pdf № 274, October

DOI: 10.19110/2221-1381-2017-10-3-8 

We present a complex for interpretation of the potential fields for geology using a direct modeling. This method allows to verify various geological hypotheses as well as to model density, magnetic and thermal properties of the geological environment. We performed 2D- and 3D-modeling of magnetic properties taking into consideration the demagnetization effect and inhomogeneity of magnetized field. The graphical interface allows to build cross-sections along arbitrary profile.

Keywords: geological interpretation, modeling, temperature field, anomalous gravity, anomalous magnetic field.

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DOI: 10.19110/2221-1381-2017-10-9-19

In the course of studies of the Lower and Upper Proterozoic formations of the Subpolar Urals, there was a need for a clearer geological interpretation and clarification of their age. This work is intended to offer, at least in part, additional criteria for the dismemberment of the above Precambrian formations. In this article, we present the results of studies, including those obtained from field work in the Subpolar Urals. Using the methods of macrostructure analysis, as well as microstructural analysis, which consisted in determining the orientations of the optical axes of quartz in thin sections, it was shown that for the deposits of the Nyartin complex, the Manhobeu and Shokurya suites, the unifying criterion was the presence of can be that they contain relict isoclinal folds absent in sediments of the Puiva suite and overlying formations. For the complexes and two suites mentioned above, the patterns of the stereographic diagrams of the distributions of optical quartz axes to a certain extent coincide, and the patterns from the diagrams for the Puiva suite are clearly distinguished. All this allows to classify the Nyartin complex, the Manhobeu and Shokurya formations to a structural level separate from the Puiva suite.

Keywords: Subpolar Urals, Precambrian, structural geology, folds, microstructure analysis, optical axes of quartz.

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DOI: 10.19110/2221-1381-2017-10-20-25

The mineral composition of conodont elements is known in details; however their organic matter is studied in a less degree. The previous investigations had demonstrated that organic matter, consisting less than 4 % of a conodont element, was composed of collagen-like protein (Kemp, 1997, 2000, 2002; Rosseeva et al., 2011; Zhuravlev & Shevchuk, 2017). This work is aimed at characterizing of the structure of organic matter of the lamellar tissue of the Frasnian conodont element. The studied conodont element (CAI = 1, temperature of catagenesis <60 °С) was demineralized in 1N HCl, dried, and investigated with AFM (Ntegra Prima, NT-MDT, CKP «Geonauka», Syktyvkar). The organic matter of conodont element possesses globular, not fibrillary, nanostructured. The globules of 40—60 nm in size are ordered into linear (0.3—1.5 um wide) and isometric (200—260 nm) structures. Absence of any residues of fibrillar nanostructures, characteristic for collagen I and II, suggests either denaturation of collagen, or presence of non-fibrillar collagen (e.g. IV type of collagen). The observed nanostructures differ significantly from those of gelatins, thus denaturation of collagen is of low probability. The supposition, that collagen of conodont elements is non-fibrillar, is more probable. The conodonts demonstrate extremely specific biomineralization based on non-fibrillar collagen probably of epithelial origin. Thus vertebrate affinities of conodonts are not proved by study of the organic component of conodont elements.

Keywords: conodonts, organic matter, atomic force microscopy.

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DOI: 10.19110/2221-1381-2017-10-26-30

We have studied the morphological and chemical features of garnets from coarse clastic metaterrigenous rocks in Paleozoic basement of Western Subpolar Urals. The garnets are represented by rhombododecahedrons, cuboctahedra and intergrowths of crystals of different habit. The internal structure of the studied grains is homogeneous — they do not have zonality and do not contain inclusions. Regardless of the morphology, four groups of garnets are distinguished by their chemical composition: pyrope-grossular-almandine, grossular-pyrope-almandine, grossular almandine-pyrope and almandine-grossular. The absence of rounding and perfect preservation of the surface of the grains and their intergrowths indicates an insignificant distance from the source areas. The comparison of the morphological and chemical characteristics of the studied garnets with typomorphic features of garnets from various rock species suggested that the source of the garnets was metamorphic rocks of the basement, at present widespread in the southern part of the Lyapinsky anticlinorium in the axial zone of Central Ural uplift and, possibly, contact-metasomatic structures associated with introduction of granitoids.

Keywords: garnet, chemical composition, clastic material, source areas.

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DOI: 10.19110/2221-1381-2017-10-31-41

The values of density and velocity in the samples of the predominant rocks from the Archaean section of the Kola superdeep borehole (SG-3), drilled in the northern frame of the Pechenga palaeorift structure, were studied. The main part of rocks of the SG-3 Archaean section is represented by gneisses, schists and amphibolites. Their main rock forming minerals are plagioclase, hornblende, mica and quartz. The structure of the rocks is mainly medium-grained, the texture is nematogranoblastic and lepidogranoblastic. The elastic anisotropy and orientation of the rock texture were estimated by the acoustopolariscopy method, the density and velocity of compression and shear waves were determined in the laboratory and the mentioned characteristics were calculated by mineral composition. The measured sample velocities are unusually low, which can be explained by the decompaction effect of deep rocks. The values of the velocity characteristics that are close to those for the conditions of the rock deep occurrence are obtained by calculation with regard to their specific mineral composition. The average values of the velocity of compression and shear waves for gneisses calculated by mineral composition are 6.38 ± 0.16 km/s and 3.52 ± 0.14 km/s, respectively. The average of the compression wave velocity for schists is 6.40 ± 0.13 km/s, of the shear wave velocity — 3.46 ± 0.09 km/s, and for amphibolites 6.84 ± 0.13 km/s and 3.82 ± 0.08 km/s, respectively. The ratios of the values of compression and shear moduli in different rocks exhibit the same trends as the average velocities. However, their values are lower in schists, medium in gneisses and grater in amphibolites.

Keywords: Kola superdeep borehole (SG-3), deep rocks, properties, densities, compression and shear wave velocities.

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