Southeastern North China Craton Research Articles

Zinc isotopic systematics of deep crustal xenoliths from the southeastern North China craton and implications for intra-crustal differentiation

Zinc isotopic systematics of deep crustal xenoliths from the southeastern North China craton and implications for intra-crustal differentiation

Geochemical constraints of lamprophyres: Clues of Mesozoic tectonic interaction between the South China Block and North China Craton in Northern Jiangsu Province

Early Cretaceous lamprophyre dykes widely occurred in the southeastern margin of the North China Craton (NCC), which are the important probes to understand the enrichment and depletion processes that modified the subcontinental lithospheric mantle of the NCC. In this research, one lamprophyre site (Liguo), which is the nearest lamprophyre to the South China Block (SCB) ever discovered in the NCC, had been used to analyze the influence of the deeply subducted SCB on the lithospheric evolution of the southeastern NCC. This lamprophyre was investigated by apatite U Pb dating with the age of 136 Ma, and it is depleted in HFSE, enriched in LILE and Sr–Nd–Pb isotope compositions ( 87 Sr/ 86 Sr (i) = 0.708038 to 0.709305, ε Nd (t) = −8.0 to −9.8, 206 Pb/ 204 Pb (t) ratios of 17.477 to 17.536, 207 Pb/ 204 Pb (t) of 15.548 to 15.552, and 208 Pb/ 204 Pb (t) of 37.944 to 38.004). Interpretations of minerals and whole rock elemental data suggest the Liguo lamprophyre was derived from 1 to 5% partial melting of garnet lherzolite; and MELTS modeling indicates fractional crystallization of ~26.5% clinopyroxene, ~0.1% spinel and ~ 3.5% garnet under 2.5 Gbar. Together with the Pb isotopic compositions of the contemporaneous lamprophyres in the Jiaodong Peninsula, it suggested that the mantle source of the Liguo lamprophyre was mainly modified by melts derived from partial melting of the subducted South China continental crust in the Triassic. In contrast, the magma sources for the lamprophyres in Jiaodong Peninsula were mainly modified by hydrous fluids derived from the subducted Paleo–Pacific oceanic crust in the Jurassic. Finally, it is concluded that the lithospheric mantle in the southeastern margin of the NCC is heterogeneous, and the subducted SCB could be the source of the enriched component in the southern margin of the NCC. • Liguo lamprophyre recorded the Mesozoic tectonic interaction between the SCB and NCC. • The lithospheric mantle in southeastern NCC is heterogeneous. • Subducted SCB is the source of the enriched component in the southern NCC.

Eikonal surface wave tomography of central and eastern China

SUMMARY Eikonal tomography has become a key approach to image lithospheric structures with surface waves recorded by dense regional arrays. Its main advantage is that phase velocities can be determined directly from phase measurements without resolving a tomographic inverse problem. Here, we apply a new smoothing spline eikonal tomography approach to a selection of 40 large (Mw larger than 6.5) teleseismic events recorded by the permanent seismic stations of the CEArray. We first apply a time–frequency filter to isolate the fundamental mode of Rayleigh waves and cross-correlate the cleaned and isolated surface wave records to measure precise relative traveltimes. The phase measurements are then unwrapped and corrected for cycle skipping. Finally, we derive phase-velocity maps from the gradient of the reconstructed traveltime fields, using the eikonal equation. We obtain finely resolved phase-velocity maps from 25 to 150 s period that are inverted to obtain a 3-D shear wave velocity model which is in good agreement with previous tomographic studies. The lithospheric architecture emerging from the phase-velocity maps and 3-D S-wave velocities correlates with surface geology and major tectonic provinces. In particular, the architecture of the narrow rift systems, the South China Craton, and the North China Craton (NCC) are revealed with unprecedented details. The South China Craton is characterized by very high velocities beneath the Sichuan Basin. The NCC shows more complex structures with two high-velocity anomalies beneath the Ordos Basin and the southeastern NCC and low-velocity anomalies beneath the Cenozoic rift systems.

