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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 activity of melts and fluids may have played a key role in inducing the destruction of the eastern North China Craton in the early Cretaceous. Carbonate melts are important agents in mantle metasomatism and can significantly modify the physical and chemical properties of the subcontinental lithospheric mantle. Carbonate metasomatism can be identified by specific geochemical indices in clinopyroxene, such as high Ca/Al and low Ti/Eu ratios. This study presents the spatial and temporal variations of carbonate metasomatism in the lithospheric mantle beneath the eastern North China Craton. Three types of carbonate metasomatism are classified based on the geochemical compositions of clinopyroxene in mantle peridotites. Clinopyroxene formed by Type 1 carbonate metasomatism is characterized by very high Ca/Al ratios (15-70) and 87Sr/86Sr ratios (0.706-0.713). Clinopyroxene derived from Type 2 carbonate metasomatism shows relatively high Ca/Al ratios (5-18) and 87Sr/86Sr ratios (0.703-0.706). However, clinopyroxene resulting from Type 3 carbonate metasomatism has low Ca/Al ratios (5-9) and 87Sr/86Sr ratios (0.702-0.704). Deep (garnet-bearing) and shallow (spinel-bearing) lithospheric mantle beneath the Sulu orogen and surrounding areas in the eastern North China Craton were affected by intense Type 1 carbonate metasomatism before the late Triassic. The deep subduction of the South China Block with its accompanying carbonate sediments was the trigger for Type 1 carbonate metasomatism, which reduced strength of the lithospheric mantle and provided a prerequisite for the destruction of the eastern North China Craton in the early Cretaceous. After the destruction of the eastern North China Craton, the ancient relict lithospheric mantle, represented by spinel harzburgite xenoliths hosted in the late Cretaceous to Cenozoic basalts, only recorded Type 2 carbonate metasomatism. This implies that the lithospheric mantle experienced the intense Type 1 carbonate metasomatism was completely destroyed and not preserved during decratonization. Spinel lherzolite xenoliths hosted in the late Cretaceous to Cenozoic basalts represent the young, fertile lithospheric mantle formed after the cratonic destruction and only a few samples record Type 2 and 3 carbonate metasomatisms. We suggest that carbonate melts derived from the subduction-modified asthenospheric mantle with variable proportions of recycled crustal material was responsible for the Type 2 and 3 carbonate metasomatisms. The carbonate metasomatism of the lithospheric mantle beneath the Jiaodong Peninsula and surrounding areas is very pervasive and is spatially consistent with the remarkable thinning of lithospheric mantle and giant gold deposits in this region. Therefore, we conclude that carbonate metasomatism in the lithospheric mantle played a crucial part in the modification, destruction and gold deposits in the eastern North China Craton. [ABSTRACT FROM AUTHOR]

Deep-water canyon systems can provide important sandstone reservoirs for deep-water oil and gas exploration in the South China Sea; however, the sedimentary provenance of the Central Canyon in the Qiongdongnan Basin remains controversial. In this work, detrital zircon grains from three drilling sandstones in the Upper Miocene Huangliu Formation in the western part of the Central Canyon were analysed by LA-ICP-MS for U-Pb ages, in order to constrain their provenance. One hundred and ninety-one zircon grains yield concordant U-Pb ages ranging from 28.6 to 3285 Ma. Most of them show oscillatory or linear zoning in CL-images and high Th/U ratios (>0.1), suggesting that they are magmatic zircons. Three major age clusters at about 30 Ma ( N=6), 220-270 Ma ( N=29), and 420-440 Ma ( N=13), and five minor age clusters at 70-110 Ma ( N=7), 150-170 Ma ( N=4), 800-850 Ma ( N=11), 1800-2000 Ma ( N=16), and 2400-2600 Ma ( N=7), can be identified in the age spectrum, which are very similar to those of the Upper Miocene sandstones and modern river sands in the Red River area, but different from those of other nearby regions (e.g., Hainan Island, the Pearl River area, and the Mekong River area) in Southeast Asia. The major age peak at about 30 Ma in our samples is consistent with the timing of tectonothermal events in the Red River Fault Zone. Therefore, we suggest that the provenance of the western part of the Central Canyon, in the Qiongdongnan Basin, was fed dominantly by the Paleo-Red River system during the Late Miocene. [ABSTRACT FROM AUTHOR]

The Neogene sediments of Gansu Group from northwestern China contain eolian and fluvial deposits. The origins of these sediments are very important for exploring the onset of Asian inland aridification, the pattern of paleo-atmospheric circulation, and the regional tectonics and geomorphic evolution during the Miocene. Here we present detrital-zircon age spectra of typical eolian and fluvial deposits from highlands and subsidence basin, and compare them with those of surrounding eroded mountain (such as the West Qinling Mountains and Liupan Mountains) materials and Quaternary loess derived from the Asian inlands. The results reveal that (1) the detrital-zircon age spectrum of the Miocene eolian sample is remarkably different from the eroded materials of the West Qinling Mountains and the Miocene fluvial deposits from Tianshui region, but very similar to the Quaternary loess deposits. This indicates that the provenance of Miocene eolian sediments is similar with the Quaternary loess, and thus further confirms the previous conclusions that the distribution of Asian arid lands and the pattern of atmospheric circulation during the Miocene are broadly similar with the Quaternary. (2) The detrital-zircon age spectrum of the fluvial deposits (with age about 11.5 Ma) from Tianshui region is different from the eroded materials of West Qinling Mountains, but similar with that of the Liupan Mountains to the east, which may suggest that the Liupan Mountains have already been exhumed by 11.5 Ma. [ABSTRACT FROM AUTHOR]

