Publication Date:
2023-11-02
Description:
Abstract
Phase relations in the MgSiO〈sub〉3〈/sub〉–MgAl〈sub〉2〈/sub〉O〈sub〉4〈/sub〉–Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 system are investigated at 27 GPa and 2000–2600 K using a multi‐anvil apparatus. The AlAlO〈sub〉3〈/sub〉 content in the bridgmanite increases from 8.6 to 20.0 mol% with increasing temperature from 2000 to 2600 K, while the MgAlO〈sub〉2.5〈/sub〉 content remains nearly constant, that is, 3–4 mol% at these temperatures. Therefore, the presence of an additional Al‐bearing phase suppresses the oxygen vacancy substitution for Al〈sup〉3+〈/sup〉 in bridgmanite. Conversely, significant amounts of the Al〈sub〉8/3〈/sub〉O〈sub〉4〈/sub〉 component can be dissolved into the calcium‐ferrite type MgAl〈sub〉2〈/sub〉O〈sub〉4〈/sub〉–Mg〈sub〉2〈/sub〉SiO〈sub〉4〈/sub〉–Al〈sub〉8/3〈/sub〉O〈sub〉4〈/sub〉 phase (CF‐phase), implying that the CF‐phase likely contains some amount of vacancies. Therefore, the CF‐phase could also be a candidate mineral for transporting volatiles into the lower mantle. Our results, combined with previous studies on Al‐bearing bridgmanite, indicate that, once the Al per formula unit exceeds 0.12 in bridgmanite, the MgAlO〈sub〉2.5〈/sub〉 content remains nearly constant and the AlAlO〈sub〉3〈/sub〉 component becomes dominant.
Description:
Plain Language Summary:
Bridgmanite, the most abundant mineral in the Earth's mantle, can contain Al〈sup〉3+〈/sup〉 in the forms of MgAlO〈sub〉2.5〈/sub〉 and AlAlO〈sub〉3〈/sub〉. To constrain the substitution mechanism of Al〈sup〉3+〈/sup〉 in bridgmanite, we investigate the MgAlO〈sub〉2.5〈/sub〉 and AlAlO〈sub〉3〈/sub〉 contents in bridgmanite coexisting with a calcium‐ferrite type phase and corundum at different temperatures. Our results demonstrate that the MgAlO〈sub〉2.5〈/sub〉 content reaches saturation (3–4 mol%) when an additional Al‐bearing phase exists in the system.
Description:
Key Points:
The MgAlO〈sub〉2.5〈/sub〉 content in bridgmanite remains constant with temperature when bridgmanite coexists with corundum and the CF‐phase.
The MgAlO〈sub〉2.5〈/sub〉 content in bridgmanite reaches a solubility of 3–4 mol% when bridgmanite coexists with an additional Al‐bearing phase.
A significant amount of the Al〈sub〉8/3〈/sub〉O〈sub〉4〈/sub〉 component can be dissolved into the CF‐phase.
Description:
HORIZON EUROPE European Research Council
http://dx.doi.org/10.13039/100019180
Description:
Japan Society for the Promotion of Science London
http://dx.doi.org/10.13039/501100000646
Description:
cooperative research program of the Earthquake Research Institute
Description:
https://doi.org/10.5281/zenodo.7512647
Keywords:
ddc:549
;
Al‐bearing bridgmanite
;
Al substitute mechanism
;
phase relation
;
volatile
Language:
English
Type:
doc-type:article
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