Secondary magnetic inclusions in detrital zircons from the Jack Hills, Western Australia, and implications for the origin of the geodynamo

Weiss, B. P. et al. (2018) Secondary magnetic inclusions in detrital zircons from the Jack Hills, Western Australia, and implications for the origin of the geodynamo. Geology, 46(5), pp. 427-430. (doi: 10.1130/G39938.1)

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The time of origin of Earth’s dynamo is unknown. Detrital zircon crystals containing ferromagnetic inclusions from the Jack Hills of Western Australia have the potential to contain the oldest records of the geodynamo. It has recently been argued that magnetization in these zircons indicates that an active dynamo existed as far back as 4.2 Ga. However, the ages of ferromagnetic inclusions in the zircons are unknown. Here we present the first detailed characterization of the mineralogy and spatial distribution of ferromagnetic minerals in Jack Hills detrital zircons. We demonstrate that ferromagnetic minerals in most Jack Hills zircons are commonly located in cracks and on the zircons’ exteriors. Hematite is observed to dominate the magnetization of many zircons, while other zircons also contain significant quantities of magnetite and goethite. This indicates that the magnetization of most zircons is likely to be dominantly carried by secondary minerals that could be hundreds of millions to billions of years younger than the zircons’ crystallization ages. We conclude that the existence of the geodynamo prior to 3.5 Ga has yet to be established.

Item Type:Articles
Additional Information:These analyses were supported by National Science Foundation grant EAR1647504, Thomas F. Peterson, Jr., and a Chamberlin Postdoctoral Fellowship to Boehnke.
Glasgow Author(s) Enlighten ID:Einsle, Dr Joshua Franz
Authors: Weiss, B. P., Fu, R. R., Einsle, J. F., Glenn, D. R., Kehayias, P., Bell, E. A., Gelb, J., Araujo, J. F.D.F., Lima, E. A., Borlina, C. S., Boehnke, P., Johnstone, D. N., Harrison, T. M., Harrison, R. J., and Walsworth, R. L.
College/School:College of Science and Engineering > School of Geographical and Earth Sciences > Earth Sciences
Journal Name:Geology
Publisher:Geological Society of America
ISSN (Online):1943-2682
Published Online:01 March 2018
Copyright Holders:Copyright © 2018 Geological Society of America
First Published:First published in Geology 46(5):427-430
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher

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