Highlights: [•] TTG in the interior of the Dunhuang blocks was formed at ∼2.7–2.6Ga. [•] Tarim experienced two-stage (∼2.7–2.6 and ∼2.5Ga) intrusion of Archean TTG. [•] Tarim was characterized by episodic generation of juvenile continental crust. [•] Paleoproterozoic and Paleozoic tectonothermal events were prevail in the Tarim craton. [•] Paleoarchean continental crust as old as ∼3.4Ga may have existed in the Dunhuang block [Copyright &y& Elsevier]

Abstract: Eclogite-hosted garnet–spinel–corundum–quartz-bearing titanohematite veins and lenses (10–20cm in width) are described for the first time in the Sulu ultrahigh-pressure metamorphic terrane. Some of the lenses were aligned parallel to the foliation of the host eclogite, suggesting that they were the product of ductile deformation of one titanohematite layer. A vein composed of titanohematite+ilmenite+hematite+spinel+garnet+corundum+quartz+K-feldspar+albite was studied in detail. Ti–Fe oxides account for up to >80% and Al-rich phases for ∼15% of the total volume of this vein. Electron microprobe analyses show that the titanohematite solid solution was made up of 0.75 hematite+0.25 ilmenite. The unusual mineral assemblage of garnet+spinel+corundum+quartz implies that this vein could have experienced high temperatures (>900°C). Although the garnets showed well-defined Mg and Mn diffusion zoning in the rim as a result of the high temperature event, slight Mg and Mn growth zoning was preserved in the core. Thus, we suggest that the Sulu UHP terrane could have experienced a short-lived, high-temperature (>900°C) stage during exhumation. Garnets in the titanohematite vein were characterized by extremely low trace-element contents. Petrological and geochemical features of the veins suggest that they could be metamorphic products of igneous cumulates composed of magnetite+plagioclase±clinopyroxene. [Copyright &y& Elsevier]

Abstract: Hydrothermally altered rocks are products of fluid–rock interactions, and typically preserve numerous quartz veins that formed as chemical precipitates from fluids that fill up cracks. Thus, quartz veins are the record of the fluid system that involved fracture flow in the direction of changing temperature or pressure. In order to decipher the fluid activity in the Sulu ultrahigh-pressure (UHP) terrane in eastern China, quartz veins together with an adjacent eclogite lens and the host gneiss were studied. In one location a deformed quartz vein is located at the boundary between the host gneiss and the eclogite lens. The amphibolite-facies overprinting of the eclogite lens decreases from the rim to the core of the lens, with fresh eclogite preserved in the core. The foliated biotite gneiss contains felsic veins and residual phengites. Zircon rims from the gneiss are characterized by melt-related signatures with steep HREE patterns, high Hf contents and negative Eu anomalies, and a pool of weighted average 206Pb/238U analyses reveal an age of 219±3Ma (2σ), which is younger than the UHP metamorphic age (236±2Ma, 2σ) recorded by zircons from the eclogite lens. This suggests that the gneiss in the Sulu UHP terrane could have suffered from partial melting due to phengite dehydration during the “hot” exhumation stage. The formation age of the quartz vein (219±2Ma, 2σ) defined by zircon rims agrees well with the partial melting time (219±3Ma, 2σ) of the host gneiss. The initial 176Hf/177Hf ratios of zircon rims from the quartz vein are obviously lower than zircons from the eclogite lens, but overlap with the coeval zircon domains from the nearby granite dikes produced by partial melting of orthogneiss. These observations suggest that the quartz vein and corresponding fluid flow could be associated with partial melting of the host gneiss. On the other hand, amphibole-bearing and HREE-rich zircon rims from the amphibolite pool an amphibolite-facies metamorphic age of 217±5Ma (2σ), overlap with the formation age of the quartz vein. This implies that retrogression of the eclogite lens could have been caused by melting-induced fluid flow. Based on the above observations, we speculate that partial melting of the gneiss in the continental subduction-related UHP belt could have induced a significant fluid flow during the exhumation stage, and thus contributed significantly to the extensive retrogression of eclogites in the Sulu UHP terrane. [Copyright &y& Elsevier]

