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Now showing items 1 - 13 of 13

  • HOT WATER CIRCULATING PUMP

    A hot water circulating pump, which comprises a pump housing (1), a pump impeller (4) arranged within the pump housing (1) and driven by an electric motor. The electric motor is arranged in the axial direction of the pump impeller (4). A motor housing (2) is connected to the pump housing (1) via a first flange pair. A junction box (3) is arranged outside of the motor housing (2). The junction box (3) is used for accommodating electrical and/or electronic components of a motor control device and an electrical connection of the motor. The junction box (3) is provided with at least three spaces, comprising one axial space (31) and two radial spaces (32 and 33), both of the radial spaces (32 and 33) being in communication with the axial space (31). With the described arrangement, the structure of the junction box (3) is improved, not only are the accommodating spaces of the junction box (3) enlarged, but the demand for structural compactness and great cooling effects also is satisfied.
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  • Metamorphism, fluid behavior and magmatism in oceanic subduction zones

    Wei, Chunjing   Zheng, Yongfei  

    Based on the updated results of experimental petrology and phase equilibria modelling and combined with the available thermal structure models of subduction zones, this paper presents an overview on the dehydration and melting of basic, sedimentary and ultrabasic rocks that occur in the different stages during oceanic subduction processes and their influences on magmatism above subduction zones. During the subduction at the forearc depth of <90-100 km, the basic and ultrabasic rocks from most oceanic slabs can release very small amounts of water, and significant dehydration may occur in the slab superficial sediments. Strong dehydration occurs in both basic and ultrabasic rocks during subduction at the subarc depth of 90-200 km. For example, more than 90% water in basic rocks is released by the successive dehydration of chlorite, glaucophane, talc and lawsonite in the subarc depths. This is diversely in contrast to the previous results from synthetic experiments. Ultrabasic rocks may undergo strong dehydration through antigorite, chlorite and phase 10 A at the subarc depth of 120-220 km. However, sediments can contribute minor fluids at the subarc depth, one main hydrous mineral in which is phengite (muscovite). It can stabilize to similar to 300 km depth and transform into K-hollandite. After phengite breaks down, there will be no significant fluid release from oceanic slab until it is subducted to the mantle transition zone. In a few hot subduction zones, partial melting (especially flux melting) can occur in both sediments and basic rocks, generating hydrous granitic melts or supercritical fluids, and in carbonates-bearing sediments potassic carbonatite melts can be generated. In a few cold subduction zones, phase A occurs in ultrabasic rocks, which can bring water deep into the transition zone. The subducted rocks, especially the sediments, contain large quantities of incompatible minor and trace elements carried through fluids to greatly influence the geochemical compositions of the magma in subduction zones. As the geothermal gradients of subduction zones cannot cross the solidi of carbonated eclogite and peridotite during the subarc subduction stage, the carbonate minerals in them can be carried into the deep mantle. Carbonated eclogite can melt to generate alkali-rich carbonatite melts at >400 km depth, while carbonated peridotite will not melt in the mantle transition zone below a subduction zone.
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  • Hydrothermal ore deposits in collisional orogens

    Zheng, Yongfei   Mao, Jingwen   Chen, Yanjing   Sun, Weidong   Ni, Pei   Yang, Xiaoyong  

    Hydrothermal ore deposits at convergent plate boundaries represent extraordinary metal enrichment in the continental crust. They are generally associated with felsic magmatism in extensional settings at high thermal gradients. Although their formation is common during accretionary orogeny, more and more ore deposits have been discovered recently in the collisional orogens of China. Because collisional orogeny was operated in a compressional regime at low thermal gradients, it is not favorable for mobilization of ore-forming elements and thus for the production of hydrothermal ore deposits. Nevertheless, continental collision is generally preceded by oceanic subduction, which enables the preliminary enrichment of ore-forming elements in the mantle wedge due to chemical metasomatism by subducting slab-derived fluids. This gave rise to metal pre-enriched domains in the overriding lithosphere, which may be reactivated by extensional tectonism for hydrothermal mineralization either immediately during accretionary orogeny or at a later time during and after collisional orogeny. It is these tectonic processes that have resulted in the progressive enrichment of ore-forming elements through the geochemical differentiation of the subducting oceanic crust, the metasomatic mantle domains and the mafic juvenile crust, respectively, at different depths. Finally, the reactivation of metal pre-enriched domains by continental rifting in the orogenic lithosphere is the key to the metallogenesis of collisional orogens. (C) 2019 Science China Press. Published by Elsevier B.V. and Science China Press. All rights reserved.
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  • The timing of continental collision between Indian and Asia

