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Northeast China hosts one of the largest Cenozoic intraplate volcanic regions in the world. However, the mechanisms that generate the volcanism, its spatial-temporal distribution, and compositional signatures remain highly debated due to the lack of high-resolution images of the mantle's thermochemical structure. We jointly inverted new surface-wave dispersion data, surface heat flow, geoid height, and elevation data to image the fine-scale thermal and compositional structures beneath northeast China and infer regions of partial melting in the mantle. Our model reveals a complex circulation pattern in the asthenosphere and a highly variable lithospheric structure. Combining predictions from our model with independent geochemical data from recent basaltic volcanism, we demonstrate that the generation, location, and composition of intraplate volcanism in this region are controlled by the interaction between shallow asthenospheric circulation and lithospheric thickness. The modeling approach and correlations between basaltic composition and mantle state identified in our study are globally applicable to assessing mantle conditions over time in other continental regions.

Most of Earth’s volcanism occurs at tectonic plate boundaries associated with subduction or rifting processes. The mantle plume hypothesis is an important supplement to plate tectonics for explaining some high-volume intraplate volcanic fields. However, many intraplate magmatic provinces occur as low-volume, monogenetic basaltic-suite fields that are neither associated with plate-boundary processes nor attributable to mantle plumes, and the origin of such magmatism has long been debated. Identification of their source characteristics and possible mechanisms that trigger mantle melting will provide essential insights into Earth’s mantle heterogeneity and also develop our knowledge of tectonic plate movement through time. Here, we report new geochronology, mineral chemistry (especially olivine), and whole-rock chemical and Sr-Nd-Pb-Hf isotopic compositions on Cenozoic intracontinental alkaline basalts from the northwestern Tarim craton (central Asia), aiming to better assess the origin of Earth’s low-volume effusive intraplate volcanic fields. The basalts (ca. 42 Ma) have olivine (e.g., mean Ni abundances of ∼2250 ppm, mean Mn/Zn ratios of 13.7) and whole-rock chemistry consistent with their derivation from a mixed peridotite-pyroxenite source. Moderately depleted Sr-Nd-Pb-Hf isotopes (87Sr/86Sr = 0.7039−0.7053; εNd = +4.0 to +5.5; 206Pb/204Pb = 18.247−18.535; εHf = +8.1 to +8.7) require a young (ca. 500 Ma) oceanic crust recycled into the source, possibly related to subduction events during the assembly of Pangea. Estimated thermal-chemical conditions indicate that the original melting occurred in a relatively dry (H2O = 1.4 ± 0.9 wt%) and reduced (logfO2 ΔFMQ = −0.97 ± 0.21, where FMQ is fayalite-magnetite-quartz) asthenosphere under a mantle potential temperature of ∼1420 °C and a pressure of ∼3.7 GPa (corresponding to a depth of ∼120 km). Combining these data with regional tectonic history and geophysical data (high-resolution P-wave tomography), we propose that the long-lasting India-Eurasia collision triggered asthenospheric upwelling, focusing melts along translithospheric zones of weakness; this model provides a robust explanation for the observed Cenozoic intracontinental volcanism in central Asia. The integrated geochemical and geophysical evidence reveals that plate subduction−induced mantle upwelling represents a likely mechanism for the generation of many regions of plume-absent intraplate magmatism within continents.

