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TitlePaleomagnetism indicates that primary magnetite in zircon records a strong Hadean geodynamo
 
AuthorTarduno, J A; Cottrell, R D; Bono, R K; Oda, H; Davis, W JORCID logo; Fayek, M; van 't Erve, O; Nimmo, F; Huang, W; Thern, E; Fearn, S; Mitra, G; Smirnov, A V; Blackman, E G
SourceProceedings of the National Academy of Sciences of the United States of America vol. 117, no. 5, 2020 p. 2309-2318, https://doi.org/10.1073/pnas.1916553117 Open Access logo Open Access
Image
Year2020
Alt SeriesNatural Resources Canada, Contribution Series 20190492
PublisherUnited States National Academy of Sciences
Documentserial
Lang.English
Mediapaper; on-line; digital
File formatpdf; html
Subjectsgeophysics; geochronology; geochemistry; Science and Technology; Nature and Environment; geomagnetic fields; remanent magnetism; paleomagnetism; paleomagnetic interpretations; magnetite; radiometric dating; lead lead dates; zircon dates; precipitation; magnetization; electron microscope analyses; magnetic field intensity; inclusions; lithium geochemistry; Archean; Hadean; Precambrian
Illustrationsphotomicrographs; plots; equal-area stereonet projections; spectra; Concordia diagrams; time series
ProgramScience Laboratory Network
Released2020 01 21
AbstractDetermining the age of the geomagnetic field is of paramount importance for understanding the evolution of the planet because the field shields the atmosphere from erosion by the solar wind. The absence or presence of the geomagnetic field also provides a unique gauge of early core conditions. Evidence for a geomagnetic field 4.2 billion-year (Gy) old, just a few hundred million years after the lunar-forming giant impact, has come from paleomagnetic analyses of zircons of the Jack Hills (Western Australia). Herein, we provide new paleomagnetic and electron microscope analyses that attest to the presence of a primary magnetic remanence carried by magnetite in these zircons and new geochemical data indicating that select Hadean zircons have escaped magnetic resetting since their formation. New paleointensity and Pb-Pb radiometric age data from additional zircons meeting robust selection criteria provide further evidence for the fidelity of the magnetic record and suggest a period of high geomagnetic field strength at 4.1 to 4.0 billion years ago (Ga) that may represent efficient convection related to chemical precipitation in Earth's Hadean liquid iron core.
Summary(Plain Language Summary, not published)
One of the important questions in Earth evolution is when the geodynamo that creates the Earth's magnetic field became established. Determining the age of the geomagnetic field is of paramount importance for understanding the evolution of the planet because the field shields the atmosphere from erosion by the solar wind. The oldest Earth materials, dating to greater than 4 billion years, are individual zircon grains eroded from an ancient crust and deposited in much younger sedimentary rocks. This study determined the magnetic field strength of individual zircon grains to ascertain the magnetic field strength at the time the grains were formed. The capabilities of the GSC SHRIMP ion probe was used to determine the ages of the grains, which established that the material was in part greater than 4 billion years old. The study interpreted a high geomagnenitc field strength at 4.0-4.1 billion years indicative of efficient convection of the geodynamo.
GEOSCAN ID321634

 
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