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Determining subduction‐related processes is crucial for understanding lithological heterogeneity, as substantial quantities of slabs are recycled into the mantle. Molybdenum isotopes are valuable for distinguishing sources materials due to the significant isotope differences between the crust and the mantle. In this study, we systematically investigate Mo isotopes in a suite of well‐characterized continental basalts from Keluo and Halaha‐Chaoer, located in Northeast China. The δ98Mo values of Keluo range from −0.41 to −0.23‰, with an average of −0.34‰, while Halaha‐Chaoer samples ranged from −0.18 to −0.12‰, with an average of −0.15‰. The δ98Mo values of Keluo basalts are lighter than the mean value of fresh oceanic basalts (−0.21‰), whereas those of Halaha‐Chaoer basalts are similar to oceanic basalts. Combined with other geochemical indications (LOI, Ce/Pb, La/Yb and so on), the Mo isotopic variations cannot be attributed to chemical weathering, continental crust contamination or magmatic processes. Instead, the δ98Mo variations in this study are explained by the incorporation of different oceanic crustal materials into the magma sources. Correlations of δ98Mo with Ba/Th, Th/U, 143Nd/144Nd indicated that both sediment and altered oceanic crust have significantly influenced these variations. This study demonstrates the potential of Mo isotopes to distinguish different types of recycled oceanic crust materials. [ABSTRACT FROM AUTHOR]

Using data from the regional broadband dense temporary array deployed by the ChinArray project, we applied the three-dimensional (3D) Kirchhoff migration method of the teleseismic P-wave receiver function to investigate discontinuity structures of the mantle transition zone (MTZ) in the central and western parts of the North China Craton (NCC) using a high-resolution 3D velocity model of the East Asian region. The results show that the 410-km discontinuity beneath the Datong Volcano is depressed by ∼10 km, indicating the presence of a high-temperature anomaly near the depth of 410 km, which is likely related to small-scale mantle upwelling caused by the dehydration of the stagnant Pacific Plate in the MTZ. The upwelling of hot material provides a heat source for surface magmatic activity. Beneath the Bohai Bay Basin, significant subsidence of the 660-km discontinuity is observed, and the transition zone here is extensively thickened. It's suggested that the anomalies in this region are related to the stagnation of the Pacific slab in the MTZ. Although the thickness of the transition zone west of the North-South Gravity Lineament appears normal, we propose that the subducting front of the Pacific slab did not cross the gravity lineament in the NCC. In comparison, the small-scale subsidence of the 660-km discontinuity and the thickening of the MTZ observed north of the Hannuoba Volcano likely indicate that the slab crossed the gravity lineament at its turning point and remained in the MTZ. Furthermore, a local thickening of the MTZ is observed in the Dabie orogenic belt of the Qinling Mountains. This is believed to be a combined effect of lithospheric delamination into the transition zone in the lower Yangtze region and the stagnation of the Pacific Plate. [ABSTRACT FROM AUTHOR]

Deep carbon cycle is crucial for mantle dynamics and maintaining Earth's habitability. Recycled carbonates are a strong oxidant in mantle carbon-iron redox reactions, leading to the formation of highly oxidized mantle domains and deep carbon storage. Here we report high Fe3+/ΣFe values in Cenozoic intraplate basalts from eastern China, which are correlated with geochemical and isotopic compositions that point to a common role of carbonated melt with recycled carbonate signatures. We propose that the source of these highly oxidized basalts has been oxidized by carbonated melts derived from the stagnant subducted slab in the mantle transition zone. Diamonds formed during the carbon-iron redox reaction were separated from the melt due to density differences. This would leave a large amount of carbon (about four times of preindustrial atmospheric carbon budget) stored in the deep mantle and isolated from global carbon cycle. As such, the amounts of subducted slabs stagnated at mantle transition zone can be an important factor regulating the climate. [ABSTRACT FROM AUTHOR]

Abundant mafic-felsic intrusions distributed in the Altyn Orogen record orogenic histories related to Proto-Tethys and Paleo-Tethys evolution. Zircon U-Pb dating of the intrusive rocks in the eastern Altyn Orogen identifies at least three major tectono-magmatic episodes, yielding ages of ∼426, ∼376–373 and ∼269–254 Ma. The first two emplacement episodes correspond to the post-collisional magmatism in the Altyn Orogen. The ∼426 Ma granitoids possess adakitic characteristics coupled with enriched isotopes, suggesting that they originated from partial melting of thickened lower continental crust induced by upwelling asthenospheric mantle after slab break-off of the South Altyn Ocean Plate. Next, the ∼376–373 Ma mafic-intermediate rocks and coeval granitoids represent a large thermal event that involved mantle melting with induced new juvenile lower continental crust melting in a post-collisional extensional setting. Finally, the ∼254 Ma diabase dykes intruded into the ∼269 Ma granitoids, which were related to the widespread Late Paleozoic magmatism resulting from Paleo-Tethys Ocean subduction. Post-collisional magmatism in the Altyn Orogen significantly enhances understanding of the tectono-magmatic evolution in the northern Tibetan Plateau. The penetrative influence of Paleo-Tethys Ocean subduction was more extensive than previously thought. [ABSTRACT FROM AUTHOR]

