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

From: Jörn Koblitz <koblitz_at_meteoritecentral.com>
Date: Thu Apr 22 10:32:51 2004
Message-ID: <E5E6112EA31FA24CB448E091C6883C050EBB76_at_server2000.microfab.de>

Dear John,

I think, for chondrites, regolith breccias (monomict or genomict) are =
quite more abundant than polymict breccias. The opposite is true for =
achondrites. Polymict breccias, especially eucrites (howardites are =
polymict by definition!) are quite often polymict (there is an unusual =
high fraction of polymict eucrites from Antarctica), whereas regolith =
breccias are rather common only for lunaites (e.g. anorthositic highland =
breccias), which are - by definition - achondrites. A nice example for =
another regolithic achondrite is the howardite Kapoeta (higly =
solar-gas-rich material).

Regarding the H/Ls (Bremervoerde, NWA 1955, Tieschitz...): these aren't =
polymict breccias containing H and L lithologies, but members of a group =
intermediate between H and L chondrite in terms of composition and =
isotopic signatures. They likely come from a parent body (PB) distinct =
from the PBs of both, the L and H chondrites. Though they are breccias, =
they are not mixing products of L and H material.

Best wishes,
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
_________________________________________________________________________=
______




> -----Urspr=FCngliche Nachricht-----
> Von: j.divelbiss_at_att.net [mailto:j.divelbiss@att.net]
> Gesendet: Dienstag, 16. M=E4rz 2004 19:44
> An: J=F6rn Koblitz
> Cc: bernd.pauli_at_paulinet.de; Meteorite-list@meteoritecentral.com
> Betreff: Re: AW: [meteorite-list] Amgala, Tsarev and Zag
>=20
>=20
> Joern,
>=20
> Thanx for the clarification on regolith versus the basic=20
> breccia types.=20
>=20
> As far as chondrites go...is a genomict breccia with a=20
> regolith history like Zag more or less unusual when compared=20
> to a polymict breccia for chondrites, as in the supposed case=20
> for Amgala? I ask this since you did point out that=20
> achondrites are the ones that usually have the polymict=20
> breccias, and not chondrites.=20
>=20
> Does this make NWA 1955 (H/L 3-4) a polymict breccia also? Or=20
> does its classification as being unequilibrated chondrite=20
> make it different than a breccia per say?
>=20
> John
>=20
> > Tsarev noble gas data data:
> >=20
> > 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
> >=20
> > Reference: Herzog G. F., Vogt S., Albrecht A., Xue S., Fink=20
> D., Klein J.,=20
> > Middleton R., Weber H. W. and Schultz L. (1997) Complex=20
> exposure histories for=20
> > meteorites with "short" exposure ages. Meteoritics 32, 413-422.
> >=20
> > According to this, Tsarev isn't a regolith breccia.
> >=20
> > BTW: A regolith breccia can be either polymict (different=20
> source types of=20
> > clasts, e.g., H3 + L6), xenolithic (some minor exotic=20
> (non-host type) clasts,=20
> > e.g. CM clasts in L6 host), genomict (same material type=20
> but different=20
> > petrologic grades, e.g. H3 + H5), or monomict (e.g. light=20
> H3 + dark H3=20
> > (irradiated) lithologies). Usually, regolith breccias are=20
> monomict or genomict=20
> > breccias. Achondrites are often polymict breccias (e.g.=20
> howardites, eucrites,=20
> > diogenits, ureilites, lunaites).
> >=20
> > Regards,
> > Joern
> >=20
> >=20
> ______________________________________________________________
> _________________
> > 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
> >=20
> ______________________________________________________________
> _________________
> >=20
> >=20
> >=20
> > > -----Urspr=FCngliche Nachricht-----
> > > Von: bernd.pauli_at_paulinet.de [mailto:bernd.pauli@paulinet.de]
> > > Gesendet: Montag, 15. M=E4rz 2004 21:20
> > > An: Meteorite-list_at_meteoritecentral.com
> > > Betreff: [meteorite-list] Amgala, Tsarev and Zag
> > >=20
> > >=20
> > > Adam wrote:
> > >=20
> > > > I do not believe it is going to classify as a
> > > > regolith breccia but rather a polymict breccia.
> > >=20
> > > Adam also wrote:
> > >=20
> > > > I thought one distinction made for a regolith breccia is that
> > > > there are signs of crystal damage caused by the solar wind
> > >=20
> > > Martin A. chirped:
> > >=20
> > > > Tsarev which is brecciated but not polymict
> > > > is also altered by solar winds, isn't it?
> > >=20
> > > Hello Adam, Martin, and List,
> > >=20
> > > There are 3 types of inert and/or noble gases in some meteorites:
> > >=20
> > > (1) those produced by cosmic ray bombardment (cosmogenic);
> > > (2) those resulting from radioactive decay of elements=20
> (radiogenic)
> > > in the meteorite;
> > > (3) those present originally (=3D trapped or primordial gases).
> > >=20
> > > 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.
> > >=20
> > > These gases are 4^He, 20^Ne, 36^Ar, 84^Kr, 132^Xe.
> > >=20
> > > There are two different sources for these inert/noble gases:
> > >=20
> > > (a) solar-type gas
> > > (b) planetary-type gas
> > >=20
> > > To find out "what is what" and "which is which", meteoriticists
> > > consider the relative amounts and, above all, ratios of a number
> > > of isotopes.
> > >=20
> > > J.T. Wasson proposed the following arbitrary
> > > definition of a solar gas-rich meteorite:
> > >=20
> > > - 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
> > >=20
> > > 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).
> > >=20
> > > There is an abstract paper by Honda et al. but they only discuss
> > > cosmogenic nuclides (see: Reference) - again of little help.
> > >=20
> > > 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":
> > >=20
> > > t1 =3D 8 million years, radius ca. 200 cm
> > > t2 =3D ca. 0.3 million years, radius ca. 140 cm
> > >=20
> > >=20
> > > Best wishes,
> > >=20
> > > Bernd
> > >=20
> > >=20
> > > References:
> > >=20
> > > VOGT S.K. et al. (1993) On the Bur Ghelulai H5 chondrite and other
> > > meteorites with complex exposure histories (Meteoritics 28,=20
> > > 1993, 71-85).
> > >=20
> > > HONDA M. et al. (1992) Cosmogenic nuclides in the
> > > Tsarev chondrite (Meteoritics 27-3, 1992, 234-235).
> > >=20
> > > WASSON J.T. (1974) Meteorites Classification and Properties
> > > (Springer-Verlag, Berlin, Heidelberg, New York, pp. 97-109).
> > >=20
> > > SEARS D.W. (1978) The Nature and Origin of
> > > Meteorites (Adam Hilger Ltd. Bristol, pp. 110-115).
> > >=20
> > > McSWEEN H.Y. (1999) Meteorites and Their Parent Planets
> > > (Cambridge University Press, Glossary, pp. 41-44,=20
> 111-112, 244-248).
> > >=20
> > >=20
> > > ______________________________________________
> > > Meteorite-list mailing list
> > > Meteorite-list_at_meteoritecentral.com
> > > http://www.pairlist.net/mailman/listinfo/meteorite-list
> > >=20
> >=20
> > ______________________________________________
> > Meteorite-list mailing list
> > Meteorite-list_at_meteoritecentral.com
> > http://www.pairlist.net/mailman/listinfo/meteorite-list
>=20
Received on Thu 18 Mar 2004 12:40:40 PM PST