Yangtze Craton Research Articles

Pressure–temperature–time (P–T–t) evolution of fore-arc and foreland schist in the Qinling Orogenic Belt, China: Implications for Late Paleozoic and Triassic subduction termination

The Qinling Orogenic Belt (QOB) is a segment of the larger Central China Orogen and marks the amalgamation of the South and North China Cratons during a protracted period spanning the Neoproterozoic through to Triassic. The complex evolution of the QOB has been extensively studied through U–Pb zircon geochronology, but lacks fundamental characterisation of its time-integrated thermal history. Moreover, the comparatively few metamorphic studies that exist focus exclusively on high-pressure rocks at the margins of major tectonic divisions within the QOB. Samples for this study are metapelitic schists sourced from the Qinling Mountains, North Qinling Belt (NQB), deep in the QOB interior. Cordierite schist has metamorphic monazite age affinities to Late Triassic magmatism and metamorphism in the South Qinling Belt (SQB) occurring at 230–220 Ma. Calculated phase equilibria modelling constrains metamorphism to 1.0–2.0 kbar and 530–545 °C, corresponding to a steep apparent thermal gradient between ~275–530 °C/kbar. This probably represents contact metamorphism of the Liuling Group turbidite sequence by intruding magma. Garnet–staurolite schist has metamorphic monazite age data that overlaps with Late Paleozoic events occurring between 420 and 400 Ma. Calculated phase equilibria modelling constrains peak metamorphism to ~7.1 kbar and 615 °C, corresponding to a shallower thermal gradient of ~87 °C/kbar. This represents Barrovian-style metamorphism of fore-arc sedimentary units during arc–continent collision marking the closure of the Shangdan Ocean. Metamorphism of these fore-arc sequences has a comparable thermal gradient to Guishan Complex equivalents in the Tongbai Orogen, which is a continuation of the Qinling Orogen to the east. This study establishes previously undocumented contact metamorphism in the northern SQB and Barrovian-style metamorphism in the NQB, providing key constraints for tectonic models that explain the evolution of the QOB and broader Central China Orogen.

Petrogenesis and Ore Genesis of the Lengshuiqing Magmatic Sulfide Deposit in Southwest China: Constraints from Chalcophile Elements (PGE, Se) and Sr-Nd-Os-S Isotopes

The Lengshuiqing magmatic Ni-Cu ore deposit is hosted in four small mid-Neoproterozoic mafic-ultramafic intrusions in the western margin of the Yangtze craton in China. The ore-bearing intrusions were emplaced into early Neoproterozoic metamorphosed volcanic-sedimentary rocks, granites, and diorites. The intrusions are dominated by lherzolite, olivine websterite, websterite, and gabbro, with sulfide mineralization associated with ultramafic rocks in the lower parts of the intrusions. The forsterite contents of olivine crystals in the Lengshuiqing ore-bearing intrusions are up to 86 mol %, indicating that their parental magma experienced moderate degrees of fractional crystallization. Olivine crystals in the intrusions are depleted in Ca (

Cryptic encrusting communities in a Middle Devonian mesophotic paleoenvironment of the Holy Cross Mountains, Poland

The Middle Devonian (Givetian) chaetetid sponges and alveolitid tabulate corals that inhabited mesophotic paleoenvironments of the southern shelf of Laurussia (Holy Cross Mountains, Poland) have been studied with respect to encrustation patterns. These epibiotic communities are characterized by modest diversity and high dominance, and show distinct polarization with respect to the exposed and cryptic sides of the host's skeletons. The most abundant davidsoniid brachiopods and microconchids show strong preferences toward the lower (cryptic) sides, while auloporid tabulate corals dominate on the exposed sides of the hosts. The remaining and much rarer epibionts, cornulitids and rugose corals, show no clear preferences. In some shallow-water Silurian paleoenvironments, auloporids are known to dominate the cryptic sides of the hosts. Thus, considering the auloporid tabulates as photosymbiotic corals, their absence or rarity in the Middle Devonian cryptic habitats might have resulted from insufficient irradiance levels in otherwise depleted light conditions. As a result, the available space and lack or lower competition for the area with faster-growing colonial auloporids, enabled solitary encrusters to colonize the cryptic niches. The scarce bioerosion traces and rather low diversity of epibionts in our case may indicate that these mesophotic reefs developed in a nutrient-poor, oligotrophic habitats. The davidsoniid-dominated, cryptic encrusting communities were widespread in some paleoenvironments during the Middle Devonian, being known from both Laurussia and South China craton. However, such mesophotic cryptic communities, characterized by distinct polarization in comparison to open-surface environments, contrast with other Givetian deep-water, aphotic cryptic communities reported so far, where such polarization is hardly visible.

