A search for thermal excursions from ancient extraterrestrial impacts using Hadean zircon Ti-U-Th-Pb depth profiles

Sunshine S. Abbott, T. Mark Harrison, Axel K. Schmitt, Stephen J. Mojzsis

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33 Citations (Scopus)

Abstract

Few terrestrial localities preserve more than a trace lithic record prior to ca. 3.8 Ga greatly limiting our understanding of the first 700 Ma of Earth history, a period inferred to have included a spike in the bolide flux to the inner solar system at ca. 3.85-3.95 Ga (the Late Heavy Bombardment, LHB). An accessible record of this era may be found in Hadean detrital zircons from the Jack Hills, Western Australia, in the form of μm-scale epitaxial overgrowths. By comparing crystallization temperatures of pre-3.8 Ga zircon overgrowths to the archive of zircon temperature spectra, it should, in principle, be possible to identify a distinctive impact signature. We have developed Ti-U-Th-Pb ion microprobe depth profiling to obtain age and temperature information within these zircon overgrowths and undertaken a feasibility study of its possible use in identifying impact events. Of eight grains profiled in this fashion, four have overgrowths of LHB-era age. Age vs. temperature profiles reveal a period between ca. 3.85-3.95 Ga (i.e., LHB era) characterized by significantly higher temperatures (approximately 840-875 °C) than do older or younger zircons or zircon domains (approximately 630-750 °C). However, temperatures approaching 900 °C can result in Pb isotopic exchange rendering interpretation of these profiles nonunique. Coupled age-temperature depth profiling shows promise in this role, and the preliminary data we report could represent the first terrestrial evidence for impactrelated heating during the LHB.

Original languageEnglish
Pages (from-to)13486-13492
Number of pages7
JournalProceedings of the National Academy of Sciences of the United States of America
Volume109
Issue number34
DOIs
Publication statusPublished - Aug 21 2012

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Keywords

  • Early earth
  • Impact crater
  • Lunar cataclysm
  • Secondary ion mass spectrometry

ASJC Scopus subject areas

  • General

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