Except for extensive studies in core formation and volatile-element depletion processes using radiogenic Ag isotopes (i.e., the Pd–Ag chronometer), recent research has revealed that the mass fractionation of silver isotopes is in principle controlled by physicochemical processes (e.g., evaporation, diffusion, chemical exchange, etc.) during magmatic emplacement and hydrothermal alteration. As these geologic processes only produce very minor variations of δ109Ag from −0.5 to +1.1‰, more accurate and precise measurements are required. In this work, a robust linear relationship between instrumental mass discrimination of Ag and Pd isotopes was obtained at the Ag/Pd molar ratio of 1:20. In Au–Ag ore deposits, silver minerals have complex paragenetic relationships with other minerals (e.g., chalcopyrite, sphalerite, galena, pyrite, etc.). It is difficult to remove such abundant impurities completely because the other metals are tens to thousands of times richer than silver. Both quantitative evaluation of matrix effects and modification of chemical chromatography were carried out to deal with the problems. Isobaric inferences (e.g., 65Cu40Ar+ to 105Pd, 208Pb2+ to 104Pd, and 67Zn40Ar+ to 107Ag+) and space charge effects dramatically shift the measured δ109Ag values. The selection of alternative Pd isotope pairs is effective in eliminating spectral matrix effects so as to ensure accurate analysis under the largest possible ranges for metal impurities, which are Cu/Ag ≤ 50:1, Fe/Ag ≤ 600:1, Pb/Ag ≤ 10:1, and Zn/Ag ≤ 1:1, respectively. With the modified procedure, we reported silver isotope compositions (δ109Ag) in geological standard materials and typical Au–Ag ore deposit samples varying from −0.029 to +0.689 ‰ with external reproducibility of ±0.009–0.084 ‰. A systemic survey of δ109Ag (or ε109Ag) variations in rocks, ore deposits, and environmental materials in nature is discussed.

•The Hermyingyi and Taungphila granites (S Myanmar) emplaced at 70–69 Ma.•The granites belong to the A2-type.•The granites were derived from Paleoproterozoic continental crust.•A back-arc extension related to rollback of the Neo-Tethyan slab is favored.The Late Cretaceous to Paleogene granitoids occur widespread in the Sibumasu block within Myanmar (SE Asia), which show a close association with tin-tungsten mineralization. However, the precise timing, petrogenesis and tectonic significance of these granitoids are poorly constrained so far. In this study, we present a detailed study on geochronology, elemental and Sr-Nd-Hf isotopic geochemistry for the Hermyingyi and Taungphila granites in southern Myanmar, with the aim of determining their petrogenesis and tectonic implications. LA-ICP-MS U–Pb dating of zircon grains from the two granites yield ages of 69–70 Ma, indicating a Late Cretaceous magmatic event. These granitic rocks are weakly peraluminous and belong to the high-K calc-alkaline series. They are both characterized by high SiO2, K2O + Na2O, FeOT/(FeOT + MgO) and Ga/Al ratios and low Al2O3, CaO, MgO, P2O5 and TiO2 contents, enriched in Rb, Th, U and Y, but depleted in Ba, Sr, P, and Eu, suggesting an A-type granite affinity. Moreover, they display prominent tetrad REE patterns and non-CHARAC trace element behavior, which are common in late magmatic differentiates with strong hydrothermal interaction or deuteric alteration. The granites belong to A2-type and probably formed at a high temperature and anhydrous condition. They have zircon εHf(t) values from − 12.4 to − 10.0 and whole-rock εNd(t) values from − 11.3 to − 10.6, with Paleoproterozoic TDM2 ages (1741–1922 Ma) for both Hf and Nd isotopes. Geochemical and isotopic data suggest that these A-type granites were derived from partial melting of the Paleoproterozoic continental crust dominated by metaigneous rocks with tonalitic to granodioritic compositions, without significant input of mantle-derived magma and followed by subsequent fractional crystallization. By integrating all available data for the regional tectonic evolution in SE Asia and adjacent regions, we attribute the formation of the Late Cretaceous A-type granites to a back-arc extension in the hinterland behind the subduction zone, which is induced by the rollback of the flat Neo-Tethyan subducting slab around ca. 70 Ma.

•The Zijinshan epithermal Cu-Au and Luoboling porphyry Cu-Mo mineralizations are two separate systems.•Luoboling Cu-Mo bearing porphyry is dominantly derived from an enriched mantle source.•Zijinshan epithermal Cu-Au deposit shows a mixing source of the mantle-derived and crustal materials.•Ore-bearing magmas show higher fO2 and lower temperatures than the barren ones.The Zijinshan ore district occurs as one of the largest porphyry-epithermal Cu–Au–Mo ore systems in South China, including the giant Zijinshan epithermal Cu–Au deposit and the large Luoboling porphyry Cu–Mo deposit. The mineralization is intimately related to Late Mesozoic large-scale tectono-magmatic and hydrothermal events. The Cu–Au–Mo mineralization occurs around intermediate-felsic volcanic rocks and hypabyssal porphyry intrusions. In this study, we summarize previously available Re–Os isotopes, zircon U–Pb age and trace elements, and Sr–Nd–Pb isotope data, and present new Pb–S and Re–Os isotope data and zircon trace elements data for ore-related granitoids from the Zijinshan high-sulfidation epithermal Cu–Au deposit and the Luoboling porphyry Cu–Mo deposit, in an attempt to explore the relationship between the two ore systems for a better understanding of their geneses. The ore-bearing porphyritic dacite from the Zijinshan deposit shows a zircon U-Pb age of 108–106 Ma and has higher zircon Ce4+/Ce3+ ratios (92–1568, average 609) but lower Ti-in-zircon temperatures (588–753 °C, average 666 °C) when compared with the barren intrusions in the Zijinshan ore district. Relative to the Zijinshan porphyritic dacite, the ore-bearing granodiorite porphyry from the Luoboling deposit show a slightly younger zircon U–Pb age of 103 Ma, but has similar or even higher zircon Ce4+/Ce3+ ratios (213–2621, average 786) and similar Ti-in-zircon temperatures (595–752 °C, average 675 °C). These data suggest that the ore-bearing magmatic rocks crystallized from relatively oxidized and hydrous magmas. Combined with the high rhenium contents (78.6–451 ppm) of molybdenites, the Pb and S isotopic compositions of magmatic feldspars and sulfides suggest that the porphyry and ore-forming materials in the Luoboling Cu–Mo deposit mainly originated from an enriched mantle source. In contrast, the ore-bearing porphyritic dacite in the Zijinshan Cu–Au deposit might be derived from crustal materials mixing with the Cathaysia enriched mantle. The fact that the Zijinshan Cu–Au deposit and the Luoboling Cu–Mo deposit show different origin of ore-forming materials and slightly different metallogenic timing indicates that these two deposits may have been formed from two separate magmatic-hydrothermal systems. Crustal materials might provide the dominant Cu and Au in the Zijinshan epithermal deposit. Cu and Au show vertical zoning and different fertility because the gold transports at low oxygen fugacity and precipitates during the decreasing of temperature, pressure and changing of pH conditions. It is suggested that there is a large Cu–Mo potential for the deeper part of the Zijinshan epithermal Cu–Au deposit, where further deep drilling and exploration are encouraged.Download high-res image (108KB)Download full-size image

Significant isotope fractionation of silicon provides a powerful geochemical tracer for biological and physicochemical processes in terrestrial and marine environments. The exact mechanism involved in silicon uptake as part of the biological process is not well known. The silicon uptake in biological processes is investigated using silicate adsorption onto the N-methylglucamine functional group (sugarlike structure, abbreviated as L) of Amberlite IRA-743 resin as an analogue of the formation of silicate–sugar complexes in plants. This study provides new evidence that certain sugars can react readily with basic silicic acid to form sugar–silicate chelating complexes, and the equilibrium adsorption behavior of silicate can be well described by the Langmuir isotherm with a Gibbs free energy (ΔG) of −11.94 ± 0.21 kJ·mol–1 at 293 K. The adsorption kinetics corresponds well to a first-order kinetic model in which the adsorption rate constant ka of 1.25 × 10–4 s–1 and the desorption rate constant kd of 4.00 × 10–6 s–1 are obtained at 293 K. Both ka and kd increase with increasing temperature. The bonding configurations of silicate–sugar complexes imply the principal coordination complex of hexacoordinated silicon (silicon/L = 1:3) in the liquid phase and the dominant tetracoordinated silicon in the solid phase. Similar to those of many natural processes, the biological uptake via the sugar–silicate chelating complexes favors the preferential enrichment of light Si isotopes into solids, and the Rayleigh model controls the dynamic isotope fractionation with an estimated silicon isotope fractionation factor (i.e., αsolid–solution = ) of 0.9971. This study advanced the fundamental understanding of the dynamic isotope fractionation of silicon during silicon cycling from the lithosphere to the biosphere and hydrosphere in surficial processes.

