spatial characteristics and genesis of REY deposits in China classified as alkaline carbonatite, ion-adsorption, placer, sedimentary metamorphism, marine sedimentary phosphorite and coal-hosted REY types. This study focuses on alkaline carbonatite and ion-adsorption deposits, because of their importance in terms of both exploitation and global reserves. The general characteristics, genesis, and enrichment of these REY deposit types are summarised, and eight districts have been identified as having prospectivity for REY, based on geological and geochemical data. An overview of these districts is presented, together with a detailed investigation of four important districts in terms of geological settings, mineralisation, regional deposit models and metallogenic prospect.
• KEY POINTS
• REY deposits in China can be classified as alkaline carbonatite, ion-adsorption, placer, sedimentary metamorphism and marine sedimentary phosphorite and coal-hosted REY types.
• Ion-adsorption REY in the weathering profile of granitic rocks is strongly controlled by the resistance to weathering, climate, topography and layers of weathering crust.
• Carbonatite and alkaline rocks are major hosts for REYs and commonly have high concentrations of REY-bearing accessory minerals.
• Eight districts have been identified as having prospectivity for REY in China.
The Yaolinghe Group sedimentary rocks exposed along the Dabashan fault zone are rich in pyroclastics and are thousands of meters thick. They provide key information for studying the tectonic location relationship between the Yangtze and Qinling blocks and the tectonic-sedimentary environment of the late Neoproterozoic continental margin. This study reports U–Pb and Lu-Hf isotope data of 438 and 408 detrital zircons from five samples of Yaolinghe Group sedimentary rock, collected in the Chengkou area, China. Combining the youngest detrital zircon U–Pb age for gravelly sandstone with data from previous studies, we constrained the maximum depositional time of the Yaolinghe Group sedimentary rocks in this area to ca. 650–635 Ma (i.e., Neoproterozoic Cryogenian). In the Chengkou area, the predominantly Neoproterozoic (1000–635 Ma) detrital zircons, with wide εHf(t) values ranging from −31.03 to 13.07 and an average of 2.00, were primarily derived from the adjacent regions of exhumed igneous rock in the South Qinling and Northern Yangtze blocks. Several minor age peaks at more than 1000 Ma indicate that this formation contains a small amount of recycled zircon. Further study indicates that the Yaolinghe Group sedimentary rocks were formed by near-source accumulation in a rift setting, located at the north margin of the Yangtze Block, during the breakup of Rodinia. As in previous studies, the retreat of the subducted slab may have led to continental rifting and extension of the Northern Yangtze Block, and the Yaolinghe Group sedimentary rocks in the Chengkou area recording the history of the last stage of Rodinia breakup.
To understand the crustal growth of the Qinling orogenic belt and the Mesozoic continental interaction between the North China and Yangtze blocks, it is critical to study the South Qinling accretionary complex belt, which is an important part of the Qinling orogen. Based on detailed zircon U–Pb geochronology and Hf isotopic compositional analyses of the Madao complex, this study presents constraints on the migmatization and tectonic evolution of the South Qinling orogenic belt during the Mesozoic. Zircons from leucosome samples of migmatites were found to have weak oscillatory zoning, and one sample yielded a weighted mean age that reflects the time at which the regional tectono‐thermal event initiated the anatexis (210–217 ± 2 Ma). The Hf isotopic compositions indicate that the Madao migmatites were derived from the ancient middle–Late Palaeoproterozoic crust. Zircons from mesosome samples of the migmatites that varied in age from the Palaeozoic to Neoproterozoic exhibited core‐rim textures with magmatic cores (256–1,329 Ma), indicating that they were derived from multiple sources with sedimentary protoliths. Of the 55 analysis spots on the overgrowth rims that yielded ²⁰⁶Pb/²³⁸U ages of 200–233 Ma, 40 analyses yielded a weighted age of 211.5 ± 1.0 Ma, indicating the time of anatexis due to the regional tectono‐thermal event. Combined with previously reported Mesozoic data from the South Qinling belt, these results suggest that the migmatites were probably controlled by post‐orogenic extension driven by Mesozoic orogenesis and a prolonged melting episode (from ~200 to 233 Ma). This study reinforces the interpretation that the continental crust in the South Qinling belt may have experienced complex interactions with asthenospheric mantle material during the Mesozoic.
