dTwenty-three new 40Ar/39Ar amphibole age determinations have been carried out to date major crustal boundaries in the sediment-covered crystalline basement of the western part of the East European Craton, in the area between the Baltic (Fennoscandian) and the Ukrainian Shields. That crystalline basement is characterised by a pronounced alternation of granulite-and amphibolite -facies rock belts identified from geophysical surveys and deep drill core samples. These belts strike NNE to NW and are considered to represent accretionary stacking of different Palaeoproterozoic (2.0-1.85 Ga) terranes of juvenile crust along the margins of the Archaean protocontinents of Fennoscandia, Sarmatia and Volgo-Uralia, which make up the cores of the EEC. Amphiboles were selected from drill core samples taken from (1) rocks in the internal parts of the granulite- and amphibolite-facies belts, (2) amphibolite-facies mylonites along the boundaries between the belts and along fault zones within the belts, and (3) metamorphosed mafic/intermediate dykes and mylonites along E-W-trending zones of ductile faulting superimposed upon the older beltiform structures. The oldest 40Ar/39Ar ages (1778-1740 Ma) are recorded by granulites of the Belarus-Baltic Granulite Belt, and are interpreted to date the time of cooling after peak metamorphism around 1800 Ma. Rocks from mylonites of the second group yielded 40Ar/39Ar ages in the range of 1710-1660 Ma, regardless of the previous histories of the hosting rock belts. 40Ar/39Ar ages of 1550-1450 Ma, in contrast, are obtained from the rocks of the third group. The first two of the dated events were associated with compressional tectonics during accretion and collision of the Palaeoproterozoic terranes against the Archaean nuclei of the East European Craton. The third event is closely related to anorogenic anorthosite-rapakivi granite magmatism controlled by a set of E-W-trending shear zones. (C) 2001 Elsevier Science B.V. All fights reserved. dTwenty-three new 40Ar/39Ar amphibole age determinations have been carried out to date major crustal boundaries in the sediment-covered crystalline basement of the western part of the East European Craton, in the area between the Baltic (Fennoscandian) and the Ukrainian Shields. That crystalline basement is characterised by a pronounced alternation of granulite-and amphibolite -facies rock belts identified from geophysical surveys and deep drill core samples. These belts strike NNE to NW and are considered to represent accretionary stacking of different Palaeoproterozoic (2.0-1.85 Ga) terranes of juvenile crust along the margins of the Archaean protocontinents of Fennoscandia, Sarmatia and Volgo-Uralia, which make up the cores of the EEC. Amphiboles were selected from drill core samples taken from (1) rocks in the internal parts of the granulite- and amphibolite-facies belts, (2) amphibolite-facies mylonites along the boundaries between the belts and along fault zones within the belts, and (3) metamorphosed mafic/intermediate dykes and mylonites along E-W-trending zones of ductile faulting superimposed upon the older beltiform structures. The oldest 40Ar/39Ar ages (1778-1740 Ma) are recorded by granulites of the Belarus-Baltic Granulite Belt, and are interpreted to date the time of cooling after peak metamorphism around 1800 Ma. Rocks from mylonites of the second group yielded 40Ar/39Ar ages in the range of 1710-1660 Ma, regardless of the previous histories of the hosting rock belts. 40Ar/39Ar ages of 1550-1450 Ma, in contrast, are obtained from the rocks of the third group. The first two of the dated events were associated with compressional tectonics during accretion and collision of the Palaeoproterozoic terranes against the Archaean nuclei of the East European Craton. The third event is closely related to anorogenic anorthosite-rapakivi granite magmatism controlled by a set of E-W-trending shear zones. (C) 2001 Elsevier Science B.V. All fights reserved. dTwenty-three new 40Ar/39Ar amphibole age determinations have been carried out to date major crustal boundaries in the sediment-covered crystalline basement of the western part of the East European Craton, in the area between the Baltic (Fennoscandian) and the Ukrainian Shields. That crystalline basement is characterised by a pronounced alternation of granulite-and amphibolite -facies rock belts identified from geophysical surveys and deep drill core samples. These belts strike NNE to NW and are considered to represent accretionary stacking of different Palaeoproterozoic (2.0-1.85 Ga) terranes of juvenile crust along the margins of the Archaean protocontinents of Fennoscandia, Sarmatia and Volgo-Uralia, which make up the cores of the EEC. Amphiboles were selected from drill core samples taken from (1) rocks in the internal parts of the granulite- and amphibolite-facies belts, (2) amphibolite-facies mylonites along the boundaries between the belts and along fault zones within the belts, and (3) metamorphosed mafic/intermediate dykes and mylonites along E-W-trending zones of ductile faulting superimposed upon the older beltiform structures. The oldest 40Ar/39Ar ages (1778-1740 Ma) are recorded by granulites of the Belarus-Baltic Granulite Belt, and are interpreted to date the time of cooling after peak metamorphism around 1800 Ma. Rocks from mylonites of the second group yielded 40Ar/39Ar ages in the range of 1710-1660 Ma, regardless of the previous histories of the hosting rock belts. 40Ar/39Ar ages of 1550-1450 Ma, in contrast, are obtained from the rocks of the third group. The first two of the dated events were associated with compressional tectonics during accretion and collision of the Palaeoproterozoic terranes against the Archaean nuclei of the East European Craton. The third event is closely related to anorogenic anorthosite-rapakivi granite magmatism controlled by a set of E-W-trending shear zones. (C) 2001 Elsevier Science B.V. All fights reserved.
