A record of basin-forming impact from Pb clusters in lunar zircon

T. B. Blum (Corresponding author), D. A. Reinhard, M. Coble, M. J. Spicuzza, Y. Chen, A. J. Cavosie, L. Nasdala, C. Chanmuang N., T. J. Prosa, D. J. Larson, J. Valley

Publications: Contribution to bookContribution to proceedings

Abstract

Lunar zircon grains provide constraints on the early
evolution of the Earth-Moon system, including a lower
limit on the age of the Moon, and the initiation, duration,
and spatial extent of lunar magmatism. While zircon
dating remains one of the most robust tools for lunar
geochronology, debate persists regarding the prevalence
and length scales of impact-induced Pb-mobility in the
lunar zircon population as a whole [1]. Our work applies
atom probe tomography (APT) and secondary ion mass
spectrometry (SIMS) to the study of zircon 17B-4, a
zircon grain within the matrix of lunar sample 73235.
The 40Ar/39Ar plateau age of the breccia matrix (3946 ±
95 Ma, recalculated from [2]) has been interpreted to
reflect the timing of the Serenitatis basin-forming
impact. SIMS U-Pb analyses on 17B-4 yield 207Pb/206Pb
ages between 4338 ± 12 and 4392 ± 12 Ma (2σ); the
oldest and most concordant U-Pb analysis (4392 ± 12
Ma, 99% concordant) is interpreted to reflect primary
crystallization. APT data sets contain a small number of
Pb-rich clusters, between 5-10 nm in diameter. The 207Pb/206Pb ratio within individual clusters are
statistically identical, with a combined ratio of 1.42 ±
0.07. Using a simple clustering model, this places Pb
cluster formation at 3850 +150/-170 Ma (2σ),
overlapping the 40Ar/39Ar age for the host breccia and
linking cluster formation to the Serenitatis impact event.
The multi-scale characterization of zircon 17B-4
provides a high degree of confidence that the 207Pb/206Pb
age of 4392 ± 12 Ma records primary crystallization,
making 17B-4 one of the oldest reliably dated lunar
zircons. APT data document the first known occurrence
of nanoscale Pb clustering in lunar zircon, and the first
ever correlation of Pb clustering to impact processes.
[1] Cavosie et al., (2015) Geology, 999-1002.
[2] Turner et al., (1975) Proc. 6th L.S.C., 1509-1538
Original languageEnglish
Title of host publicationGoldschmidt2019 Abstracts
Number of pages1
Publication statusPublished - Aug 2019
EventGoldschmidt 2019 - Barcelona, Spain
Duration: 18 Aug 201923 Aug 2019

Conference

ConferenceGoldschmidt 2019
Country/TerritorySpain
CityBarcelona
Period18/08/1923/08/19

Austrian Fields of Science 2012

  • 105116 Mineralogy
  • 104026 Spectroscopy

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