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We use Sr-Nd isotopes of apatite and trace element compositions of apatite-zircon pairs from a major ore layer in each of three selected magmatic Fe-Ti-V oxide ore deposits (Hongge, Panzhihua, and Taihe) in the Emeishan large igneous province (LIP) in southwestern China to contrast the magmatic controls on ore formation. The average contents of REEs in apatite from a representative ore zone/layer in each of these deposits are higher than the predicted values of apatite crystallizing from a melt with REE contents assumed to be the same as the average values of high-Ti basalts in the Emeishan LIP, confirming that the ore-forming magmas all experienced higher degrees of fractional crystallization by major silicate minerals than the average basalt. The apatites Sm/Yb and Sr/Y indicate that the Panzhihua magma was generated at a shallower depth and experienced higher degree of plagioclase fractional crystallization than Taihe and Hongge. The apatite Sr-Nd isotopes can be reproduced by ~ 8 wt% contamination with Precambrian gneiss-schist in the parental magma for Hongge and by ~ 10 wt% and ~ 25 wt% contamination with marbles in the parental magmas for Panzhihua and Taihe, respectively. A recycled, high-T altered oceanic gabbroic component in the mantle source is a viable alternative to the marble contamination model for Taihe. Coexisting zircon trace element compositions reveal that the parental magma for Taihe (ΔFMQ+4.0) is more oxidized than those for Hongge (ΔFMQ−0.4) and Panzhihua (ΔFMQ−0.7), questioning that magma oxidation played a critical role in the genesis of Fe-Ti-V oxide ore deposits in the Emeishan LIP.

Reduction process might play a critical role in the genesis of magmatic Ni-Cu sulfide deposits in convergent tectonic settings. To test this hypothesis, we have determined the oxygen fugacities (fO2) and C isotopes of several typical magmatic Ni-Cu sulfide deposits in convergent tectonic settings in western China. Two popular spinel-olivine-orthopyroxene (Spl-Ol-Opx) oxybarometers, one from Wood (1990) and the other from Ballhaus et al. (1991), are evaluated for their accuracy for this type of deposit by comparing the results with those from an independent method, the olivine-sulfide (Ol-Sul) oxybarometer of Barnes et al. (2013). We find that only the results from the Spl-Ol-Opx oxybarometer of Wood (1990) are consistent with those from the independent method. The fO2 of the sulfide-mineralized samples from the selected deposits, estimated using these two methods, are from QFM–0.56 to QFM+1.84 (quartz-fayalite-magnetite buffer). Using the Spl-Ol-Opx oxybarometer of Wood (1990), the estimated fO2 values of the sulfide-unmineralized ultramafic rocks from primitive arc cumulates in the same region, which have higher olivine Fo contents than the sulfide-mineralized rocks, are significantly higher (~QFM+2.42). The decrease of fO2 from the sulfide ore-barren to ore-bearing magmatic systems indicates that reduction process indeed played a critical role in the genesis of the studied magmatic sulfide deposits. The δ13C values of the sulfide-bearing ultramafic rocks are from –16.5 to –37.2‰ (n = 52), which are significantly lower than the primitive arc cumulates (−7.1 to −9.6‰) but similar to those of organic matter in sedimentary rocks worldwide (–15 to –35‰). The isotope data indicate assimilation of organic matter from the country rocks by the parental magmas for the studied magmatic Ni-Cu sulfide deposits, supporting the interpretation that sulfide saturation in the parental magmas were mainly induced by the reduction process associated with the addition of organic matter to the magmas.

The North Qiangtang continental block in central Tibet is a critical piece of the Pangea puzzle. This paper uses integrated geochronological and geochemical data for selected mafic dykes and dioritic enclaves in this block to evaluate its tectonic evolution in the Triassic. Zircons from two mafic dykes and the dioritic enclaves of a large arc granodiorite pluton in eastern North Qiangtang yield indistinguishable U-Pb ages from 248 ± 2 to 251 ± 3 Ma, contemporaneous with widespread arc basaltic andesites and crust-derived rhyolites in the region. The mafic dykes and coeval arc basaltic andesites have almost identical Sr-Nd isotopes (initial 87Sr/86Sr = 0.707 to 0.708, eNd = −4.4 to −3.6), and are all characterized by light REE enrichments and pronounced negative Nb-Ta anomalies. The dioritic enclaves and the hosts have indistinguishable zircon U-Pb ages, almost identical Sr-Nd isotopes (initial 87Sr/86Sr = 0.709 to 0.711, eNd = −7.4 to −5.9), and similar zircon eHf (−13.7 to −5.7), but contrasting chondrite-normalized REE patterns due to hornblende fractionation. The Sr-Nd isotope data indicate that the dioritic enclaves formed from the hybrid melts produced by mixing at depth between the arc basaltic andesites and the crust-derived rhyolites. We propose that the Early Triassic arc igneous suites are related to the northward subduction of the southern Paleo-Tethys beneath the North Qiangtang block from Early to Middle Triassic. The occurrence of several Late Triassic porphyry Cu deposits plus a VMS Ag-Pb-Zn deposit in the Yidun arc, which is the product of the southward subduction of the northern Paleo-Tethys beneath the North Qiangtang block in the Late Triassic, indicates that the arc magmas generated during the subduction of the Paleo-Tethys are fertile in ore metals. Therefore, exploration for Early–Middle Triassic porphyry Cu and VMS deposits in the southern part of the North Qiangtang block is warranted.

