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Mantle wedge melting and the formation of hydrous mafic melts in collision orogenic belts have great significance for crustal melting and the related granitic magmatism, which can provide key messages about the crustal–mantle interaction in the convergent margin. This paper reported Late-Triassic appinite (212 ± 2 Ma), which is closely associated with Late-Triassic granites. The large euhedral hornblende crystals in the appinite indicate a water-rich feature. This appinite displays low SiO2 (46.55% to 50.44%) contents, high MgO (7.62 to 10.76%) and Cr and Ni contents, with high Mg# values of 61 to 75. It also displays insignificant Eu anomalies (Eu*/Eu = 0.91 to 0.93), high Sr (596 to 676 ppm) contents and moderate Sr/Y (34 to 40) ratios; these features are similar to those of Sanukite formed by the hydrous melting of the mantle wedge. Its depleted zircon Lu-Hf isotopic composition (εHf(t) = +0.97 to +18.21) indicates a depleted mantle source. Zircons in the appinite display extremely high Ti-in zircon temperatures (>1000 °C) and high oxygen fugacity, indicating a high-temperature hydrous condition. In combination with its typical arc-like trace element geochemistry (depletion in Nb, Ta and Ti), it is proposed that this appinite represents hydrous mafic melts that derived from the melting of the depleted sub-arc mantle wedge. The occurrence of this appinite has great significance for the further understanding of Triassic granitic magmatism and potential magmatic metal ore deposits in the Qinling orogenic belt.

The Paleozoic strata are widely distributed in the northwest of the Ordos Basin, and the provenance attributes of the basin sediments during this period are still controversial. In this paper, the detrital zircon LA-MC-ICPMS U-Pb age test was conducted on the drilling core samples of the Shanxi Formation of the Upper Paleozoic in the Otuokeqi area of the Ordos Basin, and the provenance age and the characteristic of the Shanxi formation in the Otuokeqi area in the northwest were discussed. The cathodoluminescence image shows that the detrital zircon has a clear core-edge structure, and most of the cores have clear oscillatory zonings, which suggests that they are magmatic in origin. Zircons have no oscillatory zoning structure that shows the cause of metamorphism. The age of detrital zircon is dominated by Paleoproterozoic and can be divided into four groups, which are 2500~2300 Ma, 2100~1600 Ma, 470~400 Ma, and 360~260 Ma. The first two groups are the specific manifestations of the Precambrian Fuping Movement (2.5 billion years) and the Luliang Movement (1.8 billion years) of the North China Craton. The third and fourth groups of detrital zircons mainly come from Paleozoic magmatic rocks formed by the subduction and collision of the Siberian plate and the North China plate. The ε Hf t value of zircon ranges from -18.36 to 4.33, and the age of the second-order Hf model T DM 2 ranges from 2491 to 1175 Ma. The source rock reflecting the provenance of the sediments comes from the material recycling of the Paleoproterozoic and Mesoproterozoic in the crust, combined with the Meso-Neoproterozoic detrital zircons discovered this time, indicating that the provenance area has experienced Greenwellian orogeny.

In this paper, we took samples from the Mesozoic Lower Cretaceous Yingen Formation, Suhongtu Formation, Bayingebi Formation and Permian source rocks in Well YH7 and Well YH8 in Hari Sag to study the geochemical features and compared the results with early research results; Samples of the second hydrocarbon source rocks in the Yingen Formation and the Bayingebi Formation were selected for thermal simulation experiments to study the secondary hydrocarbon generation potential. By analyzing and comparing the geochemical features of the source rocks, it is found that the Mesozoic hydrocarbon source rocks in the Hari Sag are mainly deposited in a reducing environment, and some are in a weakly oxidizing-weakly reducing environment. K1y is the best II2 immature-low mature hydrocarbon source rock, K1s is the non-hydrocarbon- best II1-II2 mature hydrocarbon source rock, K1b3 is the non-hydrocarbon- good II2-III mature hydrocarbon source rock, K1b2 is the medium- best II1-III low mature- mature hydrocarbon source rock, K1b1 is the non-hydrocarbon- best Ⅱ2-Ⅲ mature- high mature hydrocarbon source rock, and P is the best III over mature hydrocarbon source rock. By the thermal simulation experiments on the secondary hydrocarbon source rock of the Yingen Formation and the Bayingebi Formation, it is found that the hydrocarbon generation and expulsion characteristics of the Mesozoic source rock samples in the Hari Sag can be roughly divided into four stages: low mature stage (0.5% < Ro < 0.7%, simulation temperature is 250 ℃ - 300 ℃), early rapid oil generation and expulsion stage (0.7% < Ro < 1.3%, simulation temperature is 300 ℃ - 400 ℃), mid-term oil cracking gas stage (1.3% < Ro < 2.0%, simulation temperature is 400 ℃ - 500 ℃), and late major gas generation stage (Ro ＞ 2.0%), simulation temperature is 500 ℃ - 550 ℃). The K1b2 hydrocarbon source rock in the late first stage and early second stage has much larger exploration potential than K1y in the first stage.

The formation of the Qilian mountains and the evolution of adjacent basins were controlled by the uplift and northeastward growth of the Tibetan Plateau. In a field survey conducted on the ...

Nano metal oxides are common combustion catalysts for enhancing the burning rate of solid propellants. Cr2O3 nanoparticles (NPs) are efficient combustion catalysts for the pyrolysis of energetic components. In this study, Cr2O3 NPs were synthesized via a modified sol–gel method and further used for studying the thermal decomposition of nitrocellulose (NC). Differential scanning calorimetry (DSC) and thermogravimetry-Fourier-transform infrared spectroscopy (TG-FTIR) analyses indicate that the Cr2O3 NPs can be safely used with NC and the mechanism of the reaction between Cr2O3/NC and pure NC follows the Avrami–Erofeev equation: f(α) = 3(1 − α)[−ln(1 − α)]1/3/2. The peak temperature and activation energy (Ea) for the thermal decomposition of Cr2O3/NC are lower than those of pure NC. NO2 was detected at a lower temperature after NC was mixed with Cr2O3 NPs; this indicated the catalytically accelerated bond cleavage of NC by Cr2O3 NPs.

