[meteorite-list] Amgala, Tsarev and Zag

From: bernd.pauli_at_paulinet.de <bernd.pauli_at_meteoritecentral.com>
Date: Thu Apr 22 10:32:50 2004
Message-ID: <DIIE.0000003E00001C10_at_paulinet.de>

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).
Received on Mon 15 Mar 2004 03:19:42 PM PST