The Effect of Pressure and Mg-Content on Ilmenite Rheology: Implications for Lunar Cumulate Mantle Overturn
- Journal Article
The viscosity of ilmenite is an important parameter that is thought to have influenced the thermal and chemical evolution of the lunar cumulate mantle. We conduct deformation experiments on two different ilmenite compositions, ilmenite100 (FeTiO3) and ilmenite40 ((Fe0.4Mg0.6)TiO3), to investigate the influence of pressure and Mg-content on the rheology of ilmenite aggregates. Experiments were conducted in a Griggs apparatus and a deformation-DIA apparatus at pressures spanning 1–5 GPa. Using the new experimental data and reanalyzed data from Dygert et al. (2016), we determine pressure-dependent flow law parameters for ilmenite100 (A = 2.183 MPa−ns−1, n = 3.0 ± 0.4, E = 276 ± 25 kJ/mol and V = 17 ± 4 cm3/mol) and ilmenite40 (A = 3.936e−7 MPa−ns−1, n = 5.7 ± 0.5, E = 283 ± 25 kJ/mol and V = 26 ± 4 cm3/mol). Over the range of experimental conditions ilmenite40 has a larger stress exponent and activation volume than ilmenite100. Extrapolation of the ilmenite100 flow law predicts a viscosity approximately five orders of magnitude lower than dry olivine and three orders of magnitude lower than wet olivine at a temperature of 1,100°C, pressure of 0.3 GPa, and stress of 0.3 MPa, conditions representative of the early ilmenite-bearing cumulate. Our estimated viscosity contrasts for a dry lunar mantle suggests that lunar cumulate mantle overturn may be dominated by longer wavelength downwellings, while a wet lunar mantle may be dominated by shorter wavelength downwellings. © 2020. American Geophysical Union. All Rights Reserved. Show more
Journal / seriesJournal of Geophysical Research: Planets
Pages / Article No.
PublisherAmerican Geophysical Union
Organisational unit09636 - Behr, Whitney / Behr, Whitney
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