North China Craton Research Articles

Crustal thickness variation of the Dabie orogenic belt: Insights from detrital zircon evidence and geological significance

The Dabie orogenic belt is characterized by widely distributed Mesozoic ultrahigh-pressure metamorphic rocks. Together with the Qinling orogenic belt, it constitutes one of the most important collisional orogens in eastern Asia. Because of intense continental subduction and collision during the Mesozoic and subsequent denudation, it remains controversial whether pre-Mesozoic convergent events happened in the region of the Dabie orogenic belt. In this study, we reconstruct the crustal thickness variation of the Dabie orogenic belt based on detrital zircon data. Results reveal three stages of crustal thickening at ca. 900-800 Ma, ca. 530-400 Ma, and ca. 250-210 Ma that are likely associated with three major convergent events that happened between the North and South China Blocks since the Neoproterozoic. The first thickening stage is possibly related to long-term subduction-accretion-collision processes along the northern margin of the South China Block. The second one corresponds to early Paleozoic ocean closure and the arc-continent collision that happened between the North and South China Blocks. The third one is a most significant thickening that represents the final collision between the North and South China Blocks during the Mesozoic. The turning point (ca. 210 Ma) of the crustal thickness curve represents the cessation of ultradeep subduction and constrains the completion of Mesozoic continental collision. Late Archean crustal thinning may be related to the onset of plate tectonics. Overall, the fluctuations of crustal thickness and detrital zircon age populations from sediments of the Dabie orogenic belt suggest interaction among Chinese continental blocks is consistent with the evolution of global supercontinent cycles.

A Late Triassic gold metallogenic event within the extended tectonic evolution of the West Qinling Orogen, central China: Constraints from U-Pb and Ar-Ar geochronology in the Yangshan gold district

The West Qinling Orogen in central China resulted from Late Devonian to Triassic collisional orogenesis involving accreted terranes along the southwestern margin of the North China Block with subsequent ocean closure and collision of the South China Block with those terranes. The Yangshan gold district, with a pre-mining resource of more than 308 t gold, is situated along the Mianlue Suture Zone on the southern margin of the orogen. The gold orebodies are mainly controlled by the ENE-trending Anchanghe-Guanyinba Fault and its subparallel second-order faults. The relatively low pressure–temperature mineralization is dominated by disseminated pyrite, arsenopyrite, and stibnite hosted in phyllite and granite dikes, accompanied by intense muscovite-silica-carbonate alteration.Four major phases of deformation related to collisional tectonics are recorded in the Yangshan gold district. Early N-S-oriented compressional deformation (D1) is characterized by an alignment of muscovite, overgrowths on framboidal pyrite, and quartz veinlets. D2 is characterized by a series of continuous ENE-trending reverse faults and folds at multiple scales related to SSE-NNW-oriented compression. D3 is related to gold mineralization and is characterized by a series of ENE-trending, largely normal faults, formed during transtensional tectonics. D4 post-dates gold mineralization and is associated with the development of nearly N-S-trending, low-displacement normal faults.New high-precision SHRIMP zircon U-Pb dating of three types of granite dikes in the Yangshan gold district yields broadly coincident ages of 216 ± 3.0 Ma to 210 ± 9.7 Ma, which is a range identical to that of existing dates of 217–211 Ma for more regional granite magmatism in this district. New Ar-Ar dating of gold-related muscovite gives an age of 210.9 ± 1.6 Ma for the Yangshan gold deposit, indicating that hydrothermal activity overlapped or post-dated the final stages of granite intrusion. Pre-226 Ma peak metamorphism of the ore-hosting rocks occurred prior to extensional ductile shear deformation that is constrained by a published 40Ar/39Ar muscovite cooling age of 223 ± 2 Ma. In good agreement, U-Pb constrained ages of retrograde metamorphism and associated late magmatism of around 215 Ma are reported for rocks along the Mianlue Suture Zone.These geological and geochronological data suggest that relatively shallow-level gold mineralization was broadly coeval with Late Triassic transtensional, orogen-parallel deformation along the regional-scale fault system, late in the tectonic evolution of the West Qinling Orogen. This is consistent with its classification as epizonal orogenic gold mineralization.