The relationship between systematic metamorphic patterns and collisional processes along the Qinling–Sulu–Odesan collisional belt between the North and South China Cratons

Abstract Along the Qinling–Sulu–Odesan collisional belt, the peak metamorphic conditions reflect systematically changing metamorphic regimes from east to west: ultra-high temperature (UHT) granulite-facies metamorphism in the Odesan area; high pressure (HP) eclogite-facies metamorphism in the Hongseong area; ultra-high pressure (UHP) eclogite-facies metamorphism in the Sulu, Dabie and Hong'an areas; HP eclogite-facies metamorphism in the Tonbai area; epidote–amphibolite- and blueschist facies metamorphism in the Wudang area; and HP granulite-facies metamorphism in the western Qinling area. Additionally, the Triassic post-collisional igneous rocks regionally intruded at both ends of the collision belt, in the west Qinling and Hongseong–Odesan areas. These observations indicate that the following collisional processes occurred along the Qinling–Dabie–Odesan collisional belt. The North China Craton and South China Craton first collided at their eastern margins (the Odesan area) with an angle of approximately 60° between their long axes. Consequently, the amount of oceanic slab subducted before the collision increased from the Odesan area to the Sulu area, resulting in an increase in the depth of slab break-off. After slab break-off occurred in the Sulu area, the lateral tearing force strengthened, decreasing the depth of slab break-off from the Sulu area to the western Qinling area as collision propagated westward.

Zircon U‐Pb age, Trace Element, and Hf Isotopic Compositions of Nordmarkite in the Lizhuang Rare Earth Element Deposit in the Western Margin of the Yangtze Block

AbstractThe Mianning–Dechang (MD) rare earth element (REE) belt, located in the northern Kangdian axis (KDA) in the western margin of the Yangtze platform, is one of the most economically significant REE mineral belts in China. REE mineralization is associated with Himalayan carbonatite–alkaline complexes. The Lizhuang nordmarkite occurred in the northern part of the MD REE belt. The majority of zircons from the Lizhuang nordmarkite are characterized by pronounced positive Ce yet slightly negative Eu anomalies and high U/Yb. Moreover, all zircons have stable Hf isotopic compositions with initial 176Hf/177Hf ratios ranging from 0.282739 to 0.282808 and an average value of 0.282773. The negative Lu/Hf and positive εHf(t) range from −0.98 to −0.94 (average value of −0.96) and from −0.56 to 1.89 (the majority is positive, with an average of 0.66), respectively. These characteristics indicate that the rock is derived from an enriched mantle and subducted material. LA‐ICP‐MS analysis of the zircons from the intrusion yields a weighted mean 206Pb/238U age of 28.57±0.61Ma. During this period, the tectonic activity in the KDA is not plate subduction but an intraplate tectonic exhibiting fold–thrust and strike–slip behaviors in the western marginal zone of the Yangtze platform (WMYB). We suggest the possibility of an existing eastward old slab subduction under WMYB combined with a regional tectonic evolution. The Lizhuang nordmarkite may be derived from an enriched mantle beneath the western part of the Yangtze craton, which originated from the remelting of the Tethys subducting slab, because of the Himalayan strike–slip that formed a special type of REE deposit called strike–slip‐type REE deposits.

