Reali Riccardo, Van Orman James A, Pigott Jeffrey S, Jackson Jennifer M, Boioli Francesca, Carrez Philippe, Cordier Patrick
University Lille, CNRS, INRA, ENSCL, UMR 8207 - UMET - Unité Matériaux et Transformations, Lille, F-59000, France.
Department of Earth, Environmental, and Planetary Sciences - Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH, 44106, USA.
Sci Rep. 2019 Feb 14;9(1):2053. doi: 10.1038/s41598-018-38449-8.
The viscosity of Earth's lower mantle is poorly constrained due to the lack of knowledge on some fundamental variables that affect the deformation behaviour of its main mineral phases. This study focuses on bridgmanite, the main lower mantle constituent, and assesses its rheology by developing an approach based on mineral physics. Following and revising the recent advances in this field, pure climb creep controlled by diffusion is identified as the key mechanism driving deformation in bridgmanite. The strain rates of this phase under lower mantle pressures, temperatures and stresses are thus calculated by constraining diffusion and implementing a creep theoretical model. The viscosity of MgSiO bridgmanite resulting from pure climb creep is consequently evaluated and compared with the viscosity profiles available from the literature. We show that the inferred variability of viscosity in these profiles can be fully accounted for with the chosen variables of our calculation, e.g., diffusion coefficients, vacancy concentrations and applied stresses. A refinement of these variables is advocated in order to further constrain viscosity and match the observables.
由于缺乏对一些影响下地幔主要矿物相变形行为的基本变量的了解，地球下地幔的粘度难以精确测定。本研究聚焦于下地幔的主要成分布里奇曼石，并通过开发一种基于矿物物理学的方法来评估其流变学性质。遵循并修订该领域的最新进展，由扩散控制的纯攀移蠕变被确定为驱动布里奇曼石变形的关键机制。因此，通过限制扩散并应用蠕变理论模型，计算了该相在下地幔压力、温度和应力条件下的应变率。进而评估了由纯攀移蠕变导致的MgSiO布里奇曼石的粘度，并与文献中可得的粘度剖面进行了比较。我们表明，这些剖面中推断出的粘度变化可以通过我们计算中所选的变量，如扩散系数、空位浓度和外加应力，得到充分解释。为了进一步限制粘度并与观测结果相匹配，提倡对这些变量进行细化。