•A simplified chemical purification procedure for Cu–Zn isotopes has been set up.•Interferences affecting Cu–Zn isotope analysis have been documented using high-resolution mass scans.•Cu and Zn have different ionization efficiencies in dry and wet plasma, and in different solution matrices.•A mechanism for Cu/Zn mass bias decoupling effect has been proposed.A revised chemical purification procedure for Cu–Zn isotopes is proposed in this study. The handing time and amounts of chemicals, such as H2O2 and HCl are largely saved with this modification. The ionization efficiencies of Cu and Zn are investigated in detail in wet and dry plasma with two kinds of skimmer cones. The ionization efficiency of Zn is depressed by HNO3 in the matrix, while HCl affects Cu and Zn ionization efficiency similarly. Potential polyatomic interferences with 68Zn+ and 70Zn+ are 40Ar14N2+ and 40Ar14N16O+ respectively, which are highly dependent on the amount of N2 in dry plasma and on the HNO3 concentration in wet plasma. Use of the DNS sample introduction device without N2 gas provides the best conditions for Cu–Zn isotope measurement. A Cu/Zn mass bias decoupling effect has been revealed in this study, and this effect appears to be dependent on the presence of HNO3 and N2 in ionizing plasma.

•The isobaric interferences in bromine isotope measurements were effectively solved.•An overall external reproducibility of ±0.1‰ for δ81Br has been achieved.•Counter cations effect was due to bromine loss and diffusive isotope fractionation.A new, feasible procedure for high-precision bromine isotope analysis using multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) is described. With a combination of HR mass resolution mode and accurate optimization of the Zoom Optics parameters (Focus Quad: −1.30; Zoom Quad: 0.00), the challenging problem of the isobaric interferences (40Ar38ArH+ and 40Ar40ArH+) in the measurement of bromine isotopes (79Br+, 81Br+) has been effectively solved. The external reproducibility of the measured 81Br/79Br ratios in the selected standard reference materials ranged from ±0.03‰ to ±0.14‰, which is superior to or equivalent to the best results from previous contributions. The effect of counter cations on the Br+ signal intensity and the instrumental-induced mass bias was evaluated as the loss of HBr aerosol in nebulizer and potential diffusive isotope fractionations.

The selective adsorption of metasilicate species by N-methyl D-glucamine functional groups in Amberlite IRA 743 resin was observed, which is clarified as the formation of sugar-metasilicate complexes and possible physical adsorptions. The existence of metasilicate matrices causes obvious discrepancies in the δ11B values of silicate materials. It opens the possibility for exploring relevant procedures for the separation/purification of silicon from geological samples.

•Three-column ion-exchange procedure was modified for boron separation/purification.•The PTIMS-Cs2BO2+-static double-collection method has been established.•The dominant effects that cause deviation on measured δ11B were discussed.In order to eliminate boron loss and potential isotopic fractionation during chemical pretreatment of natural samples with complex matrices, a three-column ion-exchange separation/purification procedure has been modified, which ensures more than 98% recovery of boron from each step for a wide range of sample matrices, and is applicable for boron isotope analysis by both TIMS and MC-ICP-MS. The PTIMS-Cs2BO2+-static double collection method was developed, ensuring simultaneous collection of 133Cs211B16O2+(m/z 309) and 133Cs210B16O2+ (m/z 308) ions in adjacent H3–H4 Faraday cups with typical zoom optics parameters (Focus Quad: 15 V, Dispersion Quad: −85 V). The external reproducibilities of the measured 11B/10B ratios of the NIST 951 boron standard solutions of 1000 ng, 100 ng and 10 ng of boron by PTIMS method are ±0.06‰, ±0.16‰ and ±0.25‰, respectively, which indicates excellent precision can be achieved for boron isotope measurement at nanogram level boron in natural samples. An on-peak zero blank correction procedure was employed to correct the residual boron signals effect in MC-ICP-MS, which gives consistent δ11B values with a mean of 39.66±0.35‰ for seawater in the whole range of boron content from 5 ppb to 200 ppb, ensuring accurate boron isotope analysis in few ppb boron. With the improved protocol, consistent results between TIMS and MC-ICP-MS data were obtained in typical geological materials within a wide span of δ11B values ranging from −25‰ to +40‰.

Because the variation in chlorine isotopic abundances of naturally occurring chlorine bearing substances is significant, the IUPAC Inorganic Chemistry Division, Commission on Isotopic Abundances and Atomic Weights (CIAAW-IUPAC) decided that the uncertainty of atomic weight of chlorine (Ar(Cl)) should be increased so that the implied range was related to terrestrial variability in 1999 (Coplen, T. B. Atomic weights of the elements 1999 (IUPAC Technical Report), Pure Appl. Chem.2001, 73(4), 667–683; and then, it emphasized that the standard atomic weights of ten elements including chlorine were not constants of nature but depend upon the physical, chemical, and nuclear history of the materials in 2009 (Wieser, M. E.; Coplen, T. B. Pure Appl. Chem.2011, 83(2), 359–396). According to the agreement by CIAAW that an atomic weight could be defined for one specified sample of terrestrial origin (Wieser, M. E.; Coplen, T. B. Pure Appl. Chem.2011, 83(2), 359–396), the absolute isotope ratios and atomic weight of chlorine in standard reference materials (NIST 975, NIST 975a, ISL 354) were accurately determined using the high-precision positive thermal ionization mass spectrometer (PTIMS)-Cs2Cl+-graphite method. After eliminating the weighing error caused from evaporation by designing a special weighing container and accurately determining the chlorine contents in two highly enriched Na37Cl and Na35Cl salts by the current constant coulometric titration, one series of gravimetric synthetic mixtures prepared from two highly enriched Na37Cl and Na35Cl salts was used to calibrate two thermal ionization mass spectrometers in two individual laboratories. The correction factors (i.e., K37/35 = R37/35meas/R37/35calc) were obtained from five cycles of iterative calculations on the basis of calculated and determined R(37Cl/35Cl) values in gravimetric synthetic mixtures. The absolute R(37Cl/35Cl) ratios for NIST SRM 975, NIST 975a, and ISL 354 by the precise calibrated isotopic composition measurements are 0.319876 ± 0.000067, 0.319768 ± 0.000187, and 0.319549 ± 0.000044, respectively. As a result, the atomic weights of chlorine in NIST 975, NIST 975a, and ISL 354 are derived as 35.45284(8), 35.45272(21), and 35.45252(2) individually, which are consistent with the issued values of 35.453(2) by IUPAC in 1999.

The isobaric ions interference induced from organic matter is one of the major problems for the measurement of boron isotopic composition by thermal ionization mass spectrometry (TIMS). However, the exact compounds (or structure) of organic matter are still unknown so far. The experimental characterization on organic matters in natural biocarbonate samples has been performed with Fourier transform infrared spectra (FTIR), Laser Raman and TG-DSC-MS in this work. From the results of infrared and Raman spectra, the organic matter with amide group is detected initially, and the thermal decomposition characteristic patterns of biocarbonate samples from TG-MS confirm that possible organic functional groups existing in the natural samples are amide group (i.e., CONH2), and amide acid group (i.e., COORNH2), which is in very good agreement with the results of FTIR and Laser Raman analysis. In the measurement of TIMS, two reagents, acetamide and EDTA that contain carbonyl group (CO) and amide group (NH2), are designed to add into NIST SRM 951 solution, and the results indicate that the presence of acylamino(CONH2) could bring negative shifts for 11B/10B ratios and lower δ11B value, and the ratios are gradually close to the real value when the organic matters in samples are consumed on heating filament in TIMS. Our experiments have shown that the acylamino group (CONH2) indeed exists in the biocarbonate samples and interferes in the measurement of boron isotopic composition by TIMS.Graphical abstractHighlights► We confirm the isobaric ion inference in the TIMS boron isotope measurement. ► We verify possible functional groups with FTIR, Laser Raman and TG-MS. ► We confirm the existence and influence of amide group in the TIMS measurement. ► The isobaric ion inference comes from the organic compounds with amide group in biocarbonates.