Knowledge of the subduction to postcollision tectonic transition in response to oceanic closure is crucial for tracking the final stage of orogenic evolution. Here, we report new geochronology, geochemistry, and isotopic data for Carboniferous magmatism in East Junggar (NW China), southwestern Central Asian orogenic belt, which may record such processes following the closure of the Kalamaili Ocean (a branch of the Paleo-Asian Ocean). The early Carboniferous calc-alkaline volcanic rocks (dominated by basalt and basaltic andesite) yielded zircon U-Pb ages of ca. 340–330 Ma and are characterized by arc-like trace-element patterns showing enrichment of light rare earth elements (LREEs) and large ion lithophile elements (LILEs; e.g., Pb) but depletion of high field strength elements (HFSEs; e.g., Nb, Ta, and Ti). Combined with their variable Ba/Nb (9.80–454) and low Nb/La (0.21–0.54) and Sm/Yb (1.77–3.08) ratios as well as depleted mantle–like Sr-Nd-Pb-Hf (whole-rock 87Sr/86Sri = 0.7037–0.7040; εNd[t] = +3.5 to +5.9; 206Pb/204Pbi = 17.728–17.996; zircon εHf[t] = +11.8 to +18.8) isotopic values, we suggest that they were produced by melting of a lithospheric mantle wedge fluxed by slab-derived fluids under spinel-facies conditions. With whole-rock 40Ar/39Ar dating of ca. 320 Ma, the late Carboniferous mafic dikes have geochemical features and Sr-Nd-Pb (87Sr/86Sri = 0.7039–0.7041; εNd[t] = +6.6 to +6.8; 206Pb/204Pbi = 17.905–17.933) isotopic compositions similar to those of the early Carboniferous volcanics, but they show less pronounced Pb anomalies and negative Nb and Ta anomalies. They are interpreted to have formed by partial melting of a spinel-bearing lithospheric mantle metasomatized by limited influx of subduction-related fluids. The late Carboniferous felsic volcanic rocks (dacite and rhyolite) yielded zircon U-Pb ages of ca. 305 Ma and are geochemically equivalent to those of A2-type granites in East Junggar. They have juvenile isotopic compositions (εNd[t] = +4.5 to +6.8; εHf[t] = +13.3 to +18.7) and relatively young Nd and Hf model ages that roughly coincide with the ages of the ophiolites in the area, suggesting that they could have originated from melting of a juvenile basaltic lower crust. Whole-rock geochemistry, assimilation–fractional crystallization (AFC), and isotopic mixing modeling argue for insignificant crustal contamination for the Carboniferous magmatism. We suggest that the early Carboniferous lavas erupted in an island-arc setting related to the northward subduction of the Kalamaili oceanic crust, whereas the late Carboniferous magmatism formed in a postcollisional extensional regime in response to slab breakoff or lithospheric delamination. Combined with regional geological information, we propose that a rapid tectonic transition from oceanic subduction to postcollisional extension may have occurred in East Junggar during the Carboniferous, marking the final closure of the Kalamaili Ocean, which most likely took place ca. 330–320 Ma. This study provides overall geochronological and petrogeochemical evidence to better constrain the amalgamation of the southwestern Central Asian orogenic belt and may be of great importance for understanding the final stage of orogenic evolution elsewhere.

The Central Asian Orogenic Belt (CAOB) is one of the world's largest and longest-lived accretionary orogens that has been regarded as an important area of crustal growth during the Phanerozoic, yet the growth mechanism is still under debate. A combined study of petrology, geochronology and geochemistry for drilling-sampled early Carboniferous volcanic rocks from the Junggar Basin (NW China), southwestern CAOB, aims to constrain their petrogenesis and implications for Phanerozoic crustal growth. The volcanics show a bimodal-type suite, dominated by basalts, basaltic andesites and subordinate rhyolites, and have consistent zircon U–Pb ages of 334–336 Ma. The mafic rocks exhibit arc-like trace-element distribution patterns characterized by enrichment of LILEs (e.g., Pb) and LREEs but depletion of HFSEs (e.g., Nb, Ta and Ti). They have juvenile isotopic signatures of zircon ɛHf(t) (+11.4 to +15.4) and whole-rock ɛNd(t) (+7.8 to +8.5), with initial (87Sr/86Sr)i of 0.7040–0.7054 and (206Pb/204Pb)i of 17.681–17.817. These geochemical features, together with their variable Ba/La (4.28–44.2) but low (Tb/Yb)N (1.24–1.85) and Sm/Yb (1.65–3.44) ratios, suggest that the mafic volcanics could be derived from a main spinel-bearing mantle source metasomatized by subduction-related fluids. In contrast, the felsic samples are geochemically equivalent to A2-type granite, with high contents of SiO2, Zr, Ga, and show strong depletions in Eu, Sr and Ti. They have zircon Hf (ɛHf(t) = +12.0 to +15.3) and whole-rock Sr-Nd-Pb isotopic compositions ((87Sr/86Sr)i = 0.7032–0.7038; ɛNd(t) = +7.8 to +8.1; (206Pb/204Pb)i = 17.973–18.004) similar to the coeval mafic rocks. These observations, along with the model calculations using MELTS, favor a derivation of felsic rocks from the mafic magma by fractional crystallization. We suggest that the early Carboniferous bimodal-type volcanism formed in a localized back-arc extension within an overall convergent setting, presumably triggered by slab roll-back of the subducting Paleo-Junggar Ocean plate. This bimodal-type magmatism recorded a significant vertical crustal growth event in the Junggar Basin during the Phanerozoic. We propose that oceanic subduction (flare-ups) not only leads to the lateral accretion of arcs, but also results in the vertical growth of mantle-derived materials and subsequent magma differentiation during slab roll-back (flare-lulls); this may considerably change our view of the models of crustal growth in CAOB.

