Shim S H, Duffy T S, Shen G
Department of Geosciences, Princeton University, Princeton, NJ 08544, USA., CARS, University of Chicago, Chicago, IL 60637, USA.
Science. 2001 Sep 28;293(5539):2437-40. doi: 10.1126/science.1061235.
Unexplained features have been observed seismically near the middle (approximately 1700-kilometer depth) and bottom of the Earth's lower mantle, and these could have important implications for the dynamics and evolution of the planet. (Mg,Fe)SiO3 perovskite is expected to be the dominant mineral in the deep mantle, but experimental results are discrepant regarding its stability and structure. Here we report in situ x-ray diffraction observations of (Mg,Fe)SiO3 perovskite at conditions (50 to 106 gigapascals, 1600 to 2400 kelvin) close to a mantle geotherm from three different starting materials, (Mg0.9Fe0.1)SiO enstatite, MgSiO3 glass, and an MgO+SiO2 mixture. Our results confirm the stability of (Mg,Fe)SiO3 perovskite to at least 2300-kilometer depth in the mantle. However, diffraction patterns above 83 gigapascals and 1700 kelvin (1900-kilometer depth) cannot presently rule out a possible transformation from Pbnm perovskite to one of three other possible perovskite structures with space group P2(1)/m, Pmmn, or P4(2)/nmc.
在地幔中部（约1700公里深度）和下地幔底部附近，通过地震观测发现了一些无法解释的特征，这些特征可能对地球的动力学和演化具有重要意义。（Mg,Fe）SiO3钙钛矿预计是深部地幔中的主要矿物，但关于其稳定性和结构的实验结果存在差异。在此，我们报告了从三种不同起始材料（Mg0.9Fe0.1）SiO 顽火辉石、MgSiO3玻璃和MgO+SiO2混合物出发，在接近地幔地热的条件（50至106吉帕斯卡，1600至2400开尔文）下对（Mg,Fe）SiO3钙钛矿进行的原位X射线衍射观测。我们的结果证实了（Mg,Fe）SiO3钙钛矿在地幔中至少到2300公里深度的稳定性。然而，目前在83吉帕斯卡和1700开尔文（1900公里深度）以上的衍射图案无法排除从Pbnm钙钛矿向具有空间群P2(1)/m、Pmmn或P4(2)/nmc的其他三种可能钙钛矿结构之一转变的可能性。
