Your browser doesn't support javascript.
loading
The effect of potassium on aluminous phase stability in the lower mantle.
Rogmann, Elena-Marie; Jennings, Eleanor S; Ross, Jennifer; Miyajima, Nobuyoshi; Walter, Michael J; Kohn, Simon C; Lord, Oliver T.
Afiliação
  • Rogmann EM; School of Earth Sciences, University of Bristol, Bristol, BS8 1RJ UK.
  • Jennings ES; School of Earth Sciences, University of Bristol, Bristol, BS8 1RJ UK.
  • Ross J; Bayerisches Geoinstitut, Universität Bayreuth, Bayreuth, Germany.
  • Miyajima N; Present Address: School of Natural Sciences, Birkbeck, University of London, London, WC1E 7JL UK.
  • Walter MJ; School of Earth Sciences, University of Bristol, Bristol, BS8 1RJ UK.
  • Kohn SC; Bayerisches Geoinstitut, Universität Bayreuth, Bayreuth, Germany.
  • Lord OT; School of Earth Sciences, University of Bristol, Bristol, BS8 1RJ UK.
Contrib Mineral Petrol ; 179(5): 52, 2024.
Article em En | MEDLINE | ID: mdl-38686218
ABSTRACT
The aluminous calcium-ferrite type phase (CF) and new aluminous phase (NAL) are thought to hold the excess alumina produced by the decomposition of garnet in MORB compositions in the lower mantle. The respective stabilities of CF and NAL in the nepheline-spinel binary (NaAlSiO4-MgAl2O4) are well established. However with the addition of further components the phase relations at lower mantle conditions remain unclear. Here we investigate a range of compositions around the nepheline apex of the nepheline-kalsilite-spinel compositional join (NaAlSiO4-KAlSiO4-MgAl2O4) at 28-78 GPa and 2000 K. Our experiments indicate that even small amounts of a kalsilite (KAlSiO4) component dramatically impact phase relations. We find NAL to be stable up to at least 71 GPa in potassium-bearing compositions. This demonstrates the stabilizing effect of potassium on NAL, because NAL is not observed at pressures above 48 GPa on the nepheline-spinel binary. We also observe a broadening of the CF stability field to incorporate larger amounts of potassium with increasing pressure. For pressures below 50 GPa only minor amounts (<0.011(1)KK+Na+Mg) of potassium are soluble in CF, whereas at 68 GPa, we find a solubility in CF of at least 0.088(3)KK+Na+Mg. This indicates that CF and NAL are suitable hosts of the alkali content of MORB compositions at lower mantle conditions. For sedimentary compositions at lower mantle pressures, we expect K-Hollandite to be stable in addition to CF and NAL for pressures of 28-48 GPa, based on our simplified compositions. Supplementary Information The online version contains supplementary material available at 10.1007/s00410-024-02129-w.
Palavras-chave

Texto completo: 1 Coleções: 01-internacional Base de dados: MEDLINE Idioma: En Revista: Contrib Mineral Petrol Ano de publicação: 2024 Tipo de documento: Article

Texto completo: 1 Coleções: 01-internacional Base de dados: MEDLINE Idioma: En Revista: Contrib Mineral Petrol Ano de publicação: 2024 Tipo de documento: Article