School of Biological, Earth and Environmental Sciences, University College Cork, Cork, Ireland.
Institute of Precambrian Geology and Geochronology of the Russian Academy of Sciences, nab. Makarova 2, St. Petersburg, 199034, Russia.
Nat Commun. 2022 Dec 6;13(1):7517. doi: 10.1038/s41467-022-35110-x.
Ferropericlase (Mg,Fe)O is the second most abundant mineral in Earth's lower mantle and a common inclusion found in subcratonic diamonds. Pyrolitic mantle has Mg# (100 × Mg/(Mg+Fe)) ~89. However, ferropericlase inclusions in diamonds show a broad range of Mg# between 12 and 93. Here we use Synchrotron Mössbauer Source (SMS) spectroscopy and single-crystal X-ray diffraction to determine the iron oxidation state and structure of two magnesiowüstite and three ferropericlase inclusions in diamonds from São Luiz, Brazil. Inclusion Mg#s vary between 16.1 and 84.5. Ferropericlase inclusions contain no ferric iron within the detection limit of SMS, while both magnesiowüstite inclusions show the presence of monocrystalline magnesioferrite ((Mg,Fe)FeO) with an estimated 47-53 wt% FeO. We argue that the wide range of Fe concentrations observed in (Mg,Fe)O inclusions in diamonds and the appearance of magnesioferrite result from oxidation of ferropericlase triggered by the introduction of subducted material into sublithospheric mantle.
尖晶石 (Mg,Fe)O 是下地幔中第二丰富的矿物，也是亚克拉通金刚石中常见的包裹体。地幔的 Mg#（100×Mg/(Mg+Fe)）约为 89。然而，金刚石中的尖晶石包裹体的 Mg# 范围很宽，在 12 到 93 之间。在这里，我们使用同步辐射 Mössbauer 源（SMS）光谱和单晶 X 射线衍射来确定来自巴西圣路易斯的两颗镁铁尖晶石和三颗尖晶石包裹体的铁氧化态和结构。包裹体的 Mg# 在 16.1 到 84.5 之间变化。SMS 检测到的尖晶石包裹体不含三价铁，而两种镁铁尖晶石包裹体都存在单斜晶的镁铁尖晶石 ((Mg,Fe)FeO)，估计其 FeO 含量为 47-53wt%。我们认为，金刚石中 (Mg,Fe)O 包裹体中观察到的铁浓度范围很宽，以及镁铁尖晶石的出现，是由于俯冲物质进入亚岩石圈地幔时触发了尖晶石的氧化。
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