Crustal recycling is an important cause of mantle heterogeneity and can have significant control on basalt compositions. Recycled components from the subducted (Paleo-) Pacific slab have frequently been recognized in Cenozoic basalts from the eastern North China Craton (NCC). However, it still remains unclear if the subducted Paleo-Asian oceanic slab contributed to intraplate basalts in this Craton. In a search of evidence for the recycled components from this slab, we have studied the Ar Ar age and elemental and Sr-Nd-Pb isotope compositions of newly-discovered basalts from the Langshan area and compiled a regional synthesis of Cenozoic alkali basalts from the northwest NCC. This region is far from the Pacific domain but near the suture zone of the Paleo-Asian Ocean. With a Late Cretaceous eruption age (~89 Ma), Langshan basalts have low silica and high FeO, MgO and alkali contents, high incompatible elemental concentrations, positive Sr, Eu, Ba, Nb, Ta and negative Pb and Ti anomalies with high Ce/Pb, Nb/U, Ba/Rb and low Rb/Sr ratios, superchondritic Zr/Hf ratios, and uniform radiogenic isotopes (ɛNd(t) = 2.20–2.51, 87Sr/86Sri = 0.703807–0.704348, 206Pb/204Pbi = 18.200–18.384, 207Pb/204Pbi = 15.470–15.515, 208Pb/204Pbi = 38.007–39.430). These compositional characteristics are shared by the compiled Cenozoic alkali basalts from northwest NCC. The low silica and high MgO, FeO and alkali contents together with the positive Nb, Ta and negative Ti anomalies were probably controlled by silica-deficient garnet pyroxenite in the mantle source. The partial melting is estimated to have occurred in the asthenosphere under an average mantle potential temperature of 1300–1450 °C and a pressure of ~2.5 GPa. The positive Sr, Eu, Ba, Nb, Ta anomalies and the canonical indices (high Ce/Pb, Nb/U, Ba/Rb and low Rb/Sr ratios) indicate the involvement of a subducted oceanic igneous slab. Considering 1) the particular tectonic locality of the study region, 2) the inferred northward increase of silica-deficient pyroxenite in the mantle source of Cenozoic alkali basalts, 3) the evidence for strong lithospheric modification beneath the northwest NCC induced by slab-derived components, and 4) the longevity of subducted slabs in convecting mantle, the subducted Paleo-Asian oceanic materials could have introduced ubiquitous mantle heterogeneity beneath the northwest NCC and played a significant role in the generation of the Late Cretaceous to Cenozoic intraplate alkali basalts there.

