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

作者：Smirnov Aleksey V^*; Evans David A D

来源：Earth and Planetary Science Letters, 2015, 416: 35-45.

DOI：10.1016/j.epsl.2015.02.012

• paleointensity
• Precambrian

Absolute geomagnetic paleointensity measurements were conducted on samples from six mafic dikes of the similar to 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 mu T, which corresponds to a virtual dipole moment of 6.65 +/- 0.98 A m(2). 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.

• 出版日期2015-4-15