[meteorite-list] "Primitive" Ureilites

[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