The Sarmatia megablock as a fragment of the Vaalbara supercontinent: Correlation of geological events at the Archean‒Paleoproterozoic transition     

K. A. Savko  A. V. Samsonov  V. M. Kholin  N. S. Bazikov 《Stratigraphy and Geological Correlation》2017,25(2):123-145

The results of correlation between geological events in the period of 2.8?2.0 Ga provide grounds to assume that the Sarmatia lithospheric megablock definable in the southern part of the East European Craton belonged to the ancient Vaalbara supercontinent consisting of the Pilbara and Kaapvaal cratons. In the period of 2.8?2.6 Ga, all of them represented fragments of the continental crust consolidated at approximately 2.8 Ga and subjected to continental rifting, which was accompanied by intense basite volcanism. In the period of 2.50?2.45 Ga, these three cratons were characterized by similar tectonic settings and accumulation of banded iron formations. Precisely these banded iron formations of the largest Transvaal, Hamersley, Kursk, and Kremenchug?Krivoi Rog iron ore basins accumulated in the period of 2.50?2.45 Ga in a single oceanic basin serve as a basis for adequate paleotectonic reconstructions of the Vaalbara supercontinent. In the period of 2.45?2.20 Ga, all three cratons were subjected to a long-lasting break in sedimentation followed by activation of continental rifting with terrigenous sediment deposition, which terminated with basite volcanism ca. 2.2 Ga. These events gave start to the Vaalbara breakup, which represented a multistage process with alternating divergence and convergence phases of supercontinent fragments until the Kaapvaal and Zimbabwe, Pilbara and Yilgarn, and Sarmatia and Volgo-Uralia cratons, respectively, became eventually united.  相似文献   

Long-range coherence of the radar field scattered by a rotating mercury     

I. V. Kholin 《Solar System Research》2004,38(6):449-454

We consider the spatial-temporal properties of the speckle patterns formed when coherent radio waves are scattered by planets. At a speckle diameter of only a few kilometers, the speckle patterns are shown to be displaced in frozen form by distances larger than the Earths diameter due to the spin-orbital motion; i.e., long-range coherence of the radar field takes place. We estimate the coherence losses of the echo signals from Mercury due to the decorrelation of the patterns, which do not exceed or comparable to 10^-4 in order of magnitude for ground-based interferometers. Such small losses imply a high degree of frozenness of the speckle pattern everywhere within the Earth, i.e., on a global scale. This allows us to formulate and solve the unprecedented problems of precision measurements of the instantaneous spin vector components for terrestrial planets by using radars distributed all over the globe.Translated from Astronomicheskii Vestnik, Vol. 38, No. 6, 2004, pp. 513–518.Original Russian Text Copyright © 2004 by Kholin.  相似文献   

Sorption on Humic Acids as a Basis for the Mechanism of Primary Accumulation of Gold and Platinum Group Elements in Black Shales     

Varshal  G. M.  Velyukhanova  T. K.  Chkhetiya  D. N.  Kholin  Yu. V.  Shumskaya  T. V.  Tyutyunnik  O. A.  Koshcheeva  I. Ya.  Korochantsev  A. V. 《Lithology and Mineral Resources》2000,35(6):538-545

