鐵方鎂石

鐵方鎂石（英語：Ferropericlase）或菱鎂礦（magnesiowüstite, 是一種鎂和鐵的氧化物，化學式為 (Mg,Fe)O。它與矽酸鹽鈣鈦礦（silicate perovskite） ((Mg,Fe)SiO₃) 被認爲為地幔的主要成分之一。矽酸鹽鈣鈦礦是具有鈣鈦礦結構的矽酸鎂鐵。一些天然鑽石中的包裹體含鐵方鎂石。含異常高鐵質的鑽石可能來自最下的地幔 ^[1] 。在地核附近的地幔有一些離散的超低地震波速區，這些被認為是鐵方鎂石積聚処，因為在高壓高溫下，地震波在穿鐵方鎂石時會明顯減慢^[2] 。 2018 年 5 月，方鎂石被證明在下地幔的高壓下，具有異向性。根據這異向性，地震學家和地質學家能由不同方向的地震波和波速度變化量，來判斷這些超低速帶是否確實是方鎂石^[3]。

自旋過渡帶

研究地幔礦物中鐵元素的電子自旋態變化，是在鐵方鎂石中進行的實驗。樣品在激光加熱的金剛石壓砧，達到下地幔的高溫高壓條件，使用同步加速器 X 射線光譜儀測量自旋狀態。結果表明，在從 1000 公里到 2200 公里的深度範圍內，隨着深度的增加，鐵從高自旋狀態向低自旋狀態變化^[4] ^[5]^[6] 。這自旋狀態的變化導緻密度隨深度的增加值比預期的高，也造成粘度的強烈變化^[7]。

地幔豐度

鐵方鎂石 (Mg,Fe)O 約佔地球下地幔體積的 20%，僅次於矽酸鹽鈣鈦礦 (Mg,Fe)SiO3 礦物相；它也是下地幔中鐵的主要礦物^[8]。在地幔過渡帶的底部，γ-橄欖石互變轉化為鈣鈦礦和鐵方鎂石的混合物。反應如下：

γ–(Mg,Fe)₂[SiO₄] ↔ (Mg,Fe)[SiO₃] + (Mg,Fe)O

下地幔的礦物相也常被稱為菱鎂礦（magnesiowüstite）^[9]。

參考文獻

^ Kopylova, M.G. 2006. Ferropericlase from the lowermost mantle and its geodynamic significance". Archived from the original on 2016-03-03. Retrieved 2008-03-18.
^ "Strange Blobs Beneath Earth Could Be Remnants of an Ancient Magma Ocean". Space.com. Retrieved 2018-10-01.
^ Finkelstein, Gregory J.; Jackson, Jennifer M.; Said, Ayman; Alatas, Ahmet; Leu, Bogdan M.; Sturhahn, Wolfgang; Toellner, Thomas S. (18 May 2018). "Strongly Anisotropic Magnesiowüstite in Earth's Lower Mantle" (PDF). Journal of Geophysical Research: Solid Earth. 123 (6): 4740–4750. Bibcode:2018JGRB..123.4740F. doi:10.1029/2017jb015349. ISSN 2169-9313.
^ Wentzcovitch, R. M.; Justo, J. F.; Wu, Z.; da Silva, C. R. S.; Yuen, D. A.; Kohlstedt, D. (2009). "Anomalous compressibility of ferropericlase throughout the iron spin cross-over". Proc. Natl. Acad. Sci. U.S.A. 106 (21): 8447–8452. arXiv:1307.3270. Bibcode:2009PNAS..106.8447W. doi:10.1073/pnas.0812150106. PMC 2681316. PMID 19439661.
^ Marcondes, Michel L.; Zheng, Fawei; Wentzcovitch, Renata M. (2020-09-25). "Phonon dispersion throughout the iron spin crossover in ferropericlase". Physical Review B. 102 (10): 104112. arXiv:2003.12348. Bibcode:2020PhRvB.102j4112M. doi:10.1103/PhysRevB.102.104112. S2CID 214693280.
^ Justo, J. F.; Morra, G.; Yuen, D. A. (2015). "Viscosity undulations in the lower mantle: The dynamical role of iron spin transition". Earth Planet. Sci. Lett. 421: 20–26. Bibcode:2015E&PSL.421...20J. doi:10.1016/j.epsl.2015.03.013.
^ "Researchers locate mantle's spin transition zone, leading to clues about earth's structure". Archived from the original on 2010-05-27.
^ Researchers locate mantle’s spin transition zone, leading to clues about earth’s structure Archived 2010-05-27 at the Wayback Machine
^ Ferropericlase on Mindat.org

[Kopy”-1] Kopylova, M.G. 2006. Ferropericlase from the lowermost mantle and its geodynamic significance". Archived from the original on 2016-03-03. Retrieved 2008-03-18.

[Stra”-2] "Strange Blobs Beneath Earth Could Be Remnants of an Ancient Magma Ocean". Space.com. Retrieved 2018-10-01.

[Fink”-3] Finkelstein, Gregory J.; Jackson, Jennifer M.; Said, Ayman; Alatas, Ahmet; Leu, Bogdan M.; Sturhahn, Wolfgang; Toellner, Thomas S. (18 May 2018). "Strongly Anisotropic Magnesiowüstite in Earth's Lower Mantle" (PDF). Journal of Geophysical Research: Solid Earth. 123 (6): 4740–4750. Bibcode:2018JGRB..123.4740F. doi:10.1029/2017jb015349. ISSN 2169-9313.

[Wentz”-4] Wentzcovitch, R. M.; Justo, J. F.; Wu, Z.; da Silva, C. R. S.; Yuen, D. A.; Kohlstedt, D. (2009). "Anomalous compressibility of ferropericlase throughout the iron spin cross-over". Proc. Natl. Acad. Sci. U.S.A. 106 (21): 8447–8452. arXiv:1307.3270. Bibcode:2009PNAS..106.8447W. doi:10.1073/pnas.0812150106. PMC 2681316. PMID 19439661.

[Marc”-5] Marcondes, Michel L.; Zheng, Fawei; Wentzcovitch, Renata M. (2020-09-25). "Phonon dispersion throughout the iron spin crossover in ferropericlase". Physical Review B. 102 (10): 104112. arXiv:2003.12348. Bibcode:2020PhRvB.102j4112M. doi:10.1103/PhysRevB.102.104112. S2CID 214693280.

[”Justo”-6] Justo, J. F.; Morra, G.; Yuen, D. A. (2015). "Viscosity undulations in the lower mantle: The dynamical role of iron spin transition". Earth Planet. Sci. Lett. 421: 20–26. Bibcode:2015E&PSL.421...20J. doi:10.1016/j.epsl.2015.03.013.

[Resea”-7] "Researchers locate mantle's spin transition zone, leading to clues about earth's structure". Archived from the original on 2010-05-27.

[”locate”-8] Researchers locate mantle’s spin transition zone, leading to clues about earth’s structure Archived 2010-05-27 at the Wayback Machine

[Ferro”-9] Ferropericlase on Mindat.org

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