Deformation of (Mg,Fe)O Ferropericlase to Temperatures of 1150 K and Pressures of 96 GPa: Implications for Mantle Flow and Seismic Anisotropy
Abstract:Ferropericlase (Mg,Fe)O is thought to be the second most abundant mineral in Earth’s lower mantle. Due to its potentially weak rheological behavior it may play a key role in controlling rheology of the lower mantle and in generating seismic anisotropy . At pressures between approximately 40 GPa and 70 GPa at 300 K, the ferrous iron in ferropericlase undergoes a spin crossover from high-spin to low-spin state . Our understanding of the deformation behavior of both high- and low-spin ferropericlase is incomplete, particularly at high-temperatures. The only published deformation study on (Mg,Fe)O through the spin transition pressure region has limited pressure resolution and was measured at 300 K .
Here, we present new results from synchrotron radial x-ray diffraction measurements on the deformation behavior of (Mg,Fe)O at high-pressures, covering the spin crossover pressure range, and high-temperatures. One set of experiments was performed on (Mg0.8-0.9Fe0.1-0.2)O at the Advanced Light Source (Lawrence Berkeley National Laboratory) up to 96 GPa at 300 K. A second suite of data were collected at the Extreme Conditions Beamline of PETRA III (DESY), where (Mg0.8Fe0.2)O was compressed at constant temperature to 70 GPa (at 850 K) and 40 GPa (at 1150 K). In all experiments, pressure was remotely increased using a gas membrane system, which allows for obtaining a very fine pressure resolution.
From our data, we calculate the yield strength of ferropericlase, which we find to increase by a factor of about three throughout the lower mantle. Furthermore, we infer likely slip system activities of ferropericlase in Earth’s lower mantle based on our experimental data and elastic viscoplastic self-consistent (EVPSC) modelling. We will discuss the effect of the increase of ferropericlase strength on the fate of subducting slabs and we will show potential implications for seismic anisotropy observations in D``, where low-spin ferropericlase is characterized by very large elastic anisotropy .
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