Sedimentary responses to the East Asian monsoon and sea level variations recorded in the northern South China Sea over the past 36 kyr

Sediment grain size is an important proxy to detect sedimentary process and record paleoenvironmental variations in continental slopes. Grain size measurements were performed for 298 samples of the 5.96-m-long core PC338 spanning the past 36 kyr recovered from the northern South China Sea (SCS). Results show that sea level and climatic influences on grain size distributions are crucial. A turbidite formed during the Last Glacial Maximum (LGM) is ascribed to the favorable topography close to the Red River estuary induced by the low sea level. Four end-member (EM) components for the normal sediment layers were unmixed using a lognormal parametric end member modeling (EMM). With the sea level decreasing, more EM4 (∼15–100 μm) and less EM1 (∼0–2 μm) supplied the SCS slope. Because EM2 (∼2–10 μm) consisted of fluvial suspension is dominated by the East Asian summer monsoon (EASM) precipitation, it has the potential to substitute for the EASM intensity. EM2 varied in-phase with many south China paleoclimate records and the 30°N July insolation over the past 36 kyr, and cooling climate events (including the LGM, Heinrich events H1 and H3, Younger Dryas, 8.2 ka and 10.3 ka) lowered the EM2 content. Our results further confirm the synchronous EASM evolution in the South China continent mainly forced by the Northern Hemisphere summer insolation.

Bauxite to eclogite: Evidence for late Permian supracontinental subduction at the Red River shear zone, northern Vietnam

We have investigated the geological processes recorded in aluminous granulites from the Red River shear zone in northern Vietnam using mineral and whole-rock chemistries, fluid inclusions, metamorphic pressure–temperature paths, and geochronology. The granulites are extremely rich in Al2O3 (36.3–50.9wt%), TiO2, and total Fe2O3, and poor in SiO2 (7.9–24.1wt%), MgO, CaO, Na2O, and K2O. The granulites are enriched in high-field-strength elements and rare earth elements, and severely depleted in large-ion lithophile elements. These features strongly suggest the protolith was lateritic bauxite. Moreover, the other elemental concentrations and the Zr/Ti ratios point to basaltic rock as the precursor of the bauxite. Some of the aluminous granulites contain high-pressure mineral inclusions of kyanite, staurolite, siderite, and rutile, none of which are observed in the matrix. Abundant primary carbonic fluid inclusions are observed in garnet, corundum, and staurolite, but are rare in quartz and zircon. The average densities of fluid inclusions in garnet, corundum, staurolite, quartz, and zircon are 1.00±0.06, 1.07±0.04, 1.09±0.03, 0.29±0.07, and 1.15±0.05g/cm3, respectively. The mineral features not only in the matrix and but also in garnet from all rock types, isochemical phase diagrams obtained for each bulk rock composition, and Zr-in-rutile thermometry indicate an early eclogite-facies metamorphism (~2.5GPa at 650°C) and a subsequent nearly isothermal decompression. Zircons yield a wide range of U–Pb ages from 265 to 36Ma, whereas the dark luminescent cores of the zircons, which contain high-density CO2 inclusions, yield a concordia age of 257±8Ma. These observations suggest that the dark luminescent zircon cores were formed at the same time as the garnet, corundum, and staurolite that contain high-density CO2 fluid inclusions. Based on the carbonic fluid inclusion isochore and the densities as well as calculated phase diagram, the concordia age can be regarded as recording a prograde stage of metamorphism under conditions lower than 600°C and 0.7GPa. Our new data provide the following geological and tectonic constraints: 1) the eruption of basalt occurred before the Permian, possibly related to subduction of the Paleo-Tethys Plate beneath the Indochina craton near the paleo-equator in the Devonian–Carboniferous; 2) strong weathering transformed the basalt to bauxite before the late Permian; 3) the uppermost continental crust, including the bauxites, was subducted in the late Permian due to the collision of the Indochina and South China cratons, leading to eclogite-facies metamorphism; 4) the rocks were then exhumed; and 5) shearing-related thermal events took place until the Paleogene.

The tectonic boundary between the Okcheon and Taebaeksan basins, South Korea: A restraining bend of a continental transform fault between the South and North China Cratons

AbstractThe geological relationship between the Okcheon and Taebaeksan basins of the Okcheon belt on the Korean peninsula is a key issue in reconstructing the tectonic evolution of the peninsula. The boundary between the two basin sequences has been variously interpreted as a conformable, unconformable, or thrust contact, without clear evidence being provided for any of these hypotheses. Detailed examination of structures and microfabrics of deformed rocks adjacent to the contact in the Bonghwajae area suggests that the boundary between the two basin sequences is a thrust. Based on the U–Pb ages of detrital zircons from metasedimentary rocks and pre‐existing geologic data from the Okcheon belt, the thrust is a relay structure between two segments of a continental transform fault along which the Okcheon Basin was juxtaposed against the Taebaeksan Basin during the Permian–Triassic suturing of the North and South China Cratons.