Geochemistry and Isotopic Characteristics of Apatite and Zircon From Late Jurassic Granites in the Jiaobei Terrane, East China: Implications for Petrogenesis and Geodynamic Setting

The North China Craton (NCC) was stable for more than 2.0 Gyr before a Jurassic–Cretaceous large-scale lithospheric thinning event, but the geodynamic setting during the early phases (Late Jurassic) of NCC reworking remains controversial. We present new petrological and whole-rock geochemical data, zircon and apatite geochemistry, U–Pb ages, O isotopic data, and Sr–Nd isotopic data for two phases of Late Jurassic granite (Linglong and Luanjiahe) from the Jiaobei terrane, southeastern NCC. LA-ICP-MS zircon U-Pb dating suggests that the Linglong granite formed about 6 Myr earlier than Luanjiahe granite (158 Ma vs 152 Ma), after the inception of the paleo-Pacific plate subduction. High zircon U/Yb ratios, high δ18O values [7.89 ± 0.10‰ to 7.67 ± 0.14‰ (2σ)], and inherited zircon age spectra, as well as high apatite F/Cl ratios and Sr–Nd isotopic compositions, suggest that the Linglong and Luanjiahe granites formed by partial melting of ancient thickened lower continental crust of the NCC and Yangtze Craton. Magma evolution modelling based on Rb and Rb/Nb data suggests a similar decoupled assimilation-fractional crystallization process for the generation of Linglong and Luanjiahe granite but with different assimilation degrees. The water contents of parental magma evaluated by using whole-rock Ba, Sr and apatite F, Cl data indicate that the Linglong granite was formed in a relatively water-rich environment than Luanjiahe. This is consistent with the presence of amphibole and minor negative Eu anomalies in the Linglong granite, as water input can promote amphibole fractionation and suppresses plagioclase crystallization. Considering the similar magma sources but distinct water contents of the granites, and the oblique Paleo-Pacific plate subduction setting in the Late Jurassic, the fluids were likely released from the ocean plate beneath a stacked thickened crust. Since the earliest mafic dikes (OIB-type) in the NCC are coeval with the Luanjiahe granite, we suggest that the lower water contents of the Luanjiahe granite were associated with roll-back that resulted in an increasing distance from slab to continental crust. Such a tectonic transition from subduction compression (158 Ma) to initial extension (152 Ma) in the Late Jurassic perhaps possibly marks the beginning of the reworking of the NCC.

Azimuthally Anisotropic Structure in the Crust and Uppermost Mantle in Central East China and Its Significance to Regional Deformation Around the Tan‐Lu Fault Zone

AbstractSeismic anisotropy can be linked to different mechanisms, structures, and sources. We constrained the 3‐D depth‐dependent shear wave speed isotropic and azimuthally anisotropic structures with Rayleigh wave phase velocity from ambient noise in central Eastern China. We compared the results with other models and found that in the upper crust, the maximum horizontal stress direction differs mainly from the anisotropy that coincides with the strikes of major faults and geologic structures. We inferred that the anisotropy within proximity of faults might be related to fault fabrics, including fractures that strike parallel to the fast axes. The Tan‐Lu Fault controls the anisotropy in the crust to the uppermost mantle. The direction of fast axes in the fault zone is NNE‐SSW to N‐S, coinciding with the fault strike and trend that matches the fault shape on the surface. Southeastern North China craton has a weak anisotropy in the crust and uppermost mantle. The sources are possibly connected to the thrusting, tight trending folds, and dipping thrusts observed to be sub‐parallel to the Dabie Orogenic Belt (DOB). We propose that the NNE‐SSW Zhangbaling uplift group comes from the extension and ductile shearing in the Tan‐Lu Fault zone and the dragging of the northeastern South China Craton in the crust and the uppermost mantle. The N‐S polarized fast axes in the lower crust and uppermost mantle across the Sulu orogen and Xuzhou thrust‐and‐fold belt are the products of the resultant effect of subduction and deep Tan‐Lu faulting.

Lithospheric thinning of the North China craton: Insights from Early Cretaceous intermediate–mafic dyke swarms in Jiaodong peninsula

The coupling/decoupling relationships between shallow crustal deformation and deep mantle tectono-magmatic activities, during lithospheric thinning and destruction of cratons, remain hotly debated in the last decades. Multidisciplinary studies were done on intermediate–mafic dyke swarms diffusively located in southern Jiaodong peninsula, southeastern North China craton (NCC) to explore the crustal and lithospheric mantle responses to regional tectonic extension. Uniform ages (122–121 Ma) of the dykes indicate intensive magma generation at the mantle depth around 122 Ma related to large-scale tectonic extension of regional lithospheric mantle. Systemic anisotropy of magnetic susceptibility (AMS), geochemical, and Sr-Nd isotope analyses suggest that the dykes were originated from enriched lithospheric mantle sources and emplaced along crustal fractures formed in a WNW-ESE oriented extensional stress field. We show that the Jiaodong lithosphere experienced two stages of Early Cretaceous tectonic evolution, i.e., an early stage (135–122 Ma) lithospheric thinning characterized by large-scale tectonic extension of the crust and limited magmatic activities of crustal sources, and a late stage (122–108 Ma) lithospheric root collapse dominated by intensive tectonic extension and magmatism in the lithospheric mantle level. The decoupling crust-mantle evolution during lithospheric thinning and destruction of the NCC is ascribed to continuous tectonic extension in WNW-ESE direction.