The Chinese Loess Plateau (CLP), which is located in the central part of China, mainly contains two sequences: the Quaternary loess-paleosol sequence and the late Miocene-Pliocene Red Clay sequence. U-Pb ages of detrital zircon from the Quaternary loess-paleosol sequences indicate that the current spatial pattern of central Asian aridification was largely established during the early Quaternary. U-Pb ages of detrital zircon from the underlying Red Clay sequences demonstrate that the northern source regions were important contributors for the dust since the late Miocene, except for the periods of ∼8 Ma and ∼5.5 to ∼4 Ma. These two periods correspond to increased and decreased dust deposition in the North Pacific, respectively, ascribed to the late Miocene aridification of the Qaidam Basin (in the west of the CLP) and the early Pliocene aridification of the Tarim Basin (in the west of the CLP). We attribute the increase of the Qaidam Basin-derived North Pacific dust fluxes to the uplift of the NE Tibetan Plateau. Such uplift also controlled the climatic and environmental changes in central Asian during the late Miocene. This study highlights the dynamical process of the central Asian aridification during the late Miocene-Pliocene.

The ∼800 km long Heihe River in northwestern China originates from the North Qilian Mountain, and passes through the Beishan Mountain before it reaches the Juyanhai Lake. Geologically, the river crosscuts the North Qilian Orogenic Belt, the Alax Terrane, and the Beishan Orogenic Belt. LA-ICP-MS U-Pb dating of detrital zircon from Heihe River sediments shows four age groups: 2700–1700 Ma, 1700–650 Ma, 650–358 Ma, and 358–230 Ma, and age peaks at ∼2450 Ma, ∼1850 Ma, ∼950 Ma, ∼520 Ma, 505 Ma, ∼480 Ma, ∼450 Ma, ∼430 Ma, ∼380 Ma, ∼320 Ma, and ∼295 Ma. The age distribution patterns indicate that Heihe River sediments were mainly sourced from the North Qilian Orogenic Belt. The detrital zircon ages demonstrate that the North Qilian Orogenic Belt may have Archean to late Paleoproterozoic rocks. Several tectonothermal events are also identified: opening of the North Qilian Ocean (part of the Paleo-Tethys Ocean) at early Neoproterozoic, subduction of oceanic lithosphere and formation of a trench-arc-basin system at late Neoproterozoic to late Ordovician, closure of the oceanic basin at late Ordovician, and collision of the Qaidam and Alax terranes at early Devonian. Our study indicates that the formation of the North Qilian Orogenic Belt was mainly related to the formation and closure of the Paleo-Tethys Ocean.

The Cenozoic uplift of Qilian Mountains is critical to comprehend the uplift and extension of the Tibet Plateau as well as the formation of the first and second steps in China’s topography. This study summarized dynamic stratigraphic realm comprehensively on the basis of stratigraphic correlation of different Cenozoic sedimentary basin regions of the Qilian Mountains and adjacent mountains. This facilitated the re-creation of the tectonic-sedimentary evolutionary process of the Qilian Mountains and their surrounding areas. The results indicate that during the Early Paleogene (Paleocene-Eocene), the Qilian Mountains were part of an uplift realm. During the Oligocene, Guide-Xining-Lanzhou-Linxia sag basin at the northern margin of the West Qinling Mountains came into being and was subjected to sedimentation. The Suli Basin located between the North and South Qilian paleo-uplifts began to form and undergo sedimentation. Intracontinental orogenic extrusion and basin detachment occurred at the Qilian Mountains during the Miocene, which caused successive uplifts of various mountains, including the Laji, South Qinghai, Jishi, Liupan, and South Shule Mountains. Until Pliocene, Qilian Mountains uplifted continuously and resulted in the shrink, extinction and being eroded of the basins, and aeolian red clay started to accumulate.

Iron, Co and Ni are first row transition metals and are all able to combine with S, As, and Sb to form disulphides, sulpharsenides and sulphantimonides, respectively, all of which exhibit substitutions of metal and metalloid elements in their structures. As an important tracer in the geochemistry of ore deposits, S isotope fractionation in sulphides can be used to analyse the ore-forming process and the source of ore-forming elements. However, there have been few studies of S isotope fractionation in sulpharsenides and sulphantimonides. Studying the isotope fractionation of the various members of this structural group can provide systematic information regarding S isotope fractionation in transition metal disulphides, sulpharsenides and sulphantimonides. In this paper, the S isotope fractionation parameters for Fe, Co and Ni sulpharsenides and sulphantimonides were calculated using first-principles methods based on density functional theory in the temperature range of 0–1000 °C. Our calculations show that the order of heavy S isotope enrichment is arsenopyrite > cobaltite > gudmundite > costibite > gersdorffite > ullmannite. For sulphides with the same anion pair, the main factor affecting S isotope fractionation is the metal-sulphur bond strength. For most of the sulphides studied in this paper, S isotope fractionation arising from substitution of metalloid elements is much smaller than that of metal elements.

Pb isotopes are considered an ideal tool for identifying material sources and tectonic settings of various petrogeneses and mineralizations. A high precision method for in-situ Pb isotopic analysis by femtosecond laser-ablation multi-collector inductively coupled plasma mass spectrometry (fsLA-MC-ICP-MS) was first established in China by the State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University. This new method has been used to measure Pb isotopic compositions for inclusions, minerals, glasses, metals, etc., because of its negligible element fractionation and well-corrected mass discrimination. However, Pb isotopic studies on typical deposits using fsLA-MC- ICP-MS have until now rarely been reported globally. The Tongyu copper deposit in the Shaanxi Province, China is one of the most important VHMS deposits with industrial value and is also a typical example of mineralization associated with subduction and metallogenesis during the Caledonian orogeny in the western part of the North Qinling Orogen. Previous studies of this deposit have focused mainly on geological features and ore-forming ages, but detailed isotopic geochemical studies on the ore-forming material sources and tectonic settings were lacking.

The effects Fe 2 O 3 nanoparticles on the thermal decomposition of nitrocellulose (NC) have been investigated by the differential scanning calorimetry (DSC) method and the thermogravimetry with Fourier transform infrared analysis (TG-IR). DSC analysis shows that Fe 2 O 3 can be safely used with NC, and the thermal decomposition reactions of Fe 2 O 3 -NC composite and NC follow the same thermal decomposition mechanism of Avrami-Erofeev equation f(α) = 1.5(1–α)[–ln(1–α)] 1/3 in differential form. The as-prepared nanoparticles could reduce the activation energy of the decomposition reaction and the critical temperature of thermal explosion of NC. In addition, TG-IR analysis indicated that Fe 2 O 3 nanoparticles play a crucial role in promoting the O NO 2 bond cleavage and secondary autocatalytic reactions in condensed phase. This contribution suggests that introducing Fe 2 O 3 nanostructure may be a promising way to accelerate the thermal decomposition of NC.