As the eastern part of the Central Orogenic Belt, Qinling-Dabie Orogenic Belt has a complicated tectonic-sedimentary history. On the basis of a systematic research on the lithostratigraphy, fossil assemblages, isotopic geochronology and tectonics of 4 secondary and 13 three-level tectonic units, this paper divides the study area into 18 types of sedimentary basins, and discusses its tectonic-sedimentary evolution from Neoproterozoic to Mesozoic: (1) Neoproterozoic-Early Paleozoic: North Qinling was magmatic arc and forearc basin; South Qinling experienced intracontinental rift to interplatform basin-platform to continental-margin rift; Dabie-Sulu experienced intracontinental rift to interplatform basin-platform. (2) Late Paleozoic: North Qinling was marine-continental alternation epeiric sea; Mianlüe oceanic basin opened in the Devonian; South Qinling was backarc shelf and interplatform basin-platform at the same time. (3)Triassic: continental collision orogeny, stage of foreland basins. (4) Jurassic-Cretaceous: stage of fault basins and depressional basins.
The tectonic evolution of South Qinling, which is a main part of the Qinling orogenic belt, is still in dispute and deformation history of South Qinling is poorly studied. In this paper, detailed structural, microstructural, quartz c-axis fabric analysis, and geochronology results for the Madao gneiss in South Qinling are presented to characterize the deformation history. Results show that rocks in the northern part (Tiefodian-Laozhanggou) experience general shearing and deform at relative low temperature. The shear sense generally is south to north. In contrast, rocks in the southern part (Laozhanggou-Panjiahe) are weakly sheared with pure shear features and evidence of high-temperature deformation. Based on the analyses, we conclude that there exist two distinct deformation geometries in the Madao gneiss and accordingly we can divide the deformation into two stages. The early stage is represented by regional shortening, while the late stage features northward thrust shearing and evidence shows that it was a progressive process between them. LA-ICP MS U-Pb dating of zircons from pre-deformational migmatite veins yields age of 198.5 ± 2.0 Ma. This result, in combination with the age of post-deformational granite, indicates that the northward thrust shearing of the Madao gneiss occurred in the Late Triassic. In view of these results and other reported data in South Qinling, we propose that deformation in Madao gneiss may result from the initial collision and subsequent northward accretion in Late Triassic.
The Indosinian post-collisional Wulong pluton intruded into the Mesoproterozoic Fuping Group, South Qinling, central China. In the southern part of the pluton, some mafic enclaves have sharp or gradational contact relationships with the host biotite granodiorite. Geochemistry, zircon LA-ICP MS (laser ablation inductively-coupled plasma mass spectrometry) U-Pb chronology and Sr-Nd-Pb isotope geochemistry of the pluton are reported in this paper. The biotite granodiorite shows close compositional similarities to high-silica adakite. Its chondrite-normalized REE patterns are characterized by strong HREE depletion (Yb = 0.33-0.96 10−6 and Y = 4.77-11.19 times 10−6), enrichment of Ba (775–1386 times10−6) and Sr (643–1115 × 10−6) and high Sr/Y (57.83–159.99) and Y/Yb (10.99-14.32) ratios, as well as insignificant Eu anomalies (δEu = 0.70-0.83), suggesting a feldspar-poor, garnet±amphibole-rich residual mineral assemblage. The mafic enclaves have higher MgO (4.15-8.13%), Cr (14.79–371.31 times 10−6), Ni (20.00–224.24 times 10−6) and Nb/Ta (15.42-21.91) than the host granodiorite, implying that they are mantle-derived and might represent underplated mafic magma. Zircon LA-ICP MS dating of the granodiorite yields a 206Pb/238U weighted mean age of 208±2 Ma (MSWD=0.50, 1s̀), which is the age of emplacement of the host biotite granodiorite. This age indicates that the Wulong pluton formed during the late-orogenic or post-collisional stage (≤242±21 Ma) of the South Qinling belt. The host biotite granodiorite displays 87Sr/86Sr = 0.7059-0.7062, ISr = 0.7044-0.7050, 143Nd/144Nd = 0.51236-0.51238, εNd(t) = −2.26 to −2.66, 206Pb/204Pb = 18.099-18.209, 207Pb/204Pb = 15.873-15.979 and 208Pb/204Pb = 38.973-39.430. Those ratios are similar to those of the Mesoproterozoic Yaolinghe Group in the South Qinling. Furthermore, its Nd isotopic model age (˜1.02 Ga) is consistent with the age (˜1.1 Ga) of the Yaolinghe Group. Based on the integrated geological and geochemical studies, coupled with previous studies, the authors suggest that the Wulong adakitic biotite granodiorite was probably generated by dehydration melting of the Yaolinghe Group-like thickened mafic crust, triggered by underplating of mafic magma at the boundary of the thickened mafic crust and hot lithospheric mantle, and that the Wulong adakitic biotite granodiorite may have resulted from thinning and delamination of the lower crust or breakoff of the subducting slab of the Mianlue ocean during the Indosinian post-collisional orogenic stage of the Qinling orogenic belt.