The subducting Pacific slab stagnates in the mantle transition zone and creates a big mantle wedge (BMW) system in East Asia. A similar BMW structure may have already existed since the Early Cretaceous (>120 Ma), but how such a structure evolved from Early Cretaceous to the present day remains unclear. We address this issue by comparing compositions and source heterogeneity of the 106–58 Ma basalts from Liaodong Peninsula and its adjacent areas (LPAA) in eastern China, with those formed in the modern BMW setting. The LPAA basalts display oceanic island basalts–like trace element patterns. Elemental and isotopic compositions of these basalts and their olivine phenocrysts point to peridotite and two recycled components in their source. One recycled component is altered lower oceanic crust given the low δ18Oolivine (2.8–5.2‰) of the ~99 Ma Liaoyuan alkali basalts. The second component consists of altered upper oceanic crust and pelagic sediments indicated by high δ18Oolivine (>6.0‰), represented by the ~58 Ma Luanshishanzi alkali basalts. The depleted mantle-like isotopes of these two components suggest derivation from a young HIMU source with characteristics of the Izanagi plate (e.g. Indian Ocean-type Sr-Nd-Pb-Hf isotopes), which may have resided in the mantle transition zone at that time. Our results reveal strong similarities between chemical and source characteristics of the mantle sampled by the 106–58 Ma LPAA basalts and those derived from the modern BMW. This implies that the BMW structure has been present since the Early Cretaceous, probably having lasted more than 120 Myr, and modulating the chemical properties of the upper mantle and influencing a variety of geological processes. [ABSTRACT FROM AUTHOR]

Heavy rare earth elements (HREEs) are critical metals in advanced technologies. Here, we report unusual REE patterns and O–Hf–Nd isotopic compositions of composite granites from the Zhaibei HREE deposit. The complex consists of two Mesozoic granites with ages of 188 and 170 Ma. The older granites are characterized by higher HREE contents and negative Ce anomaly and contain cerianite veinlets. Their REE-rich minerals also show strong Ce depletion, indicating a high oxidation state. Magmatic zircons have variables δ18O (6.1–9.4‰) and εHf(t) (−6 to 0), towards a depleted mantle contribution. Lower δ18O (~5.4 vs 6.6‰) and higher εNd(t) (approximately −3 vs −11) values in the altered apatite rim compared to the core and primary phase result from subduction-derived fluids. In contrast, the younger granites have lower REE contents and lack a Ce anomaly. They show mantle-derived Nd (apatite εNd(t) = 1–2), Hf (zircon εHf(t) = 3–8), and O (zircon and apatite δ18O = 4.6–5.7‰) isotopic compositions. Therefore, we infer that a REE-rich fluid migrated from the flat subducting slab and flushed the subsolidus granitic mush in the Early Jurassic. This caused volatile saturation and degassing, leading to the generation of highly oxidized fluids. These processes may cause temporary oxidizing conditions in post-magmatic hydrothermal stages, resulting in the oxidation of Ce3+ to Ce4+. The resulting Ce fractionation from other REE3+ promoted HREE enrichment in the granites. [ABSTRACT FROM AUTHOR]

The far limit of a plate subduction process and its related far‐field dynamic process are fundamental topics for plate tectonics. The Great Khingan Range (GKAR) in the western flank of NE China is currently under the far‐field influence of the Pacific plate subduction. Benefiting from the newly deployed seismic arrays in the northern GKAR, we take full advantage of seismic data from both temporary and permanent networks and employ an improved scheme of the H‐κ stacking method by introducing surface wave dispersion to obtain the integrated maps of Moho depth and crustal bulk Vp/Vs ratio in this region. Our results show that the Moho depth has a giant step near the North–South Gravity Lineament (NSGL). Meanwhile, the distribution of bulk Vp/Vs ratio presents a north–south difference roughly by 50°N, where the south subregion consists of a collage of high and low Vp/Vs ratio; by contrast, the north subregion is characterized by unified high values. The east‐west structural discrepancies across the NSGL from the Earth's surface to the mantle transition zone indicate the difference in the strength of modifications between the near and far‐fields from the Pacific plate subduction. The complicated distribution of the Vp/Vs ratio in the south subregion supports that secondary small‐scale upwellings underneath the Cenozoic volcanic groups dominate the tectonic reworking in this area. The lack of Cenozoic volcanism and a more straightforward distribution of the Vp/Vs ratio in the north subregion might allude to a tectonically inactive part of NE China. Plain Language Summary: We use an improved H‐κ stacking method to construct an integrated map of Moho depth and crustal bulk Vp/Vs ratio across the Great Khingan Range (GKAR). Our results show a significant step in the Moho depth near the North–South Gravity Lineament, which probably marks the boundary between near‐ and far‐field locations from the subduction. We also identify a prominent discrepancy in the crustal bulk Vp/Vs ratio between the south and north subregions of the GKAR. The south subregion is characterized by a collage of high and low Vp/Vs ratio, while the north subregion has a much more straightforward pattern. The localized high Vp/Vs ratio in the south subregion coincides with the Cenozoic volcanism, which tells us the far‐filed effects of the subduction are dominated by a secondary small‐scale mantle upwelling. In contrast, the unified high Vp/Vs ratio and no sign of Cenozoic magmatism in the south subregion may indicate a tectonically inactive region in NE China. The unique mechanism of the far‐field effects and the particular location of the north subregion of the GKAR can explain how the north–south difference in crustal property is formed. Key Points: A new integrated map of Moho depth and bulk Vp/Vs ratio across the Great Khingan Range (GKAR) is built with an improved H‐κ stacking methodThe far‐filed effects of the stagnant Pacific slab on the GKAR are most likely achieved by a small‐scale secondary mantle upwellingThe north subregion of the GKAR is tectonically inactive, which may have retained its crustal state since the Paleozoic Era [ABSTRACT FROM AUTHOR]