Nano metal oxides are common combustion catalysts for enhancing the burning rate of solid propellants. Cr

The North Yili Block is one of the major continental constituents of the Central Asian Orogenic Belt (CAOB), study of its basement evolution and tectonic origin is essential for the understanding of the accretionary history of the CAOB and the reconstruction of global supercontinent as well. We conducted field geological, geochronological and geochemical investigations on the mafic dikes intruding in the highly deformed Proterozoic carbonate in the North Yili Block, NW Chinese Tianshan. Zircon U–Pb dating results suggest that the gabbro and gabbroic diorite dikes and associated granitic vein formed in 776–778 Ma. Element and isotope geochemical data reveal that these intrusive rocks derived from an OIB-like mantle source, and were variably influenced by fraction crystallization and important crustal contamination, thus, a continental rifting setting is proposed for these dikes. Our new data provide the first evidence for a Neoproterozoic continental intra-plate magmatism occurred in the North Yili Block, this event can be linked with the coeval continental rifting-related magmatism in northern Tarim and in other microcontinents within the SW CAOB (e.g., Central Kazakhstan, Kyrgyzstan Middle Tianshan). Based on the comparison on the Neoproterozoic to early Paleozoic stratigraphic sequences between the North Yili and Tarim blocks, it is suggested that the North Yili Block most likely originated from the Tarim Block, and is potentially one additional constituent member of the Rodinia supercontinent.

Three Fe2O3 particle samples with the same crystal structure but different morphologies were prepared by the hydrothermal method and then combined with Al nanoparticles to produce Al/Fe2O3 thermites using ultrasonic mixing. The properties of Fe2O3 and Al/Fe2O3 were studied using a combination of experimental techniques including scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). The influences of the three Al/Fe2O3 thermites on the combustion properties of the AP/HTPB (ammonium perchlorate/hydroxyl-terminated polybutadiene) composite propellant were investigated in comparison to those of Fe2O3. The results show that the Al/Fe2O3 thermites are better than Fe2O3 in enhancing the combustion performance of AP/HTPB. Furthermore, the surface area, which depends on size and mophology, of Fe2O3 particles was found to play a vital role in improving the burning rate of the thermites-containing propellant formulation, with the smallest particles with the largest surface-to-volume (S/V) ratio performing the best. The enhanced catalytic property of the granular-shape Fe2O3 and the corresponding thermite is attributed to the large specific surface area of Fe2O3. The different thermal behaviors of these three superthemites were supposed to be attributed to the surface site of Fe2O3 particles. This work provides a better understanding on the catalytic properties of thermites that are important for combustion applications.

Granulite-facies metamorphic rocks in the Tongbai orogen have great implications for the evolution of the whole Qinling–Tongbai–Dabie orogenic belt. However, the age and tectonic setting of the granulite-facies metamorphism have not been well constrained yet. In this contribution, BSE imaging, trace element analysis and U–Pb dating of monazite were undertaken for three felsic granulites, a gneiss and a leucosome from the Tongbai orogen. Most monazite grains from the granulite and gneiss samples exhibit no zoning, relatively low Th/U ratios, significant depletion in HREEs and Y, and negative Eu anomalies, indicating their formation under granulite-facies metamorphic conditions. Their formation ages range from 423 ± 2 to 430 ± 3 Ma with a weighted mean of 426 ± 5, which is taken as the timing of the peak granulite-facies metamorphism. In the leucosome sample, the monazite shows a euhedral to subhedral shape, coupled with a core and rim structure. Besides being depleted in HREEs and Y, both of them have significantly negative Eu anomalies and variable U contents (1220–13323 ppm) and Th/U ratios (7.2–136.7). This suggests that their formation was coeval with the crystallization of feldspar, metamorphic zircon, and garnet. The monazites yield a weighted mean age of 426 ± 3 Ma, suggesting nearly coeval partial melting during granulite-facies metamorphism. The relationship between metamorphic monazite and zircon within the same metamorphic sample is complex as revealed by metamorphic monazite and zircon U–Pb ages for the gneiss, granulite and leucosome samples. In the other two granulite samples, the monazite yields U–Pb ages of 423 ± 2 and 425 ± 3 Ma, whereas only little overgrowth or recrystallization of metamorphic zircon. This indicates that monazite is more sensitive than zircon in recording of metamorphic age even at the granulite-facies conditions. Combined with previous metamorphic zircon U–Pb age results, the prograde, peak, and retrograde stages of the granulite-facies metamorphism in the Tongbai orogen can be constrained at ca. 440, 426, and 415 Ma, respectively. Therefore, the granulite-facies metamorphism would have lasted for more than 20 Myr. The prolonged granulite-facies metamorphism might result from the continuous northward subduction of the Paleotethyan oceanic crust beneath the North Qinling terrane.

Migmatites are predominant in the North Qinling (NQ) orogen, but their formation ages are poorly constrained. This paper presents a combined study of cathodoluminescence imaging, U–Pb age, trace element and Hf isotopes of zircon in migmatites from the NQ unit. In the migmatites, most zircon grains occur as new, homogeneous crystals, while some are present as overgrowth rims around inherited cores. Morphological and trace element features suggest that the zircon crystals are metamorphic and formed during partial melting. The inherited cores have oscillatory zoning and yield U–Pb ages of c. 900 Ma, representing their protolith ages. The early Neoproterozoic protoliths probably formed in an active continental margin, being a response to the assembly of the supercontinent Rodinia. The migmatite zircon yields Hf model ages of 1911 ± 20 to 990 ± 22 Ma, indicating that the protoliths were derived from reworking of Palaeoproterozoic to Neoproterozoic crustal materials. The anatexis zircon yields formation ages ranging from 455 ± 5 to 420 ± 4 Ma, with a peak at c. 435 Ma. Combined with previous results, we suggest that the migmatization of the NQ terrane occurred at c. 455–400 Ma. The migmatization was c. 50 Ma later than the c. 490 Ma ultra-high-P (UHP) metamorphism, indicating that they occurred in two independent tectonic events. By contrast, the migmatization was coeval with the granulite facies metamorphism and the granitic magmatism in the NQ unit, which collectively argue for their formation due to the northward subduction of the Shangdan Ocean. UHP rocks were distributed mainly along the northern margin and occasionally in the inner part of the NQ unit, indicating that they were exhumed along the northern edge and detached from the basement by the subsequent migmatization process.

Single grain zircon U-Pb geochronology has demonstrated great potentials in extracting tectonic and atmospheric circulation signal carried by aeolian, fluvial, and fluviolacustrine sediments. A routine in this sort of studies is analyzing 100–150 grains and then compares zircon U-Pb age spectra between the measured sample and the potential sources. Here we compared the zircon U-Pb age results of the late Miocene-Pliocene Red Clay sequence of two neighboring sites from the Chinese Loess Plateau where similar provenance signal is expected. Although the results from the 5.5 Ma sediment support this prediction, the results from the 3 Ma sediment at these two sites differ from each other significantly. These results emphasize the importance of increasing analysis number per sample and combining the zircon U-Pb geochronology with other provenance tools in order to get reliable provenance information.

