Dabieshan Orogen Research Articles

Late Mesozoic development of the southern Qinling–Dabieshan foreland fold-thrust belt, Central China, and its role in continent–continent collision

The southern Qinling–Dabieshan foreland fold-thrust belt is a key region in which to investigate the continental–continental collision between North China and South China. We provide structural evidence of a diachronous dextral strike-slip thrusting deformation from the Middle Triassic in the east to the late Late Triassic in the west, which indicates a northwestward oblique subduction and suturing of the South China plate under the North China–Qinling–Dabieshan plate. We also identify a later phase of intracontinental deformation that included an orthogonal intracontinental collision and south-vergent thrusting during the Early and Middle Jurassic, indentation of South China into the Qinling–Dabieshan Orogen and arc-shaped extrusions of the southern Qinling–Dabieshan foreland fold-thrust belt from the Late Jurassic to the Cretaceous. Our results reveal that the long-term intracontinental collision rotated clockwise in a northwest–southeast-vergent direction in the Late Triassic to northeast–east–southwest–west-vergent in the Late Cretaceous. This collision may have been driven by a north-vergent subduction of the Meso-Tethys Ocean in the south, west-vergent subduction of the Izanagi plate in the east, and south-vergent compression of the Eurasia plate in the north.

Hydration and dehydration in the lower margin of a cold mantle wedge: implications for crust–mantle interactions and petrogeneses of arc magmas

Garnet orthopyroxenites from Maowu (Dabieshan orogen, eastern China) were formed from a refractory harzburgite/dunite protolith. They preserve mineralogical and geochemical evidence of hydration/metasomatism and dehydration at the lower edge of a cold mantle wedge. Abundant polyphase inclusions in the cores of garnet porphyroblasts record the earliest metamorphism and metasomatism in garnet orthopyroxenites. They are mainly composed of pargasitic amphibole, gedrite, chlorite, talc, phlogopite, and Cl-apatite, with minor anhydrous minerals such as orthopyroxene, sapphirine, spinel, and rutile. Most of these phases have high XMg, NiO, and Ni/Mg values, implying that they probably inherited the chemistry of pre-existing olivine. Trace element analyses indicate that polyphase inclusions are enriched in large ion lithophile elements (LILE), light rare earth elements (LREE), and high field strength elements (HFSE), with spikes of Ba, Pb, U, and high U/Th. Based on the P–T conditions of formation for the polyphase inclusions (˜1.4 GPa, 720–850°C), we suggest that the protolith likely underwent significant hydration/metasomatism by slab-derived fluid under shallow–wet–cold mantle wedge corner conditions beneath the forearc. When the hydrated rocks were subducted into a deep–cold mantle wedge zone and underwent high-pressure–ultrahigh-pressure (HP–UHP) metamorphism, amphibole, talc, and chlorite dehydrated and garnet, orthopyroxene, Ti-chondrodite, and Ti-clinohumite formed during prograde metamorphism. The majority of LILE (e.g. Ba, U, Pb, Sr, and Th) and LREE were released into the fluid formed by dehydration reactions, whereas HFSE (e.g. Ti, Nb, and Ta) remained in the cold mantle wedge lower margin. Such fluid resembling the trace element characteristics of arc magmas evidently migrates into the overlying, internal, hotter part of the mantle wedge, thus resulting in a high degree of partial melting and the formation of arc magmas.

