Russian Journal of Earth Sciences
Vol. 5, No. 3, June 2003
Early Precambrian mafic rocks of the Fennoscandian shield
as a reflection of plume magmatism: Geochemical types and formation stages
N. A. Arestova, S. B. Lobach-Zhuchenko, V. P. Chekulaev, and E. G. Gus'kova
Abstract
The analysis of radiometric ages of Early Precambrian
basites of the Fennoscandian shield, from the most ancient ones,
> 3.1 Ga, to 2.40 Ga, resolves five age groups of the basites. Each
of these stages is shown to time span interval of 70-80 m.y. The
early stages of the high-T mafic magmatism ( > 3.1 and 2.99-2.91 Ga)
are confined to within the oldest core of continental crust in
the Fennoscandian shield - the Vodlozero domain with crustal age of
3.2-3.4 Ga. The next stage of mafic magmatism (2.88-2.80 Ga)
occurred within the Kola and western Karelian domains with crustal
ages of 3.0 and 3.1 Ga and on the north of the younger, central
Karelian domain.
The last of the Archean stages of high-temperature mafic magmatism with
ages of 2.72-2.66 Ga occurs in the north Karelian belts, in the Karelian part
of the
Belomorian area (the regions of Lake Notozero and the Tupaya Guba Bay of Lake
Kovdozero) and possibly, in the western Karelian domain. This magmatism took
place also immediately after the subduction processes at the boundary of the
Karelian and Belomorian domains.
The Early Proterozoic high-T mafic magmatism at 2.50-2.41 Ga was both
the most areally extensive and continuos such episode in the Fennoscandian shield.
Nearly all the researchers of the high-T basites of this stage attribute this
magmatism to the ascent of a deep mantle super-plume. Paleomagnetic data
provide further evidence that at 2.5-2.41 Ga a long-lived heat source occupied
virtually the entire area of the present day Fennoscandian shield.