Paleointensity of the early geodynamo (2.45 Ga) as recorded in Karelia: A single-crystal approach
- 1Department of Earth and Environmental Sciences, University of Rochester, Rochester, New York 14627, USA
- 2Department of Earth Physics, Saint Petersburg State University, Saint Petersburg 199034, Russia
Abstract
We report Thellier paleointensity results from single plagioclase crystals derived from ca. 2.45 Ga border dikes of the Burakovka layered intrusion (Karelia, Russia). Rock magnetic and transmission electron microscope analyses indicate that these plagioclase crystals contain pseudosingle- to single-domain magnetite inclusions. Fifteen determinations from four dikes meet reliability criteria and yield an average paleointensity of 43.2 ± 10.8 μT, which corresponds to a virtual dipole moment of 8.43 ± 2.11 × 1022 Am2. Although our result is unlikely to adequately represent the time-averaged field, the mean and range of values are similar to those of the present-day field. These values suggest that the inner core, which may stabilize the geodynamo, had started to grow by Early Proterozoic time.
Footnotes
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↵GSA Data Repository item 2003056, Tables DR1–DR3, Thellier results and unaveraged and averaged paleointensity parameters, is available from Documents Secretary, GSA, P.O. Box 9140, Boulder, CO 80301-9140, editinggeosociety.org, or at http://www.geosociety.org/pubs/ft2003.htm.
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- Accepted January 23, 2003.
- Received October 10, 2002.
- Revision received January 21, 2003.
- Geological Society of America