Tourmaline is an abundant boron-rich alumosilicate mineral with complex chemistry and rich in Fe, Mg, Al, Si elements. In this study, tourmaline samples were decomposed by alkali fusion method, and then the boron was separated and purified using three different procedures. It was found that both Fe3+ and Al3+ ions, rich in tourmaline samples seriously, which affected the accurate determination of boron concentration by Azomethine-H spectrophotometric method and also caused a loss of boron by specific adsorption when large amount of amorphous hydroxide precipitate formed in ion-exchange columns. The addition of small amount of EDTA can eliminate the influence, but brings serious isobaric interference on boron isotopic analysis by TIMS. Finally, a three-column ion-exchange procedure was established including the first mixed resin column, the peristaltic pump coupled boron specific resin column, and the second mixed resin column, which ensures the full recovery of boron (> 99%) from tourmaline samples with complex matrices. The PTIMS-Cs2BO2+-static double-collection method was established by selecting H3-H4 Faraday cups and optimizing parameters in Zoom Optics (Focus Quad: 15; Dispersion Quad: −85) in a Triton TI mass spectrometer. The determined average 11B/10B value of NIST SRM 951 standard boron solution was 4.05044±0.00012 (2σ, n = 8, 1 μg B), which was superior to the dynamic collection method in internal/external precision. A δ11B value of −0.3% for NIST SRM 951 through the same pretreatment procedure was obtained, indicating that there was no isotopic fractionation occurred during the extraction procedure. The comparison of boron isotopic compositions in natural samples by TIMS and MC-ICP-MS after the chemistry procedure indicated that δ11B values determined by the static PTIMS-Cs2BO2+ method were in good agreement with that by MC-ICP-MS.

The emission behavior of polyatomic ions Cs2Cl+ and Cs2BO2+ in the presence of various carbon materials (Graphite, Carbon, SWNTs, and Fullerenes) in the ionization source of thermal ionization mass spectrometry (TIMS) has been investigated. The emission capacity of various carbon materials are remarkably different as evidenced by the obvious discrepancy in signal intensity of polyatomic ions and accuracy/precision of boron and chlorine isotopic composition determined using Cs2Cl+-graphite-PTIMS/Cs2BO2+-graphite-PTIMS methods. Combined with morphology and microstructure properties of four selected carbon materials, it could be concluded that the emission behavior of the polyatomic ions strongly depends on the microstructure of the carbon materials used. A surface-induced collision mechanism for formation of such kinds of polyatomic ions in the ionization source of TIMS has been proposed based on the optimized configuration of Cs2BO2+ and Cs2Cl+ ions in the gas phase using a molecular dynamics method. The combination of the geometry of the selected carbon materials with the configuration of two polyatomic ions explains the structure effect of carbon materials on the emission behavior of polyatomic ions, where graphite samples with perfect parallels and equidistant layers ensure the capacity of emission to the maximum extent, and fullerenes worsen the emission of polyatomic ions by blocking their pathway.

At modern cold seeps, the anaerobic oxidation of methane (AOM) is the dominant pathway for methane consumption in marine sediments. AOM, which is mediated by a consortium of methane oxidizing archaea and sulfate reducing bacteria, is proposed to be responsible for authigenic carbonate formation. A methane-derived carbonate chimney was collected from the Shenhu area, northern South China Sea. The membrane lipids and their very low carbon isotopic compositions (−115‰ to −104‰) in the Shenhu chimney suggest the presence of an AOM process. Three specific archaeal and bacterial biomarkers were detected, including Ar, DAGE 1f, and monocyclic MDGD. Their strongly depleted δ13C values (−115‰ to −104‰), which are lower than those of the normal marine lipids in sediments, reveal biogenic methane as their origin. The carbonate deposits exhibiting a chimney structure indicate that a vigorous methane-rich fluid expulsion may have occurred at the seafloor. We propose that the decomposition of gas hydrates at depth is the likely cause of seepage and cold seep carbonate formation in the Shenhu area.

High precision zircon U-Pb dating indicates that main intrusive bodies (Tong’an, Niumiao, Huashan, Lisong), and a mafic microgranular enclave in the Huashan-Guposhan complex were formed at 160–163 Ma. The ɛHf(t) values of zircons from the Huashan granite vary from −2.8 to +0.3 and those from the Lisong granite vary from −2.3 to +0.3, which are obviously different with those values (+2.6 to +7.4) of the mafic enclaves from the Lisong granite. These Hf isotopic data indicate that the mafic enclaves and host granites were crystallized from different sources of magmas, providing evidence for mafic-felsic magma mixing processes. The highest ɛHf(t) value of zircons from the mafic enclaves is up to +7.4, indicating that the mafic magma was originated from a relatively depleted mantle source. Studies on regional geology and the contemporaneous mafic and alkaline rocks in this area indicate that the mafic magma was not originated from reworking of basaltic juvenile crust, but from partial melting of the mantle. However, it remains to be resolved whether the mafic magma was derived from partial melting of the asthenosphere or the lithospheric mantle. The Huashan granite and the Lisong granite were formed from hybrid magma of mantle-derived and crust-derived magmas, and the mafic enclaves are considered as remains of mantle-derived magma during mixing processes. The ɛHf(t) values of zircons from the Niumiao diorite vary from −1.1 to +2.1, and those from the Tong’an quartz monzonite vary from −1.7 to +1.7. These values are lower than those from the mafic enclaves, suggesting that the diorite and monzonite were formed from different source-derived magma with the mafic enclaves. The ɛHf(t) values for the Niumiao diorite and the Tong’an monzonite are only slightly higher than those for the Hushan granite and the Lisong granite. Abundant mafic enclaves also occur in the Niumiao diorite and in the Tong’an monzonite. Thus, we suggest that the Niumiao diorite and the Tong’an monzonite were probably also formed from the same hybrid magma as the granites but come through less degree of fractional crystallization and crustal contamination. The strong mantle-derived and crust-derived magma mixing caused by an intense crustal extension and thinning in the Mid-Late Jurassic may be the major mechanism for generating the diorites and granites in southeastern Hunan and northeastern Guangxi belt in South China.

The Shenhu area is one of the promise target areas for marine gas hydrate exploration in the northern margin of the South China Sea. Pore water samples were collected from two piston cores (8.75 and 8.52 m) in site HS-A and site HS-B in the Shenhu area, and their major anion and cation contents and trace element contents have been analyzed in this study. Cl− concentrations in pore waters are similar to the seawater value and no systematic change along depth profiles has been found for the Cl− content in both sites. In site HS-A, the SO42− contents show a limited range in pore waters from 0 to 3 m depths, but a dramatic decrease is documented in depth below 3 m. Other elements such as Ca2+, Mg2+ and Sr2+ show similar variation patterns as the SO42−, i.e., no variation in 0–3 m, but large decrease in depth below 3 m. In site HS-B, both the SO4 and Ca2+, Mg2+ and Sr2+ display a decrease pattern along the depth profile, but in 0–3 m the variation is less significant than those in depth below 3 m. In both sites HS-A and HS-B, I contents show a dramatic increase along depth profiles. Calculations show that the SMI depths are very shallow (10 and 11 m) in both sites, and the sulfate flux and I flux are very high. These geochemical characteristics and anomalies at Shenhu are quite similar to those found in other gas hydrate locations in the world, and a genetic link is suggested to be related to the gas hydrate occurrence at depths in the study area. In summary, we suggest that combined geochemical parameters in shallow sediment pore waters are useful indicators to indicate the gas hydrate occurrence at depths.

The emission behavior of polyatomic ions in the ionization source of thermal ionization mass spectrometry (TIMS) was investigated. The results suggest that the presence of a graphite promoter plays a key role for the formation and stable emission of polyatomic ions, such as M2X+, M2BO2+, Cs2NO2+, and Cs2CNO+. Our data further implied that the intensity of M2X+ and M2BO2+ increases and the emission temperature decreases with increasing cationic and anionic radius. During the boron isotopic measurement using the Cs2BO2+−graphite−PTIMS method, the isobaric interference ion Cs2CNO+ cannot be transformed from nitrate or organic compounds containing an amide group but can be induced by the existence of trace amounts of boron because of its special electron-deficiency property (B3+). Characterization on the planar crystalline structure of various graphite samples with SEM, TEM, and Raman spectroscopy confirmed the relationship of the emission capacity of polyatomic ions and the crystal microstructure of graphite and provides direct evidence that graphite with a perfect parallel and equidistant layer orientation shows a beneficial effect on the emission of polyatomic ions in TIMS. The mechanism study on the formation of polyatomic ions opens the possibility to establish high precision methods for isotopic composition analysis of more nonmetal elements with the TIMS technique.

