21 March, 2012 – Seminar

When: 4pm on Wednesday, March 21st, 2012
Where: DIAS, Geophysics Section, 5 Merrion Square, Dublin 2, (library)

Speaker: Dr. Fabrice Gaillard from Institut des Sciences de la Terre d’Orleans
Title: Partial melting and electrical conductivity of the mantle.

Abstract:

The identification of highly conductive regions in the Earth’s mantle has long been intriguing for the Geosciences community because peridotite rocks are not conductive. Supplementary materials must be added to ordinary peridotite in order to make the mantle conductive and mineral physicists, petrologists, geochemists and geophysicists have different point of views concerning the nature of this conductive component. A long standing interpretation has been water and its incorporation as impurities in mantle minerals such as olivine. The possibility of correlating high conductivity with high mantle water content has considerably impacted the scientific literature but disappointingly, most recent experimental constraints refute this elegant model. The ancient petrological model of mantle melting has recently been re-adopted with, as added value, the role of volatiles (H-C-Cl-F) on mantle melting. Several points will be tackled in this talk. Can volatiles allow mantle melting in the entire upper (and lower) mantle? What sort of melts is then produced? How they may deviate from the standard basaltic compositions? What is their impact on mantle conductivity? Can we recognize these melts in electromagnetic images of mantle conductivity? Can we then correlate electrical heterogeneity to chemical heterogeneities, ie. volatiles, redox,… ? Inbrief, can we reconcile the petrological mantle with the electrical mantle?