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

Autor(en)

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

Abstrakt

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.

Organisation(en)

Department für Lithosphärenforschung, Institut für Mineralogie und Kristallographie

Externe Organisation(en)

Universität Heidelberg, Leopold-Franzens-Universität Innsbruck, Russian Academy of Sciences

Seiten

123-147

Publikationsdatum

09-2023

Peer-reviewed

Ja

ÖFOS 2012

105116 Mineralogie, 105113 Kristallographie

Schlagwörter

ASJC Scopus Sachgebiete

Geochemistry and Petrology

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/6966f319-c9e6-4b7b-8de6-de17941da84d