The Crystallization Age of Eucrite Zircon
G. Srinivasan,1*
M. J. Whitehouse,2
I. Weber,3
A. Yamaguchi4
Eucrites are a group of meteorites that represent the first
planetary igneous activity following metal-silicate differentiation
on an early planetesimal, similar to Asteroid 4 Vesta, and,
thus, help date geophysical processes occurring on such bodies
in the early solar system. Using the short-lived radionuclide
182Hf as a relative chronometer, we demonstrate that eucrite
zircon crystallized quickly within 6.8 million years of metal-silicate
differentiation. This implies that mantle differentiation on
the eucrite parent body occurred during a period when internal
heat from the decay of
26Al and
60Fe was still available. Later
metamorphism of eucrites took place at least 8.9 million years
after the zircons crystallized and was likely caused by heating
from impacts, or by burial under hot material excavated by impacts,
rather than from lava flows. Thus, the timing of eucrite formation
and of mantle differentiation is constrained.
2 Laboratory for Isotope Geology, Swedish Museum of Natural History, SE-104 05 Stockholm, Sweden.
3 Institute for Planetology, Department of Geosciences, University of Münster, D-48149 Münster, Germany.
4 National Institute of Polar Research, Tokyo 173-8515, Japan.
* To whom correspondence should be addressed. E-mail: srini{at}geology.utoronto.ca