Unique intraplate volcano eruptions and westward volcano migration since the Oligocene have been observed in northeast China, where an overriding continental zone is tectonically controlled by the subduction of the northwestern Pacific plate and the opening of Japan Sea. Interestingly, these intraplate magmatic events occur around a subsiding basin (the Songliao Basin), but no volcanic activity has been observed within the Songliao Basin. The geodynamic mechanism responsible for these volcanoes remains unclear. To address the geodynamic process beneath northeast China, we conducted numerical models constrained by data from regional reconstruction and seismic and volcanic studies. The vertical velocity field of mantle convection and lithospheric partial melting structures derived from our models show that mantle upwelling and melting centers migrate from east to west in northeast China with the westward propagation of the sub-horizontal slab in the transition zone, leading to the observed volcano migration. Also, with the subduction retreat of the northwestern region of the Pacific plate and the opening of the Japan Sea, significant lithospheric thickness differences developed between the Changbaishan-Mudanjiang region and the Songliao Basin, leading to lithospheric unstable dripping. This dripping structure prevents the partial melting of the lithosphere but facilitates the subsidence of the Songliao Basin. Moreover, the lithospheric dripping model successfully predicts upper mantle structures consistent with the proposed tomography model, the observed Moho depth, and surface topography variations. Thus, lithospheric dripping induced by lithospheric thickness differences and the retreating subduction of the Pacific slab provides a robust mechanism for the unique geodynamic processes in northeast China. [ABSTRACT FROM AUTHOR]

The subcontinental lithospheric mantle (SCLM) is now suggested by many workers to play a role in the formation of orogenic gold deposits in active continental margins, given that the gold and volatiles may be introduced into the SCLM during plate subduction. The giant Cretaceous Jiaodong gold province within the North China block occurs in a convergent margin setting where there is no terrane accretion, thus eliminating from consideration the commonly accepted metal and fluid source reservoir for orogenic gold--the metamorphosed upper crust of an active orogenic belt. Thus, the auriferous fluids were released below the high-grade Archean cratonic rocks from either enriched SCLM or directly from the subducted oceanic slab. Mercury (Hg) isotopes allow fingerprinting of isotopically distinct reservoirs, discriminating between the two possibilities. We present Hg isotope data for a set of pyrite grains, native gold, and lamprophyres from six main gold districts in the Jiaodong gold province. These samples dominantly yielded near-zero Δ199Hg (0‰ ± 0.1‰), within uncertainty of the mantle Δ199Hg value. The results provide novel evidence that the SCLM predominantly controlled the Hg budget of the Jiaodong gold deposits, implying that the SCLM acted as a buffer for the crustal mass-independent fractionation Hg signatures and a storage reservoir for gold and volatiles. Consequently, during slab subduction, gold and volatiles were recycled and stored within the SCLM and were later released from the mantle during uplift and relaxation of compressional tectonics. [ABSTRACT FROM AUTHOR]

It is well established that Cretaceous magmatism in the South China Block (SCB) is related to the Paleo‐Pacific subduction. However, the starting time and the associated deep crust‐mantle processes are still debatable. Mafic dike swarms carry important information on the deep earth (including mantle) geodynamics and geochemical evolution. In the Jiangnan Orogen (South China), there is no information on whether the Mesozoic magmatic activities in this region are also directly related to the Pacific subduction or not. In this study, we present detailed zircon U‐Pb geochronological, whole‐rock element and Sr‐Nd isotope data for Early Cretaceous Tuanshanbei dolerite dikes, and provide new constraints on the condition of the lithospheric mantle and mantle dynamics of the SCB during that time. LA‐ICP‐MS zircon U‐Pb dating suggests that this dolerite erupted in the Early Cretaceous (∼145 Ma). All samples have alkaline geochemical affinities with K2O + Na2O = 3.11–4.04 wt%, K2O/Na2O = 0.50–0.72, and Mg# = 62.24–65.13. They are enriched in LILE but depleted in HFSE with higher initial 87Sr/86Sr ratio (0.706896–0.714743) and lower εNd(t) (–2.61 to –1.67). They have high Nb/U, Nb/La, La/Sm and Rb/Sr, and low La/Nb, La/Ta, Ce/Pb, Ba/Rb, Tb/Yb and Gd/Yb ratios. Such geochemical signatures suggest that the fractional crystallization is obvious but crustal contamination play a negligible role during magmatic evolution. Tuanshanbei dolerite were most likely derived from low‐degree (2%–5%) partial melting of a phlogopite‐bearing mantle material consisted of ∼85% spinel peridotite and ∼15% garnet peridotite previously metasomatized by asthenosphere‐derived fluids/melts with minor subduction‐derived fluids/melts. Slab‐rollback generally lead to the upwelling of the hot asthenosphere. The upwelling of asthenosphere consuming the lithospheric mantle by thermo‐mechanical‐chemical erosion. The lithospheric mantle may have partially melted due to the heating by the upwelling asthenosphere and lithospheric extension. It is inferred that the Tuanshanbei dolerite might be associated with the initial slab rollback and corresponding lithospheric extension occurred potentially at ca. 145 Ma. [ABSTRACT FROM AUTHOR]