Ultrabasic rocks in the Mianxian-Lueyang ophiolitic melange zone include harzburgite and dunite which exhibit LREE depletion
with remarkable positive Eu anomaly. The diabase dike swarm shows LREE enrichment but slightly negative Eu anomaly. Metamorphosed
volcanic rocks can be divided into two groups in terms of their REE geochemistry and trace element ratios of Ti/V, Th/Ta,
Th/Yb and Ta/Yb. One is the MORB-type basalt with LREE depletion, representing the fragments of oceanic crust and implying
an association of the MORB-type ophiolite and an ancient ocean basin between theQinling and Yangtze plates during the Middle
Paleozoic-Early Mesozoic era. The other comprises the island-arc volcanic rocks including tholeiitic basalt and a large amount
of calc-alkaline intermediate-acid volcanic rock, which could not be the component of the ancient oceanic crust but the result
of magmatism at the continental margin. This indicates that the Mianxian-Lueyang limited ocean basin had undergone a whole
process of development, evolution and vanishing from Devonian-Cretaceous to Permian. And the Qinling area had become an independent
lithospheric microplate, on the southern side of which there were exhibited the tectonic characteristics of active continental
margins during the Late Paleozoic-Early Mesozoic. That is to say, the Qinling cannot be simply considered as a result of collision
between the Yangtze and North China plates.
The Jian Cha Ling gold deposit is sited in folded and faulted Palaeoproterozoic rocks of the uplifted Mian-Lue-Yang block, adjacent to the Mianlue suture zone within the West Qinling mineral province, along the northern margin of the South China craton. Early Mesozoic gold mineralization at Jian Cha Ling, which has a pre-mined resource of about 536,000oz Au, is controlled by the so-called F 1 45 fault. The fault is a generally steeply N-dipping, WNW-trending deformation zone that is the result of dislocation along bedding planes, early foliation and axial planar surfaces of regional folds. The fault zone marks the contact between serpentinized, lower greenschist-facies dunites, harzburgites and minor gabbroic units in the footwall, and a metasedimentary sequence in the hanging wall that is dominated by metadolomite, metalimestone and phyllitic schists. Brittle–ductile deformation, partitioning of strain along pre-existing zones of weakness, and the formation of intrashear zone lozenges contributed to the development of a complex fault zone geometry. Variations in both dip and strike of discrete dislocation surfaces related to oblique, sinistral–reverse movement along the F 1 45 fault zone focussed auriferous hydrothermal fluids along three dominant structural orientations. Gold was preferentially deposited along shallowly NNE-dipping and shallowly to moderately NNW-dipping fault segments, and is also associated with shallowly WSW-dipping, dolomite-dominated vein sets. Disseminated, economic gold grades (>4g/t Au) are restricted to the footwall ultramafic rocks to within about 5 to 10m of the contact with the hanging wall. Gold is related to laminated, realgar- and orpiment- bearing sheeted veins and hydrothermal breccias, as well as slickolites and fault gouge. Gold-bearing vein sets are located within the relatively undeformed, ultramafic intrashear zone lozenges. Gold-related alteration is dominated by extremely fine-grained, arsenic-bearing sulphide minerals and dolomite, with additional white mica and clay minerals. The structural setting of the deposit, combined with published data on the geological evolution of the West Qinling mineral province, suggest that the Jian Cha Ling gold deposit developed in an uplifted basement block during the final phases of northward subduction and suturing of the South China craton with the South Qinling orogen along the Mianlue Suture Zone, during the changeover from a compressional to transpressional tectonic regime in Late Triassic to Middle Jurassic times.
The geologic framework of the Qinling orogen was built up through interplay of three blocks, the North China block (including the North Qinling), the South Qinling, and the South China block, separated by the Shangdan and Mianlue sutures. The Shangdan suture resulted from Middle Paleozoic collision of the North China block and the South Qinling. The Mianlue suture resulted from Late Triassic collision of the South Qinling and the South China block. Present upper crust of the Qinling is structured dominantly by thrust–fold systems. The North Qinling displays thick-skinned deformation with crystalline basement involved, whilst the South Qinling is characterized by thin-skinned thrusts and folds detached above the Lower Sinian. Two types of Precambrian basement, crystalline and transitional, are defined according to lithology and metamorphic grade and different in age. Stratigraphic and sedimentary architecture is characterized by distinct zonation.
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