Refertilization of depleted peridotites widely occurs in lithospheric mantle but is poorly understood in a continental subduction channel. The Sulu orogenic belt is a typical ultra-high pressure (UHP) terrane formed by continental subduction and collision. To understand the complex metasomatic processes on peridotites during continental subduction, we combined detailed petrographic and geochemical studies for fertile garnet lherzolites (Chijiadian) from the Sulu UHP terrane, as well as refractory peridotites (Xugou and Lijiatun) for comparison. The fertile garnet lherzolites (Chijiadian) are not residues of low-degree partial melting, but they formed from refertilization processes during peak-UHP metamorphic stages (garnet-facies) in a continental subduction channel, as reflected by abundant clinopyroxene (12 vol%) and garnet (12 vol%), low bulk-rock Mg# of 91 and high Al 2 O 3 of 2.4–3.3 wt%. Garnet, clinopyroxene, and orthopyroxene display secondary poikilitic textures and often contain early phases of olivine, spinel, and garnet inclusions, indicating later precipitation of these minerals into depleted peridotite protoliths. The clinopyroxenes show enrichment of large ion lithophile elements (LILE) and high 87Sr/86Sr of 0.7061–0.7084. The estimated pressure-temperature are 720–770 °C at 4.4–4.8 GPa, consistent with previous constraints on UHP conditions. These features suggest strong refertilization processes at UP-UHP conditions (garnet-facies) in continental subduction channels. The metasomatic agents for refertilization would be basaltic-intermediate melts which incorporated continental materials. Similarly, Xugou harzburgites and Lijiatun dunites also record the subducted continental signatures with enrichment of LILE and high Sr isotopes on clinopyroxenes (87Sr/86Sr: 0.7050 to 0.7065). However, Xugou harzburgites and Lijiatun dunites overall do not display the same typical refertilization features as for Chijiadian, as reflected by low abundances of clinopyroxene and high Mg# of 92–93. Consequently, continental subduction could lead to diverse types of metasomatism of refractory peridotites, including refertilization at UP-UHP metamorphic stages in subduction channels, as in other tectonic settings. • Secondary garnet lherzolites formed from refertilization at high-pressure condition in the subduction channel. • Continental subduction could lead to diverse types of metasomatism. • Continental subduction also drives the formation of refertilized lherzolites as other tectonic settings. [ABSTRACT FROM AUTHOR]

• Negative Ce anomaly in the Gaoyuzhuang and Hongshuizhuang formations provides the evidence of transient oxygenation of the Mesoproterozoic ocean. • The proposed Ce anomaly depth model provide a quantitative constrain the surface environment of the Yanshan Basin. • Transient oxygenations could have provided vital niches for the evolution of eukaryotes. Predominantly anoxic conditions with a heterogeneous stratified water column are widely accepted for the Mesoproterozoic ocean. However, transient and episodic oxygenation during the Mesoproterozoic has been recently hypothesized, which may have been an important trigger for eukaryote evolution. In this study, we analyzed the Ce anomalies of the Gaoyuzhuang and Hongshuizhuang formations in North China, to investigate the Earth's surface environment during the Mesoproterozoic. Our data of negative Ce anomalies in the Gaoyuzhuang and Hongshuizhuang formations, reaching 0.73 and 0.84, respectively, suggest transient oxygenations of the surface environment. We applied a Ce N /Ce N * depth model to quantify these transient oxygenations and the results suggest that the atmospheric oxygen level would have increased by 0.01–0.03% present atmospheric level (PAL), 0.02–0.05% PAL, and 0.1–0.4% PAL, with the respective initial levels of 0.05% PAL, 0.1% PAL, and 1% PAL, in the Gaoyuzhuang and Hongshuizhuang formations. Our results suggest that although oxygen levels in the Mesoproterozoic were low, transient oxygenation may have occurred in the surface ocean, which would have provided vital niches for the evolution of eukaryotes. [ABSTRACT FROM AUTHOR]

Ocean island basalts (OIBs) with Zn isotopic ratios higher than the normal mantle (δ66Zn = 0.17 ± 0.08‰) or mid-ocean ridge basalts (MORBs; δ66Zn = 0.27 ± 0.06‰) generally also have an enriched Sr-Nd isotopic signature, suggesting carbonate-bearing eclogites, whose protolith is inferred to be subducting altered oceanic crust, in their mantle source. On the contrary, continental intraplate basalts with high δ66Zn usually show depleted Sr-Nd isotopic signatures (i.e., decoupled Zn-Sr-Nd isotopic composition). To elucidate the origin of the decoupled Zn-Sr-Nd isotopic composition in continental intraplate basalts, we report the discovery of both coupled and decoupled Zn-Sr-Nd isotopic data for a suite of Cenozoic continental intraplate basalts from the Zhejiang province, Southeast China. These basalts display clear spatial and temporal geochemical variations, with early-stage inland low-silica samples presenting moderately enriched Sr-Nd isotopic signatures and high δ66Zn (coupled Zn-Sr-Nd isotopic composition, similar to OIBs), and later-stage coastal high-silica samples that display a pronounced δ66Zn decrease with increasing SiO 2 and 87Sr/86Sr and with decreasing alkali contents and 143Nd/144Nd (decoupled Zn-Sr-Nd isotopic composition). The early-stage basalts with coupled high Zn-Sr-Nd isotopic signatures are also more enriched in incompatible elements than any other basalts from eastern China reported so far. We explain the spatial and temporal geochemical variations of these basalts as the result of two main melting events: 1) the low-silica early-stage magmatism mostly occurs inland and results from high-pressure partial melting of a carbonated eclogite-bearing asthenospheric mantle. Because of the presence of a thick lithosphere limits the melting of the depleted mantle component, the signature of the Zn-Sr-Nd isotopically enriched, and more fusible carbonated eclogite is preserved. 2) At the later stage, magmatism mostly occurs on the coast where the subcontinental lithosphere is thinner. Hence, decompression melting progresses to shallower depth, resulting in an increase of the contribution from the depleted peridotite matrix and a dilution of the signal from the isotopically enriched fusible component. Further upwelling and in-situ melting at the base of the subduction-modified sub-continental lithospheric mantle (SCLM) explains both the decoupled Zn-Sr-Nd isotopic signature of the coastal basalts and their major and trace element variability. We further propose that decompression melting is driven by small-scale convection resulting from variations of lithospheric thickness. Our data highlight the importance of dynamic melting of carbonated eclogite-bearing asthenosphere and subsequent lithospheric melting in preservation and destruction of the coupled enriched Zn-Sr-Nd isotopic signature of carbonated eclogite component and generation of the apparent decoupled Zn-Sr-Nd isotopic signal commonly observed in continental intraplate basalts. [ABSTRACT FROM AUTHOR]

