^1,2,3,4L.F. White,⁵D.E. Moser,³J.R. Darling,⁴B.G. Rider-Stokes,^1,2,5B. Hyde,^1,2K.T. Tait,⁶K. Chamberlain,^7,8A.K. Schmitt,³J. Dunlop,⁴M.Anand
Earth and Planetary Science Letters 636, 118694 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2024.118694]
¹Department of Natural History, Royal Ontario Museum, Toronto, Ontario, M5S 2C6, Canada
²Department of Earth Sciences, University of Toronto, Toronto, Ontario, M5S 3B1, Canada
³School of Earth and Environmental Science, University of Portsmouth, Portsmouth, PO1 3QL, UK
⁴School of Physical Sciences, The Open University, Milton Keynes MK7 6AA, UK
⁵Western University, London, Ontario, Canada N6A 3KL
⁶Department of Geology and Geophysics, University of Wyoming, 1000 E. University Ave, Laramie, Wyoming 82071-3006, USA
⁷Institute of Earth Sciences, Ruprecht-Karls-Universitat Heidelberg, Im Neuenheimer Feld 236, D-69120 Heidelberg, Germany
⁸John de Laeter Centre, Curtin University, Bentley. WA 6102, Australia
Copyright Elsevier

A long-standing paradigm in planetary science is that the inner Solar System experienced a period of intense and sustained bombardment between 4.2 and 3.9 Ga. Evidence of this period, termed the Late Heavy Bombardment is provided by the 40Ar/39Ar isotope systematics of returned Apollo samples, lunar meteorites, and asteroidal meteorites. However, it has been largely unsupported by more recent and robust isotopic age data, such as isotopic age data obtained using the U-Pb system. Here we conduct careful microstructural characterisation of baddeleyite, zircon, and apatite in six different eucrites prior to conducting SIMS and LA-ICP-MS measurement of U, Th, and Pb isotopic ratios and radiometric dating. Baddeleyite, displaying complex internal twinning linked to reversion from a high symmetry polymorph in two samples, records the formation of the parent body (4554 ± 3 Ma 2σ; n = 8), while structurally simple zircon records a tight spread of ages representing metamorphism between 4574 ± 14 Ma and 4487 ± 31 Ma (n = 6). Apatite, a more readily reset shock chronometer, records crystallisation ages of ∼4509 Ma (n = 6), with structurally deformed grains (attributed to impact events) yielding U-Pb ages of 4228 Ma (n = 12). In concert, there is no evidence within the measured U-Pb systematics or microstructural record of the eucrites examined in this study to support a period of late heavy bombardment between 4.2 and 3.9 Ga.