Wiek izotopowy K-Ar, skał podłoża krystalicznego północno-wschodniej Polski

Abstract

Wiek izotopowy K-Ar, skał podłoża krystalicznego północno-wschodniej PolskiK-Ar AGE OF THE ROCKS OF THE CRYSTALLINE BASEMENT OF NORTH-EAST POLANDSummaryThe crystalline basement of north-east Poland is a part of the lower stage of the Precambrian East European platform. Three stratigraphic-structural complexes are distinguished in the basement: the Pre-Svecofennokarelian, the Svecofennokarelian, and the Gothian complex. Repeated igneous metamorphic processes account for the fact that only the final phase of the basement evolution can be dated by K-Ar methods. The scheme of the metamorphic-igneous events is as follows (Fig. 1).1. So far the individual ages (1 600-2 000 m.y.) of some Podlasie complex rocks are the only values that correspond to the Svecofennokarelian cycle.2. The ages of the majority of the Podlasie complex rocks fall between 1 340 and 1 560 m.y. with two well-pronounced maximums at 1 386 ± 37 and 1 542 ± 40 m.y. (Figs. 2, 3). These data point to a rejuvenation due to the Gothian regional metamorphism.3. The Gothian cycle was terminated by anorogenic intrusions of the rapakivi-type granitoids (1 972 ± 38 m.y.) of the Suwałki massif rocks (1 391 m.y.) and possibly by the Kętrzyn intrusion (Figs. 5, 6).4. The Pre-Svecofennokarelian oval-shaped granitoid massifs (the Mazovia, Dobrzyń and the Pomerania massifs) were rejuvenated due to granitization (1 350 ± 37 m.y.) lifted up to the shallower parts of the Earth's crust and subsequently cut by younger granitoid veins (about 1 340 m.y.).5. The south-westernmost part of the area examined with the Kampinos complex was rejuvenated due to the Dalsland metamorphism (1 230 m.y.; Fig. 4).6. During the Late Palaeozoic (about 300 m.y.) the basic and alkaline intrusions (Ełk, Pisz, Tajno and others) intruded the deep fractures of the rigid basement.