Does Heterogeneous Strain Act as a Control on Seismic Anisotropy in Earth's Lower Mantle?
Does Heterogeneous Strain Act as a Control on Seismic Anisotropy in Earth's Lower Mantle?
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DOI：
10.3389/feart.2020.540449
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发表时间：
2020-10-14
影响因子：
2.9
通讯作者：
Miyagi, Lowell
中科院分区：
文献类型：
--
作者：
Couper, Samantha;Speziale, Sergio;Miyagi, Lowell
下地幔物质的塑性变形和结构发育可导致地震各向异性，因此研究下地幔物质的变形对解释下地幔流动具有重要意义。大多数以前的变形实验记录下地幔压力下的纹理发展已经进行了单相样品和/或在室温下。然而，真实的岩石在高温下变形，并且是多相的，因此变形可能不同于单相的变形。在这里，我们报告的高温金刚石压砧单元变形实验的多相组合的布里奇曼石，铁方镁石，和ringwoodite压缩从类似的28到类似的39 GPa和连续加热在1,000 K的恒温。我们采用弹粘塑性自洽的方法来模拟作为变形机制的函数的织构和晶格应变的Bridgmanite。模拟表明，在（100）[010]上的大约一半的滑移活动容纳了桥镁石的变形，其余部分在（100）[001]和/或（100）之间分裂< 011 >。硼镁石的结构与最低地幔的大多数地震观测结果一致。虽然有两个Bridgmanite和ringwoodite的纹理发展，铁方镁石不发展连贯的纹理在整个实验过程中。晶格应变的分析表明，缺乏连贯的纹理发展铁方镁石是由于非均质塑性变形所造成的微结构相互作用所施加的其他阶段。因此，硼镁石和铁方镁石结构的变化可能导致横向变化，复杂的各向异性。我们的二元地幔混合物的bridgmanite和铁方镁石模型表明，应变和纹理分区的变化可以解释所观察到的下地幔各向异性的范围。
Plastic deformation and texture development in minerals of the lower mantle can result in seismic anisotropy, and studying deformation of lower mantle materials is therefore important for interpreting lower mantle flow. Most previous deformation experiments documenting texture development at lower mantle pressures have been conducted on single-phase samples and/or at room temperature. However, real rocks deform at high temperature and are poly-phase and deformation is therefore likely different from that of a single phase. Here we report on high temperature diamond anvil cell deformation experiments on a multiphase assemblage of bridgmanite, ferropericlase, and ringwoodite compressed from similar to 28 to similar to 39 GPa and resistively heated at a constant temperature of 1,000 K. We employ the elasto-viscoplastic self-consistent method to model both texture and lattice strain of bridgmanite as a function of deformation mechanisms. Simulations indicate deformation of bridgmanite is accommodated by about half of slip activity on (100)[010] with the remainder split between (100)[001] and/or (100)< 011 >. Texture in bridgmanite is consistent with most seismic observations in the lowermost mantle. Although there is texture development in both bridgmanite and ringwoodite, ferropericlase does not develop coherent texture throughout the course of the experiment. Analysis of lattice strains suggests that the lack of coherent texture development in ferropericlase is due to heterogeneous plastic deformation resulting from microstructural interactions imposed by other phases. Variations in texturing of bridgmanite and ferropericlase could therefore cause laterally varying, complex anisotropy. Our models for binary mantle-like mixtures of bridgmanite and ferropericlase show that changes in strain and texture partitioning can explain the range of observed lower mantle anisotropies.