Jonas PAPE¹, Bidong ZHANG², Fridolin SPITZER³, Alan E. RUBIN², andThorsten KLEINE³
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14075]
¹Institut für Planetologie, University of Münster, Münster, Germany
²Department of Earth, Planetary & Space Sciences, University of California, Los Angeles, California, USA
³Max Planck Institute for Solar System Research, Göttingen, Germany
Published by arrangement with John Wiley & Sons

Complex interelement trends among magmatic IIIF iron meteorites are difficult to explain by fractional crystallization and have raised uncertainty about their genetic relationships. Nucleosynthetic Mo isotope anomalies provide a powerful tool to assess if individual IIIF irons are related to each other. However, while trace element data are available for all nine IIIF irons, Mo isotopic data are limited to three samples. We present Mo isotopic data for all but one IIIF irons that help assess the genetic relationships among these irons, together with new Mo and W isotopic data for Fitzwater Pass (classified IIIF), and the Zinder pallasite (for which a cogenetic link with IIIF irons has been proposed). After correction for cosmic-ray exposure, the Mo isotopic compositions of the IIIF irons are identical within uncertainty and confirm their belonging to carbonaceous chondrite (CC)-type meteorites. The mean Mo isotopic composition of group IIIF overlaps those groups IIF and IID, but a common parent body for these groups is ruled out based on distinct trace element systematics. The new Mo isotopic data do not argue against a single parent body for the IIIF irons, and suggest a close genetic link among these samples. In contrast, Fitzwater Pass has distinct Mo and W isotopic compositions, identical to those of some non-magmatic IAB irons. The Mo and W isotope data for Zinder indicate that this meteorite is not related to IIIF irons, but belongs to the non-carbonaceous (NC) type and has the same Mo and W isotopic composition as main-group pallasites.

Bidong ZHANG^1,2, Yangting LIN³, Jialong HAO³, Devin L. SCHRADER^4,5,Meenakshi WADHWA⁵, Randy L. KOROTEV⁶, William K. HARTMANN⁷, andAudrey BOUVIER^2,8
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14078]
¹Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, Los Angeles, California, USA
²Department of Earth Sciences, The University of Western Ontario, Ontario, London, Canada
³Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing,China
⁴Buseck Center for Meteorite Studies, Arizona State University, Arizona,Tempe, USA
⁵School of Earth and Space Exploration, Arizona State University, Arizona,Tempe, USA
⁶Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University, St. Louis,Missouri, USA
⁷Planetary Science Institute, Arizona,Tucson, USA
⁸Bayerisches Geoinstitut, Universität Bayreuth, Bayreuth, Germany
Published by arrangement with John Wiley & Sons

About half of the lunar meteorites in our collections are feldspathic breccias. Acquiring geochronologic information from these breccias is challenging due to their low radioactive-element contents and their often polymict nature. We used high-spatial-resolution (5 μm) NanoSIMS (nanoscale secondary ion mass spectrometry) U-Pb dating technique to date micro-zircons in the lunar feldspathic meteorites Dhofar 1528 and Dhofar 1627. Three NanoSIMS dating spots of two zircon grains from Dhofar 1528 show a discordia with an upper intercept at 4354 ± 76 Ma and a lower intercept at 332 ± 1407 Ma (2σ, MSWD = 0.01, p = 0.91). Three spots of two zircon grains in Dhofar 1627 define a discordia with an upper intercept at 3948 ± 30 Ma and a lower intercept at 691 ± 831 Ma (2σ, MSWD = 0.40, p = 0.53). Both samples likely experienced shock metamorphism caused by impacts. Based on the clastic nature, lack of recrystallization and the consistent U-Pb and Pb-Pb dates of the zircons in Dhofar 1528, the U-Pb date of 4354 Ma is interpreted as the crystallization age of its Mg-suite igneous precursor. Some of the Dhofar 1627 zircons show poikilitic texture, a crystallization from the matrix impact melt, so the U-Pb date of 3948 Ma corresponds to an impact event, likely the Imbrium basin-forming event. These data are the first radiometric ages for these two meteorites and demonstrate that in situ (high spatial resolution) U-Pb dating has potential for extracting geochronological information about igneous activities and impact events from lunar feldspathic and polymict breccias.