Ab initio thermal expansion and thermoelastic properties of ringwoodite (γ-Mg2SiO4) at mantle transition zone conditions
European Journal of Mineralogy(2022)
摘要
Abstract. Thermal convection in the Earth's mantle is driven by
lateral variations in temperature and density, which are substantially
controlled by the local volume thermal expansion of the constituent mineral
phases. Ringwoodite is a major component of the lower mantle transition
zone, but its thermal expansivity and thermoelastic properties are still
affected by large uncertainties. Ambient thermal expansion coefficient
(αV0), for instance, can vary as much as 100 % according to different experimental investigations available from the literature. In this work, we perform ab initio density functional theory calculations of
vibrational properties of spinel-structured Mg2SiO4 ringwoodite in order to provide reliable thermophysical data up to mantle transition zone conditions. Temperature- and pressure-dependent thermal expansivity has been obtained by phonon dispersion calculations in the framework of
quasi-harmonic approximation (QHA) up to 25 GPa and 2000 K. Theoretical
analysis of vibrational spectra reveals that accurate prediction of IR and
silent modes, along with their relative mode Grüneisen parameters, is
crucial to define thermal expansivity. A six-parameter analytical function
is able to reproduce ab initio values fairly well in the whole investigated
P–T range, i.e., αV(P,T)=(1.6033×10-5+8.839×10-9T+11.586×10-3T-1-6.055T-2+804.31T-3) ×exp(-2.52×10-2P), with temperature in kelvin and pressure in gigapascal. Ab initio static and isothermal bulk moduli have been derived
for ringwoodite along with their P, T and cross derivatives, i.e., K0 = 184.3 GPa, KT,300 K = 176.6 GPa, K0′ = 4.13, KT,300K′ = 4.16, ∂KT∂TP = −0.0233 GPa K−1 and ∂2KT∂P∂T0=1.0×10-4 K−1. Computed thermal expansivity and thermoelastic properties support
the evidence that QHA performs remarkably well for Mg2SiO4
ringwoodite up to mantle transition zone temperatures. Since volume thermal
expansion of ringwoodite is strongly pressure-dependent and its pressure
dependence becomes more marked with the increasing temperature,
internally consistent assessments and empirical extrapolation of
thermoelastic data to deep mantle conditions should be taken with care to
avoid inaccurate or spurious predictions in phase equilibrium and mantle
convection numerical modeling.
更多查看译文
AI 理解论文
溯源树
样例
生成溯源树,研究论文发展脉络
Chat Paper
正在生成论文摘要