40Ar-39Ar studies of whole rock nakhlites: Evidence for the timing of formation and aqueous alteration on Mars

Timothy D. Swindle, Erik K. Olson

Research output: Contribution to journalArticlepeer-review

30 Scopus citations

Abstract

20-25 mg whole rock samples of the nakhlites Lafayette and Nakhla have been analyzed via the 40Ar39Ar technique, in part to verify their formation ages, but primarily, in an attempt to determine the timing of aqueous alteration in these martian meteorites. As in previous studies, plateaus in apparent age are observed at about 1300 Ma (1322 ± 10 for Lafayette, 1332 ± 10 and 1323 ± 11 for Nakhla), presumably corresponding to crystallization ages. The plateaus are not entirely flat, perhaps reflecting the effects of recoil during creation of 39Ar in the nuclear irradiation. The first 5-20% of the K-derived Ar released from all three samples give apparent ages <1300 Ma. Coupled with the fact that chronometric isotopic studies of nakhlites typically show some disturbance, we believe the low temperature pattern represents more recent (than 1300 Ma formation of martian aqueous alteration products such as iddingsite. No low temperature plateaus are observed. This is consistent with petrographic evidence for multiple formation events, although the lack of low temperature plateaus is far from conclusive. On the other hand, if there was a single time of alteration, we believe that it will be difficult, if not impossible, to determine it using the K-Ar system.

Original languageEnglish (US)
Pages (from-to)755-766
Number of pages12
JournalMeteoritics and Planetary Science
Volume39
Issue number5
DOIs
StatePublished - May 2004

ASJC Scopus subject areas

  • Geophysics
  • Space and Planetary Science

Fingerprint

Dive into the research topics of '40Ar-39Ar studies of whole rock nakhlites: Evidence for the timing of formation and aqueous alteration on Mars'. Together they form a unique fingerprint.

Cite this