We analyzed 49,592 teleseismic receiver functions (RFs) recorded by 278 CEArray stations to image the mantle transition zone (MTZ) beneath the South China Block to understand the origins of deep velocity anomalies and their potential links to subduction and intraplate volcanism. We employed a fast‐marching method and a high‐resolution 3‐D velocity model (FWEA18) derived from full waveform inversion in computing P‐to‐S conversion times to better image the 410‐ and 660‐km discontinuities. Our results indicate that the common‐conversion‐point stacking of RFs using 3‐D conversion times yielded better migration images of the two discontinuities. The images revealed a slightly depressed 410‐km with a few small uplifted patches, and showed that the 660‐km beneath the western Yangtze Craton is depressed by 10–25 km, which is likely caused by the stagnant Paleo‐Pacific slab. The 660‐km beneath the southern Cathaysia Block has a 5–15 km high plateau with a topographic low at its central part. The lateral dimension of the topographic low is ∼150 km and is located beneath the central Pearl River Mount Basin near Hong Kong. We speculate that the topographic low occurs within the Hainan plume with a temperature excess of ∼300–400 K and is caused by the garnet phase transition. The displaced deep plume enters the MTZ and spreads nearly horizontally at the base. The plume evolves into two channels with a minor one toward the northeast and a major one toward the southwest, which keep moving upward to the 410‐km. The southwest channel is likely the source that feeds the Hainan volcanoes. Plain Language Summary: Using data from seismic stations in the South China Block, we investigated the mantle transition zone (MTZ) to understand the origins of deep velocity anomalies and their associations with subduction and intraplate volcanism. By applying advanced techniques and a ground‐truth reference model, we obtained clearer images of the 410‐ and 660‐km discontinuities. The images showed that the 410‐km discontinuity is slightly depressed with some small uplifted areas. Additionally, the 660‐km discontinuity beneath the western Yangtze Craton is depressed due to the presence of a stagnant slab from the ancient Pacific Ocean. In contrast, beneath the southern Cathaysia Block, the 660‐km discontinuity forms a high plateau with a central low area. This area located near Hong Kong may be related to a plume originating from the lower mantle. The plume, with elevated temperatures, enters the MTZ and spreads horizontally. It then evolves into two channels, with one moving toward the northeast and the other toward the southwest. The southwest channel likely supplies magma to the volcanoes in Hainan. These findings provide insights into the complex processes occurring deep within the Earth's mantle in the South China region. Key Points: FWEA18 is used in migrating CEArray receiver functions to image the mantle transition zone beneath the South China BlockThe 660‐km is depressed ∼10–25 km by stagnant slabs beneath the northwestern part of the blockThe Hainan volcanoes are fed by a displaced lower mantle plume beneath the central Pearl River Mouth Basin [ABSTRACT FROM AUTHOR]

In recent years, due to the changing climate conditions and the continuous deepening of water resource conservation measures, the groundwater level in northern China has gradually risen, leading to the increasingly prominent issue of anti-floating in existing buildings and structures. The development and adoption of reliable anti-floating reinforcement techniques for existing structures are crucial for ensuring the quality of such reinforcements. Therefore, focusing on the limitations of the anchor method for anti-floating reinforcement, this paper proposes a new type of anti-floating prestressed compression anchor that features a full-length anti-compressive steel pipe with a bearing body at the end and uses non-bonding tendons throughout its length. Firstly, the structural form of this pressure-type anchor is introduced; subsequently, combined with the results of on-site pull-out tests of the anchor, an analysis is conducted on the working principle, lateral resistance distribution, and internal force transfer mechanism of the new anti-floating anchor, and its load-bearing characteristics are elucidated. Finally, relying on actual anti-floating reinforcement projects and through numerical calculations, the changes in internal forces under different anti-floating conditions of existing structures reinforced with the new anchor compared to conventional anchors are contrasted. Research findings and engineering practice indicate that this new anti-floating anchor improves the mechanical performance of the grout body of the anchor, solves the water seepage problem at the anchor location of the waterproof slab, effectively suppresses cracking of the foundation waterproof slab after reinforcement, and enhances the anti-floating and durability of existing structures. [ABSTRACT FROM AUTHOR]

The newly identified Neoproterozoic Yuanmou high-Nb mafic and adakitic rocks at the western margin of the Yangtze Block in South China are investigated for petrogenesis and geodynamic implications. Zircon U-Pb ages show the adakitic granodiorite host and mafic microgranular enclaves (MMEs) were synchronously emplaced at 811-806 Ma, and were cut by an 802 ± 11.5 Ma mafic dike. The medium-grained granodiorites consist mainly of plagioclase, quartz, K-felspar, biotite, and amphibole. High SiO2 (62.8-67.5 wt%), Al2O3 (13.1-16.8 wt%) contents, high Sr/Y (17.4-49.0), and (La/Yb)N (16.3-52.6) but low Y (6.83-16.1 ppm) and Yb (0.74-1.82 ppm) concentrations of the granodiorites point toward their calc-alkaline and adakitic nature. Further, their high Dy/Yb (1.52-2.31) and Gd/Y (2.35-4.43) and low K2O/Na2O (0.22-0.48) and Th/La (0.14-0.20) ratios, constant bulk rock εNd(t) (-0.5 to -1.5) and zircon εHf(t) (0.0 to +2.3) values, suggest that the granodiorites were derived from partial melting of a mafic lower crustal source. The MMEs in the granodiorites and mafic dike intrusions are composed of amphibole, plagioclase, clinopyroxene, and olivine, and have similar chemical compositions, such as high Nb (15.7-41.9 ppm) and TiO2 (2.13-3.39 wt%) contents and high Nb/U (18.7-30.9) values, akin to alkaline high-Nb basalts (HNB). Their variable Ba/Nb (7.68-79.2), Nb/Zr (0.09-0.16), high Nb/Th (5.47-6.68), and low Th/Zr (0.01-0.03) and La/Nb (1.03-1.37) ratios indicate a mantle source modified by melts derived from subducted oceanic crust and sediments. The Yuanmou HNB with high εNd(t) (+4.8 to +6.9) were probably generated during back-arc extension by decompression melting of a mantle source metasomatized by adakitic slab melts formed during earlier stages of the subduction. This implies that the location of the back-arc was far from the subducted oceanic slab, possibly due to a slab rollback process. In this scenario, HNB intrusions provided the heat for partial melting and adakitic melt formation in the mafic lower crust. The model suggests that the Yuanmou and other similar associations of HNBs and adakitic rocks emplaced along the western margin of the Yangtze Block are products of a widespread Neoproterozoic back-arc extension. [ABSTRACT FROM AUTHOR]