High-volume volcanic fields which are observed at continental intraplate setting are generally known as the large igneous provinces (LIPs), fed by hot and active plumes upwelling from the deep mantle. However, the source and mechanism of low-volume effusive volcanism within continental interiors remains poorly unknown. Here, we present a combined study of 40Ar/39Ar geochronology, mineral chemistry, whole-rock major and trace elements as well as Sr-Nd isotopes of Jurassic basalts from the Karamay area, Junggar terrane (NW China), aiming to determine their formation ages, constrain the petrogenesis and reveal their tectonic implications. New whole-rock 40Ar/39Ar dating yields consistent ages of 189.4–193.3 Ma for magma emplacement. The basalts exhibit a columnar joint structure and porphyritic texture with phenocryst minerals of olivine (Fo63–79), clinopyroxene (Wo39–46En38–47Fs12–22) and plagioclase (An25–54). They have SiO2 contents ranging from 45.0–51.8 wt% and belong to alkaline series (δ 2.7–13.3, average of 5.0). The basalts are characterized by oceanic island basalt (OIB)-like trace element distribution patterns with enrichment in L-MREE, HFSE (e.g., Nb and Ta) and LILE (e.g., K, Sr and Ba), and slight depletion in HREE, relative to normal mid-ocean ridge basalt (N-MORB). Positive eNd(t) (+3.0), low to moderate 87Sr/86Sri (0.7048–0.7049) isotopic compositions, and trace element ratios (e.g., high Nb/U > 49.0 and Ce/Pb > 13.9) suggest that crust contamination was insignificant in the formation process. P–T estimates of major phenocryst minerals in these basalts reflect high crystallization temperatures (>1100 °C) but low pressures (

Transformation of refractory cratonic mantle into more fertile lithologies is the key to the fate of cratonic lithosphere. This process has been extensively studied in the eastern North China Craton (NCC) while that of its western part is still poorly constrained. A comprehensive study of newly-found pyroxenite xenoliths from the Langshan area, in the northwestern part of this craton is integrated with a regional synthesis of pyroxenite and peridotite xenoliths to constrain the petrogenesis of the pyroxenites and provide an overview of the processes involved in the modification of the deep lithosphere. The Langshan pyroxenites are of two types, high-Mg# [Mg2+/(Mg2++Fe2+)*100 = ∼90, atomic ratios] olivine-bearing websterites with high equilibration temperatures (880–970 oC), and low-Mg# (70–80) plagioclase-bearing websterites with low equilibration temperatures (550–835 oC). The high-Mg# pyroxenites show trade-off abundances of olivine and orthopyroxene, highly depleted bulk Sr–Nd (εNd = +11·41, 87Sr/86Sr = ∼0·7034) and low clinopyroxene Sr isotopic ratios (mean 87Sr/86Sr = ∼0·703). They are considered to reflect the reaction of mantle peridotites with silica-rich silicate melts derived from the convective mantle. Their depletion in fusible components (e.g., FeO, TiO2 and Na2O) and progressive exhaustion of incompatible elements suggest melt extraction after their formation. The low-Mg# pyroxenites display layered structures, convex-upward rare earth element patterns, moderately enriched bulk Sr–Nd isotopic ratios (εNd = -14·20– -16·74, 87Sr/86Sr = 0·7070–0·7078) and variable clinopyroxene Sr-isotope ratios (87Sr/86Sr = 0·706–0·711). They are interpreted to be crustal cumulates from hypersthene-normative melts generated by interaction between the asthenosphere and heterogeneous lithospheric mantle. Combined with studies on regional peridotite xenoliths, it is shown that the thinning and refertilization of the lithospheric mantle was accompanied by crustal rejuvenation and that such processes occurred ubiquitously in the northwestern part of the NCC. A geodynamic model is proposed for the evolution of the deep lithosphere, which includes long-term mass transfer through a mantle wedge into the deep crust from the Paleozoic to the Cenozoic, triggered by subduction of the Paleo-Asian Ocean and the Late Mesozoic lithospheric extension of eastern Asia.

