AW: [meteorite-list] Amgala, Tsarev and Zag

From: j.divelbiss_at_att.net <j.divelbiss_at_meteoritecentral.com>
Date: Thu Apr 22 10:32:50 2004
Message-ID: <031620041844.9435.48e4_at_att.net>

Joern,

Thanx for the clarification on regolith versus the basic breccia types.

As far as chondrites go...is a genomict breccia with a regolith history like Zag more or less unusual when compared to a polymict breccia for chondrites, as in the supposed case for Amgala? I ask this since you did point out that achondrites are the ones that usually have the polymict breccias, and not chondrites.

Does this make NWA 1955 (H/L 3-4) a polymict breccia also? Or does its classification as being unequilibrated chondrite make it different than a breccia per say?

John

> Tsarev noble gas data data:
>
> he_3 he_4 ne_20 ne_21 ne_22 ar_36 ar_38 ar_40
> 1,58 121 0,54 0,54 0,60 0,42 0,11 575
> 2,07 108 0,78 0,82 0,88 0,83 0,20 1635
> all values: x 10E-8 cc STP/g
>
> Reference: Herzog G. F., Vogt S., Albrecht A., Xue S., Fink D., Klein J.,
> Middleton R., Weber H. W. and Schultz L. (1997) Complex exposure histories for
> meteorites with "short" exposure ages. Meteoritics 32, 413-422.
>
> According to this, Tsarev isn't a regolith breccia.
>
> BTW: A regolith breccia can be either polymict (different source types of
> clasts, e.g., H3 + L6), xenolithic (some minor exotic (non-host type) clasts,
> e.g. CM clasts in L6 host), genomict (same material type but different
> petrologic grades, e.g. H3 + H5), or monomict (e.g. light H3 + dark H3
> (irradiated) lithologies). Usually, regolith breccias are monomict or genomict
> breccias. Achondrites are often polymict breccias (e.g. howardites, eucrites,
> diogenits, ureilites, lunaites).
>
> Regards,
> Joern
>
> _______________________________________________________________________________
> Joern Koblitz
> MetBase Editor
> The MetBase Library of Meteoritics and Planetary Sciences
> Benquestrasse 27
> D-28209 Bremen, Germany
> phone: +49 421 24 100 24
> fax: +49 421 24 100 99
> email: info_at_metbase.de
> _______________________________________________________________________________
>
>
>
> > -----Ursprüngliche Nachricht-----
> > Von: bernd.pauli_at_paulinet.de [mailto:bernd.pauli@paulinet.de]
> > Gesendet: Montag, 15. März 2004 21:20
> > An: Meteorite-list_at_meteoritecentral.com
> > Betreff: [meteorite-list] Amgala, Tsarev and Zag
> >
> >
> > Adam wrote:
> >
> > > I do not believe it is going to classify as a
> > > regolith breccia but rather a polymict breccia.
> >
> > Adam also wrote:
> >
> > > I thought one distinction made for a regolith breccia is that
> > > there are signs of crystal damage caused by the solar wind
> >
> > Martin A. chirped:
> >
> > > Tsarev which is brecciated but not polymict
> > > is also altered by solar winds, isn't it?
> >
> > Hello Adam, Martin, and List,
> >
> > There are 3 types of inert and/or noble gases in some meteorites:
> >
> > (1) those produced by cosmic ray bombardment (cosmogenic);
> > (2) those resulting from radioactive decay of elements (radiogenic)
> > in the meteorite;
> > (3) those present originally (= trapped or primordial gases).
> >
> > No. (3) is what we are interested in to find out if Amgala, Tsarev
> > and Zag have or have not been altered by solar wind particles.
> >
> > These gases are 4^He, 20^Ne, 36^Ar, 84^Kr, 132^Xe.
> >
> > There are two different sources for these inert/noble gases:
> >
> > (a) solar-type gas
> > (b) planetary-type gas
> >
> > To find out "what is what" and "which is which", meteoriticists
> > consider the relative amounts and, above all, ratios of a number
> > of isotopes.
> >
> > J.T. Wasson proposed the following arbitrary
> > definition of a solar gas-rich meteorite:
> >
> > - The 20^Ne/22^Ne ratio should be greater than 2.5
> > - Ne isotopic data should plot above the dashed line
> > you find on p. 102 and on p. 111 of Wasson's and
> > Sears' books (see: Reference)
> > - The 4^He content should exceed 2 x 10^-5 cm^3 g^-1
> > - The 20^Ne / 36^Ar ratio should be greater than 0.3
> >
> > Unfortunately, I don't have any of these isotope data handy for
> > Tsarev :-( What I do have are some 3^He and 21^Ne data from
> > the MPI Mainz but they are of little help at the moment).
> >
> > There is an abstract paper by Honda et al. but they only discuss
> > cosmogenic nuclides (see: Reference) - again of little help.
> >
> > Anyway, Tsarev is a special case and as such mentioned in a
> > research article by S.K. Vogt et al. The authors group Tsarev
> > with a number of other H and L chondrites that underwent a
> > complex "two-stage exposure history":
> >
> > t1 = 8 million years, radius ca. 200 cm
> > t2 = ca. 0.3 million years, radius ca. 140 cm
> >
> >
> > Best wishes,
> >
> > Bernd
> >
> >
> > References:
> >
> > VOGT S.K. et al. (1993) On the Bur Ghelulai H5 chondrite and other
> > meteorites with complex exposure histories (Meteoritics 28,
> > 1993, 71-85).
> >
> > HONDA M. et al. (1992) Cosmogenic nuclides in the
> > Tsarev chondrite (Meteoritics 27-3, 1992, 234-235).
> >
> > WASSON J.T. (1974) Meteorites Classification and Properties
> > (Springer-Verlag, Berlin, Heidelberg, New York, pp. 97-109).
> >
> > SEARS D.W. (1978) The Nature and Origin of
> > Meteorites (Adam Hilger Ltd. Bristol, pp. 110-115).
> >
> > McSWEEN H.Y. (1999) Meteorites and Their Parent Planets
> > (Cambridge University Press, Glossary, pp. 41-44, 111-112, 244-248).
> >
> >
> > ______________________________________________
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> >
>
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Received on Tue 16 Mar 2004 01:44:23 PM PST