Arc magmatism can provide crucial information about crustal recycling and growth in subduction zones. However, the crustal material transfer process and mechanism from subducting slab to overlying mantle wedge are controversial. Here, we present detailed petrological, geochronological, geochemical, and Sr-Nd-Hf isotopic data, and previously published data for two episodes of subduction-related magmatism in the Northern Yili Block, NW China, to study these issues in relation to the recycling of continental crust and the growth of two separate magmatic episodes at 400-350 Ma and 350-300 Ma, respectively. The Nd-Sr isotope modeling results, low Nd/Sr, and variable Hf/Nd ratios demonstrate that the arc magmatism of these two episodes could be derived from two distinct mélange sources that formed at the slab-mantle interface during subduction of the Junggar oceanic plate. In the first episode, magmatic rocks exhibit high Th/Yb and (La/Sm)N ratios and the decoupling of Nd-Hf isotopes, which leads to an interpretation that the primary magmas were derived from sources mainly mixed by sediments and mantle-wedge peridotites. In contrast, the magmas of the second episode exhibit high Ba/La and Ba/Th ratios and the coupling of Nd-Hf isotopes, which implies that these magmas were likely produced from mélange diapirs dominated by the mixing of midoceanic-ridge basalts and mantle peridotites. The episodes of Nd-Hf isotopic decoupling and coupling coincided with crustal material recycling and crustal growth in subduction zones, respectively. Considering that the Northern Yili Block at 400-350 Ma was characterized mainly by enriched Nd-Hf isotopes of magmatic rocks and no development of the forearc accretionary complex, while the Northern Yili Block at 350-300 Ma featured high εHf(t)-εNd(t) values of magmatic rocks, occurrences of extension-related magmatism, and distribution of the forearc accretionary complex and immature back-arc basin, we propose that these two different mélange sources probably developed in response to subduction transition. That is, one resulted from advancing and the other was relevant to retreating regime. The partial melting of these mélanges in the mantle wedge generated intermediate felsic magmas, which might have acted as a leading mechanism for crustal recycling and growth of the accretionary orogenic belt. [ABSTRACT FROM AUTHOR]

• O isotopes can effectively identify the altered oceanic crust in the TTG source. • Subduction failure led to partial melting of the oceanic crust under medium pressure. • Subduction success gave rise to the mantle source of mafic igneous rocks. • Archean subduction experienced a series of processes from failure to success. When and how plate tectonics started and evolved to the style as we know it today is a fundamental yet highly controversial question. Numerical geodynamic modelling predicts that the transition into plate tectonics in the Archean was episodic with possible alternation between success and failure of subduction. However, direct geological evidence for failed subduction is scarce. While this possibility has been suggested by numerical modelling, it is still lack of geological evidence. Here we present a combined study of zircon U-Pb ages and Hf-O isotopes, as well as whole-rock major and trace elements, for meta-igneous rocks from the Alxa Block in the westmost North China Craton (NCC). Two periods of Late Archean magmatism ca. 2.75 Ga and 2.5 Ga are identified to occur surrounding a pre-3.0 Ga continental nucleus. Geochemical analyses of the ca. 2.75 Ga meta-mafic and meta-felsic igneous rocks show two different modes of tectonic regime. The felsic rocks resemble typical Archean TTG (tonalite-trondhjemite-granodiorite) in composition, with variable ε Hf (t) values from -2.8 to 11.0 and δ18O values from 4.3 ‰ to 7.9 ‰. Petrogenetic modelling suggests that their magmatic source was the ca. 3.1–2.75 Ga oceanic crust that was hydrothermally altered at different temperatures and then mixed with the older continental crust and partially melted in lower crust in the garnet stability field. This requires tectonic accretion of the oceanic crust to the continental nucleus, signifying an attempted or failed subduction. On the contrary, the meta-mafic rocks exhibit arc-like trace element patterns and calc-alkaline evolution trend, indicating a metasomatic mantle source due to successful subduction of the oceanic slab to subarc depths. Taken together, the present results provide robust constraints on the behavior of oceanic slab at the Archean convergent margin, where successful oceanic subduction would be achieved after several failed attempts. Such failure-success processes of oceanic subduction may be applicable to the whole NCC and other cratons elsewhere in the world, reflecting the gradual maturation of plate tectonics in the Archean, consistent with predictions of numerical modelling. [ABSTRACT FROM AUTHOR]

The Mesozoic tectono-thermal evolution of eastern South China plays an important role in forming the abundant magmatic rocks and associated giant polymetallic deposits. The middle-late Mesozoic granitoids in Mufushan and adjacent regions (e.g., Lianyunshan, Wangxiang, Taohuahsan, etc.) represent the western front of the southeast China magmatic province. However, the tectonic regimes and petrogenesis of the magmatic rocks are still elusive. Here, we report zircon U Pb ages, geochemistry, and Sr-Nd-Hf-Pb isotopic data for the granitic rocks in the Mufushan region, in combination with data available from the literatures, to discriminate the middle-late Mesozoic tectono–magmatic history of the Mufushan complex in north-central South China Block. New zircon U Pb dating suggests that the Mufushan two-mica monzogranites were emplaced at 149–144 Ma, a short time after the 153–151 Ma granodiorites. These late Jurassic felsic magmas share broad similarities in geochemical-isotopic characteristics, with significant enrichment in LREEs and LILEs (e.g., Ba, Rb, Th, and K), depletion in some HFSEs (e.g., Nb, Ta, Ti, and P) and positive Pb anomalies, similar to those of arc-type rocks. The common existence of Neoproterozoic zircons within the magmatic rocks indicates a certain amount of ancient material involved in the genesis of the magma. The two-mica monzogranites have ε Hf (t) values ranging from −13.4 to +3.5, overlapping with those of the granodiorites (−11.3 to +6.6), but both are lower than contemporaneous diorites (−2.4 to +0.59), suggesting a greater incorporation of enriched materials into the source for the granitoids. The two-mica monzogranites and granodiorites have ε Nd (t) values ranging from −7.9 to −8.8 and − 10 to −7.9, with corresponding two-stage Nd model ages of 1.7–1.6 Ga and 1.6 Ga, respectively, falling within their two-stage Hf model ages of 2.0–1.4 Ga and 1.8–1.4 Ga, respectively. Compared with the geochemical and isotopic compositions of the coeval magmatic rocks in eastern South China, we favor that the late Jurassic Mufushan granodiorites evolved from variable mixing and differentiation of the diorites and granitoids, accompanied by a continuous magma assimilation. The presence of late Jurassic highly fractionated granites suggests an extensive magma differentiation in eastern South China and the well-developed early Cretaceous A-type granites in eastern South China reflect a dominant extensional tectonic regime induced by slab roll-back of the Izanagi plate. The involvement of subduction-related melts facilitated the underplating of mantle-derived magma and crustal heating, triggering intensive partial melting of the lithosphere and magma enrichment, as well as the polymetallic deposits in eastern South China. [Display omitted] • The late Jurassic granitic rocks in Mufushan were derived from a common source. • Neoproterozoic crustal materials were involved in middle-late Mesozoic magmatism. • Mesozoic magmas were subjected to significant modification by slab-derived components. • The slab-roll back of the oceanic Plate beneath ESCB likely began by the middle Jurassic. [ABSTRACT FROM AUTHOR]

