کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
6428520 | 1634740 | 2015 | 11 صفحه PDF | دانلود رایگان |
- New paleointensity data from the â¼2.41 Ga Widgiemooltha Dike Swarm (Yilgarn craton).
- The mean and range of paleointensity values similar to those of the recent field.
- A compositional geodynamo established by the Archean-Proterozoic boundary.
Absolute geomagnetic paleointensity measurements were conducted on samples from six mafic dikes of the â¼2.41 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.
Journal: Earth and Planetary Science Letters - Volume 416, 15 April 2015, Pages 35-45