Search

The Solonker zone is widely accepted as the suture between the North China Craton and the Siberia–Mongolia continental plate. The Baolige granite complex is located to the north side of the Solonker Suture and is mainly composed of monzogranite and granite. Zircon U–Pb ages, geochemistry, and Sr‐Nd‐Hf isotopic data of the Baolige granites were presented to constrain their petrogenesis and tectonic settings. Two monzogranite samples from Baolige yielded weighted mean zircon 206Pb/238U ages of 310.7 ± 2.1 Ma (mean square of weighted deviates (MSWD) = 1.3) and 307.4 ± 1.6 Ma (MSWD = 0.77), whereas the granite intruded into the monzogranite yielded an age of 296.2 ± 2.0 Ma (MSWD = 1.2). Both the Baolige monzogranite and granite contain high contents of SiO2, K2O, and Al2O3, low contents of TiO2, MgO, and CaO, and are peraluminous high‐K calc‐alkaline. These rocks are characterized by enrichments of K, Rb, U, Pb, Th, and light rare earth elements and depletions of Nb, Ta, Ti, and heavy rare earth elements and contain slightly negative or no Eu anomalies, similar to typical arc‐related granitoids. The Ti‐in‐zircon thermometry yielded 650–759 °C for the monzogranite and 645–796 °C for the granite. The monzogranite shows positive zircon εHf(t) values (4.7–13.2) and whole‐rock εNd(t) values (3.6–5.2), with TDM2(Hf) ages of 1,324–557 Ma and TDM2(Nd) ages of 1,015–821 Ma, and ISr of 0.70363–0.70386. The granite shows εHf(t) values of 15.6–20.9 and εNd(t) values of 4.0–5.1, with TDM2(Nd) ages of 957–832 Ma, and ISr of 0.70364–0.70406. Geochemical evidence indicates that the Baolige granite complex is highly fractionated I‐type and was likely formed by partial melting of the Neoproterozoic juvenile crust in a continental arc setting. We concluded that the Paleo‐Asian Ocean may have undergone north‐dipping subduction beneath the Siberia–Mongolia continental plate during the Late Carboniferous, and the subduction may have continued to the Early Permian (ca. 296 Ma). [ABSTRACT FROM AUTHOR]

The exceptionally thick Middle Permian Zhesi Formation is considered key to understanding the late Palaeozoic tectonic setting of the North China-Mongolia segment of the Central Asian Orogenic Belt, yet its sedimentary environment and provenance remain ambiguous. An integrated approach incorporating detailed field observation and measurement, framework petrography, whole-rock geochemistry and detrital zircon U-Pb geochronology is applied here to investigate this problem. The framework petrography and whole-rock geochemical characteristics jointly suggest that the Zhesi Formation was derived primarily from felsic upper continental crust, with the source rocks undergoing intermediate weathering and short-distance transportation. Furthermore, the source rocks were composed of granites/granitoids that occurred in a transitional recycled orogen. LA-ICP-MS U-Pb detrital zircon data from sandstone samples show two main age groups of 480-410 and 290-265 Ma. Accordingly, we deduce that the dominant provenance of the Zhesi Formation was northerly early to mid-Palaeozoic orogenic belt, late Palaeozoic granites/granitoids and volcanics, with a possible contribution from the Hunshandake Block. The subsiding depositional environment of this succession is in response to the Middle Permian extensional tectonic setting of the orogenic belt. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The Yangshan gold deposit, Gansu Province, is the largest gold deposit in China and the best representative of the western Qinling gold province. Granite dykes can be observed in the orefield, of which some are spatially associated with the gold orebodies. Gold mineralization was debated between magmatic hydrothermal and metamorphic hydrothermal models in previous studies due to a shortage of precise isotopic ages of the granite dykes in the orefield. In this contribution, we report in-situ zircon LA-ICP-MS U-Pb ages combined with Hf isotope and REE data. The age of granite dykes is constrained to be 220.2 ± 3.1 Ma, coeval with the regional development of Triassic granitoids, which resulted from the northward subduction of the Mian-Lue oceanic plate. The εHf(t) values of inherited and new zircon grains from the granite dykes show that the granite dykes have a complex source dominated by sediments which were sourced from the North China Craton, Yangtze Craton and Qinling Orogen, and accumulated in a fore-arc setting. The granite dykes were derived from partial melting of the fore-arc sediment prism induced by the fluids sourced from metamorphic devolatilizaiton of the underthrust Mian-Lue oceanic plate. The Yangshan gold deposit was formed at about 190 Ma, some 30 Myr later than the intrusion of the granite dykes, ruling out the possibility that gold mineralization was caused by Triassic granitic magmatism. The Yangshan gold deposit is a transitional system between Carlin- and orogenic-types that resulted from continental collision orogeny, metallogeny and fluid flow. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The Qinling Orogen in central China preserves the records of a complex geological and tectonic history, and also carries abundant mineral resources. Previous investigations on the Qinling Orogen have identified that the final transition from the Palaeo-Tethys Ocean to a continental orogen occurred in the Triassic, although the timing of the oceanic closure and the tectonic affinity of the Triassic Qinling belt have been poorly constrained. In this contribution, we compile the palaeomagnetic data and geological evidence related to sedimentation, magmatism and mineral systems. The palaeomagnetic data show that the Palaeo-Tethys Ocean in the Qinling Orogen gradually closed westward during the Triassic, terminating in the beginning of the Jurassic. Triassic strata are widely developed in the Qinling Orogen and conformably overlie the Permian strata. They are composed of carbonates and siliciclastic rocks that were strongly deformed and weakly metamorphosed during the Late Triassic to Late Jurassic. The Triassic magmatic rocks are dominated by I-type granitoids, with subordinate S-type and alkaline granites and minor carbonatite dykes, with a clear northward transition in lithology and geochemical features from the Mian-Lue Suture. Different types of Triassic mineral systems have been reported from this region, including sedimentary-hosted epizonogenic hydrothermal Hg-Sb, Pb-Zn ± Ag, Au deposits, metamorphic hydrothermal lodes of Au, Ag-Pb-Zn, Mo-Au and Mo, magmatic hydrothermal systems including porphyry Mo, breccia pipe Au, and carbonatite-hosted Mo deposits. We infer that the Triassic Qinling Orogen witnessed synchronous oceanic plate subduction in the west and continental linkage in the east, with a transition from oceanic basin to continental orogen through gradual subduction-related consumption of the oceanic plate. The Palaeo-Tethys Ocean closed in a westward scissor-like fashion in the Triassic and continental collision and extensive crustal shortening in the Jurassic, following which post-collisional extension occurred in the Early Cretaceous. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editors discuss various reports within the issue on topics including palaeomagnetic data and geological evidence related to sedimentation, magmatism, and mineral systems in the Qinling Orogen, China, the age of granitic dykes in the Yangshan gold field, and the Huachanggou gold (Au) deposit in Shaanxi Province.

