Aktualny stan badań utworów prekambryjskich w Polsce i kierunki ich rozwoju

Wacław Ryka, Leszek Sawicki

Abstract


 Skały prekambryjskie tworzą podłoże całego kraju, lecz zostały szczególniej wyróżnione i zbadane w trzech regionach: na prekambryjskiej platformie wschodnioeuropejskiej i w Karpatach, gdzie tworzą fundament krystaliczny ukryty pod skałami pięter osadowych, oraz na Dolnym Śląsku, gdzie są włączone w system fałdów waryscyjskich, wypiętrzone i odsłonięte. Skały prekambryjskie różnią się nie tylko położeniem, ale także budową tektoniczną i strukturalną, metamorfizmem regionalnym, wiekiem i stylem przebudowy. Odmiennie kształtowały się dzieje ich badań i niejednolity jest stopień rozpoznania.

 

THE PRESENT STATE AND DIRECTIONS OF STUDIES ON THE PRECAMBRIAN ROCKS OF POLAND

 

Although the whole basement of Poland is built of Precambrian rocks, these rocks were recorded and recognized in three regions only. They form crystalline basement overlain by rocks of sedimentary stages in the Precambrian Platform and the Carpathians, being incorporated in the Variscan fold system, uplifted and exposed in the Lower Silesia. Precambrian rocks of these three regions differ in location as well as in tectonic and structural units, regional metamorphism, age and style of reactivation. The history of studies of these rocks is also different, similarly as the degree of knowledge. In Poland, these rocks built crystalline basement on which rocks of Paleozoic and Meso-Cenozoic sedimentary stages were originating and undergoing structural rebuilding. The development of the latter was determined by movements of crystalline basement blocks, responsible for regional and tectonic differentiation of the sedimentary covers.

The studies of crystalline basement of the East-European Platform were initiated in 1954 by making three drillings preceded by geophysical surveys. In the next years, there took place intense development in there studies, determined by search for metal ore deposits and bitumens in the sedimentary cover of the Platform.

The geological studies on the crystalline basement are concentrated in the Geological Institute which makes possible appropriate planning of the works and synchronization of geophysical, drilling and mapping programs. On the basis of results of petrographic, mineralogical, geochemical, geochronological and deposit studies of core material from almost 200 boreholes, and rich geophysical data (including those from magnetic and gravimetric semi-detailed and detailed mapping), it was possible to prepare petrological map of the top of crystalline basement in the scale 1:500 000 and, subsequently, the map in the scale 1:200 000 in 34 sheets. The tectonic model and stratigraphic scheme of rocks of the crystalline basement were also prepared. The studies have been crowned with discovery of vanadium-bearing titanomagnetite deposit in anorthosites in the Suwałki area and demonstration of its resources. Moreover, chemogenic hematite taconites were found at Łochów near Warsaw at 2400 m depth, and concentrations of rare earth elements – in nepheline syenites and carbonatites in the areas of Ełk and Tajno.

The history of studies on the Precambrian basement of the Carpathians and southern Poland began when crystalline rocks were found by a drilling at Rzeszotary in 1909. However, at that time it was not certain whether the drilling entered an exotic or autochtoneous crystalline massif. This question has not been solved before the end of the sixties, when deep drillings penetrated the Carpathian Flysch and entered crystalline basement. The knowledge of crystalline basement in this part of Poland is unsatisfactory as petrological maps, tectonic model and stratigraphic scheme are still missing. The available data show that the basement is strongly eroded ill the west, where the Carpathian Flysch rests on amphibolites fades metamorphic rocks, whereas in the east the Flysch rests on strongly diagenesed or weakly metamorphic rocks of the uppermost Precambrian.

After the world war II, the Geological Institute began studies on crystalline rocks of the Lower Silesia, with detailed geological mapping of areas for which maps were still missing. Up to the present, 100 sheets of geological map in the scale 1: 25000 are completed and the remaining ones are in preparation.

To carry out programs of stratigraphic, lithological, petrographic and tectonic studies and search for deposits, there has been called into existence the Lower Silesian Branch of the Geological Institute in Wrocław.

Along with time, the Lower Silesian Branch of the Geological Institute started introducing modern research techniques, as e.g. mesoscopic analysis in studies on tectonics, petrotectonic studies, geochemical analysis, analysis of radiogenic age, physical studies of rocks, geophysical studies, and biostratigraphic studies of “silent rock series”. The developments in the studies were accompanied by widening their range by deep drillings, especially in the forefield of the Sudety Mts. The results of these studies markedly changed views on stratigraphy, lithological development and metamophic alterations of the Precambrian.


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