92Nb-92Zr and the Early Differentiation History of Planetary Bodies
C. Münker,1*
S. Weyer,1
K. Mezger,1
M. Rehkämper,1
F. Wombacher,1
A. Bischoff2
The niobium-92-zirconium-92
(92Nb-92Zr) extinct radioactive decay system
(half-life of about 36 million years) can place new time constraints on
early differentiation processes in the silicate portion of planets and
meteorites. Zirconium isotope data show that Earth and the oldest lunar
crust have the same relative abundances of 92Zr as
chondrites. 92Zr deficits in calcium-aluminum-rich
inclusions from the Allende meteorite constrain the minimum value for
the initial 92Nb/93Nb ratio of the solar system
to 0.001. The absence of 92Zr anomalies in terrestrial and
lunar samples indicates that large silicate reservoirs on Earth and the
moon (such as a magma ocean residue, a depleted mantle, or a crust)
formed more than 50 million years after the oldest meteorites formed.
1 Zentrallabor für Geochronologie,
Mineralogisches Institut, Universität Münster,
Corrensstrasse 24, 48149 Münster, Germany.
2 Institut für Planetologie, Universität
Münster, Wilhelm Klemm Strasse 10, 48149 Münster, Germany.
*
To whom correspondence should be addressed. E-mail:
muenker{at}nwz.uni-muenster.de
