Séminaire ISTeP - Benjamin Cochain

(ISTeP)

Viscosity of depolymerised silicate melts at high pressure

We present here the results of in-situ viscosity measurements on MgSiO3, CaMgSi2O6 and CaSiO3 melts up to 7 GPa using the falling-sphere viscometry technique in a Paris-Edinburgh Cell[1]. We found a negative pressure dependence of the viscosity up to 7 GPa both along liquidus and at constant temperature. Our results are in agreement with our previous viscosity measurements on Fayalite melt[1] which have also shown a negative pressure dependence but are in contrast with previous studies on depolymerised silicate melts on a similar pressure range[2]. We will show that the pressure variations can likely be associated with structural changes such as the increase in Mg-O, Ca-O and Fe-O coordinations with pressure. The results also show that silicate melt viscosity strongly depends on the melt structure and composition. This has important implications for models of planetary differentiation but also for interpreting the transport properties of modern magmas today. In addition our results compare favourably to the available numerical simulations[3] and will therefore help to constrain numerical models of depolymerized silicate melt viscosity.
1. H. E. Spice, C. Sanloup, B. Cochain, C. de Grouchy, Y. Kono, submitted to GCA
2. Y. Wang, T. Sakamaki, L.B. Skinner, Z. Jing, T. Yu, Y. Kono, C. Park, G. Shen, M.L. Rivers, S.R. Sutton, Nature Communications 5 (2014)
3. B. Karki., L. Stixrude, Science 328, 740–742 (2010)

20/03/2015 à 12h30, Salle Fourcade (Tour 55/56, 4ème étage)