SIMS U‐Pb dating of micro‐zircons in the lunar meteorites Dhofar 1528 and Dhofar 1627

Author:

Zhang Bidong12ORCID,Lin Yangting3,Hao Jialong3,Schrader Devin L.45ORCID,Wadhwa Meenakshi5ORCID,Korotev Randy L.6ORCID,Hartmann William K.7,Bouvier Audrey28ORCID

Affiliation:

1. Department of Earth, Planetary and Space Sciences University of California, Los Angeles Los Angeles California USA

2. Department of Earth Sciences The University of Western Ontario Ontario London Canada

3. Key Laboratory of Earth and Planetary Physics Institute of Geology and Geophysics Chinese Academy of Sciences Beijing China

4. Buseck Center for Meteorite Studies Arizona State University Arizona Tempe USA

5. School of Earth and Space Exploration Arizona State University Arizona Tempe USA

6. Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences Washington University St. Louis Missouri USA

7. Planetary Science Institute Arizona Tucson USA

8. Bayerisches Geoinstitut, Universität Bayreuth Bayreuth Germany

Abstract

AbstractAbout 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.

Funder

National Aeronautics and Space Administration

Publisher

Wiley

Subject

Space and Planetary Science,Geophysics

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