Universität zu Köln

Laura, Rzehak J. A., Sebastian, Kommescher, Liam, Hoare, Florian, Kurzweil, Peter, Sprung, Felipe, Leitzke P. and Raul, Fonseca O. C. (2022). Redox-dependent Ti stable isotope fractionation on the Moon: implications for current lunar magma ocean models. Contrib. Mineral. Petrol., 177 (8). NEW YORK: SPRINGER. ISSN 1432-0967

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Abstract

In terrestrial magmas titanium is predominantly tetravalent (Ti4+), in contrast, lunar magmas are more reduced (IW-1) and hence approximately 10% of their bulk Ti content is trivalent (Ti3+). Changes in oxidation state and coordination number are both important parameters that can serve to drive Ti stable isotope fractionation. As such, mineral-mineral and mineral-melt Ti stable isotope fractionation factors determined for terrestrial samples may not be appropriate for lunar samples that formed under more reducing conditions. To address this issue, several experiments were carried out in gas mixing furnaces over a range of fO(2) (air to IW-1) to determine Ti stable isotope fractionation factors for minerals, such as ilmenite, clinopyroxene and rutile that are highly abundant on the Moon. Results show that the extent of Ti stable isotope fractionation significantly increases with decreasing fO(2). For example, the isotopic difference between ilmenite and residual melt (Delta Ti-49(ilmenite-melt)) is resolvably lower by similar to 0.44 parts per thousand from terrestrial-like FMQ-0.5 to lunar-like IW-1 at an intermediate precision of +/- 0.003 parts per thousand (95% c.i. OL-Ti). This confirms that fractionation factors determined for terrestrial conditions are indeed not applicable to lunar settings. Our new fractionation factors for ilmenite, clinopyroxene and silicate melt are mostly consistent with those previously determined by ab initio modelling based on density-functional theory. Using our new experimental data in conjunction with previously published high-precision HFSE data and Ti stable isotope data of lunar basalts, we modelled the solidification of the Lunar Magma Ocean (LMO). The model for LMO solidification included fractionation of Ti stable isotopes not only by Ti-oxides, but also by typical lunar silicate minerals as pyroxene or olivine. The resulting delta Ti-49 for urKREEP and ilmenite-bearing cumulates are within error of previous estimates, but also indicate that ilmenite-bearing cumulates must have contained around 15% ilmenite.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Laura, Rzehak J. A. UNSPECIFIED UNSPECIFIED UNSPECIFIED Sebastian, Kommescher UNSPECIFIED UNSPECIFIED UNSPECIFIED Liam, Hoare UNSPECIFIED UNSPECIFIED UNSPECIFIED Florian, Kurzweil UNSPECIFIED UNSPECIFIED UNSPECIFIED Peter, Sprung UNSPECIFIED UNSPECIFIED UNSPECIFIED Felipe, Leitzke P. UNSPECIFIED UNSPECIFIED UNSPECIFIED Raul, Fonseca O. C. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-680065
DOI:	10.1007/s00410-022-01947-0
Journal or Publication Title:	Contrib. Mineral. Petrol.
Volume:	177
Number:	8
Date:	2022
Publisher:	SPRINGER
Place of Publication:	NEW YORK
ISSN:	1432-0967
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language MARE BASALTS; OXYGEN FUGACITY; SILICATE MELTS; TRACE-ELEMENTS; AB-INITIO; TITANIUM; MANTLE; EARTH; DIFFERENTIATION; CRYSTALLIZATION Multiple languages Geochemistry & Geophysics; Mineralogy Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/68006