Results of the study of the geodynamics of the Ossetian part of the Central Caucasus based on satellite geodesy and regional seismicity data

В результате проведённой работы была получена информация о геодинамическом поведении ос- новных тектонических блоков Земной коры (ЗК) в границах Горной Осетии. Принимая полученную информацию как первичную, в рамках данной работы продемонстрировано несколько методических приёмов по её матема- тической обработке. В частности, приёмы интерполяции дискретно представленных данных позволили вы- полнить построение поля скоростей GPS-пунктов в условной системе координат, проведено сопоставление его с полем распределения сейсмической энергии по территории. Выявленные локальные деформационные аномалии ЗК логично вписываются в тектоническую схему региона, установленную независимыми геологиче- скими и геофизическими методами. As a result of the work carried out, information was obtained on the geodynamic behavior of the main tectonic blocks of the Earth’s crust (GC) within the boundaries of Mountainous Ossetia. Taking the information received as primary, within the framework of this work, several methodological techniques for its mathematical processing are demonstrated. In particular, the methods of interpolation of discretely presented data made it possible to construct the velocity fi eld of GPS points in a conventional coordinate system, and compare it with the fi eld of seismic energy distribution over the territory. The identifi ed local deformation anomalies of the ZK logically fi t into the tectonic scheme of the region, established by independent geological and geophysical methods.

Deep Structure, Tectonics and Petroleum Potential of the Western Sector of the Russian Arctic

The evolutionary-genetic method, whereby modern sedimentary basins are interpreted as end-products of a long geological evolution of a system of conjugate palaeo-basins, enables the assessment of the petroleum potential of the Western sector of the Russian Arctic. Modern basins in this region contain relics of palaeo-basins of a certain tectonotype formed in varying geodynamic regimes. Petroleum potential estimates of the Western Arctic vary broadly—from 34.7 to more than 100 billion tons of oil equivalent with the share of liquid hydrocarbons from 5.3 to 13.4 billion tons of oil equivalent. At each stage of the development of palaeo-basins, favourable geological, geochemical and thermobaric conditions have emerged and determined the processes of oil and gas formation, migration, accumulation, and subsequent redistribution between different complexes. The most recent stage of basin formation is of crucial importance for the modern distribution of hydrocarbon accumulations. The primary evolutionary-genetic sequence associated with the oil and gas formation regime of a certain type is crucial for the assessment of petroleum potential. Tectonic schemes of individual crustal layers of the Western sector of the Russian Arctic have been compiled based on the interpretation of several seismic data sets. These schemes are accompanied by cross-sections of the Earth’s crust alongside reference geophysical profiles (geo-traverses). A tectonic scheme of the consolidated basement shows the location and nature of tectonic boundaries of cratons and platform plates with Grenvillian basement as well as Baikalian, Caledonian, Hercynian, and Early Cimmerian fold areas. Four groups of sedimentary basins are distinguished on the tectonic scheme of the platform cover according to the age of its formation: (1) Riphean-Mesozoic on the Early Precambrian basement; (2) Paleozoic-Cenozoic on the Baikalian and Grenvillian basements; (3) Late Paleozoic-Cenozoic on the Caledonian basement; (4) Mesozoic-Cenozoic, overlying a consolidated basement of different ages. Fragments of reference sections along geo-traverses illustrate features of the deep structure of the main geo-structures of the Arctic shelf and continental regions of polar Russia.

Upper Kama potassium salt deposit tectonic scheme based on physical modeling results and geological and geophysical data