The metasomatized sub-continental lithospheric mantle (SCLM) is increasingly proposed to play a key control in the formation of giant gold (Au) deposits. However, the extent of Au enrichment in metasomatized SCLM and the Au contents of its derivative partial melts remain poorly constrained. Lamprophyres are derived from low-degree melting of metasomatic and fusible components in the SCLM, and could provide fundamental information about the metasomatized source and metal release compared to mantle peridotites and/or pyroxenites. The giant Jiaodong Au province (> 5000 tons, ∼ 120 Ma) in the eastern part of the North China Craton (NCC) is an ideal locality to assess the Au endowment of metasomatized SCLM which may serve as the source of Au, as indicated by the presence of mantle-dominated volatiles in auriferous fluids associated with the deposits. Based on detailed petrological studies, we analyzed Au, S, Cu and platinum-group element (PGE) contents of the SCLM-derived lamprophyres that are temporally (130–121 Ma) and spatially associated with the Jiaodong lode Au deposits. The lamprophyre dykes were emplaced in the deep crust and did not experience significant degassing and sulfide segregation, and the sulfide saturation occurred at a late stage during magma cooling, as demonstrated by sulfide petrography, S contents, Cu/S and Cu/Pd ratios of the lamprophyres. The relatively oxidized (ΔFMQ +1 – +2), hydrous (2–4 wt.% H 2 O) lamprophyres display variable and generally low Au contents (0.04–3.59 ng/g, mainly 1–3 ng/g, n = 31), as well as low PGE and Cu contents. Their high Au/Cu (N) and Au/Pd (N) ratios together with high Ba/Nb indicate a discernible Au addition to their source, resulting from multi-stage mantle metasomatism related to subduction. However, the average Au contents of the metasomatized SCLM before large-scale Au mineralization are heterogeneous and overall in a range of 0.5–1.5 ng/g. The values are higher than that of depleted SCLM (< 0.5 ng/g) but are still lower than or similar to the fertile upper mantle (1.2–1.7 ng/g). These results indicate that mantle metasomatism related to subduction replenished some amount of Au into previously depleted SCLM, leading to local or regional Au enrichment. However, such processes evidently did not result in remarkable Au enrichment of the mantle source beneath the eastern part of the NCC. We thus propose that the metasomatized SCLM and magmas derived from it, though without anomalously high Au contents, could still provide large amounts of Au for large-scale Au mineralization. Importantly, metasomatic volatiles from the metasomatized SCLM exert a key role, and they enable efficient release of Au from mantle sources, promote Au transportation along trans-lithospheric fault channels and subsequent enrichment and precipitation via magmatic-hydrothermal processes for giant Au deposits. [ABSTRACT FROM AUTHOR]

Substantial quantities of sediments are known to enter the deep lithosphere at subduction zones, but the extent to which sediments melt and the process involved in sediment contribution to the deep lithosphere are inadequately understood. Vigorous debate continues about whether the subducted sediment component is terrigenous or pelagic and transported as a hydrous melt, an aqueous fluid, or bulk sediment. In this contribution, we conduct an integrated study on a variety of deep-seated xenoliths in the Neogene Hannuoba basalts from the northern margin of the North China Craton. Among these xenoliths, clinopyroxenite xenoliths are compositionally and isotopically distinct. Mineral chemistry shows that the clinopyroxenite xenoliths come from a depth near the MOHO, rather than from the mantle as suggested previously. The clinopyroxenite xenoliths have extremely evolved Sr-Nd-Hf isotopic compositions and are interpreted to have a late Archean protolith age. The extremely low contents of Cr and Ni for the clinopyroxenite xenoliths preclude a magmatic origin. Instead, a metasomatic origin is suggested, which is strongly supported for the clinopyroxenites by the occurrence of hydrous minerals and high contents of large-ion-lithophile elements (K, Rb, Ba, Th and Sr) and light rare earth elements, as well as elevated δ18O (9.9–11.3‰) and light δ26Mg (−1.04‰ to −1.42‰) isotopic compositions. Furthermore, their high high-field-strength element (Nb, Ta, Zr and Hf) contents indicate that the metasomatic agent is a hydrous melt, rather than an aqueous fluid. The metasomatic melts are considered to be derived from a mixed source of sedimentary carbonates and ancient, felsic continental materials. A combination of zircon ages and oxygen isotope data for the clinopyroxenite xenoliths further restricts the timing of metasomatism to the late Paleozoic. Considering the regional tectonic setting, the sediments most likely came from the subducted Paleo-Asian oceanic slab. Thus the Hannuoba clinopyroxenite xenoliths provide direct evidence for melting of the subducted Paleo-Asian oceanic slab sediment and its interaction with the deep lithosphere. The data show that melting of subducted sediments can take place at a much shallower depth than commonly thought and place an independent constraint on future models of slab geotherms. [ABSTRACT FROM AUTHOR]

