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Viscosity of mafic magmas at high pressures

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.
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C Cochain, Chrystèle Sanloup, C Leroy, Y Kono. Viscosity of mafic magmas at high pressures. Geophysical Research Letters, American Geophysical Union, 2017, 44 (2), pp.818-826 ⟨10.1002/2016GL071600⟩. ⟨hal-01452772⟩



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