Bulk element and isotopic compositions, single zircon U–Pb ages and trace element compositions of the Triassic high-Mg adakitic andesites (HMAs) from the Linxi area in the Inner Mongolia–Daxinganling orogenic belt (IMDOB) were studied to understand the area's petrogenesis and implications for Phanerozoic crustal growth. The Linxi HMAs are characterized by typical features of high-SiO 2 adakite with high Mg# and high Cr and Ni contents. Coarse clinopyroxene (cpx) phenocrysts with reverse zoning were found. These cpx phenocrysts have cores with lower Mg# and Ni contents, and higher incompatible element contents (e.g., Zr and La) compared with their mantles and rims. Bulk rock Sr–Nd isotopic compositions ( 87 Sr/ 86 Sr I = 0.70382–0.70396 and e Nd(t) = 3.2–4.5) fall in the range of mid-ocean ridge basalts (MORB) and modern subduction-related adakites. Single zircon U–Pb dating by LA-ICP-MS suggests an eruption at ca. 238 Ma. Combined with the tectonic setting and Precambrian zircon age spectrum, these features suggest that the Linxi HMAs could be derived from the subducted Paleo-Asian oceanic slab with sediments shed from the North China Craton and hybridized by peridotite in the mantle. Trace element-age variations of zircons indicate that the oceanic crust was formed during Carboniferous–early Permian times, and then subducted during ca. 270–260 Ma. Melting of the subducted oceanic slab and hybridization by peridotite could have been initiated at ca. 250 Ma. It is suggested that the southern accretionary zone between the North China Craton and the Solonker suture in the IMDOB, where the Linxi HMAs are located, could have been consolidated by Carboniferous–Permian times. This implies that the Linxi HMAs could have been derived from partial melting of a fossil oceanic slab after the subduction, and subduction-related melting might have been delayed if the slab was subducted under an old, cold craton. Although we are unsure of the true extent of the fossil oceanic slab, the genesis of the Linxi HMAs is essentially a snapshot of the melting of a subducted slab lagging behind subduction, and melting of the fossil oceanic slab could have played an important role in the Phanerozoic crustal growth in the IMDOB.

Platinum group element (PGE) abundances in the upper continental crust (UCC) are poorly constrained with published values varying by up to an order of magnitude. We evaluated the validity of using loess to estimate PGE abundances in the UCC by measuring these elements in seven Chinese loess samples using a precise method that combines NiS fire assay with isotope dilution. Major and trace elements of the Chinese loess show a typical upper crustal composition and PGE abundances are consistent with literature data on Chinese loess, except for Ru, which is a factor of 10 lowe than published values. We suggest that the high Ru data and Ru N /Ir N values of Chinese loess reported by Peucker-Ehrenbrink and Jahn (2001) ( Geochem. Geophys. Geosys. 2 , 2001GC000172) are an analytical artifact, rather than a true geochemical characteristic of loess because likely sources of loess are not significantly enriched in Ru and transport and deposition processes cannot preferentially enrich Ru in loess. The effect of eolian fractionation on PGE abundances in loess appears to be limited because Chinese loess from different locations shows similar PGE patterns and concentrations. This conclusion is supported by strong positive correlations between the PGE (except for Pt) and other compatible elements such as Fe 2 O 3 , Ni, Cr, Co. Using a compilation of PGE data for loess from China, Argentina and Europe, including our data but excluding one sample with an anomalously high Pt content, we propose average PGE abundances for global loess of Ir = 0.022 ppb (ng/g), Ru = 0.030 ppb, Rh = 0.018 ppb, Pt = 0.599 ppb, and Pd = 0.526 ppb, and suggest that these are the best current estimates for the PGE abundances of the UCC.

The Zhongchuan district is an important component of the metallogenic belt in the Western Qinling. The Zhongchuan granite pluton occurring in the centre of the Zhongchuan metallogenic area has been poorly constrained, though the Triassic granite in Western Qinling has been well documented. In-situ zircon U–Pb ages, Hf isotopic compositions and whole-rock geochemical data are presented for host granite and mafic microgranular enclaves (MMES) from the Zhongchuan pluton, in order to constrain its sources, petrogenesis and tectonic setting of the pluton. The distribution of major, trace and rare earth elements apparently reflect exchange between the MMES and the host granitic rocks mainly due to interactions between coeval felsic host magma and mafic magma. The zircon U–Pb age of host granite (231.6 ± 1.5 to 235.8 ± 2.3 Ma) has overlapping uncertainty with that of the MMES (236.6 ± 1.3 Ma), establishing that the mafic and felsic magmas were coeval. The Hf isotopic composition of the MMES (eHf(t) = −13.4 to 4.0) is distinct from the host granite (eHf(t) = −15.7 to 0.0), indicating that both enriched subcontinental lithosphere mantle (SCLM) and crustal sources contributed to their origin. The zircons have two-stage Hf model ages of 1064 to 1798 Ma for the host granite and 858 to 1747 Ma for the MMES. This suggests that the granitic pluton was likely derived from partial melting of a Late Mesoproterozoic crust, with subsequent interaction with the SCLM-derived mafic magmas in tectonic affinity to the South China Block. Copyright © 2012 John Wiley & Sons, Ltd.

An integrated study of petrology, zircon U–Pb age, and geochemistry was reported for a Paleoproterozoic granitic pluton from the Kongling terrain in the northern part of the Yangtze Block. The Quanqitang pluton is composed mainly of alkali feldspar, quartz, biotite and plagioclase. Zircon U–Pb dating yields a 207Pb/206Pb age of ca.1.85 Ga, which represents its intrusion age. The Quanqitang pluton has high SiO2 (72.6–74.4 wt.%), K2O (5.09–5.56 wt.%) and Na2O (3.02–3.36 wt.%), and low Fe2O3 (2.56–3.19 wt.%) and MgO (0.25–0.37 wt.%). It is metaluminous (A/CNK = 0.93–0.98) and belongs to the high-K calc-alkaline series. On the chondrite-normalized REE diagram, all the samples invariably show a relatively enrichment in light rare earth elements (LREEs) with high (La/Yb)N ratios (10.6–21.7) and strong negative Eu anomalies. Their primitive-mantle normalized spidergrams display negative Ba, Nb, Ta, Sr, P, Eu and Ti anomalies. The calculated zirconium saturation temperatures range from 802 to 861 °C with an average of 845 °C. Zircons from the granites have eHf(t) values ranging from − 17.6 to − 20.9, corresponding to two-stage Hf modal ages of 3.6 to 3.8 Ga. Based on the geochemical features, it is inferred that the granites were generated by the dehydration melting of Archean tonalitic gneisses with a plagioclase-rich residual assemblage. The granites chemically belong to the A2-type granites, and have an intrusion age younger than the possible ca. 2.0 Ga collisional event in the Yangtze Block. This suggests that they formed in a post-collisional tectonic setting, and thus a tectonic regime switch from collision to extension might have occurred in the Yangtze Block before ca. 1.85 Ga. The occurrence of the A2-type granite indicates that the Kongling microcontinental block became a stabilized craton at ca. 1.85 Ga.