Three types of carbonates have been found in the Miocene basalt in the Dongbahao area (Inner Mongolia), including wide veins and veinlets of carbonate in basalt and carbonates in peridotite xenoliths. Except for the dolomitic zonation in the basalt, all of the carbonates are calcite. Despite their different appearances, they share almost identical geochemical characteristics of low LILE (low large ion lithophile element), HFSE (high field strength element), and REE (rare earth elements) contents (ΣREE = 0.51–137 ppm); negative Ce anomalies; and low Ce/Pb ratios (0.51–74.5). Moreover, they show high δ 18 O SMOW values (20.95–22.61‰) and 87 Sr/ 86 Sr ratios (0.7087 ± 0.0003 (1σ, n = 17)). These characteristics indicate a sedimentary precursor for these carbonates. However, the occurrence and petrographic characteristics imply an igneous origin for the carbonates rather than a hypergene process. Further, the trace element compositions of the silicate melt and carbonate melt in the calcite-dolomite-silicate zonations fall on the same variation lines in the plots of Y-Ho, La-Yb, Li-Pb and Ba-Cu. It is suggested that these melts could have evolved from one magma system or could have been equilibrated. Given the partition coefficients of REEs and alkali elements (Cs, Rb, and K) between the carbonate melt and silicate melt, it can be inferred that these melts could have been formed from a primary H 2 O-Si-bearing Mg-Ca-carbonate melt by an immiscibility process at 1–3 GPa. Considering the southward subduction of the Paleo-Asian ocean along the northern margin of the North China Craton (NCC), these carbonate melts could have been derived from the melting of subducted sedimentary carbonate rocks. Interestingly, these carbonates have quite depleted carbon isotopic compositions (δ 13 C PDB = −8.23‰ to −11.76‰) but moderate δ 18 O SMOW values, implying coupled H 2 O-CO 2 degassing during subduction and/or recycling to the Earth’s surface. Low-δ 13 C PBD carbonates appearing at the global scale may suggest an underestimated path of CO 2 emission back to the atmosphere. [ABSTRACT FROM AUTHOR]

An integrated study of zircon U–Pb ages and Hf–O isotopic compositions, whole rock elemental and Sr–Nd isotope geochemistry was conducted on three lithologically diverse middle Jurassic plutons from the Eastern Hebei area of the North China Craton (NCC), in order to reveal both their petrogenesis and possible tectonic affinity. The three plutons have consistent magmatic zircon U–Pb ages from 167 ± 1 Ma to 173 ± 1 Ma. The Nianziyu pluton has typical characteristics of appinite with low SiO 2 (43.7–52.6%), high Ca, Mg, Fe and H 2 O contents. It possesses subduction-related trace element patterns, enriched Nd–Hf isotopic signatures as well as elevated zircon δ 18 O values (6.2–7.2‰), arguing for an enriched mantle source metasomatized by fluids related to subduction. The Shuihutong monzogranites have high silica (SiO 2 = 75.4–75.9%) and alkali contents, low Ca contents and striking negative Ba, Sr and Eu anomalies. Samples from the pluton have more evolved Nd–Hf isotopic values and are considered to be most likely derived from anatexis of ancient lower continental crust. Hybridization between mantle- and ancient lower crust-derived magmas is proposed for the mafic microgranular enclave-bearing Baijiadian granitoids, which are characterized by variable ε Nd (t) and ε Hf (t) values. Integrated with the regional geologic history, we suggest that the formation of the three middle Jurassic plutons were related to the subduction of the Paleo-Pacific ocean plate beneath the NCC. Their petrogenetic differences reflect complex magmatic processes in subduction settings involving melting of multiple sources, possible partly facilitated by fluid metasomatism and water-rich magma injection, accompanied with various degrees of magma mixing. The appearance of middle Jurassic appinitic rocks leads us to propose that the NCC destruction and lithosphere thinning were facilitated and controlled by the weakening of the lithospheric mantle after hydration because of the subduction of the paleo-Pacific ocean plate. The lower crust of the craton was also reactivated at the same time due to the subduction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Linglong and Guojialing granitoids were strongly depleted in S and Au. • Mafic magmas underplated in Jiaodong before 130 Ma were also poor in S and Au. • Magma underplating had not enriched the Jiaodong lower crust in sulfides and Au. • The crust was unlikely to be the primary Au source of the Jiaodong gold deposits. Mantle-derived magmas widely underplated the lower crust of eastern North China Craton (NCC) during the large-scale extension in the Mesozoic. The giant Jiaodong gold deposits formed at 120 ± 5 Ma, slightly later than the extensive magma underplating. It remains poorly constrained whether the magma underplating had pre-enriched the crust in significant sulfides and gold (Au) via sulfide accumulation, facilitating subsequent regional Au mineralization in the Jiaodong. In this study, we applied high-precision methods to determine the concentrations of S, Cu, Ag, and Au in the Mesozoic mafic and felsic igneous rocks related to the Jiaodong gold deposits. The studied samples include Guojialing granodiorites (n = 7) and their coeval mafic microgranular enclaves (MMEs, n = 13), as well as two Linglong granites. The Linglong and Guojialing granitoids display no sulfides and extremely low Au concentrations, so they are unlikely to be the major Au source. The MMEs resulted from Mesozoic magma underplating and related magma mixing at ∼130 Ma. The MMEs are also free of sulfides and show remarkably low concentrations of S, Cu, Ag, and Au. The S concentrations of MMEs are far lower than those required for sulfide saturation. This indicates that the S- and Au-depleted nature of MMEs was unlikely caused by sulfide segregation of sulfide-saturated magmas but inherited from the S- and Au-poor parental magmas. Therefore, the mantle-derived mafic magmas in the Jiaodong Peninsula, which had underplated the lower crust before 130 Ma, probably have not led to the extensive sulfide accumulation and gold pre-enrichment in the deep crust. [ABSTRACT FROM AUTHOR]

