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Al and H incorporation and Al-diffusion in natural rutile and its high-pressure polymorph TiO2 (II)

Joachim-Mrosko, Bastian ; Konzett, Jürgen ; Ludwig, Thomas ; Griffiths, Thomas ; Habler, Gerlinde ; Libowitzky, Eugen ; Stalder, Roland

Minor Minerals, Major Implications: Using Key Mineral Phases to Unravel the Formation and Evolution of Earth's Crust, 2024, Vol.537, p.123-147 [Periódico revisado por pares]

The Geological Society of London

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  • Título:
    Al and H incorporation and Al-diffusion in natural rutile and its high-pressure polymorph TiO2 (II)
  • Autor: Joachim-Mrosko, Bastian ; Konzett, Jürgen ; Ludwig, Thomas ; Griffiths, Thomas ; Habler, Gerlinde ; Libowitzky, Eugen ; Stalder, Roland
  • Assuntos: Magmatic studies ; Tectonics
  • É parte de: Minor Minerals, Major Implications: Using Key Mineral Phases to Unravel the Formation and Evolution of Earth's Crust, 2024, Vol.537, p.123-147
  • Descrição: Rutile is an important accessory mineral in metamorphic rocks and is used as a geothermobarometer or geochronometer. This study aims to bridge the gap between diffusion studies in simplified and complex natural systems by investigating the incorporation and mobility of Al in natural rutile and its high-pressure polymorph TiO2 (II). Experiments were performed at 0.1 MPa to 7 GPa, 1223–1373 K, at buffered μ(Al2O3) and with fO2 constrained to ≤CCO, which is the equilibrium between graphite and a CO-CO2 gas phase. Based on electron probe microanalysis, secondary ion mass spectrometry and Fourier transform infrared analyses, we suggest a complex combination of mechanisms to explain the incorporation of Al and H in natural rutile and TiO2 (II). This includes: (1) the incorporation of Al3+ on octahedral Ti-sites charge balanced by the formation of oxygen vacancies; and (2) the incorporation of oxygen in interstitial positions charge balanced by hydrogen interstitials. Determined Al-diffusivities in natural TiO2 are approximately eight to nine orders of magnitude faster compared to previously published data. A possible explanation includes a significantly enhanced rate of ionic diffusion through the combined effect of hydrolytic weakening, enhanced Al-diffusion through extended defects and to a minor extent oxygen fugacity variations. Consequently, results of this study question that the inferred high closure temperatures for the Al-in-rutile geothermobarometer can be applied to all natural systems.
  • Títulos relacionados: Geological Society, London, Special Publications
  • Editor: The Geological Society of London
  • Idioma: Inglês
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