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The Great Xing′an and Lesser Xing′an ranges are characterized by immense volumes of Mesozoic granitoids. In this study, we present major and trace element geochemistry, U–Pb geochronology and systematic Sr–Nd–Hf isotopes for the representative samples, in order to constrain their petrogenesis and the tectonic evolution in NE China. The granitoids generally have high SiO2 (66.5–78.8 wt.%) and Na2O + K2O (7.0–8.9 wt.%) contents and belong to high‐K calc‐alkaline to shoshonitic series. All of them show enrichment in Rb, Th, U, Pb and light rare earth elements (LREE), and depletion in Nb, Ta, P and Ti. Zircon U–Pb dating suggests that there was continuous magmatism in both the Great Xing′an Range and the Lesser Xing′an Range during the Jurassic–Early Cretaceous interval. Seven Jurassic granitoids have (87Sr/86Sr)i values of 0.704351 to 0.707374, with ϵNd(t) values of −3.4 to 2.4 and ϵHf(t) values of 0.8 to 11.3, indicating that they originated from mixed sources involving depleted mantle and pre‐existing crustal components. One Early Cretaceous sample yields (87Sr/86Sr)i value of 0.706184, ϵNd(t) value of 0.6, and ϵHf(t) values of 7.0 to 8.2, which is in accordance with previous studies and indicates a major juvenile mantle source for the granitoids in this period. In the Jurassic, the magmatism in the Great Xing′an Range was induced by the subduction of the Mongol–Okhotsk Ocean, while the contemporaneous magmatism in the Lesser Xing′an Range was related to the subduction of the Palaeo‐Pacific Ocean. In the Early Cretaceous, extensive magmatism in NE China was probably attributed to large‐scale lithospheric delamination. Copyright © 2014 John Wiley & Sons, Ltd.

The Chalukou giant Mo deposit in the Heilongjiang Province, northeastern China, is a porphyry deposit hosted in an intermediate-felsic complex surrounded by Mesozoic volcano-sedimentary rocks. The mineralization process is composed of four stages, including quartz + K-feldspar (Stage I), quartz + molybdenite (Stage II), pyrite + chalcopyrite + quartz ± other sulphides (Stage III) and carbonate ± fluorite ± quartz (Stage IV). The mineralization is generally associated with intense K-feldspar-, fluorite-, phyllic-and propylitic alteration. Primary fluid inclusions (FIs) in quartz include four compositional types, i.e. pure carbonic (PC-type), aqueous-carbonic (C-type), daughter mineral-bearing (S-type) and aqueous (W-type) inclusions. Halite, sylvite and hematite are recognized as the daughter minerals in Stage I S-type FIs, whereas molybdenite and chalcopyrite occur as daughter minerals in Stage II S-type FIs. High-salinity and high pressure (>220 MPa) FIs exist in Stage I quartz veins, characterized by homogenization through halite dissolution at temperatures of 324 to 517°C. The paucity of coexisting vapour-rich FIs with similar homogenization temperatures at this stage indicates that the initial S-type inclusions have directly exsolved from the magma rather than boiling off of a low-salinity vapour. Stage I quartz has captured the C-and W-type FIs, which have totally homogenized at 270-530°C with salinities of 1.6-17.0 wt.% NaCl equiv. At Stage II, the coexistence of all FI types were only observed at pressures of 150-218 MPa and temperatures of 352-375°C, with two salinity clusters of 0.9-16.6 wt.% NaCl equiv. and 37-56 wt.% NaCl equiv. Stage III quartz contains W-type FIs with homogenization temperatures of 158-365°C, salinities of 0.5-9.0 wt.% NaCl equiv., and minimum pressures of 12-116 MPa; whilst Stage IV fluorite or calcite only contains W-type FIs with homogenization temperatures of 121-287°C, salinities of 0.5-5.3 wt.% NaCl equiv., and minimum pressures of 10-98 MPa. The estimated trapping pressure from Stages II to III suggests an alternating lithostatic-hydrostatic fluid-system caused by fluid boiling. Ore fluids at the Chalukou Mo deposit may have been evolved from a CO 2 -rich, high-salinity, and high-oxygen fugacity (fO 2 ) magma system, to a CO 2 -poor, low-salinity, and low-fO 2 epithermal system. Two key points may have contributed to the formation of the Chalukou giant Mo deposit: The magmatic origin and fluid boiling that has resulted in decompression and rapid precipitation of metals.

ARTICLES GEOLOGY Citation: Zhu L M, Ding Z J, Yao S Z, et al. Ore-forming event and geodynamic setting of molybdenum deposit at Wenquan in Gansu Province, Western Qinling.The Wenquan molybdenum deposit is associated with a Triassic granite in this area. The Wenquan granite is enriched in LILE and LREE, poor in HFSE, and has significantly higher contents of alkali (K 2 O+Na 2 O) and Sr, Ba than those of the island arc volcanic rocks. These geochemical characteristics are similar to post-collisional granites in high K calc-alkaline series. Studies of major elements, trace elements, REEs and chronology of the Wenquan pluton show that, in the geodynamic transition stage of continent-continent convergence to extension, the partial melting of the enriched lithospheric mantle generated the basaltic magma and triggered the partial melting of the thickened lower crust which produceded the acidic magma, and the Wenquan pluton was formed by mixing of the two magmas. Molybdenite Re-Os isotopic dating gave Os model ages of 212.7±2.6 Ma to 215.1±2.6 Ma with a weighted mean of 214.1±1.1 Ma, and an Re-Os isochron age of 214.4±7.1 Ma. These ages are close to K-Ar ages (223 to 226 Ma) and a SHRIMP zircon U-Pb age (223±7 Ma) for the Wenquan granite within the error range, but relatively younger. This implies that the Mo mineralization occurred in a late stage of the magmatic intrusion, and the metallogenesis took place in the transition stage from syn-collision to post-collision in the tectonic setting of the Qinling Orogenic Belt (QOB) after continental collision between the North China Block (NCB) and the South China Block (SCB). This process is also corresponding to the geological events of metamorphism and deformation in South Qinling, closure of the Mian-Lue oceanic basin, and exhumation of the Dabie-Sulu ultrahigh-pressure metamorphic rocks. The large-scale continent-continent collision between NCB and SCB in the middle Triassic triggered significant crustal thickening and exhumation of subducted slab. In the late Triassic, the tectonic setting was transformed to the transition stage from collision to extension. Materials from the asthenospheric mantle would ascend into the root of the lower crust, which could induce partial melting of the lower crust and generate Mo-enriched granitic magma. The ore-forming elements enriched in the fluid derived from the condensation and fraction of the magma resulted in the Mo mineralization. The Mo deposits in the QOB are mainly formed in two episodes, namely 220± Ma and 140± Ma. The two episodes of metallogenesis were developed in the tectonic transition settings from compression to extension, but they were in the different stages of the tectonic evolution. The occurrence of the Wenquan Mo-bearing pluton indicates that the Triassic tectonic-magmatic belt of Western Qinling is another favorable region for

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