Universität zu Köln

Rzehak, Laura J. A., Kommescher, Sebastian, Kurzweil, Florian, Sprung, Peter, Leitzke, Felipe P. and Fonseca, Raul O. C. (2021). The redox dependence of titanium isotope fractionation in synthetic Ti-rich lunar melts. Contrib. Mineral. Petrol., 176 (3). NEW YORK: SPRINGER. ISSN 1432-0967

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Abstract

Equilibria between Ti oxides and silicate melt lead to Ti isotope fractionation in terrestrial samples, with isotopically light Ti oxides and isotopically heavy coexisting melt. However, while Ti is mostly tetravalent in terrestrial samples, around 10% of the overall Ti is trivalent at fO(2) relevant to lunar magmatism (similar to IW-1). The different valences of Ti in lunar samples, could additionally influence Ti stable isotope fractionation during petrogenesis of lunar basalts to an unknown extent. We performed an experimental approach using gas mixing furnaces to investigate the effect of Ti oxide formation at different fO(2) on Ti stable isotope fractionation during mare basalt petrogenesis. Two identical bulk compositions were equilibrated simultaneously during each experiment to guarantee comparability. One experiment was investigated with the EPMA to characterize the petrology of experimental run products, whereas the second experiment was crushed, and fabricated phases (i.e., oxides, silicates and glass) were handpicked, separated and digested. An aliquot of each sample was mixed with a Ti double-spike, before Ti was separated from matrix and interfering elements using a modified HFSE chemistry. Our study shows fO(2)-dependent fractionation within seven samples from air to IW-1, especially Ti-49(armalcolite-melt) and Ti-49(armalcolite-orthopyroxene) become more fractionated from oxidized to reduced conditions (-0.092 +/- 0.028- -0.200 +/- 0.033 parts per thousand and -0.089 +/- 0.027- -0.250 +/- 0.049 parts per thousand, respectively), whereas Ti-49(orthopyroxene-melt) shows only a minor fractionation (-0.002 +/- 0.017-0.050 +/- 0.025 parts per thousand). The results of this study show that Ti isotope fractionation during mare basalt petrogenesis is expected to be redox dependent and mineral-melt fractionation as commonly determined for terrestrial fO(2) may not be directly applied to a lunar setting. This is important for the evaluation of Ti isotope fractionation resulting from lunar magmatism, which takes place under more reducing conditions compared to the more oxidized terrestrial magmatism.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Rzehak, Laura J. A. UNSPECIFIED UNSPECIFIED UNSPECIFIED Kommescher, Sebastian UNSPECIFIED UNSPECIFIED UNSPECIFIED Kurzweil, Florian UNSPECIFIED UNSPECIFIED UNSPECIFIED Sprung, Peter UNSPECIFIED UNSPECIFIED UNSPECIFIED Leitzke, Felipe P. UNSPECIFIED UNSPECIFIED UNSPECIFIED Fonseca, Raul O. C. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-582032
DOI:	10.1007/s00410-020-01769-y
Journal or Publication Title:	Contrib. Mineral. Petrol.
Volume:	176
Number:	3
Date:	2021
Publisher:	SPRINGER
Place of Publication:	NEW YORK
ISSN:	1432-0967
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language Geochemistry & Geophysics; Mineralogy Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/58203