Collision and rotation of the South China block and their role in the formation and exhumation of ultrahigh pressure rocks in the Dabie Shan orogen

Terra Nova, 24, 339–350, 2012AbstractStudies of regional plate‐scale processes that may influence the exhumation of ultra‐high pressure (UHP) metamorphic rocks are few despite their potential importance. Here, we review and summarize available age constraints along with the Qinling‐Dabie Shan orogen, which separates the North China Block (NCB) from the South China Block (SCB). We find that collision‐related events in the west and extension‐related events in the east, where the large Dabie Shan UHP terrane is located, were contemporaneous. Available palaeomagnetic data indicate clockwise rotation of the SCB relative to the NCB during this time. Previous work indicated that the collision propagated from east to west where indentation of the SCB into the Qinling‐Dabie Shan orogen was active in the Hannan Dome area at 165 ± 3 Ma as constrained by new 40Ar/39Ar dates on synkinematic sericite in an indentation‐related mylonitic shear zone. While this contraction was occurring in the west, exhumation of the UHP terrane was occurring in the Dabie Shan in the east. We propose that the collision of the SCB with the NCB occurred not only in a scissor‐like fashion, as previously suggested, but also involved a later rotation about a pole west of the Dabie Shan during the closure of the Mianlue Ocean. As a consequence of this rotation, extension occurred between the South China Block and North China Block east of the pole of rotation leading to extensional exhumation of the Dabie Shan orogen. This microcontinent‐scale rotation of the SCB may have provided an important component in the exhumation of the largest UHP terrane in the world.

Tracing exhumation of the Dabie Shan ultrahigh-pressure metamorphic complex using the sedimentary record in the Hefei Basin, China

Jurassic rocks in the Hefei Basin were deposited by braided-fluvial and alluvial-fan systems, characterized by a general coarsening-upward sequence. Multiproxy provenance analyses demonstrate that the sediment source areas for the Hefei Basin are composed of a variety of rocks, including ultrahigh-pressure (UHP) and high-pressure (HP) metamorphic rocks and Yangtze basement rocks of the axial Dabie Shan metamorphic complex, the Luzhenguan complex granite, low- and medium-grade metamorphic rocks, and the Yangshan Group sandstone in the North Huaiyang fold and thrust belt. A Middle Jurassic section in the western part of the basin is characterized by relatively high e Nd values (at 176 Ma), ranging from −13.8 to −11.3, whereas a section in the middle part of the basin has higher 147 Sm/ 144 Nd ratios, from 0.1168 to 0.1266 and somewhat lower e Nd values (at 176 Ma), from −15.0 to −14.5. Sediments in a section in the eastern part of the basin have the lowest e Nd values (at 176 Ma), ranging from −22.0 to −14.6, the highest T DM values, from 1.8 to 2.4 Ga, and low 147 Sm/ 144 Nd ratios, from 0.0937 to 0.1067. Provenance analyses of detrital compositions and Nd isotopic compositions of the sediments in the Hefei Basin clearly demonstrate that the depth of exhumation in the Dabie Shan orogen increases from the west to the east; the unroofing ages of the UHP and HP metamorphic rocks change from Early Jurassic to Late Jurassic westward. The exhumation rate during the Late Triassic and Jurassic is inferred to have increased eastward from ∼1.4 mm/a to ∼2.5 mm/a on average. The sediments in the basin record the episodic thrusting events and periodic unroofing in the orogen.

Phase equilibria of HP–UHP mica-schists in Jiangling, Eastern Dabieshan orogen

The HP–UHP metamorphic terrane of Jiangling, eastern Dabieshan comprises extensively distributed granitic gneisses, mica-schists and numerous eclogite blocks. The mica-schists generally contain garnet, phengitic muscovite, biotite, plagioclase, quartz, rutile and a small amount of epidote and hornblende. Study on petrography and phases equilibria in the NCKMnFMASH system indicates that the present mineral assemblages in mica-schists are not in equilibrium. The earlier stage of mineral assemblage represented by garnet and phengite reflects a HP–UHP condition. The garnet compositions and the phengite Si contents give a PT condition of 580–600 °C at 2.6–2.8 GPa. The garnet zonation records an earlier progressive metamorphic process which may be associated with the appearance of glaucophane, jadeite and lawsonite. The later stage of mineral assemblage characterized by the presence of biotite and plagioclase reflects a PT condition of 620–635 °C at 0.9–1.1 GPa, belonging to the HP amphibolite facies. The main mineral assemblage in mica-schists from the Jiangling region has recorded a complete HP–UHP metamorphic process.

