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Effects of Spin Transition and Cation Substitution on the Optical Properties and iron partitioning in Carbonate Minerals

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Acta Geologica Sinica(English Edition) 2023年第1期97卷 350-357页

作者： HU Jun XU Liangxu LIU Jin YUE Donghui Center for High Pressure Science(CHiPS) State Key Laboratory of Metastable Materials Science and TechnologyYanshan UniversityQinhuangdaoHebei 066004China Center for High Pressure Science and Technology Advanced Research Beijing 100193China Heilongjiang Province Key Laboratory of Superhard Materials Department of PhysicsMudanjiang Normal UniversityMudanjiangHeilongjiang 157012China

The high-pressure behavior of deep carbonate dictates the state and dynamics of oxidized carbon in the Earth's mantle,playing a vital role in the global carbon cycle and potentially influencing long-term climate change.Optical absorption and Raman spectroscopic measurements were carried out on two natural carbonate samples in diamond-anvil cells up to 60 GPa.Mg-substitution in high-spin siderite FeCO_(3)increases the crystal field absorption band position by approximately 1000 cm^(-1),but such an effect is marginal at>40 GPa when entering the low-spin state.The crystal field absorption band of dolomite cannot be recognized upon compression to 45.8 GPa at room temperature but,in contrast,the high-pressure polymorph of dolomite exhibits a strong absorption band at frequencies higher than(Mg,Fe)CO_(3)in the lowspin state by 2000–2500 cm^(-1).Additionally,these carbonate minerals show more complicated features for the absorption edge,decreasing with pressure and undergoing a dramatic change through the spin crossover.The optical and vibrational properties of carbonate minerals are highly correlated with iron content and spin transition,indicating that iron is preferentially partitioned into low-spin carbonates.These results shed new light on how carbonate minerals evolve in the mantle,which is crucial to decode the deep carbon cycle.

关键词： carbonate petrology/mineralogy mantle high pressure diamond-anvil cell iron spin transition iron partitioning deep carbon cycle

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Deciphering Chemical and Seismic Heterogeneities of the Earth's Deep Mantle

Deciphering Chemical and Seismic Heterogeneities of the Eart...

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第十八届中国高压科学学术会议

作者：林俊孚 Center for High Pressure Science & Advanced Technology Research (HPSTAR)(高科) Department of Geological Sciences The University of Texas at Austin(德州大学)

In this talk,I will use recent mineral physics results to address possible seismic and geochemical heterogeneities in the deep Earth’s interior.Based on seismic observations,Earth’s interior is made of a few distinct layers that are separated by distinct seismic discontinuities.Within these layers,however,there are much less seismic variations,but recent high-resolution seismic tomography has revealed seismic heterogeneities that suggest possible chemical and/or thermal heterogeneities in these layers.On the other hand,geochemical analysis of mantle peridotites,mid-ocean ridge basalts,and chondrites has indicated possible isotope fractionations within the deep Earth.Specifically,terrestrial basalts have non-chondritic Si and Fe isotopic compositions,which could reflect partitioning of these elements into the core,although other interpretations exist.The advent of high-pressure mineral physics research using diamond anvil cell coupled with laser and synchrotron X-ray spectroscopic techniques,together with the use of high-quality single crystal samples,permits direct evaluations of the mineral physics and chemistry of the lower-mantle phases at relevant conditions of the deep Earth.Here I will attempt to establish full elastic constrains on the mantle seismic models,and also evaluate Fe isotope fractionation factors using high-pressure nuclear resonant inelastic X-ray scattering(NRIXS)at deep mantle conditions.Single-crystal elastic constants of the lower-mantle phases at high pressures will be used to evaluate their seismic parameters and to refer heterogeneities of the region.On the other hand,the derived force constants of Fe bonds in basaltic glasses,lower-mantle minerals(bridgmanite and ferropericlase),and Fe alloys allow us to put constraints on important aspects of chemical heterogeneities in the deep interior and to build a deep-Earth geochemical model to evaluate if the specific Si and Fe isotopic compositions of the silicate Earth reflect core partitioning.These recent research results will be used to dec

关键词： Lower Mantle iron partitioning iron Isotope Fractionation Seismic Heterogeneities

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