A refined late-Cryogenian – Ediacaran earth history of South China: Phosphorous-rich marbles of the Dabie and Sulu orogens

The late-Cryogenian – Ediacaran geological framework for South China is constructed principally from sedimentary successions preserved in the central and western regions of the Yangtze Block. New stratigraphic and carbonate-carbon isotope data allow us to extend that framework into the exhumed HP-UHP subduction complexes of the eastern Dabie and Sulu orogens that separate the South and North China cratons. Those data show that marble and phosphorous-rich (P-rich) units in those complexes were originally part of an Ediacaran shallow-marine shelf-carbonate platform. The basal pebbly schist (metadiamictite) and lowermost P-rich marble of the Jinping Formation (Haizhou Group) in the Sulu Orogen matches in both facies character and C-isotope profile that of the Marinoan-equivalent glacial-cap carbonate couplet of the Nantuo and Doushantuo formations. The Daxinwu Formation (Susong Group) in the eastern Dabie Orogen contains a marble unit that has, for several hundreds of metres, a strikingly uniform C-isotope profile of low δ13C positive values and is overlain by a P-rich graphitic schist; these features match those of the late Ediacaran to early Cambrian Dengying Formation. These correlations establish that the HP-UHP metasedimentary rocks, many of which were once considered to be Palaeo- to Mesoproterozoic in age, are a Neoproterozoic-age cover sequence of the continental margin of the Yangtze Block. Further, their widespread development limits their utility as indicators of offset across the Tan-Lu fault zone and, instead, favours tectonic models that interpret that feature as a continental-scale tear fault formed during the Mesozoic collision and suturing of the North and South China cratons.

Origins of ore-forming fluid and material of the quartz–vein type Mo deposits in the East Qinling–Dabie molybdenum belt: A case study of the Qianfanling Mo deposit

The Qianfanling quartz–vein type molybdenum deposit is located in the East Qinling–Dabie Mo belt. The Mo mineralization in the deposit is mainly present as structurally controlled Mo-bearing quartz veins. Based on chromatography analysis of the Qianfanling Mo deposit, the gas compositions of fluid inclusions in quartz dominantly contain H2O and relatively high concentrations of CO2 (11.019 to 18.554mol%). Cations and anions of liquid compositions of fluid inclusions are mainly Na+ and Ca2+, and SO42− and Cl−, respectively. The characteristics of gas and liquid compositions of fluid inclusions in quartz indicate that the Qianfanling Mo deposit formed under conditions of high oxygen fugacity. Analytical results of He-Ar isotopes of fluid inclusions in pyrite from the Qianfanling Mo deposit show that 3He/4He ratios vary from 0.02438 to 0.0796 Ra (Ra is the 3He/4He ratio of air=1.40×10−6), with F4He values of 252,509–885,224. The calculated Hemantle values range from 0.18 to 0.87%, with an average of 0.39%. 40Ar/36Ar ratios are 694.4–1473.4, with the estimated 40Ar* (radiogenic 40Ar) proportion of 79.9%. These He-Ar isotopic data indicate that most of the He in the fluid inclusions was derived from the crust, with negligible atmospheric He and only a very small input from the mantle probably. Furthermore, the Ar in the ore-forming fluid was mainly derived from the crustal source, with minor atmospheric Ar involved. 17 Re–Os model ages of 15 molybdenite samples from the 4 quartz-vein type Mo deposits (Qianfanling, Daxigou, Maogou, and Zhifang) range from 215.0 to 248.2Ma, with a mean value of 235.6Ma, which is close to the age of peak collision between the North China and Yangtze Cratons. The Re contents in molybdenite from the 4 deposits range from 0.19 to 39.16ppm, with an average of 17.41ppm, indicating a crust-dominated source. Re contents in molybdenite from Mesozoic Mo deposits in different ages and types in the East Qinling–Dabie Mo belt show different characteristics of ore sources. Combined with gas and liquid compositions and He-Ar isotopic characteristics of fluid inclusions, as well as Re contents in molybdenite of this paper and previous studies, we suggest that the ore-forming fluid and material of the Qianfanling Mo deposit were mainly derived from crustal magmatic source. This magmatic source could have formed by partial melting of deep crustal rocks under a certain condition during the collision between the North China and Yangtze Cratons.

