Outlines of the Precambrian basement of Estonia

The crystalline basement of Estonia can be subdivided into two major geological units - North Estonian amphibolite and South Estonian granulite complexes. The amphibolite facies terrain consists of a sequence of metavolcanics and -sediments, which resemble those of the island arc sequences in southern Finland. The South Estonian granulites, probably belonging to the Belarus-Baltic Granulitic Belt, show the peak metamorphism conditions of about 800°C and 5-6 kbar. U-Pb isotopic data demonstrate that the Estonian basement has formed during the Palaeoproterozoic, 1.9-1.8 Ga ago and is composed of magmatic, volcanic, and sedimentary components across major structural zones. The granulite metamorphism postdates these ages (1.79-1.73 Ga). The youngest igneous rocks in the basement belong to the Fennoscandian Palaeo-Mesoproterozoic Rapakivi Province and include the composite Riga batholith, as well as at least five minor stock-like porphyritic K-granite plutons (ca. 1.6 Ga).