Silicon stable isotope fractionation between metal and silicate at high-pressure, high-temperature conditions as a tracer of planetary core formation

Abstract

The largest differentiation event in Earth and other terrestrial planets was the high-pressure, high-temperature process of metal core segregation from a silicate mantle. The abundant element silicon (Si) can be partially sequestered into the metallic core during metal-silicate differentiation, depending on pressure, temperature and planetary oxidation state. Knowledge of the Si content of a planet's core can constrain the conditions of core formation, but in the absence of direct samples from planetary cores, quantifying core Si content is challenging. One relatively new tool to study core formation in terrestrial planets is based on combining measurements of the Si stable isotopic composition of planetary crust and mantle samples with measurements of the Si stable isotope fractionation between metal and silicate at high-temperature and high-pressure conditions. In this study we present the results of a small set of high-pressure, high-temperature (HPT) experiments and combine these with a review of literature data to investigate how the Si isotope fractionation behaviour between metal and silicate varies as a function specifically of experimental run time and temperature. We show that although there is no debate about the sign of fractionation, absolute values for Si isotope fractionation between metal and silicate are difficult to constrain because the experimental database remains incomplete, and because Si isotopic measurements of metals in particular suffer from the absence of a true inter-laboratory comparison. We conclude that in order to derive accurate quantitative estimates of the Si content of the core of the Earth or other planets a wide range of additional experiments will be required.

Nickel isotope fractionation during metal-silicate differentiation of planetesimals: Experimental petrology and ab initio calculations

“…McManus et al, 2002;Rouxel et al, 2003;Hohl et al, 2015;Noordmann et al, 2015;Wang et al, 2016;Baronas et al, 2018) to metal silicate dif ferentiation in planets and asteroids (e.g. Poitrasson et al, 2005Poitrasson et al, , 2009Georg et al, 2007;Schoenberg and von Blanckenburg, 2006;Luais, 2007;Hin et al, 2013;Bonnand et al, 2016;Kempl et al, 2016;Mahan et al, 2017;Liu et al, 2017;Bourdon et al, 2018).…”

Introduction: Planetary geosciences, the Dutch contribution to the exploration of our solar system

“…In this special issue, Kempl et al (2016) kick off with a study closely associated with the early stages of planet formation in our solar system. They provide an overview of current knowledge of the fractionation of silicon isotopes between coexisting metal and silicate at high-pressure, high-temperature conditions.…”