The Liziyuan goldfield is located along the northern margin of the western part of the Qinling Orogen (WQO). The goldfield consists of five gold-only deposits hosted by metavolcanic rocks, and one polymetallic (Au–Ag–Pb) deposit hosted by the Tianzishan Monzogranite. As the Liziyuan goldfield appears to be spatially and temporally related to the Jiancaowan Porphyry, the study of the deposit provides a crucial insight into the relationship between tectonic-magmatic events and gold metallogenesis in the WQO. In this paper, we present whole-rock major and trace element geochemistry, and in situ zircon U–Pb and Lu–Hf isotopic data from the Tianzishan Monzogranite and Jiancaowan Porphyry. The two granitic plutons are enriched in LILEs and LREEs, depleted in HFSEs and have zircon e Hf ( t ) values between −14.1 and −5.1 for the Tianzishan Monzogranite and between −21.0 and −8.4 for the Jiancaowan Porphyry. These characteristics indicate that the granites are derived from the crust. The Tianzishan Monzogranite has LA-ICP-MS zircon U–Pb ages of 256.1 ± 3.7 to 260.0 ± 2.1 Ma, which suggests that it was emplaced in the WQO during the convergence of the North and South (Yangtze) China cratons in the early stage of the Qinling Orogeny. In contrast, the porphyry has a LA-ICP-MS zircon U–Pb age of 229.2 ± 1.2 Ma, which is younger than the peak collision age, but corresponds to the widespread Late Triassic post-collisional granitic plutons in the WQO. The Tianzishan Monzogranite has somewhat higher Sr contents (196–631 ppm), lower Y (2.23–19.6 ppm) and Yb (0.20–2.01 ppm) contents, and a positive Eu/Eu* averaging 1.15. These characteristics suggest the pluton was derived from partial melting of the thickened crust. In contrast, the relatively higher MgO content (0.85–2.08 wt%) and Mg no. (43.4–58.2) of the Jiancaowan Porphyry indicates that insignificant amounts of subcontinental lithospheric mantle-derived mafic melts were involved in the generation of the magma. The Liziyuan goldfield is hosted by faults in greenschist-facies metamorphic rocks. Fluid inclusion studies suggest that gold was precipitated from CO 2 -rich, low-salinity and medium temperature fluids. This feature is consistent with the other orogenic gold deposits throughout the world. The field relationships and zircon U–Pb ages of the two granitic plutons suggest that gold mineralization is coeval with or slightly younger than the emplacement of the Jiancaowan Porphyry. Therefore, both the porphyry and deposit formed during the post-collisional stage of the Qinling Orogen.

The Xitieshan terrane is one of four metamorphic terranes in the North Qaidam metamorphic belt, which is an early Paleozoic high-pressure to ultrahigh-pressure (HP-UHP) metamorphic belt in NW China. However, conclusive evidence and precise timing of UHP metamorphism in the Xitieshan terrane have not been well documented. In this study, we report an integrated study of zircon grains from an amphibolite in the Xitieshan terrane in terms of mineral inclusions, trace elements, and U-Pb age systematics. The first record of coesite is reported as an inclusion in a metamorphic zircon, which provides unambiguous evidence for the UHP metamorphism of the Xitieshan terrane. The metamorphic zircon domains have weak or no zoning, very low Th/U ratios, insignificant Eu anomalies, and flat HREE patterns. Zircon grains contain inclusions of garnet, omphacite and rutile, in addition to the coesite inclusion. These inclusions indicate that the metamorphic zircon grains formed under UHP metamorphic conditions. The metamorphic zircon grains were dated by the SIMS and LA-ICPMS methods and yield weighted mean ages of 432 ± 14 and 441 ± 9 Ma, respectively. Combined with previous results, the HP-UHP metamorphism of the Xitieshan terrane may have lasted 460–440 Ma with the peak UHP metamorphism at 441 ± 9 Ma. A compilation of the reported geochronological data reveals that all four terranes of the North Qaidam metamorphic belt might have experienced coeval UHP metamorphism during the early Paleozoic (420–450 Ma), and thus may have suffered a coherent subduction, UHP metamorphism, and exhumation cycle.

article i nfo Mesozoic granitoids are widespread in the southern margin of the North China Craton, and of particular geo- logical interests because of their indication for lithospheric evolution and close association with porphyry Mo mineralization. In this contribution, in situ LA-ICP-MS U-Pb, Hf isotope and trace element analyses of zircon crystals have been combined to constrain the emplacement time and petrogenesis of the Heyu granitic bath- olith which hosts the Yuchiling porphyry Mo system, Henan Province, China. As inferred from field investiga- tions, the concentrically zoned Heyu batholith mainly consists of four texturally distinguishable phases, and displays a pattern of monotonically decreasing U-Pb age from 143.0±1.6 Ma for Phase 1, through 138.4± 1.5 Ma for Phase 2, through to ca. 135 Ma for Phase 3, and to 133.6±1.3 Ma for the Mo-mineralized Yuchiling granite porphyry (Phase 4). The eHf(t) values (�27.7 to �3.4) and the two stage Hf model ages (1403 to 2924 Ma) of zircon grains, together with the ages of local strata, suggest that the magmas forming the Heyu batholith were dominantly sourced from the crust, with input of a mantle component. The higher Ce/Ce* ratios of the zircon crystals in the mineralized Yuchiling porphyry compared to those in the Mo- barren phases suggests that fluids exsolved from oxidic magmas might be more favorable for Mo enrichment. A regional synthesis suggests that intensive lithospheric thinning in the southern margin of the North China Craton should not be earlier than 130 Ma.