Geochemistry, 40Ar/39Ar geochronology, and geodynamic implications of Early Cretaceous basalts from the western Qinling orogenic belt, China

The Qinling-Dabie orogenic belt was formed by the collision of the North and South China Cratons during the Early Mesozoic and subsequently developed into an intracontinental tectonic process during late Mesozoic. Field investigations identified the presence of late Mesozoic basalts in the Duofutun and Hongqiang areas in the western Qinling orogenic belt. The petrogenesis of these basalts provides an important constraint on the late Mesozoic geodynamics of the orogen. The representative basaltic samples yield the 40Ar/39Ar plateau age of about 112 Ma. These samples belong to the alkaline series and have SiO2 ranging from 44.98 wt.% to 48.19 wt.%, Na2O + K2O from 3.44 wt% to 5.44 wt%, and MgO from 7.25 wt.% to 12.19 wt.%. They demonstrate the right-sloping chondrite-normalized REE patterns with negligible Eu anomalies (1.00–1.10) and PM-normalized patterns enriched in light rare earth element, large ion lithophile element and high field strength element, similar to those of OIB rocks. These samples additionally show an OIB-like Sr-Nd isotopic signature with εNd(t) values ranging from +6.13 to +10.15 and initial 87Sr/86Sr ratios from 0.7028 to 0.7039, respectively. These samples are geochemically subdivided into two groups. Group 1 is characterized by low Al2O3 and high TiO2 and P2O5 contents, as well as high La/Yb ratios (>20), being the product of the high-pressure garnet fractionation from the OIB-derived magma. Group 2 shows higher Al2O3 but lower P2O5 contents and La/Yb ratios (<20) than Group 1, originating from asthenospheric mantle with input of delaminated lithospheric component. In combination with available data, it is proposed for the petrogenetic model of the Early Cretaceous thickened lithospheric delamination in response to the asthenospheric upwelling along the western Qinling orogenic belt.

Zircon Geochronological Evidence for Participation of the North China Craton in the Protolith of Migmatite of the North Dabie Terrane

The plate affiliation of the North Dabie terrane (NDT) has been controversial. To address this fundamental question, an integrated study of internal structure, in-situ U-Pb dating and trace element analysis in zircons and field investigation for migmatite in the NDT was carried out, which reveals participation of crustal rocks of the North China craton (NCC) in the protolith in addition to the more common crustal rocks of the Yangtze craton (YC). The evidence of an NCC affinity for protolith of migmatite in the NDT is the ∼2.5 Ga (2 486±14 and 2 406±26 Ma) magamtic age and ∼1.8 Ga (1 717±79 Ma) metamorphic age in the relict zircon domains because these two age groups are characteristic for the evolution of the NCC. The evidence of a YC affinity for protolith of migmatite in the NDT is the more common 0.7–0.8 Ga (e.g., 787±12 Ma) magamtic zircon age. Mid-Neoproterozoic magmatic age (0.7–0.8 Ga) is a symbol of YC basement rocks. In view of the widely exposed YC crustal components in the NDT, we suggest that the protolith of the NDT is mainly crustal rocks from the YC with minor crustal components from the NCC. The zircon rim domains and new growth grains from all the migmatite samples are characterized by anatectic zircons and have a widely concordant ages ranging from 112.2±2.8 to 159.6±4.3 Ma with several peak values, suggesting a long lasting multistage anatexis. In conclusion, the NDT has a mixed protolith origin of both the YC and the NCC crustal rocks were strongly remoulded by anatexis during orogenic collapse.

Mid-Neoproterozoic amphibolite facies metamorphism at the northern margin of the Yangtze craton

