The mineral Davemaoite (CaSiO3-perovskite, the third most abundant mineral in lower mantle layer of jordens interior) has been discovered on the surface of the Earth for the first time. It was found trapped inside a diamond. Perovskite is found naturally ONLY in lower mantle layer of the interior of the Earth under extremely high temperature and pressure conditions. This first-ever discovery of interior jord mineral in nature is important to geology for better understanding of dynamics of deep Earth.
Perovskitt er et mineral som består av kalsiumtitanoksid (CaTiO3). Ethvert annet mineral med lignende krystallstruktur kalles perovskitt. Dette gjør perovskitt til en klasse forbindelser som har samme type krystallstruktur som CaTiO3 (perovskittstruktur).
Kalsium-silikat perovskitt (CaSiO3-perovskitt eller CaPv) er et viktig mineral fordi det er det tredje mest tallrike mineralet1 (7 volum%) i det nedre mantellaget av jordens interior and plays a significant role in the heat dynamics of jordens interior. To put things in perspective, of the three layers of Earth, the mantle layer, between dense super-heated core and thin outer crust layer, makes up 84% of jordens total volume while the lower mantle layer alone comprises 55 percent of the Earth and extends from 670 and 2900 km in depth. The below table gives a snapshot view of place of perovskite in jordens innsiden.
Tabell: Sted for perovskittrike lag i jordens indre
Perovskites along with other minerals in the mantle layer play a key role in the dynamics of deep jord involving heat transfer from core towards surface, called mantle convection. Despite its abundance and importance, perovskite has never been retrieved from the lower mantle layer, because it loses its structure on being removed from its high-pressure conditions.
Researchers have now reported Funnet of calcium silicate perovskite as a diamond inclusion in a natural sample. The diamond was found in Orapa mine, Botswana decades ago and was purchased by a mineralogist of USA in 1987. The team of researchers had been studying the diamond for few years for any entrapped deep-Earth mineral.
Forskerteamet ledet av Oliver Tschauner brukte synkrotronrøntgendiffraksjon for å studere den indre strukturen til de uendelig små mørke flekkene i en diamant antatt å være perovskitt fra det nedre mantellaget og var i stand til å finne definitive bevis på strukturelt bevart kubisk CaSiO3-perovskitt der2.
Further structural and chemical studies indicated that the mineral had large amounts of trapped potassium implying that this perovskite could host three of the major heat-producing elements (uranium and thorium were previously known) which influence heat generation in jordens interior. They named the mineral “davemaoite” (after geophysicist Ho-kwang “Dave” Mao) which was approved as a new natural mineral. The researchers think that the mineral may have originated from lower mantle layer between 650 and 900 km deep below the Earth’s surface 3,4.
Overraskende nok, CaSiO3 perovskite was reported to be discovered in a deep-Earth diamond from South Africa in 2018 however the research team had not claimed official discoveryhttps://www.scientificeuropean.co.uk/sciences/biology/discovery-of-nitrogen-fixing-cell-organelle-nitroplast-in-a-eukaryotic-algae/ of a new mineral 5.
Denne oppdagelsen, i forbindelse med ytterligere funn av flere mineraler i fremtiden, skulle berike forståelsen av utviklingen av jordkappen.
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Referanser:
- Zhang Z., et al 2021. Termisk ledningsevne av CaSiO3 perovskitt ved lavere mantelforhold. Physical Review B. Volume 104, Issue 18 – 1. Publisert 4. november 2021. DOI: https://doi.org/10.1103/PhysRevB.104.184101
- Fei, Y. 2021. Perovskitt hentet fra den nedre mantelen, Science. Publisert 11. nov 2021. Vol. 374, utgave 6569 s. 820-821. Vitenskap (2021). GJØR JEG: https://doi.org/10.1126/science.abm4742
- Tschauner, O. et al. Oppdagelse av davemaoitt, CaSiO3-perovskitt, som et mineral fra den nedre mantelen. Vitenskap. 11. november 2021. Vol 374, utgave 6569 s. 891-894. GJØR JEG: https://doi.org/10.1126/science.abl8568
- University of Nevada 2021. Nyheter – Forskning i korte trekk: Første gangs indre jordmineral oppdaget i naturen. [Lagt ut 15. november 2021. Tilgjengelig på nett på https://www.unlv.edu/news/release/research-brief-first-ever-interior-earth-mineral-discovered-nature
- Nestola, F., Korolev, N., Kopylova, M. et al. CaSiO3 perovskitt i diamant indikerer resirkulering av havskorpen inn i den nedre mantelen. Nature 555, 237–241 (2018). https://doi.org/10.1038/nature25972
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