    Zheng, Yongfei   Wu, Fuyuan  

    The timing of continental collision between India and Asia has been controversial for a long time because of the difficulty in screening isotopic ages for different types of tectonothermal event along the convergent continental boundary. After distinguishing the collisional orogeny from the precollisional accretionary orogeny and the postcollisional rifting orogeny, an age range of 55 +/- 10 Ma is obtained to mark the collisional orogeny in the Early Cenozoic rather than throughout the Cenozoic. This age range provides the resolution to the timing of tectonic reactivation not only for reworking of the marginal arc systems in the Early Cenozoic but also for overprinting of granulite facies metamorphism on eclogites in the Late Cenozoic. In particular, superimposition of the rifting orogeny on both accretionary and collisional orogens in the Late Cenozoic is the key to the reactivation of both Gangdese and Himalayan orogens for contemporaneous metamorphism and magmatism at high thermal gradients. Therefore, rise of the plateau may be caused by underplating of the asthenospheric mantle for rifting orogeny in the composite Himalayan-Tibetan orogens after foundering of their roots in the Late Cenozoic. (C) 2018 Science China Press. Published by Elsevier B.V. and Science China Press. All rights reserved.
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  • The timing of continental collision between Indian and Asia

    Zheng, Yongfei   Wu, Fuyuan  

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  • The transport of water in subduction zones

    Zheng, YongFei   Chen, RenXu   Xu, Zheng   Zhang, ShaoBing  

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  • The Slab-Mantle Interaction in Continental Subduction Channels

    ZHENG, Yongfei  

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  • Developing plate tectonics theory from oceanic subduction zones to collisional orogens

    Zheng, YongFei   Chen, YiXiang   Dai, LiQun   Zhao, ZiFu  

    Crustal subduction and continental collision is the core of plate tectonics theory. Understanding the formation and evolution of continental collision orogens is a key to develop the theory of plate tectonics. Different types of subduction zones have been categorized based on the nature of subducted crust. Two types of collisional orogens, i.e. arc-continent and continent-continent collisional orogens, have been recognized based on the nature of collisional blocks and the composition of derivative rocks. Arc-continent collisional orogens contain both ancient and juvenile crustal rocks, and reworking of those rocks at the post-collisional stage generates magmatic rocks with different geochemical compositions. If an orogen is built by collision between two relatively old continental blocks, post-collisional magmatic rocks are only derived from reworking of the old crustal rocks. Collisional orogens undergo reactivation and reworking at action of lithosphere extension, with inheritance not only in the tectonic regime but also in the geochemical compositions of reworked products (i.e., magmatic rocks). In order to unravel basic principles for the evolution of continental tectonics at the post-collisional stages, it is necessary to investigate the reworking of orogenic belts in the post-collisional regime, to recognize physicochemical differences in deep continental collision zones, and to understand petrogenetic links between the nature of subducted crust and post-collisional magmatic rocks. Afterwards we are in a position to build the systematics of continental tectonics and thus to develop the plate tectonics theory.
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  • New Lu-Hf geochronology constrains the onset of continental subduction in the Dabie orogen

    Cheng, Hao   Zhang, Chao   Vervoort, Jeffrey D.   Wu, Yuanbao   Zheng, Yongfei   Zheng, Shu   Zhou, Zuyi  