The genesis of hypozonal orogenic gold deposits is highly controversial, with both crustal metamorphic fluids and variously derived sub-crustal fluids suggested as fluid and metal sources. The Lower Jurassic Danba gold deposit, a rare Phanerozoic hypozonal orogenic gold deposit on the western margin of the Yangtze Craton, China, provides an opportunity to resolve these controversies. Danba is characterized by biotite–amphibole alteration and pyrrhotite-dominant ore assemblages formed at ~ 500–600 °C. The δ34S values of ore-related pyrrhotite range from + 3.1 to + 9.9‰, in sharp contrast to those of syn-sedimentary pyrrhotite from Devonian host rocks which are between − 6.8 and − 9.5‰. The Pb isotope compositions of ore-related pyrrhotite, with 206Pb/204Pb = 17.85–18.25 and 207Pb/204Pb = 15.48–15.67, are less radiogenic and more variable than those of unaltered host rocks. These differences, combined with the hypozonal feature of the deposit, indicate that ore metals and sulfur were derived from a sub-crustal, rather than a local crustal source. The PGE patterns of ore-related pyrrhotites are similar to those of sulfides in Baltic mantle lithosphere that was metasomatized by aqueous fluids in terms of marked enrichment of Pd and Ru but significantly differ from those of magmatic intrusions and related magmatic–hydrothermal deposits. This suggests that the metals that formed the Danba deposit were transported via aqueous fluid from metasomatized mantle lithosphere rather than from a magmatic source. The δ18O of mantle fluid calculated from hydrothermal quartz and biotite ranges from 10 to 12‰. The anomalously high S and O isotope ratios and variable Pb isotope ratios, together with PGE data, support a model in which the inferred mantle lithosphere source was significantly hydrated, metasomatized, and fertilized by fluid derived from subducted oceanic sediments with elevated δ34S and δ18O values. Geological evidence suggests that this subduction event was Neoproterozoic in age. This study defines a model in which hydrated and metasomatized mantle lithosphere was formed during early subduction, but it was over 500 million years later, during later Lower Jurassic asthenosphere upwelling, that metal- and sulfur-rich fluid was released into the crust to form the Danba gold deposit.

Regional rail transit is a comprehensive rail transit system with multiple standards that is formed to meet the needs of urban agglomeration economic integration. The combination of multiple standards makes the road network larger in scale and more complex, so its safety guarantee and emergency maintenance are facing greater challenges. On the one hand, the possibility of multiple concurrent failures/accidents and their overall impact on the road network increase; on the other hand, emergency maintenance resources cannot be invested indefinitely, and reasonable configuration is required. Therefore, how to optimize the emergency maintenance decision for concurrent failures of the road network under the condition of limited emergency maintenance resources has become an important issue that needs to be considered. In response to this problem, this paper proposes a genetic algorithm-based regional rail transit emergency maintenance decision-making optimization method, and establishes a maintenance decision-making optimization mathematical model with the lowest overall transport capacity risk of the road network as the optimization goal. The genetic algorithm is used to solve the optimization mathematical model, and the verification based on simulation example is carried out in conjunction with the rail transit network in the Chengdu-Chongqing area. The verification results show that compared with the commonly used shortest path rescue resource scheduling method, this method can reduce the transport capacity risk of the road network by about 10.37%.

Understanding the deformation mechanisms of olivine has been considered as the crucial factor in tracing the dynamic processes from seismic anisotropy. Due to extensive overprinting of deformation and alteration, natural examples of original magmatic fabric of olivine are scarce. In this study we selected one wehrlite and three dunite samples from a deep borehole in the Poyi mafic-ultramafic intrusion in the Tarim Craton. The fresh samples show adcumulate texture and plastic deformation of dry olivine (10ppm H2O). Thermobarometer calculations yield crystallization conditions at 200-400MPa and >1,124-1,275 degrees C. Olivine developed a B-type fabric characterized by a concentration of [001] axes parallel to the interpreted lineation and that of [010] axes normal to the interpreted foliation. Activation of [001] and [100] dislocations is confirmed by microstructural observations. Simulation of gravity-driven compaction process reveals extremely rapid compaction of kilometer-scale crystal mush in the Poyi magmatic system. During the early compaction with high porosity, crystallographic habit of olivine may produce shape-preferred orientation and the related B-type fabric. In the final stage of compaction and crystallization, the initial shape-preferred orientation was gradually overprinted, whereas the weak B-type fabric has remained with dislocation creep and dislocation-accommodated grain boundary sliding. Calculated seismic velocities of peridotite samples show low P and S wave anisotropies, with the fastest S wave polarization direction normal to the foliation. Hence, a mush-dominated ultramafic intrusion exhibits weak seismic anisotropy, which has potential to better understand seismic anisotropy in the transcrustal magmatic systems.

The consumption of the Changning–Menglian Palaeo-Tethys ocean in the Triassic formed the Lincang granitic batholith in the southwestern China, once the oceanic supra-subduction zone. The batholith provides us a critical window to understand the nature of the crustal basements and the process of Palaeo-Tethyan termination. Here we report zircon U-Pb ages and Hf isotopes, and whole-rock elements and Sr-Nd isotopes of granitic samples from the central part of the Lincang batholith. The geochemical results reveal two genetic types of granites indicated by low-K and high-K affinities, respectively. The Group 1 low-K granitoids dated at 237–229 Ma are low-K calc-alkaline and metaluminous to peraluminous (A/CNK = 0.75–1.29), with K2O contents of 0.13–1.33 wt%, K2O/Na2O ratios of 0.03–0.30, Rb/Sr ratios < 0.18, and initial 87Sr/86Sr = 0.71693 and εNd(t) = −10.8. In contrast, the Group 2 high-K granitoids dated at 239–200 Ma are calc-alkaline and peraluminous (A/CNK = 1.02–1.20), with higher K2O contents (3.15–4.7 wt%), K2O/Na2O ratios (1.15–2.00) and Rb/Sr ratios (0.77–2.62), and more enriched isotopic compositions (initial 87Sr/86Sr = 0.73129 to 0.74037, εNd(t) = −13.1 to −11.0) as well as highly negative zircon εHf(t) values of −16.8 to −6.7. The formation time of these granitoids is compatible with that of the post-collision of the Palaeo-Tethys, subsequently to the magmatic gap (250–240 Ma) coupling with the syn-collision stage. The magmatic source discriminations suggest that the low-K granitoids were derived from partial melting of the dehydrated low-K amphibolite source and the high-K granitoids were dominantly from the psammitic source with minor mantle-derived magma involvement. Using the geochemical variations of the granitic rocks related to the Palaeo-Tethyan closure, we reveal melting of multiple crustal sources rather than a sole source to construct the Lincang batholith.