• The metabasites and TTG gneiss in the Linshan complex mainly formed at 2.6–2.5 Ga. • The metabasites in the Linshan complex formed in a Neoarchean back-arc basin. • There may have been several Neoarchean "forearc-arc-backarc" systems in the NCC. The onset of plate tectonics and crustal growth processes in the early Earth have been controversial scientific issues in the geoscience. The North China Craton (NCC) preserves widespread 3.8–2.5 Ga rocks, providing an ideal place to understand early continent formation and evolution. The Linshan complex located in the southern segment of the Central Orogenic Belt (COB) of the NCC, is mainly composed of TTG (tonalite-trondhjemite-granodiorite)-diorite gneisses and metamorphic volcanic-sedimentary units dominated by gabbro, basalt, basaltic andesite and biotite-plagioclase gneiss. Detailed mapping on the scale of 1:100 of a structural transect shows that the Linshan complex has mainly experienced two major deformation events including top-to-the-SE thrust faults and late NE-trending high-angle normal faults. Detailed zircon U-Pb dating shows that gabbro, basaltic andesite, and TTG gneiss mainly formed at ca. 2.52–2.50 Ga. Gabbros and basalts display enrichment of LREE and negative Nb and Ta anomalies, and basaltic andesites display mixed MORB-IAT geochemical affinities. Basalts and basaltic andesites are members of the Nb-enriched basalt series with high absolute Nb contents (>6 ppm). TTG gneisses are geochemically divided into high-pressure and low-pressure TTGs. High-pressure TTGs are characterized by high ratios of La/Yb cn (26.29–45.73) and fall into the adakitic region in the La/Yb cn -Yb cn diagram. Considering the close contact with Nb-enriched basaltic series, it is proposed that high-pressure TTGs may have formed by partial melting of a subducting oceanic slab with garnet and amphibole and/or rutile as residues. Low-pressure TTGs are characterized by low ratios of La/Yb cn and Sr/Y with marked negative Eu anomalies, indicating partial melting at shallow crustal levels. Regional tectonic relations have defined the Neoarchean Dengfeng island arc-forearc accretionary complex to the east of the Linshan complex. Thus, we propose that the gabbros-basalts-basaltic andesites in the Linshan complex mostly formed in a Neoarchean suprasubduction back-arc basin by rifting of a TTG-dominated island arc terrane. The final closure of the back-arc basin resulted in their tectonic juxtaposition forming thrust-imbricated structures. There may have been several Neoarchean "forearc-island-arc-backarc" systems in the NCC that are similar to modern accretionary tectonic orogens, indicating that plate tectonics has been in operation since at least 2.55–2.50 Ga. [ABSTRACT FROM AUTHOR]

Carbonate melts play an essential role in the deep carbon cycle between Earth's surface and interior. Most previous studies proposed that the source of carbonate melt resulted from the recycling of subducted oceanic slabs. Recent studies on orogenic rocks show that continental subduction may also deliver carbonate sediments into the deep mantle. However, these rocks usually have undergone complex geological processes and strong modifications during exhumation. Here we report evidence of continental subduction-triggered carbonate metasomatism of the lithospheric mantle from a suite of mantle xenoliths entrained by the Cenozoic Qixia basalts from the southeastern North China Craton (NCC). Both petrological (the same variation of mineral modal content as in carbonate melt-peridotite reaction experiments, the replacement of olivine and orthopyroxene by clinopyroxene, and the presence of apatite) and geochemical (high Ca/Al, La N /Yb N , and low Ti/Eu ratios in clinopyroxene) evidence show mantle xenoliths record obvious signals of carbonated silicate melt metasomatism. The high 87Sr/86Sr ratios of 0.7094–0.7100 in clinopyroxene of these xenoliths indicate that the carbonated silicate melt was derived from subducted continental crust rather than oceanic crust and asthenosphere mantle. The carbonated silicate melt could be produced by carbonate dissolution during continental subduction or resulted from the partial melting of the diapiric carbonate-rich sediments. An estimation suggests a carbon input flux of 14 ± 7 Mt yr−1 associated with the Yangtze continental subduction, approximately 20–50% of the estimated total carbon input flux of the global oceanic subduction. It is therefore important to include the contribution of continental subduction when deciphering deep carbon recycling and its effects. • Qixia mantle xenoliths from North China Craton suffered carbonate metasomatism. • Carbonated silicate melt was derived from the subducted Yangtze Block. • Continental subduction plays an essential role in the deep carbon cycle. • Input flux of 14 ± 7 Mt. C yr−1 is estimated during Yangtze continental subduction. [ABSTRACT FROM AUTHOR]