    The Tongbai-Dabie-Sulu orogen contains several eclogite-bearing terranes that were largely metamorphosed in Triassic time. Although petrologic and geochronologic data from these terranes have provided essential information on the geodynamic history of the orogenic cycle, the timing of onset of continental collision between Sino-Korean craton and the Yangtze craton is still unknown. To better our understanding of the transitional time of oceanic to continental subduction in this orogen, we have dated an eclogite with continental affinity in the Tongbai Mountains, located in the very west part of the Tongbai-Dabie-Sulu orogen, central China, using Lu-Hf geochronology. These eclogites formed at pressure temperature conditions of 1.8-2.1 GPa and 490-540 degrees C. Mineral-whole rock ages of multi-garnet fractions from three localities yield Lu-Hf ages of 256.4 +/- 2.6 Ma, 252.3 +/- 3.4 Ma and 246.9 +/- 3.2 Ma. Garnet porphyroblasts from the three samples display evidence of prograde zoning but the major portion of the garnet grains grew exclusively at eclogite-facies conditions due to the occurrence of omphacite inclusions from core to rim. Taking the spherical geometry effect into account, these Lu-Hf ages are, therefore, interpreted to reflect high-pressure eclogite-facies metamorphism instead of the early phase of garnet growth despite the well-preserved prograde major- and trace-element zoning in garnets. Our results allow for a more detailed and complete picture of the tectonic evolution of the Tongbai-Dabie-Sulu orogen during the transitional time of oceanic to continental subduction. These new Lu-Hf ages mark the timing of onset of continental collision between Sino-Korean craton and the Yangtze craton, suggesting that the entry of the leading edge of the Yangtze craton continent into the Sino-Korean craton trench occurred no later than ca. 256 Ma. (C) 2010 Elsevier B.V. All rights reserved.
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  • Mesozoic mafic magmatism in North China:Implications for thinning and destruction of cratonic lithosphere

