Journal article
Shock stage distribution of 2280 ordinary chondrites- Can bulk chondrites with a shock stage of S6 exist as individual rocks?

Publication Details
Bischoff, A.; Schleiting, M.; Patzek, M.
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Meteoritics & Planetary Science
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The brecciation and shock classification of 2280 ordinary chondrites of the
meteorite thin section collection at the Institut f€ur Planetologie (M€unster) has been
determined. The shock degree of S3 is the most abundant shock stage for the H and LL
chondrites (44% and 41%, respectively), while the L chondrites are on average more heavily
shocked having more than 40% of rocks of shock stage S4. Among the H and LL
chondrites, 40–50% are “unshocked” or “very weakly shocked.” Considering the petrologic
types, in general, the shock degree is increasing with petrologic type. This is the case for all
meteorite groups. The main criteria to define a rock as an S6 chondrite are the solid-state
recrystallization and staining of olivine and the melting of plagioclase often accompanied by
the formation of high-pressure phases like ringwoodite. These characteristics are typically
restricted to local regions of a bulk chondrite in or near melt zones. In the past, the
identification of high-pressure minerals (e.g., ringwoodite) was often taken as an automatic
and practical criterion for a S6 classification during chondrite bulk rock studies. The shock
stage classification of many significantly shocked chondrites (>S3) revealed that most
ringwoodite-bearing rocks still contain more than 25% plagioclase (74%). Thus, these bulk
chondrites do not even fulfill the S5 criterion (e.g., 75% of plagioclase has to be
transformed into maskelynite) and have to be classified as S4. Studying chondrites on
typically large thin sections (several cm2) and/or using samples from different areas of the
meteorites, bulk chondrites of shock stage S6 should be extremely rare. In this respect, the
paper will discuss the probability of the existence of bulk rocks of S6.


Last updated on 2019-06-08 at 15:48