LA‐ICP‐MS zircon U–Pb age, whole‐rock geochemistry, Sr–Nd–Pb isotope, and zircon Hf isotope constraints on the origin and dynamic setting of Mesozoic mafic dykes, Henan Province, southeastern North China Craton

Mafic dykes from the Henan Province within the southeastern North China Craton (NCC) were sampled. Herein, we present new zircon laser ablation‐inductively coupled plasma‐mass spectrometry U–Pb age, whole‐rock geochemical, Sr–Nd–Pb isotopic, and zircon Hf isotopic data for the five areas where these mafic dykes outcrop. The mafic dykes are all dolerite and were emplaced between 121.6 ± 1.1 Ma and 131.7 ± 1.2 Ma. These are characterized by enrichment in some of the large‐ion lithophile elements (e.g., Rb, Ba, Th, U, K, and Sr), light rare earth elements, and depletion in high‐field‐strength elements (Nb, Ta, Hf, and Ti) and Eu (Eu/Eu* is between 0.62 and 0.96) relative to chondrite‐ and primitive mantle‐values. The dykes have high initial Sr isotopic ratios ([87Sr/86Sr]i = 0.7056–0.7058), negative εNd (t) ratios (−12.3 to −12.1), relatively constant Pb isotopic ratios ([206Pb/204Pb]i = 16.771–16.778; [207Pb/204Pb]i = 15.461–15.467; [208Pb/204Pb]i = 36.850–36.857), negative εHf (t) (−14.9 to −3.5), as well as old Nd (TDM2; 2.22–2.54 Ga) and Hf (TDM2; 2.99–4.34 Ga) model ages. These geochronological, geochemical, and isotopic data indicate that the investigated Henan Province dykes were likely derived from magmas generated by low to moderate degree partial melting (1.0–10%) of an EM1‐like garnet lherzolite mantle source. Moreover, the mafic melts fractionated olivine, clinopyroxene, plagioclase, Ti‐bearing oxides (e.g., ilmenite, titanite, apatite, etc.) prior to emplacement, and assimilated only minimal amounts of crustal material. Several possible models have previously been proposed to explain the origin of Mesozoic magma activities in Henan Province. However, here we propose a foundering model for the mafic dykes studied, involving the foundering of eclogite from thickened lower crust due to the collision between the Yangtze Block, Qinling ocean crust, and southeastern NCC.

Clockwise P–T–t paths with considerable heating processes during decompression from high-pressure mafic granulites in the Wuhe Complex, southeastern North China Craton

The Wuhe Complex lies in the southern section of the Jiao–Liao–Ji mobile/orogenic belt (JLMB/JLJB), critical for understanding the Proterozoic tectonic evolution of the southeastern North China Craton (NCC). Detailed microstructural observations, mineral chemistry, phase equilibria modeling, and zircon and titanite chronological dating were conducted on the mafic granulites from the Wuhe Complex. Five stages of mineral assemblages were identified: the prograde stage (Pl1 + Cpx1 + Amp1 + Ilm1 + Ap1 ± Qz1 ± Kfs1 ± Ttn1 ± Py1), the pressure–peak stage (the core of matrix plagioclase and Grt2a + Cpx2a + Rt2a + Qz2a + Liq2a ± Amp2a ± Kfs2a ± Ttn2a), the temperature–peak stage (the rim of garnet porphyroblast and Pl2b + Cpx2b + Amp2b + Liq2b ± Ilm2b ± Qz2b ± Rt2b), the retrograde stage (Pl3 + Cpx3 + Opx3 + Amp3 + Ilm3 + Ap3 ± Grt3 ± Qz3 ± Scp3), and the cooling stage (Mag4 ± Chl4 ± Py4 ± Ccp4). Traditional thermobarometry calculations and phase equilibria modeling illustrated that clockwise metamorphic pressure–temperature (P–T) paths were retrieved, passing from 9.4 to 13.4 kbar/701 ℃–781 ℃ (prograde stage) through 16.3–17.2 kbar/807 ℃–846 ℃ (pressure–peak stage), and through 10.2–10.8 kbar/895 ℃–912 ℃ (temperature–peak stage) to 5.6–9.1 kbar/803 ℃–883 ℃ (retrograde stage). Hence, the high-pressure (HP) granulites show clockwise P–T paths with heating processes (∼80 ℃) from the lower crust (pressure–peak stage) to the middle-lower crust (temperature–peak stage). Therefore, HP mafic granulites might be buried to the depth of ∼ 57 km, with a slow exhumation rate. The metamorphic zircon and titanite grains from HP mafic granulites yield U–Pb ages of 1991–1758 Ma and 1832–1810 Ma, respectively. The 1832–1810 Ma might represent the retrograde time when HP mafic granulites cooled to 820 ℃–800 ℃. Therefore, the HP mafic granulites of the Wuhe Complex record the Late Paleoproterozoic subduction/collision orogenic event of the southeastern NCC; therefore, the JLMB/JLJB is a prolonged orogenic belt.