Revisiting the stratigraphical, sedimentological and provenance evolution of Lingshan Island, offshore of east China: Implications for the destruction of the north China craton

The Cretaceous strata of Lingshan Island, offshore of East China, are a key sedimentary archive for understanding the destruction of the North China Craton (NCC). However, there has been limited progress in characterizing its stratigraphical, sedimentological and provenance evolution in the context of the progressive lithospheric thinning and magmatism associated with the destruction of the NCC. We report field logging data, sandstone framework petrography, and detrital and volcanic zircon U–Pb geochronology data from the Cretaceous strata of Lingshan Island, and correlate these data with coeval sediments in the Jiaolai Basin and volcanic units in the East China. Our results indicate rapid deposition of the Laiyang and Qingshan groups from c. 124–123 Ma with an upward thickening and coarsening succession from the lacustrine turbidites of the Laiyang Group to the deltaic rocks of the Qingshan Group, accompanied by an increase in volcanic activity up-section. Sandstone petrology and detrital zircon U–Pb ages indicates that the source areas for the Laiyang and Qingshan Groups were syn-depositional volcanic rocks and plutonic rocks, with some contributions from the Yangtze Craton and Sulu terrane. Our compilation of detrital zircon U–Pb ages (n = 8513) from the Cretaceous strata of Lingshan island and the Jiaolai Basin in the hinterland implies provenance contributions from four different sources. The zircon Th/U ratios from this large dataset suggests that Cretaceous magmatic zircons formed in an extensional setting (Th/U ratios >1 but with significant variation). The Eu anomalies in magmatic zircons (n = 550) from the Jiaodong Peninsula indicate continuous lithospheric thinning in Eastern China since c. 130 Ma, leading to the destruction of the NCC. Based on all available data, Lingshan Island most likely was a rift basin during the Cretaceous.

Compositionally variable basement and tectonic affinity of the Bainaimiao arc belt: Implications for crustal growth of the Central Asian Orogenic Belt

As an important part of the southeastern boundary of the Central Asian Orogenic Belt (CAOB), the Bainaimiao arc belt, particularly its tectonic affinity and Precambrian basement composition, is an important element to provide new insights about the crustal growth of the CAOB. However, these remain poorly understood. This paper presents new geochronological, whole-rock geochemical and zircon Hf isotope data on early Paleozoic intrusive rocks from the Bainaimiao arc belt in the southeastern CAOB. The Ordovician gabbroic diorites in the Zhengxiangbaiqi area of the western Bainaimiao arc belt have low SiO2 contents (51.73–54.82 wt%), high TiO2 (0.99–1.07 wt%) and TFe2O3 contents (9.68–9.89 wt%), depletions in Nb, Ta and Ti, and positive εHf(t) values (6.8–11.3). These rocks generated from partial melting of a mantle wedge that has been metasomatized by subducted-derived fluids. The Silurian monzogranites in the Zhengxiangbaiqi area have high contents of SiO2 (72.61–75.12 wt%) and K2O (2.75–4.12 wt%), positive εHf(t) values (0.7–9.3) and abundant Precambrian inherited zircons. These monzogranites originated from partial melting of the thickened juvenile crustal components with significant ancient crustal contamination. The Silurian granites and granodiorites in the Faku area of the eastern Bainaimiao arc belt are characterized by high Na2O contents (4.00–4.52 wt%), high Sr/Y ratios, low MgO (1.15–1.74 wt%) and K2O contents (0.52–1.42 wt%), low K2O/Na2O ratios, and positive εHf(t) values ranging from 0.6 to 8.1. These rocks were derived from partial melting of a subducted slab interacted with mantle peridotite. New zircon U-Pb-Hf isotope data from these early Paleozoic intrusive rocks combined with previous results indicate that the Precambrian basement of the Bainaimiao arc belt is laterally heterogeneous, with Neoarchean-Paleoproterozoic basement beneath the western Bainaimiao arc belt and Paleo-Mesoproterozoic basement beneath the central Jilin area in the eastern Bainaimiao arc belt. The Bainaimiao arc belt has a tectonic affinity different from the North China Craton (NCC) and represents a composite arc system consisting of an ensialic island arc with a basement composition similar to that of the Precambrian microcontinents in the CAOB in the Bayan Obo-Damaoqi-Bainaimiao-Zhengxiangbaiqi and central Jilin areas and an oceanic island arc in the Ongniud-Faku and southern Jilin areas. The involvement of composite arc systems in the amalgamation of the accretionary orogenic belt could be an important mechanism for crustal growth in the CAOB.

Structural patterns and ages of Permian-Triassic multistage strike-slip faulting in the Chifeng area, southeastern Inner Mongolia, China: Implications for the final closure of the Paleo-Asian Ocean

