Chandler Brian, Bernier Joel, Diamond Matthew, Kunz Martin, Wenk Hans-Rudolf
Department of Earth and Planetary Science, University of California, Berkeley, CA 94720, USA.
The Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
Sci Adv. 2021 Jan 1;7(1). doi: 10.1126/sciadv.abd3614. Print 2021 Jan.
Understanding dynamics across phase transformations and the spatial distribution of minerals in the lower mantle is crucial for a comprehensive model of the evolution of the Earth's interior. Using the multigrain crystallography technique (MGC) with synchrotron x-rays at pressures of 30 GPa in a laser-heated diamond anvil cell to study the formation of bridgmanite [(Mg,Fe)SiO] and ferropericlase [(Mg,Fe)O], we report an interconnected network of a smaller grained ferropericlase, a configuration that has been implicated in slab stagnation and plume deflection in the upper part of the lower mantle. Furthermore, we isolated individual crystal orientations with grain-scale resolution, provide estimates on stress evolutions on the grain scale, and report {110} twinning in an iron-depleted bridgmanite, a mechanism that appears to aid stress relaxation during grain growth and likely contributes to the lack of any appreciable seismic anisotropy in the upper portion of the lower mantle.
了解下地幔中相变过程的动力学以及矿物的空间分布，对于建立一个全面的地球内部演化模型至关重要。我们在激光加热金刚石砧室中，利用多晶晶体学技术（MGC）和同步加速器X射线，在30 GPa压力下研究了布里奇曼石[（Mg，Fe）SiO]和铁方镁石[（Mg，Fe）O]的形成，报告了一个由较小晶粒的铁方镁石组成的相互连接网络，这种结构与下地幔上部的板块停滞和地幔柱偏转有关。此外，我们以晶粒尺度分辨率分离出了单个晶体取向，给出了晶粒尺度上应力演化的估计值，并报告了贫铁布里奇曼石中的{110}孪晶，这一机制似乎有助于晶粒生长过程中的应力松弛，并且可能是下地幔上部缺乏明显地震各向异性的原因。