The North China Craton (NCC) provides a world-class example for how the destruction of a cratonic root can significantly influence metal and energy resources. The Bohai Bay Basin and Ordos Basin are two super basins that developed in the eastern and western NCC, respectively. Both basins witnessed the decratonization of NCC. However, their dominant energy-producing layers are vastly different, with vast Paleozoic natural gas resources in the Ordos Basin but mostly Cenozoic oil resources in the Bohai Bay Basin. The distinct hydrocarbon evolution periods of the two basins since the late Paleozoic coincides with different stages of the NCC destruction. However, the direct association between the NCC destruction and hydrocarbon evolution has not been has not been explicitly revealed or studied in detail. In this comprehensive review, a four-stage hydrocarbons accumulation model related to NCC destruction is presented: 1) Homogeneous late Paleozoic (ca. 299–252 Ma) source and reservoir rocks formation across the entire craton due to the activation of cratonic margins; 2) divergent evolution from the early Mesozoic (ca. 252–165 Ma) caused by the initiation of westward flat subduction of the Paleo-Pacific slab, where the west NCC formed thick sedimentary strata (marked by the Yanchang Formation in the late Triassic) while east NCC experienced a depositional hiatus; 3) NCC destruction peak in the mid-late Mesozoic (ca. 165–66 Ma) that contributed to the voluminous natural gas generation in the west, resulting from the thermal perturbation of delamination or slab rollback; 4) continuous Cenozoic extension and elevated geothermal field (ca. <66 Ma) related to mantle upwelling (ca. 35–20 Ma) caused by the present-day Pacific slab subduction, resulting in thick lacustrine deposition of Cenozoic and maturation of Upper Paleozoic source rocks. We thus conclude that both differences and similarities between the two super basins of North China can be explained by the shared Paleozoic depositional conditions and the inhomogeneous Mesozoic destruction state across the craton. This entire process was initiated by the westward subduction of the paleo-Pacific plate that resulted in the change of tectonic regime of eastern China. The intense decratonization in the eastern NCC resulted in the partial destruction of the Paleozoic reservoirs, while continuous Cenozoic extension facilitated the formation of significant oil resources in the Bohai Bay Basin. This study highlights the importance of investigating the more homogeneous Paleozoic strata for undiscovered hydrocarbon resources. • Inhomogeneous North China Craton destruction on super basins formation is revealed. • Contrasting hydrocarbon enrichment models related to craton evolution is proposed. • Stable lithospheric structure benefits Paleozoic oil and gas in western craton. • Lithospheric thinning contributes to Cenozoic oil and gas in eastern craton. [ABSTRACT FROM AUTHOR]

[Display omitted] • Neoproterozoic high-Mg andesites and gabbros in western Yangtze Block. • There would be a tectonic switch from subduction to back-arc extension in the western Yangtze Block. • Protracted marginal subduction retreat caused the external rifting in Rodinia. The western Yangtze Block is an ideal place for investigating the Precambrian tectonic evolution of the South China Craton and the geodynamic mechanism responsible for the breakup of Rodinia. However, the Neoproterozoic tectonic evolution of the western Yangtze Block has not been fully elucidated; in particular, the driving mechanism has changed from an arc setting to a rift setting. Here, we present new zircon U–Pb geochronology and O–Hf isotopic compositions, whole-rock geochemistry, and Sr–Nd isotope data for Yanbian andesites and Shimian gabbros from the western Yangtze Block, South China. The ca. 850–840 Ma Yanbian andesites are high-Mg andesites with moderate SiO 2 (56.75–60.21 wt%) and high MgO (4.24–6.44 wt%) and Mg# (52–66). These rocks show enrichments in large-ion lithophile elements (LILEs; e.g., Rb, Ba, Sr, and K) and light rare earth elements (LREEs) and depletions in high-field strength elements (HFSEs; e.g., Nb, Ta and Ti) and display decoupled Nd–Hf isotopes (ε Nd(t) = +3.9 to + 5.0, ε Hf(t) = +9.7 to + 13.1) and relatively high zircon δ18O values (5.82–7.72 ‰); these findings indicate that these rocks were derived from a mantle wedge enriched by slab fluids and sediment melts. The ca. 820–810 Ma Shimian calc-alkaline gabbros are characterized by enriched LREEs and LILEs (e.g., Rb, Sr, and K) and depleted HFSEs (e.g., Nb, Ta and Ti). These rocks show decoupled Nd–Hf isotopes (ε Nd(t) = +3.2 to + 4.2, ε Hf(t) = +3.1 to + 7.5) and relatively low zircon δ18O values (4.28–5.31 ‰), indicating that they were formed by partial melting of mantle wedge metasomatized by sediment and oceanic slab melts. Compiled geochronological data suggest that Neoproterozoic subduction-related magmatism along the western Yangtze Block formed a long-term active arc system. Slab retreat in this subduction zone led to a shift in the tectonic setting from a compressional setting to an extensional setting in the Yangtze Block during the middle to late Neoproterozoic. Moreover, the temporal link between retreating subduction zone and extensional tectonics in the Yangtze Block suggests that protracted subduction retreating resulted in external rifting in Rodinia. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Tarim Craton experienced both active and passive rifting during the Cryogenian. • The rift system shows a two-tiered architecture with narrow-deep Cryogenian grabens overlain by a broad Ediacaran depression. • Both active and passive rifting are thought to have been triggered by retreating subduction in the late Neoproterozoic. The Cryogenian-early Paleozoic succession in the Tarim Craton is generally regarded as a continuous rift sequence that followed the prolonged superplume-related breakup of Rodinia. However, the rift architecture and origin of the late Neoproterozoic basin are poorly known, but these are important for the understanding of the tectonic evolution of the basin and for the evaluation of the hydrocarbon potential. This paper aims to elucidate the rift architecture, distribution, origin and evolution of the late Neoproterozoic Tarim Basin by integrating outcrop investigations with well and seismic data. The late Neoproterozoic magma-rich active rifting primarily occurred in the northeastern part of the basin, whereas other areas experienced slightly younger magma-poor passive rifting. The Ediacaran succession overlaps in the northern basement uplift to show a pre-Ediacaran unconformity occurs in the northern Tarim Craton, while a sub-Cambrian unconformity traverses the entire Tarim Craton and presents a distinct truncation in the southern basement uplift. A tiered architecture exists in which narrow, deep Cryogenian grabens are overlain by a broad Ediacaran depression. Two NE-striking rift systems developed in the northeastern and southwestern Tarim. It can be inferred from the compiled data that the late Neoproterozoic rift basin evolution in the Tarim Craton can be divided into four stages: early Cryogenian rifting, late Cryogenian fault-graben, Ediacaran intracratonic depression, and end-Ediacaran regional uplifting. These results suggest that documented Neoproterozoic retreating subduction-related slab failure/detachment processes led to both active and passive rifting, which contributed to the diverse continental rift architecture and evolution of the late Neoproterozoic Tarim Basin. [ABSTRACT FROM AUTHOR]