The East Qinling Molybdenum Belt (EQMB), central China, hosting tens of Mesozoic magmatic hydrothermal Mo deposits, is one of the largest molybdenum belts in the world. Recently, a new type of Mo mineralization characterized by molybdenite-fluorite veins was discovered with ongoing prospecting at the Tumen area in the Huaxiong block, representing the southernmost tectonic unit of the North China Craton. The molybdenite-fluorite veins occur in faults or ductile shear zones cross-cutting the Neoproterozoic Luanchuan Group. At the Tumen deposit, CO2-rich, aqueous and daughter mineral-bearing fluid inclusions are observed in fluorite. These fluid inclusions resemble those reported from magmatic hydrothermal Mo systems formed in intracontinental tectonic settings and yield homogenization temperatures up to 450 °C, with salinities up to 39.8 wt.% NaCl equiv, suggesting that the mineralization resulted from a magmatic fluid system. Seven molybdenite analyses from the molybdenite-fluorite veins yield Re-Os isotope ages ranging from 845.8 ± 7.3 to 965.3 ± 7.2 Ma, with an isochron age of 847.4 ± 7.3 Ma (2 σ, MSWD = 23), marking the timing of mineralization as Neoproterozoic. These ages are broadly comparable with the 844.3 ± 1.6 Ma age reported from the Shuangshan syenite located near the mining area, and the ca. 830 Ma gabbros occurring within the same tectonic unit, indicating that the deposit was possibly related to Neoproterozoic rifting at the southern margin of the North China Craton. The age data correspond to the transition from the culmination of the assembly of the Neoproterozoic supercontinent Rodinia to the beginning of its break-up. Our results provide new insights into the regional tectonics and show that the Mo mineralization is not related to the much younger Mesozoic Yanshanian magmatism as considered in previous studies. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The worldwide 2.33−2.06 Ga unique positive δ13Ccarb excursion has been correlated with the Great Oxidation Event (GOE). The Dashiqiao Formation in the Liaohe Group of the northeastern North China Craton formed at 2.2−2.174 Ga and hosts one of the world-class magnesite deposits. Here we present major element and C and O isotope analyses of 22 samples from the Dashiqiao Formation and use the data to evaluate the impact of the GOE in the North China Craton, as well as the genesis of the Dashiqiao giant magnesite deposits. Six dolomitic marble samples from a ~600 m thick interval with 1.10 ± 0.04 of MgO/CaO (mol) ratios show higher δ13CPDB values of 0.6−1.4‰ (average 1.2 ± 0.3‰) than those of normal marine carbonates over the globe. However, they display lower δ18OSMOW of 16.4−19.5‰ (average 18.2 ± 1.1‰) as compared to their contemporaneous counterparts, suggesting that the primary carbonates in the Dashiqiao Formation should possess a positive δ13C anomaly (possibly 4.2‰) reflecting the impact of the GOE, and that the δ13C and δ18O values have been depleted in post-sedimentation diagenesis and/or regional metamorphism. The >550 m thick magnesite layer in the studied section has MgO/CaO ratios ranging from 4.45−200.00. These rocks show δ13C and δ18O values of 0.1−0.9‰ and 9.2−16.9‰, with average values of 0.4 ± 0.2‰ and 13.3 ± 2.5‰, respectively, obviously lower than those of the underlying dolomites. The depletions of 13C and 18O in magnesites relative to dolomitic marbles are interpreted to be the result of hydrothermal alteration related to regional metamorphism leading to rock recrystallization and mass exchange. This interpretation is further confirmed from the hanging-wall dolomitic marble and the veinlet-filled magnesite from the ore layer. The former contains mega-crystals of cylindrical talc and has δ13C of −2.6‰ and δ18O of 14.1‰, indicating that a local fluid-rock interaction between (argillaceous) dolomite and (siliceous) hydrothermal fluids poor in 13C and 18O resulted in the formation of talc and further depletion both in δ13C and in δ18O. The veinlet-filled magnesite yields δ13C and δ18O values of −2.7‰ and 16.2‰, respectively, showing lower δ13C but higher δ18O than those of massive magnesite in the adjacent strata. Our observation thus strongly supports the interpretation that the massive magnesite interacted with low-δ13C fluids which were possibly sourced from meteoric water at low temperature during post-ore time. Thus, the formation of the Dashiqiao magnesite deposits involved primary sedimentation, diagenesis, regional metamorphism, hydrothermal replacement and local post-ore fluid-rock interaction. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This study presents new integrated stratigraphic, sedimentary, and geochronological data for Silurian to Devonian sedimentary rocks in the central North Qilian Belt (NQB), NW China. These data constrain the timing and processes involved in the Palaeozoic tectonic transition from compression to extension in the NQB. This study indicates that the Angzanggou Formation probably formed in a foreland basin setting during 439–430 Ma compression associated with the closure of the North Qilian Ocean. The terrestrial sedimentary rocks overlying the formation were most likely deposited in a superimposed basin at 409–388 Ma as a result of the post‐orogenic extension of the NQB, an event that involved initial post‐orogenic extension‐related sedimentation. Silurian–Devonian sediments were derived from multiple sources, including the NQB, Central Qilian Block (CQB), and Alxa and Dunhuang blocks. Convergence between the CQB and the Alxa Block propagated westward, leading to the scissor‐like closure of the North Qilian Ocean during the Middle to Late Silurian and the oblique docking and collision of these two blocks. This is evidenced by a lack of middle–upper Silurian sedimentary rocks in the middle and eastern NQB compared with the well‐developed and well‐preserved sedimentary strata in the western segment. Devonian retrogradation and intracontinental extension‐related magmatism in the NQB also provide evidence of long‐lived tectonic extension of the lithosphere. Combining these new data with previously published data for the NQB and the wider region suggests that the Devonian terrestrial strata were deposited in a post‐orogenic extensional setting similar to that in the North Qaidam and East Kunlun belts, indicating that the Palaeozoic large‐scale tectonic transition from compression to extension in these three belts most likely started during the Early Devonian. [ABSTRACT FROM AUTHOR]

The Xunyang Hg-Sb orefield, Shaanxi Province, containing two large (Gongguan and Qingtonggou) and tens of small to medium Hg-Sb deposits, is located in the southern Qinling Orogen. Ore bodies of the deposits are hosted in Devonian dolomite and controlled by a fault system. Ores are mainly present as massive veins, disseminations, breccias and fine veinlets, with cinnabar (Hg) and stibnite (Sb) being the dominant ore minerals. Gangue minerals include quartz, calcite and dolomite. Hydrothermal minerals (quartz and calcite) only contain aqueous fluid inclusions with low homogenization temperature (135-274 °C) and salinity (1.23-12.3 wt.% NaCl equiv.), supporting an epizonogenic hydrothermal origin. The carbon, oxygen and hydrogen isotope data indicate that the ore-forming fluids were mainly sourced from epizonogenic to metamorphic devolatilization of the Sinian−Triassic strata that possibly underthrusted beneath the orefield, with inflow of the circulating meteoric water. Sulphur isotope ratios of stibnite and cinnabar range from 2‰ to 12‰, suggesting a contribution from sedimentary sulphate or sulphate-bearing fluids potted in strata, which is coincident with the δ34S values (3.4-8.6‰) of diagenetic pyrite in the strata. The conclusion drawn from sulphur isotopes is fully supported by the Pb isotope signatures. In addition, the 87Sr/86Sr ratios gradationally increase from ore-hosting dolostones, through ore-barren calcite or low-grade ores, to high-grade ores, indicating that a portion of the fluids originated from a source with higher 87Sr/86Sr values than the host-rocks, which is possibly composed of the Neoproterozoic−Lower Palaeozoic basement of the Xunyang Basin. Integrating the data from ore geology, fluid inclusion microthermometry and stable, radioactive isotope geochemistry, it can be concluded that the deposits in the Xunyang Hg-Sb orefield were formed by epizonogenic hydrothermal fluids mainly sourced from the strata via structural deformation during the North China−Yangtze continental collision. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The Dashui porphyry granitoids in the western Qinling Orogen are spatially associated with the Dashui gold deposit, but their ages and tectonic setting have not been well defined yet in previous studies. This paper reports the results and understandings obtained from our original study in geochronology and isotope and element geochemistry. SHRIMP zircon U-Pb dating yielded ages of 213.7 ± 2.7 Ma for granitic stock and 215.1 ± 2.5 and 210.2 ± 1.6 Ma for granitic dikes. The granitoids are characterized by high LREE but low HREE and HFSE. They have (87Sr/86Sr) i ratios of 0.706 to 0.709 and εNd(t) values of −5.3 to −7.6. The majority of zircons in the Dashui granitoids have εHf(t) values ranging from −6.2 to 6.7 and TDM2(Hf) ages from 743 to 1464 Ma. The isotope signatures, together with La/Y and Mg# values, show that the magmas are mainly sourced from partial melting of a subducted slab, and possibly assimilated immature sediments during upward migration. Thus, the Dashui granitoids most likely formed in a volcanic arc where supra-subduction zone melts assimilated lower crustal material no later than 215 Ma. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Reconstructing the Late Palaeozoic tectonic process of the Hegenshan Ophiolite Belt is critical for evaluating the protracted accretion and collision history of the south‐eastern Central Asian Orogenic Belt. The Carboniferous–Permian sedimentary rocks near the Erenhot area are key to revealing the evolutionary history of the Hegenshan Ocean. In this study, new stratigraphic, geochemical, and detrital zircon U–Pb age analyses were conducted on three Carboniferous–Early Permian strata (viz., Halatumiao, Amushan, and Benbatu formations). Deposition of the Halatumiao Formation began around 313 Ma, inferred from a zircon U–Pb age from a lower tuff layer. The end of deposition is constrained by two later intrusive high‐K granite plutons that give ages of 277–285 Ma. The predominant detrital zircon group in these strata is characterized by ages of 340–290 Ma, high positive εHf(t) values, and juvenile TDM2 ages, which suggest adjacent and unitary juvenile provenances. The Halatumiao Formation mainly consists of blackish fine‐grained sedimentary rocks with a thickness of 6–7 km implying a high sedimentation rate and a stable hydrodynamic condition. Thus, the Halatumiao Formation most likely indicates the existence of a deep and wide ocean basin under an effect of long‐lived and continuous extension. The Amushan Formation has a comparable depositional age to the Halatumiao Formation, based on three detrital zircon Palaeozoic age populations with peaks of 317, 389, and 441 Ma, but contains more complex provenances. The Benbatu Formation has an earlier deposition age between ca. 324 and 314 Ma. Its detrital zircons yield a predominant age group at around 410–440 Ma but lack syn‐sedimentary Late Palaeozoic age. Unlike the Halatumiao Formation, the two other formations are considerably smaller in terms of their deposition thickness and outcrop area. The transition from Benbatu to Amushan and Halatumiao formations records the development of a gradually deeper and wider ocean basin in response to a back‐arc extensional setting from the Late Carboniferous to the Early Permian. [ABSTRACT FROM AUTHOR]

The Jinchuan deposit, which is located in the Longshoushan uplift (LU) on the southwest margin of the Alxa Block (AB), is the third largest Ni‐Cu deposit in the world. There are igneous rocks in the LU that widely developed in ~830 Ma, which include ore‐bearing ultramafic rock and ore‐poor mafic‐ultramafic rocks. These rocks were produced in an intracontinental extension‐rift environment, which is likely related to the Rodinia supercontinent (RS) breakup. However, contemporary magmatic rocks are absent in the AB, except the ~830 Ma igneous rocks in the LU. In this study, we present two types of metamorphic mafic‐ultramafic rocks at the border of Jinchuan II and IV mineral areas, which is inside the F17 fault zone. One type is a red‐coloured altered rock formed by ultramafic rock oxidation; there are a small number of zircons with multiple ages in the rock, which are considered to be inherited and metamorphic (hydrothermal) zircons. The other type is a chlorite tremolite schist formed by the metamorphism of fault clastics; there are a large number of zircons developed in this rock, which are mostly magmatic zircons with ages between 900 and 800 Ma and a few hydrothermal zircons. Analysis of the trace elements, the 900–800 Ma zircons, have high (Sm/La)N, low Ce/Ce*, and high Th/U values, which fit the characteristics of typical magmatic zircons. There are also high Y, U, HREE, Nb, and Ta values, which indicates that the host rocks were mostly larvikite and dolerite, and high