Coordinated U–Pb geochronology, trace element, Ti-in-zircon thermometry and microstructural analysis of Apollo zircons

U‐Pb SIMS ages of Apollo 14 zircon: Identifying distinct magmatic episodes

“…; Crow et al. ). The latter interpretation is based on zircon age distribution patterns from different Apollo landing sites, which only show a minor age peak at ~3.9 Ga, which was interpreted as the Imbrium impact event (e.g., Liu et al.…”

“…Moreover, the majority of grains <4.2 Ga do not show any igneous growth zoning (Crow et al. ) and zircons <4.1 Ga have often small grain sizes (<50 μm) and show evidence for partial Pb loss (textural or as discordant U‐Pb ages, Zhang et al. ; Crow et al.…”

“…; Crow et al. ). The exceptions are a few grains that exhibit secondary microstructures and where the age can, thus, not be taken as the magmatic crystallization age (Grange et al.…”

“…) with age peaks at ~4.20, ~4.25, and ~4.33 Ga (Crow et al. and references within). The majority of these zircon ages were interpreted as crystallization ages and thus as representing different periods of KREEP magmatism (Nemchin et al.…”

“…; Hopkins and Mojzsis ; Crow et al. ), but together indicate the presence of major age peaks at ~4.35, ~4.20, and ~4.00 Ga. A more detailed evaluation of these ages reveals differences in the zircon age distributions between separate landing sites, such as the ~3.90 and 4.00 Ga peaks observed in zircons from Apollo 12 and 14 (e.g., Nemchin et al. ; Liu et al.…”