In order to asses the contribution of sorption by complexation to the concentration of noble metals at early stages of the formation of their deposits in black shales, the sorption of Au(III), Pt(IV), Rd(II), Rh(III), Ru(IV), and Os(IV) ions was studied on ash-free preparations of humic acids (HA) separated from peat of the Tver region and marine sediment samples taken on the Peruvian shelf. Data on the nature and protolytic characteristics of oxygen-containing HA functional groups were obtained. It has been shown that carboxyl groups and phenol oxygroups, which ensure the HA complexation with ions of noble metals, are present in the HA structure. The dissociation constant values for HA carboxyl groups (pK_a) and the distribution function of these groups in their pK_a values have been established. It has been revealed that the pK_a value for both of the HA groups varies within two orders of magnitude: the average value is equal to 6.1 for HA from peat and 7.0 for HA from marine sediments. A fairly high and similar for both of the HA groups sorption capacity with respect to Au(III), Rd(II), Rh(III), Ru(IV), and Os(IV) ions was established in model experiments. It is equal to 320–350 mg g^–1 for Au, 100–110 mg g^–1 for Pd, 11–12 mg g^–1 for Rh, 16–19 mg g^–1 for Ru, and 23 mg g^–1 for Os. The study of platinum(IV) sorption revealed that humic acids from peat and marine sediments do not virtually sorb Pt(IV), and this observation is important for understanding genetic features of the formation of noble metal deposits in black shales. Based on sorption isotherms for Au(III), Pd(II), Rh(III), and Ru(IV), the conditional affinity constant values for HA sorption centers with respect to ions of these metals were calculated by the method of quantitative physicochemical analysis. These values prove that complex compounds forming at the HA surface possess a high strength: the log values for the Au(III)–HA, Pd(II)–HA, Rh(III)–HA, and Ru(IV)–HA compounds are equal to 6.0, 5.0, 3.2, and 3.5, respectively.  相似文献   

The effect of rotation on the stress-strain state of a cosmic body moving in the atmosphere     

V. A. Andrushchenko  A. N. Galenko  V. A. Goloveshkin  N. N. Kholin 《Kinematics and Physics of Celestial Bodies》2007,23(4):178-184

We consider a model problem on the destruction of a cosmic body in the atmosphere of a planet. The stress-strain state of a meteoroid is determined in the two-dimensional elastic formulation. We show that the rotation of the body considerably accelerates the process of its destruction.  相似文献   

Interaction of Cr(III) with the humus acids of soil,water, and bottom sediments     

I. Ya. Koshcheeva  S. D. Khushvakhtova  V. V. Levinskii  V. N. Danilova  Yu. V. Kholin 《Geochemistry International》2007,45(2):178-184

The interaction of Cr(III) with humus acids [fulvic (FA) and humic (HA) acids] was studied in the systems Cr(III)-FA, Cr(III)-HA, and Cr(III)-FA-HA. Chromium(III) reacts with FA extracted from the headwaters of the Moscow River and from the Krapivenka River (a tributary of Lake Seliger) to form a highly soluble high-molecular-weight Cr(III)-hydroxofulvate complexes with \(\bar \beta _{11} \) = 1.93 × 10⁶ and 5.70 × 10⁶, respectively. Humic acids extracted from peat in the Tver area and the sapropel of Lake Seliger behave as complexing sorbents with conditional affinity constants logβ = 3.78 and 3.23 for Cr(III) sorption at HA sites in the peat and sapropel, respectively. In the three-component system Cr(III)-FA-HA, the Cr(III) distribution coefficient between solution and precipitate is controlled by the pH value and FA content in the solution and decreases by 1–1.5 orders of magnitude with increasing fulvic acid content.  相似文献   

U–Pb isotopic age of apatite-bearing carbonatites in the Kursk block,Voronezh crystalline massif (central Russia)     

A. Yu. Albekov  N. M. Chernyshov  M. V. Ryborak  V. S. Kuznetsov  E. B. Salnikova  V. M. Kholin 《Doklady Earth Sciences》2017,473(1):271-272

In the central part of the European part of Russia in the southeastern part of the Kursk tectonic block, some deposits and occurrences of apatite genetically related to the alkaline–carbonatite complex have been revealed. The results of U–Pb analysis of titanite provided the first confident age estimate of silicate–carbonate (phoscorite) rocks in the Dubravin alkaline–ultramafic–carbonatite massif: they formed no later than 2080 ±13 Ma, which indicates their crystallization in the pre-Oskol time during the final stage of the Early Paleoproterozoic (post-Kursk time) stabilization phase of the Kursk block of Sarmatia (about 2.3–2.1 Ga).  相似文献