Genesis of High-Mg Adakites in the Southeastern Margin of North China Craton: Geochemical and U-Pb Geochronological Perspectives

In the eastern North China Craton (NCC), Mesozoic tectonics was dominated by the Paleo-Pacific subduction rollback and the Tanlu crustal-scale fault movement. The regional transtension had generated extensive adakitic magmatism, some Cu-Au ore-forming but others not. To establish the geodynamic setting and any metallogenic link for the adakites from the southeastern NCC margin, we analyzed the ore-barren adakitic rocks from underground mines in the Huaibei-Linhuan coalfield (where surface igneous outcrops are scarce), and compared their ages and geochemistry with other mineralized and ore-barren adakites across Eastern China. Zircon U-Pb dating reveals two magmatic episodes in the Huaibei-Linhuan coalfield: 1) early-Early Cretaceous (ca. 130–129 Ma) (quartz-)diorite and granodiorite, and 2) late-Early Cretaceous (ca. 115.8 and 105.8 Ma) microgabbro and dolerite. Whole-rock geochemistry indicates that the (quartz-)diorite and granodiorite are high-Mg adakitic, featured by low K2O/Na2O (avg. 0.33), high Sr/La (avg. 44.3), and lack of correlation between SiO2 (fractionation index) and Sr/Y (avg. 56.55) and MREE/HREE (avg. 1.09), resembling typical adakites derived from oceanic-slab partial melting. Geochronological correlation with the regional tectonic events suggests that the slab-melting may have been caused by the Paleo-Pacific subduction rollback. Further extension and crustal thinning in the late-Early Cretaceous along the southern Tanlu fault may have formed the gabbro-dolerite in the coalfield. Geochemical comparison suggests that parental magma of the Huaibei-Linhuan adakites may have had similar water content [similar zircon 10,000*(Eu/Eu*)/Y and Eu/Eu* ratios] to typical porphyry Cu-Au ore-forming magmas, yet the former may have been considerably more reduced (lower zircon Ce/Nd and whole-rock V/Sc ratios). We considered that the assimilation of Carboniferous-Permian coal seams in the area may have further lowered the magma fO2 and thus its potential to form Cu-Au mineralization.

First discovery of gold in kimberlite in Xuzhou, Northern Jiangsu Province

Several individual particle native golds were observed in two Mesozoic Group II kimberlites dikes in the southeastern margin of North China Craton (NCC). This discovery provides new information of the nature of the Mesozoic lithospheric mantle beneath the southeastern NCC, the metallogenic setting of gold deposits in the Jiaodong peninsula and the metallogenic theory of decratonic gold deposits.