The tectonic setting of the continental margin of the Yangtze craton during the Neoproterozoic has long been a subject of debate. The Douling Complex is a small segment of crystalline basement in the northern Yangtze craton; the study of which may provide useful insights into the tectonic evolution of this area. In this paper we report medium-grade regional metamorphism that occur in the Douling Complex. Petrographical textures and mineral compositions suggest that amphibolite facies rocks from the Douling Complex underwent a progressive metamorphic evolution from staurolite–kyanite grade to sillimanite grade. Conventional geothermobarometry defines P–T conditions to be 490–560 °C and 6–7.5 kbar for prograde metamorphic stage and 630–720 °C and 8–11 kbar for peak metamorphic stage. The post-peak evolution is characterized by decompression and thermal relaxation. Metamorphic zircons from garnet amphibolites and metapelites and magmatic zircons from a syn-deformed pegmatite pod yield U–Pb ages between 820 ± 5 Ma and 779 ± 3 Ma, with two populations at ca. 820–815 Ma and ca. 790–780 Ma, respectively. Biotites from metapelites also give two 40Ar/39Ar plateau ages of 814 ± 4 Ma and 790 ± 5 Ma. It is inferred that peak metamorphism occurred at ca. 820–815 Ma and subsequent cooling took place at ca. 790–780 Ma. Considering the distinct Precambrian crustal history of the Douling Complex, together with medium-grade amphibolite facies metamorphism accompanied by a clockwise P–T path, we propose that these observations provide evidence for the collision of the small Douling block with the northern margin of the Yangtze craton during the Mid-Neoproterozoic. Immediately after this collision, a newly accreted Andean-type active continental margin may have formed along the northern Yangtze craton.

Juxtaposition of allochthonous terranes in the central Korean Peninsula: Evidence from zircon U-Pb ages and O-Hf isotopes in Jurassic granitoids

The eventual docking of an exotic continental mass over the course of a Wilson cycle is marked by intracontinental sites of prograde metamorphism, contractional deformation, and syn- or post-collisional magmatism. This study shows that inherited premagmatic zircon in subsequently emplaced granitoid rocks provides another line of evidence for the collisional orogeny. Following the continental collision between the North and South China Cratons, Jurassic granitoids intruded widely throughout the central Korean Peninsula in association with the subduction of the Paleo-Pacific plate. The latest Early to Middle Jurassic (177–167Ma) granitoids occur throughout the cratonic Gyeonggi Massif, whereas Early Jurassic (194–184Ma) granitoids occur locally along the Okcheon Metamorphic Belt to the southeast of the massif. These two spatiotemporal groups differ profoundly in their age patterns and O-Hf isotopic signatures of inherited zircon. The younger group yields a typically North China-like Archean-Paleoproterozoic (mostly 2.5–1.8Ga) zircon inheritance. In contrast, inherited zircons from the older group exhibit exclusively Neoproterozoic (ca. 0.9–0.7Ga) and Paleozoic (ca. 0.4Ga) cluster along with Archean-Paleoproterozoic populations. The exotic feature of the protolith of the older group is further indicated by significantly lower δ18O (−0.9 to +4.9‰) and positive εHf (+3 to +15) values of the Cryogenian zircon cores. The results of zircon analysis demonstrate that South and North China-like terranes were juxtaposed infracrustally along the southeastern margin of the Gyeonggi Massif during the pre-Jurassic collisional orogeny, and then selectively provided major source material to the older and younger Jurassic granitoids, respectively.

Neoproterozoic rifting in the Upper Yangtze Continental Block: Constraints from granites in the Well W117 borehole, South China

Well W117 in the Sichuan Basin reveals a suite of ~814 Ma quartz monzonites, unconformably overlain by Sinian clastic and carbonate sediments. The quartz monzonites contain no muscovite and amphibole, and are characterized by high SiO2 (72.26–77.93%), total alkali, and TFe2O3/MgO content, and low P2O5 and CaO abundance, with variable A/CNK ratio (0.93–1.19), classified as metaluminous to weakly aluminous highly fractionated I-type granites. They are preserved in the Neoproterozoic rift and exhibit restricted negative εNd(t) values (−7.0 to −5.2) and variable zircon εHf(t) values (−13.9 to 2.3), suggesting their generation via melting of both ancient and juvenile crustal materials in an extensional setting. Their parent magmas were formed in a low-temperature condition (831–650 °C) and finally emplaced at ca. 9–10 km below the surface, indicating that the intrusion underwent exhumation before the deposition of Sinian sag basin. Such geological processes, together with evidence for Neoproterozoic structures in the surrounding area, support that the Upper Yangtze craton experienced two main phases of rifting from 830–635 Ma. The Well W117 granites and its overlying sediments record a geodynamic evolution from orogenic collapse to continental rifting, and to thermal subsidence, probably related to the Rodinia supercontinent breakup.

