[meteorite-list] Ureilite Origins

From: Kashuba, Ontario, California <mary.kashuba_at_meteoritecentral.com>
Date: Mon Sep 6 15:32:05 2004
Message-ID: <00cf01c49448$2df1e440$6401a8c0_at_VALUED2CAD4949>

Bernd and List,

Aside from the origin of ureilites, it appears that traces of chondrules are
found in polymict ureilites and are probably from impactors - like the
chondrules sometimes found in howardites. See Mr. Weir's page on DaG 319.
I might be lucky enough to have a thin section of DaG 319 that contains a
chondrule. Tell me what you think.

http://www.johnkashuba.com/Ach_DaG_319_Ureilite_-_Polymict.html

Regards,

John Kashuba
Ontario, California

----- Original Message -----
From: <bernd.pauli_at_paulinet.de>
To: <Meteorite-list_at_meteoritecentral.com>
Sent: Monday, September 06, 2004 11:31 AM
Subject: [meteorite-list] Ureilite Origins


> They had to have been carbonaceous meteorites of some sort to begin
> with, but the articles I've seen don't seem to offer a clear picture
> of what they were like before they were shocked. CM, perhaps?


Hello Marc, Fr?d?ric, and List,

Here is what I've harvested during the last few minutes:


Cyrena Anne Goodrich, Lunar and Planetary
Laboratory, University of Arizona

Invited Review - Ureilites: A critical review
(Meteoritics 27-4, 1992, pp. 327-352):

1) Nilpena contains clasts of carbonaceous chondrite matrix material.
   Detailed petrographic and mineralogic studies have shown that this
   material has close affinities to CI - and differs substantially from
   CM-matrix (Brearley and Prinz, 1989; 1992).

Fr?d?ric, "close affinities to CI" would also explain why we do not find any
chondrules or relict chondrules in ureilites - there have never been any.

But, ... now look at this - it is from the same review by C.A. Goodrich:

2) CI-matrix clasts in Nilpena have an oxygen-isotope composition plotting
   on the extension of the Allende mixing line on the 17^O-rich side of the
   terrestrial fractionation line, rather than within the field of CI matrix
   compositions (Brearley and Prinz, 1992).

So the starting material may have been CI- o r CV-like. If it was
CV-like, we
might really expect to find traces of chondrules or at least chondrule
precursor
material.

Best wishes,

Bernd

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Received on Mon 06 Sep 2004 03:31:59 PM PDT