Evolution of Microstructural Properties in Sheared Iron‐Rich Olivine
Evolution of Microstructural Properties in Sheared Iron‐Rich Olivine
复制标题
DOI：
10.1029/2020jb019629
复制
发表时间：
2021-02
期刊：
影响因子：
--
通讯作者：
Chao Qi;Y. Zhao;M. Zimmerman;Daeyeong Kim;D. Kohlstedt
中科院分区：
文献类型：
--
作者：
Chao Qi;Y. Zhao;M. Zimmerman;Daeyeong Kim;D. Kohlstedt
富含铁的橄榄石在力学上弱于地幔成分的橄榄石，约为Fo90，因此更适合在广泛的实验室条件下进行研究。为了研究铁含量对变形产生的晶体择优取向(CPO)和晶粒度的影响，我们分析了成分为Fo70、Fo50和fo0的橄榄石样品在300 MPa的无水和有水条件下的扭转变形的微观结构。电子背散射衍射(EBSD)观察表明，在低应变下，CPO从(010)[100]和(001)[100]滑移系上的位错滑移引起的D型组构向(010)[100]滑移系上的位错滑移引起的A型组构的转变，而在高应变下，与铁含量和有水/无水条件无关。据报道，随着应变的增加，FO90的面料也出现了类似的演变。径向地震各向异性随应变的增加而增大，在每个样品的剪切应变为∼3.5时，径向地震各向异性达到最大值∼1.15，这表明自然变形的富铁橄榄石岩石的地震各向异性可以很好地近似于富铁橄榄石的地震各向异性。基于EBSD观测，我们得到了再结晶晶粒度与应力成反比的∼1.2次方压力计。随着含铁量的增加，再结晶晶粒尺寸增大。我们的实验结果不仅有助于理解地球上地幔的微结构演化，也有助于理解火星上橄榄石中铁含量较高的地幔的微结构演化。
Iron‐rich olivine is mechanically weaker than olivine of mantle composition, ca. Fo90, and thus is more amenable to study under a wide range of laboratory conditions. To investigate the effects of iron content on deformation‐produced crystallographic preferred orientation (CPO) and grain size, we analyzed the microstructures of olivine samples with compositions of Fo70, Fo50, and Fo0 that were deformed in torsion under either anhydrous or hydrous conditions at 300 MPa. Electron backscatter diffraction (EBSD) observations reveal a transition in CPO from D‐type fabric, induced by dislocation glide on both the (010)[100] and the (001)[100] slip systems, at low strains, to A‐type fabric, caused by dislocation glide on the (010)[100] slip system, at high strains for all of our samples, independent of iron content and hydrous/anhydrous conditions. A similar evolution of fabric with increasing strain is also reported to occur for Fo90. Radial seismic anisotropy increases with increasing strain, reaching a maximum value of ∼1.15 at a shear strain of ∼3.5 for each sample, demonstrating that the seismic anisotropy of naturally deformed olivine‐rich rocks can be well approximated by that of iron‐rich olivine. Based on EBSD observations, we derived a piezometer for which recrystallized grain size decreases inversely with stress to the ∼1.2 power. Also, recrystallized grain size increases with increasing iron content. Our experimental results contribute to understanding the microstructural evolution in the mantle of not only Earth but also Mars, where the iron content in olivine is higher.