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12EARTH SCIENCES
TECTONIC INVERSION OF THE DNIEPER-DONETS BASIN
Bartashchuk O.
Karazin Name Kharkiv National University, Assistant professor of the Department of Mineralogy, Petrography, and Minerals
ABSTRACT
The structural deformations of the sedimentary cover of the Dnieper-Donets basin (DDB) of the stages of platform tectonic activation in the zone of its articulation with the Donets Foldbelt (DF) were studied. Based on the structural analysis of the geocarting materials of the territory of the Western Donets Graben (WDG), using field definitions of the directions of tectonic movements along the faults, structural patterns of different age tec-tonites were analyzed. It was found that folded deformations in three structural floors identified in the sedimentary cover (Hercinian, Laramian, and Attic) were controlled by overthrusts and reverse faults of the north, northwest, and southeast azimuths with a significant component of horizontal displacements along them. A feature of inverse tectonics is the formation of dynamically conjugated lattices of thrusts of the Late Hercynian and Alpine (Laramian and Attic phases) stages of orogenesis, which control layered cover-thrust dislocations and linear, coulisse jointed uplift-folding
The set of identified deformation structures is considered as part of the regional system of tectonic thrust of repeatedly deployed, crushed into geomass folds of sedimentary rocks from the southeast, from the DF, to the northwest - into the weakly deployed syneclise cover of the basin. The main structural element of the cover-folded system, which determines the inverse tectonic style, is the wedge-shaped tectonic segment of the geomass wedging. Its northeastern flank is formed by zones of open Paleozoic structures - Torsko-Drobishivskaya, North-Donetsk, Matrossko-Toshkovskaya, south-west - by echelons of scaly folded covers controlled by lattices of Hercynian and Alpine thrusts. The axis of the segment is formed by Petrovsko-Novotroitska, Komyshuvakhska, Dru-zhkivsko-Kostyantinovska and Main uplift-anticlines.
Based on the identification of the tectonic style of inversion deformations, it was established that the rifto-genic structure of the WDG was completely destroyed by collision deformations with the formation of the West Donetsk Cover-Folded Tectonic Region. According to the style and intensity of deformations, in its northern part, the Lugansko-Komyshuvakhsky Area is distinguished by coulisse jointed uplift-folding, and in the south by the Kalmius-Toretsky Area of scaly thrust covers.
Keywords: tectonite lattice, thrust cover, uplift-folding, West-Donetsk Cover-Folding Region.
Formulation of the problem. The crust of the Sarmatian plate of the East European Platform has experienced repeated stresses and deformations due to collision interaction with adjacent folded belts and active tectonic plates [1, 2]. It is known that the geody-namic regime of the inversion stages of the evolution of the sedimentary basin of the in-plate paleorift geo structure of the DDB was determined by the external counter stress pressure of submeridional directions [3, 4]. At the same time, each of the activation stages ended with the formation of its own plan of inversion deformations; therefore, modern tectonics of the depression are the result of previous inversion stages of the evolution of the riftogenic structure [5]. Based on this, the study of the structural consequences of tectonic inversion with the aim of understanding the natural mechanisms of the structural-kinematic evolution of the earth's crust is relevant for regional geotectonics.
Analysis of recent research and publications. Important for the knowledge of the mechanisms of inversion tectonics are materials of geo-mapping of the transition zone between the DDB and the DF using instrumental measurements of the vergence of tectonites [6].
According to the geomapping data, three stratigraphic floors were detected in the sedimentary cover of the transition zone: between the poorly dislocated Miocene and the undisturbed Pliocene
anthropogen - due to the manifestation of Attic movements; between the Upper Cretaceous and the Oligocene due to Laramian one; on the border of Mesozoic and Paleozoic as a manifestation of the Zaalic and Pfalz (Herzinian) one. The riftogenic structure is complicated by the lattice tectonites of the post-stratum stages of platform activation, which control the deformation folding and cause the formation of three inversion structural floors -Herzinian (Zaalic-Pfalz), Laramian and Attic.
The Herzinian floor has a fold-down structure formed by the collision movements of the southwest direction [6]. The Hertzinian thrust lattice controls the cover-folding system of the of thrusting sedimentary geomas in the direction of the south side in the WDG, which is formed by the echelons of tectonic cover plates and coulisses jointed uplift-folds. The northeastern wing of the system is bounded by the Svyatogorsk and Sentyanivsk thrusts, the southwestern by Kotlinsk, Mertsalovsk and Novoselivsk one, which separate it from the formed on the northern slopes of the Azov massif of the South Donbas Melange Zone. It is divided in half by the coulisses of the axial Sulino-Konstantinovsk slip-strike thrust. The echelons of smaller thrust control the cover plates, which complicate the tectonics of the Komyshivakha-Limansky, Bakhmutsky and Kalmius-Toretsky depression of the axial zone.
