Statistical features and analysis of tectonic jointing from cretaceous-neogene deposits of the Ukrainian Carpathians
Journal Title: Геодинаміка - Year 2014, Vol 17, Issue 2
Abstract
Purpose. Statistical features and the distribution of the data orientation over 8 000 tectonic joints from flysch and molasses deposits of Skyba and Boryslav-Pokuttya nappes with some statistical parameters (K, C) are demonstrated. The main system of joints and the ratio of dip angles are analyzed. Relationship between statistical features of joints, the age of rocks, the tectonic position and the geological history of the Ukrainian Carpathians are defined. Methodology. The statistical parameters for the data of the tectonic joints orientation were calculate with use the eigenvalue ratio method N. Woodcock. Results. Two statistical parameters for tectonic joints are determined in the areas of the Skyba and Boryslav-Pokuttya nappes: C (strength parameter), which indicates the degree of grouping of joints orientations data around the direction, and K (shape parameter), which shows the shape of the distribution of joints orientations data on the stereogram – cluster or girdle distributions. Analyzed joints orientation data (strike, dip direction and dip angle) from more than 150 points of observation in the streams and valleys of Rybnyk and Opir rivers (basin of Stryy River), Sukil River, Bystrytsya Nadvirnianska River, Prut River, and from outcrops near the settlements of Bolekhiv, Dolyna, Nadvirna. Rose-diagrams, histograms of dip angle, stereograms of poles in isolines of joints orientations data, Woodcock diagrams were built with software Stereo 32 (K. Röller, C. Trepmann) and Fabric 8.0 (E. Wallbrecher). Originality. The major systems, the ratio of perpendicular (to the stratum) and oblique joints of flysch and molasses deposits, the strength parameter and shape parameter characterize tectonic regimes of Skyba and Boryslav-Pokuttya nappes. Younger joints have mainly girdle distribution (0 К 1), but older ones have girdle and cluster distributions (0 К ∞). All measured tectonic joints are formed six major systems. For the first time the correlation between age, lithological features of rocks, statistical and quantitative parameters of joins in different tectonic units (the nappe, thrusts) and the change of stress and strain state during geological history of the formation of the Ukrainian Carpathians have been determined. Low degree and the girdle distribution of joints indicate the uninterrupted process of different parageneses joints formation in deposits during the end of Upper Cretaceous to Cenozoic. Practical significance. Low values of the statistical parameters of joints (C, K) indicate a complex stress and strain state of the study area and confirm the changes of stress fields, the rotation axis of maximum compression and tension (σ1, σ3), determined by the tectonophysical research, during the fold-thrust process in the Ukrainian Carpathians. The results obtained by the eigenvalue ratio method can be used in the reconstruction of stress fields with structural-paragenetic method as a way to control for the dividing the even-aged group parageneses of the tectonic joints that formed in the homogeneous deformation regime.
Authors and Affiliations
Y. M. Vikhot
Keywords
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