Fe-periclase reactivity at Earth’s lower mantle conditions: Ab-initio geochemical modelling

Merli, Marcello; Bonadiman, Costanza; Diella, Valeria; Sciascia, Luciana; Pavese, Alessandro

doi:10.1016/j.gca.2017.07.030

Cited by 4 publications

(2 citation statements)

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“…The slight differences with respect to the values of Isaak et al [57] and Srivastava [102] at low temperature are due to the constraint P th (300 K, 1 bar) = 0, assumed to be valid in those works; this assumption lacks a theoretical justification, because thermal vibrations obviously occur already at T = 0 K (zero-point motions), and their effects cannot be disregarded; (iii) Although the lower mantle consists primarily of bridgmanite, the thermal pressure of MgO seems to be representative of that of the lower mantle [103,104] owing to the peculiar thermoelastic and transport properties of periclase. Lower mantle thermodynamics and rheology are thus largely controlled by periclase and its Fe-bearing analogue (ferropericlase) [16,[107][108][109][110]. (14) and (15) Calculated results of this work are compared to selected experimental data obtained by hydrostatic or quasi-hydrostatic compression in the diamond-anvil cell [90][91][92][93] and ultrasonic measurements [94][95][96][97].…”

Section: P-v-t Equation Of State (Eos)mentioning

confidence: 99%

First Principles Thermodynamics of Minerals at HP–HT Conditions: MgO as a Prototypical Material

Belmonte

2017

Minerals

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Ab initio thermodynamic properties, equation of state and phase stability of periclase (MgO, B1-type structure) have been investigated in a broad P-T range (0-160 GPa; 0-3000 K) in order to set a model reference system for phase equilibria simulations under deep Earth conditions. Phonon dispersion calculations performed on large supercells using the finite displacement method and in the framework of quasi-harmonic approximation highlight the performance of the Becke three-parameter Lee-Yang-Parr (B3LYP) hybrid density functional in predicting accurate thermodynamic functions (heat capacity, entropy, thermal expansivity, isothermal bulk modulus) and phase reaction boundaries at high pressure and temperature. A first principles Mie-Grüneisen equation of state based on lattice vibrations directly provides a physically-consistent description of thermal pressure and P-V-T relations without any need to rely on empirical parameters or other phenomenological formalisms that could give spurious anomalies or uncontrolled extrapolations at HP-HT. The post-spinel phase transformation, Mg 2 SiO 4 (ringwoodite) = MgO (periclase) + MgSiO 3 (bridgmanite), is taken as a computational example to illustrate how first principles theory combined with the use of hybrid functionals is able to provide sound results on the Clapeyron slope, density change and P-T location of equilibrium mineral reactions relevant to mantle dynamics.

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Section: P-v-t Equation Of State (Eos)mentioning

confidence: 99%

First Principles Thermodynamics of Minerals at HP–HT Conditions: MgO as a Prototypical Material

Belmonte

2017

Minerals

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“…The Cluster Expansion method [8] (see [9] for a review. In the case of applications to natural systems, see [10,11]) allows one to exploit a theoretically robust approach, which makes it possible to explore the properties of solid mixings even at extreme conditions, though at exceedingly demanding computing costs [12,13]. In fact, the "cluster expansion method" requires investigation of as many configurations as possible, resorting to super cells to mimic atomic disorder in a crystal.…”

Section: Introductionmentioning

confidence: 99%

Beyond the Vegard's law: solid mixing excess volume and thermodynamic potentials prediction, from end-members