Although the term orogenic gold has become widely accepted over the past 20 years for disseminated- to lode-style gold deposits that formed in a variety of tectonic environments within convergent margins, models for orogenic gold systems have remained controversial. The main debates include interpretation of stable isotope and fluid inclusion data that are particularly equivocal for orogenic gold systems, the nature of lithospheric control on the generation of orogenic gold belts, and more critically, the role of deep crustal regional metamorphism or alternatively metasomatized and fertilized mantle lithosphere as sources of ore metals and fluids. The giant to world-class orogenic gold systems of China, now the premier gold producer globally, are in gold provinces or belts of several ages that are mostly marginal to Precambrian cratons or blocks, including the North China Craton and South China Block, an amalgamation of the Yangtze Craton and Cathaysia Block. Deposits from these gold provinces provide crucial evidence to constrain genetic debates. Importantly, following the acceptance that the giant Jiaodong gold province formed over 1700 million years after regional metamorphism in the host terrane, an increasing number of deposits, including the Phanerozoic hypozonal deposit at Danba, are shown to have postdated regional metamorphism and formed from components that were not derived from the host crustal rock sequences. A subcrustal model involving devolatilization of fertilized mantle lithosphere, that was metasomatized via earlier subduction processes involving oceanic sediments and/or altered oceanic crust, is compatible with a variety of data. This includes 40Ar/36Ar vs. 3He/4He mantle-like plots for gold-related pyrite, sulfur isotope compositions of ore-related sulfides that are incompatible with a crustal source, and PGE distribution patterns of spatially related mafic dykes that implicate elevated sulfide contents of underlying mantle lithosphere. Chinese orogenic gold deposits formed in a variety of tectonic regimes from syn-subduction slab rollback, post-subduction slab breakoff, and lithosphere thinning along craton margins, to continent collision. In all cases, lithosphere-scale shear zones and faults were the conduits for ore fluids and metals derived episodically from devolatilization of a subducted slab and/or long-lived metasomatized and fertilized mantle. These fluids deposited gold mineralization in rock sequences adjacent to subsidiary shear zones and faults from crustal depths of >20 km to The characteristics of the widespread orogenic gold systems of China strongly implicate a sub-crustal fluid and metal source for orogenic gold in a variety of gold provinces. Based on deposits from outside of China, where gold provinces are more distal to Precambrian cratons, this source is most likely from the devolatilization of down-going subduction zones and sediment wedges in addition to devolatilization of previously fertilized mantle lithosphere as implied by the Chinese examples.

The Podong mafic-ultramafic intrusion is one of many Ni-Cu sulfide-mineralized intrusions in the Beishan-Tianshan Orogenic Belt in northern Xinjiang, western China. The temporal and lithological variations of the Ni-Cu mineralized intrusions in Beishan are much less constrained than those in Tianshan. This paper provides the first set of geochronological and geochemical data for the Podong magmatic sulfide deposit that is present in the Beishan region. The host intrusion is composed of lherzolite, troctolite, gabbronorite and gabbro. Ni-Cu mineralization occurs as disseminated sulfides in gabbronorite (± olivine). The zircon U-Pb age of gabbronorite is 270 ± 2.7 Ma, identical to the zircon U-Pb age of the nearby Poyi magmatic sulfide deposit that is hosted in troctolite and ultramafic rocks. These ages together define a new episode of Ni metallogeny in the Beishan region, which is ∼10 Ma younger than that in the Tianshan region to the north. The Fo contents of olivine in the Podong mafic-ultramafic intrusion are from 76 to 87 mol%, lower than the values for the nearby Poyi mafic-ultramafic intrusion. The Podong mafic-ultramafic rocks are characterized by eNd(t) values from −0.61 to +1.92, low to elevated initial 87Sr/86Sr ratios (0.7055–0.7090), and pronounced negative Nb-Ta anomalies. The Sr-Nd isotope data indicate that the parental magma of the Podong intrusion experienced 0–13 wt% crustal contamination, which cannot fully account for the observed negative Nb-Ta anomalies in the rocks. Sulfur isotope compositions of the Podong deposit are similar to those of Pre-Permian sedimentary rocks in the area as well as typical mantle values. The results support the premise that fractional crystallization and assimilation of siliceous crustal materials may have played a key role in triggering sulfide saturation in the Podong magma, although the involvement of external sulfur cannot be completely ruled out. Like other Permian magmatic sulfide deposits in the Beishan-Tianshan Orogenic Belt, the PGE tenors of bulk sulfides in the Podong deposit are extremely low, indicating a severely PGE-depleted parental magma. The Cu/Pd ratios of the Podong magmatic sulfide deposit are significantly higher than the mantle values, consistent with previous sulfide segregation at depth. The results from the Podong magmatic sulfide deposit confirm that widespread Ni metallogeny in a convergent tectonic zone is very protracted and the mineralized lithologies are highly variable, which have significant implications for regional Ni-Cu exploration.

Previous studies show that Permian bimodal magmatism is widespread in the Tianshan region, the southern part of the Central Asian Orogenic Belt in northern Xinjiang, NW China. We have found that such bimodal magmatism extended farther to the south in the Beishan region. Our new zircon U-Pb age data show that the dolerite and granite dykes in the Poyi area of the region were emplaced at ~270 Ma, >20 myr after subduction ended in the region. The dated dolerite dyke is characterized by pronounced negative Nb-Ta anomalies, high eNd(t) from +4.3 to +5.1 and low initial 87Sr/86Sr ratios from 0.7051 to 0.7060 for whole rocks, plus high eHf(t) from +8.96 to +13.0 and elevated δ18O from 5.8 to 6.5‰ for zircon crystals, which indicate a subduction-modified mantle source and moderate degrees of crustal contamination ( 25 myr) and show no age progression in a single direction, which are inconsistent with the results of mantle plume magmatism. Whole rocks from the Permian granite dyke in the Poyi area are characterized by strong negative Nb-Ta anomalies, negative eNd(t) from −2.4 to −1.6 and high initial 87Sr/86Sr from 0.7080 to 0.7088. Magmatic zircon crystals from the granite dyke have eHf(t) from +0.86 to +5.64 and δ18O from 6.5 to 7.2‰. The isotope compositions of the granite dyke are within the ranges of the pre-Permian crustal rocks in the region, indicating a predominantly crustal source. Based on these data, we propose that partial melting in the crust was induced by underplating of mantle-derived mafic magmas, some of which were emplaced in the upper parts of the crust to form the broadly coeval dolerite dykes and mafic-ultramafic intrusions. The results from this study support the view that post-subduction bimodal magmatism is important for continental crustal growth and differentiation.