The Middle–Lower Yangtze River metallogenic belt (MLYRMB), extending from Daye in Hubei Province in the west to Zhenjiang in Jiangsu Province in the east, hosts a number of large polymetallic (Cu–Au–Mo, Fe, Zn, Pb, and Ag) deposits and constitutes one of the most important metallogenic belts in China. The Cu–Au–Mo deposits in the Jiurui district are an important component of the MLYRMB. In this study we carried out precise and detailed zircon U–Pb dating for all types of magmatic rocks from the Wushan ore deposit in the Jiurui district. Three samples of Cu–Au–Mo-related porphyries from different ore belts at Wushan were analyzed and yielded zircon U–Pb ages of 148.0 ± 1.0 Ma, 145.4 ± 0.9 Ma and 147.3 ± 0.9 Ma, respectively. A series of dykes were emplaced immediately following the Cu–Au–Mo-related porphyries at Wushan. A dark-colored basic dyke which intruded into the granodiorite porphyry at Wujia gold deposit near Wushan was dated at 144.5 ± 1.2 Ma. Two lamprophyre dykes taken from the north ore belt at Wushan underground mining stops were dated at 143.6 ± 0.9 Ma and 144.3 ± 0.9 Ma, respectively. A late-stage dyke which was also taken from the Wushan north ore belt yielded an age of 142.6 ± 1.0 Ma and might represent the end of magmatism in the Wushan ore deposit. These new geochronological data demonstrate that the time range of magmatism in the Wushan ore deposit is approximately between 148 Ma and 143 Ma, showing that the magmatic activity at Wushan was rapid and intensive. The ages of Cu–Au–Mo-related porphyries from other areas in the Jiurui district, such as the Dongleiwan, Yangjishan and Chengmenba ore deposits, were also measured and yielded zircon U–Pb ages of 141.5 ± 1.7 Ma, 143.4 ± 1.4 Ma and 146.6 ± 1.0 Ma, respectively. Combined with those previously reported zircon U–Pb age results from the Jiurui district, the present age data set demonstrates that extensive magmatism in the Jiurui district was coeval and intensive, marked by a magmatic activity in the age range of 148 to 138 Ma and peaked between 148 Ma and 142 Ma. According to the statistics of all those precise zircon U–Pb ages, the Cu–Au–Mo-related porphyries in the Edong and Tongling districts in the MLYRMB show similar ages, and they have a slightly younger peak age and a longer duration than that of the Jiurui district. The geographic shape of the MLYRMB in the Cretaceous shows an arcuate structure, the Jiurui district is located at the transitional point of the arcuate structure and the Edong and Tongling districts are situated on both sides of the arcuate structure. Considering that the Jiurui district has a slightly older peak age and a shorter duration of magmatic activity than that in the Edong and Tongling districts, it seems that the arcuate structure of the MLYRMB played an important role in the formation of these Cu–Au–Mo-related porphyries. Consequently, we suggest that the genesis of the Late Mesozoic magmatic rocks along the MLYRMB may have been due to a tectonic activity developed from southeast to northwest, which probably has a close relationship with the subduction of the paleo-Pacific plate beneath the Eurasian plate in Mesozoic times.Download full-size imageResearch highlights► The Cu–Au related magmatic rocks at Jiurui ore districts are dated at 148–138 Ma and peaked at 148–142 Ma. ► The genesis of the Late Mesozoic magmatic rocks along the Middle–Lower Yangtze River metallogenic belt has a close relationship with the subduction of the paleo-Pacific plate. ► The Late Mesozoic magmatism in the Middle–Lower Yangtze River metallogenic belt was affected by the arcuate structure.

Direct radiometric dating of the Lower/Middle Permian epochs has not been well accomplished. Shales and bedded cherts of the geologically well-documented Middle Permian Gufeng Formation are exposed in the Chaohu area, Anhui province, South China. Through detailed field examination and mapping of the Gufeng stratigraphic section, we found at least four volcanic ash beds within the basal shale strata. This new discovery indicates the existence of prominent volcanic activity during Gufeng sedimentation and provides the opportunity to precisely date the age of the Middle Permian. Zircon grains separated from two near-basal horizon yield LA‐ICP‐MS U–Pb ages of 272.0 ± 5.5 Ma (MSWD = 2.6) and 271.5 ± 3.3 Ma (MSWD = 1.7). As the first precise isotopic age (272 Ma) of the Middle Permian Gufeng Formation in South China, our data offer precise geochronological constraints for the division and correlation of Middle Permian not only in South China but also worldwide.Download full-size imageHighlights► Volcanic ash beds are found in the basal Gufeng Formation of the Middle Permian in South China. ► Zircons from two volcanic ash beds yield precise ages of 272.0 ± 5.5 Ma and 271.5 ± 3.3 Ma. ► The age of 272 Ma may represent the first precise date for the Lower/Middle Permian boundary.

•The Dawan deposit is a hydrothermal-reworked sedimentary hosted uranium deposit.•Sulfur in ore-forming fluids was derived from diagenetic sulfur in the host strata.•Uranium in ores was derived from the U-rich meta-sedimentary strata.•Ore-forming fluid was derived from deeply circulated, oxidized, meteoric water.•Exploration should focus on organic- and pyrite-rich sedimentary strata with faults.The Dawan deposit in southern Hunan Province is one of the large-scale metasedimentary rock-hosted uranium deposits in China. Uranium orebodies occur mainly as big vein type and disseminated veinlet type, and are chiefly hosted within the Cambrian metasedimentary rocks, but some small ore veins can extend into the Jurassic Jinjiling granites. The dominant uranium ore minerals include pitchblende and coffinite. Coffinite often replaces and rims the pre-existing pyrite, and pitchblende occurs as veinlets and disseminated grains filled the fracture zones of metasedimentary rocks. It is suggested that the coffinite was most likely formed by initial reduction of U6 + to U4 + by pyrite from an oxidized Si-rich fluid at an early mineralization stage, whereas the pitchblende may have formed at a later stage in a relatively reduced and Si-poor fluid. Chlorite alteration is widespread and is inter-grown with pitchblende in ores. Electron microprobe analysis reveals that the chlorite belongs to Mg-rich clinochlore, which is different to the Fe-rich chlorite in most granite-hosted and volcanic rock-hosted uranium deposits in South China. The hydrothermal alteration temperatures were estimated to be 189–227 °C according to chlorite geothermometer. The ores show similar trace element characteristics to those of metasedimentary wall-rocks, but different from those of the Jinjiling granites. Negative Ce anomalies of the ores indicate an oxidized hydrothermal fluid, which was most likely derived from circulated meteoric water. The εNd(t) values of the ores are lower than those of the Jinjiling granites, but fall into the range of the basement strata. Sulfur isotopic compositions of hydrothermal pyrites vary from − 9.5‰ to − 7.7‰, similar to those from the wall-rocks, which implies that the sulfur in ore-forming fluids was mainly derived from diagenetic sulfur in the sedimentary strata. Pyrite in ores shows highly radiogenic lead isotopic compositions (206Pb/204Pb = 19.684–89.234 and 207Pb/204Pb = 15.722–19.683). In a plot of 206Pb/204Pb vs. 207Pb/204Pb, the data show a good linear array and yield an isochron age of 479 ± 69 Ma (MSWD = 1.6), which is much older than the granites but relatively close to the age of the host metasedimentary strata, indicating that the uranium source was probably derived from the wall-rock strata. It is suggested that the Dawan deposit is a hydrothermally reworked uranium deposit (referred to as the carbonaceous-siliceous-pelitic rock type by many Chinese geologists) with a close relationship with the host metasedimentary rocks. The Dawan deposit has no genetic relationship to the Jinjiling granite, contrary to what was previously suggested, and therefore the exploration in this area should focus on the conjunct occurrence of the Cambrian metasedimentary rocks rich in organic carbon and pyrite and the tectonic faulting which fractured and brecciated the strata.

•The lamprophyres were from partial melting of the local enriched lithospheric mantle.•Mesozoic lithospheric mantle was a phlogopite- and/or amphibole-bearing lherzolite.•The mantle was metasomatized by slab-derived hydrous fluids of Paleo-Pacific plate.•Continuous modification transformed old cratonic mantle to Mesozoic enriched mantle.Mesozoic lamprophyres are widely present in gold province in the Jiaodong Peninsula. In this study, we analyzed major and trace elements and Sr–Nd–Pb isotopic compositions of lamprophyres from the Linglong and Penglai Au-ore districts in the Jiaodong Peninsula, in an attempt to better understand Mesozoic lithospheric evolution beneath the eastern North China Craton. These lamprophyre dikes are calc-alkaline in nature, and are characterized by low concentrations of SiO2, TiO2 and total Fe2O3, high concentrations of MgO, Mg# and compatible element, enriched in LREE and LILE but variably depleted in HFSE. They display initial 87Sr/86Sr ratios of 0.709134–0.710314, εNd(t) values of − 13.2 to − 18.3, 206Pb/204Pb of 17.364–17.645, 207Pb/204Pb of 15.513–15.571 and 208Pb/204Pb of 37.995–38.374. Interpretation of elemental and isotopic data suggests that the Linglong and Penglai lamprophyres were derived from partial melting of a phlogopite- and/or amphibole-bearing lherzolite in the spinel–garnet transition zone. The parental magma might have experienced fractionation of olivine and clinopyroxene, and minor crustal materials were incorporated during ascent of these mafic magmas. Before ~ 120 Ma of emplacement of these calc-alkaline lamprophyres, the ancient lithospheric mantle was variably metasomatized by hydrous fluids rather than melts from subducted/foundered continental crust. It is proposed that continuous modification by slab-derived hydrous fluids from the Paleo-Pacific plate converted the old cratonic lithospheric mantle to Mesozoic enriched lithospheric mantle. Geodynamic force for generation of these lamprophyres may be related to large scale lithospheric thinning coupled with upwelling of the asthenosphere beneath the North China Craton. Continental arc-rifting related to the Paleo-Pacific plate subduction is favored as a geodynamic force for the cratonic lithosphere detachment.Download full-size image