On the southern side of the graben, field surveys highlighted the South Donbass Melange Zone [6]. It is composed of blocks of Precambrian crystalline rocks, volcanogenic-terrigenous thickness of the Devonian, carbonate slabs of lower carbon, which are pulled one over the lattice of "Styl'sky" thrusts in the southwestern direction, which causes a quasi-layered deposition of the block. The melange is erupted by volcanics of the andesite-trachy-andesite and South-Donbas complexes, which determine the upper age limit of its formation, the Zaalic phase of Herzinian orogenesis. The melange zone is the southern limitation of the tectonic cover distribution area covered by the "Donets Scaly-Inferior Zone", which is distinguished as part of the "Herzinian folded region" [6].
The Laramian structural floor has a fold-down structure formed by collision movements in the northern rhumbs [7]. The thrust lattice controls the System of deposition of sedimentary geomas from the DF in the direction of the DDB, which is composed of echelons of tectonic coverings and the spherical joint anticlinal uplift-folds, separated by narrow synclines. The northeastern border of the System is the North Donets thrust, the southern one is the Samara thrust. Almost in half, it is separated by the coulisses articulated branches of the Diamond, Samara and Axial thrusts. The anti- and synforms and plates of the tectonic cover were flexed due to the bending of the joints of the folds and the long axes of the tectonic blocks.
The lattice of the Laramian thrusts controls the propagation of cover-fold deformations, which are distinguished within the «Laramian Folded Region» [6].
The Attic structural floor of the WDG also has a fold-thrusting structure, which is controlled by the "Shumilovsk dislocation complex" of tectonites (Fig. 3) [8]. The northeast vergence thrusts form a lattice, which controls a system of transverse thrusting of geomas of sedimentary thickness from the axial part to the northern side of WDG. It consists of large coulisses articulated plate-covers formed by the planes of Dileevsky, Mariivsky and Lisichansky thrustis. The formation of smaller cover scales is controlled by Seleznovsky, Longitudinal, South Pavlovsky, Sanzharivsky, and Main Irmine thrusts.
Attic movements led to the further fragmentation of the sedimentary cover on the lens-like plan tectonic blocks up to the first tens of kilometers, and caused the one to move in the northwest. This was the basis for the allocation in the southeast of the DDB and in the WDG "Areas of scaly thrustis" [6]. The aim of the research is the tectonophysical identification of deformation structures formed in the southeastern part of the DDB at the Hercynian and Alpine stages of orogenesis. Deformations of the Cimmerian stage have not been investigated due to the complete denudation of the Mesozoic complex in the zone of articulation of DDB and the (WDG) due to the Cenozoic erosion. Based on the structural-kinematic analysis of the tectonite lattices of the Hercynian, Laramian and Attic structural floors, the following were studied: 1 - structural-tectonic frame-
work controlling the propagation of collision deformations; 2- tectonic style of collision deformations to determine the natural mechanism of tectonic inversion. Analytical materials are the latest geo-mapping data on the territory of the WDG [6].
Results and Discussion. Three main angular and stratigraphic disagreements were identified in the sedimentary cover of graben, formed at the stages of tectonic inversion: 1) between a weakly deployed Miocene and an undeployed Pliocene anthropogen - as a result of the Attic phase of late Alpine orogenesis, during which Attic tectonites formed; 2) between the Upper Cretaceous and the Oligocene - as a result of the La-maric phase of the early Alpine movements, which formed the Lamarian tectonites; 3) on the border of the Mesozoic and Paleozoic, as a manifestation of the Zaal and Pfalz folding phases, which formed the Late Her-cynian lattice of tectonites. At the same time, each generation of tectonites has its own azimuthal orientation of the directions of motion along them (vergence) and controls the structure of three dislocation floors (Hert-sinian, Laramian and Attic) [6].
The Hercynian structural floor was formed for the Zaal and Pfalz phase of orogenesis by collision movements in the southwestern rumbas [6]. Its structure is controlled by the lattice of tectonites of the "Stylsky" dynamo-metamorphic complex [7]. The intensity of structural deformations is heterogeneous in the WDG: it is maximum in its southwestern part, decreasing toward the center and on the northeastern flank. This determines the variations in the depth of the Pre-Mesozoic erosion and the completeness of the sedimentary section in the graben: in the north-eastern and central parts, the Mesozoic base overlaps the erosion surface, in the southwestern part the Hercynian floor with a sharp angular disagreement overlaps the Oligocene-Miocene sedimentary cover, in the southeast in the south on the erosion surface with angular disagreement lie Pliocene-Quaternary sediments.