• Late Cretaceous basalts are related to the Paleo-Pacific subduction. • The coastal arc-like basalts originated from sediment-hybridized mantle wedge. • The inland transitional basalts originated from asthenosphere enriched by slab melt. • Retreating dynamics promoting slab opening may explain their coexistence. Cretaceous arc-like, ocean island basalt (OIB)-like, and transitional basalts erupted on the eastern South China Block (SCB), and their petrogenesis was possibly related to the subduction of the Paleo-Pacific plate. However, the detailed petrogenesis in terms of slab subduction, magma sources, and the spatial distribution of the different types in the coastal and inland regions is poorly understood. Here we conduct a comparative study on the Late Cretaceous basalts from both coastal and inland regions. Our compiled age data demonstrate that the basalts in the coastal regions erupted in the period of 104–81 Ma. They show low Nb/La (<0.8), Nb/Y (<0.7), and other typical arc-like signatures, e.g., negative Nb-Ta anomalies, variable enrichment of LILE and LREE, and more radiogenic Sr-Nd isotopic compositions. In contrast, the basalts in the inland regions erupted at 86–71 Ma. They are characterized by high Nb/La (>0.9), slightly negative to positive Nb-Ta anomalies; they mostly possess positive ε Nd (t) values and geochemical features transitional to OIB-like basalts. The systematic geochemical differences may imply the spatial heterogeneity in their magma sources. The three end-member mixing model suggests that the isotopic signatures of arc-like basalts largely resulted from partial melting of the mantle wedge metasomatized by the subducted sediments, while those of transitional basalts likely resulted from depleted mantle source metasomatized by melts from altered oceanic crust (AOC) with minor sediments. We suggest that the retreating of the Paleo-Pacific plate promoted the melting of sediment-hybridized mantle wedge, and then triggered the opening of a slab window and asthenosphere-slab interactions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Neoproterozoic adakitic granodiorites, gabbro-diorites and high-K granites in South China. • The western Yangtze Block was an arc belt related to the oceanic slab subduction during the Neoproterozic. • The Neoproterozoic magmatism was triggered in an oceanic slab window in the western Yangtze Block. Neoproterozoic igneous rocks are widespread along the margins of the Yangtze Block and record key information on the tectonic evolution of the South China Craton. In this paper, we present a comprehensive study of zircon U-Pb ages, whole-rock geochemistry and Sr-Nd-Hf isotopes on the Neoproterozoic granodiorites, gabbro-diorites, and high-K granites in the western Yangtze Block. The granodiorites, gabbro-diorites and high-K granites were dated at 848 ± 5.3 Ma, 824 ± 5.1 Ma and 819 ± 1.5 Ma, respectively. The granodiorites have high Sr (567 ∼ 607 ppm) contents and Sr/Y (84.4 ∼ 88.0) ratios and low alkalis (Na 2 O + K 2 O = 4.3 ∼ 4.9 wt%) and Y (6.6 ∼ 7.1 ppm) and Yb (0.7 ∼ 0.9 ppm) contents, similar to typical adakitic rocks. They show low MgO (0.9 ∼ 1.3 wt%), Cr (15.2 ∼ 26.7 ppm) and Ni (3.6 ∼ 4.4 ppm) contents and positive ε Nd(t) (+1.7 to + 4.2) and ε Hf(t) (+3.0 to + 8.2) values. The parental magmas for granodiorites were generated by partial melting of thickened juvenile mafic lower crust. The gabbro-diorites are characterized by the enrichment in LREEs, significantly negative Nb, Ta and Ti anomalies, and positive ε Nd(t) (+2.2 to + 4.2) and ε Hf(t) (+5.8 to + 10.4) values. They are inferred to be derived from partial melting of lithospheric mantle modified by subduction-related fluids. The high-K granites display high Zr + Nb + Ce + Y (208 ∼ 366 ppm) and alkali (Na 2 O + K 2 O = 7.6 ∼ 8.4 wt%) contents, high 10000*Ga/Al (2.31 ∼ 2.64) ratios and zircon saturation temperatures, similar to A-type granites. We suggest that these granites were formed by the partial melting of felsic crustal materials under low pressure and high temperature conditions. The association of granodiorites, gabbro-diorites and high-K granites indicates Neoproterozoic oceanic slab subduction in the western Yangtze Block. We suggest that a subducting oceanic slab window can account for Neoproterozoic magmatism in the western Yangtze Block. [ABSTRACT FROM AUTHOR]