Proterozoik i dolny paleozoik Polski południowo-zachodniej

Abstract

W skład waryscyjskiego (hercyńskiego) podłoża Polski południowo-zachodniej wchodzą m.in. utwory późnoproterozoiczne i wczesnopaleozoiczne. Analiza najnowszych materiałów geologicznych, w tym datowań izotopowych i paleontologicznych, prowadzi do następujących wniosków: 1. Najstarszy kompleks skalny - gnejsy bloku Gór Sowich – został skonsolidowany prawdopodobnie w wyniku orogenezy dalslandzkiej (grenwilskiej). 2. Kompleksy, którym przypisuje się wiek wendyjsko-dolnokambryjski, uległy sfałdowaniu w środkowym lub górnym kambrze i w dolnym ordowiku. 3. Oba fałdowania przedzielone były intruzjami granitoidów datowanych radiometrycznie na górny kambr i dolny ordowik. Intruzje granitoidów oraz skały ich osłony odsłonięte są dziś w różnych poziomach ścięcia erozyjnego - w poziomach najgłębszych na wschodzie w obrębie kopuły kłodzko-orlickiej i w poziomie najpłytszym w zachodniej części bloku przedsudeckiego.THE PROTEROZOIC AND LOWER PALEOZOIC OF SOUTH-WESTERN POLAND The platform of south-western Poland represents a marginal, north-eastern fragment of the Bohemian Massif. and its Variscan (Hercynian) basement -eastern section of the Saxo-Thuringian Zone. The basement comprises various strata, including Upper Proterozoic and Lower Paleozoic rocks. Conclusions drawn from a review of the published data, including radiometric and paleontological datings of Upper Proterozoic and Lower Paleozoic series, are as follows: 1. The rock complex defined as the oldest. comprises gneisses of the Sowie Góry block. formed of a mudstone-graywacke series and yielding Upper Proterozoic microfossils (mainly Acritarcha). The earliest stage of deformations and regional metamorphism may be related to the Dalslandian (Grenville) orogeny. 2. Younger rock series, paleontologically dated at the Vendian and Lower (or Middle) Cambrian, occur in the Kłodzko - Góry Orlickie Mts dome, Karkonosze lzera block, Góry Kaczawskie Mts region, and Fore-Sudetic Block. In the two latter units they are represented by diabase-keratophyre series and accompanying greenstones and phyllites (Fig. 1). \3. Limestones (so-called Wojcieszów Limestones), interfingering with the diabase-keratophyre series, are dated at the Middle Cambrian on the basis of the record of Cambrotrypa sudetica Gunia. However, this unique fossil may be also of the Lower Cambrian age. 4. The above rocks and accompanying phyllites and sericite-quartz schists gradually pass north-westwards into higher lithostratigraphic members of the Lusation Graywacke Formation, so called Kamenz Beds. 5. The above mentioned (points 2 - 4) metamorphic strata of sedimentary and volcanic origin probably became folded in Middle and Late Cambrian and Early Ordovician times. Foldings has taken place in two phases. separated by time of origin of granitoid intrusions (for which radiometric datings are available). 6. The above rock complexes and series have been subjected to metamorphism varying from deep subfacies of the amphibolite facies in eastern part of the studied area to the greenstone fades in the western part.7. Data which would make possible dating of ultramafic (serpentinitcs) rocks and basic ones (gabbros) are still missing. The Author is inclined to interpret the rocks as related to the Upper Proterozoic -Lower Cambrian diabase-keralophyre series. This point of view seems supported by records of picrites among diabases, greenstones, and keratophyres found by drillings in area of the Fore-Sudetic Block, west of Wrocław. 8. In area of the Bohemian Massif, the lowermost Paleozoic rocks resting on the Upper Proterozoic are represented by continental conglomerates and sandstones of the Žitec-Hluboš Formation. The rocks are assigned to the Lower Cambrian but this dating is not supported by any record of marine fauna. Undoubtful Middle Cambrian trilobite fauna is known from the overlaying Jince Formation. The Late Cambrian was the time of intense volcanic activity, interpreted as subsequent acid subaerial volcanism. This agrees with the below given (point 9) information on the age of the granitoid intrusions. 9. Radiometric data show that granitoid intrusions originated in Late Cambrian - Early Ordovician times. The intrusions became subjected to strong stresses and recrystallization in the Ordovician and thereafter. 10. Striking similarities in age and evolution of rocks of the Kłocko -Góry Orlickie Mts dome. Karkonosze-Izera Block, and Fore·Sudetic area indicate that these areas represent fragments of a single structure built of supracrustal complexes folded and subjected to regional metamorphism already before the Late Cambrian. Granitoid intrusions, exposed nowadays similarly as the whole structure at various levels of erosional truncation (Fig. 2), represent important components of the structure. 11. Tectonic movements younger than the Sardic (Grampian, AItai, Salairian) are responsible for juxtaposition of strata differing in degree of metamorphism and (in the case of Palaeozoic ones) fades development, in the present structure of the Sudety Mts. These questions will be discussed in a separate paper, dealing with development and differentiation of Paleozoic rocks of south-western Poland.