New palaeomagnetic data for Palaeoproterozoic AMCG complexes of the Ukrainian Shield

Abstract

A palaeomagnetic study of rocks for two Palaeoproterozoic anorthosite-mangerite-charnockite-granite (AMCG) complexes in the Ukrainian Shield was done to put additional constraints on the interpretation of palaeogeography of Fennoscandia and Volgo-Sarmatia in the Palaeoproterozoic. With this study, 5 sites of Korsun-Novomyrhorod and 3 sites of Korosten AMCG complexes in central and north-western parts of the shield, respectively, were chosen for palaeomagnetic sampling given the geological, modern geochronological and previous palaeomagnetic data. Primary remanent magnetization was isolated on samples of anorthosites, Gabbro, and monzonites within a narrow time interval of U-Pb geochronology dataset of 1.76—1.75 Ga. The palaeomagnetic poles calculated for Korosten and Korsun-Novomyrhorod complexes are almost identical, which indicates that the Volyn and Ingul Domains developed within a single structure of the Ukrainian Shield since at least 1.75 Ga. The new palaeomagnetic pole calculated for all 8 sites (Plat=22.7 °N, Plon=167.4 °E, A95=3.3°) agrees well with previous studies by Elming et al. [2001, 2010]. The selection of the most reliable palaeomagnetic poles for Fennoscandia and Volgo-Sarmatia of this time indicates that the present position of the Ukrainian Shield relative to Fennoscandia is not the same as for about 1.75 Ga, when Fennoscandia occupied a subequatorial position within palaeolatitudes of 5—20 °N, and Volgo-Sarmatia was located close to the equator and rotated relative to Fennoscandia counterclockwise by about 40° compared to its present position.

Keywords

• ukrainian shield
• proterozoic
• palaeomagnetism
• amcg complexes
• tectonic reconstruction