Pb-Pb Dating of Terrestrial and Extraterrestrial Samples Using Resonance Ionization Mass Spectrometry

We are developing an in situ, rock‐dating spectrometer for spaceflight called the Chemistry, Organics, and Dating EXperiment (CODEX). CODEX will measure Rb‐Sr compositions and determine ages of samples on the Moon or Mars and can be augmented to obtain Pb‐Pb ages. Coupling Rb‐Sr and Pb‐Pb measurements broadens the suite of samples that can be dated and could provide tests of concordance. Here we assess whether geochronologically meaningful Pb‐Pb data could be measured in situ by tuning the prototype CODEX to acquire Pb‐Pb data from a suite of well‐characterized specimens from the Earth, Moon, and Mars. For Keuhl Lake Zircon 91500 our 207Pb/206Pb age of 1,090 ± 40 Ma is indistinguishable from the accepted age. In each of the Martian meteorites we studied, we could not resolve more than a single component of Pb and could not uniquely determine ages; nevertheless, our isotopic measurements were consistent with most previous analyses. On the other hand, we uniquely determined ages for three lunar meteorites. Our age for MIL 05035 is 3,550 ± 170 Ma, within 2σ of published ages for this specimen, in spite of it having
Key Points We have measured Pb in meteorites from the Moon and Mars, and a terrestrial zircon, using a prototype dating instrument for spaceflightOur instrument reproduces dates for the zircon and two lunar samples, and our Mars results are consistent with previous Pb studiesOur NWA 032 result is the first Pb‐Pb isochron age for this sample but is unexpected (3.76 Ga), and discordant with other isotopic system