The closure of the Paleo-Asian Ocean (PAO) to the north of the North China Craton (NCC) holds significance in comprehending the Phanerozoic continental evolution of East Asia. However, the timing of the final closure of the PAO, tectono-magmatic records of this process in the northern margin of the NCC, and related geodynamics remain to be resolved. Here we undertaken detailed macro- and micro-structural investigations on the E-W-striking and NNE-striking fault system in the Chifeng area, northern edge of the NCC. Combined with new zircon U-Pb and muscovite 40Ar/39Ar dating, we delineated three phases of strike-slip faulting in the research region during the Permian-Triassic, including WNW-ESE-striking and NE-SW-striking ductile sinistral shearing at ∼ 270–258 Ma and 258–246 Ma, respectively, and subsequent ∼ E-W-oriented ductile–brittle dextral shearing at ∼ 230–209 Ma. Based on analysis of paleotectonic stress fields, we propose that the first two-stage deformation shared a regional unified N-NNE contractional setting, while the late ∼ E-W-striking dextral shearing reflected a distinct regional NNW-SSE shortening event. The regional magmatism reveals three age peaks of ∼ 270 Ma, ∼250 Ma and ∼ 230 Ma, corresponding well to the above three-phase deformation. Further, zircon Hf isotopic data imply that the composition of juvenile material in regional deep-seated crust gradually increased from Permian to Triassic. The N-NNE contraction may be controlled by the eastward scissor-like final closure of the PAO during the Middle Permian-Early Triassic. The middle-late Late Triassic NNW-SSE contraction is likely influenced by the remote effect of the low-angle southward subduction of the Mongol-Okhotsk oceanic plate.

Preservation of Archean mafic lower continental crust worldwide

Mafic granulite xenoliths found in Archean cratons have generally been inferred to form from post-Archean basaltic underplating, implying that the Archean mafic lower crust was removed perhaps via delamination. Here based on an integrated study of granulite terrain, granulite xenoliths and lower crustal-derived granitoids, we make a compelling case that most of the Tertiary alkali basalt-entrained mafic granulite xenoliths from the northern North China craton are restites left after partial melting of the late Archean mafic lower crust to produce the Mesozoic granitoids. This runs counter to archetypical Mesozoic basaltic underplating as commonly believed. We further show that the Archean mafic lower crust persists on a cratonic scale in the North China craton presently. Re-examination of mafic granulite xenoliths from many other cratons that were considered to be products of Proterozoic underplating shows that most of them have similar genetic mechanism to the present case, suggesting that they may form in the Archean. This attests to preservation of the Archean mafic lower crust globally, contrary to the widely held concept that much of the Archean mafic lower crust has delaminated. We predict preservation of such mafic lower crust beneath all Archean cratons. It suggests that the quantity of Archean rocks in the lower crust may be much greater than that exposed.

Anisotropic tomography and mantle dynamics of the North China Craton

SUMMARY We present high-resolution 3-D images of isotropic P-wave velocity (Vp), azimuthal anisotropy (AAN) and radial anisotropy (RAN) down to 700 km depth beneath the North China Craton (NCC) and adjacent areas, which are obtained by inverting a great number of high-quality arrival time data recorded at 1374 portable seismic stations and 635 permanent stations in the study region. Our results reveal new and detailed features of the upper mantle structure beneath the NCC. Varying structural heterogeneities are revealed beneath different tectonic blocks, and differences also exist between northern and southern parts of each block. The fast velocity directions (FVDs) of azimuthal anisotropy are mainly NW–SE under the Alaxa block, and NE–SW beneath the Tibetan Plateau. The FVDs present an arc transition along the boundary faults separating the Tibetan Plateau, the Alaxa block, the western NCC, and the Sichuan basin. Low-Vp anomalies with positive RANs (i.e. horizontal Vp > vertical Vp) are revealed at 100–200 km depths under the Tibetan Plateau, reflecting frozen-in anisotropy in the thick lithosphere. Significant low-Vp anomalies with a circular AAN pattern exist at 0–700 km depths beneath the Datong volcano. In addition, negative RAN occurs right below the volcano, whereas positive RANs appear around it, suggesting that the Datong volcano is fed by hot upwelling flow from the lower mantle associated with collapsing of subducted slab materials down to the lower mantle. The eastern NCC shows complex Vp AANs and RANs. Seismic anisotropy exhibits east–west variations in the upper mantle across the Tanlu fault zone. The west of the Tanlu fault shows negative RANs (vertical Vp > horizontal Vp), whereas its east shows positive RANs at 300–500 km depths. The low-Vp anomaly under the Datong volcano is connected with a large low-Vp anomaly beneath the eastern NCC above ∼250 km depth, suggesting that the hot upwelling flow under Datong may migrate laterally to the asthenosphere under the eastern NCC and contribute to the lithospheric delamination and destruction there.