Introduction. The territory of the Upper Kama potassium salt deposit (UKPSD) which has been actively developed since 1932, is characterized by abnormal technogenic overload on the geological environment. This load destroys the natural balance of the geological environment, the restoration of which is accompanied by hazardous dynamic events, from rockbursts to induced earthquakes of various magnitudes. Dynamic conditions of UKPSD is determined by many factors, among which a significant role is played by tectonic factors. Tectonic structure in the form of tectonic features or criteria (or other equal conditions) are taken into account first of all when fulfilling dynamic zoning of UKPSD territory and predicting the areas of possible manifestation of dynamic events. As soon as structural and tectonic elements of geological environment are characterized by similarity and hierarchy, it is advisable to study the tectonics of the deposit at various scales by corresponding geological and geophysical methods applying physical simulation data. Research methodology. Tectonic structures similarity and hierarchy (with a crack analysed as a copy of a fault), determined the two-stage technique of studying the tectonic structure of UKPSD territory. At the first stage, according to physical simulation data, areas influenced by the deep faults enclosing the Solikamsk depression and UKPSD were reconstructed. At the second stage, analyses was carried out of UKPSD fault strike azimuths determined by geological and geophysical methods. Research results. According to the results of the physical simulation, the dimensions of the area of dynamic impact of all faults enclosing the Solikamsk depression taking into account their kinematic type, and strikes and kinematics of faults within the zone of each fault were determined. Statistical analysis was carried out together with rose diagrams of strike azimuths of faults in the foundation and faults in UKPSD depth determined according to the results of magnetic field local anomalies interpretation, geomorphological data, satellite and aerial images. Summary. Tectonic scheme of UKPSD is not random. It is determined basically by the kinematics of deep faults enclosing UKPSD, and the tectonics of the foundation.

The model of the Bodaibo graben formation: geological and geophysical aspects

The problem of the Bodaibo graben formation has been considered within the framework of the proposed tectonic scheme of the Baikal-Patom fold belt crystalline basement — the Paleoproterozoic Baikal-Viluisk granulite-gneiss belt, which divides the foundation of the Siberian platform into Anabar-Mirninsky, Nepsko-Botuobinsky and Aldan-Stanovoi geoblocks. The Baikal-Viluisk granulite-gneiss belt is expressed by a system of blocks having a common northeastern direction and forming uplifts and grabens. As a result of the transpession interaction of the Nepsko-Botuobinsky and Anabar-Myrninsky geoblocks with Aldan-Stanovoi one in the Paleoproterozoic, the frontal part of the former was elevated with the formation of metamorphic rocks of Sarma-Tonod zone of outcrops and with the simultaneous descending of the Aldan-Stanovoi geoblock marginal part and the formation of the Olokit and Bodaibo grabens. The Olokyt graben was filled with the detrital material from the Nepsko-Botuobinsky and Anabar-Mirninsky geoblocks, and the Bodaibo graben — mainly by the products of the metamorphic rocks destruction of the Aldano-Stanovoy shield, including the gold-bearing metabasite complexes.

Contribution à la connaissance du précambrien récent en Europe Occidentale et développement géochronologique du Briovérien en Bretagne (France)

The study of Precambrian formations in central and western Europe has interested geologists for a long time. Most of these presumed Precambrian rocks are actually gneisses, whose last metamorphism occurred in the Hercynian orogeny, so that chronostratigraphic investigations (that is, investigations of the typical stratigraphic evolution) are not possible. However, there are several regions where Precambrian rocks have not been transformed by the later Hercynian orogeny; these are situated in Bohemia (Czechoslovakia), in Thuringia (Eastern Germany), in the Cantabrian Mountains (Spain), and in several regions of France, especially in Brittany. All of the rocks in these regions are petrographically rather monotonous and fossils are rare and of untypical species. Only the combination of classical geological methods with isotopic analyses (K-Ar and Rb-Sr) of suitable rocks has permitted the development of a chronological and stratigraphical scheme in Brittany.The oldest rocks, highly metamorphosed, belong to the Pentevrian, with ages of 900–1200 m.y. The Pentevrian is an orogenic unit and not a stratigraphic one. After a period of 150–200 m.y. for which no record of sedimentation and erosion remains, the upper Precambrian (Brioverian) stratigraphie system began. Older ages than the Pentevrian are presently known only in northern Europe.The stratigraphic subdivisions previously proposed for Normandy and Brittany can be confirmed by radioactive datings. The system began with arkoses and basaltic volcanic ashes (700 m.y.), followed by important submarine diabases (670 m.y.). Following them, the middle Brioverian began without any tectonic movement, with some thin horizons of black silica schists of about 630 m.y. and continued with very fine-clastic schists and shales several hundred meters thick. After a tectonic phase, the upper Brioverian period commenced, with important phyllitic (flysch) series, which show in the upper parts tillites and other glacial phenomena. This period was followed by important tectonic movements, folding, and granitic intrusions, including the great granitic pluton in western Normandy at 560 m.y. After an evidently short period of erosion the Georgian (Cambrian) period commenced, with a transgression conglomerate.These results are briefly compared with the evolution of the younger Precambrian in the other European regions. Except for northern Europe and the British Isles the same stratigraphic and tectonic scheme appears in each region.