Geochemistry and 40Ar/39Ar age of Early Carboniferous dolerite sills in the southern Baltic Sea

The Early Carboniferous magmatic event in the southern Baltic Sea is manifested by dolerite intrusions. The presumable area in which the dolerite intrusions occur ranges from 30 to 60 km in east-west direction, and is about 100 km in north-south direction. The dolerites were sampled in well D1-1 and investigated by applying chemical analysis and 40Ar/39Ar step-heating dating. Dolerites are classified as alkali and sodic, characterized by high TiO2 (3.92, 3.99 wt%) and P2O5 (1.67, 1.77 wt%) and low MgO (4.89, 4.91 wt%) concentrations, enriched in light rare earth elements, originated from an enriched mantle magma source and emplaced in a continental rift tectonic setting. The 351 +/- 11 Ma 40Ar/39Ar plateau age for groundmass plagioclase indicates a considerable age gap with the 310-250 Ma magmatism in southern Scandinavia and northern Germany. The magmatic rocks in the Baltic Sedimentary Basin are coeval with alkaline intrusions of NE Poland. Both magmatic provinces lie in the northwestward prolongation of the Pripyat-Dnieper-Donetsk Rift (370-359 Ma) and may constitute a later phase of magmatic activity of this propagating rift system.