Palaeomagnetic results from Early Mesozoic strata in the Qaidam Basin and their implications for the formation of the Northern China Domain

SUMMARY The Northern China Domain is located between the Central Asian Orogenic Belts to the north and the Kunlun–Qinling belt to the south, and it comprises the North China, Alxa and Tarim blocks. The relationships among the Northern China domain and the southern tectonic elements such as the Qaidam Basin/Terrane are debated because of the major modification by crustal deformation in the late Mesozoic–Cenozoic. To address this issue, we conducted a palaeomagnetic and high-precision radiometric dating study of Triassic volcanic rocks and Middle Jurassic strata in the Qaidam Terrane. Our objective was to determine the relationship between the Qaidam Terrane with the Tarim Block and the North China Block (NCB) during the late Palaeozoic and early Mesozoic. Four volcanic samples yielded zircon U-Pb ages of 236–243 Ma. The characteristic remanent magnetizations (Middle Triassic: D = 40.2°, I = 54.6°, α95 = 3.4°; Middle Jurassic: D = 27.4°, I = 48.0°, α95 = 7.9°) passed the fold and reversal tests, and yielded Middle Triassic and Middle Jurassic palaeopole positions at 57.6° N, 178.2° E, A95 = 4.0° and 65.8° N, 197.6° E, A95 = 7.8°, respectively. Based on these new poles, combined with other reliable data, we compared the apparent polar wander path (APWP) of the Qaidam Terrane with those of the NCB and Tarim Block. The results show that, from the Carboniferous through Early Cretaceous, the APWP of the Qaidam Terrane resembles that of the Tarim Block, but it is quite different from that of the NCB. Combined with other reported evidence, we conclude that the Qaidam Terrane was an independent dynamic unit during the late Palaeozoic until its connection with the Tarim Block, which was followed by continuous eastward motion. During this process, the connection between the Qaidam Terrane and the NCB–Alxa blocks occurred in the Middle Triassic, and subsequently the Qaidam Terrane underwent multiple tectonic responses to collisions with the Qiangtang Terrane, Lhasa Terrane and the India Plate, before the formation of its modern tectonic configuration.

Age and genesis of the Tongshan banded iron formation in the Zhongtiao region, North China Craton

Banded iron formations (BIFs) occur extensively within the late Neoarchean supracrustal successions of the North China Craton (NCC). The Zhongtiao region is located on the southern margin of the NCC and is a terrane that may host BIFs. The region is well known for exposed early Precambrian rocks, such as the Sushui Complex, which can be divided into three lithological units: Neoarchean tonalite-trondhjemite-granodiorite (TTG) rocks, Paleoproterozoic multi-phase granitoids, and supracrustal rocks (i.e., the Sushui Group). Despite previous studies focused on the granites within the Sushui Complex, limited information is available on the supracrustal rocks and the potential for associated BIFs that have undergone amphibolite-facies metamorphism. Here, for the first time, we conduct petrological, geochronological, and geochemical studies on a newly discovered BIF layer (i.e., the Tongshan BIF) and the associated metamorphosed volcanic and sedimentary rocks in the Sushui Group. This study constrains the formation age of the Tongshan BIF, its source characteristics, and the redox state of the depositional environment. SHRIMP zircon U–Pb analyses on biotite plagioclase gneiss (the footwall rock of the BIF) demonstrate that the Tongshan BIF was formed at ca. 2583.1 ± 9.8 Ma. The Tongshan BIF, occurrs in a volcano-sedimentary succession, and may have been deposited in a continental margin arc along the southern segment of the NCC and may best be considered as an Algoma-type BIF. Given a 2.58 Ga depositional age for the Tongshan BIF and the Sushui Group, and the more restricted depositonal nature of Algoma-type BIFs, this work highlights the potential for the identification of additional BIF layers in the Zhongtiao region.Two distinctive sedimentary facies are recognized in the Tongshan BIF based on mineral composition: an oxide facies BIF, composed of magnetite and quartz, and a silicate facies BIF, composed of magnetite, amphibole, and quartz. The Tongshan BIF displays distinct seawater-like, shale-normalized REY characteristics, including super-chondritic Y/Ho ratios, HREE enrichment relative to LREE, and positive La, Gd, and Y anomalies. Consistently positive Eu anomalies are also observed, indicating the influence of a high-T hydrothermal input. No true negative Ce anomalies occur in the Tongshan BIF, suggesting a dominantly anoxic water column contemporaneous to deposition. Further, the lack of true negative Ce anomalies extensively occurring in the Tongshan BIF is consistent with other BIFs observed globally, and confirms that ferruginous (anoxic and Fe-rich) conditions were maintained in deep seawater before to the GOE.

Late Tonian (ca. 780–750 Ma) bimodal magmatism in the Ogcheon Metamorphic Belt, Korea, at the eastern margin of North China Craton

