Evidence for a Fe3+-rich pyrolitic lower mantle from (Al,Fe)-bearing bridgmanite elasticity data
Evidence for a Fe3+-rich pyrolitic lower mantle from (Al,Fe)-bearing bridgmanite elasticity data
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DOI：
10.1038/nature21390
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发表时间：
2017-03-23
期刊：
影响因子：
64.8
通讯作者：
Ziberna, L.
中科院分区：
文献类型：
--
作者：
Kurnosov, A.;Marquardt, H.;Ziberna, L.
地球下地幔的化学成分可以通过结合地震观测和矿物物理弹性测量来确定（1-3）。然而，缺乏地球上最丰富的矿物（Mg，Fe，Al）（Si，Al，Fe）O-3桥镁石（也称为硅酸盐钙钛矿）的实验室数据，阻碍了任何结论性的结果。在这里，我们报告的单晶弹性数据（Al，Fe）轴承bridgmanite（Mg0.9Fe0.1Si0.9Al0.1）O-3测量使用高压布里渊光谱和X射线衍射。我们的测量结果表明，（铝，铁）轴承bridgmanite的弹性行为是显着不同的行为的MgSiO 3 endmember 2，4。我们使用我们的数据来模拟下地幔顶部的地震波速度，假设热解（5）地幔成分，并解释了硼镁石和铁方镁石之间铁分配的深度依赖性变化（6，7）。我们发现我们的矿物物理学预测与地震初步参考地球模型（8）之间非常一致，深度至少为1，200公里，表明上地幔和浅层下地幔的化学均匀性。在浅下地幔桥晶岩中需要约为2的高Fe 3 +/Fe 2+比值来匹配地震数据，这意味着在等化学地幔中存在金属铁。我们计算的速度越来越不符合下地幔的深度大于1,200公里，这表明或者是改变了布里奇曼石阳离子排序或减少了下地幔的三价铁含量。
The chemical composition of Earth's lower mantle can be constrained by combining seismological observations with mineral physics elasticity measurements(1-3). However, the lack of laboratory data for Earth's most abundant mineral, (Mg, Fe, Al)(Si, Al, Fe)O-3 bridgmanite (also known as silicate perovskite), has hampered any conclusive result. Here we report single-crystal elasticity data on (Al, Fe)-bearing bridgmanite (Mg0.9Fe0.1Si0.9Al0.1)O-3 measured using high-pressure Brillouin spectroscopy and X-ray diffraction. Our measurements show that the elastic behaviour of (Al, Fe)-bearing bridgmanite is markedly different from the behaviour of the MgSiO3 endmember2,4. We use our data to model seismic wave velocities in the top portion of the lower mantle, assuming a pyrolitic(5) mantle composition and accounting for depth-dependent changes in iron partitioning between bridgmanite and ferropericlase(6,7). We find excellent agreement between our mineral physics predictions and the seismic Preliminary Reference Earth Model(8) down to at least 1,200 kilometres depth, indicating chemical homogeneity of the upper and shallow lower mantle. A high Fe3+/Fe2+ ratio of about two in shallow-lower-mantle bridgmanite is required to match seismic data, implying the presence of metallic iron in an isochemical mantle. Our calculated velocities are in increasingly poor agreement with those of the lower mantle at depths greater than 1,200 kilometres, indicating either a change in bridgmanite cation ordering or a decrease in the ferric iron content of the lower mantle.