Detrital zircon U–Pb geochronology and Lu–Hf isotopic analysis of the Neoproterozoic Penglai Group and their comparisons with coeval sedimentary strata of the southeastern North China Craton: provenance, tectonic affinity and implications

The results of U–Pb dating and Hf isotopic analyses of detrital zircons from the Penglai Group in the Jiaobei terrane of the North China Craton (NCC) gave age populations of 1300–1000, 1500–1300, 1700–1500, 1800–1700 and >1800 Ma. The age spectra, variations in U and Th contents, Th/U ratios and Hf isotopic compositions of the detrital zircons of the Penglai Group are identical to those of the Tonian strata of the southeastern NCC. The Penglai Group rocks also have a similar litho- and biostratigraphy and tectonic setting to these Tonian strata, suggesting that the Penglai Group has a tectonic affinity with the NCC and was deposited during the Tonian. The detrital zircon age populations of the Penglai Group are consistent with the multiple magmatic and thermal metamorphic events in the NCC, especially the 1300–1000 Ma intermediate–acid and/or acid igneous rocks of the Korean Peninsula, and we therefore propose that the Penglai Group is mainly sourced from the NCC. The detrital zircon populations of 1300–1000, 1500–1300, 1700–1500 and 1800–1700 Ma show both positive and negative ε Hf(t) values, which, combined with late Paleoproterozoic–Neoproterozoic basic magmatism represented by large volumes of diabase sills in the NCC, suggests that the NCC experienced strong crust–mantle interactions that might have triggered continuous, multi-stage rifting in the NCC during the late Paleoproterozoic (1.8 Ga)–Neoproterozoic. Supplementary material: LA-ICP-MS U-Th-Pb analyses data and Lu-Hf isotopes analytical data are available at: https://doi.org/10.6084/m9.figshare.c.4816317

A Palaeoarchean–Mesoarchean micro-continent entrained in the Jiao-Liao-Ji Belt at the southeastern North China Craton: evidence from the zircon record in the Bengbu area

AbstractThe Bengbu area in the southeastern North China Craton (NCC) consists predominantly of Archean–Palaeoproterozoic (gneissic) granitoids with minor supracrustal rocks (the Fengyang and Wuhe groups). This study presents new zircon laser ablation – inductively coupled plasma – mass spectrometry U–Pb and Lu–Hf isotopic data and trace-element contents for these granitoids, which improve understanding the Archean–Palaeoproterozoic crustal evolution of the NCC. Magmatic zircon U–Pb data reveal that zircons in the (gneissic) granitoids were generated by multi-stage events at 2.93, 2.73, 2.53–2.52 and 2.18–2.13 Ga. Metamorphic zircon U–Pb data obtained from these rocks show two distinct metamorphic ages of 2.49–2.52 and 1.84 Ga, suggesting that the Bengbu area experienced a regional metamorphic event at the end of the Neoarchean Era and encountered reworking by a tectonothermal event associated with the formation of the Palaeoproterozoic Jiao-Liao-Ji Belt. Trace-element compositions of magmatic zircons reveal the highest Ti concentrations (8.08±3.38 ppm) and growth temperatures (718±44 °C) for the zircons aged 2.13–2.17 Ga and an increase in zircon U/Yb ratios from 2.93 Ga (0.34±0.12) through 2.73 Ga (0.96±0.42) to 2.53 Ga (1.05±0.46), but an evident decrease at 2.17–2.13 Ga (0.61±0.40 ppm). Similar Palaeoarchean xenocrystic and detrital zircons with negativeɛHf(t) values, late Mesoarchean magmatic zircons with juvenile Hf isotopic features, early Neoarchean magmatic zircons with model ages of 2.9–3.0 Ga, and two regional metamorphic events at 2.52–2.48 and 1.88–1.80 Ga in the Bengbu and Jiaobei areas indicate a Palaeoarchean–Mesoarchean micro-continent entrained in the Jiao-Liao-Ji Belt at the southeastern NCC.

Measuring the ‘Great Unconformity’ on the North China Craton using new detrital zircon age data

Abstract New detrital zircon ages confirm that the Neoproterozoic strata of the southeastern North China Craton (NCC) are mostly of early Tonian age, but that the Gouhou Formation, previously assigned to the Tonian, is Cambrian in age. A discordant hiatus of >150–300 myr occurs across the NCC, spanning most of the late Tonian, Cryogenian, Ediacaran and early Cambrian periods. This widespread unconformable surface is akin to the Great Unconformity seen elsewhere in the world and highlights a major shift in depositional style from largely erosional, marked by low rates of net deposition, during the mid- to late Neoproterozoic to high rates of transgressive deposition during the mid- to late Cambrian. The age spectra for the southeastern NCC and northern India are consistent with a provenance affinity linking the NCC and East Gondwana by c. 510 Ma. Supplementary material: Sample descriptions, sampling GPS locations and a compiled dataset of detrital zircon U–Pb LA-ICP-MS dating results are available at https://doi.org/10.6084/m9.figshare.c.3571119

