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Research subject. A geochemical study of Cambrian-Ordovician deposits was carried out within the area of the Duderhof dislocations of the platform cover of the southern frame of the Baltic shield. Materials and methods. The ICP-MS method was used to study 14 samples of sandstones, limestone, phosphorites and black shales, which comprise both weakly dislocated stratified formations (stratified horizons) and strongly deformed formations, as well as secant dome-like and dike-like bodies. Results. Geochemical studies showed that, in the zones of tectonic disturbances, lower Paleozoic deposits are characterized by high concentrations of a number of trace elements, significantly exceeding the Clark values for sedimentary rocks. This applies to such chemical elements, as Be, Sc, V, Co, Ni, Cu, Mo, Pb, Th and U. At the same time, the concentrations of V and U are higher than those in the developed fields of Estonia and Sweden. An analysis of the cambriansands of the sablin formation showed that the eastern (Archean) part of the Baltic shield could not have been the source of food for their formation. The presence of leucoxene in the sands of the Sablinsky formation, a mineral formed by ilmenite under the influence of high temperatures, and the presence of mechanically unstable minerals in dike-like formations, indicate the influence of deep fluids on the sedimentary cover, whose flows moved along fault zones and carried the above-mentioned chemical elements to the near-surface layers of the earth’s crust. All this points to the endogenous rather than exogenous (glacial) nature of secondary structural-material transformations in the area of the Duderhof dislocations, as well as their genetic relationship with deformations in the Baltic-Mezen shear zone.
Research subject. A geochemical study of Cambrian-Ordovician deposits was carried out within the area of the Duderhof dislocations of the platform cover of the southern frame of the Baltic shield. Materials and methods. The ICP-MS method was used to study 14 samples of sandstones, limestone, phosphorites and black shales, which comprise both weakly dislocated stratified formations (stratified horizons) and strongly deformed formations, as well as secant dome-like and dike-like bodies. Results. Geochemical studies showed that, in the zones of tectonic disturbances, lower Paleozoic deposits are characterized by high concentrations of a number of trace elements, significantly exceeding the Clark values for sedimentary rocks. This applies to such chemical elements, as Be, Sc, V, Co, Ni, Cu, Mo, Pb, Th and U. At the same time, the concentrations of V and U are higher than those in the developed fields of Estonia and Sweden. An analysis of the cambriansands of the sablin formation showed that the eastern (Archean) part of the Baltic shield could not have been the source of food for their formation. The presence of leucoxene in the sands of the Sablinsky formation, a mineral formed by ilmenite under the influence of high temperatures, and the presence of mechanically unstable minerals in dike-like formations, indicate the influence of deep fluids on the sedimentary cover, whose flows moved along fault zones and carried the above-mentioned chemical elements to the near-surface layers of the earth’s crust. All this points to the endogenous rather than exogenous (glacial) nature of secondary structural-material transformations in the area of the Duderhof dislocations, as well as their genetic relationship with deformations in the Baltic-Mezen shear zone.
Detailed studies of the deeply metamorphosed Early Precambrian rocks of the Northern Ladoga region allowed us to distinguish three deformation stages of the Svecofennian tectogenesis during which there occurred significant structural and compositional transformations of the "cover (Paleoproterozoic) – basement (Archean)" system. In addition to the structural-paragenetic analysis, which allowed to allocate transversal structural paragenesis in both floors, there are some other opportunities in the recognition of their-hosted granitoid veined bodies with a positive Eu anomaly. The rock varieties with this anomaly are always high in barium and do not show a direct correlation between the Eu anomaly and (La/Yb)n, Ca and Sr. This is contrary to the ideas about the occurrence of a positive Eu anomaly due to the substitution of divalent strontium by Eu++ and suggests that the formation of such rocks took place under the influence of deep reduced fluids. It was found that granitoids with a positive Eu anomaly were formed during the first and last stages of the structure evolution, with a predominance of brittle deformations and a deep-reduced fluid breakthrough. At the second stage, with the dominant manifestation of plastic deformations, when such fluids could be "blocked" within the system, there was a formation of granitoids with low barium concentrations and a negative Eu anomaly.
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