SHRIMP U–Pb zircon ages of the Hida metamorphic and plutonic rocks, Japan: Implications for late Paleozoic to Mesozoic tectonics around the Korean Peninsula

AbstractA new U–Pb zircon geochronological study for the Hida metamorphic and plutonic rocks from the Tateyama area in the Hida Mountains of north central Japan is presented. The U–Pb ages of metamorphic zircon grains with inherited/detrital cores in paragneisses suggest that a metamorphic event took place at around 235–250 Ma; the cores yield ages around 275 Ma, 300 Ma, 330 Ma, 1 850 Ma, and 2 650 Ma. New age data, together with geochronological and geological context of the Hida Belt, indicate that a sedimentary protolith of the paragneisses is younger than 275 Ma and was crystallized at around 235–250 Ma. Detrital ages support a model that the Hida Belt was located in the eastern margin of the North China Craton, which provided zircon grains from Paleoproterozoic to Paleozoic rocks and also from Archean and rare Neoproterozoic rocks. Triassic regional metamorphism possibly reflects collision between the North and South China Cratons.

Zircon U–Pb chronology, Hf isotope analysis and whole-rock geochemistry for the Neoarchean-Paleoproterozoic Yudongzi complex, northwestern margin of the Yangtze craton, China

The Archean-Paleoproterozoic high-grade basement of Yudongzi complex is a key to understanding the early Precambrian crustal evolution of the Yangtze craton. It comprises mainly orthogneiss, paragneiss and amphibolite, whose protoliths are tonalitic-trondhjemitic-granitic (TTG), sedimentary and basic-intermediate volcanic rocks, respectively. The TTG gneiss, amphibole plagiogneiss and biotite plagiogneiss yield magmatic zircon LA-ICP-MSU–Pb ages of 2815±18Ma (MSWD=0.92), 2692±26Ma (MSWD=0.59) and 2449±4Ma (MSWD=0.94), respectively. Metamorphic overgrowths on zircon from amphibolite have an age of 1848±5Ma (MSWD=0.71). TTG gneisses show medium Sr/Y and variable high (La/Yb)N ratios with low Y and Yb contents. They are characterized by positive Eu anomaly and distinct depletion of HREE together with negative Nb, Ta and Ti, implying amphibole, garnet and minor rutile as residual phases. Their positive εHf(t) values of +2.1 to +8.1 with TDM2 of ca. 2.80–3.10Ga suggest significant reworking of juvenile crust. Amphibole plagiogneisses display a strong enrichment of LREEs and depletion of Nb, Ta and Ti. Additionally, a relative enrichment of Ba, Rb, Pb and Zr, as well as high Cr and Ni contents and Mg# values, imply a mantle source with the addition of continental crust material. Zircon εHf(t) values vary between −0.9 and +3.9, suggesting a proportionally significant input of juvenile material and therefore interaction between the mantle and pre-existing continental crust. Biotite plagiogneisses show negative εHf(t) values between −3.4 and −0.1 with a few positive εHf(t) values ranging from +0.1 to +1.5. Together with TDM2 ages of ca. 2.80–3.00Ga, these εHf(t) values suggest that these rocks were mainly generated by reworking of ancient crust. Thus, the Yudongzi complex exposed in the northern part of the Yangtze craton has experienced significant reworking of juvenile crust at ca. 2.80Ga and subsequent crustal growth at ca. 2.70Ga, followed by a second stage of reworking of ancient crust at ca. 2.45Ga. During the Late Paleoproterozoic, the Yudongzi complex was probably involved in the amalgamation of the Paleoproterozoic supercontinent Columbia, and affected by a post-collisional metamorphic event at ca.1.85Ga.