The early history of the Yangtze Block has not been well constrained yet, due to the scarce outcrops of Archean to Paleoproterozoic rocks. In this study, we report an integrated study of zircon U–Pb age, major and trace element data and Sr–Nd–Hf isotope compositions for gray gneisses from the Houhe complex in the northwestern part of the Yangtze Block. Zircon U–Pb dating yields a weighted mean 207 Pb/ 206 Pb age of 2081 ± 9 Ma for a gneiss. This age is interpreted as the formation age of the Houhe complex and thus the Houhe complex represents the oldest rocks found in the western part of the Yangtze Block. The gray gneisses from the Houhe complex range in SiO 2 contents from 58.63% to 68.59% and Na 2 O from 3.88% to 5.28%, and have relatively high Fe 2 O 3 contents of 2.86–6.69%, Al 2 O 3 of 16.01–18.88%, and MgO of 0.97–2.65%. These rocks show low Sr (149–390 ppm), Cr (9.07–45.1 ppm) and Ni (4.97–21.3 ppm) contents, but high Y (12.9–32.7 ppm) and Yb (0.95–2.25 ppm). They are characterized by a relative enrichment in LILEs and LREEs, but a depletion in HFSEs. These features are similar to those of calc-alkaline granitoids, suggesting that their formation might be related to a subduction-related process or remelting of preexisted arc rocks. Compiled age spectra of Archean to Paleoproterozoic zircon grains reveal that the western and eastern parts of the Yangtze Block have similar Archean and early Paleoproterozoic age ranges, indicative of the occurrence of an old continental nucleus in both parts. On the other hand, there are large amounts of ca. 2050–2400 Ma zircon grains revealed in the western part of the Yangtze Block, implying that there might be a microcontinent with an active-type continental margin during the Paleoproterozoic times in the western part of the Yangtze Block. Because of the poor outcrops of Archean to Paleoproterozoic rocks in the Yangtze Block, it is no possible to establish the exact nature of such an active margin yet. The occurrence of ca. 2.0 Ga khondalitic and metasedimentary rocks has been documented in the eastern part of the Yangtze Block, implying that there might be a passive-type continental margin in the eastern part of the Yangtze Block. At ca. 2.0 Ga, the collision between the western microcontinent and the eastern part may have resulted in the final arc-continental collision and the amalgamation of the Yangtze Block.

LA-(MC)-ICPMS trace element, U–Pb and Hf isotope analyses were performed on zircons from continental-derived retrograde high-pressure metamorphic rocks, which were attested by the occurrence of HP mineral inclusions in metamorphic zircons, from the Huwan shear zone in the western Dabie orogen. Zircons in a schist sample are mostly detrital and gave U–Pb ages from 1212 to 2312 Ma, suggesting that the detritus were derived from multiple sources or suffered partial Pb-loss during subsequent metamorphism. Magmatic zircons in an amphibolite sample yielded an upper intercept U–Pb age of 1806 ± 63 Ma, which was interpreted as its protolith formation age. The zircons in the amphibolite show a weighted e Hf ( t ) value of − 16.3, and a weighted Hf model age of 3455 Ma, suggesting that the protolith was derived from reworking of ancient continental materials. Metamorphic zircons in a quartz-rich leucosome sample and the amphibolite sample gave weighted mean 206 Pb/ 238 U ages of 241 ± 1 and 243 ± 4 Ma, respectively. These metamorphic zircons contain mineral inclusions of garnet and omphacite and are characterized by relatively flat HREE patterns with slight negative Eu anomalies. This indicates that they formed in the presence of garnet but the absence of plagioclase, and thus under eclogite facies conditions. The U–Pb age of ca. 243 Ma is consistent with eclogite-facies metamorphic ages of the juvenile oceanic crust in the western Dabie orogen, suggesting that the initial continental subduction for high-pressure metamorphism of the whole Dabie orogen can be traced back to ca. 243 Ma. In addition, the western Dabie HP-UHP orogenic belt might have suffered multi-slice subduction and exhumation during the Triassic.

The South Tianshan is located to the north of the Tarim block and defines the southern margin of the Paleozoic Central Asian Orogenic Belt (CAOB). This study presents new structural data, geochronological and geochemical results for the Wuwamen ophiolite mélange in the Chinese segment of the South Tianshan. In the south, the Wuwamen ophiolite mélange shows typical block-in-matrix fabrics and occurs in the footwall of a south-dipping thrust fault, hanging wall of which is composed of weakly metamorphosed and deformed Lower Paleozoic marine to deep marine sequences from the South Tianshan. In the north, a southdipping thrust fault juxtaposes the Wuwamen ophiolite mélange in its hanging wall against the high-grade and strongly deformed metasedimentary rocks from the Central Tianshan in its footwall.

The amalgamation of South (SCB) and North China Blocks (NCB) along the Qinling-Dabie orogenic belt involved several stages of high pressure (HP)-ultra high pressure (UHP) metamorphism. The new discovery of UHP metamorphic rocks in the North Qinling (NQ) terrane can provide valuable information on this process. However, no precise age for the UHP metamorphism in the NQ terrane has been documented yet, and thus hinders deciphering of the evolution of the whole Qinling-Dabie-Sulu orogenic belt. This article reports an integrated study of U–Pb age, trace element, mineral inclusion and Hf isotope composition of zircon from an eclogite, a quartz vein and a schist in the NQ terrane. The zircon cores in the eclogite are characterized by oscillatory zoning or weak zoning, high Th/U and 176Lu/177Hf ratios, pronounced Eu anomalies and steep heavy rare earth element (HREE) patterns. The zircon cores yield an age of 796 ± 13 Ma, which is taken as the protolith formation age of the eclogite, and implies that the NQ terrane may belong to the SCB before it collided with the NCB. The ɛHf(t) values vary from −11.3 to 3.2 and corresponding two-stage Hf model ages are 2402 to 1495 Ma, suggesting the protolith was derived from an enriched mantle. In contrast, the metamorphic zircon rims show no zoning or weak zoning, very low Th/U and 176Lu/177Hf ratios, insignificant Eu anomalies and flat HREE patterns. They contain inclusions of garnet, omphacite and phengite, suggesting that the metamorphic zircon formed under eclogite facies metamorphic conditions, and their weighted mean 206Pb/238U age of 485.9 ± 3.8 Ma was interpreted to date the timing of the eclogite facies metamorphism. Zircon in the quartz vein is characterized by perfect euhedral habit, some oscillatory zoning, low Th/U ratios and variable HREE contents. It yields a weighted mean U–Pb age of 480.5 ± 2.5 Ma, which registers the age of fluid activity during exhumation. Zircon in the schist is mostly detrital and U–Pb age peaks at c. 1950 to 1850, 1800 to 1600, 1560 to 1460 and 1400 to 1260 Ma with an oldest grain of 2517 Ma, also suggesting that the NQ terrane may have an affinity to the SCB. Accordingly, the amalgamation between the SCB and the NCB is a multistage process that spans c. 300 Myr, which includes: the formation of the Erlangping intra-oceanic arc zone onto the NCB before c. 490 Ma, the c. 485 Ma crustal subduction and UHP metamorphism of the NQ terrane, the c. 430 Ma arc-continent collision and granulite facies metamorphism, the 420 to 400 Ma extension and rifting in relation to the opening of the Palaeo-Tethyan ocean, the c. 310 Ma HP eclogite facies metamorphism of oceanic crust and associated continental basement, and the final 250 to 220 Ma continental subduction and HP–UHP metamorphism.

