[meteorite-list] "Primitive" Ureilites

From: j.divelbiss_at_att.net <j.divelbiss_at_meteoritecentral.com>
Date: Tue Sep 28 18:49:20 2004
Message-ID: <092820042247.15129.4159EA0F0005920900003B1921602807489C9C070D040A90070BD206_at_att.net>

Thanx Bernd, Adam and Matt,

Now that I'm home from work I can look up some references for my own sanity.

First off, I couldn't recall that Ureilites were described as primitive, which only confirms I have a bad memory.

According to McSween's book, Meteorites and Their Parent Planets, the list of primitive achondrites includes:

acapulcoites
angrites
brachinites
lodranites
ureilites
winonaites

And the book's section on Ureilites states that "The olivine and pyroxene assemblage appears to have formed 4.5 billion years ago, but some radiogenic isotopes were redistributed at 4.0 billion years ago."

So ureilites are primitive!!!

Silly me,

John

PS Does anyone have a small piece of lodranite for sale? It is still missing from my collection.




-------------- Original message from bernd.pauli_at_paulinet.de: --------------

> Matt Morgan wrote:
>
> > I always thought that all ureilites were "primitive".
>
> On the one hand, ureilites are igneous (= evolved) rocks - i.e. they
> were formed by the solidification of a molten magma and this implies
> differentiation processes of a planetary-sized asteroidal body.
>
> On the other, and this causes scientists a lot of headaches, ureilites display
> several p r i m i t i v e characteristics. Among these are the following:
>
> - high abundances of siderophile elements,
> - carbon which contains planetary-type noble gases
> - oxygen isotopic signature of unequilibrated (= primitive / unprocessed)
> solar system materials
>
> A.H.Treiman, J.L.Berkley (1994) Igneous Petrology of the New Ureilites
> Nova 001 and Nullarbor 010 (Meteoritics 29-6, 1994, 843-848, excerpt):
>
> "Ureilites are achondrite meteorites, composed principally of olivine,
> pyroxenes, and graphite. Ureilites display a bewildering variety of
> "primitive" and "evolved" characteristics, so that little of their origin
> is known with certainty."
>
> References:
>
> CHIKAMI J. et al. (1996) Ureilite formation process with regard
> to the LEW 88774 ureilite (Meteoritics 31-4, 1996, A027-A028).
>
> WANG M.-S. and LIPSCHUTZ M.E. (1994) Constraints on ureilite
> origin from trace-element contents (Meteoritics 29-4, 1994, 546).
>
> Goodrich C.A. (1992) Ureilites: A critical
> review (Meteoritics 27-4, 1992, 327-352).
>
>
> Best wishes,
>
> Bernd
>
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Received on Tue 28 Sep 2004 06:47:44 PM PDT