Early Neoproterozoic emplacement of the diabase sill swarms in the Liaodong Peninsula and pre-magmatic uplift of the southeastern North China Craton

Diabase sill swarms are widespread within the Neoproterozoic sedimentary rocks in the Liaodong Peninsula (named as the Dalian mafic sill swarms), eastern North China Craton (NCC). Our new zircon LA-ICP-MS U–Pb and baddeleyite SIMS Pb–Pb dating results on five diabase sill samples emplaced into the Qiaotou, Cuijiatun and Xingmincun Formations in the Liaodong Peninsula indicate their emplacement during the early Neoproterozoic (Tonian) period at 0.92–0.89Ga and pre-magmatic regional uplift prior to ca. 0.92–0.89Ga. The above results provide important constraints on the upper boundary of the Neoproterozoic strata and their macroscopic carbonaceous fossils and organic-walled microfossils in the eastern and southeastern NCC and indicate they are Tonian in age. The early Neoproterozoic Dalian diabase sills belong to the tholeiitic series and are characterized by low contents of SiO2 and K2O, high contents of TiO2, Fe2O3T and MgO, slight light REE (LREE)-enrichment and no Eu anomalies on chondrite-normalized REE patterns, enrichment of high field strength element (HFSE) and lack of negative Nb, Ta, Zr, Hf, P and Ti anomalies on primitive mantle-normalized spidergrams; and exhibit geochemical characteristics of within plate basalt on discrimination diagrams. The newly identified Dalian diabase sills, together with the previously reported Xu-Huai and Sariwon mafic sills and the Dashigou mafic dykes, constitute an early Neoproterozoic (0.92–0.89Ga) large igneous province in the NCC (Sino-Korean Craton). Formation of the early Neoproterozoic diabase sill (dyke) swarms in the NCC is probably related to a continental rifting event that have led to breakup of southeastern NCC from some other continents in the Rodinia supercontinent. Breakup of the NCC from the Rodinia supercontinent at around 0.92–0.89Ga is also supported by pre-magmatic regional uplift of the southeastern NCC prior to ca. 0.92–0.89Ga and evolution trend of the Dalian diabase sills from within plate basalt to mid-ocean ridge basalt on the Zr/Y vs. Zr discrimination diagram.

Complex evolution of the lower crust beneath the southeastern North China Craton: The Junan xenoliths and xenocrysts: Reply

In our paper, we suggested that the Junan granulite xenoliths and xenocrysts record evolution of the Precambrian lower crust beneath the southeastern North China Craton (NCC). Yuan and Xia (2015) disagree with us. However, they have not fully considered the evolutional histories of the NCC lithosphere, and geochemical and isotopic compositions of the Junan xenoliths. We also contend that they have misinterpreted the available geophysical data. Synthesizing the geochronological characteristics of the NCC lower crust, nature of the Junan granulite xenoliths, and reinterpretation of the resistivity profile, we again emphasize that the Junan granulite xenoliths are tectonically affiliated to the NCC lower crust, and the Junan zircon data could reflect the complex evolution of the lower crust beneath the southeastern NCC.

Evolution of the lithospheric mantle beneath the southeastern North China Craton: Constraints from mafic dikes in the Jiaobei terrain

Two stages of mafic dikes with ages of ~117–116Ma and ~95–87Ma, respectively, are identified in the Jiaobei terrain based on zircon U–Pb ages. The Early Cretaceous mafic-intermediate dikes (ECMDs) and Late Cretaceous mafic dikes (LCMDs) show distinct geochemical and isotopic features. The ECMDs are enriched in large ion lithophile elements (LILE, Rb, Sr, Ba, U and Th) and light rare earth elements (LREE, La, Ce, Pr, Nd, Sm and Eu) with a strong depletion in high field strength elements (HFSE, Nb, Ta, Ti and P). They show uniformly high (87Sr/86Sr)i (0.70841–0.71387), low εNd(t) values (−18.1 to −13.2), positive (206Pb/204Pb)i (17.07–17.90) and negative εHf(t) (−21.0 to −6.1) values. These rocks were derived from partial melting of an enriched lithospheric mantle, and the enrichment of the mantle source resulted from source metasomatism imparted by the melts generated from remelting of the subducted lower crust of the Yangtze Craton (YC). In contrast, the LCMDs show lower SiO2 (41.5–50.1wt.%), lack of HFSE depletion and are depleted in whole rock Nd and zircon Hf isotope. They are interpreted to have sourced from a newly accreted depleted lithospheric mantle generated through continuous erosion of older enriched lithospheric mantle by asthenospheric upwelling, leaving out minor remnants of the older mantle in the newly accreted lithospheric mantle. The geochemical and isotopic characteristics reported in our study demonstrate that the lithospheric mantle beneath the southeastern North China Craton (NCC) was generally enriched during the Early Cretaceous (~120Ma) and the mechanism of the enrichment may be related to source metasomatism caused by the subducted lower crust of the YC. However, in Late Cretaceous, the lithospheric mantle beneath southeastern NCC was highly heterogeneous, which might be related to asthenospheric non-uniform erosion. The ~116–87Ma marks the transition from enriched lithospheric mantle to depleted asthenospheric mantle.

