EVIDENCE OF ARC-RELATED SVECOFENNIAN MAGMATIC ACTIVITY IN THE SOUTHWESTERN MARGIN OF THE EAST EUROPEAN CRATON IN POLAND

Abstract

The Precambrian basement of northeastern Poland forms the western part of the present-day East European Craton. The central part of this area, with moderately uniform potential fields of variably oriented magnetic and gravity anomalies, has been penetrated by a six boreholes, samples from which consist of calc-alkaline granodiorite orthogneiss (Okuniew 1), calc-alkaline monzonite (Rajsk 1 and 2), and calc-alkaline orthoamphibolite (Lomza 1, 2 and 3). Geochemical features of the most drilled rocks — particularly depletion in Th–U, Nb, P and Ti relative to primitive mantle and position on trace element discrimination diagrams (Y vs. Nb, Y + Nb vs. Rb, Hf–Rb–Ta and La–Y–Nb) — are consistent with a volcanic arc environment. The results of U–Pb age measurements show that arc-related magmatic activity took place between 1.82 and 1.80 Ga. These data may be compared to analytical results from the Transcandinavian Igneous Belt in the southwestern part of the East European Craton, where continental crust was formed in several arc systems mainly between 1.91 and 1.86 Ga. Overall, the data suggest a general decrease in the age of the intrusive rocks towards the south–southwest of the East European Craton.