EUROPROBE News 9
SVEKALAPKO: Evolution of Palaeoproterozoic and Archaean
Lithosphere
by Sven-Erik Hjelt (Oulu), Stephen Daly (Dublin) and
Svekalapko colleagues
One of the best places on Earth for studying the thermal and mechanical
processes controlling the evolution of ancient lithosphere is the Fennoscandian Shield.
This well-exposed, composite craton, cored by the Late Archaean granite-greenstone
Karelian belt, and flanked to the northeast and southwest by Palaeoproterozoic orogens, is
ideal terrain for testing plate tectonic theory and seeking to understand the contrasted
signatures of Archaean and Proterozoic lithosphere. Ophiolites, magmatic arcs, fore- and
back-arc basins and accretionary wedges are identified with confidence in the Proterozoic;
their presence in the Archaean is conjectural. The Svecofennian Orogen, dominating much of
Finland and Sweden, resulted in the accretion of vast volumes of thick juvenile crust; by
contrast, in Russia north of Karelia, the Lapland-Kola Orogen is predominantly composed of
Archaean crust, reworked during the Palaeoproterozoic.
A considerable geological, geochemical and geophysical data base provides
the foundation for focused new EUROPROBE investigations. Deep seismic refraction profiles
have defined the velocity structure of the shield; shallow CMP reflection profiles in
Russia give unique insight into upper crustal structure. Deep and superdeep drillholes
(including Kola) provide exceptional opportunities for calibrating further geophysical
data.
EUROPROBE's multidisciplinary investigation of the Fennoscandian Shield
SVEKALAPKO (SVEcofennian-KArelia-LAPland-KOla) focuses on the following key issues:
Establishing
the character of the deep lithosphere (lower crust and upper mantle) and its relationship
to the asthenosphere below the different parts (Lapland-Kola, Karelia and Svecofennia) of
the Fennoscandian Shield. The latter provides unusually favourable bedrock conditions for
major geophysical experiments aimed at defining lithosphere-asthenosphere relationships,
particularly electromagnetic probing and deep tomography studies. An important target is
the deep structure of the highly anomalous (c. 60 km thick) juvenile Svecofennian crust,
where correlation with gravity data and topographic relief are lacking.
Defining
the crustal evolution across the Shield to establish the timing of formation of the
different major structures and their relationship to the underlying deeper lithosphere;
this will provide insight into ore genesis and contribute to further exploration efforts.
Particular interest concerns:
The
Archaean evolution of the Karelian terrane and the extent to which it has been reworked in
post-Archaean time.
The
Proterozoic suturing, with the local preservation of ophiolites and prominent boundaries
between reworked Archaean and juvenile Proterozoic rocks.
The
evidence for subduction-related magmatism and development of Proterozoic fore- and
back-arc basins.
The
analysis of crustal and upper mantle xenoliths.
The
effects of Palaeozoic (Devonian), potentially plume-related magmatism on lithospheric
structure of the Kola-White Sea areas.
The Fennoscandian Shield is a key element in the reconstruction of the
Laurussian mega-continent. EUROPROBE studies will promote integration with Canadian
Lithoprobe geoscience.
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