Y, Ce, Yb, Th, Gd, and Er values indicate a within‐plate basaltic origin. All these 900–800 Ma zircons have a εHf (t) in the range of −2 to −7, which is similar to the Jinchuan ore‐bearing ultramafic rock with a partial melting origin of enriched mantle. The absence of detrital zircon age peaks in the Neoproterozoic indicates that the AB has been separated from the North China Craton since the Neoproterozoic to Paleozoic. The detrital zircons in the Yangtze Block (YB) strata with Neoproterozoic ages are slightly younger than those in the AB, with more depleted εHf (t) values, which is similar to the zircons from the Jiangnan Orogen igneous rocks. All this evidence indicates that the AB may have experienced at least 100 Myr of intracontinental extension‐rift environment from 900 to 800 Ma during the Neoproterozoic and participated in the breakup of the RS. However, the location of the AB during the Rodinia may not have been beside the YB. [ABSTRACT FROM AUTHOR]

The East Qinling region in central China, hosting several tens of Mesozoic magmatic-hydrothermal Mo deposits, is one of the largest molybdenum belts in the world. The Zhifang Mo deposit is hosted in volcanic rocks of the Xiong'er Group in the Waifangshan area, Qinling Orogen. Previous studies variously correlated the mineralization in this deposit with Yanshanian magmatism or Palaeo-Mesoproterozoic volcanic-hydrothermal events. The orebodies are associated with quartz veins and controlled by subsidiary faults of the Machaoying Fault. The ore-forming process can be divided into the early, middle and late stages and is characterized by quartz-pyrite, quartz-polymetallic sulphide and quartz-carbonate veins, respectively. The early-stage quartz is structurally deformed, suggesting a compressional tectonic regime; the middle-stage sulphides fill the fractures of the early-stage assemblages and show no deformation, suggesting a tensional setting; the late-stage veins mostly infill the open-space fissures. Three types of fluid inclusions (FIs) are identified at the Zhifang deposit: H2O-NaCl (W-type), CO2-rich (C-type) and daughter mineral-bearing inclusions (S-type). Fluid inclusions of early-stage quartz homogenize between 380 and 470 °C, with salinities ranging from 0.4 to 9.6 wt.% NaCl equiv., whereas the late-stage calcite contains only the W-type FIs with homogenization temperatures of lower than 240 °C, and salinities of 0.4-8.7 wt.% NaCl equiv. This indicates that the ore fluid system evolved from CO2-rich, probably metamorphic hydrothermal to CO2-poor, meteoric fluid. All three types of FIs can be observed in the middle-stage quartz, and even in the microscopic domain of a crystal, suggesting that this heterogeneous association was trapped from a boiling fluid system. These FIs homogenized at temperatures ranging from 250 to 360 °C and display two salinity clusters of <18.5 and 29.1-29.9 wt.% NaCl equiv. These results suggest that metal precipitation resulted from fluid boiling. The estimated trapping pressures of FIs range from 101 to 285 MPa, suggesting an alternating lithostatic-hydrostatic fluid system, which was controlled by a fault-valve at the depth of 10 km. The δ34S values of ore minerals from the Zhifang Mo deposit show a range between −11.8‰ and 6.0‰, with a bimodal distribution. The early-stage pyrite has a positive δ34S value of 6.0‰ that is similar to the host rocks of the Xiong'er Group and the Taihua Supergroup, suggesting that the wall rocks contributed much of the sulphur to the early-stage pyrite during fluid-rock interaction. However, the δ34S values of the middle-stage sulphides have negative mean and restricted range from −11.8‰ to −4.5‰. The widespread rutile grains coexisting with molybdenite in the middle-stage correlate the negative δ34S values with relatively oxidized fluids. We consider phase separation as an efficient mechanism for ore-fluid oxidation and molybdenum deposition based on fluid inclusions and sulphur isotope data. Geological, fluid inclusion and sulphur isotope data of the Zhifang Mo deposit suggest that the Mo mineralization is unrelated to the Yanshanian magmatism or the Palaeo-Mesoproterozoic volcanic-hydrothermal event. Here we propose that the Zhifang Mo deposit may be considered as an orogenic mineral system, with its formation in an active continental margin related to the northward subduction of the Mian-Lue oceanic plate during the Triassic. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]