Crustal thickness and Poisson's ratio in southwest China based on data from dense seismic arrays

AbstractCrustal thickness and Poisson's ratio are important parameters to characterize regional isostasy state and material composition or state. Using the teleseismic waveform data from 141 permanent stations and 785 temporary stations in southwest China, we obtain the crustal thickness and average Poisson's ratio by theH‐κstacking of receiver functions. In the west (the SE Tibetan Plateau and the Yunnan‐Burma‐Thailand block) and southeast (the Cathaysian block and southern Yangtze craton) of the study region, there are high correlation coefficients for the crustal thicknesses between what we obtain from the receiver functions and what we calculate from the Airy isostasy model, indicating that a state of isostasy can be achieved at the crust‐mantle boundary beneath these two regions. In the northeast (northern Yangtze craton), the correlation coefficient is lower, indicating that the effect of the lithosphere needs to be considered for a regional isostasy. Intermediate Poisson's ratios (0.26 ≤ σ ≤ 0.28) are found beneath the northern Panzhihua‐Emeishan region. Combing the high‐velocity features from previous study, we speculate that it may be related to the Emeishan large igneous province. High Poisson's ratios (σ &gt; 0.28) are found beneath the SE Tibetan Plateau and the nearby strike‐slip faults, such as the Anninghe‐Zemuhe fault and the northern Xiaojiang fault. Combing the low‐velocity zones from previous study, we speculate that there may be partially melted and lower crustal flow.

Precambrian tectonic affinity of theNorthQinlingMicrocontinent: Constraints from the discovery ofMesoproterozoic magmatic zircons in theQinlingGroup

This paper presents new results on zircon U–Pb dating of a two‐mica schist from the Qinling Group in the core of the North Qinling Orogenic Belt (NQB), Central China, with the aim of constraining the formation time of the Qinling Group, and the tectonic affinity of the North Qinling Microcontinent. Zircon U–Pb dating indicates that the protolith of the metasedimentary rock in the Qinling Group was deposited later than ~1502 Ma. The Qinling Group in the NQB represents a long‐lived unit, and its formation age can be constrained to the period between the Paleoproterozoic and early Neoproterozoic. The zircon age populations of the studied sample can be divided into two major populations of 1559–1642 and 1470–1548 Ma, and one subordinate population of 1717–1794 Ma, indicating their provenances were mainly attributed to the NQB and subordinately from the North China Craton (NCC) and the Yangtze Craton (YZC). And the distribution of the early Neoproterozoic magmatic events and the Nd–Pb whole‐rock isotopes, zircon Hf isotopes, and trace element compositions of the Precambrian basement rocks in the NQB is significantly different from those in the NCC and YZC, indicating that the NQB cannot be a southern sector of the NCC, or a northern sector of the YZC, and was an independent microcontinent from the Paleoproterozoic to the early Neoproterozoic.

Regional Middle Paleozoic metamorphism in the southwestern Gyeonggi Massif, South Korea: Its implications for tectonics in Northeast Asia

The Hongseong area in the southwestern Gyeonggi Massif in South Korea is considered to represent the eastward extension of the Qinling–Dabie–Sulu collision belt in China. We have carried out zircon U–Pb SHRIMP dating and P–T estimations of the gneisses and amphibolites in the eastern Wolhyeonri complex within the Hongseong area in order to constrain their metamorphic and tectonic evolutions. The protoliths of the migmatitic biotite gneisses formed during the Neoproterozoic and underwent granulite-facies metamorphism (750–880°C, 12–15kbar) at 442–413Ma. These rocks subsequently experienced amphibolite-facies retrograde metamorphism at 585–660°C and 7.5–10.3kbar. Mylonitic biotite gneiss, hornblende gneiss, and folded amphibolite in the study area yield metamorphic ages that range from 429 to 420Ma. The protoliths of some garnet amphibolites that formed at 470–456Ma are arc magmatic rocks; they experienced metamorphism at the boundary between amphibolite- and eclogite-facies (ca. 625–700°C and 13–15.5kbar) before 418Ma and underwent retrograde amphibolite-facies metamorphism (ca. 625–700°C and 8–9kbar) at 418–405Ma. These data suggest that a regional intermediate-P/T metamorphic event occurred during the Middle Paleozoic. In contrast, Paleoproterozoic augen gneiss blocks enclosed in the Deokjeongri gneiss complex preserve evidence of high-pressure (HP) metamorphism (840–960°C, 17–21.8kbar) at 234–230Ma, which are similar to the previously reported results from eclogite blocks in this area. The occurrence of Middle Paleozoic regional metamorphism before the Permo-Triassic HP metamorphism in the Hongseong area may be correlated with the Middle Paleozoic metamorphism in the Qinling belt in China; such regional metamorphic events were caused by the collision of microcontinents with the North or South China Cratons prior to the collision between the North and South China Cratons in the Permo-Triassic.