It is intriguing whether the formation of granulite in an orogenic belt is related to magmatism and crustal growth. The Tongbai orogen is one of the particular areas in the Qinling–Tongbai–Dabie–Sulu orogen that contains both granulites and associated arc magmatic rocks, and thus is an optimal place to address this issue. However, the formation age and genesis of the granulites and their relations to the magmatic rocks have not yet been well constrained. In situ LA (MC)-ICPMS U–Pb dating, and trace element and Lu–Hf isotope analyses were undertaken on zircon grains from gneiss, granulite, gabbro and granodiorite samples. Most zircons in three granulite samples and a gneiss sample have core–rim structures. The cores have oval or rounded shapes, oscillatory zones, high Th/U ratios and variable U–Pb ages, suggesting a detrital genesis. The youngest group of the detrital zircons yields a weighted mean 206 Pb/ 238 U age of 450 ± 5 Ma, which is interpreted as the maximum depositional age of their protoliths. A major age cluster is ca. 450–490 Ma, corresponding to prolonged arc magmatism in the northern Tongbai and Qinling orogens. Another group of ages range from 660 to 950 Ma, implying that the Qinling Group of the Tongbai orogen belongs to the South China Block (SCB). Metamorphic zircons in the granulites have weak or no zoning, low Th/U ratios and REE contents, negative Eu anomalies, and relatively flat HREE patterns, which indicate that they formed contemporaneously with garnet and plagioclase, and thus under granulite-facies metamorphic conditions. Their weighted mean age of 424 ± 4 Ma is taken as the best estimated age of the granulite-facies metamorphism. Zircons in a leucosome sample have significant negative Eu anomalies and relatively flat HREE patterns with a formation age of 428 ± 4 Ma, indicating partial melting coeval with the granulite-facies metamorphism. Metamorphic zircons in the gneiss show apparently negative Eu anomalies, and variable Th/U ratios and HREE contents. They yield a weighted mean 206 Pb/ 238 U age of 438 ± 4 Ma, which was suggested to record the timing of the prograde metamorphism. Zircon grains in a gabbro and a granodiorite yield U–Pb ages of 432 ± 4 and 424 ± 4 Ma, respectively, which are interpreted as their formation ages and identical to the ages of the granulite-facies metamorphism. They have positive e Hf ( t ) values of up to 5.1, showing clear evidence for crustal growth during their formation. The appearance of the Silurian granulite-facies metamorphism and magmatism in the Tongbai orogen provides a good paradigm of coeval granulite-facies metamorphism, magmatism and crustal growth in an arc-continent collision orogenic belt.

The Dehe granitic pluton intruded the Xiahe Group which is in the core complex of the North Qinling Orogenic Belt (NQOB). It shows gneissic bedding and possesses typical S-type granite minerals such as muscovite and garnet. LA-ICP-MS U-Pb isotopic dating of the Dehe granite yielded a weighted average age of 925±23 Ma which represents the emplacement age of the pluton. Most of the ɛHf(t) values are negative, and the two-stage model ages are consistent with the age of the Qinling Group. The isotope data show that the Dehe granite was formed in the following geological setting: in the syn-collision setting of the NQOB in the Neoproterozoic, crustal thickening induced partial melting of materials derived from the Qinling complex, and then the maga upwelled and intruded into the Xiahe Group. The formation of the Dehe S-type granite implied the occurrence of a convergent event in the QOB during the Neoproterozoic.

The North China craton and the Yangtze craton (South China) both contain Archean rocks in eastern China. Unlike the North China craton, where Archean rocks are widespread, in the Yangtze craton the exposed Archean rocks are only known in the Kongling terrain (360 km2). Zircon U-Pb ages and Lu-Hf isotopic compositions of three granodioritic-trondhjemitic gneisses and three metasedimentary rocks from the Kongling terrain were analyzed by LA-ICP-MS and LA-MC-ICP-MS. Igneous zircons in one trondhjemitic gneiss in the north of the Kongling terrain have an age of 3302±7 (1σ) Ma. Evidence from cathodoluminescence imaging, variations in Th/U and degree of U-Pb age discordance suggest that apparently younger zircons in the same population are variably disturbed 3302 Ma grains. Thus, this trondhjemitic gneiss is the oldest known rock in South China and predates the earlier reported ∼2900 Ma granitoid magmatism by 400 Ma. Zircon cores from one granodioritic gneiss in the north of the Kongling terrain also give a concordant age group at 3200 to 3300 Ma. Regardless as inherited or not, these cores crystallized from a magma indistinguishable in age with the trondhjemite. Concordant U-Pb ages for igneous zircons in one granodioritic gneiss in the south of the Kongling terrain yielded a weighted average 206Pb/207Pb age of 2981±13 Ma (2σ, MSWD=9.7, n=21). The zircon age and initial Hf isotopic compositions are similar to those of widespread granitoid gneisses from the north of the Kongling terrain (2903-2947 Ma), and indicate that the south and north of the Kongling terrain are correlative. The results also reinforce that magmatism of the whole Kongling terrain mainly occurred at 2900 Ma. Available Hf isotopic data from the Kongling terrain show that juvenile crustal additions occurred mainly between 3150 and 3800 Ma with a significant peak at 3300 to 3500 Ma. The ∼3300 Ma zircons from the trondhjemitic gneiss have Hf crust formation ages of 3450 to 3730 Ma, some of which have nearly chondritic eHf (t). The whole-rock depleted mantle Nd model age of this rock is 3400 Ma, close to its age of magmatism and consistent with the Hf model age. Its eNd value at 3300 Ma is nearly chondritic (1.26). These lines of evidence suggest that the 3300 Ma trondhjemite represent juvenile crust additions to the pre-existing continental crust.

Zircon trace element, U-Pb age, and Lu-Hf isotope composition were determined for two eclogite samples from the Xinxian ultrahigh-pressure (UHP) unit in the western Dabie orogen to constrain its exhumation processes. Cathodoluminescence imaging reveals that most zircons are metamorphic, while some have inherited magmatic cores in one sample. The magmatic cores have high Th/U and Lu/Hf ratios, high trace element contents, and a clear negative Eu anomaly, consistent with their igneous genesis. They yield an upper intercept age of Ma and a positive eHf(t) value of 8.0, arguing for reworking of early Mesoproterozoic crust during the middle Neoproterozoic in the western Dabie orogen. The metamorphic zircons contain mineral inclusions of garnet, omphacite, rutile, and quartz. They are characterized by low Nb, Ta, Y, and heavy rare earth elements (HREE) contents, a nearly flat HREE pattern, and an insignificant negative Eu anomaly. These indicate that the metamorphic zircons formed under high-pressure (...