Merli

Pavese

2020

Physics Letters A

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Highlights• The Energy and Volumes data are obtained via first principles modelling.• The state functions, E(V , T )s, of each end members are expanded in a polynomial basis in V Mix (the volume of the solid solution) and linearly summed in Vegard's scheme.• Consequentely, EMIX and all the excess functions can be easily derived. AbstractA method has been developed, herein presented, to model binary solid solutions' volume, enthalpy and Gibbs energy using the energy state functions, E(V,S), of the endmembers only. The E(V,S)s are expanded around an unknown mixing volume, VMix, and the fundamental equilibrium equation -(∂E/∂V)S = P is used to determine VMix. VMix allows us to model enthalpy, straightforwardly. The same argument holds using Helmholtz energy, F(V,T), in place of E(V,S), and the equilibrium equation becomes -(∂F/∂V)T = P. One can readily determine the Gibbs free energy, too. The method presented remarkably simplifies computing of solid mixings' thermodynamic properties and makes it possible to preserve crystal structure symmetry that would undergo reduction because of the introduction of disordered super-cells.

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Aluminium distribution in an Earth’s non–primitive lower mantle

Merli

Bonadiman

Pavese

2020

Geochimica et Cosmochimica Acta

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10The aluminium incorporation mechanism of perovskite was explored by means of quantum mechanics in combination with 11 equilibrium/off-equilibrium thermodynamics under the pressure-temperature conditions of the Earth's lower mantle (from 24 12 to 80 GPa). Earth's lower mantle was modelled as a geochemically non-primitive object because of an enrichment by 3 wt% of 13 recycled crustal material (MORB component). The compositional modelling takes into account both chondrite and pyrolite 14 reference models. 15 The capacity of perovskite to host Al was modelled through an Al 2 O 3 exchange process in an unconstrained 16 Mg-perovskite + Mg-Al-perovskite + free-Al 2 O 3 (corundum) system. Aluminium is globally incorporated principally via an 17 increase in the amount of Al bearing perovskite [Mg-Al-pv(80 GPa)/Mg-Al-pv(24 GPa) % 1.17], rather than by an increase 18 in the Al 2 O 3 content of the average chemical composition which changes little (0.11-0.13, mole fraction of Al 2 O 3 ) and tends 19 to decrease in Al. The Al 2 O 3 distribution in the lower mantle was described through the probability of the occurrence of given 20 compositions of Al bearing perovskite. The probability of finding Mg-Al-perovskite is comparable to Mg-perovskites. Per-21 ovskite with Al 2 O 3 mole fraction up to 0.15 has an occurrence probability of $28% at 24 GPa, increasing up to $43% at 22 80 GPa; on the contrary, perovskite compositions in the range 0.19-0.30 Al 2 O 3 mole fraction drop their occurrence proba-23 bility from 9.8 to 2.0%, over the same P-range. In light of this, the distribution of Al in the lower mantle shows that, among 24 the possible Al bearing perovskite phases, the (Mg 0.89 Al 0.11 )(Si 0.89 Al 0.11 )O 3 composition is the likeliest, providing from 5 to 25 8% of the bulk perovskite in the pressure range from 24 to 80 GPa. The occurrence of the most Al rich composition, i.e. 26 (Mg 0.71 Al 0.29 )(Si 0.71 Al 0.29 )O 3 , is a rare event (probability of occurrence < 1.7%). This study predicts that perovskite may glob-27 ally host Al 2 O 3 in terms of 4.3 and 4.8 wt% (with respect to the non-primitive lower mantle mass), thus accounting for $90% 28 and 100% of the bulk Al 2 O 3 estimated in the framework of pyrolite and chondrite reference models, respectively. A calcium-29 ferrite type phase (on the MgAl 2 O 4 -NaAlSiO 4 join) seems to be the only candidate that can compensate for the 10% gap of the 30 perovskite Al incorporation capacity, in the case of a pyrolite non-primitive lower mantle model.31

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Fe-periclase reactivity at Earth’s lower mantle conditions: Ab-initio geochemical modelling

Cited by 4 publications

References 99 publications

First Principles Thermodynamics of Minerals at HP–HT Conditions: MgO as a Prototypical Material

First Principles Thermodynamics of Minerals at HP–HT Conditions: MgO as a Prototypical Material

Beyond the Vegard's law: solid mixing excess volume and thermodynamic potentials prediction, from end-members

Aluminium distribution in an Earth’s non–primitive lower mantle

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