The distinct submarine volcanic-hosted iron ore deposits in the Awulale Iron Metallogenic Belt are the most important sources for iron in the Chinese Western Tianshan metallogenetic province, although, the exact tectonic setting for their formation remains poorly constrained. A compilation of published and new geochronological and geochemical data suggests a protracted magmatism from ca. 450 to 290 Ma was in close spatial and temporal proximity to the iron deposits. The different magmatic rocks have broadly similar arc-like geochemical signatures such as LREE and LILE enrichments, HREE and HFSE depletions, Nb–Ta–Ti negative anomalies and flat HREE patterns, all of which are attributed to magmatic differentiation and/or partial melting in relatively thin crust due to long-term extension. The contrasting whole-rock Nd isotopic patterns of the igneous rocks and the well-defined peak metamorphism (ca. 320–310 Ma) of the subduction-zone high-pressure rocks indicate that ca. 450–321 Ma magmatic rocks with an increasingly positive eNd(t) shift were formed during the northward subduction of the South Tianshan Ocean, where slab rollback resulted in an extensional setting in the southern Yili-Central Tianshan Block. In contrast, the synchronicity of the ca. 320–310 Ma subduction-zone peak metamorphism and magmatic flare-up with uniformly positive eNd(t) values is interpreted as the consequence of slab break-off subsequent to the oceanic subduction and the continental collision. By inference, the late-stage (ca. 309–290 Ma) magmatism was likely constructed in a post-collisional setting. The submarine volcanic-hosted iron mineralization exclusively occurred coeval with the peak metamorphism and intensive magmatism, probably suggesting slab break-off as the exact tectonic setting for iron mineralization. Consequently, the western extension of the Awulale Iron Metallogenic Belt occurring roughly parallel to the South Tianshan Orogen may have significant potential for prospecting the submarine volcanic-hosted iron ore deposits.

The petrogenesis of the rift-related Late Carboniferous–Early Permian mafic igneous rocks (basaltic lavas, dolerite dykes and mafic–ultramafic intrusive rocks) from the Sibumasu block in the eastern end of Cimmeria was still ambiguous. This petrogenesis is related to understand the drive for the formation of Neo-Tethys which was developed along the margin of Cimmeria, and to the generation of magmatic sulfide deposit via partial melting of previously subduction-modified mantle induced by rifting of continental margin. Most of the mafic rock samples belong to the subalkaline series, with lithologies varying from basalt to basaltic andesite. Magmatic zircons from the doleritic dykes yield weighted mean 206Pb/238U ages of 308.7 ± 2.5 Ma. The eHf(t) values of zircon are ranging from 3.2 to 11.8, which are much lower than those of the coeval depleted mantle (eHf(t) ≈ 16 at 305 Ma). The igneous series share similar features, such as elevated light rare earth elements, negative Nb-Ta anomalies and enriched Sr-Nd-Hf isotopes. Based on geochemical analyses of the mafic igneous series in the northern part of Sibumasu, we suggest that the primary melts of the mafic igneous rocks were derived from a fertile subcontinental lithospheric mantle (SCLM) which was previously modified by oceanic subduction, and these rocks were intruded and erupted in a passive plate margin during plate extension. The subsequent melting-induced softening of SCLM triggered the evolution of continental margin from the rift to the open of Neo-Tethys Ocean. The proposed model emphasizes that the melt generated from previously-modified SCLM in a continental rift setting is beneficial for the generation of magmatic sulfide deposit.

The consumption of the Palaeo-Tethyan ocean from Permian to Triassic formed the Changning-Menglian suture zone (CMSZ) in southwest China, where abundant eclogites with diverse geochemical signatures have been discovered in recent years. Eclogites are known as specific products during the orogenic evolution from subduction to collision, which play an important role in reconstruction of the orogenic process and bear implications for rutile mineralization. Here we use the phengites Ar-Ar isotopes, rock-forming mineral and whole-rock compositions, and Nd isotopes of Mengku eclogites, together with previous data of eclogites and relevant basalts from the CMSZ to address these issues. The phengites Ar-Ar dating of the Mengku eclogites yields a metamorphic age of 244 ± 2.0 Ma. Garnets in the eclogites show evident compositional zonation, corresponding to a prograde process from core to rim as evidenced by the variation of minerals enclosed in garnets. Four types of rutile are recognized in eclogites: mineral inclusion (ru1), granular (ru2), beaded (ru3) and wispy (ru4). Granular and beaded rutile that formed in the peak metamorphic stage contributes the most to the rutile mineralization. The Mengku eclogites show enriched LREEs with high (La/Yb)N ratios of 8.89–10.88, positive Nb-Ta anomalies and negative eNd(t) values from −0.63 to −0.07, similar to the average compositions of the OIB-type volcanic rocks exposed in the CMSZ. Modeling results indicate that the protoliths of OIB-type eclogites were derived from an enriched garnet lherzolite source while those of MORB-type were either from a primitive or from a depleted spinel lherzolite source. The OIB-type eclogites have much higher TiO2 contents (2.49–4.25 wt%) than the MORB-type eclogites (1.05–2.75 wt%), which reflects different modes of rutile in the two types of eclogites. This observation is highly consistent with the higher TiO2 contents in OIB-type than in MORB-type volcanic rocks from the CMSZ, indicating that the Ti enrichment in protoliths are first-order control on the formation of high-Ti rutile ores. Our results and the integrated previous studies of paleomagnetism, biogeography, magmatism and metamorphism suggested that the Palaeo-Tethyan subduction lasted from Late Carboniferous to Late Triassic (ca. 313–230 Ma) and the eclogite-type rutile exhumed back to the surface after ca. 230 Ma. Identification of OIB-type eclogites and the high-Ti eclogites with weakly retrograde metamorphism can be key evaluative factors for Ti exploration in the CMSZ.