The Linglong granite is one of the most important Mesozoic plutons in the Shandong Peninsula, eastern China, and its petrogenesis has long been controversial, particularly with regard to the nature of source region and geodynamic setting. Our new precise zircon U–Pb dating results reveal that the Linglong granite was emplaced in the Late Jurassic (157–160 Ma). In addition, abundant inherited zircons are identified in the granite with four groups of age peaked at ~ 208, ~ 750, ~ 1800 and ~ 2450 Ma. Geochemical studies indicate that the Linglong granite is weakly peraluminous I–type granite, and is characterized by high SiO2, Sr and La, but low MgO, Y and Yb contents, strongly fractionated REE pattern and high Sr/Y and La/Yb ratios. It also exhibits high initial 87Sr/86Sr ratios (0.7097 to 0.7125), low εNd(t) (− 17.7 to − 20.3) and variable zircon εHf(t) (− 22.2 to − 8.7) values. Calculation of the zircon saturation temperature (TZr) reveals that the magma temperatures are 760 ± 20 °C, and the lowest TZr value of 740 °C may be close to initial magma temperature of this inheritance-rich rock. Interpretation of the elemental and isotopic data suggests that the Linglong granite has some affinities with the adakite, and was most likely derived from partial melting of thickened lower crust without any significant contribution of mantle components. The presence of a large number of inherited zircons and variable Sr–Nd–Hf isotopic compositions reveal that the Linglong granite probably has multiple sources consisting of the lower crust of both South China Block and North China Block, as well as the collision-related alkaline rocks and UHP metamorphic rocks. The continental arc-rifting related to the Izanagi plate subduction was the most likely geodynamic force for formation of the Jurassic Linglong adakatic granite in the Shandong Peninsula.Highlights► The Linglong granite was intruded at 157–160 Ma. ► The Linglong granite shows geochemical affinity with adakite. ► Abundant inherited zircons show four U–Pb age peaks (208, 750, 1800 and 2450 Ma). ► Multiple sources include lower crust of SCB and NCB, collision-related alkaline rocks, UHP metamorphic rocks.

Black shales occur widely in the Lower Cambrian and Neoproterozoic strata on the Yangtze Platform, South China. In this study, Lower Cambrian black shales from Xiuning section and Late Neoproterozoic black shales from Weng’an section were studied and Pb isotopic compositions were analyzed following a stepwise acid-leaching technique. The 206Pb/204Pb ratios in both sections show large variations, from 18.906 to 43.737 in the Weng’an section and from 24.811 to 38.110 in the Xiuning section. In contrast, the ranges for 207Pb/204Pb and 208Pb/204Pb values in both sections are relatively smaller from 15.649 to 17.126 and 37.744–38.199 in the Weng’an section, and from 16.034 to 16.783 and 38.602–39.391 in the Xiuning section, respectively. These data yielded two Pb isotope isochron ages of 536±39 and 572±36 Ma, respectively. These ages well accord with other published data and we suggest that they represent the depositional ages for the Lower Cambrian Hetang Formation and the upper Neoproterozoic Doushantuo Formation in South China.

•The Jurassic syenite–granodiorites–dacite in South China related to an Andean-type subduction•Syenite derived from partial melting of lithosphere mantle with minor crustal materials•Granodiorite and dacite originated from mafic lower crust or subduction-modified mantle sources.In situ zircon U–Pb ages and Hf isotope data, major and trace elements and Sr–Nd–Pb isotopic compositions are reported for coeval syenite–granodiorites–dacite association in South China. The shoshonitic syenites are characterized by high K2O contents (5.9–6.1 wt.%) and K2O/Na2O ratios (1.1–1.2), negative Eu anomalies (Eu/Eu* = 0.65 to 0.77), enrichments of Rb, K, Nb, Ta, Zr and Hf, but depletion of Sr, P and Ti. The adakitic granodiorite and granodiorite porphyry intrusions are characterized by high Al2O3 contents (15.0–16.8 wt.%), enrichment in light rare earth elements (LREEs), strongly fractionated LREEs (light rare earth elements) to HREEs (heavy rare earth elements), high Sr (438–629 ppm), Sr/Y (29.2–53.6), and low Y (11.7–16.8 ppm) and HREE contents (e.g., Yb = 1.29–1.64 ppm). The calc-alkaline dacites are characterized by LREE enrichment, absence of negative Eu anomalies, and enrichment of LILEs such as Rb, Ba, Th, U and Pb, and depletion of HFSEs such as Nb, Ta, P and Ti.Geochemical and Sr–Nd–Hf isotopic compositions of the syenites suggest that the shoshonitic magmas were differentiated from parental shoshonitic melts by fractional crystallization of olivine, clinopyroxene and feldspar. The parent magmas may have originated from partial melting of the lithospheric mantle with small amount contribution from crustal materials. The adakitic granodiorite and granodiorite porphyry have Sr–Nd–Pb isotopic compositions that are comparable to that of the mafic lower crust. They have low Mg# and MgO, Ni and Cr contents, abundant inherited zircons, low εNd(t) and εHf(t) values as well as old whole-rock Nd and zircon Hf model ages. These granodiorites were likely generated by partial melting of Triassic underplated mafic lower crust. The Hf isotopic compositions of the dacites are relatively more depleted than the Cathaysia enriched mantle, suggesting those magmas were derived from the partial melting of subduction-modified mantle sources. The coeval shoshonitic, high-K calc-alkaline and calc-alkaline rocks in Middle to Late Jurassic appear to be associated with an Andean-type subduction. This subduction could have resulted in the upwelling of the asthenosphere beneath the Cathaysia Block, which induced partial melting of the mantle as well as the mafic lower crust, and formed an arc regime in the coastal South China during Middle to Late Jurassic.Download high-res image (254KB)Download full-size image

The Shi-Hang zone is an important NE trending Mesozoic magmatic belt composed of granites with relative high εNd(t) values and young TDM model ages in South China. However, the petrogenesis and the tectonic environment for the Shi-Hang zone magmatic rocks remain controversial. We report here mineral chemistry, geochemical and Sr–Nd–Hf isotopic data for the Cailing and Furong granites and mafic microgranular enclaves (MMEs) from the Qitianling granite batholith in southern Hunan province, South China. The Qitianling granite batholith is a multi-staged composite pluton with three phases (Cailing, Furong, and Huangtangling) according to their ages and petrography. The Cailing (163–160 Ma) and Furong (157–153 Ma) phases are mainly composed of porphyritic amphibole–biotite monzogranite, and they share similar geochemical and isotopic characteristics. Both of them show similar SiO2 contents from 66.50 to 70.28%, and metaluminous A/CNK values of 0.80 to 0.98. The granites are characterized by high contents of large ion lithosphile elements (LILE) such as Rb, Th, U, Pb; high field strength elements (HFSE) such as Nb, Ta, Zr, Hf; and Zr + Nb + Ce + Y contents > 350 ppm, and high 10,000 ∗ Ga/Al ratios > 2.6. Chondrite-normalized REE patterns show relative enrichment of light rare earth elements (LREEs) and significant negative Eu anomalies. Mineralogical and geochemical features suggest that the Cailing and Furong granites are A-type, which can be further classified as A2 subtype. They have relatively lower (87Sr/86Sr)i ratios (0.7091–0.7132), higher εNd(t) values (− 5.5 to − 7.6) and younger Nd isotopic model ages (1.48–1.56 Ga) than those common S-type granites in South China. Zircon εHf(t) values vary from − 8.1 to − 3.7. The MMEs in the Cailing phase show similar trace element and Sr–Nd isotopic characteristics with the host granites. But zircons from the MMEs show different εHf(t) values (− 6.4–+ 2.6) with those from the host granites (− 8.1 to − 3.7). This indicates that the MMEs and host granites were crystallized from different sources of magmas, providing direct evidence for mafic–felsic magma mixing processes. The isotope data indicate that the Cailing and Furong granites from the Qitianling batholith were derived from a hybrid magma consisting of about 80% felsic magma derived from old crust and about 20% mantle-derived mafic magma. The strong magma mixing at about 160–155 Ma caused by intra-arc rifting or back arc extension related to subduction of the Paleo-Pacific plate, is favored to explain the petrogenesis of the Cailing and Furong granites, as well as the Shi-Hang zone.Download full-size imageHighlights► The Cailing and Furong granites from the Qitianling batholith in south China belong to A-type granite. ► Geochemical and isotopic studies indicate a mafic-felsic magma mixing process. ► An intra-arc rifting or back arc extension setting is proposed for the extensive magmatism.