Abstract: The trace element, Li and Sr isotopic compositions of major minerals in peridotite xenoliths from Kuandian, North China Craton (NCC) were analyzed in situ to investigate Pacific slab subduction-related mantle modification beneath the eastern NCC. The 87Sr/86Sr ratios (0.70282–0.70553) are positively correlated with the La/Nb and U/Nb ratios for clinopyroxenes (Cpx). Based on the trace element distribution patterns, three types of Cpx were identified. Type 1 Cpx are characterized by significant Nb–Ta–Ti depletions and the highest Sr isotopic ratios (up to 0.70553); Type 2 Cpx display Nb (or Ta) depletions and highly variable Nb and Ta fractionation; and Type 3 Cpx show no significant Nb or Ta depletion or even weak Ta enrichment and have the lowest Sr isotopic ratios (0.70282–0.70323). Some Cpx display a pattern of increasing Ca+Mg±Si from the cores to the rims, indicating addition of Ca+Mg±Si-rich fluids derived from a serpentinized peridotite layer above the subducting slab. These features indicate an ancient mantle metasomatic event associated with the subduction of the altered Pacific oceanic crust, which may contribute substantially to the destruction of the eastern NCC. The variations in the Li contents and isotopic compositions of major minerals in the Kuandian peridotite xenoliths encode both the melt/fluid metasomatism and the cooling process. The Li contents in the Cpx (up to 34.8ppm) and orthopyroxenes (Opx) (up to 28.0ppm) are typically higher than those in the coexisting olivines (Ol) (<9.19ppm), suggesting silicate melt metasomatism. Considering the rapid diffusion rate of Li in minerals at mantle temperature, the Li enrichment and low δ7Li values in the rims of most Ol, Cpx and Opx may have arisen from diffusive fractionation due to faster diffusion of 6Li compared to 7Li during a latest Li-rich melt/fluid metasomatic process shortly before the host magma eruption. On the other hand, a few Ol grains show decreased Li contents and higher δ7Li values from the cores to the rims. This could imply Li isotope fractionation caused by cooling-induced Li redistribution during and/or after the host magma eruption, because D Li Ol/Cpx decreases significantly with decreasing temperature and 6Li diffuses faster than 7Li. [Copyright &y& Elsevier]

Abstract: A rare large clinopyroxene megacryst (referred to as type 1) collected from the Hannuoba basalt, North China was studied. It is distinguished from the prevalent clinopyroxene megacrysts (type 2) by garnet and orthopyroxene exsolutions and by elemental and Sr–Nd isotopic compositions. The type 1 clinopyroxene megacryst has higher Cr and Nb contents and Mg# (82.9) than the type 2 clinopyroxene megacrysts as well as more evolved Sr and Nd isotopic compositions (87Sr/86Sr=0.704520, 143Nd/144Nd=0.512350) than clinopyroxene megacrysts elsewhere. These characteristics suggest that the type 1 clinopyroxene megacryst could have been formed by a recycled crust-related melt–peridotite reaction and that the melt formed in the rutile unstable field. The type 2 clinopyroxene megacrysts exhibit good correlations between Mg# and major and trace element compositions. Type 2 Sr–Nd isotopic compositions cluster at the least evolved end of the Hannuoba basalt composition. These observations imply that the type 2 clinopyroxene megacrysts were crystallized from the host lava at high pressure. The type 1 clinopyroxene megacryst contains abundant coherent cryptocrystalline lamellae and orthopyroxene exsolutions. The bulk composition of the cryptocrystalline lamellae, composed of fine plagioclase and olivine, shows typical chemical features of garnet with a Sr isotopic composition similar to the clinopyroxene host. These observations indicate that the cryptocrystalline lamellae are decomposition products of garnet exsolutions in the clinopyroxene megacryst. P–T estimates suggest that garnet exsolution in the clinopyroxene megacryst could have occurred at 2.75GPa and 1290°C. This garnet exsolution could be caused by increasing pressure or decreasing temperature, as indicated by experimental results. Although the temperature decreases during basalt eruption, the much quicker decrease in pressure will suppress the garnet exsolution in clinopyroxene. Therefore, we suggest that the type 1 clinopyroxene megacryst could have experienced pre-Mesozoic crustal uplifting and thickening at the north margin of the North China Craton. Garnet decomposition could have taken place prior to orthopyroxene exsolution during the eruption of the host lava. [Copyright &y& Elsevier]