The recently discovered Kemozibayi mafic-ultramafic intrusion and its associated magmatic Cu-Ni sulfide deposits are located at the southern margin of the Chinese Altai Mountain, Central Asian Orogenic Belt in north Xinjiang, NW China. The intrusion is composed of olivine websterite, norite, gabbro and diorite. Disseminated and net-textured Ni-Cu sulfide ores are hosted in the center of the gabbro. In this work, new zircon U-Pb ages, Hf-O isotopic and sulfide S isotopic data, and whole rock and mineral chemical analyses are combined in order to elucidate the characteristics of the mantle source, nature of subduction processes, degree of crustal contamination, geodynamic setting of bimodal magmatism in the region, and the metallogenic potential of economic Cu-Ni sulfide deposit at depth. SIMS zircon U-Pb dating of the gabbro yields Permian ages (278.3 ± 1.9 Ma), coeval with the Kalatongke Cu-Ni deposit and with Cu-Ni deposits in the Eastern Tianshan and Beishan areas. Several lines of evidence (positive eHf(t) from + 7.1 to + 13.3, Al2O3, TiO2 and SiO2 contents in clinopyroxene from olivine websterite, high whole rock TiO2 contents) suggest that the primary magma of the Kemozibayi intrusion was a calc-alkaline basaltic magma derived from depleted mantle, and that the degree of partial melting in the magma source was high. The evolution of the Kemozibayi mafic-ultramafic complex was strongly controlled by fractional crystallization and the crystallization sequence was olivine websterite, norite, and then gabbro. This is evidenced by whole rock Fe2O3 contents that are positively correlated with MgO and negatively correlated with Al2O3, CaO and Na2O, similar LREE enrichment and negative Nb, Ta, Hf anomalies in chondrite and primitive mantle-normalized patterns, and a decrease in total REE and trace elements contents and magnetite content from gabbro through to norite and olivine websterite. Varied and low eHf(t) (+ 7.1 to + 13.3) and high δ18O values (+ 6.4‰ to + 7.2‰) in zircon, high La/Ba, and Rb/Y ratios, and low Nb/La ratios in whole rock samples, suggest 5–10% contamination by subduction related fluid and 10–15% contribution from an upper crustal component. The clinopyroxene TiO2 and Alz values (percentage of tetrahedral sites occupied by Al) in the Kemozibayi intrusion show characteristics of rift cumulate rocks, but minor arc cumulate features, indicating that the mantle source might have experienced a lower degree of subduction metasomatism. A high degree of partial melting of the depleted mantle and subducted oceanic sediments with related fluid metasomatism and crustal contamination in the Kemozibayi mafic-ultramafic intrusion are appropriate for the formation of an economic copper and nickel sulfide deposit. Crustal contamination, crustal S addition and early fractionation of olivine and sulfide induced S saturation and the formation of immiscible sulfide in the Kemozibayi intrusion. With no obvious olivine and Ni-rich sulfide co-crystallization, the Cu grade in the present orebody is higher than the Ni grade, and the proportion of mafic rocks is high in the Kemozibayi mafic-ultramafic complex. Cumulatively, these features suggest that the mafic-ultramafic intrusion underwent early olivine and Ni sulfide segregation, and that deeper or extended portions of the present intrusive body may host Ni mineralization.

The ubiquitous presence of undulose extinction and subgrain boundaries in olivine crystals is commonly perceived as originating in the mantle, however these plastic deformation features are also well developed in the Poyi ultramafic intrusion, NW China. In this case, olivine was deformed through kinetic processes in a crustal magma chamber, rather than by deformation processes in the upper mantle. Moreover, accumulation and textural coarsening were critical to the characteristics of crystal size distributions (CSDs) of olivines in the Poyi intrusion. The axial deformational compaction of crystal mush was revealed by virtue of other quantitative textural analyses (e.g., spatial distribution patter, alignment factor and aspect ratio). Additionally, based on the contrast of density between crystal matrix and interstitial melt, adequate stress was generated by the km-scale crystal framework in Poyi body (~ 2–11 MPa) which triggered the distortion of grain-lattice in olivine. The deformation mechanisms of olivine primarily are dislocation creep and dislocation-accommodated grain boundary sliding (DisGBS), while diffusion creep is subsidiary. This study has revealed various kinetic processes in a magmatic system by first demonstrating the genetic relationship between mineral deformation and axial compaction of crystal mush while highlighting the uncertainty of employing the deformation features of olivine in peridotite xenoliths as an indicator for a mantle origin. In contrast to the olivine populations of xenocrysts that underwent fragmentation during ascent, the deformed primitive olivines in compaction exhibit a distinct shortage of small grains, which is conducive to delimiting these two types of deformed grains.

