[meteorite-list] Re: Ureilites/Venus
From: Steven Singletary <jumper_at_meteoritecentral.com>
Date: Thu Apr 22 09:49:01 2004
Yes, 3.74 Ga. Thanks Bernd. I've read that paper several times but can
never get the "4" right. I keep mixing the age up with something else.
So, in terms of the previous post re the ureilites from Venus, they cannot
come from a body prior to differentiation.
>Hello Steven and List,
>One of the problems of the Sm-Nd systematics of ureilites is that
>this system suggests they were produced by planetary differentiation
>processes. On the other hand, ureilites also have primitive character-
>istics (high abundances of siderophile elements, planetary-type noble
>gases, oxygen isotopic signature of unequilibrated solar system
>materials). Cyrena Anne Goodrich states that the ultramafic ureilite
>assemblage formed at about 4.55 Ga but that their Sm-Nd and Rb-Sr
>isotopic systematics have been subsequently disturbed. Thus, some
>ureilites do have old ages (~ 4.55 Ga), whereas others show evidence
>of later processing at ~ 3.74 and 4.23 Ga.
>GOODRICH C.A. (1992) Ureilites: A critical
>review (Meteoritics 27, 1992, 327-352).
Dept. Earth, Atmospheric, and Planetary Sciences
Cambridge, Ma., 02139
Received on Tue 18 Sep 2001 05:29:03 PM PDT