Neoproterozoic rift-related rocks of the North China Craton (NCC), including the Korean Peninsula, provide crucial information for global supercontinent reconstruction during the Rodinia breakup and Gondwana assembly. Here, we report not only zircon and baddeleyite U-Pb ages but also zircon Hf isotopic and bulk rock compositions of amphibolites in the Ogcheon Metamorphic Belt (OMB), Korea. Zircon occurs as either primary phase or secondary one replacing igneous baddeleyite. Primary zircons analyzed from three amphibolites yielded the weighted mean 206Pb/238U ages of 755 ± 5 Ma (n = 19), 772 ± 3 Ma (n = 9), and 779 ± 13 Ma (n = 12), respectively; this result is corroborated by the baddeleyite age of ∼760–745 Ma. Secondary zircons define discordia lines with lower intercepts corresponding to the Jurassic or Cretaceous age of granites emplaced adjacent to the amphibolite. In conjunction with the occurrence of coeval (ca. 762–745 Ma) metatrachytes, our result suggests that late Tonian bimodal magmatism has lasted for ∼30 m.yr. in the OMB. Moreover, positive εHf(t) values (4.9–21.4) of zircon in amphibolites indicate a depleted mantle source of mafic magma, whereas trace element compositions attest to an intraplate setting for the crystallization. A compilation of Nb-Th and Zr–Zr/Y data suggests that the intraplate setting is also pertinent to ca. 950–750 Ma mafic rocks from the Gyeonggi Marginal Belt, Korea, as well as the NCC. Such a tectonomagmatic correlation is corroborated by detrital zircon age spectra of metasedimentary rocks in the OMB equivalent to those of early Tonian rocks in the NCC. In marked contrast to tectonic scenarios conjecturing a linkage between the OMB and the Nanhua rift, South China Craton (SCC), we conclude that the Ogcheon Belt provides rare geologic-geochronologic evidence for late Tonian breakup of the Rodinia supercontinent at the eastern NCC margin.

Late Neoarchean-early Paleoproterozoic K-rich granitoid rocks and mafic dykes from the Liaodong Bay Depression, Bohai Sea Basin: Implications for cratonization of the North China Craton

Late Neoarchean to early Paleoproterozoic potassic granites and mafic dykes are widely distributed across the Eastern Block (EB) of the North China Craton (NCC), which provide important information about the geodynamic origin and tectonic evolution of Archean terranes. Here, we are first to report the zircon U–Pb–Hf isotopic and whole-rock compositions of potassic granites and mafic dykes from the Liaoxi Rise of the Liaodong Bay Depression (LBD) in the offshore Bohai Sea Basin (OBSB) of the northeastern NCC. The potassic granites have crystallization ages of 2499–2460 Ma and are characterized by variable SiO2 content (63.2 to 72.3 wt%) and high K2O (3.27–6.88 wt%). In addition, they show geochemical features akin to post-collisional related granites and possess positive zircon εHf(t) values of 0.9 to 4.95, suggesting that they mainly originated from the partial melting of high-K mafic rocks and formed under the post-collisional setting. The mafic dykes have a crystallization age of 2485 Ma. They show high Nb (8.64–9.39 ppm) and high Nb/U ratio (10.3–14.8), as well as radiogenic initial zircon Hf isotopes (﹢1.26–﹢4.39). These values indicate affinities with Nb-enriched basalts and that they originated from mantle-derived magma under a subduction-related back-arc extensional setting. Combined with previous research results, we believed that magmatic rocks of the LBD area may have formed under remote effects of oceanic slabs being subducted from the northwest to southeast of the eastern Hebei–western Liaoning Province back-arc basin system during the late Neoarchean to early Paleoproterozoic. Meanwhile, the K-rich granitoid rocks and coeval mafic dyke sequences imply the increased maturity of the continental crust and late Neoarchean to early Paleoproterozoic basement initiation of cratonization in the NCC.

Petrogenesis of 2.7–2.65 Ga TTGs in the Wutai Complex: Constraints on the Neoarchean crustal evolution of the North China Craton

The Wutai complex, located on the boundary between the Eastern and Western Blocks of the North China Craton (NCC), offers valuable insight into early crustal growth and evolution of the NCC. In this study, a suite of 2.7–2.65 Ga TTG gneisses has been identified in the Wutai complex. Zircon grains from eight samples indicate that their protoliths were emplaced between 2706 Ma and 2640 Ma. The trondhjemites have low K2O/Na2O, high La/Yb and Sr/Y ratios, and positive Eu anomalies. The observed trend of decreasing Dy/Yb and Dy/Dy* ratios with increasing La/Yb ratios support for an amphibole-dominated fractional crystallization process during the TTG formation. Zircon Hf and oxygen isotope analyses (εHf(t) = 3.5–7.0, TDM = 2.86–2.71 Ga; δ18O = 5.5–6.3 ‰) indicate that the parental magma may originate from juvenile crustal sources altered by surface water at low temperature. When combined with the previous studies of volcanic rocks and TTGs formed around 2.5 Ga, it becomes evident that the Wutai complex experienced significant crustal growth during the period from 2.7 to 2.5 Ga. The identification of 2.7–2.65 Ga magmatic activity as well as the older detrital/xenocryst zircons up to 3.6 Ga, provide increasing evidence that the Wutai complex has a much longer and nearly continuous geological history. Combined with geological evidence, zircon data compilations and the Re-depletion model age distribution of the mantle xenoliths of the NCC, it can be inferred that the period from 2.6 to 2.5 Ga was likely the most significant for the crustal generation within the NCC's geological history.