The North China Craton (NCC) witnessed Mesozoic vigorous tectono-thermal activities and transition in the nature of deep lithosphere. These processes took place in three periods: (1) Late Paleozoic to Early Jurassic (~170 Ma); (2) Middle Jurassic to Early Cretaceous (160–140 Ma); (3) Early Cretaceous to Cenozoic (140 Ma to present). The last two stages saw the lithospheric mantle replacement and coupled basin-mountain response within the North China Craton due to subduction and retreating of the Paleo-Pacific plate, and is the emphasis in this paper. In the first period, the subduction and closure of the Paleo-Asian Ocean triggered the back-arc extension, syn-collisional compression and then post-collisional extension accompanied by ubiquitous magmatism along the northern margin of the NCC. Similar processes happened in the southern margin of the craton as the subduction of the Paleo-Tethys ocean and collision with the South China Block. These processes had caused the chemical modification and mechanical destruction of the cratonic margins. The margins could serve as conduits for the asthenosphere upwelling and had the priority for magmatism and deformation. The second period saw the closure of the Mongol-Okhotsk ocean and the shear deformation and magmatism induced by the drifting of the Paleo-Pacific slab. The former led to two pulse of N-S trending compression (Episodes A and B of the Yanshan Movement) and thus the pre-existing continental marginal basins were disintegrated into sporadically basin and range province by the Mesozoic magmatic plutons and NE-SW trending faults. With the anticlockwise rotation of the Paleo-Pacific moving direction, the subduction-related magmatism migrated into the inner part of the craton and the Tanlu fault became normal fault from a sinistral one. The NCC thus turned into a back-arc extension setting at the end of this period. In the third period, the refractory subcontinental lithospheric mantle (SCLM) was firstly remarkably eroded and thinned by the subduction-induced asthenospheric upwelling, especially those beneath the weak zones (i.e., cratonic margins and the lithospheric Tanlu fault zone). Then a slightly lithospheric thickening occurred when the upwelled asthenosphere got cool and transformed to be lithospheric mantle accreted (~125 Ma) beneath the thinned SCLM. Besides, the magmatism continuously moved southeastward and the extensional deformations preferentially developed in weak zones, which include the Early Cenozoic normal fault transformed from the Jurassic thrust in the Trans-North Orogenic Belt, the crustal detachment and the subsidence of Bohai basin caused by the continuous normal strike slip of the Tanlu fault, the Cenozoic graben basins originated from the fault depression in the Trans-North Orogenic Belt, the Bohai Basin and the Sulu Orogenic belt. With small block size, inner lithospheric weak zones and the surrounding subductions/collisions, the Mesozoic NCC was characterized by (1) lithospheric thinning and crustal detachment triggered by the subduction-induced asthenospheric upwelling. Local crustal contraction and orogenesis appeared in the Trans-North Orogenic Belt coupled with the crustal detachment; (2) then upwelled asthenosphere got cool to be newly-accreted lithospheric mantle and crustal grabens and basin subsidence happened, as a result of the subduction zone retreating. Therefore, the subduction and retreating of the western Pacific plate is the outside dynamics which resulted in mantle replacement and coupled basin-mountain respond within the North China Craton. We consider that the Mesozoic decratonization of the North China Craton, or the Yanshan Movement, is a comprehensive consequence of complex geological processes proceeding surrounding and within craton, involving both the deep lithospheric mantle and shallow continental crust.

The granitic rocks of the Tarim large igneous province (LIP) are temporally and spatially related to mafic intrusions. However, their tectonic setting and genetic relationship are debated. Here, we report geochemical, and zircon U–Pb–Hf isotopic results for three alkali feldspar granitic plutons in the Halajun area, western margin of the Tarim Block. Zircon U–Pb ages suggest these plutons were emplaced at 268–275 Ma, coeval with the neighbouring mafic–ultramafic complexes and syenitic rocks. These granitic rocks have high contents of SiO2, alkalis, Rb, Th, Zr and REE (except Eu), and high ratios of FeO*/MgO and Ga/Al, and show strong depletions in Ba, Sr, Eu, which are commonly observed in the A1-type granites. Zircon Hf isotopes reveal a limited range ofεHf(t) values from −1.0 to +3.5 for different samples from three granitic plutons, obviously higher than those (mostly

