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A helium stratified and ingassed lower mantle: resolving the helium paradoxes

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Acta Geochimica 2020年第1期39卷 4-10页

作者： Honggang Zhu Xuefang Li Yingkui Xu Faculty of Earth Sciences China University of GeosciencesWuhan 430074China State Key Laboratory of Ore Deposit Geochemistry Institute of GeochemistryChinese Academy of SciencesGuiyang 550081China CAS Center for Excellence in Comparative Planetology HefeiChina Lunar and Planetary Science Research Center Institute of GeochemistryChinese

It is generally believed a variation of 3He/4He isotopic ratios in the mantle is due to only the decay of U and Th,which produces4 He as well as *** we show that not only3He/4He isotopic ratios but also helium contents can be fractionated by thermal diffusion in the lower *** driving force for that fractionation is the adiabatic or convective temperature gradient,which always produces elemental and isotopic fractionation along temperature gradient by thermal diffusion with higher light/heavy isotopic ratio in the hot *** theoretical model and calculations indicate that the lower mantle is helium stratified,caused by thermal diffusion due to*400℃temperature contrast across the lower *** highest3He/4He isotopic ratios and lowest He contents are in the lowermost mantle,which is a consequence of thermaldiffusion fractionation rather than the lower mantle is a primordial and undegassed ***,oceanicisland basalts derived from the deepest lower mantle with high3He/4He isotopic ratios and less He contents—the long-standing helium paradox,is solved by our *** vigorous convection in the upper mantle had resulted in disordered or disorganized thermal-diffusion effects in He,Mid-ocean ridge basalts unaffected by mantle plume have a relatively homogenous and lower!3He/4He isotopic *** model also predicts that 3He/4He isotopic ratios in the deepest lower mantle of early Earth could be even higher than that of Jupiter,the initial He isotopic ratio in our solar system,because the temperature contrast across the lower mantle in the early Earth is the largest and less4 He had been produced by the decay of U and ***,the early helium-stratified lower mantle owned the lowest He contents due to over-degassing caused by the largest temperature ***,succeeding evolution of the lower mantle is a He ingassed process due to secular cooling of the deepest *** explains why significant amount of He pro

关键词： Helium paradox Thermal diffusion mantle convection Adiabatic temperature gradient Primordial mantle Ingassed lower mantle

Complexity and Geodynamics of Ore-accumulating Basins in the Qinling Orogenic Belt,China

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Acta Geologica Sinica(English Edition) 2000年第3期74卷 458-465页

作者： FANG Weixuan ZHANG Guowei LU Jiying LI Yaling LODG Institute of Geochemistry Chinese Academy of SciencesGuiyang Northwest Geological Exploration Bureau CNNCXi’an Department of Geology Northwest UniversityXi’an Chengdu University of Technology Chengdu

Researches were made of different continental-margin and intraplate basin systems in the Qinling microplate in terms of hydrothermal deposition, geodynamics of basin formation, hydrothermal sedimentary rock facies, sy... 详细信息

关键词： geodynamics ore-accumulating basin shallow extension deep convergence mantle convection basin complexity basin-mountain coupling Qinling

Progress in studies on the structure and physical properties of the mantle in China

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Earthquake Science 2008年第5期21卷 526-534页

作者：臧绍先周蕙兰魏荣强 Department of Geophysics Peking University Graduate University Chinese Academy of Sciences

The studies on the structure and physical properties of the mantle by Chinese geophysicists from 2003 to 2007 are reviewed in this report. It mainly contains studies on the seismic velocity structure of the mantle,anisotropy of the mantle,mantle discontinuities,mantle convection and the physical properties of mantle. The review concerns mainly the contents,the methods used and the results of the studies. It can be found that new progress in the study on the structure and physical properties of mantle has been made in the last four years in China. In some preexis-tent areas much progress has been made,advanced methods have been adopted,extensive international co-operation has been conducted in many ways,and the scope of the co-operation has gradually expanded. More-over,some new fields appear as well.

关键词： mantle structure physical property of the mantle mantle discontinuity mantle convection seis-mic velocity anisotropy

Pervasion degree of convective mixing and investigations of mantle mixing

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Earthquake Science 2009年第4期22卷 323-329页

作者： Rongshan Fu National Geophysical Observatory at Mengcheng Mengcheng 233500 China Key Laboratory of Crust-mantle Materials andEnvironments Chinese Academy of Science Hefei 230026 China School of Earth and Space Science University of Science and Technology of China Hefei 230026 China

Geodynamic studies have shown that mantle convection is like a giant blender to make the original heterogeneous mantle mixing and homogenizing. However, some models, especially from geochemical data show that the modem mantle may still contain a number of reservoir bodies with different chemical composition. Then, the modern mantle is homogeneous？ Authors have defined a box replacement degree of convective mantle mixing and pervasion degree of convective mantle mixing （that equals to initial density of tracing elements divided by final density of tracing elements） to investigate the mantle mixing. The previous results have shown that after four billion years the mantle is basic uniform and the box replacement of the convective mantle is more than 80% in steady-state convection models. This paper calculates and discusses the pervasion degree of convective mantle mixing in detail. For the initial state we will set some 10°× 10°（spacing 0.25°） tracing boxes, which includes 1 681 tracer, at the top and bottom of the mantle, and then track the motions of these tracers, and investigate the convective mixed pervasions. The results show that at the initial stage though the convective mixing pervasions are very different from mode to mode, after running for some time, the convective mixing pervasions for most modes are going to be a constant and the tracers are more evenly distributed in the whole mantle.

关键词： mantle mixing mantle convection box replacement degree pervasion degree

Deep Mechanical Background for the Cenozoic Volcanism in the Tibetan Plateau

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Journal of China University of Geosciences 2005年第4期16卷 334-339页

作者： Xiong Xiong Wang Jiye Teng Jiwen Institute of Geodesy and Geophysics Chinese Academy of Sciences Wuhan 430077 China Institute of Geology and Geophysics Chinese Academy of Sciences Beij ing 100101 China Graduate School Chinese Academy of Sciences Beijing 100038 China Institute of Geology and Geophysics Chinese Academy of Sciences Beijing 100101 China

The principle prerequisite for the formation of a volcano is the generation of a channel for magma transportation. There is little research on the deep mechanical mechanism for the formation of a magma transportation channel in the Tibetan plateau. Based on the subcrustal mantle convectiongenerated stress field inversed by gravity anomalies, together with its relationship to the Cenozoic volcanism in the plateau, and the mechanism of crustal fracture formation, as well as the numerical results of the evolution of mantle convection beneath the plateau, this paper investigates the deep mechanical mechanism for the formation of a magma transportation channel in the Tibetan plateau. There are two significant extensional convection-generated stress zones beneath the plateau, in which the volcanic rocks in the central and northern parts of the plateau are distributed. The Linzizong volcanism in southern Tibet correlates the upwelling mantle flow prior to the India-Asia collision or during the early stage of the collision. The magnitude of the stress is - 100 MPa, which is the same order of force that causes crustal fractures. The evidence implies that the mantle convection-generated stress is one of the principle causes of crustal fractures, and furthermore, the formation of the magma transportation channel in the Tibetan plateau.

关键词： mantle convection stress field Tibetan plateau volcanism magma channel.

Dynamic modeling for crustal deformation in China:comparisons between the theoretical prediction and the recent GPS data

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Dynamic modeling for crustal deformation in China:comparison...