In the axial zone of the WDG, echelons of thrusts of southwestern vergence control tectonic plates and smaller scales of covers, which complicate the tectonics of the Bakhmut, Komishevakh-Limansk and Kalmius-Toretskaya depressions. On the southern side of the Graben, the South Donbass Melange Zone is distinguished, which is the southwestern boundary of the Kalmius-Toretska depression [7]. It is composed of blocks of crystalline rocks of Precambrian, volcanic-terrigenous strata of the Upper Devonian, carbonate deposits of the Lower Carboniferous, up to the first kilometers in size. Blocks are pushed against each other along "Stylsky" tectonites to the south-west at gentle angles of up to 300, which accounts for the quasi-layered occurrence of melange in the Paleozoic. Melange breaks through the volcanic bodies of the andesite-trachyandesite and South Donbass igneous complexes, which determines the upper boundary of the Zaal phase of orogenesis.
The structure of the Laramian folded floor is controlled by the lattice of the "Ostromogilsky" complex of mudstones and propylites of northern vergence [Goryainov, 2004]. The axis of the East Shebelinska, Oskolska, Makeevska and North-Donetska synclines
are considered to be the northeastern boundary of the floor development [6]. In the axial zone of the WDG, the dislocation structure of the floor is controlled by thrust echelons. The amplitudes of horizontal movements along the main thrusts - North-Donetsky, Diamond and Drobishevsky reach the first kilometers. The lattice of thrusts, together with the zones of anticlinal reverse folds controlled by them and salt diapirs complicating them, underwent structural-material transformations of deep hydrothermal-metasomatic fluid systems with the formation of mercury-polymetallic ore fields in separate regions of the WDG [7]. Limitations of the Laramian folded deformations from the north, west, and south became the basis for the separation of the "Laramian folded region" in the transition zone between the DDB and the Donets Foldbelt [6].
The Attic structural floor has a fold-thrust structure controlled by the "Shumilovsky" dislocation complex [7]. The "Shumilovsky" tectonites of northern vergence form a thrust lattice along which large tectonic plate-covers are formed [8]. The largest is the Maryev-sky thrust with an amplitude of horizontal movements in the wings of up to 4.5 km, the other thrusts have amplitudes of several hundred meters: Lisichansky - 300350 m, Main Irminsky - 300-320 m. Tectonic movements along them led to further fragmentation of sedimentary complexes on lenticular blocks in the plan up to the first tens of kilometers, and caused their advance to the north-west, in the direction of the DDB. This became the basis for the allocation of the "zone of scaly thrusts" on the territory of the WDG [6]. The set of deformation tectonic structures, which is controlled by the "Shumilovsky" complex of tectonites, forms the Donets Ridge and Priazov Upland in the day surface.
An analysis of the thrust lattice of the Hercynian structural floor shows that the thrust tectonic framework of the southwestern vergence controls the cover-folded system of transverse thrust of sedimentary ge-omass. On the northeastern slopes of the Graben, the Hercynian system is limited by the wings of articulated branches of the New and Sentyanovsky overthrusts, in the southeast - by the Kotlinsky, Aleksandrovsky and Mertsalovsky overthrusts. The ones control the southern zone of transverse extrusion of geomass from the axial zone to the southern border of Graben. A kinematic analysis of the tectonites pattern indicates that the tectonic transport of geomass in the thrust system was carried out from the northern border and from the axial zone of the Graben towards the southern border. In the axial zone of the Graben, the integumentary-folded system is divided in half by the coulisse articulated branches of the Sulino-Konstantinovsky strike-slip thrust.
In the thrust wing of the Hercynian system, the inter-thrust blocks of elongated, scaly shape have a northeastern strike. In their frontal parts, fault-forming uplift-anticlines with steep northeastern wings and gently sloping southwestern ones, which in the rear parts of the blocks pass into monoclines, are formed. On the western flank of the integumentary-folded system, the base of the Mesozoic cover plunges westward, to a depth of more than 3 km within the Orchikovsky basin
of the DDB. In the submerged parts of the axial hollows, in the castles of the syncline, the remains of the Lower Permian chemogenic sequence are preserved, the bottom part of the Paleozoic section and the Pre-cambrian foundation at the borders of the Hercynian tectonic blocks are cut by relicts of the rift structure -faults. To the west, with the Paleozoic complexes plunging towards the Orchik basin of the DDB, the depth of the Paleozoic erosion section gradually decreases; therefore, a lower Permian section is growing in the hinges of the synclines. In the extreme northeast of the Graben, under the base of the Mesozoic, the Middle Carboniferous lies in the allochthonous wing, which indicates an increase in the depth of the Pre-Mesozoic erosion section in this direction.
