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Pervasive remagnetization of detrital zircon host rocks in the Jack Hills, Western Australia and implications for records of the early geodynamo

Authors :
Benjamin P. Weiss
Samuel A. Bowring
Jahandar Ramezani
E. Bruce Watson
Robert S. Coe
Adam C. Maloof
Roger R. Fu
T. Mark Harrison
Joseph L. Kirschvink
Nicholas D. Tailby
Dustin Trail
Nicholas L. Swanson-Hysell
Veronica Hanus
Source :
Earth and Planetary Science Letters. 430:115-128
Publication Year :
2015
Publisher :
Elsevier BV, 2015.

Abstract

It currently is unknown when Earth's dynamo magnetic field originated. Paleomagnetic studies indicate that a field with an intensity similar to that of the present day existed 3.5 billion years ago (Ga). Detrital zircon crystals found in the Jack Hills of Western Australia are some of the very few samples known to substantially predate this time. With crystallization ages ranging from 3.0–4.38 Ga, these zircons might preserve a record of the missing first billion years of Earth's magnetic field history. However, a key unknown is the age and origin of magnetization in the Jack Hills zircons. The identification of >3.9 Ga (i.e., Hadean) field records requires first establishing that the zircons have avoided remagnetization since being deposited in quartz-rich conglomerates at 2.65–3.05 Ga. To address this issue, we have conducted paleomagnetic conglomerate, baked contact, and fold tests in combination with U–Pb geochronology to establish the timing of the metamorphic and alteration events and the peak temperatures experienced by the zircon host rocks. These tests include the first conglomerate test directly on the Hadean-zircon bearing conglomerate at Erawandoo Hill. Although we observed little evidence for remagnetization by recent lightning strikes, we found that the Hadean zircon-bearing rocks and surrounding region have been pervasively remagnetized, with the final major overprinting likely due to thermal and/or aqueous effects from the emplacement of the Warakurna large igneous province at ∼1070 million years ago (Ma). Although localized regions of the Jack Hills might have escaped complete remagnetization, there currently is no robust evidence for pre-depositional (>3.0 Ga) magnetization in the Jack Hills detrital zircons.

Details

ISSN :
0012821X
Volume :
430
Database :
OpenAIRE
Journal :
Earth and Planetary Science Letters
Accession number :
edsair.doi.dedup.....a4dabf296d74b24a274bd99149b83a32
Full Text :
https://doi.org/10.1016/j.epsl.2015.07.067