Universität zu Köln

Kommescher, S., Fonseca, R. O. C., Kurzweil, F., Thiemens, M. M., Muenker, C. and Sprung, P. (2020). Unravelling lunar mantle source processes via the Ti isotope composition of lunar basalts. Geochem. Perspect. Lett., 13. S. 13 - 19. PARIS CEDEX 05: EUROPEAN ASSOC GEOCHEMISTRY. ISSN 2410-3403

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Abstract

Formation and crystallisation of the Lunar Magma Ocean (LMO) was one of the most incisive events during the early evolution of the Moon. Lunar Magma Ocean solidification concluded with the coeval formation of K-, REE- and P-rich components (KREEP) and an ilmenite-bearing cumulate (IBC) layer. Gravitational overturn of the lunar mantle generated eruptions of basaltic rocks with variable Ti contents, of which their delta Ti-49 variations may now reflect variable mixtures of ambient lunar mantle and the IBC. To better understand the processes generating the spectrum of lunar low-Ti and high-Ti basalts and the role of Ti-rich phases such as ilmenite, we determined the mass dependent Ti isotope composition of four KREEP-rich samples, 12 low-Ti, and eight high-Ti mare basalts by using a Ti-47 Ti-49 double spike. Our data reveal significant variations in delta Ti-49 for KREEP-rich samples (+0.117 to +0.296 parts per thousand) and intra-group variations in the mare basalts (-0.030 to +0.035 parts per thousand for low-Ti and +0.009 to +0.113 parts per thousand for high-Ti basalts). We modelled the delta Ti-49 of KREEP using previously published HFSE data as well as the b 49 Ti evolution during fractional crystallisation of the LMO. Both approaches yield delta Ti-49(KREEP) similar to measured values and are in excellent agreement with previous studies. The involvement of ilmenite in the petrogenesis of the lunar mare basalts is further evaluated by combining our results with element ratios of HFSE, U and 1h, revealing that partial melting in an overturned lunar mantle and fractional crystallisation of ilmenite must be the main processes accounting for mass dependent Ti isotope variations in lunar basalts. Based on our results we can also exclude formation of high-Ti basalts by simple assimilation of ilmenite by ascending melts from the depleted lunar mantle. Rather, our data are in accord with melting of these basalts from a hybrid mantle source formed in the aftermath of gravitational lunar mantle overturn, which is in good agreement with previous Fe isotope data.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Kommescher, S. UNSPECIFIED UNSPECIFIED UNSPECIFIED Fonseca, R. O. C. UNSPECIFIED UNSPECIFIED UNSPECIFIED Kurzweil, F. UNSPECIFIED UNSPECIFIED UNSPECIFIED Thiemens, M. M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Muenker, C. UNSPECIFIED UNSPECIFIED UNSPECIFIED Sprung, P. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-343797
DOI:	10.7185/geochermlet.2007
Journal or Publication Title:	Geochem. Perspect. Lett.
Volume:	13
Page Range:	S. 13 - 19
Date:	2020
Publisher:	EUROPEAN ASSOC GEOCHEMISTRY
Place of Publication:	PARIS CEDEX 05
ISSN:	2410-3403
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language FRACTIONAL CRYSTALLIZATION; MAGMA OCEAN; TITANIUM; IRON; ORIGIN; CRUST; MOON; DIFFERENTIATION; EARTH Multiple languages Geochemistry & Geophysics Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/34379