Quantitative P–T–X constraints on orthopyroxene‐bearing high‐pressure granulites in felsic–metapelitic rocks: evidence from the Huangtuling granulite, Dabieshan Orogen

AbstractHigh‐pressure granulites are generally characterized by the absence of orthopyroxene. However, orthopyroxene is reported in a few high‐pressure, felsic–metapelitic granulites, such as the Huangtuling felsic high‐pressure granulite in the North Dabie metamorphic core complex in east‐central China, which rarely preserves the high‐pressure granulite facies assemblage of garnet + orthopyroxene + biotite + plagioclase + K‐feldspar + quartz. To investigate the effects of bulk‐rock composition on the stability of orthopyroxene‐bearing, high‐pressure granulite facies assemblages in the NCKFMASHTO (Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–Fe2O3) system, a series of P–T–X pseudosections based on the melt‐reintegrated composition of the Huangtuling felsic high‐pressure granulite were constructed. Calculations demonstrate that the orthopyroxene‐bearing, high‐pressure granulite facies assemblages are restricted to low XAl [Al2O3/(Na2O + CaO + K2O + FeO + MgO + Al2O3) < 0.35, mole proportion] or high XMg [MgO/(MgO + FeO) > 0.85] felsic–metapelitic rock types. This study also reveals that the XAl values in the residual felsic–metapelitic, high‐pressure granulites could be significantly reduced by a high proportion of melt loss. We suggest that orthopyroxene‐bearing, high‐pressure granulites occur in residual overthickened crustal basement under continental subduction–collision zones and arc–continent collision belts.

Lithospheric thickness beneath the Dabie Shan, central eastern China fromSreceiver functions

P and S receiver functions obtained from a portable array of 34 broad-band stations in east central China provide a detailed image of the crust–mantle and lithosphere–asthenosphere boundaries (LAB) in the Dabie Shan and its adjacent areas. Clear S-to-P converted waves produced at the LAB show a thin lithosphere beneath the whole study area. Based on our results, the thickest lithosphere of 72 km is observed beneath the southern part of the area within the Yangtze craton, whereas beneath the North-China platform, the lithosphere is only 60 km thick. S receiver functions also reveal, in good agreement with P receiver functions, a maximum depth of the Moho beneath the Dabie Shan orogen at approximately 40 km. Furthermore, we interpret the structural difference at 32° latitude as the probable location of the mantle suture formed between the Yangtze and the Sino-Korean cratons.

Apatite-fission-track geochronology and its tectonic correlation in the Dabieshan orogen, central China

Apatite-fission-track geochronology and its tectonic correlation in the Dabieshan orogen, central China

Dislocation structure of the crust-mantle boundary and low-velocity body within the crust beneath the Dabie Shan collision orogen

From April of 2001 to March of 2002, a passive seismic array experiment was carried out in the Dabie Shan and its adjacent region. In this experiment, totally 34 broadband seismic stations were deployed along a profile across the Dabie Shan orogen and North-China platform. This profile is about 500 km long from Cuilin (34°40′N, 114°49′E), Henan Province, to Dajipu (30°20′N, 115°03′E), Hubei Province. The space between stations is about 3-8 km in the Dabie Shan orogenic belt and about 15-20 km in other area. The receiver function profile and S-wave velocity structure of the crust and upper mantle down to 100 km depth along the profile are investigated in terms of the receiver function techniques (Liu et al., 1996, 2000). Our results show that the crust beneath the Dabie Shan orogen has an obviously asymmetric blocked structure in the direction perpendicular to the mountain strike. The maximal crustal thickness reaches to 42 km. The crust-mantle boundary has a dislocation structure correlated to the crustal blocks and the largest offset reaches to 8 km. In the kernel of the orogen exists a low-velocity body inside the crust, which is separated into two parts corresponding to the South Dabie and North Dabie on the surface, respectively. Probably a vertical divergent movement between both took place in history. The crust below this low-velocity area has a positive gradient velocity structure with the depth, and the upper mantle down to the depth of 70 km has the lower S-wave velocity than its both sides. Beneath the Dabie Shan, however, a high-velocity anomaly exists in the upper mantle below 70 km.

