Deformation of a crystalline olivine aggregate containing two immiscible liquids: Implications for early core–mantle differentiation

Abstract

Deformation-assisted segregation of metallic and sulphidic liquid from a solid peridotitic matrix is a process that may contribute to the early differentiation of small planetesimals into a metallic core and a silicate mantle. Here we present results of an experimental study using a simplified system consisting of a polycrystalline Fo 90 -olivine matrix containing a small percentage of iron sulphide and a synthetic primitive MORB melt, in order to investigate whether the silicate melt enhances the interconnection and segregation of FeS liquid under deformation conditions at varying strain rates. The experiments have been performed at 2 GPa, 1450 • C and strain rates between 1 × 10 −3 s −1 to 1 × 10 −5 s −1 . Our resultsshow that the presence of silicate melt actually hinders the migration and segregation of sulphide liquid by reducing its interconnectivity. At low to moderate strain rates the sulphide liquid pockets preserved a roundish shape, showing the liquid behavior is governed mainly by surface tension rather than by differential stress. Even at the highest strain rates, insignificant FeS segregation and interconnection were observed. On the other hand the basaltic melt was very mobile during deformation, accommodating part of the strain, which led to its segregation from the matrix at high bulk strains leaving the sulphide liquid stranded in the olivine matrix. Hence, we conclude that deformation-induced percolation of sulphide liquid does not contribute to the formation of planetary cores after the silicate solidus is overstepped. A possible early deformation enhanced core-mantle differentiation after overstepping the Fe-S solidus is not possible between the initial formation of silicate melt and the formation of a widespread magma ocean.

Stability and nature of the volume collapse of ε-Fe2O3 under extreme conditions

“…It is worthwhile to notice the stability of the structure up to 27 GPa where a change in the volume occurs (see below). These data were analyzed through a fit to a third-order Birch–Murnaghan equation and allowed us to determine the volume ( V 0  = 424.0(2) Angstrom 3 ), bulk modulus ( B 0  = 173(3) GPa) and its derivative ( B 0 ’ = 3.8) at zero pressure. Ab initio theoretical calculations agree nicely with the evolution of the experimental data with a small overestimation of the volume and a comparable bulk modulus, B 0  = 168(2) GPa with the same derivative ( B 0 ’ = 3.8), as shown in Fig.…”

“…Understanding the mechanisms behind the formation of the Earth and its differentiation to the present structure has been a subject of intense debate in the last decades 1–3 . The physical and chemical properties of the main constituents of the Earth at specific pressure (P) and temperature (T) conditions played a fundamental role during the differentiation processes, which ultimately lead to the present chemical distribution and layered structure to silicate crust, mantle and metallic core.…”

Magma ascent in planetesimals: Control by grain size

“…Rudge, 2018), in particular for systems with several immiscible liquid phases. For example, the wetting angles formed between metal liquids with silicate minerals in the presence of a silicate melt remains unclear, leaving open the debate around a possible percolation threshold for metal liquids at low melt fractions (Cerantola et al, 2015). Further work needs to be undertaken to better quantify these effects.…”

“…However, if volatiles are exsolved before the onset of silicate melting, Fu and Elkins-Tanton (2014) argue that the segregation rate of dry melt is mostly controlled by the oxygen fugacity and the degree of melting. The oxygen fugacity determines (or is determined by) the relative abundance of FeO and Fe-FeS in the pri-mordial rock, with parts of the latter potentially lost to the core by percolation before the onset of major silicate melting (Yoshino et al, 2003;Cerantola et al, 2015;Ghanbarzadeh et al, 2017). Higher oxygen fugacity may therefore result in more Fe-rich silicate melts with reduced (or even inverted) density contrast relative to the host rock.…”

Late metal–silicate separation on the IAB parent asteroid: Constraints from combined W and Pt isotopes and thermal modelling

“…This includes both the residues of silicate melting and the melts themselves, plus abundant chondritic lithologies (e.g., Benedix et al, 2000;Hunt et al, 2017a;Ruzicka and Hutson, 2010). However, partial core formation could set in via incomplete percolative flow through the silicate matrix, which would leave portions of the metal in the mantle (Bagdassarov et al, 2009;Cerantola et al, 2015). An additional constraint is provided by the mixing of molten metal with cool silicates during the parent body break-up and reassembly at 10 to 14 Ma after CAI (Benedix et al, 2000;Theis et al, 2013).…”