Rozwój tektoniczny obszaru miedzionośnego Monokliny Przedsudeckiej

Wojciech Salski


Tectonic development of the copper-bearing area of the Fore-Sudetic Monocline

The subject of tectonic studies was the area situated in the southwestern part of the Fore-Sudetic Monocline in the vicinity of Lubin and Polkowice (figs 1 & 4). Rotliegendes, Zechstein and Buntsandstein rocks participate in its structure. Rotliegendes is representated mainly by fine- grained sandstones. Zechstein starts with sandy deposits of Weisliegendes and copper-bearing shales; it is overlain by dolomites and limestones, anhydrytes and clayey shales. Buntsandstein consists of sandstones with clayey shale intercalations. Those deposits spread out in the direction NE—SE and dip monoolinallly towards N—E, a t an angle of 2—6°. The rock series, mentioned above, are overlain discordantly by the Tertiary and Quaternary. The sedimentary complex of the Fore-Sudetic Monocline adjoins from S—W the Fore-Sudetic Block, composed of crystalline rocks (fig. 1), mainly of the Ptroterozoic age. In the neighbourhood of the Block there are a number of faults, whose throws are from several dozen do over 100 metres, oriented NW—SE. They constitute the dislocation system of the middle part of the Odra River (Oberc , 1967 b). On the grounds of numerous drillings done in the vicinity of Lubin and Polkowice, there have been also ascertained faults running SW—-NE, W1—E and N—S (Tomaszewski, 1963; Preidl, 1967). They all fade out in the top of Buntsandstein and do not affect the continuity of Tertiary beds. The tectonic model, revealed by means of bore-holes, pointed to a simple, block structure of the Permian-Mesozoic complex. The development of mining industry in that region has greatly increased the possibilities of tectonic surveying. In the base of Zechstein deposits there have been found indications of meso tectonic intraformational deformations, commonly represented by small structural forms. They are, above all, drag folds whose axes are oriented NW—SE and, subordinately, W—E. Two generations of fault striae and slickenslides surfaces, running SW—NE and S—N (fig. 2), correspond to them geometrically and genetically. There also occur frequent small thrusts, tectonic wedges, small synclines and anticlines and detached sandstone blocks among shales and dolomites. Longer axes of those forms are oriented NW—SE. Truncations and displacements of the surface of joints, faults and mineral veins are due to intraformational movements. Within Zechstein and Buntsandstein deposits there have been found brachysynclinal and brachyanticlinal forms, whose inclination of limbs is up to several degrees. Axes of most of them extend NW—SE. Local deviations of the strike of beds and the direction of dip within the monocline are connected with the formation of those structures. Apart from the morphological differentiation of intraformational deformations, the geological structure of the Permian-Mesozoic complex was mostly the result of faulting tectonics. The prevailing dislocations are those running NW—SE and W—E, as well as faults of the strike-slip type. The main characteristics of the first group of dislocations are: variable spatial orientation (from NNW—SSE to WNW—ESE), great differentiation of amount of throws and their horizontal extent, concentration in particular zones, and predominance of displacements of the gravitational type. It is characteristic of parallel faults that they have considerable throws and are reversed. Faults oriented NW—SE fade out on them or are slipped (fig. 4). Strike-slip faults are a frequent phenomenon, especially in Zechstein limestone-dolomite rocks. They are characterized by diversified orientation; the prevailing direction is, however, that of SW—NE or SSW—NNE. In Permian and Triassic deposits joints constitute two conjugated systems (S1 and S2, and P1 and P2), as well as a single set of joints D (fig. 5). The above arrangement underwent locally advances modifica tions, as far as the number of directions and the percentage of joints in them are concerned. Morphology of the surfaces of joints, their spatial extent and frequency of occurrence are very diversified. Analogously to the faults, the whole system of joints had been undergoing reorientation. A considerable differentiation of orientation of individual tectonic forms, rebuilding a part of them, as well as regional conditions point to a poly phases structural development of the copper-bearing area (Milewicz 1973 a, Oberc 1967 a, Salski 1975 a, Sokołowski 1967). The Laramide phase was the strongest one within the Fore-Sudetic Monocline, which resulted in its final formation. That phase, most probably, is responsible of formation of brachysynclines and brachyanticlines, mesotectonic intraformational deformations and strike-slip faults. All tectonic forms that had been undergoing repeated deformations are older and were formed in the Kimmeridgian phase. The present state of geological investigations enable us to distinguish several stages in the development of the area under discussion: 1. Formation of faults, running NW—SE, and joints representing the direction S1, S2, and D, a t the time of the Kimmeridgian movements. 2. Cicatrization of fractures in the Permian and Buntsandstein rocks by gypsum, barite and calcite and, in the ore-bearing horizon — by copper sulphides. 3. Formation of dislocation zones of the parallel course and the conjugated system of joints Pi and P2 at the beginning of the Laramide phase. Development of intraformational displacements oriented S—N, and strike-slip faults. 4. Formation of brachysynclines and brachyanticlines, mesotectonicintraformational deformations and strike-slip faults oriented SW—SE, at the time of full intensification of the Laramide phase. 5. Formation of younger system of faults, oriented NW—SE, and further development of fissures a t the closing phase of the Laramide revolution. The tectonic model of copper-bearing area presented above differs from the hitherto existing views of the structure of the Monocline. Its most essential characteristics are: the presence of two fault directions: NW—SE and W—E, occurrence of brachysynclines and brachyanticlines, mesotectonic intraformational deformations and strike-slip faults. The model has not confirmed, however, the existence of dislocation zone of the course SW—NE or SSW—NNE (Krasoń, Sokołowski 1966, 1967, Wyżykowski 1963). Such an arrangement changes essentially the distribution of tectonic blocks (fig. 6).

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