Apatite-fission-track geochronology and its tectonic correlation in the Dabieshan orogen, central China

Apatite-fission-track geochronology and its tectonic correlation in the Dabieshan orogen, central China

Tectonic evolution of the Dabieshan orogen: In the view from polyphase deformation of the Beihuaiyang metamorphic zone

The Beihuaiyang metamorphic zone was formed by the Early Mesozoic collision of the North and South China Blocks. It consisted of the Foziling and Luzhenguan complexes and was thought to have never afforded a deep subduction. A similar feature of the deformation in the Dabieshan UHP metamorphic rocks implies that these different tectonic units share the same geodynamic background. The early stage of deformation can be preserved on account of their relatively shallower subduction than that for UHP rocks. On the basis of an analysis of the geo- logical structure and geochronological results, five deformational stages have been recognized: a D1-Early compressional deformation which represents the continental subduction; a D2-Early exhumation deformation producing a syn-convergence exhumation; a D3-Main deformation, represented by an exhumation deformation with Late Triassic age; a D4-Doming and its margin extensional gravity collapse deformation and finally a D5-regional extensional deformation of Cretaceous that was mostly introduced by the migmatization and plutonism.

Late Cretaceous-Cenozoic exhumation history of Tiantangzhai region of Dabieshan Orogen: Constraints from (U-Th)/He and fission track analysis

Integrated fission track and (U-Th)/He analysis is carried out on 6 apatite and 6 zircon samples from a near vertical section in The Tiantangzhai region at the core of the present Dabieshan orogen. The result shows that the region experienced cooling/exhumation during the Late Cretaceous and Early Tertiary period. Age-elevation relationships for different dating systems and different minerals suggest a pulse of rapid exhumation at ∼110 Ma before present, preserved in the structurally highest samples. At lower elevations, ages begin to decrease with decreasing elevation, suggesting lower exhumation rates since 90 Ma. Two periods of different exhumation rates are identified since 90 Ma. The average apparent exhumation rate for the period of 43.4–22.5 is 0.062 km/Ma, whereas that for the period of 76.4–47.4 Ma is 0.039 km/Ma.

Crustal structure and exhumation of the Dabie Shan ultrahigh-pressure orogen, eastern China, from seismic reflection profiling

Crustal-penetrating seismic reflection data across the ultrahigh-pressure (UHP) Dabie Shan orogen show that the Yangtze craton was subducted beneath the Sino-Korean craton, forming a bivergent orogenic fabric strikingly similar to normal (non-UHP) collision belts. Hence preservation of UHP minerals (coesite and diamond) may be unrelated to differences between collisional histories, but may be due to opportunities for subsequent intracrustal uplift of material that is routinely returned from mantle depths into the lower crust in most collisional orogens. Only a narrow channel (≤5 km) now exists from the mantle into the crust through which UHP material was returned to lower-crustal depths as thin slabs. We image the Dabie Shan as a crustal-scale dome formed during postcollisional intracrustal uplift by core-complex-type exhumation of the lower crust, tectonically unrelated to the earlier exhumation from >100 km to <35-40 km.

Late Cretaceous-Cenozoic exhumation history of Tiantangzhai region of Dabieshan Orogen: Constraints from (U-Th)/He and fission track analysis

Late Cretaceous-Cenozoic exhumation history of Tiantangzhai region of Dabieshan Orogen: Constraints from (U-Th)/He and fission track analysis

Geochronological Constraints on the Post-Collisional (150-75 Ma) Thermal Extension in the Dabieshan Orogen, Central China

Geochronological Constraints on the Post-Collisional (150-75 Ma) Thermal Extension in the Dabieshan Orogen, Central China