Late accretion to the Moon recorded in zircon (U–Th)/He thermochronometry

Nigel M. Kelly, Rebecca M. Flowers, James R. Metcalf, S. Mojzsis

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

We conducted zircon (U–Th)/He (ZHe) analysis of lunar impact-melt breccia 14311 with the aim of leveraging radiation damage accumulated in zircon over extended intervals to detect low-temperature or short-lived impact events that have previously eluded traditional isotopic dating techniques. Our ZHe data record a coherent date vs. effective Uranium concentration (eU) trend characterized by >3500 Ma dates from low (≤75 ppm) eU zircon grains, and ca. 110 Ma dates for high (≥100 ppm) eU grains. A progression between these date populations is apparent for intermediate (75–100 ppm) eU grains. Thermal history modeling constrains permissible temperatures and cooling rates during and following impacts. Modeling shows that the data are most simply explained by impact events at ca. 3950 Ma and ca. 110 Ma, and limits allowable temperatures of heating events between 3950–110 Ma. Modeling of solar cycling thermal effects at the lunar surface precludes this as the explanation for the ca. 110 Ma ZHe dates. We propose a sample history characterized by zircon resetting during the ca. 3950 Ma Imbrium impact event, with subsequent heating during an impact at ca. 110 Ma that ejected the sample to the vicinity of its collection site. Our data show that zircon has the potential to retain 4He over immense timescales (≥3950 Myrs), thus providing a valuable new thermochronometer for probing the impact histories of lunar samples, and martian or asteroidal meteorites.

Original languageEnglish
Pages (from-to)222-235
Number of pages14
JournalEarth and Planetary Science Letters
Volume482
DOIs
Publication statusPublished - Jan 15 2018

Fingerprint

Moon
moon
Uranium
zircon
accretion
uranium
histories
history
Meteorites
modeling
heating
Heating
radiation damage
resetting
impact melts
SNC meteorites
Radiation damage
breccia
lunar surface
temperature effect

Keywords

  • (U–Th)/He thermochronometry
  • Apollo 14
  • bombardment
  • Moon
  • thermal modeling
  • zircon

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

Cite this

Late accretion to the Moon recorded in zircon (U–Th)/He thermochronometry. / Kelly, Nigel M.; Flowers, Rebecca M.; Metcalf, James R.; Mojzsis, S.

In: Earth and Planetary Science Letters, Vol. 482, 15.01.2018, p. 222-235.

Research output: Contribution to journalArticle

Kelly, Nigel M. ; Flowers, Rebecca M. ; Metcalf, James R. ; Mojzsis, S. / Late accretion to the Moon recorded in zircon (U–Th)/He thermochronometry. In: Earth and Planetary Science Letters. 2018 ; Vol. 482. pp. 222-235.
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