Ancient porosity preserved in ordinary chondrites: Examining shock and compaction on young asteroids

Jon M. Friedrich, Alan E. Rubin, Sky P. Beard, Timothy Swindle, Clark E. Isachsen, Mark L. Rivers, Robert J. Macke

Research output: Contribution to journalArticle

16 Citations (Scopus)

Abstract

We use a combination of 2D and 3D petrographic examination and 40Ar-39Ar analyses to examine the impact histories of a suite of seven ordinary chondrites (Baszkówka, Miller, NWA 2380, Mount Tazerzait, Sahara 98034, Tjerebon, and MIL 99301) that partially preserve their ancient, but postaccretionary, porosity ranging from 10 to 20%. We examine whether materials that seem to be only mildly processed (as their large intergranular pore spaces suggest) may have more complex shock histories. The ages determined for most of the seven OCs studied here indicate closure of the 40Ar-39Ar system after primary accretion, but during (Baszkówka) or shortly after (others) thermal metamorphism, with little subsequent heating. Exceptions include Sahara 98034 and MIL 99301, which were heated to some degree at later stages, but retain some evidence for the timing of thermal metamorphism in the 40Ar-39Ar system. Although each of these chondrites has olivine grains with sharp optical extinction (signaling an apparent shock stage of S1), normally indicative of an extremely mild impact history, all of the samples contain relict shock indicators. Given the high porosity and relatively low degree of compaction coupled with signs of shock and thermal annealing, it seems plausible that impacts into materials that were already hot may have produced the relict shock indicators. Initial heating could have resulted from prior collisions, the decay of 26Al, or both processes.

Original languageEnglish (US)
Pages (from-to)1214-1231
Number of pages18
JournalMeteoritics and Planetary Science
Volume49
Issue number7
DOIs
StatePublished - 2014

Fingerprint

ordinary chondrite
chondrites
asteroids
asteroid
compaction
shock
porosity
metamorphism
history
heating
histories
annealing
pore space
chondrite
olivine
collision
extinction
accretion
closures
examination

ASJC Scopus subject areas

  • Geophysics
  • Space and Planetary Science

Cite this

Friedrich, J. M., Rubin, A. E., Beard, S. P., Swindle, T., Isachsen, C. E., Rivers, M. L., & Macke, R. J. (2014). Ancient porosity preserved in ordinary chondrites: Examining shock and compaction on young asteroids. Meteoritics and Planetary Science, 49(7), 1214-1231. https://doi.org/10.1111/maps.12328

Ancient porosity preserved in ordinary chondrites : Examining shock and compaction on young asteroids. / Friedrich, Jon M.; Rubin, Alan E.; Beard, Sky P.; Swindle, Timothy; Isachsen, Clark E.; Rivers, Mark L.; Macke, Robert J.

In: Meteoritics and Planetary Science, Vol. 49, No. 7, 2014, p. 1214-1231.

Research output: Contribution to journalArticle

Friedrich, Jon M. ; Rubin, Alan E. ; Beard, Sky P. ; Swindle, Timothy ; Isachsen, Clark E. ; Rivers, Mark L. ; Macke, Robert J. / Ancient porosity preserved in ordinary chondrites : Examining shock and compaction on young asteroids. In: Meteoritics and Planetary Science. 2014 ; Vol. 49, No. 7. pp. 1214-1231.
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