Viscosity of mafic magmas at high pressuresReport as inadecuate

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* Corresponding author 1 iSTeP - Institut des Sciences de la Terre de Paris 2 Scottish Universities Physics Alliance SUPA 3 PGM2 - Pétrologie, géochimie, minéralogie magmatiques iSTeP - Institut des Sciences de la Terre de Paris 4 IMPMC - Institut de minéralogie, de physique des matériaux et de cosmochimie 5 Geophysical Laboratory Carnegie Institution

Abstract : While it is accepted that silica-rich melts behave anomalously with a decrease of their viscosity at increased pressures P, the viscosity of silica-poor melts is much less constrained. However, modeling of mantle melts dynamics throughout Earth-s history, including the magma ocean era, requires precise knowledge of the viscous properties of silica-poor magmas. We extend here our previous measurements on fayalite melt to natural end-members pyroxenite melts MgSiO 3 and CaSiO 3 using in situ X-ray radiography up to 8 GPa. For all compositions, viscosity decreases with P, rapidly below 5 GPa and slowly above. The magnitude of the viscosity decrease is larger for pyroxene melts than for fayalite melt and larger for the Ca end-member within pyroxene melts. The anomalous viscosity decrease appears to be a universal behavior for magmas up to 13 GPa, while the P dependence of viscosity beyond this remains to be measured. These results imply that mantle melts are very pervasive at depth.

Author: C Cochain - Chrystèle Sanloup - C Leroy - Y Kono -



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