Deformational structures and stress field of the south-western Crimea in the context of the evolution of Western-Black basin
Journal Title: Геодинаміка - Year 2014, Vol 17, Issue 2
Abstract
The purpose of this paper is to describe and analyze the deformations of the mesolevel (slickensides, fractures, faults) in the rock complexes of different age, to reconstruct the stress fields which corresponds to them. The results of interpretation will be compared with the previous studies as well as with known seismic sections and with earthquake focal mechanisms of Crimean-Caucasian seismogenic zone , analyzing them in the context of tectonic evolution of Western-Blak Sea Basin. To define the tectonic stages, specifying the age of deformation. Methodology. The deformations were studied in two sedimentary complexes of different ages. Cosedimentary fractures and faults were studied in the Lower Cretaceous deposits and deformations in the contact between Upper Jurassic and Lower Cretaceous rocks. The other studied group of deformational objects were investigated in outcrops of Upper Cretaceous - Neogene rock complex. In the processing and interpretation of the slickensides the kinematic method and the program Win Tensor [Devlaux, Sperner, 2003] was used, and the program Stereo 32 by K. Ruller and K.Trepmann was used to build the stereograms. Results of the analysis allow us to define at least two generalized stages in the tectonic evolution of South Western Crimea (SWC). About the extational stages the slickensides of normal type are evidenced by the normal faults which contain the relict slickensides, tectonic breccias and traces of attached marine organisms. The strike azimuth of the slickensides is 250°-320°. The corresponding stress fields are characterized by N-S, NE-SW and NW-SE orientation of the extensional axis. According to new stratigraphy dating and structural analysis it is possible to conclude that the period of normal faulting started at least in valanginian-barremian, which is connected to the opening of Western Black Sea Basin during Early Cretaceous [Hippolit et al., 2014, Sheremet et al. 2014]. Reinterpretation of the seismic profile DSS 25 which crosses western part of the Black-Sea in the submeridional direction, shows the latitudinal normal fault of high amplitude along the margin of the continental shelf slope, which could be used during the rifting stage of the opening of the Western Black Sea Basin [Yegorova et al.,2010; Baranova et al., 2008]. This fault is located on the western marine prolongation of the series of normal faults of Early Cretaceous, which were defined in SWC, and it could be of the same age. The compressional stage is fixed in the Upper Cretaceous - Neogene rocks with strike-slip and thrusted structures, which are related with the compression during Paleocene-Early Miocene. The stress-field which corresponds to those structures is characterized by several orientation of the axis of compression. In the western part of the study area the SW-NE compression is prevails, but for the Central and Eastern part there are N-S and SE-NW compression. In the some outcrops of the Upper Jurassic-Lower Cretaceous sedimentary complex the strike-slip and reverse faults are observed. The recovered stress field shows N-S and NW-SE orientation of the axis of compression. Respectively, some compressional deformation studied previously in the Tavrik Unit, Middle Jurassic and Lower Cretaceous could be reactivated in the period of Cenozoic compression. Cenozoic compression stages are clearly distinguished in the CDP seismic sections, fixing thrusts and folds at the thrust faults. Our data shows also the compression during Miocene, but those deformations are not commensurate with those during Paleocene-Early Eocene and Late Eocene-Oligocene. The resent compression of latitudinal and meridional trending was defined on the base of 26 earthquake focal mechanisms. At the same time, seven mechanisns pointed out to extension (the same results we obtained from the analysis of young normal faults). According to the results of recovering of the stress axis it is possible to conclude that the compression deformation appeared because of the pressure of Black Sea plate to the Crimea but recent normal faults are connected to the continue of the dippening of Black Sea Basin and with the denudation of Crimea Mountains. Originality. Deformation of mesolevel in the Upper Cretaceous-Neogene rocks are described for the first time. Obtained for them the compression field evidences of the manifestation of Cenozoic deformation in the study area. The normal type tectonic slickensides for the first time considered in the context of the opening of the Western Black Sea basin. Age frames for stages of deformation of rock complexes of SWC are specified. Practical significance. The information about stress-strain condition of WSC is very important for the prediction of the negative exo- and endogenous geological processes: the seismic activity, landslides and other dangerous events. Clarifying of the geodynamic model is necessary for further seismic predictability, engineering geological investigations and preparation of various types of cartographic documents.
Authors and Affiliations
A. Murovskaya, J. -C. Ippolite, Ye. Sheremet, T. Yegorova
Keywords
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