    Zheng, Yongfei   Xu, Zheng   Zhao, Zifu   Dai, Liqun  

    The North China Craton (NCC) has been thinned from > 200 km to < 100 km in its eastern part. The ancient subcontinental lithospheric mantle (SCLM) has been replaced by the juvenile SCLM in the Meoszoic. During this period, the NCC was destructed as indicated by extensive magmatism in the Early Cretaceous. While there is a consensus on the thinning and destruction of cratonic lithosphere in North China, it has been hotly debated about the mechanism of cartonic destruction. This study attempts to provide a resolution to current debates in the view of Mesozoic mafic magmatism in North China. We made a compilation of geochemical data available for Mesozoic mafic igneous rocks in the NCC. The results indicate that these mafic igneous rocks can be categorized into two series, manifesting a dramatic change in the nature of mantle sources at 121 Ma. Mafic igneous rocks emplaced at this age start to show both oceanic island basalts (OIB)-like trace element distribution patterns and depleted to weakly enriched Sr-Nd isotope compositions. In contrast, mafic igneous rocks emplaced before and after this age exhibit both island arc basalts (IAB)-like trace element distribution patterns and enriched Sr-Nd isotope compositions. This difference indicates a geochemical mutation in the SCLM of North China at 121 Ma. Although mafic magmatism also took place in the Late Triassic, it was related to exhumation of the deeply subducted South China continental crust because the subduction of Paleo-Pacific slab was not operated at that time. Paleo-Pacific slab started to subduct beneath the eastern margin of Eruasian continent since the Jurrasic. The subducting slab and its overlying SCLM wedge were coupled in the Jurassic, and slab dehydration resulted in hydration and weakening of the cratonic mantle. The mantle sources of ancient IAB-like mafic igneous rocks are a kind of ultramafic metasomatites that were generated by reaction of the cratonic mantle wedge peridotite not only with aqueous solutions derived from dehydration of the subducting Paleo-Pacific oceanic crust in the Jurassic but also with hydrous melts derived from partial melting of the subducting South China continental crust in the Triassic. On the other hand, the mantle sources of juvenile OIB-like mafic igneous rocks are also a kind of ultramafic metasomatites that were generated by reaction of the asthenospheric mantle underneath the North China lithosphere with hydrous felsic melts derived from partial melting of the subducting Paleo-Pacific oceanic crust. The subducting Paleo-Pacific slab became rollback at 144 Ma. Afterwards the SCLM base was heated by laterally filled asthenospheric mantle, leading to thinning of the hydrated and weakened cratonic mantle. There was extensive bimodal magmatism at 130 to 120 Ma, marking intensive destruction of the cratonic lithosphere. Not only the ultramafic metasomatites in the lower part of the cratonic mantle wedge underwent partial melting to produce mafic igneous rocks showing negative epsilon (Nd)(t) values, depletion in Nb and Ta but enrichment in Pb, but also the lower continent crust overlying the cratonic mantle wedge was heated for extensive felsic magmatism. At the same time, the rollback slab surface was heated by the laterally filled asthenospheric mantle, resulting in partial melting of the previously dehydrated rocks beyond rutile stability on the slab surface. This produce still hydrous felsic melts, which metasomatized the overlying asthenospheric mantle peridotite to generate the ultramafic metasomatites that show positive epsilon (Nd)(t) values, no depletion or even enrichment in Nb and Ta but depletion in Pb. Partial melting of such metasomatites started at 121 Ma, giving rise to the mafic igneous rocks with juvenile OIB-like geochemical signatures. In this context, the age of 121 Ma may terminate replacement of the ancient SCLM by the juvenile SCLM in North China. Paleo-Pacific slab was not subducted to the mantle transition zone in the Mesozoic as revealed by modern seismic tomography, and it was subducted at a low angle since the Jurassic, like the subduction of Nazca Plate beneath American continent. This flat subduction would not only chemically metasomatize the cratonic mantle but also physically erode the cratonic mantle. Therefore, the interaction between Paleo-Pacific slab and the cratonic mantle is the first-order geodynamic mechanism for the thinning and destruction of cratonic lithosphere in North China.
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  • Mesozoic mafic magmatism in North China: Implications for thinning and destruction of cratonic lithosphere

    Zheng, Yongfei   Xu, Zheng   Zhao, Zifu   Dai, Liqun  

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  • Oxidation mechanism of chalcopyrite revealed by X-ray photoelectron spectroscopy and first principles studies

    Xiong, Xiaolu   Hua, Xiaoming   Zheng, Yongfei   Lu, Xionggang   Li, Shenggang   Cheng, Hongwei   Xu, Qian  

    X-ray photoelectron spectroscopic (XPS) studies revealed that the iron site on the chalcopyrite (CuFeS2) surface was preferably oxidized to the Cu site when exposed to an oxidizing environment. Extensive density functional theory calculations were performed to investigate the surface structure of chalcopyrite and its reaction with both molecular oxygen (O-2) and water. The adsorption and dissociation of a single O-2 molecule, a single H2O molecule, as well as both molecules at the Fe and Cu sites on the CuFeS2 (001) surface were studied. Consistent with our experimental observation, the Fe site was found to be preferred for the adsorption and dissociation of O2 due to its lower energy barrier and greater exothermicity. The dissociation of H2O on the CuFeS2 (001) surface by itself was found to be unfavorable both thermodynamically and kinetically. However, the surface formed upon O-2 dissociation was predicted to be much more reactive with H2O, which was attributed to favorable hydrogen transfer to the O site formed upon O-2 dissociation to hydrogen transfer to the S site due to the much weaker S-H bond than the O-H bond. (C) 2017 Elsevier B.V. All rights reserved.
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  • “Calculation of oxygen isotope fractionation in anhydrous silicate minerals.” Geochimica et Cosmochimica Acta: Erratum To Yong-Fei Zheng (1993) 57, 1079–1091

    Yong-Fei Zheng  

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