Increasing terrigenous input into the continental margin seawater during the late Ediacaran, North China

The late Ediacaran period encompasses widespread glacial deposits and early animal radiation. The temporal and spatial context of these events is not well established. The possible links between the glacial deposits and late Ediacaran fossils are critical for understanding the co-evolution of early animals and marine environments. This study presents a detailed geochemical reconstruction from the Tuerkeng Formation on the western margin and the Dongpo Formation on the southern margin along the North China Craton (NCC). The two fossiliferous late Ediacaran formations cover a critical interval between the end of the Zhengmuguan-Luoquan glaciation and the occurrence of late Ediacaran tubular fossils (e.g., Shaanxilithes). The two formations' similar and intermediate CIA values indicate moderate weathering under a warm and humid climate. Stratigraphic covariation of water-insoluble elements in samples from Tuerkeng and Dongpo formations suggest a rapid input of terrestrial materials at the beginning of deglaciation, and these terrestrial materials continued to be input into the shallow marine environment along the western and southern margins of NCC during the deposition of the two formations. Accompanied by the continental weathering and erosion of fresh rocks during the postglacial period of late Ediacaran, abundant nutrients as well as the terrigenous materials would be continuously transported into the continental margin seawater, which may ultimately lead to the rise of the Ediacaran biota. Our results provide new insights into paleoenvironment conditions along the continental margin of NCC and highlight the critical role of the postglacial terrigenous input in the evolution of early animals.

Permian Granitic Plutons from the Northern Margin of the North China Craton: Implications for the Tectonic Evolution of the Central Asian Orogenic Belt

As the world’s largest accretionary orogen, the Central Asian Orogenic Belt (CAOB) underwent continuous juvenile crustal growth in the Phanerozoic. The northern margin of the North China Craton (NCC) and its adjacent area form the eastern segment of the CAOB, which is a key area for learning about the geological evolution of the Paleo-Asian Ocean (PAO). In the Permian, the west of the northern margin of the NCC was a post-collision extensional environment, while the east was in a subduction stage. As a connecting area, the Permian evolution of the PAO in the middle of the northern margin of the NCC has not been systematically studied. In order to fill the gap and understand the continuous temporal and spatial evolutionary process of the PAO, this paper focuses on the Permian granitic rocks in the Chifeng area. Zircon U-Pb dating and the geochemical analysis of whole-rock major and trace elements were conducted to build a granite chronological framework, and to discuss the genesis and tectonic background of the granitic rocks, along with tectono-magmatic evolutionary history in the Chifeng area. The respective LA-ICP-MS zircon U-Pb dating results from eight samples are 269 ± 1, 268 ± 3, 260 ± 4, 260 ± 1, 260 ± 1, 255 ± 2, 254 ± 2 and 256 ± 1 Ma, respectively. These results, combined with previous data, revealed that the Permian granitic rocks had undergone three events of magmatism: (1) monzogranitic-syenitic phase (294–284 Ma; Cisuralian); (2) monzogranitic phase (269–260 Ma; Guadalupian) and (3) late monzogranitic-syenitic phase (256–254 Ma; Lopingian). From the Early Permian (294–284 Ma) to the Middle Permian (269–260 Ma), granites with fine-medium-grained locally porphyritic texture and massive structure showed a high-potassium calc-alkaline series formed in a compressional setting, indicating a continuous collision between the Xing’an-Mongolian Orogenic Belt (XMOB) and the NCC. During the Late Permian-Early Triassic (256–248 Ma), granites with massive structure and medium-grained texture in the Chifeng area were magmatism dominated by A- and I-type granites of high-potassium calc-alkaline series, combined with the coeval basic rocks, which constituted a typical “bimodal” rock assemblage. This suggests that the Chifeng area was located in an extensional setting where the subducting slab broke off during the collision between the XMOB and NCC. These granitic plutons from the Permian are believed to have been generated by the subduction-collision of the Paleo-Asian oceanic crust beneath the NCC, according to emplacement time and occurrence location. Our findings provide strong evidence for Permian continuous temporal and spatial tectonic evolution and the characterization of the eventual closure of the PAO in Chifeng area at the northern margin of the NCC.

