The earliest history of the Moon and the Earth; zircon geochronological evidence

Robert Pidgeon
Deaprtment of Applied Geology Curtin University

Alexander Nemchin
Deaprtment of Applied Geology Curtin University

Marion Grange
Department of Applied Geology Curtin University

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Abstract
The earliest history of the Moon and the Earth; zircon geochronological evidence

R.T.Pidgeon, A.A. Nemchin and M. L. Grange.

Department of Applied geology
Curtin University
Perth, WA, Australia.


Abstract

Zircons found in early sediments on Earth and in lunar breccias provide the only evidence of a pre- 4 Ga history for the Earth and the Moon. Even so the information they provide is only fragmentary, as they only register events that are capable of growing zircons or of resetting their U-Pb ages. In some cases, where zircons occur in igneous rock fragments in lunar breccias, the zircon U-Pb ages can be related to igneous events. However, it is commonly observed that zircons occur as separate grains in lunar soils and breccias and in these cases the magmatic source rocks are not known. Also rarely, where the U-Pb systems of zircons are seen to have been disturbed, the disturbance can be related to a large impact event, although the linking of the disturbance to an actual observed impact has not been made. Nevertheless zircons from the Apollo lunar landing sites provide strong evidence on what appears to be magmatic age peaks and also major impact events on the Moon. On earth ancient detrital zircons from the Jack Hills and Mt Narryer in Western Australia show age peaks that indicate igneous events. In this paper we consider the consistency and implications of these age peaks for the record of events on the early Earth and Moon.