[meteorite-list] Ureilites/Venus

From: Bernd Pauli HD <bernd.pauli_at_meteoritecentral.com>
Date: Thu Apr 22 09:49:01 2004
Message-ID: <3BA7A458.D069A419_at_lehrer1.rz.uni-karlsruhe.de>

Steven Singletary wrote:

> When we look at the Sm-Nd systematics of ureilites, we find some of the
> ureilites give Sm-Nd ages of 3.79 Ga. This is long after differentiation
> occurred (and yet another puzzling aspect of the ureilites). If we take 4.56
> Ga as the beginning of the solar system ...that gives almost 800 million
> years in which to mix and redistribute the isotopes.


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.

Reference:

GOODRICH C.A. (1992) Ureilites: A critical
review (Meteoritics 27, 1992, 327-352).


Best wishes,

Bernd
Received on Tue 18 Sep 2001 03:45:28 PM PDT