An analysis of the thrust lattice of the Laramian structural floor shows that the thrust tectonic skeleton of the northern vergence controls the Alpine integumentary-fold system of longitudinal thrust of geomass wedge-shaped in morphology, encompassing echelons of tectonic covers complicated by zones of rocker-length jointed sections tens - hundreds of kilometers and separated by narrow synclines. The folded integumentary system composes the body of the tectonic wedge of geomas that we emit on the territory of the transition zone between the DDB and the chipboard of the West Donetsk. The north-eastern border of the segment is the North-Donetsky, Drobishevsky and Lisichansky thrusts, in the thrust wings of which rocker-jointed anticlinal zones are formed - the North-Donetsky, Torsko-Drobishevskaya and Matrossko-Toshkovskaya southwestern - Samara thrusts. Almost in half, the body of the segment is divided by the rocker-jointed branches of the Diamond, Samara and Axial shear-reverse faults, in the raised wings of which the largest linear, fracture, rocker-jointed Veliko-Komishevakhskaa, Petrovsky-Novotroitska, Dru-zhkovsky-Konstantinovska and Main anticlinal folds are formed.
An analysis of the thrust lattice of the Attic structural floor indicates that the lattice of thrusts of northeastern vergence controls the system of transverse thrust of geomasses to the northeast in the eastern part of the WDG - from the axial part to the northern side. It consists of plate-covers of gentle bedding formed along the main - Dileevsky, Main Irminsky, Maryevsky thrusts and smaller - Seleznevsky, Longitudinal, South Pavlovsky and Sanzharovsky thrusts.
The results of a structural analysis of the tectonite patterns of the three structural floors indicate that the syneclise, weakly deployed sedimentary stratum of the southeast of the DDB is complicated by cover-thrust and reverse-folded deformations controlled by dynamically conjugated thrust lattices. Along the backstage rows of thrusts in the riftogenic structure of the WDG platform sedimentary cover, tectonic disruptions were laid, along which plates and scales of tectonic covers were formed, extended linear anti- and synforms. The set of deformation structures composes the structural-teectonic framework of two different-age cover-folded systems of tectonic thrust of sedimentary geomasses of a regional scale - Hercynian and Alpine, first distinguished in the Paleozoic cover of the WDG.
An analysis of the comparative scheme of tecton-ites of the Hercynian, Larami, and Attic structural floors indicates that a dynamically conjugated lattice of thrusts and shear-upthrusts together with echelons of tectonic covers and wings of anticlinal folded zones form the structural-tectonic framework of the regional system of post-rift deformations of the WDG sedimentary cover. It stands out as a part of the West-Donetsk tectonic folded integument, which covers the territory of the transition zone between the DDB and the chipboard.
The main structural element of the region is the tectonic wedging segment, formed as a result of the invasion of repeatedly deployed sedimentary geomasses from the particleboard side into the WDG. West Donetsk Region consists of two tectonic regions that differ in the style and intensity of deformation of the sedimentary cover of the WDG. In the southwestern part, the Kalmius-Toretsky region of scaly tectonic covers is distinguished, which from the south is limited to the South Donbass melange zone. The north-eastern half of the segment is occupied by the Lugansk-Kamyshe-vakhsky region of the rocker-joint linear folding, which is limited from the north by the undiluted Mesozoic-Cenozoic platform cover.
Conclusions. The above data lead us to the conclusion that the riftogenic structure in the southeast of the DDV is destroyed by integumentary folded deformations at the stages of platform activation. At the initial stage of tectonic inversion, in the Late Hercynian era, on the thrust tectonic framework of the southeastern vergence, the Hercynian system of transverse thrust of geomasses was formed. At the main stage of inversion, according to the system of alpine tectonites, an intensively deployed Mesozoic-Cenozoic allochthonous comrade was pushed over the Hercynian neoautoch-thon and an Alpine geomass longitudinal thrust system
was formed. Thus, colossal deformations led to the formation of the West Donetsk tectonic folded cover region, which covers both thrust systems, which we first identified in the transition zone between the DDV and the folded Donbass.
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МЕТОДЫ УЧЕТА ВЛИЯНИЯ МЕСТНЫХ ГРУНТОВЫХ УСЛОВИЙ НА СЕЙСМИЧЕСКУЮ ОПАСНОСТЬ СТРОИТЕЛЬНОЙ ПЛОЩАДКИ
Семенова Ю.В.
канд. физ. - мат. наук, ст. науч. сотр., Институт геофизики им. С.И. Субботина НАН Украины,
г. Киев, Украина
METHODS FOR TAKING INTO ACCOUNT THE INFLUENCE OF LOCAL GROUND CONDITIONS ON THE SEISMIC HAZARD OF A CONSTRUCTION SITE
Semenova Yu.
PhD, senior researcher,
Subbotin Institute of Geophysics of the National Academy of Sciences of Ukraine, Kyiv
АННОТАЦИЯ
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