Influence of iron on the elastic properties of wadsleyite and ringwoodite
Influence of iron on the elastic properties of wadsleyite and ringwoodite
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DOI：
10.1029/2011jb008378
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发表时间：
2010-12
影响因子：
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通讯作者：
M. Núñez-Valdez;P. D. Silveira;R. Wentzcovitch
中科院分区：
文献类型：
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作者：
M. Núñez-Valdez;P. D. Silveira;R. Wentzcovitch
[1]我们通过第一性原理研究了铁对b相（wadsleyite）和g相（ringwoodite）弹性性质的影响，这两种相是橄榄石的多晶型物，分别是过渡区上部和下部最丰富的矿物。我们的研究旨在补充实验，以了解410公里和520公里的不连续性的细节。在静态条件下测定b-g-（Mg 1-xFex）2SiO 4（x = 0.125）的全弹性张量Cij、体模量（K）和剪切模量（G）。研究了单晶中的波传播各向异性和具有择优取向的聚集体中的极化各向异性，并与无铁的wadsleyite和ringwoodite进行了比较，以彻底了解铁的影响。我们研究了铁对由于相变引起的速度对比的影响，并得出结论，铁在a → B转变过程中增强了DVP和DVS，但在B → g转变过程中抑制了它们。如果B → g跃迁对520 km不连续性有显著贡献，则后者可能有助于局部抑制该不连续性。我们发现，横向变化的铁，dx，产生的横向速度的非均匀性比类似的横向变化的温度，dT，这两个生产比从地震层析成像研究中提取的值。然而，与dT相反，dx产生负值的密度与纵波和横波速度比。这可能被认为是铁浓度横向变化的指纹。这些负比值似乎与Karato和Karki（2001年）编制的上地幔和过渡带地球动力学模型推断的结果相似。
[1] We investigate by first‐principles the influence of iron on the elastic properties of the b–phase (wadsleyite) and g–phase (ringwoodite), polymorphs of olivine, the most abundant minerals of the upper and lower parts of the transition zone, respectively. Our study aims to complement experiments to understand details of the 410 km and 520 km discontinuities. The full elastic‐tensor Cij, bulk (K), and shear (G) moduli are determined under static conditions for b–g–(Mg1–xFex)2SiO4 with x = 0.125. Wave propagation anisotropy in single crystals and polarization anisotropy in aggregates with preferred orientation are investigated and compared with those of iron‐free wadsleyite and ringwoodite for a thorough understanding of the effect of iron. We examine the effect of iron on velocity contrasts due to phase changes and conclude that iron enhances DVP and DVS across the a → b transition but suppresses them across the b → g transition. The latter might contribute to suppress locally the 520 km discontinuity if this has a significant contribution from the b → g transition. We show that lateral variation of iron, dx, produces lateral velocity heterogeneity ratios similar to those produced by lateral variations of temperature, dT, both producing ratios comparable to values extracted from seismic tomography studies. However, in contrast with dT, dx produces negative values for density to longitudinal and shear wave velocity ratios. This might be considered the fingerprint of lateral variations of iron concentration. These negative ratios appear similar to results inferred from geodynamical models compiled by Karato and Karki (2001) for the upper mantle and transition zone.