A computer simulation study of (OH) defects in olivine

Abstract

Abstract. Recent experiments (Miller et al. 1987; Bell and Rossman 1992;Bai and Kohlstedt 1992) have shown that olivine, the dominant mineral in the Earth's upper mantle, can contain substantial amounts of water in the form of OH. There is uncertainty, however, as to the mechanisms by which water dissolves into the mineral structure and as to the site it occupies in the host lattice. We have therefore used atomistic computer simulation techniques based on the Born model of solids, to investigate the structures and energies of OH defects in olivine. Our calculations suggest that the most favourable route for incorporation of OH into olivine involves reactions with water accompanied by the reduction of ferric iron for which we obtain a solution energy of 0.46 eV. We propose therefore that the OH content will be largely controlled by the concentration of Fe 3 +.

A computer simulation study of the effect of pressure on Mg diffusion in forsterite

“…In addition the polarization of oxygen was described using the shell model of Dick and Overhauser (1958). These potentials, which were also used by Wright and Catlow (1994) and Jaoul et al (1995) with the code CASCADE (Leslie, 1981), have proven to be very reliable for diffusion studies.…”

“…Results of computational studies on defects and diffusion in olivine are becoming more and more available: for example, on OH defects (Wright and Catlow, 1994; Brodholt and Refson, 2000;Braithwaite et al, 2002Braithwaite et al, , 2003 and on oxygen defects and diffusion (Brodholt, 1997;Walker et al, 2003). Note that Si diffusion remains difficult to investigate using atomistic methods as discussed by Braithwaite et al (2003).…”

Evidence from numerical modelling for 3D spreading of [001] screw dislocations in Mg2SiO4forsterite

“…This model has been extensively used for studies of the thermodynamic and structural properties of perfect forsterite [28][29][30] as well as studies of surfaces [31][32][33] and point defects [34][35][36][37].…”

Estimation of oxygen diffusivity from anion porosity in minerals.

“…Sharp (1991) developed a technique for corre lating crystal grain size with the oxygen isotope compositions of a silicate or oxide mineral hosted by a marble in order to quantify the diffusion co efficients of oxygen in that mineral. Recent efforts using atomistic simulation methods have proven very promising in predicting the structural, ther modynamic, point defect and diffusional properties of a range of minerals (e.g., Catlow and Price, 1990;Purton and Catlow, 1990;Patel et al, 1991;Wright and Catlow, 1994;Vocadlo et al, 1995;Wright et al, 1996). By defining an interatomic potential function to describe the total energy of a system in terms of atomic positions, the atomistic approach has been employed by Wright et al (1995) to investigate the diffusion of oxygen and hydroxyl groups in grossular garnet.…”