| Summary: | The East European Craton in western Fennoscandia was mostly formed by the accretion of distinct terranes at c. 1.8 Ga. TTG magmatic rocks in the age range 1.86-1.84 Ga are abundant in the crystalline crust of S, central and NW Lithuania. In the south, TTG rocks compose the large Randamonys massif. A Zm347 tonalite yielded an 1859±5Ma concordia age, while a Vr268 diorite was dated at 1848±6 Ma. A strongly deformed 7Gr granitic rock in adjacent NW Belarus gave a similar 1844±8 Ma igneous age. In central Lithuania, the Glv99 igneous mafic granulites display magmatic 1839±15 Ma and metamorphic 1809±9 Ma ages. The nearby Grz105 gneissic granite was intruded at c. 1837±6 Ma, while the Kz65 granite further north was emplaced at 1844±5 Ma [1]. The area to the south and west of the above described rocks in Lithuania and in N Poland is dominated by younger c. 1.83-1.79 Ga magmatic rocks. The fragments of a c. 1.83-1.82 Ga volcanic island arc in Sweden [2], N Poland and Lithuania [3] compose a considerable part of this younger domain. The distribution of 1.86-1.84 Ga magmatic arc-related rocks in Lithuania likely delineates fragments of a convergent continental margin. It continues northwestwards across the Baltic Sea into south-central Sweden, and southwards to N Poland and NW Belarus.
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