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Petrological geodynamics of mantle melting Ⅲ.AlphaMELTS+multiphase flow:The effect of water

Geoscience Frontiers 2020年第4期11卷 1381-1402页

作者： Massimiliano Tirone 161 Ninos Heroes Sur JocotepecJalisco 45800Mexico

The influence of water is evaluated in this last contribution of a series aiming to study the petrological and dynamic evolution of mantle *** is considered to be either a chemical component in the melt or solid assemblage but it can also be present as a pure water phase in a oversaturated environment.A three-phase-flow model was developed for this *** a limited set of conditions has been applied to the 1-D upwelling mantle column.A range of fixed temperatures(1150-1450℃) and water contents in the solid mantle(0,0.02 wt.%,0.2 wt.%) have been imposed at the entry point(120 km deep) for the two melting models introduced in the previous installments,dynamic equilibrium melting(DEM) and dynamic fractional melting(DFM) *** expected,for a given temperature at the base of the mantle column,the depth of the first melt formation increases with higher water content in the *** the first melt is created,very negligible amount of melt is formed over a certain depth interval which approximately ends at the depth where the first melting of the dry mantle would take *** melt is present as a dynamic phase thorough the entire region regardless whether the DEM or DFM model has been *** a quasi-steady state regime,the melt and residual mantle compositions vary significantly over depth,depending on the conditions imposed to the model(DEM,DFM,bottom temperature and water content).Several distinctions can be made at the extraction point(top of the mantle column=15 km deep).For DEM and DFM models at this lowest depth,the most influential factor affecting the melt composition after the quasi-steady state condition has been reached is the temperature at the base of the *** general,for a high temperature model,the input water in the mantle does not seem to play a significant role on the bulk composition of the melt(except for the water content in melt).But at low temperature water does have some noticeable influence on the variation o

关键词： Petrology mantle melting Geodynamics Thermodynamics AlphaMELTS Numerical modeling

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Extreme geochemical fractionation during mantle melting:Insights from Hf-Nd isotopically ultra-depleted eclogite

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Geoscience Frontiers 2024年第6期15卷 156-166页

作者： Kun Zhou Yi-Xiang Chen Yong-Fei Zheng Ren-Xu Chen Yueheng Yang School of Earth and Space Sciences University of Science and Technology of ChinaHefei 230026China State Key Laboratory of Lithospheric and Environmental Co-evolution University of Science and Technology of ChinaHefei 230026China Center of Excellence for Comparative Planetology Chinese Academy of SciencesHefei 230026China State Key Laboratory of Lithospheric and Environmental Co-evolution Institute of Geology and GeophysicsChinese Academy of SciencesBeijing 100029China

Extreme fractionation of elements and isotopes in mafic igneous rocks is abnormal in deciphering the source nature and melting conditions of mafic ***,identification of geochemically ultra-depleted mafic melts and their mantle sources has great bearing on the property of crust-mantle differentiation at plate *** is illustrated by extreme Hf-Nd isotope fractionation in ultrahigh-pressure eclogites from the Sulu orogen in east-central *** addition to the previous finding of ultrahighεNd(0)values,we report here new data of whole-rock trace elements and Lu-Hf isotopes in eclogites and related rocks from the same *** present results show extremely high Lu/Hf ratios and abnormally highεHf(0)values of up to 576 for the eclogites,significantly different from the garnet amphibolites and other eclogite-facies metamorphic rocks in the same *** feature is coupled with the ultrahighεNd(0)values as well as the severe depletion of light rare earth elements(LREE)and high field strength elements(HFSE).Because HFSE and LREE are immobile in aqueous solutions and the effect of melt extraction is insignificant during the continental deep subduction,the extreme fractionation of Lu/Hf and Sm/Nd indicate their origination from a geochemically ultra-depleted mantle *** eclogites have the depleted mantle Hf model ages of 1.27 Ga to 1.61 Ga,similar to the depleted mantle Nd model ages of 1.39 Ga to 1.67 Ga as previously *** suggests that the protolith of the extremely highεHf-εNd eclogites was a kind of mafic igneous rocks derived from fractional crystallization of geochemically ultra-depleted mafic melts,which were produced by partial melting of the highly refractory lithospheric mantle during a series of seafloor spreading initiation-failure cycles at a divergent plate margin after the breakup of supercontinent Columbia in the Early *** mafic igneous rocks were located in a passive continental margin in the Lat

关键词： mantle melting Element fractionation Sub-ridge mantle Spreading initiation Ultra-depleted melt

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