Langrand Christopher, Andrault Denis, Durand Stéphanie, Konôpková Zuzana, Hilairet Nadège, Thomas Christine, Merkel Sébastien
Univ. Lille, CNRS, INRA, ENSCL, UMR 8207 - UMET - Unité Matériaux et Transformations, F-59000, Lille, France.
Université Clermont Auvergne, CNRS, IRD, OPGC, Laboratoire Magmas et Volcans, F-63000, Clermont-Ferrand, France.
Nat Commun. 2019 Dec 12;10(1):5680. doi: 10.1038/s41467-019-13482-x.
Bridgmanite, the dominant mineral in the Earth's lower mantle, crystallizes in the perovskite structure and transforms into post-perovskite at conditions relevant for the D[Formula: see text] layer. This transformation affects the dynamics of the Earth's lowermost mantle and can explain a range of seismic observations. The thickness over which the two phases coexist, however, can extend over 100 km, casting doubt on the assignment of the observed seismic boundaries. Here, experiments show that the bridgmanite to post-perovskite transition in (Mg[Formula: see text],Fe[Formula: see text])SiO[Formula: see text] is fast on geological timescales. The transformation kinetics, however, affects reflection coefficients of [Formula: see text] and [Formula: see text] waves by more than one order of magnitude. Thick layers of coexisting bridgmanite and post-perovskite can hence be detected using seismic reflections. Morever, the detection and wave period dependence of D[Formula: see text] reflections can be used to constrain significant features of the Earth's lowermost mantle, such as the thickness of the coexistence layer, and obtain information on temperature and grain sizes.
布里奇曼石是地球下地幔中的主要矿物，以钙钛矿结构结晶，并在与D″层相关的条件下转变为后钙钛矿。这种转变影响地球最底层地幔的动力学，并能解释一系列地震观测结果。然而，两相共存的厚度可以延伸超过100千米，这使得对观测到的地震边界的归属产生了疑问。在此，实验表明，在地质时间尺度上，（Mg₀.₉Fe₀.₁）SiO₃中布里奇曼石向后钙钛矿的转变很快。然而，转变动力学对P波和S波反射系数的影响超过一个数量级。因此，可以利用地震反射探测到共存的布里奇曼石和后钙钛矿的厚层。此外，D″反射的探测和波周期依赖性可用于约束地球最底层地幔的重要特征，如共存层的厚度，并获取有关温度和晶粒尺寸的信息。