Understanding the rheological behavior of the Tibetan Plateau and its response to geodynamic processes requires a clear knowledge of the composition, evolution and lithological properties of the deep crust. Here we present U–Pb–Hf isotopes of zircons, bulk-rock geochemistry and mineral compositions for seven intermediate gneiss xenoliths and their host Early Mesozoic granites (205 ± 6 Ma) in the central Lhasa terrane to probe the deep crust beneath Southern Tibet. The xenoliths contain plagioclase, amphibole, titanite, allanite, quartz, biotite and muscovite, with accessory Fe–Ti oxides, apatite and zircon. Bulk-rock and mineral geochemistry suggests that these xenoliths have a magmatic origin and experienced deformation and amphibolite-facies metamorphism (equilibration at pressures of 0.46–0.83 GPa and temperatures of ~ 650 °C), before they were captured by the host granite at ~ 205 Ma. Zircons in these xenoliths show complex microstructures, including inherited cores, magmatic or metamorphic bands, and high U–Th hydrothermal rims. Inherited zircon cores record U–Pb ages from 2277 Ma to 517 Ma. Igneous zircons show a range of concordant U–Pb ages, suggesting a protracted magmatism from 236 Ma to 203 Ma. Metamorphic zircon zones record the timing of amphibolite-facies metamorphism from 224 to 192 Ma, while the high U–Th hydrothermal rims show a subsequent fluid activity until ~ 150 Ma. Unradiogenic Hf isotopic compositions of both xenoliths and host granites [xenolith e Hf (t) = − 11.2 to 0; host granite e Hf (t) = − 17.3 to − 3.3] indicate that the Early Mesozoic deep crust in the central Lhasa terrane originated mainly from ancient (i.e., Proterozoic) crust, with little or no interaction with juvenile magmas. This study suggests a possible continental differentiation mechanism during crustal reworking; progressive melting may initiate from the lower mafic crust (at ca. 236 Ma) and gradually migrate into the sediment-rich upper crust (until ca. 203 Ma). The reworking results in the transition from small fluxes of intermediate magmas to voluminous peraluminous S-type granite in a convergent depth.

The eastern North China Craton (NCC), where an initially diamondiferous deep cratonic mantle root was lost during Paleozoic and Mesozoic time, represents a prime natural laboratory to study the processes and mechanisms of continental lithospheric mantle destruction and replacement, which remain, however, controversial. In this study, detailed petrography, whole-rock and mineral compositions of spinel-facies peridotite xenoliths from Cenozoic basalts in the Huinan area, northeastern NCC, are presented to provide new constraints on the transformation of the subcontinental lithospheric mantle (SCLM). These xenoliths define two groups based on textural observation and mineral modes: Group 1 peridotites show protogranular textures and consist of harzburgites and dunites. They have low Al2O3 contents in whole-rock and orthopyroxene (0.53–1.06 wt.% and 2.10–3.21 wt.%, respectively), high olivine modes (79–96%), whole-rock MgO (44.8–47.9 wt.%) and Mg# (100 Mg/(Mg + FeT) molar: 90.1–90.7), suggesting that they were derived from moderately refractory SCLM. In contrast, Group 2 xenoliths display porphyroclastic to protogranular textures and consist of lherzolites and harzburgites with rare spinel-pyroxene intergrowths. They have overall higher Al2O3 (1.48–3.23 wt.% and 3.02–4.65 wt.%, respectively) in whole-rock and orthopyroxene, lower olivine modes (64–83%), MgO (38.6–44.5 wt.%) and whole-rock Mg# values 87.6–90.1, and they may represent fertile SCLM. Peridotites of both groups have similar equilibration temperatures (i.e., 923–977 °C and 881–1110 °C, respectively), which are not correlated with Mg# in olivines, suggesting that they coexist over a range of depths. However, clinopyroxenes in the Group 1 xenoliths display LREE-enriched and convex-upward REE patterns, whereas those in Group 2 mainly show LREE-depleted and spoon-shaped REE patterns, with minor LREE-enriched and convex-upward ones. In addition, spinel-pyroxene intergrowths indicative of garnet destabilization are ubiquitous in Group 1, consistent with variable Al2O3 over a narrow range of Mg# in some opx and low HREE in some cpx, but rare in Group 2 peridotites. Interaction of the fertile mantle with melts similar to the Cenozoic basalts at high melt–rock ratios eradicated most signatures of their origin in the garnet stability field, whereas the refractory peridotites, which reacted with residual melts or fluids at low melt/fluid-rock ratios, retained evidence for the former presence of garnet. We suggest that, combined, these observations are best reconciled if portions of ancient refractory lithosphere, which were partly delaminated during multiple subduction episodes affecting the eastern NCC, were re-accreted together with fertile mantle during asthenospheric upwelling driven by extension.