Two tales of the continental lithospheric mantle prior to the destruction of the North China Craton: Insights from Early Cretaceous mafic intrusions in western Shandong, East China

Weakened lithospheric zones such as the Dabie–Sulu orogenic belt and Tan-Lu fault zone played important roles in the destruction of the North China Craton (NCC) during the late Mesozoic. Early Cretaceous mafic intrusions in western Shandong, contemporary with extensive magmatism during the destruction of the NCC, delineate two spatially distinct mantle domains (EM1- and EM2-like) beneath the craton’s interior and weakened lithospheric zones, respectively. The Jinan and Zouping gabbros from the craton interior (∼128Ma) show fractionated LREE and nearly flat HREE patterns ([La/Yb]N=2.94–8.95; [Dy/Yb]N=1.23–1.69) with notable negative Ta, Nb and Ti anomalies. They have strong negative ɛNd(t) (−15.7 to −7.1), low initial 87Sr/86Sr (0.7039–0.7060) and negative zircon ɛHf(t) of −20.0 to −6.2. These “crustal fingerprints” cannot be explained by crustal contamination, but were likely derived from a hybrid mantle source. Crustal delamination or detachment during the Early Paleoproterozoic might be responsible for the involvement of Early Precambrian crustal materials in the Mesozoic mantle source beneath the southeastern NCC. In comparison, the Early Cretaceous mafic igneous rocks from regions (e.g., Yinan, Mengyin and Fangcheng) adjacent to the Dabie–Sulu orogenic belt and Tan-Lu fault zone have higher 87Sr/86Sr ratios (0.7059–0.7119), suggesting modification of the lithospheric mantle by melts/fluids derived from the Yangtze crust. The Mesozoic crustal delamination may have triggered the destruction of the lithospheric root beneath the Dabie–Sulu orogenic belt, whereas the lithospheric thinning beneath the interior of the southeastern NCC is attributed to the thermo-mechanical erosion by lateral convective asthenosphere.

U–Pb ages and Hf isotope data from detrital zircons in the Neoproterozoic sandstones of northern Jiangsu and southern Liaoning Provinces, China: Implications for the Late Precambrian evolution of the southeastern North China Craton

The tectonic evolution of the North China Craton (NCC) from the Late Mesoproterozoic to the Neoproterozoic has been unclear. This paper reports the results of LA–ICP–MS U–Pb dating and in situ Hf isotope analysis of detrital zircons from Neoproterozoic strata in the northern Jiangsu and southern Liaoning provinces of southeastern NCC, and we go onto discuss how these results help constrain the Late Precambrian evolution of the NCC. Most analyzed zircon grains exhibit oscillatory growth zoning, and they have relatively high Th/U ratios (>0.4) and positive Ce anomalies as well as negative Eu anomalies, all of which suggests a magmatic origin. The detrital zircons from the Xinxing and Jinshanzhai formations in northern Jiangsu Province give weighted mean ages of 1753, 1635, 1486, and 1121Ma, and 2515, 2305, 1856, 925, and 825Ma, respectively, and the detrital zircons from the Diaoyutai and Xingmincun formations in southern Liaoning Province give ages of 1745, 1619, 1484, 1175, and 1077Ma, and 1798, 1623, 1150, 1020, and 934Ma, respectively. These results, together with previously published ages, indicate that (1) the Neoproterozoic strata in the northern Jiangsu and southern Liaoning provinces were deposited during a period from the Late Mesoproterozoic to Neoproterozoic, and (2) the sediments in the Neoproterozoic strata were sourced mainly from igneous rocks of Late Paleoproterozoic, Mesoproterozoic, and Early Neoproterozoic age, as well as from the ancient Precambrian basement of the NCC. The concordia plots for 291 detrital zircon grains give three prominent age groups of 1.86–2.5, 1.5–1.8, and 0.9–1.2Ga. The detrital zircon ages of 1.86–2.5Ga in the Neoproterozoic strata tie in with most of the Precambrian tectonic–magmatic–thermal events that occurred in the NCC. Zircon ages of 1.6–1.8Ga can be linked to rift magmatism of Late Paleoproterozoic age in the NCC. The detrital zircon ages of 0.9–1.2Ga can be related to Grenville-aged magmatism in the southeastern NCC. The zircons show negative ɛHf (t) values (−8.8 to −0.1), suggesting that the source rocks were dominated by reworked ancient Precambrian crust. The positive ɛHf (t) values (+0.3 to +10.8) and Hf model ages indicate that growth of continental crustal occurred at ∼2.7Ga, ∼1.9Ga, and ∼1.5Ga in the southeastern NCC.

