On the elusive isotopic composition of lunar Pb
MetadataShow full item record
Highly radiogenic Pb isotope compositions determined for volcanic glass beads from the Apollo 14 soil sample 14163 are similar to those commonly determined for mare basalts and are correlated with chemical variations observed in the beads. This indicates that Pb unsupported by in-situ U decay has a similar origin in both glass beads and mare basalt samples and is likely to reflect variations of 238U/204Pb (µ) in the lunar mantle. An alternative explanation that this Pb is a result of late equilibration with the radiogenic Pb present in soil is less likely as it would imply that all other characteristics of glass beads such as their chemistry must also be a consequence of equilibration near the lunar surface. Regardless of the origin of unsupported Pb, observed variations of Pb isotope compositions in the glass beads and mare basalts appear to be a result of two component mixing between a primitive reservoir with a µ -value similar to the Earth’s mantle and KREEP with a µ-value in excess of several thousand. This range cannot be explained by the fractionation of major rock forming minerals from the crystallising Lunar Magma Ocean and instead requires substantial extraction of sulphide late in the crystallisation sequence. The proportion of sulphide required to produce the inferred range places limits on the starting l of the Moon prior to differentiation, demanding a relatively high value of about 100–200. Low µ indicated by several basalt samples and previously analysed volcanic glass beads can be explained by the preservation of an early (but post Ferroan Anorthosite) sulphide rich reservoir in the lunar mantle, while a complete range of Pb isotope compositions observed in the glass beads and mare basalts can be interpreted as mixing between this sulphide rich reservoir and KREEP.
Showing items related by title, author, creator and subject.
Ancient volcanism on the Moon: Insights from Pb isotopes in the MIL 13317 and Kalahari 009 lunar meteoritesSnape, J.; Curran, N.; Whitehouse, M.; Nemchin, Alexander; Joy, K.; Hopkinson, T.; Anand, M.; Bellucci, J.; Kenny, G. (2018)Lunar meteorites provide a potential opportunity to expand the study of ancient (>4000 Ma) basaltic volcanism on the Moon, of which there are only a few examples in the Apollo sample collection. Secondary Ion Mass ...
Lunar basalt chronology, mantle differentiation and implications for determining the age of the MoonSnape, J.; Nemchin, Alexander; Bellucci, J.; Whitehouse, M.; Tartèse, R.; Barnes, J.; Anand, M.; Crawford, I.; Joy, K. (2016)Despite more than 40 years of studying Apollo samples, the age and early evolution of the Moon remain contentious. Following the formation of the Moon in the aftermath of a giant impact, the resulting Lunar Magma Ocean ...
Constraining the timing and sources of volcanism at the Apollo 12 landing site using new Pb isotopic compositions and crystallisation agesSnape, J.; Davids, B.; Nemchin, Alexander; Whitehouse, M.; Bellucci, J. (2018)The basaltic suites collected at the Apollo 12 landing site have been interpreted as representing a stratigraphic sequence of volcanic flows emplaced in the Oceanus Procellarum region between approximately 3100–3300 Ma. ...