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Julia Fox
Dr. Jeff Lawlis, teacher and Science Department Chair at the Merle-Smith Campus, recently published an article entitled "High-Temperature Deformation of Enstatite-Olivine Aggregates" in the Journal of Geophysical ResearchIt is based upon his PhD research.
Plain Language Summary
The rheology of Earth's upper mantle is generally modeled using mechanical flow laws determined for aggregates composed only of olivine minerals, in spite of the polyphase nature of mantle rocks. In this study, we investigated the effect of phase volume proportions on the high‐ temperature deformation properties of aggregates composed of the two most abundant minerals in the upper mantle, olivine and enstatite. The samples were deformed under dry conditions in triaxial compression at 1150– 1300°C, under oxygen fugacity fixed at the Ni/NiO solid buffer, and confining pressures of 300 or 450 MPa, at conditions where enstatite has two different crystallographic structures. At both pressures, in the dislocation creep regime, where deformation occurs mostly by the motion of dislocations along slip planes within mineral grains, the strengths of all the two‐phase mixtures lie between the uniform strain rate and the uniform stress bounds, which assume iso‐strain and iso‐stress conditions, respectively, in all the grains comprising each aggregate. Extrapolating these bounds to temperatures and strain rates expected in nature indicates that the viscosity of mantle rocks can be modeled adequately with the dislocation creep flow law for olivine.

Bystricky, M., Lawlis, J., Mackwell, S., & Heidelbach, F. (2024). High-temperature deformation of enstatite-olivine aggregates. Journal of Geophysical Research: Solid Earth, 129, e2023JB027699. https://doi.org/10.1029/2023JB027699
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