Zircon U-Pb geochronology, geochemistry and Sr-Nd-Pb isotopes from the metamorphic basement in the Wuhe Complex: Implications for Neoarchean active continental margin along the southeastern North China Craton and constraints on the petrogenesis of Mesozoic granitoids

We report zircon U-Pb geochronology, geochemistry and Sr-Nd-Pb isotope data from mafic granulites and garnet amphibolites of the Wuhe Complex in the southeastern margin of the North China Craton (NCC). In combination with previous data, our results demonstrate that these rocks represent fragments of the ancient lower crust, and have features similar to those of the granulite basement in the northern margin of the NCC. A detailed evaluation of the Pb isotope data shows that Pb isotopes cannot effectively distinguish the role of the Yangtze Craton basement from that of the NCC basement with regard to the source and generation of magmas, at least for southeastern NCC. The age data suggest that the protoliths of the granulites or amphibolites in the Wuhe Complex were most likely generated in Neoarchean and that these rocks were subjected to Paleoproterozoic (1.8–1.9 Ga) high-pressure granulite facies metamorphism. This study also shows that the Precambrian metamorphic basement in the southeastern margin of the NCC might have formed in a tectonic setting characterized by a late Neoarchean active continental margin.

Zircon U–Pb geochronology and major, trace elemental and Sr–Nd–Pb isotopic geochemistry of mafic dykes in western Shandong Province, east China: Constrains on their petrogenesis and geodynamic significance

Mesozoic mafic dykes in western Shandong Province (Luxi), SE, the North China Craton (NCC) provide an opportunity to examine the nature of their mantle source and the secular evolution of the Mesozoic lithospheric mantle beneath SE NCC. Chronological, geochemical and Sr–Nd–Pb isotopic analyses were carried out on two selected Mesozoic mafic dykes from Mengyin and Zichuan in western Shandong, respectively. Detailed SHRIMP zircon U–Pb dating yields emplacement ages of 144 ± 2 Ma for the Mengyin mafic dykes and of 143 ± 2 Ma for the Zichuan mafic dykes. Both are enriched in LILE (Rb, Ba, Sr, Pb) and LREE without Eu anomalies, but are depleted in HFSE (Nb, Ta and Ti). The dykes have relatively radiogenic Sr ( 87Sr/ 86Sr) i (0.706 ~ 0.707) and negative ε Nd(t) (− 6.5 to − 4.4), but remarkably unradiogenic Pb ( 206Pb/ 204Pb = 16.99–18.36). Both dykes may have experienced crystal fractionation of olivine and clinopyroxene. The Mengyin mafic dykes are characterised by high MgO (9.66–17.97 wt.%), Mg # (66–74), Cr (809–1208 ppm) and Ni (171–390 ppm), indicative of derivation from mantle-derived melts with minor fractionation. In contrast, the Zichuan mafic dykes have relatively low MgO (3.38–4.14 wt.%), Cr (24–56 ppm) and Ni (14–24 ppm), suggesting that they may have originated from an extremely evolved magma. There is evidence in support of multiple enrichment events induced by hybridism of foundering lower crust at mantle depths. For example, phlogopite, amphibole and rutile metasomatism may have affected the lithospheric mantle beneath Mengyin, whereas phlogopite and carbonatite metasomatism modified the lithospheric mantle below Zichuan. This study sheds light also on the geodynamic significance of the 144–143 Ma mafic dykes, for example, we propose that lithospheric thinning underneath southeastern NCC of eastern China was caused by the removal of the lower lithosphere (mantle and lower crust).