The Central Tianshan Block (CTB) is one of the major continental constituents of the western Central Asian Orogenic Belt (CAOB). Its nature and origin is essential for understanding the accretionary processes and the reconstruction of the architectural framework of the CAOB. The Wuwamen Metamorphic Complex (WMC), which is believed to represent the basement of the CTB, was incorporated into the Wuwamen ophiolitic melange during the Paleozoic evolution of the South Tianshan Ocean. The WMC is mainly composed of amphibolite-facies volcano-sedimentary rocks, including migmatites, orthogneisses, amphibolites, schists and locally marbles. Zircon U–Pb geochronology suggests that the protoliths of the interlayered biotite-two feldspar and biotite-plagioclase-hornblende gneisses in the Yangjuan area were formed between 2529 and 2513 Ma and overprinted by amphibolite-facies metamorphism between 1815 and 1809 Ma. Subsequently, the gneisses were intruded by ∼1724 Ma meta-mafic dykes and ∼787 Ma leucogranite dykes/veins. Geochemical data reveal that the biotite-two feldspar gneisses have high-silica adakite affinities with high SiO2 and Na2O contents as well as high Sr/Y ratios (61–117) and slightly evolved zircon Hf isotopic compositions. Consequently, they are interpreted to be the products of partial melting of relatively old subducted oceanic crust. In contrast, the interlayered biotite-plagioclase-hornblende gneisses have high MgO, Cr, Co and Ni contents and prominent negative Nb–Ta–Ti anomalies, indicating derivation from partial melting of an ancient sub-continental lithospheric mantle in a continental arc setting. The ∼1.72 Ga meta-mafic dykes have geochemical similarities of typical Fe-Ti basalts and are characterized by incompatible element enrichments and primitive Sr–Nd–Hf isotopic signatures ((87Sr/86Sr)i = 0.703446 − 0.703535); ɛNd(t) = +6.49 to +6.90; zircon ɛHf(t) = +0.57 to +10.6), which is consistent with partial melting of a relatively fertile, isotopically depleted asthenospheric mantle in a post-collisional extensional setting. In addition, the ∼787 Ma leucogranites are trondhjemitic in composition and display extremely low total REE contents and highly evolved Nd–Hf isotopic signatures (ɛNd(t) = −4.71 to −4.53; zircon ɛHf(t) = −19.4 to −13.0). They are thought to have no petrogenetic relationship with the host orthogneisses and to be products of a foreign melt injection. Our new data provide robust evidence for a Neoarchean–Paleoproterozoic basement of the CTB. Comparison of the tectono-thermal-magmatic events reveals that the CTB and the Tarim Craton have a partly overlapping Precambrian crustal evolution, and thus the CTB could have originated from the Tarim Craton. However, a major difference between both is the presence of juvenile Mesoproterozoic magmatism in the CTB and its absence in the Tarim Craton and, therefore, further geological and geochronological research is required to determine the precise origin of the CTB and its tectonic affinity with adjacent terranes in the western CAOB.

The deformation features (e.g., undulose extinction and subgrain boundaries) and low Ca content (

The link of the widespread Late Permian–Triassic magmatism in the southwestern corner of the South China block to a subduction zone or the Emeishan mantle plume is debated. We have carried out an integrated geochronological-petrological-geochemical study of four mafic dikes in the Gulinjing–Nanxi area of this region to shed new light on the issue. Zircon grains from the Gulinjing–Nanxi mafic dikes yield U Pb ages from 254 ± 2 to 250 ± 2 Ma, indicating that they are coeval with abundant felsic intrusive-extrusive rocks in the region, but are 6–7 myr younger than the nearby Emeishan flood basalts and associated mafic-ultramafic intrusions. The Gulinjing–Nanxi mafic dikes are characterized by light rare-earth element enrichments and pronounced negative Nb Ta anomalies, similar to typical arc basalts worldwide, plus enriched Sr-Nd-Hf isotope compositions (initial 87Sr/86Sr from 0.7088 to 0.7103, eNd(t) from −6.6 to −4.6, and zircon eHf(t) from −3.7 to −0.3). The isotopes and incompatible trace element ratios indicate that the parental magmas for the Gulinjing–Nanxi mafic dikes are consistent with contaminated arc mafic magmas, but not contaminated Emeishan flood basalts in the region. This, together with a significant age difference between the mafic dikes and the Emeishan flood basalts and associated mafic-ultramafic intrusions in the nearby areas, support the interpretation that the Gulinjing–Nanxi mafic dikes are unlikely to be parts of the Emeishan mantle plume. Based on regional igneous association and the distribution of known paleo subduction zones in the surrounding regions, we conclude that the Gulinjing–Nanxi mafic dikes are linked to Paleo-Pacific subduction to the south, and not Paleo-Tethys subduction to the west.

The Huangshannan mafic–ultramafic intrusion is a Permian Ni–Cu sulfide-bearing intrusion in the southern margin of the Central Asian Orogenic Belt. The intrusion consists of an ultramafic unit, which is composed of lherzolite and olivine websterite, and a mafic unit, which is composed of olivine gabbronorite, gabbronorite and leuco-gabbronorite. This intrusion was formed by two separate pulses of magma: a more primitive magma for the early ultramafic unit and a more evolved magma for the late mafic unit. U–Pb isotope geochronology of zircon from the mafic unit yields an age of 278 ± 2 Ma. According to its olivine and Cr-rich spinel compositions, the estimated parental magma of lherzolite for the Huangshannan intrusion has 12.4 wt.% MgO, indicating picritic affinity. Fractional crystallization modeling results and the presence of rounded sulfide inclusions in an olivine crystal (Fo 86.7) indicate that sulfide immiscibility was achieved at the beginning of olivine fractionation. Co-magmatic zircon crystals from gabbronorite have a δ18O value close to 6.5‰, which is 1.2‰ higher than the typical mantle value and suggests significant crustal contamination (∼20%). The positive eHf(t) values of co-magmatic zircon (which vary from +9.2 to +15.3) and positive whole rock eNd(t) values (which vary from +4.7 to +7.8) also indicate that the parental magma was derived from a depleted mantle source and contaminated by 5–20% juvenile arc crust and then by ∼5% upper crustal materials. However, modeling results of sulfur content at sulfide saturation reveal that such a large amount of crustal contamination is not sufficient to trigger sulfide saturation in the parental magma, which strongly suggests that external sulfur addition, probably during contamination, has played a critical role in causing sulfide immiscibility. Furthermore, the arc magmatism geochemical signatures of the Huangshannan intrusion, such as significant Nb and Ta depletion relative to La and low Ca contents in olivine, are interpreted as the result of slab-derived fluid modification during previous subduction. We speculate that the contamination of juvenile arc crust may have occurred in the lower crust because of picritic magma underplating and that partial melting in the mantle was triggered by the impingement of a mantle plume or lithosphere delamination in a post-subduction environment.

