A flow law for ilmenite in dislocation creep: Implications for lunar cumulate mantle overturn. Issue 2 (21st January 2016)

• Record Type: Journal Article
• Authors: Dygert, Nick; Hirth, Greg; Liang, Yan
• Is Part Of: Geophysical research letters. Volume 43:Issue 2(2016)
• Page Start: 532
• Page End: 540
• Publication Date: 2016-01-21
• Subjects: ilmenite -- lunar -- cumulate overturn -- dislocation creep -- Griggs apparatus; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2015GL066546
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: We present results from new deformation experiments and a dislocation creep flow law for synthetic ilmenite. The flow law predicts an effective viscosity more than 3 orders of magnitude lower than dry olivine at mantle stresses and temperatures. Using the flow law, we predict that lunar ilmenite‐bearing cumulates (IBC) will be weakened by the presence of low‐viscosity ilmenite. Dense, low‐viscosity IBC are expected to flow into the lunar interior by a process known as cumulate mantle overturn. Low‐viscosity IBC that sink to the core‐mantle boundary may be dynamically stable with respect to upwelling. A hot, stable layer of IBC surrounding the lunar core would suppress the development of a core dynamo. A layer of partially molten IBC can also explain the inferred zone of seismic attenuation around the lunar core, as well as a low‐viscosity layer suggested by tidal dissipation. Key Points: Viscosity of ilmenite was measured to parameterize a dislocation creep flow law Ilmenite has a low effective viscosity compared to olivine at mantle temperatures Ilmenite affects the style and scale of lunar mantle convection and structure