Direct age constraints on the magnetism of Jack Hills zircon

Richard J M Taylor; Steven M Reddy; David W Saxey; William D A Rickard; Fengzai Tang; Cauê S Borlina; Roger R Fu; Benjamin P Weiss; Paul Bagot; Helen M Williams; Richard J Harrison

doi:10.1126/sciadv.add1511

Direct age constraints on the magnetism of Jack Hills zircon

Sci Adv. 2023 Jan 6;9(1):eadd1511. doi: 10.1126/sciadv.add1511. Epub 2023 Jan 6.

Authors

Richard J M Taylor¹, Steven M Reddy^{2

3}, David W Saxey^{2

3}, William D A Rickard^{2

3}, Fengzai Tang¹, Cauê S Borlina⁴, Roger R Fu⁵, Benjamin P Weiss⁴, Paul Bagot⁶, Helen M Williams¹, Richard J Harrison¹

Affiliations

¹ Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK.
² School of Earth and Planetary Sciences, Curtin University, Bentley, WA 6102, Australia.
³ Geoscience Atom Probe Facility, John de Laeter Centre, Curtin University, Bentley, WA 6102, Australia.
⁴ Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
⁵ Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA.
⁶ Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK.

Abstract

A potential record of Earth's magnetic field going back 4.2 billion years (Ga) ago is carried by magnetite inclusions in zircon grains from the Jack Hills. This magnetite may be secondary in nature, however, meaning that the magnetic record is much younger than the zircon crystallization age. Here, we use atom probe tomography to show that Pb-bearing nanoclusters in magnetite-bearing Jack Hills zircons formed during two discrete events at 3.4 and <2 Ga. The older population of clusters contains no detectable Fe, whereas roughly half of the younger population of clusters is Fe bearing. This result shows that the Fe required to form secondary magnetite entered the zircon sometime after 3.4 Ga and that remobilization of Pb and Fe during an annealing event occurred more than 1 Ga after deposition of the Jack Hills sediment at 3 Ga. The ability to date Fe mobility linked to secondary magnetite formation provides new possibilities to improve our knowledge of the Archean geodynamo.