[meteorite-list] Zircon(s) in meteorites and NWA 3148

[bernd.pauli at paulinet.de]

Hello Greg and List,

Zircons which usually occur as minerals have been reported
from lunar soils, lunar meteorites (DaG 400, SaU 169), SNCs
(Shergotty), carbonaceous chondrites (for example in Murchison
hibonites), from the Vaca Muerta mesosiderite, and several HED
meteorites - among them Stannern, Padvarnikai, Bereba, Cachari,
Jonzac, Juvinas, Millbillillie, Pasamonte, and also from the
Simmern H5 chondrite.

Well, why does Greg emphasize the occurrence of zircons
in their basaltic, unbrecciated eucrite NWA 3148?

Zircons are common in terrestrial rocks but rare in meteorites!

Their importance lies in the possibility to date the formation ages
of the respective meteorites as these zircons contain appreciable
amounts of U (uranium) and Th (thorium). This radiogenic component
allows the use of the U-Pb (uranium-lead) method which gives the
formation age of these meteorites.

The HED zircons are consistent with a formation age of 4.56 Ga (4.56
billion years). If interested in the principles of radioactive clocks,
see also:

NORTON O.R. (2002) The Cambridge Encyclopedia of Meteorites, pp.215-219.

McSWEEN H.Y. (1999) Meteorites and Their Parent Planets
(Cambridge University Press, pp. 42-46).


Best wishes,

Bernd