TY - JOUR
T1 - Isotopic composition of zinc, copper, and iron in lunar samples
AU - Moynier, F.
AU - Albarède, F.
AU - Herzog, G. F.
N1 - Funding Information:
We thank Christoph Schnabel and Peixue Ma for their efforts to develop the Zn separation chemistry; Gary Lofgren for facilitating the transfer of samples; Natalia Artemieva and Elisabetta Pierazzo for advice concerning meteorite impact; Kevin Housen for comments on lunar gardening; Christopher Herzog for advice on the modeling calculations; Paul Warren, Randy Korotev, and anonymous reviewer 2 for their critical comments; Philippe Télouk and Chantal Douchet for help with the mass spectrometer and the clean lab. Anonymous reviewer 3 and the associate editor have our special thanks for suggesting many improvements. This work was supported in part by NASA Grant NAQG5-11719 (GFH) and in part by the Programme National de Planétologie (INSU-CNRS-CNES).
PY - 2006/12/15
Y1 - 2006/12/15
N2 - We determined by ICP-MS the concentrations and isotopic ratios of Fe, Cu, and Zn in the Ti-rich lunar basalt 74275, in the lunar orange glass 74220, and in up to 10 lunar soils, namely, 14163, 15231, 64501, 66041, 68841, 69941, 70011, 72501, 75081, and 76501. Two analyses of zinc in lunar basalt 74275 give δ66Zn = 0.17‰ and 0.75‰, values within the range of those measured in terrestrial basalts; copper in lunar basalt 74275 has δ65Cu ∼ +1.4‰, which is isotopically heavier than values observed in terrestrial basalts. In the orange glass, we measured δ56Fe = -0.24‰, δ65Cu = -0.42‰, and δ66Zn ∼ -3.6‰. These values of δ are more negative than those obtained for 74275 and for typical lunar basalts, but for Cu, comparable to those observed in terrestrial sulfides and meteorites. In lunar soils we found 0.11‰ ≤ δ56Fe ≤ 0.51‰, 2.6‰ ≤ δ65Cu ≤ 4.5‰, and 2.2‰ ≤ δ66Zn ≤ 6.4‰. Insofar as we can generalize from a small sample set, S, Fe, Cu, Zn, and Cd show similar trends in isotopic fractionation on the Moon. Lunar basalts have nearly terrestrial isotopic ratios. Relative to the lunar basalt 74275, the pyroclastic glass 74220 is enriched in the lighter isotopes of Fe, Cu, and Zn, and the soils are enriched in the heavier isotopes of Fe, Cu, and Zn. The patterns in the basalts are likely inherited from the source material; the light-isotope enrichments seen in the orange glass originated during lava fountaining or, less probably, during partial condensation of vapor; and the heavy-isotope enrichments in the lunar soils were likely created by a combination of processes that included micrometeorite vaporization and sputtering. In the orange glass, the light-isotope enrichments (relative to lunar basalts) of Zn are larger than those of Cu. If these enrichments reflect accurately the isotopic composition of the gas, they suggest that Cu is more volatile than Zn in the liquid from which the gas derived. A simple model built on the known flux of micrometeorites to the lunar surface and a published estimate that micrometeorites generate 10 times their own mass of vapor, predicts heavy-isotope enrichments comparable to those observed in soils but only if the regolith gardening rate is set at about one twentieth of the generally accepted value of 1 cm/My. This discrepancy may reflect the difference in the time constants for micrometeorite milling and decimeter-scale gardening, or the importance of sputtering.
AB - We determined by ICP-MS the concentrations and isotopic ratios of Fe, Cu, and Zn in the Ti-rich lunar basalt 74275, in the lunar orange glass 74220, and in up to 10 lunar soils, namely, 14163, 15231, 64501, 66041, 68841, 69941, 70011, 72501, 75081, and 76501. Two analyses of zinc in lunar basalt 74275 give δ66Zn = 0.17‰ and 0.75‰, values within the range of those measured in terrestrial basalts; copper in lunar basalt 74275 has δ65Cu ∼ +1.4‰, which is isotopically heavier than values observed in terrestrial basalts. In the orange glass, we measured δ56Fe = -0.24‰, δ65Cu = -0.42‰, and δ66Zn ∼ -3.6‰. These values of δ are more negative than those obtained for 74275 and for typical lunar basalts, but for Cu, comparable to those observed in terrestrial sulfides and meteorites. In lunar soils we found 0.11‰ ≤ δ56Fe ≤ 0.51‰, 2.6‰ ≤ δ65Cu ≤ 4.5‰, and 2.2‰ ≤ δ66Zn ≤ 6.4‰. Insofar as we can generalize from a small sample set, S, Fe, Cu, Zn, and Cd show similar trends in isotopic fractionation on the Moon. Lunar basalts have nearly terrestrial isotopic ratios. Relative to the lunar basalt 74275, the pyroclastic glass 74220 is enriched in the lighter isotopes of Fe, Cu, and Zn, and the soils are enriched in the heavier isotopes of Fe, Cu, and Zn. The patterns in the basalts are likely inherited from the source material; the light-isotope enrichments seen in the orange glass originated during lava fountaining or, less probably, during partial condensation of vapor; and the heavy-isotope enrichments in the lunar soils were likely created by a combination of processes that included micrometeorite vaporization and sputtering. In the orange glass, the light-isotope enrichments (relative to lunar basalts) of Zn are larger than those of Cu. If these enrichments reflect accurately the isotopic composition of the gas, they suggest that Cu is more volatile than Zn in the liquid from which the gas derived. A simple model built on the known flux of micrometeorites to the lunar surface and a published estimate that micrometeorites generate 10 times their own mass of vapor, predicts heavy-isotope enrichments comparable to those observed in soils but only if the regolith gardening rate is set at about one twentieth of the generally accepted value of 1 cm/My. This discrepancy may reflect the difference in the time constants for micrometeorite milling and decimeter-scale gardening, or the importance of sputtering.
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U2 - 10.1016/j.gca.2006.02.030
DO - 10.1016/j.gca.2006.02.030
M3 - Article
AN - SCOPUS:33845432140
SN - 0016-7037
VL - 70
SP - 6103
EP - 6117
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
IS - 24
ER -