New palaeomagnetic, age and geochemical data from basic dykes of the Ukrainian shield and the timing of accretion of Fennoscandia to the Ukrainian shield

• The east European craton (EEC) can be divided into three crustal segments, Sarmatia, Volgo-Uralia and Fennoscandia (Bogdanova, 1993). Lithological and age differences suggest that these segments have autonomous geological histories and various hypotheses have been presented for the time of formation of the EEC. Here we test a hypothesis of the Fennoscandian Shield being accreted to the Ukrainian Shield, which is a part of Sarmatia, for ca 1.8 Ga ago (Elming et al., 2001).This we do by palaeomagnetic, geochronological and geochemical studies of Palaeoproterozoic basic dykes in the Ukrainian Shield. We present palaeomagnetic results from 15 dykes and geochemical data from nine of them. The palaeomagnetic and geochemical data indicate at least three different generations of dykes and Ar39-Ar40 and U-Pb (zircon) age determinations have been done on dykes from two of these dyke generations.The calculated palaeomagnetic poles, some of the defined as key poles, are combined with poles calculated from anorthosites, gabbros and sedimentary rocks to form a ca 2.2 to 1.7 Ga sequence of apparent polar wander (APW) for the Ukrainian Shield. The tectonic reconstructions based on these palaeomagnetic data support the hypothesis that the Ukrainian Shield accreted to the Fennoscandian Shield at ca 1.8 Ga, however it later rotated into its present position relative Fennoscandia. This tectonic scenario is discussed with reference to geological data.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geofysik (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geophysics (hsv//eng)

Nyckelord

Tillämpad geofysik

Applied Geophysics

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