The timing of the initial collision between the South and North China blocks constraining from the sediments in the eastern Sichuan Basin

In this study, detrital zircon U–Pb geochronology, trace element and Hf isotopic compositional data from the Early-Middle Triassic clastic rocks in the eastern Sichuan Basin were obtained to distinguish the sediment provenance and constrain the timing of the initial collision between the South China and North China blocks. Detrital zircons from the Early Triassic Feixianguan Formation clastic rocks yield one major age peak at 2476 Ma and three minor age peaks at 1886, 802 and 304 Ma. These detrital zircons may be derived from the South China Block. Detrital zircons from the Early Triassic Jialingjiang Formation clastic rocks yield multiple age peaks at 979, 856, 392 and 269 Ma, indicating a mixed sediment provenance from the South China Block and Qinling Orogenic Belt. This is the first appearance of the detritus with the Qinling Orogenic Belt affinity in the eastern Sichuan Basin. Detrital zircons from the Middle Triassic Leikoupo Formation clastic rocks yield two centralized age peaks at 447 and ca. 245 Ma. These zircons may mainly be derived from the Qinling Orogenic Belt. The results indicate an abrupt change in the detrital zircon U–Pb provenance from the South China Block to the Qinling Orogenic Belt during the Early-Middle Triassic. Integrating the provenance change and other geological characteristics, we suggest that the initial collision in the eastern Qinling Orogenic Belt occurred in the Early Triassic.

Stratigraphic distributions of biomarkers and carbon isotopes in coals constrain the Permo-Carboniferous climatic changes and floral turnovers in the north China block

The intricate relationship between climate and vegetation dynamics, particularly during the late Paleozoic ice age marked by multiple icehouse-greenhouse transitions, is a compelling aspect in Earth's historical narrative. In this study, we decipher the interactions between the Permo-Carboniferous climate fluctuations and floral turnovers within the North China Craton, based on the stratigraphic distributions of biomarkers and carbon isotopes from cored coals in Huainan coalfield, North China. Our findings reveal that the changes in n-alkane, terpane, sterane, and polycyclic aromatic hydrocarbon (PAH) distributions result from a confluence of maturation, depositional environment, and organofacies effects. Molecular maturity-sensitive ratios align with the maturity stage determined by Rock-Eval pyrolysis and petrography, categorizing the coals as high volatile bituminous A/B with a composite organic matter derived from terrestrial plants and marine algae. Notably, the 18α-22,29,30-trisnorneohopane (Ts) to 17α-trisnorhopane ratio (Ts/(Ts + Tm)), as well as C31–C34 22S/(22S + 22R) hopanes and C29 20S/(20S + 20R) steranes ratios exhibit moderate correlations with %Ro, indicative of epimerization reactions induced by maturation processes. The stratigraphic variations in pristane to phytane ratios (Pr/Ph), Pr/n-C17, Ph/n-C18, C30 αβ/(αβ+βα) hopanes, and organofacies sensitive PAH indices collectively capture a paleoenvironmental shift from reducing to oxic conditions attributed to marine regression. The systematic changes in PAH concentrations and their maturity indices reflect condensation and dealkylation reactions during the maturation process. The δ13C signature manifests a negative excursion in coals of the Artinskian Shanxi Formation and a subsequent positive excursion in the Capitanian Upper Shihezi Formation coals, respectively, reflecting changes in the δ13C values of contemporaneous atmospheric CO2 in response to regional aridity fluctuations.

Metamorphic P-T-t path of Triassic eclogite from the Rongcheng region, eastern China: implications for the tectonic evolution of Sulu orogenic belt

ABSTRACT Interpretation and inversion of P-T (Pressure-Temperature) paths of high-pressure (HP) and ultrahigh-pressure (UHP) metamorphic rocks are critical to understanding the subduction and exhumation histories of an orogen. The Sulu orogen constitutes the eastern part of the Dabie-Sulu orogen, in which, HP metamorphic rocks are relatively poorly as studied compared to the well-documented UHP metamorphic rocks. This study presents the P-T paths of HP eclogites constructed by petrography, mineral chemistry, and pseudosection modelling by using the GeoPS software within the MnNCFMASKHTO (Mn-CaO-FeO-MgO-Al2O3-SiO2-K2O-H2O-TiO2-O2) system. Sample 19LR70–1 mainly consists of omphacite, garnet, quartz, minor rutile, ilmenite, and amphibole. Sample 19LR71–1 is mainly composed of omphacite, garnet, kyanite, and accessory minerals of rutile and amphibole. These two eclogite samples recorded clockwise P-T paths with peak P-T conditions of P ≥ 21.3 kbar, T ≥ 755°C and P ≥ 23.0 kbar, T ≥ 871°C, respectively. Well-correlated U-Pb ages and trace element data show that the protoliths of eclogites were 655–699 Ma and 676–754 Ma, the metamorphic ages were 212–232 Ma, and the time of partial melting were 221–225 Ma. Combined with regional geological data, we conjectured that before 240 Ma, the South China plate was subducted to the North China craton; subsequently, at 240–220 Ma, HP eclogite facies metamorphism occurred at a depth of 60–70 km. This was followed by the exhumation of these HP metamorphic rocks, coupled with concurrent partial melting, around 220–200 Ma.

