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Unravelling lunar mantle source processes via the Ti isotope composition of lunar basalts

S. Kommescher1,

1Institut für Geologie und Mineralogie, Universität zu Köln, Germany

R.O.C. Fonseca1,2,

1Institut für Geologie und Mineralogie, Universität zu Köln, Germany
2 Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum, Germany

F. Kurzweil1,

1Institut für Geologie und Mineralogie, Universität zu Köln, Germany

M.M. Thiemens1,3,

1Institut für Geologie und Mineralogie, Universität zu Köln, Germany
3G-TIME Laboratory, Université Libre de Bruxelles, Belgium

C. Münker1,

1Institut für Geologie und Mineralogie, Universität zu Köln, Germany

P. Sprung1,4

1Institut für Geologie und Mineralogie, Universität zu Köln, Germany
4Hot Laboratory Division (AHL), Paul Scherer Institut, Villigen, Switzerland

Affiliations  |  Corresponding Author  |  Cite as  |  Funding information

Kommescher, S., Fonseca, R.O.C., Kurzweil, F., Thiemens, M.M., Münker, C., Sprung, P. (2020) Unravelling lunar mantle source processes via the Ti isotope composition of lunar basalts. Geochem. Persp. Let. 13, 13–18 .

Deutsche Forschungsgemeinschaft (DFG grants FO 698/6-1 and FO 698/11-1)
University of Cologne Advanced Post Doc grant
Graduate School of Geosciences fellowship (GSGS-2019X-07)

Geochemical Perspectives Letters v13  |  doi: 10.7185/geochemlet.2007
Received 5 August 2019  |  Accepted 24 January 2020  |  Published 28 February 2020
Copyright © The Authors

Published by the European Association of Geochemistry
under Creative Commons License CC BY-NC-ND 4.0




Figure 1 Measured Ti isotope compositions of lunar samples. All uncertainties unless stated otherwise are 95 % confidence interval (c.i.) of at least 6 measurements of the same aliquot. See main text and Supplementary Information for details. bce = breccia, ilm = ilmenite; QNB = quartz-normative basalt, olv = olivine, pgt = pigeonite.
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Table 1 Summary of reference materials and measured samples. For reference materials, n gives the number of sequences in which the material has been measured at least 6 times. Abbreviations are the same as in Figure 1. Two aliquots of OL-Ti were run through the chemical separation process and are given as OL-Ti (chemistry).
δ49Ti2 s.d.n95 % c.i.
JB-2-0.0440.02370.011
BCR-2-0.0250.01240.010
OL-Ti mean0.0000.00180.000
OL-Ti (chemistry)-0.0010.03020.137
Col-Ti mean0.2060.02180.009
Low-Ti rocks
12022Apollo 12Low-Ti ilm basalt0.0290.02260.011
12051"Low-Ti ilm basalt0.0300.02280.009
12063"Low-Ti ilm basalt0.0550.02260.012
12054"Low-Ti ilm basalt0.0280.02660.014
12007"Low-Ti olv basalt0.0060.01060.005
12053"Low-Ti pgt basalt-0.0130.02660.014
15495Apollo 15Low-Ti ONB0.0110.01760.009
15555"Low-Ti ONB-0.0080.02660.014
15556"Low-Ti ONB0.0070.03060.016
15065"Low-Ti QNB-0.0300.01460.007
15058"Low-Ti QNB-0.0100.03460.018
15545"Low-Ti QNB0.0110.03260.017
Low-Ti mean ± 2 s.d.0.0100.04712
High-Ti rocks
10017Apollo 11High-Ti ilm basalt0.0090.02460.012
10020"High-Ti ilm basalt0.0110.02260.011
10057"High-Ti ilm basalt0.0090.02460.012
74255Apollo 17High-Ti ilm basalt0.0430.01060.005
74275"High-Ti ilm basalt0.0450.01060.005
75035"High-Ti ilm basalt0.1150.02560.013
79135"High-Ti bce0.0190.01760.009
79035"High-Ti bce0.0470.01860.010
High-Ti mean 1 ± 2 s.d.0.0260.0367
High-Ti mean 2 ± 2 s.d.0.0370.0718
KREEP-rich rocks
14305Apollo 14KREEP-rich bce0.2960.03060.016
14310"KREEP basalt0.2630.03560.018
72275Apollo 17KREEP-rich bce0.1850.02660.014
68115Apollo 16KREEP-rich bce0.1170.02760.014
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Figure 2 Plots of (a) δ49Ti vs. MgO/TiO2, (b) δ49Ti vs. Ta/Hf and (c) δ49Ti vs. U that can be used to discriminate between processes leading to variations in δ49Ti. Symbols are the same as in Figure 1, black arrows indicate the direction in which a process would influence the values along y- and x-axes. Partial melting assumes the presence of ilmenite in the source, fractional crystallisation always implies fractional crystallisation of ilmenite. AFC implies the assimilation of an IBC component during ilmenite-free fractional crystallisation of a low-Ti magma. (b) The estimated Ta/Hf value of urKREEP is ~0.11 (Warren and Taylor, 2014

Warren, P.H., Taylor, G.J. (2014) The Moon. Treatise on Geochemistry (Second Edition) 2, 213–250.

). (c) Contamination by urKREEP (coloured arrow), would imply higher U contents (not observed). urKREEP is based on our first model (see Supplementary Information).
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