编号 6 (2024)

The paper characterises in detail the specific morphological type of meta-intrusive bodies system of sheeted forms that constitute the structurally unified series of gabbro-diorite-granodiorite-granite, first identified in the Serdobol complex of the svecokarelides of the southeastern part of the Fennoscandian Shield. It is shown that they belong to the transpressive nappe-thrust paragenesis of the Meyeri suture zone separating the metaterrigenous formations of the Karelides and Svecofennides on the pericratonic margin of the Archean Karelian Craton. They fill syndeformational near-fault fractures and, in addition, may be supply channels for syntectonic plutons of the early Secaucofennian tectogenesis. On the basis of petrochemical analysis their formation belonging to the complexes of tonalite-trondhjemite-granodiorite series (TTG) and adakite-like rocks formed in the accretionary-collisional system of the interaction zone of the Archean continental plate and the Secaucofenian juvenile oceanic crust is determined. Sm–Nd isotopic composition of systems of bodies of sheeted forms and the host rocks of the metaterrigenous Ladoga complex is presented; the peculiarities of their mineral and chemical composition, as well as the relics of xenogenic zircon of close age detected in the magmatic substrate are discussed. The significant influence of partial melting processes in the system “Archean basement–Palaeoproterozoic cover” on the formation of rocks of the Serdobol complex, presumably initiated by the influx of melts from the subducting slab. The processes of crustal contamination of initial magmas are considered.

The article presents the first results of isotope-geochemical (Sm‒Nd, Rb‒Sr) and geochronological (U‒Pb LA-ICP-MS) studies of Cambrian volcanic-sedimentary strata (Terek and Ezhim formations) of the Systighem terrane (Central Tuva). It was established that the origin of the primary basaltic magmas of the Terek and Ezhim formations is associated with the partial melting of a mantle source (OIB type), metasomatically worked through by processes associated with contamination during the melting of a dehydrated slab. Their formation occurred in the rift-type basins marking extension processes in the rear part of the accretionary complex with transitional or continental-type crust opposite the background of subduction of the Paleo-Asian Ocean crust beneath it.

The formation of volcanogenic-sedimentary strata of the Terek and Ezhim formations occurred closely simultaneously in the interval of 512‒510 Ma. Similar isotope-geochemical characteristics of the composition of volcanic rocks of the studied formations (ε_Nd(510) = +3.9 to –0.45 and ε_Nd(510) = +4.5 to –0.23) and the time of their formation indicate that they are a single sequence, which is in the process of folding or other tectonic processes was divided into disconnected fragments, deformed and displaced relative to each other by horizontal movements during the course of accretion-collision events. On the modern erosional section, they are represented by a series of combined tectonic plates, altered to varying degrees, thrust upon each other and, most likely, on an existing and buried continental block.

The seismotectonic position of the territory of Central and Southern Uzbekistan is analyzed. It is shown that the territory is characterized by a layered-block structure. Four large blocks of the earth’s crust are distinguished. Two blocks belong to the Turan microplate, the remaining blocks belong to the West Tian- Shan and Afghan–Tajik microplates. Positive and negative morphostructures of each geodynamic block are described. Active faults of the earth’s crust in three different directions are distinguished. In the central part of Uzbekistan, the most active are faults of the north-west strike. These faults are characterized by a long history of development, complex internal structure, high values of the amplitudes of neotectonic movements. Fault troughs are confined to such faults. Newly emerged faults of the north-east direction complicated the structure of large regional structures. If within Central Uzbekistan these faults were of secondary importance in the formation of the modern deformation structure of the earth’s crust in the study region, then in the territory of Southern Uzbekistan faults of this direction are the main ones and control modern seismicity. A probabilistic analysis of the seismic hazard of the territory of Central and Southern Uzbekistan is carried out. Three types of calculation models of seismic vibrations sources are considered: quasi-homogeneous seismological provinces, active faults of the earth’s crust and seismogenic zones. Parameterization of seismic source models is carried out, including the determination of seismic potential, recurrence parameters of earthquakes of various magnitudes, the predominant kinematic type of slip in the foci of earthquakes of each source.

The calculation of seismic impacts is carried out using several attenuation dependencies developed for the Central Asian region. The weights for the attenuation dependencies are selected based on the ranking procedure according to the degree of applicability to the study area. An assessment of seismic hazard in engineering parameters of seismic vibrations was carried out. Taking into account the recurrence periods of seismic impacts, probabilistic maps of detailed seismic zoning of the territory of Central and Southern Uzbekistan were developed.