Anisotropic Rayleigh wave tomography revealed lithospheric modification and tectonic deformation mechanisms in Hubei Province, central China

The collision of the North China and Yangtze blocks, along with multiple orogenic movements, has caused complex tectonic deformation of the lithosphere in Hubei Province. In order to reveal the stress distribution features and tectonic deformation mechanisms of the regional lithosphere, we inverted an azimuthal anisotropic structural model of the Hubei lithosphere from anisotropic Rayleigh wave tomography with data obtained from 48 broadband seismometers deployed in and around the province. Our model revealed strong lateral variations of azimuthal anisotropy in the crust and upper mantle, providing new seismological evidence for the lithospheric modification of the Yangtze block and the layered deformation of the lithosphere east of the North-South Gravity Lineament. We speculate that the primary dynamic factor causing lithospheric modification in the Yangtze block is related to the rifting events associated with the super-mantle plume, triggered by the deep subduction of the Pacific and Philippine plates. Meanwhile, the rifting event is also the main cause of the lithospheric structural layered deformation east of the North-South Gravity Lineament. The inverted anisotropic model, together with the results of previous geodetic and seismologic studies, revealed the causes and tectonic deformation mechanisms of anisotropy generation in the crust and upper mantle in Hubei Province. Crustal deformation in the Hubei region may be related to the eastward expansion of materials from the Tibetan Plateau and the ultra-high pressure metamorphic zone formed by the subduction and collision of the Yangtze and North China blocks, while upper mantle deformation is associated with subduction and collision of Yangtze and North China blocks, preserved fossil anisotropy from previous orogenic movements, and rifting events tied to the super-mantle plume induced by the deep subduction of the Pacific and Philippine plates. Moreover, we analyzed the regional crust-mantle coupling mechanism and concluded that the crust-mantle in the Dabie orogenic belt is coupled, whereas it is decoupled in other regions.

Nature of the Two Episodes of Paleoproterozoic Magmatism (2495 Ma and 2190 Ma) in the Trans-North China Orogen, North China, with Implications for the Tectonic Evolution

Abstract Understanding the temporal and spatial evolution of the North China Craton (NCC) basement, formed by amalgamation, is a crucial issue in global geosciences. The Huozhou complex is situated at the core of the Trans-North China Orogen (TNCO) in the NCC and comprises a considerable number of Palaeoproterozoic granitic gneisses, providing valuable insights into the tectonic evolution of the TNCO. In this study, comprehensive field geological surveys, petrology, chronology, geochemistry, and Hf isotope analysis were conducted to investigate the genesis and tectonic context of the Xingtangsi and Zhengnangou granitic gneisses and elucidate the TNCO’s tectonic evolution. The Xingtangsi granite gneiss yielded a magmatic zircon age of 2495±34 Ma, implying its Palaeo-proterozoic or Archean origin, as previously suggested. Its protolith was I-type peraluminous granite, primarily generated through the partial melting of pre-existing continental crust materials with a small quantity of mantle-derived magma. The Zhengnangou granitic gneiss’s protolith was A-type granite, and its magmatic zircon age was 2,190 ±11 Ma, indicating its Palaeoproterozoic origin rather than Archean. TDM1(Ma) for the Zhengnangou granitic gneiss ranged from 2,424 to 2,498 Ma, TDM2(Ma) varied from 2563 to 2684 Ma, and the εHf(t) value ranged from 1.3 to 3.3. These results suggest that it was primarily derived from newly formed crustal materials without any mantle-derived addition. Integrating our data with the literature, the ∼2.5 Ga magmatic activity in the Huozhou area may have formed in the tectonic setting of the continental arc, and ∼2.2 Ga A-type granite may have formed in a post-collisional extensional environment.

Tensile Fractures and in situ Stress Measurement Data Constraints on Cretaceous–Present Tectonic Stress Field Evolution of the Tanlu Fault Zone in Shandong Province, North China Craton

AbstractTectonic stress fields are the key drivers of tectonic events and the evolution of regional structures. The tectonic stress field evolution of the Tanlu fault zone in Shandong Province, located in the east of the North China Craton (NCC), may have preserved records of the NCC's tectonic history. Borehole television survey and hydraulic fracturing were conducted to analyze the paleo and present tectonic stress fields. Three groups of tensile fractures were identified via borehole television, their azimuths being NNW–SSE, NW–SE and NE–SW, representing multiple stages of tectonic events. Hydraulic fracturing data indicates that the study region is experiencing NEE–SWW‐oriented compression and nearly‐N–S‐oriented extension, in accordance with strike‐slip and compression. Since the Cretaceous, the orientation of the extensional stress has evolved counterclockwise and sequentially from nearly‐NW–SE‐oriented to NE–SW‐oriented and even nearly N–S‐oriented, the stress state having transitioned from strike‐slip‐extension to strike‐slip‐compression, in association with the rotating and oblique subduction of the Pacific Plate beneath the NCC, with the participation of the Indian Plate.