The convenient mantle plume model for the Permian protracted mafic–ultramafic intrusions and mafic dykes (266–286 Ma) in the Beishan–Tianshan region, northern Xinjiang, western China can be rejected, because their temporal–spatial distribution does not show a hotspot track predicted by such model. New zircon U–Pb ages reveal that two small mafic dyke clusters (Podong, 280.5 ± 2 Ma; Luodong, 266.2 ± 3.2 Ma) that are separated by only ~ 20 km in the Pobei area, the southernmost part of the Beishan–Tianshan region, have a large age difference of ~ 18 Ma. The older mafic dykes are characterized by nearly flat mantle-normalized rare-earth-element patterns, pronounced negative Nb–Ta anomalies and positive e Nd (t) values from 5.5 to 7.5, similar to the majority of the Permian mafic–ultramafic intrusions in the region. The younger mafic dykes are characterized by significant light rare-earth-element enrichments as well as pronounced negative Nb–Ta anomalies, plus lower e Nd (t) (− 1.2 to 2.6) values and higher initial 87 Sr/ 86 Sr ratios than the older mafic dykes. The observed compositional variations can be explained by source mantle heterogeneity plus different degrees of crustal contamination. Overall, the Permian mafic–ultramafic rocks in the Beishan–Tianshan region are geochemically consistent with the products of basaltic magmatism induced by lithospheric delamination and asthenosphere upwelling in a convergent tectonic zone.

The Poyi magmatic Ni-Cu sulfide deposit is situated in the Beishan fold belt in the northeastern rim of the Tarim craton. Many Permian magmatic Ni-Cu sulfide deposits, such as those in East Tianshan, are present in the adjacent Central Asian orogenic belt to the north. The Poyi deposit is hosted in a small dike-like ultramafic-troctolitic body that was emplaced into a much larger gabbroic intrusion. Our new zircon U-Pb isotope data reveal that these two intrusions formed ~6 Ma apart. The ultramafic-troctolitic intrusion was emplaced at 269.9 ± 1.7 Ma, whereas the gabbroic intrusion was emplaced at 276.1 ± 1.9 Ma. The results show that the Poyi deposit is the youngest among the major magmatic Ni-Cu sulfide deposits (≥0.2 Mt Ni) of Permian ages in the Beishan-Tianshan region. Sulfide mineralization in the Poyi deposit occurs as steeply dipping disseminated sulfide lenses mostly associated with wehrlites in the center of the dike. Olivine from the Poyi ultramafic rocks has Fo content up to 91 mol %, which is similar to the lower limit of mantle olivine and the most primitive within the Permian Beishan-Tianshan nickel belt. Like other magmatic sulfide deposits in this belt, olivine from the Poyi deposit is depleted in Ca (

Integrated zircon–olivine O–Hf isotope data have been successfully used to unravel the nature of the source mantle for the early Permian post-collisional mafic–ultramafic intrusive rocks in the southern margin of the Central Asian Orogenic Belt in NW China. Olivine crystals with forsterite (Fo) contents varying from 91 to 87 mol% from the Permian Pobei mafic–ultramafic complex in the region yield highly elevated δ18O from 6.0 to 7.2‰. These values are much higher than typical mantle values (~ 5.3‰) and are apparently at odds with the mantle-like eNd(t) values of whole rocks (4.9–5.4). Magmatic zircon crystals from troctolite and gabbroic rocks show divergent oxygen and hafnium isotopic compositions: mantle-like eHf(t) values from 5.1 to 11.9 and crust-like δ18O values from 7.6 to 10.1‰. The observed increase of δ18O values from olivine (an early crystallizing phase) to zircon (a late crystallizing phase) in the mafic–ultramafic rocks is generally consistent with an AFC process. However, this process cannot fully explain the highly elevated δ18O values (6–7‰) for the most primitive olivine containing Fo as high as mantle olivine (> 90 mol%) and the mantle-like Hf isotope composition of zircon. Mixing calculation indicates that such highly unusual isotope compositions can be explained by the previous source mantle contamination with subducted sediment-derived melts and slab-derived fluids. Our results show that the combination of zircon O–Hf isotopes and olivine oxygen isotopes is more effective than the data of zircon or olivine alone to distinguish the effect of AFC process from source contamination. The results from this study provide a new line of evidence that the sub-arc mantle is not homogeneous in oxygen isotopes.

Oxygen fugacity is a key parameter in controlling the petrogenesis of mafic-ultramafic rocks and their associated sulfide mineralization, especially in convergent settings. This study uses new and previously published experimental data on olivine-sulfide pairs to reparameterize an expression for oxygen barometry using the distribution coefficient K D FeNi for Fe-Ni exchange between olivine and sulfide. We derive a new expression, ΔQFM = (9.775 + 0.416 ∙ C Ni − K D FeNi)/4.308, where ΔQFM denotes divergence from the fayalite–magnetite–quartz buffer. The revised oxygen barometry has been applied to the Permian magmatic Ni–Cu deposits in the Central Asian Orogenic Belt, NW China. The Ni–Cu deposits in the East Tianshan—North Tianshan, Central Tianshan, and Beishan—are considered as a single mineral system, whereas the spatially separated deposits in the East Junggar are considered as a separate system. The deposit of the East Tianshan group exhibits a large range of oxygen fugacity (QFM − 2 to ~QFM + 1) and Ni tenor (metal concentration in pure sulfide, ~ 5 to 16 wt%). The Poyi and Huangshannan deposits contain high-Ni tenor sulfides, varying from 12 to 16 wt%. The relatively high Fo values (> 85 mol%) and Ni contents (> 2000 ppm) in olivine of these deposits indicate that the high-Ni tenor sulfides were segregated from less differentiated high-Ni magmas that also had relatively high oxygen fugacity (~QFM + 1). The remaining Ni–Cu deposits in the East Tianshan—the Huangshandong, Huangshanxi, Hulu, Tulaergen, Tudun, and Xiangshanzhong deposits—have intermediate Ni tenors (5–8 wt%). These sulfides correspond to intermediate Fo values (80–84 mol%) and Ni contents (700–1400 ppm) in the coexisting olivine, illustrating that they were segregated from magmas with lower Ni contents thought to be the result of a large amount (15–20%) of olivine fractionation at depth. These magmas are more reduced (− 2