Abstract: A combined study of zircon U–Pb and Lu–Hf isotopes and whole rock major and trace elements and Sr–Nd isotopes has been conducted for 10 tonalitic–trondhjemitic–granodioritic (TTG) and granitic gneisses from the Kongling terrain, the only known Archean microcontinent in the Yangtze craton, South China. The results reveal a significant magmatic event at ∼2.6–2.7Ga, in addition to the previously reported ∼2.9Ga and ∼3.2–3.3Ga magmatism. The ∼2.6–2.7Ga rocks show relatively high REE (530–1074ppm), apparently negative Eu anomaly (Eu/Eu*=0.22–0.35), low #Mg (19.51–22.63) and low LaN/YbN (10.3–24.2). Besides, they have high K-feldspar proportion and relatively evaluated (K2O+Na2O)/CaO, TFeO/MgO, Zr, Nb, Ce and Y contents. Their 10,000×Ga/Al ratios range between 3.00 and 3.54. All these features suggest that the protoliths of these gneisses are A-type granites. Most of the ∼2.6–2.7Ga zircon grains have ɛ Hf(t) values >0 (up to 7.93, close to the depleted mantle value). This clearly indicates a considerably higher proportion of new crustal components in the ∼2.6–2.7Ga granitoids compared to the ∼3.2–3.3Ga and ∼2.9Ga TTGs. Our results support the conclusion of worldwide studies of igneous and detrital zircons that age peaks at 2.65–2.76Ga represent increases in the volume of juvenile continental crust. The present study also confirms the existence of the two older magmatic events in the Kongling terrain. Both whole rock ɛ Nd(t) values (−3.74 to 1.59) and the zircon ɛ Hf(t) values (−11.18 to 3.55) for the ∼2.9Ga TTG and the Hf isotopes of ∼3.2–3.3Ga igneous zircons (−7.37 to 3.12) are chondritic or subchondritic, suggesting that they were mainly generated by reworking of older rocks with a small amount of new crustal additions. [Copyright &y& Elsevier]

• Crustal xenoliths trapped by Guojialing granodiorites display rather low Au contents. • The Precambrian metamorphic outcrop rocks also show low Au contents. • The metal contents are consistent with the metamorphic devolatilization model. • The Precambrian basement was not the main Au source for Jiaodong giant gold deposits. The Jiaodong gold deposits, eastern China define a giant gold province in the Precambrian high-grade metamorphic crustal basement. Given the early metamorphism, the crustal basement would have been so depleted in gold that cannot be the main source for the later Mesozoic gold deposits. However, previously reported gold contents from crustal rocks were variably high (e.g., >5–10 ppb) and often interpreted to reflect the contribution of crustal basement. In this study, after careful field sampling, we obtained high-precision Au and S contents (with Cu and Ag for many samples) to solve the controversial issue. The Au contents were determined by internal standardization to platinum which was obtained from isotope dilution via high-sensitivity Element XR, and/or another independent method by GFAAS after polyurethane foam pretreatment. These methods achieved low procedural blanks (<0.02 ppb) and reliable analyses of low-Au samples. The analyzed metamorphic crustal rocks are from surface outcrops (n = 30) and crustal xenoliths (n = 10) in the Jiaobei terrane, where hosts the predominant Jiaodong gold resources (>85% of 5000 t). The Archean and Paleoproterozoic metamorphic outcrop rocks were sampled far from gold deposits and faults with the minimum effect of ore-forming fluids, and they display overall low Au contents (0.20 ± 0.18 ppb and 0.47 ± 0.29 ppb, respectively). More importantly, the crustal xenoliths trapped in pre-mineralization Guojialing granodiorites were not affected by hydrothermal overprint and better reflect the pristine features of the metamorphic basement. Although the crustal xenoliths contain variable sulfides with a wide range of Cu, Ag and S contents, they show rather low Au contents (0.18 ± 0.15 ppb). These results indicate the strong depletion of Au contents in the Precambrian crustal basement, consistent with the metamorphic devolatilization model. The Precambrian metamorphic crustal basement thus was rather difficult as the main gold source for the Jiaodong gold deposits, suggesting alternative sources. [ABSTRACT FROM AUTHOR]