Both oceanic and continental HP rocks are juxtaposed in the Huwan shear zone in the western Dabie orogen, and thus provide a window for testing the buoyancy-driven exhumation of dense oceanic HP rocks. The HP metamorphic age of the continental rocks in this zone has not been well constrained, and hence it is not known if they are of the same age as the exhumation of the HP oceanic rocks. In situ laser ablation (multiple collector) inductively coupled plasma mass spectrometry (LA-(MC-)ICP-MS), U–Pb, trace element and Hf isotope analyses were made on zircon in a granitic gneiss and two eclogites from the Huwan shear zone. U–Pb age and trace element analysis of residual magmatic zircon in an eclogite constrain its protolith formation at 411 ± 4 Ma. The zircon in this sample displays eHf (t) values of +6.1 to +14.4. The positive eHf (t) values up to +14.4 suggest that the protolith was derived from a relatively depleted mantle source, most likely Palaeotethyan oceanic crust. A granitic gneiss and the other eclogite yield protolith U–Pb ages of 738 ± 6 and 700 ± 14 Ma, respectively, which are both the Neoproterozoic basement rocks of the Yangtze Block. The zircon in the granitic gneiss has low eHf (t) values of −14.2 to −10.5 and old TDM2 ages of 2528–2298 Ma, suggesting reworking of Palaeoproterozoic crust during the Neoproterozoic. The zircon in the eclogite has eHf (t) values of −1.0 to +7.4 and TDM1 ages of 1294–966 Ma, implying prompt reworking of juvenile crust during its protolith formation. Metamorphic zircon in both eclogite samples displays low Th/U ratios, trace element concentrations, relatively flat heavy rare earth element patterns, weak negative Eu anomalies and low 176Lu/177Hf ratios. All these features suggest that the metamorphic zircon formed in the presence of garnet but in the absence of feldspar, and thus under eclogite facies conditions. The metamorphic zircon yields U–Pb ages of 310 ± 3 and 306 ± 7 Ma. Therefore, both the oceanic- and continental-type eclogites share the same episode of Carboniferous eclogite facies metamorphism. This suggests that high-pressure continental-type metamorphic rocks might have played a key role in the exhumation and preservation of oceanic-type eclogites through buoyancy-driven uplift.

The Tongyu volcanic-hosted massive sulfide (VHMS) copper deposit is located in the west part of the North Qinling (NQL), Shaanxi Province. Here we report geological features and trace elemental characteristics of ores, mineralized rocks, and volcanic host rocks of this deposit. We also conducted in situ zircon U-Pb and Lu-Hf LA-ICP-MS dating and lithogeochemical study of the Meigou granodiorite, which is intruded in the south of the Tongyu mining district. It is inferred that the volcanic host rocks of the Tongyu Cu deposit belong to calc-alkaline island arc volcanic rocks, and the volcanic host rocks and the ore-forming materials share common material sources. During subduction of the Paleo-Qinling oceanic slab at around 472 Ma, high oxygen-fugacity aqueous fluid released by dehydration reaction of the subducting slab rose into the mantle wedge, leached Cu and other metal elements, and triggered partial melting of the mantle wedge. Associated with the ore-forming materials, the arc calc-alkaline magmas erupted and formed the Tongyu VHMS deposit. The weighted average zircon U-Pb age of the Meigou granodiorite is 439.3±3 Ma, suggesting its genesis is associated with the subduction event of the Paleo-Qinling oceanic plate around 440 Ma. In terms of the granitoid’s geochemical characteristics, the Mg#, Ni, and Cr contents are high. REE show strongly fractionated patterns with unobvious Eu anomalies. Sr contents are high while Y contents are low, resulting in high Sr/Y ratios. Two-stage zircon Hf model ages mostly range between 908 and 723 Ma, with eHf(t)>0. Therefore, we classify Meigou granodiorite as island arc granite with adakitic geochemical features. It was generated by interaction between mantle wedge and melt produced by partial melting of the subducted basaltic slab of the Paleo-Qinling Ocean. The Tongyu VHMS deposit was formed in the island arc tectonic setting during Ordovician-Silurian between 439.3±3 Ma and 472±11 Ma. The volcanic exhalation-sedimentation, which was contemporaneous with the submarine volcanics, produced the primary mineralization of the Tongyu Cu deposit. Afterward, the ore bodies and host rocks were reworked and overprinted intensively by structures corresponding with the overall collisional orogenic process of the Qinling Orogenic Belt during the Indosinian period. In contrast to classic VHMS deposits such as the Kuroko deposit in Japan, the Tongyu Cu deposit possesses the dual characteristics of island arc volcanic exhalation and sedimentation as well as structural reworking and overprinting. Therefore, the Tongyu VHMS Cu deposit is a volcanic exhalation and sedimentation-structural reworking and overprinting type deposit.

Simultaneous determinations of U–Pb dating and Hf isotopes on single zircon grains by excimer laser-ablation quadrupole and multiple-collector ICP-MS and petrologic and ore geochemical studies have been applied to the ore-bearing porphyry of the Jinduicheng porphyritic molybdenum deposit in East Qinling. Lithogeochemical data show that the porphyry is characteristic of high K2O, K-feldspar porphyritic calc-alkaline granitoids with 176Hf/177Hf=0.282020–0.282436 and eHf(t)=−23.7 to −8.9, which indicates its mixed origin involving a crustal and a mantle component. The weighted average U–Pb age from single zircon grains of the porphyry is 141.5±1.5 Ma. This age coincides with the oldest molybdenite Re-Os model age as dated by others, suggesting that the period of mineralization was almost simultaneous with the porphyry emplacement, or slightly later. The porphyry intrusion and the molybdenum mineralization occurred during the transition from compression to extension in the Jurassic – Cretaceous periods. The corresponding tectonic setting was the intracontinental orogenic and extension stage after collision and orogenesis between the Southern China plate and the Northern China plate. The Jinduicheng porphyry and the deposit's geochemical data indicate that the ore-forming material originated from a mixing of lower crust and upper mantle. When the molybdenum-enriched magma intruded into the upper crust along zones of structural weakness, ore-forming fluid generated by magma crystallization of the porphyry interacted with wall rock or mingled with meteoric water to form the deposit.