The Shi-Hang zone is an important NE trending Mesozoic magmatic belt composed of granites with relative high εNd(t) values and young TDM model ages in South China. However, the petrogenesis and the tectonic environment for the Shi-Hang zone magmatic rocks remain controversial. We report here mineral chemistry, geochemical and Sr–Nd–Hf isotopic data for the Cailing and Furong granites and mafic microgranular enclaves (MMEs) from the Qitianling granite batholith in southern Hunan province, South China. The Qitianling granite batholith is a multi-staged composite pluton with three phases (Cailing, Furong, and Huangtangling) according to their ages and petrography. The Cailing (163–160 Ma) and Furong (157–153 Ma) phases are mainly composed of porphyritic amphibole–biotite monzogranite, and they share similar geochemical and isotopic characteristics. Both of them show similar SiO2 contents from 66.50 to 70.28%, and metaluminous A/CNK values of 0.80 to 0.98. The granites are characterized by high contents of large ion lithosphile elements (LILE) such as Rb, Th, U, Pb; high field strength elements (HFSE) such as Nb, Ta, Zr, Hf; and Zr + Nb + Ce + Y contents > 350 ppm, and high 10,000 ∗ Ga/Al ratios > 2.6. Chondrite-normalized REE patterns show relative enrichment of light rare earth elements (LREEs) and significant negative Eu anomalies. Mineralogical and geochemical features suggest that the Cailing and Furong granites are A-type, which can be further classified as A2 subtype. They have relatively lower (87Sr/86Sr)i ratios (0.7091–0.7132), higher εNd(t) values (− 5.5 to − 7.6) and younger Nd isotopic model ages (1.48–1.56 Ga) than those common S-type granites in South China. Zircon εHf(t) values vary from − 8.1 to − 3.7. The MMEs in the Cailing phase show similar trace element and Sr–Nd isotopic characteristics with the host granites. But zircons from the MMEs show different εHf(t) values (− 6.4–+ 2.6) with those from the host granites (− 8.1 to − 3.7). This indicates that the MMEs and host granites were crystallized from different sources of magmas, providing direct evidence for mafic–felsic magma mixing processes. The isotope data indicate that the Cailing and Furong granites from the Qitianling batholith were derived from a hybrid magma consisting of about 80% felsic magma derived from old crust and about 20% mantle-derived mafic magma. The strong magma mixing at about 160–155 Ma caused by intra-arc rifting or back arc extension related to subduction of the Paleo-Pacific plate, is favored to explain the petrogenesis of the Cailing and Furong granites, as well as the Shi-Hang zone.Download full-size imageHighlights► The Cailing and Furong granites from the Qitianling batholith in south China belong to A-type granite. ► Geochemical and isotopic studies indicate a mafic-felsic magma mixing process. ► An intra-arc rifting or back arc extension setting is proposed for the extensive magmatism.

We investigated the boron isotopic composition in loess–paleosol sequences in five different profiles in the Chinese Loess Plateau. Three possible boron sources are identified: atmospheric input, carbonates, and weathered silicate rocks. Variations of [Sr], [B], δ11B and the magnetic susceptibility correlate well with the pedogenetic intensity in three out of the five studied profiles, where pedogenesis under a cold–dry climate indicates lower δ11B, lower [B], lower magnetic susceptibility and higher [Sr] values. Exceptions to the variations between the δ11B and other known proxies were observed in arenaceous soils and the Red Clay sequence: the former suggested that vertical redistribution probably occurred with the boron migration, and the latter indicated an unknown mechanism of susceptibility enhancement. A better correlation between the δ11B and magnetic susceptibility and the quantitative estimation of boron budget from each source confirms the influence of paleoenvironmental changes on boron geochemical cycle. Significant positive correlations in Sr/Ca vs. B/Ca and Mg/Ca vs. B/Ca reflect consistent enrichment behavior of those mobile elements into calcium carbonate. The preliminary results imply that boron isotopic compositions in soils can be a potential geochemical proxy to reconstruct the paleoenvironmental changes in loess–paleosol sequences.

A detailed study utilizing zircon U–Pb dating, major and trace element geochemistry, and Sr–Nd–Hf isotope geochemistry has been carried out for the Caijiang granite in Jiangxi Province and the Gaoxi granite in Fujian Province, South China. The new data indicate that the Caijiang and Gaoxi granites are Triassic (228–230 Ma) and have the petrographic and geochemical characteristics of A-type granites. In both granites, biotite occurs along the boundary of euhedral plagioclase and quartz, which implies that the primary magma could have been anhydrous. The two granites show high contents of total alkalis (Na2O + K2O = 7.81–12.15%), high field strength elements (e.g. Zr = 240–458 ppm, Y = 16.8–38.0 ppm, Nb = 13.5–33.8 ppm and Zr + Nb + Ce + Y = 382–604 ppm) and rare earth elements (total REE = 211–373 ppm) as well as high Ga/Al ratios (10000 × Ga/Al = 2.41–3.53). The lowest magmatic temperatures estimated from zircon saturation thermometer were 800–840 °C for the Caijiang granite and 820–850 °C for the Gaoxi granite, respectively. The Caijiang granite has relatively high (87Sr/86Sr)i ratios of 0.71288 to 0.72009, low εNd(t) values of − 9.9 to − 9.3, and low zircon εHf(t) values (peak value of − 7.5). Whole-rock Nd isotopic model ages and zircon Hf isotopic model ages mostly vary from 1.65 Ga to 1.80 Ga. The Gaoxi granite has also high (87Sr/86Sr)i ratios of 0.71252 to 0.71356, low εNd(t) value of − 13.8 and low zircon εHf(t) values (peak value of − 12.0). Whole-rock Nd isotopic model ages and zircon Hf isotopic model ages mostly vary from 1.95 Ga to 2.10 Ga. According to these data, we suggest that the two granites might have been derived from partial melting of Precambrian crustal rocks that had been granulitized during an earlier thermal event. Our study of the Caijiang and Gaoxi granites, together with previous studies on two Triassic alkaline syenites (Tieshan and Yangfang) in Fujian Province and one A-type granite (Wengshan) in Zhejiang Province in South China, indicate a wide transtensional tectonic environment in the Cathaysia Block that lasted at least from 254 Ma to 225 Ma. Combined with extant data for the Indosinian granites and tectonic evolution in South China, we suggest that the formation of A-type granites was related to the local NE-trending extensional faults probably caused by collision between the South China Block and the Indochina Block or the North China Block.Highlights► The Caijiang and Gaoxi granites in South China were emplaced at 228–230 Ma. ► The petrology and geochemistry of the granites reveal an A-type affinity. ► The granites were derived from partial melting of Precambrian crustal rocks. ► A wide transtensional tectonic environment occurred in Cathaysia Block at Triassic.

•Dahutang deposit is a new discovered largest tungsten deposit in the world.•The granites at Duhutang are highly fractionated S-type granites.•The granites were originated from two episodes of partial melting of different protoliths.•The G1 granite intruded during the first stage of 144 Ma.•The G2–G4 granites intruded during the second stage of 130–134 Ma.The Dahutang deposit is a newly discovered tungsten deposit, which is within the largest ones in the world with an estimated WO3 reserve of 2 million tones. W-mineralization is considered to be related with the Late Mesozoic granites in the district. However, the precise emplacement ages, sources of these granites, and their relationship with mineralization are not well understood. In this study, four mineralization-related granite bodies (G1 to G4) were identified in the Dahutang mining area, including the porphyritic-like two-mica granite (G1) (the size of its phenocrysts is from 0.2 × 0.2 cm2 to 0.7 × 0.3 cm2), middle- to fine-grained muscovite granite (G2), porphyritic two-mica granite (G3) (the size of its phenocrysts is from 0.3 × 0.2 cm2 to 0.9 × 0.6 cm2), and fine-grained two-mica granite (G4). LA-ICP-MS U–Pb dating of zircon grains from these four granite bodies yields emplacement ages of 144.0 ± 0.6 Ma, 133.7 ± 0.5 Ma, 130.3 ± 1.1 Ma and 130.7 ± 1.1 Ma, respectively. Granites contain quartz, K-feldspar and plagioclase as the principal phases, accompanied by muscovite, minor biotite and accessory minerals. Geochemically, the granites are strongly peraluminous, have high contents of alkalis, high Ga/Al ratios, enrichment in LILEs (such as Rb) and depletion in HFSEs (such as Zr, Nb, Ti). The granites formed at relatively low temperatures (679 °C to 760 °C) according to zircon saturation temperatures. Geochemical fractionation trends recorded by whole rocks and minerals permit to distinguish and model the two fractional crystallization series G1 and G2–G4. Fractional crystallization of orthoclase and albite in G1 and G4, and orthoclase and oligoclase in G2 and G3 was the principal process of magmatic differentiation that controlled Rb, Sr and Ba concentrations, whereas rare earth elements were fractionated by accessory minerals, such as apatite, zircon and monazite. The geochemical data suggest that the rocks are highly fractionated S-type granites. The granites show bulk rock εNd(t) values in the range of − 9.37 to − 5.92 and zircon εHf(t) values from − 8.44 to − 2.13, with late Mesoproterozoic TDMC ages for both Nd and Hf isotopes. Geochemical and isotopic data suggest that these highly fractionated S-type granites G1 and G2–G4 were originated from two episodes of partial melting of different protoliths which have analogous components of metamorphosed pelitic rocks from the Neoproterozoic Shuangqiaoshan Group, which are enriched in tungsten. Extreme fractional crystallization resulted in further enrichment of tungsten in the evolved granitic magma. The new presented data together with previously published data suggest that the Dahutang granitic complex was likely to be formed during lithospheric thinning and asthenospheric upwelling process in Eastern China.

