Search

The first results of the geochronological dating of the specific sill-like gabbrodiorite–granodiorite intrusive bodies within the areal extent of the Paleoproterozoic Ladoga complex, singled out at an early stage of the tectono–metamorphic evolution of the Svecofennides in the southeastern part of the Fennoscandian Shield are presented. Their affinity to the fold-and-thrust paragenetic assemblage of the Meyeri zone, which separates the northern and southern domains of the Ladoga region, in the shape of plated or tabular-like magmatic bodies that fill the feather joints of low-angle thrust faults, is shown. The results of zircon dating by two technologies of the U–Pb method, indicating the time span of the early kinematic stage of the Svecofennian tectogenesis and the according plutonic igneous and metamorphic events at ca. 1.87 Ga, as well as the time limit of the imprinted folding event of the second deformation stage at about 1.83 Ga, are compared. [ABSTRACT FROM AUTHOR]

The study of granites in the basement of the Western Siberian platform is highly relevant since they are associated with hydrocarbon deposits, which are located not only above the granite massif, but also within the metasomatically altered upper layer of granites. At the same time, granites are most easily and reliably dated by zircon, which makes the geological structure of the area easier to examine, especially when the latter is overlapped by a thick sedimentary cover. The composition of granitoids from the basement of the Traigorod–Kondakovskii licensed site of the Western Siberian megabasin, located in the northwestern part of Tomsk Region, near the border with the Khanty-Mansi Autonomous Okrug, about 40 km east of the village of Aleksandrovskoye, has been studied. This license area is located within the Aleksandrovskii arch, which is bounded by the Ust-Tymsk Depression in the southeast and the Koltogorskii Trough in the northwest. The Aleksandrovskii Arch has a complex structure, which includes the large Krivolutskii granite batholith enclosed in the Carboniferous–Devonian sedimentary (mainly carbonate) rocks and Ordovician–Silurian shales. It has been established that batholith rocks are leucogranites and granites of normal alkalinity and have undergone metasomatic alterations in the form of propylitization and argillization. Granites belong to the I-type and were probably formed from the island arc substrate. Their age, according to the results of U–Pb zircon dating, is approximately 268 Ma; i.e., the generation and intrusion of granites took place during the beginning of the formation of the Koltogorsk–Urengoi Rift, the central rift of Western Siberia (which, according to Ar–Ar basalt dating, was also formed 268 million years ago). [ABSTRACT FROM AUTHOR]