Peridotite xenoliths from the northern North China Craton (NCC) are characterized by lithological and chemical heterogeneity, related to mantle accretion and metasomatism. However, the accretion mechanism and origin of metasomatic agent are contentious. Here, we report the petrology, whole-rock major elements and Re Os isotopes, and in situ mineral major- and trace-elements as well as Sr isotopic compositions for peridotite xenoliths in the Nangaoya area to evaluate the evolution of the lithospheric mantle beneath the northern NCC. Nangaoya peridotites can be divided into Group A harzburgites and Group B lherzolites. Group A harzburgites are refractory with high Fo contents (91.8–92.9) in olivine and have low whole-rock 187Os/188Os ratios of 0.11418, giving ~2.1 Ga TRD age. Clinopyroxenes in Group A show enrichment of incompatible element with low Ti/Eu and high (La/Yb)N ratios. These characteristics indicate that Group A harzburgites should be the relics of the Archean–Paleoproterozoic “cratonic” mantle and witness carbonatite metasomatism with its agent from asthenosphere. Comparatively, Group B lherzolites are transitional with low Fo contents (90.2–91.9) in olivine and have high whole-rock 187Os/188Os ratios (0.11635–0.112502), giving 1.8–1.2 Ga TRD age. Thus, these lherzolites are considered as accretive mantle components formed by the cooling and re-extracting of the upwelling asthenosphere related to the collision of Eastern and Western blocks. Furthermore, Group B lherzolites can be subdivided into two sub-groups. Group B1 clinopyroxenes without sieve-textured rims are depleted in incompatible element, which was interpreted as weak or without metasomatism, whereas those in Group B2 lherzolites with sieve-textured rims display enriched light rare earth elements (LREE) and various trace element patterns, resulted from different types of strong metasomatism. Clinopyroxenes in Group B2–1 exhibit depletion of high field strength elements (HFSE), with high Ti/Eu but low (La/Yb)N ratios, and the cores of them have higher 87Sr/86Sr ratios (0.70355–0.70443) than the rims (0.70352–0.70406), demonstrating that Group B2–1 lherzolites may have witnessed hydrous CO2-rich silicate metasomatism from subducted plates in cores and a new stage silicate melt metasomatism from asthenosphere in rims. Group B2–2 lherzolites just record later silicate melt metasomatism. These two stage metasomatisms may be triggered by the mantle accretion events in response to the peripheral subduction in the northern NCC during the Phanerozoic. Based on the above results, we suggest that the lithospheric mantle beneath the Nangaoya area underwent multiple modifications through crust–mantle recycling or asthenosphere–lithosphere interaction related to subduction/collision processes, which plays important roles in the evolution of the mantle in the northern NCC.

Recently, biogenic toxins have received increasing attention owing to their high contamination levels in feed and food as well as in the environment. However, there is a lack of an integrative platform for seamless linking of data-driven computational methods with 'wet' experimental validations. To this end, we constructed a novel platform that integrates the technical aspects of toxin biotransformation methods. First, a biogenic toxin database termed ToxinDB (http://www.rxnfinder.org/toxindb/), containing multifaceted data on more than 4836 toxins, was built. Next, more than 8000 biotransformation reaction rules were extracted from over 300,000 biochemical reactions extracted from ~580,000 literature reports curated by more than 100 people over the past decade. Based on these reaction rules, a toxin biotransformation prediction model was constructed. Finally, the global chemical space of biogenic toxins was constructed, comprising ~550,000 toxins and putative toxin metabolites, of which 94.7% of the metabolites have not been previously reported. Additionally, we performed a case study to investigate citrinin metabolism in Trichoderma, and a novel metabolite was identified with the assistance of the biotransformation prediction tool of ToxinDB. This unique integrative platform will assist exploration of the 'dark matter' of a toxin's metabolome and promote the discovery of detoxification enzymes.

