Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
8915701 | Physics of the Earth and Planetary Interiors | 2018 | 40 Pages |
Abstract
We have undertaken an experimental investigation of the effect of iron content on the viscosity of Fe-Mg olivine aggregates deformed under hydrous conditions in order to provide a basis for comparing convection models for the mantle of Earth with those for the more iron-rich mantle of Mars. Fine-grained samples of Fe-bearing olivine with fayalite contents, Fax, of xâ¯=â¯100, 75, 50, 30 and 10 were deformed in triaxial compressive creep primarily in the dislocation creep regime under water-saturated conditions at temperatures of 1273 to 1473â¯K and a confining pressure of 300â¯MPa. Nickel sleeves around the samples of Fa10, Fa30 and Fa50 set the oxygen fugacity at the Ni:NiO buffer and thus the water fugacity at â²300â¯MPa, while Fe sleeves around samples of Fa75 and Fa100 set the oxygen fugacity at the Fe:FeO buffer and thus the water fugacity at â²200â¯MPa. Samples were deformed in triaxial compression to a maximum strain of 0.2 at differential stresses from 10 to 300â¯MPa and strain rates from 10â7 to 10-3â¯sâ1. In the dislocation creep field at a given temperature, the viscosity of samples of Fa50 is a factor of â¼10 smaller than the viscosity of samples of Fa30, while the viscosity of samples of Fa30 is a factor of â¼10 smaller than that of samples of Fa10. Our experimental results can be described by the flow law εÌdisl=CdislÏμndislXFapdislexp-(Qdisl0+αdislXFa)RTfH2Omdisl with Cdislâ¯=â¯99.7â¯MPaâ5/4â¯sâ1, ndislâ¯=â¯3.7, pdislâ¯=â¯0.5, Qdisl0â¯=â¯510â¯kJ/mol, αdislâ¯=â¯â120â¯kJ/mol, and mdislâ¯=â¯5/4. This flow law indicates that the viscosity of olivine of a specific Fe:Mg ratio is a factor of â¼10 smaller than its counterpart deformed under anhydrous conditions. In a hydrous environment at the same thermodynamic conditions, the viscosity of the more Fe-rich mantle (â¼Fa19) of Mars is a factor of â¼5 lower than that of the mantle (â¼Fa8) of Earth.
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Geophysics
Authors
Yong-Hong Zhao, Mark E. Zimmerman, David L Kohlstedt,