Direct Viscosity Measurement of Peridotite Melt to Lower-Mantle Conditions: A Further Support for a Fractional Magma-Ocean Solidification at the Top of the Lower Mantle

Longjian Xie , Akira Yoneda , Tomoo Katsura , Denis Andrault (1, 2) , Yoshinori Tange , Yuji Higo

1 OPGC - Observatoire de Physique du Globe de Clermont-Ferrand
2 LMV - Laboratoire Magmas et Volcans

As evidenced by isotope geochemistry, the persistence of primitive reservoirs indicates that the earth's lower mantle is likely to be heterogeneous. Such heterogeneity could be a legacy from magma-ocean (MO) solidification. The viscosity of MO is a key parameter to constrain the solidification type of MO. Here we directly measure the viscosity of peridotite (an analog of MO composition) melt at the pressure-temperature conditions of the deep mantle, using the in situ falling sphere method. The viscosity of peridotite melt along liquidus is in the range of 38-17 mPa s at pressures from 7 to 25 GPa, which is 0.9-0.4 times of the estimation based on the viscosity of endmember compositions. Low viscosity favors fractional solidification and chemically layering of the early mantle at least to the top lower mantle, which could be a source of heterogeneity for the present mantle.

Mots clés: magma ocean; viscosity; peridotite melt; boron-doped diamond; in situ falling sphere viscometry

Domaines: Planète et Univers [physics]; Sciences de la Terre

Longjian Xie, Akira Yoneda, Tomoo Katsura, Denis Andrault, Yoshinori Tange, et al.. Direct Viscosity Measurement of Peridotite Melt to Lower-Mantle Conditions: A Further Support for a Fractional Magma-Ocean Solidification at the Top of the Lower Mantle. Geophysical Research Letters, 2021, 48, ⟨10.1029/2021GL094507⟩. ⟨insu-03708919⟩