Analiza struktralna brachyantykliny Dobromierza (południowo-zachodnie obrzeżenie Gór Świętokrzyskich)

Abstract

STRUCTURAL ANALYSIS OF THE DOBROMIERZ BRACHYANTICLINE (SOUTH-WESTERN MARGIN OF THE MTS)SummaryThe paper presents structural analysis of Dobromierz brachyanticline (Fig. 1) from the south-western margin of the Świętokrzyskie Mts. The analysis covers faults and mesoscopic structures such as slickensides and jointing.The Dobromierz brachyanticline is cut by a large oblique-slip (sinistral and reversed) fault which resulted in wedging up of the upper links of the strata forming the brachyanticline in its core (Figs. 3–5). Bisides, another reversed fault with steeply inclined plane occurs at greater depths beneath the brachyanticline. The slip connected with the latter resulted in asymetry of the brachyanticline, as its SW limb gained the character of flexure.Three groups of small-scale faults: second-order, periclinal and radial faults (Fig. 1), are differentiated in the area of the brachyanticline. The analysis of slickensides and slickenside striae (Figs. 6–8) has shown that they primarily represent diagonal-slip displacements. Regularities in distribution of slickenside striae on variously oriented slickenside surfaces (Figs. 7–8) allow to assume that the striae resulted from displacements along earlier developed discontinuities.Geometrical interrelations between the structures presented in Fig. 9 indicate that the Dobromierz brachyanticline, the displacement along the fault cutting the brachyanticline, and the second-order faults originated in the same stress pattern, i.e., under the conditions of horizontal compression (see D. G. Bishop, 1968). The diagonal-slip character of the master fault indicates that orientation of the plane of that fault was determined by the existence of similarly inclined and oriented dislocation in the substratum. The set of second-order faults and slickenside structures originated simultaneously with the movement proceeding along the master fault and utilizing all the existing discontinuities suitably oriented for the maximum effect of shearing stresses.The final stage in the tectonic development of this area is connected with gradual vertical uplift of the whole region and interception of the role of the maximum principal stress by the gravity. Normal (periclinal and radial) faults  founded along with the brachyanticline, may have originated in those times.