Hello Abdelfattah and List,
In 1992, C.A. Goodrich wrote a very comprehensive paper about ureilite
formation. If you have access to this invited review, I strongly advise you
read it:
GOODRICH C.A. (1992) Invited Review - Ureilites: A critical review
(Meteoritics 27-4, 1992, pp. 327-352).
It is almost impossible to explain in just a few words how these
coarse-grained, ultramafic, highly fractionated, igneous rocks were formed.
Mrs. Goodrich was
well aware that ureilites have some primitive characteristics that are
difficult to
reconcile with extensive igneous processing. Among these are:
1) metal with high abundances of trace siderophile elements,
2) carbon which contains planetary-type noble gases;
3) the oxygen isotopic signature of primitive/unequilibrated
solar system materials.
Both (1) and (2) are typical of undifferentiated, chondritic (!) materials but
in
terms of mineralogy and lithophile element chemistry ureilites are absolutely
non-chondritic. They rather resemble ultramafic rocks from the Earth and Moon.
Moreover, the presence of noble gases in near-chondritic abundances is difficult
to explain because gases are expected to be lost at high temperature. This is
especially difficult to explain because none of the other major achondrite types
contain noble gases in chondritic or near-chondritic abundances.
So you probably understand that there is no easy answer to your question
but I am sure Mrs. Goodrichs Review will emlighten you!
Best regards,
Bernd
______________________________________________
Visit the Archives at http://www.meteorite-list-archives.com
Meteorite-list mailing list
[email protected]
https://pairlist3.pair.net/mailman/listinfo/meteorite-list