To better understand the origin of mid-ocean ridge basalt (MORB)-like mafic magmas and its geodynamic implications for the subduction zone system, we present an integrated study of petrology, mineralogy, geochronology and geochemistry of newly-discovered diabase dykes from the Chinese Altai, southwestern Central Asian Orogenic Belt. The diabases have zircon U Pb ages of ~386 Ma, and are mainly composed of clinopyroxene (Wo43–55En17–27Fs26–34) and albite (An0–1Ab92–99Or0–7). Although the clinopyroxenes have consistent Mg# values (up to 75) that appear to be in equilibrium with bulk compositions, they can be divided into two groups based on their differences in other geochemical variables: type ǀ has high SiO2 and CaO but low TiO2 and Al2O3 contents while type ǁ displays low SiO2 and CaO but high TiO2 and Al2O3 contents. This indicates that the two types of clinopyroxenes may share a common source but crystallized at different depths under different P-T conditions (e.g., type ǀ: 6.3 kbar (~20 km), 1227 °C; type ǁ: 15.5 kbar (~49 km), 1332 °C). The dykes have low SiO2 (44.5–48.2 wt%) and K2O (0.17–0.33 wt%), but high (Fe2O3)T (11.2–13.6 wt%) and MgO (7.16–9.90 wt%) contents, placing them within the low-K tholeiitic series. With both N-MORB- and arc-like geochemical characteristics, including weakly fractionated rare earth element (REE) patterns ((La/Yb)N 1.43–1.62), enrichment in large-ion lithophile elements (LILE) (e.g., Pb) and slightly depletion of high field strength elements (HFSE) (e.g., Nb, Ta and Ti), and highly depleted Sr Nd isotopic compositions (87Sr/86Sri 0.7039–0.7042, ɛNd(t) +8.3 to +8.6), the diabase dykes were probably derived by partial melting of a N-MORB-like asthenospheric mantle source metasomatized by subduction-related fluids under spinel-facies conditions. Melting temperatures and pressures for the primary magmas were estimated at 1371 1394 °C and 2.2 2.4 GPa, respectively. The dykes underwent insignificant crustal contamination, but trace-element modeling indicates that minor subcontinental lithospheric mantle (SCLM) components could have been involved in their source region. We suggest that the MORB-like magmatism was triggered by asthenospheric upwelling in a back-arc extensional setting, in response to the roll-back subduction of the Paleo-Asian oceanic slab. Combined with the coeval arc magmatism in the study area, we envisage that an active arc–back-arc basin system developed in the Chinese Altai during Devonian time, linked to the northward subduction of the Paleo-Asian Ocean. This study emphasizes that MORB-like mafic rocks in paleo-subduction zones could be an important tectonomagmatic process-indicator (e.g., back-arc extension), which offers a new perspective in reconstructing past tectonic regimes.

U-Pb and Hf-isotope analyses of zircon xenocrysts from drilling-sampled Carboniferous volcanic rocks suggest the presence of unexposed Eoarchean crust beneath the Junggar Basin (NW China), southwestern Central Asian Orogenic Belt (CAOB). The oldest zircon population with U-Pb ages of 3.8 Ga shows chondritic eHf(t) of −0.7 to +0.7, and Hf model ages of 3900–3952 Ma (TDM) and 3973–4062 Ma (Tcrust). Three slightly younger populations at 3.7, 3.62 and 3.45 Ga have eHf(t) of −5.7 to +2.4, TDM of 3.6–3.9 Ga and Tcrust of 3.7–4.1 Ga. The youngest xenocrysts yield U-Pb ages of 2.55 Ga with eHf(t) values of +3.7 to +8.0. Crustal mineral inclusions and the trace-element compositions of all these zircons show that they probably crystallized from granitic magmas. The observation of deeply hidden Archean crust significantly older than the exposed Phanerozoic upper crust suggests that the juvenile origin in CAOB may be overestimated, and the study of crustal growth rates through time for young orogens will require revision. By comparing the Hf isotopic signatures of ancient zircons (>3.4 Ga) worldwide, we infer that there may have been a great change in early crustal evolution at the Hadean–Archean transition (~3.9 Ga), possibly linked to the Late Heavy Bombardment (LHB).