Universität zu Köln

Leitzke, F. P., Fonseca, R. O. C., Goettlicher, J., Steininger, R., Jahn, S., Prescher, C. and Lagos, M. (2018). Ti K-edge XANES study on the coordination number and oxidation state of Titanium in pyroxene, olivine, armalcolite, ilmenite, and silicate glass during mare basalt petrogenesis. Contrib. Mineral. Petrol., 173 (12). NEW YORK: SPRINGER. ISSN 1432-0967

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Abstract

Lunar mare basalts are a product of partial melting of the lunar mantle under more reducing conditions when compared to those expected for the Earth's upper mantle. Alongside Fe, Ti can be a major redox sensitive element in lunar magmas, and it can be enriched by up to a factor of ten in lunar basaltic glasses when compared to their terrestrial counterparts. Therefore, to better constrain the oxidation state of Ti and its coordination chemistry during lunar magmatic processes, we report new X-ray absorption near edge structure (XANES) spectroscopy measurements for a wide range of minerals (pyroxene, olivine, Fe-Ti oxides) and basaltic melt compositions involved in partial melting of the lunar mantle. Experiments were conducted in 1bar gas-mixing furnaces at temperatures between 1100 and 1300 degrees C and oxygen fugacities (fO(2)) that ranged from air to two orders of magnitude below the Fe-FeO redox equilibrium. Run products were analysed via electron microprobe and XANES Ti K-edge. Typical run products had large (>100 mu m) crystals in equilibrium with quenched silicate glass. Ti K-edge XANES spectra show a clear shift in energy of the absorption edge features from oxidizing to reducing conditions and yield an average valence for Fe-Ti oxides (armalcolite and ilmenite) of 3.6, i.e., a 40% of the overall Ti is Ti3+ under fO(2) conditions relevant to lunar magmatism (IW -1.5 to -1.8). Pyroxenes and olivine have average Ti valence of 3.75 (i.e., 25% of the overall Ti is trivalent), while in silicate glasses Ti is exclusively tetravalent. Pre-edge peak intensities also indicate that the coordination number of Ti varies from an average V-fold in silicate glass to VI-fold in the Fe-Ti oxides and a mixture between IV and VI-fold coordination in the pyroxenes and olivine, with up to 82% Ti-[IV](4+) in the pyroxene. In addition, our results can help to better constrain the Ti3+/Sigma Ti of the lunar mantle phases during magmatic processes and are applied to provide first insights into the mechanisms that may control Ti mass-dependent equilibrium isotope fractionation in lunar mare basalts.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Leitzke, F. P. UNSPECIFIED UNSPECIFIED UNSPECIFIED Fonseca, R. O. C. UNSPECIFIED UNSPECIFIED UNSPECIFIED Goettlicher, J. UNSPECIFIED UNSPECIFIED UNSPECIFIED Steininger, R. UNSPECIFIED UNSPECIFIED UNSPECIFIED Jahn, S. UNSPECIFIED UNSPECIFIED UNSPECIFIED Prescher, C. UNSPECIFIED UNSPECIFIED UNSPECIFIED Lagos, M. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-163593
DOI:	10.1007/s00410-018-1533-7
Journal or Publication Title:	Contrib. Mineral. Petrol.
Volume:	173
Number:	12
Date:	2018
Publisher:	SPRINGER
Place of Publication:	NEW YORK
ISSN:	1432-0967
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language RAY-ABSORPTION SPECTROSCOPY; ISOTOPE FRACTIONATION; ALLENDE METEORITE; PLANETARY BASALTS; OXYGEN FUGACITY; CRYSTAL-GROWTH; EARTHS MANTLE; LUNAR BASALTS; MELTS; VALENCE Multiple languages Geochemistry & Geophysics; Mineralogy Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/16359