The Taoshan uranium ore district is one of the most important granite-hosted uranium producers in South China. The Taoshan granitic complex can be petrographically classified into several units of Caijiang, Huangpi, Daguzhai, and Luobuli, but the uranium deposits only occur within the Daguzhai granite unit. LA-ICP-MS zircon U–Pb dating indicates that both the Daguzhai granite and the Huangpi granite were emplaced at 154 ± 2 Ma. U contents (average 19.5 ppm) of the Daguzhai granite are higher than those of the Huangpi granite (average 7.3 ppm). The Daguzhai granite is composed of medium-grained two-mica granite, and the Huangpi granite is composed of medium- to coarse-grained biotite granite. These two granites show obvious differences in major element, trace element and isotopic geochemical characteristics. Compared to the Huangpi granite, the Daguzhai granite has higher A/CNK ratios, higher P2O5 contents and lower CaO contents, and is more enriched in Rb, Ba, U, and more depleted in Sr, Eu and Ti. The εNd(t) values of the Daguzhai granite vary from − 12.2 to − 11.0 with two-stage model ages of 1.84 to 1.93 Ga. The εNd(t) values of the Huangpi granite are slightly higher (− 9.7 to − 8.6) and the Nd model ages are younger (1.64 to 1.73 Ga). Comparative studies imply that the Daguzhai granite belongs to typical S-type and might be derived from the partial melting of parametamorphic rocks from metamorphic basement of the Zhoutan Group. In contrast, the Huangpi granite belongs to fractioned I-type, which might be derived from the partial melting of a mixture of ortho- and para-metamorphic rocks of the Zhoutan Group. These different magma sources might explain the different U contents of the two granites. In general, the source factor is an important controlling factor for the genesis of U-bearing granites in South China. U-bearing granites in South China show some common mineralogical and geochemical characteristics, which can be used to guide further exploration of granite-hosted U deposits.Research highlights► In the Taoshan U-ore district, the Daguzhai U-bearing granite and Huangpi U-barren granite are coeval at 154 ± 2 Ma. ► The Daguzhai and Huangpi granites show different major and trace element geochemical and Sr–Nd isotopic characteristics. ► The Daguzhai granite belongs to peraluminous S-type and the Huangpi belongs to fractioned I-type. ► The different magma sources controlled the different U contents in the two granites. ► Searching for granites with similar characteristics as Daguzhai is helpful for further exploration of uranium deposits in South China.

•Scheelite and wolframite are found in the Matou porphyry-type deposit.•The granodiorite porphyry was emplaced at 139.5 ± 1.5 Ma.•Detrital zircons of Archean age (2543 ± 29 Ma) have been found in the porphyry.•A high proportion of lower crust materials are involved in the Matou petrogenesis.•A delamination model is proposed for the petrogenesis in the MLYMB.Porphyry and skarn Cu–Fe–Au–Mo deposits are widespread in the Middle and Lower Yangtze River metallogenic belt (MLYMB), eastern China. The Matou deposit has long been regarded as a typical Cu–Mo porphyry deposit within Lower Yangtze part of the belt. Recently, we identified scheelite and wolframite in quartz veins in the Matou deposit, which is uncommon in other porphyry and skarn deposits in the MLYMB. We carried out detailed zircon U–Pb dating and geochemical and Sr–Nd–Hf isotopic studies of the granodiorite porphyry at Matou to define any differences from other ore-related granitoids. The porphyry shows a SiO2 content ranging from 61.85 wt.% to 65.74 wt.%, K2O from 1.99 wt.% to 3.74 wt.%, and MgO from 1.74 wt.% to 2.19 wt.% (Mg# value ranging from 45 to 55). It is enriched in light rare earth elements and large ion lithophile elements, but relatively depleted in Nb, Ta, Y, Yb and compatible trace elements (such as Cr, Ni, and V), with slight negative Eu anomalies (Eu/Eu* = 0.88–0.98) and almost no negative Sr anomalies. Results of electron microprobe analysis of rock-forming silicate minerals indicate that the Matou porphyry has been altered by an oxidized fluid that is rich in Mg, Cl, and K. The samples show relatively low εNd(t) values from −7.4 to −7.1, slightly high initial 87Sr/86Sr values from 0.708223 to 0.709088, and low εHf(t) values of zircon from −9.0 to −6.5, when compared with the other Cu–Mo porphyry deposits in the MLYMB. Zircon U–Pb dating suggests the Matou granodiorite porphyry was emplaced at 139.5 ± 1.5 Ma (MSWD = 1.8, n = 15), which is within the age range of the other porphyries in the MLYMB. Although geochemical characteristics of the Matou and other porphyries in the MLYMB are similar and all adakitic, the detrital zircons in the samples from Matou suggest that Archean lower crust (2543 ± 29 Ma, MSWD = 0.25, n = 5) was involved with the generation of Matou magma, which is different from the other porphyries in the belt. Our study suggests that the Matou granodiorite porphyry originated from partial melting of thickened lower crust that was delaminated into the mantle, similar to the other porphyries in the MLYMB, but it has a higher proportion of lower crustal material, including Archean rocks, which contributed to the formation of the porphyry and related W-rich magmatic-hydrothermal system.

The Huashan complex granitic batholith, occurred in the core of the Xiaoqinling orogen and gold mineralization belt along the south margin of the North China Craton, consists of amphibole monzogranite and biotite monzogranite in the Wengyu and Fangshanyu valleys, respectively. Zircon LA-ICP-MS U–Pb dating yields ages of 205 ± 2 Ma and 132 ± 1 Ma for the Wengyu and Fangshanyu granites, respectively, which represent the two major episodes of Mesozoic magmatism in the region. These rocks are characterized by metaluminous, high silica and total alkalinity, and have high FeOtotal/(FeOtotal + MgO) ratios, high large-ion lithophile elements (LILEs, especially Sr and Ba) and light rare earth elements (LREEs), and low heavy rare earth elements (HREEs) and Y concentrations and insignificant negative Eu anomalies. The Wengyu granites have higher Ba and Sr contents, which can be classified as high Ba–Sr granites, whereas the Fangshanyu granites show much lower Ba and Sr contents and display an adakitic affinity. Elemental and isotopic compositions suggest that the main sources of both the Wengyu and Fangshanyu granites are likely the ancient basement materials of Taihua Group. However, the high Ba and Sr contents of the Wengyu granites require addition of small amounts of enriched lithospheric mantle metasomatised by fluid/melt derived from pelagic sediments-bearing subducted slab in the sources. The Wengyu granites were most likely generated earlier by partial melting of the lowest part of the crust due to the subducted slab break-off under the post-collision extensional stage of the continental collision orogeny. The Fangshanyu granites might be mainly derived later from the partial melting of thickened lower crustal materials, representing by the Taihua Group basement rocks, corresponding to the tectono-magmatism of the post-orogeny to rift extensional environment during the tectonic transition from the Paleo-Tethys subduction-collision system to the Paleo-Pacific regime.Highlights► Two episodes (205 ± 2 Ma and 132 ± 1 Ma) of magmatism are recognized in the Huashan complex, Xiaoqinling district. ► Wengyu granite belongs to high Ba–Sr granite, whereas Fangshanyu granite displays an adakitic affinity. ► The sources of magma are most likely the ancient basement materials of Taihua Group. ► Wengyu granite was generated due to the subducted slab break-off under the post-collision extensional stage. ► Fangshanyu granite was generated during the post-orogeny to rift extensional environment.

