Geomagnetic paleointensity at ~2.41 Ga as recorded by the Widgiemooltha Dike Swarm, Western Australia

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© 2015 Elsevier B.V. Absolute geomagnetic paleointensity measurements were conducted on samples from six mafic dikes of the ~2.41 Ga Widgiemooltha swarm (Western Australia). Rock magnetic analyses indicate that the paleointensity signal is carried by nearly stoichiometric pseudosingle-domain magnetite and/or low-Ti titanomagnetite. Paleointensity values were determined using the Thellier double-heating method supplemented by low-temperature demagnetizations (the LTD-Thellier method) in order to reduce the effect of magnetic remanence carried by large pseudosingle-domain and multidomain magnetite grains. Thirty-one samples from five dikes yielded successful paleointensity determinations with the mean value of 41.2±3.8 μT, which corresponds to a virtual dipole moment of 6.65±0.98 Am2. The mean and range of paleofield strength values are similar to those of the recent Earth's magnetic field and are consistent with a compositionally driven geodynamo established by the earliest Paleoproterozoic Era. The existence of a stable, dipolar geomagnetic field during the Proterozoic indicated by paleointensity and paleodirectional data from this and prior studies seems incompatible with a young age of the inner core suggested by recent models of the Earth's thermal evolution. Acquisition of reliable paleointensity estimates using the novel approaches such as the LTD-Thellier method is crucial in constraining the development of more realistic, Earth-like models of long-term geodynamo behavior.

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Earth and Planetary Science Letters