Carbonates in subducting oceanic slabs can survive beyond slab dehydration and be transferred into the deep mantle. Such deep carbon cycling plays a critical role in generating carbonatitic to alkaline melts. However, whether and how this process has influenced the lithospheric mantle still remains enigmatic. To address these issues, here we provide a detailed petrographic, in-situ chemical and Sr isotopic study on two mantle xenoliths (a wehrlite and a melt pocket-bearing peridotite) entrained by the Changle Miocene basalts from the eastern China. The Changle wehrlite contains carbonate melt inclusions and apatites and is merely enriched in clinopyroxene relative to the Changle lherzolites. The clinopyroxenes are characterized by high (La/Yb) N (4.7–41) and low Ti/Eu (873–2292) ratios and equilibrated with carbonated silicate melt-like compositions. These petrographic and chemical features indicate that the wehrlite was formed by reaction between peridotite and carbonated silicate melts. On the other hand, the Changle melt pocket-bearing peridotite is suggested to have been produced by in-situ melting/breakdown of amphiboles of an amphibole-rich dunite. Low olivine Fo (~89), presence of amphiboles with high (La/Yb) N (~50) and low Ti/Eu (~1070) ratios suggest that such amphibole-rich dunite would have been formed by reaction of peridotite with hydrous alkaline basaltic melts from a carbonated mantle. Our data, combined with previously reported data of the Changle lherzolite xenoliths, unravel a series of mantle metasomatisms by carbonatitic to alkaline melts from carbonated mantle sources. The consistently high 87Sr/86Sr ratios (up to 0.7036) of the clinopyroxenes in both the wehrlites and lherzolites indicate the carbonate components in the mantle sources were derived from the stagnant Pacific slab within the Mantle Transition Zone. This study provides a fresh perspective on the role of deep carbon cycling from subducted oceanic slabs in chemical modification of intracontinental lithospheric mantle through reaction with different types of melts. • In-situ chemistry and Sr isotopes of two Changle peridotite xenoliths are studied • The wehrlite was formed by carbonated silicate melt-peridotite reaction • The melt-pocket bearing peridotite recorded alkaline melt-peridotite reaction • Recycling of carbonate-rich components from the stagnant Pacific slab in the MTZ • Significance of deep carbon cycle on chemical modification of lithospheric mantle [ABSTRACT FROM AUTHOR]

• The Fe speciation data help bridge the global data gap of Fe species gap during 1500–1400 Ma. • The global Fe speciation data suggest underestimated oxic depositional conditions during the Mesoproterozoic. • Oxic environment could have provided suitable habitats for complex eukaryotes and their subsequent evolution. The Mesoproterozoic (1600–1000 million years ago, Ma) is thought to have experienced important changes in ocean chemistry and eukaryote evolution. Our understanding of global redox conditions remains in its infancy, and redox data derived from the Mesoproterozoic thus far indicate heterogeneity and complexity in the realm of ocean redox, which hampers our understanding of the potential significance of variations in ocean redox on eukaryote evolution. In this study, we report analyses of Fe species and redox-sensitive trace metals of U and Mo from the Jixian Group, including the Wumishan, Hongshuizhuang and Tieling formations, as well as the Xiamaling Formation, in the Yanshan Basin in North China. The Fe speciation data from the Wumishan, Hongshuizhuang, and Tieling formations first reported in this study help bridge the global data gap of Fe species data during 1500–1400 Ma. Our data suggest likely oxic bottom water conditions for the Wumishan Formation and ferruginous bottom water conditions for the Tieling Formation. The Fe species data can distinguish ferruginous conditions for the upper Hongshuizhuang from sulfidic depositional conditions for the lower-middle Hongshuizhuang Formation. Based on Fe species and trace metal data, redox conditions likely varied from anoxic conditions with transient euxinia in the lower-middle Xiamaling Formation to oxic conditions in the upper Xiamaling Formation. The new Fe speciation data from the Yanshan Basin, when combined with previously published data, show a surprisingly high proportion of middle Proterozoic samples with very low highly reactive to total iron ratios. This suggests either a relatively large extent of oxic seafloor, or non-uniformitarian iron cycling. Resolving this discrepancy will be key to understanding the extent of suitable habitats for complex eukaryotes. [ABSTRACT FROM AUTHOR]

• Rutile xenocrysts were captured from the basement by the Yangyuan carbonatites. • The Zr-in-rutile thermometer records formation of the rutiles at 743–932 °C. • Cr and Nb contents and Hf isotopes in rutiles support pelitic granulite protoliths. • U-Pb rutile cooling ages peak at 1810 ± 4 Ma, 1735 ± 5 Ma, and 1673 ± 8 Ma. • In combination with dating results from other systems yields episodic cooling path. The amalgamation of the North China Craton along the Trans-North China Orogen at ~1.85 Ga has been widely discussed, but its thermal evolution after amalgamation is relatively poorly constrained. This study presents U-Pb ages, trace element compositions, and Hf isotopes of rutile xenocrysts carried by the Yangyuan Cenozoic carbonatites, revealing an episodic cooling history of the Trans-North China Orogen. The Zr-in-rutile thermometer records formation of the rutiles under granulite facies at 743–932 °C. Cr and Nb concentrations in rutiles support a pelitic protolith, which is consistent with 176Hf/177Hf ratios that are close to zircons from pelitic granulites in the orogen. U-Pb ages of the rutiles are cooling ages, for which three populations can be clearly delineated. In combination with dating results from other systems, three episodes of cooling can be identified: [1] active cooling after the ~1.85 Ga peak metamorphism, with a cooling rate increasing from 7.9 °C/Ma in the period 1850–1810 Ma to 15.3 °C/Ma at 1810–1792 Ma; [2] active cooling after mantle upwelling at ~1.78 Ga, with cooling rate increasing from 8.7 °C/Ma at 1780–1735 Ma to 17.2 °C/Ma between 1735 and 1719 Ma; [3] passive cooling after a rifting event at ~1.68 Ga, with cooling rate decreasing from 20.6 °C/Ma at 1680–1673 Ma to 6.9 °C/Ma in the period 1673–1633 Ma. The first two episodes correspond to exhumation-related cooling, while the last episode resulted from the rift-to-drift transition of the North China Craton due to increasing distance from the heat source during break-up of the Columbia supercontinent. [ABSTRACT FROM AUTHOR]