Early Cretaceous felsic intrusions and volcanic rocks are widespread in the Gan-Hang Belt, SE China. In this study, we report a distinctive high-Zr rhyolite (802–1145 ppm Zr) from the Dazhou uranium district in the eastern Gan-Hang Belt. SHRIMP zircon U–Pb dating shows that the Dazhou rhyolite erupted at 127.3 ± 1.7 Ma. Geochemical data indicate A-type characteristics for the Dazhou rhyolite, such as high contents of alkali elements, high Fe2O3∗/MgO and high Ga/Al ratios, enrichment in some LILEs, HFSEs, and REEs, and depletion in Sr, Ba, P, and Ti. Compared to other A-type granitoids reported previously in the same belt, the Dazhou high-Zr rhyolite shows only a slight enrichment in other HFSE elements and LREE, but has similar whole-rock Nd and zircon Hf isotopic compositions to those A-type granitoids with relatively lower Zr concentrations, indicating that all these A-type rocks may have similar magma sources. Hence, the difference of Zr contents in these rocks is not due to their different source rocks. We found that zircon grains in the Dazhou high-Zr rhyolite are generally inheritance-poor, and the calculated zircon saturation temperatures are extremely high at ∼1000 °C. It is therefore suggested that the distinctive high-Zr characteristic of the Dazhou rhyolite was a result of high-temperature suppression of zircon crystallization by ambient mafic magmas correlative with the upwelling of the asthenospheric mantle. The fundamental difference in magma temperature and magmatic evolution mechanism between the Dazhou high-Zr rhyolite and other A-type granitoid suites in the eastern Gan-Hang Belt brought about their different Zr concentrations.Highlights► A distinctive high-Zr rhyolite (802–1145 ppm Zr) is reported from the Dazhou uranium district in the eastern Gan-Hang Belt. ► The Dazhou rhyolite was erupted at 127.3 ± 1.7 Ma. ► Geochemical data indicate a A-type characteristic for the Dazhou high-Zr rhyolite. ► The calculated zircon saturation temperatures are extremely high at ∼1000 °C for the Dazhou rhyolite.

The Miao’ershan–Yuechengling batholith (MYB) is one of the largest granitic batholiths in South China. At least five individual phases have been identified for the Paleozoic granites in the MYB. SHRIMP and LA–ICP–MS zircon U–Pb dating results imply that these granites were emplaced at 435 ± 4 Ma, 427 ± 3 Ma, 417 ± 6 Ma, 404 ± 6 Ma and 382 ± 2 Ma, respectively. The ages gradually decreased from the southeast to the northwest, implying that the MYB was incrementally emplaced from the southeast to the northwest lasting from early Silurian to late Devonian. Most granites are metaluminous to weakly peraluminous, and contain low P2O5 contents (<0.15%). These granites show enrichment of Rb, Th, U and depletion of Ba, Sr, Eu, Ti. They show relatively high (87Sr/86Sr)i ratios (>0.715), low εNd(t) values (−8.9 to −6.7), and low zircon εHf(t) values (−9.5 to −4.0). These geochemical and isotopic characteristics indicate that these granites may have formed from partial melting of Paleoproterozoic basement rocks. Slight geochemical differences between different phases can be interpreted as resulting from partial melting of heterogeneous sources or different proportion mixing of meta-igneous and meta-sedimentary rocks. Zircon Hf isotope model ages vary from 1.77 to 1.93 Ga, with an average value of 1.84 ± 0.07 Ga. These data indicate that crust growth in this region took place mainly during the Paleoproterozoic (ca. 1.84 Ga), and the basement in the MYB should belong to the Cathaysia Block. The formation of the Paleozoic granites in the MYB was suggested to be related to the late orogenic magmatism of the Wuyi–Yunkai orogeny. Thus, the late orogenic magmatism in the northwestern part of the Wuyi–Yunkai orogeny must have lasted until ca. 381 Ma and took place also to the east of the Anhua–Luocheng Fault.Highlights► The Paleozoic Miao’ershan–Yuechengling granites consist of five phases. ► The ages of the five phases are 435 ± 4, 427 ± 3, 417 ± 6, 404 ± 6 and 382 ± 2 Ma, respectively. ► The granites were formed from partial melting of Paleoproterozoic basement rocks. ► Crustal growth in the studied region took place mainly at ca. 1.84 Ga.

Trace element and rare earth element (REE) concentrations in cold seep carbonates from the northern continental slope of the South China Sea are used in this study to indicate source fluid characteristics and redox conditions. Carbonate samples from the two study areas (Shenhu and Dongsha) all show low total REE concentrations (mostly 10–20 ppm). In the Shenhu area, the shale-normalized REE patterns of the chimney carbonates display slight light REE enrichment, positive Ce anomaly, and a consistently positive Gd anomaly. These carbonate chimneys show a two-stage formation history, with a slight increase in the positive Ce anomaly from the rim to core. Trace and rare earth element data suggest that the core may have formed in a more anoxic condition than the rim. In the Dongsha area, seep carbonate samples show a slight heavy REE enrichment, with both negative and positive Ce anomalies, and more positive Gd anomalies, which are consistent with precipitation in an anoxic environment. Redox sensitive trace elements, such as Mo, U, Ni, V and Co, also indicate anoxic conditions for this cold seep carbonate precipitation.

The widespread occurrence of Mesozoic granites in the Gan-Hang Belt in Southeast China is associated with similarly widespread, economically important mineralization, but the precise timing, origin, and plate tectonic significance of these granites are not well understood. We have studied two of these (Early Cretaceous) granite bodies, the Yangmeiwan granite and the Daqiaowu granitic porphyry, from the northeastern part of the Gan-Hang Belt in western Zhejiang Province by zircon U-Pb geochronology, major and trace element analyses, and Nd–Hf isotopic analyses. LA-ICP-MS and SHRIMP U–Pb dating of zircon grains from these two granites yield ages of 133–136 Ma, representing a Early Cretaceous magmatic event. These granitic rocks are metaluminous to weakly peraluminous and have a pronounced A-type geochemical signature with high Na2O + K2O, Fe2O3*/MgO and Ga/Al ratios. They show low CaO, MgO and TiO2 contents, enrichment in some LILEs (such as Rb and Th) and HFSEs (such as Zr, Y), depletion in Sr, Ba, P, Eu and Ti. They also show A2 subtype affinity and were probably formed at a high temperature (~ 810 °C for Yangmeiwan granite and ~ 850 °C for Daqiaowu granitic porphyry). These A-type granitic rocks show bulk rock εNd(t) values in the range of − 6.5 to − 3.6 and zircon εHf(t) values from − 7.8 to − 0.9, with Mesoproterozoic TDMc ages for both Nd and Hf isotopes. Geochemical and isotopic data suggest that these A-type granitic rocks were generated largely by partial melting of granulitized Mesoproterozoic metamorphic basement rocks (including parametamorphic and orthometamorphic rocks), with a possible input of mantle-derived materials and followed by subsequent fractional crystallization. Our new data together with previous published data suggest that the Cretaceous A-type granitic rocks with ages between 137 Ma and 122 Ma occurred along the Gan-Hang Belt, indicating an important Mesozoic extensional event in Southeast China. This event represents either a back-arc extension or an intra-arc rift due to the roll-back of the paleo-Pacific plate, and it started as early as ~ 137 Ma in Xiangshan and Xinlu basins. It is earlier than ~ 130 Ma as previously suggested in the studied region and later than that along the south part of the Shi-Hang Zone. With ongoing extension during slab roll-back of paleo-Pacific plate, the crust and lithospheric mantle became progressively thinned. The upwelling of asthenosphere would have triggered crustal rocks to partially melt, generating granitic magmas. Our new geochemical data also suggest that mantle-crust interaction in the formation of the A-type granitic magma along the Gan-Hang Belt gradually intensified from early to late stages between ca. 137 and ca. 122 Ma.Highlights► Two Early Cretaceous A-type granites in the Gan-Hang Belt, SE China are studied. ► These granites were formed at 133 − 136 Ma by in situ zircon U − Pb dating. ► These granites were formed via partial melting of granulitized Mesoproterozoic rocks. ► A intensified mantle-crust interaction occurred along the Gan-Hang Belt from ~ 137 Ma to ~ 122 Ma.

The selective adsorption of metasilicate species by N-methyl D-glucamine functional groups in Amberlite IRA 743 resin was observed, which is clarified as the formation of sugar-metasilicate complexes and possible physical adsorptions. The existence of metasilicate matrices causes obvious discrepancies in the δ11B values of silicate materials. It opens the possibility for exploring relevant procedures for the separation/purification of silicon from geological samples.