The Permian Huangshanxi mafic-ultramafic intrusion hosts one of the two largest magmatic sulfide deposits in the Eastern Tianshan which is situated in the southern margin of the Central Asian Orogenic Belt. In this paper we use mineral compositions and whole-rock geochemical data to decipher the genetic relationship between magma evolution and sulfide mineralization. The Huangshanxi intrusion consists of three separate intrusive units. Important sulfide mineralization occurs in the base of the last intrusive unit, an elongated, layered ultramafic body composed of lherzolite at the bottom, olivine websterite in the middle and websterite at the top. Based on olivine-liquid equilibria and mass balance, the MgO and FeO contents in the parental magma for a lherzolite sample are estimated to be 8.71 and 8.36 wt.%, respectively. The Huangshanxi mafic-ultramafic intrusive rocks and the estimated “trapped liquids” for several olivine-orthopyroxene cumulate rocks all show light rare earth element enrichments relative to heavy rare earth elements and significant Nb depletions relative to Th and La, which are similar to the characteristics of coeval basalts in the region. The arc-like geochemical features are attributed to pre-Permian mantle metasomatism by slab-derived fluids. Partial melting of the previously-modified mantle is thought to have resulted from heating by upwelling asthenosphere associated with post-subduction lithosphere delamination or by mantle plume activity. The relationship between the Fo and Ni contents of olivine crystals from the Huangshanxi sulfide-poor ultramafic rocks ( in-situ differentiation stage during which the sulfide droplets and olivine crystals settled to form the sulfide-olivine cumulate zones at the base of the Huangshanxi magmatic system.

The Permian Hulu intrusion is one of several sulphide-bearing Permian mafic–ultramafic intrusions in the eastern part of the eastern Tianshan located at the southern margin of the Central Asian Orogenic Belt (CAOB) in Xinjiang, NW China. The intrusion is composed of lherzolite, olivine websterite, gabbro, and gabbro-diorite. Disseminated and net-textured Ni-Cu sulphide ores are located at the bottom of the lopolith complex. Negative Zr, Hf, Nb, and Ta anomalies, whole-rock eNd(t) values of +5.7 to +8.8, and variable (Th/Nb)PM values (from 1.06 to 8.13) suggest that the source of the Hulu complexes is depleted mantle metasomatized by subducted slab-derived fluid and/or melt (~5% global subducted sediment and 15% slab fluid) that has experienced approximately 3% lower crustal and 10% upper crustal contamination. The Hulu intrusion is characterized by low PGE abundances i.e. 0.03–1.08 ppb Ir, 0.04–0.69 ppb Ru, 0.02–2.15 ppb Rh, 0.30–48.71 ppb Pt, and 0.21–344 ppb Pd. Our calculations indicate that if the Pd,...

The Qixin mafic-ultramafic complex is present in the southern margin of the Central Asian Orogenic Belt in northern Xinjiang where many magmatic Ni-Cu sulfide deposits occur. To determine the temporal association of the newly-discovered Ni-Cu prospect associated with the Qixin complex with the known major magmatic Ni-Cu sulfide deposits in the region, as well as the origin of sulfide mineralization in the Qixin complex, we have carried out geochronological, petrological and geochemical studies of this complex. Gabbro, olivine gabbro, norite, olivine gabbronorite, troctolite, websterite and lherzolite are the major rock types of this complex. Two drill cores completed to date show two types of sulfide mineralization associated with the complex: (1) disseminated sulfides that occur near the base of bodies of lherzolite and troctolite; (2) blotchy-massive sulfides in the hornfels country rocks. The disseminated sulfides are composed of pyrrhotite, pentlandite and chalcopyrite, whereas the blotchy-massive sulfides in the country rocks are composed of pentlandite, violarite, pyrrhotite and chalcopyrite. Zircon crystals from the Qixin olivine gabbronorite yield a U-Pb age of 286.5 ± 2.5 Ma, which is among the oldest post-subduction magmatic Ni-Cu sulfide deposits in the region. The TiO2/Al2O3 ratios of Cr-spinel and clinopyroxene from the Qixin complex are similar to those from the older, subduction-related mafic-ultramafic intrusions in the region. This and other arc-like geochemical characteristics such as whole-rock negative Nb-Ta anomalies coupled with low initial 87Sr/86Sr (0.7036–0.7057), positive eNd(t) (+2.3 to +6.0) and high eHf(t) of zircon (+8.3 to +15), indicate that the parental magma of the Qixin complex was derived from a mantle source modified by pre-Permian metasomatic processes, similar to other contemporaneous mafic-ultramafic intrusions in the region. Mixing calculations using Sr-Nd-Hf isotopes indicate that the parental magma for the Qixin mafic-ultramafic rocks experienced no more than 15 wt% contamination with siliceous country rocks. The δ34S values of different sulfide assemblages of the Qixin Ni-Cu prospect are similar and vary from 1.1 to 1.7‰, which are within the range of typical mantle values as well as that of the country rocks, providing no direct evidence for addition of external sulfur. However, the role of external sulfur in sulfide mineralization at Qixin still cannot be ruled out, as forward modelling indicates that fractional crystallization plus crustal contamination involving siliceous country rocks free of S could not have induced sulfide saturation in the Qixin magma. This may also be true for the contemporaneous magmatic Ni-Cu sulfide deposits in the region. Based on the results from this study, we suggest that fractures in the solid country rocks nearby the Qixin complex and the ultramafic bodies of the complex are preferred targets if exploration continues.