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161.
Doklady Earth Sciences - A study of the geochemical features and isotopic (Sm‒Nd and U‒Pb) age of dolerites of the Ivdel complex on the eastern slope of the Northern Urals within the... 相似文献
162.
Yu. L. Ronkin V. V. Murzin A. Gerdes A. V. Maslov D. V. Varlamov 《Doklady Earth Sciences》2018,478(1):82-87
We have been the first to study in situ the U–Pb isotopic system of aeschynite identified in the gold-bearing magnetite–chlorite–dolomite rocks of the Karabash serpentine massif in the Southern Urals. In the concordia diagram, the U–Pb LA–ICP–MS data on aeschynite are characterized by a considerable discordance, which is consistent with the regression line, the lower crossing of which with the concordia corresponds to an age of 298 ± 18 Ma, whereas the figurative ellipses of coexisting monazite reveal an almost concordant cluster corresponding to the U–Pb age of 317.3 ± 3.3 Ma. It has been established that the closure temperature of the aeschynite system is lower than that of the coexisting monazite. 相似文献
163.
Maslov A. V. Shevchenko V. P. Kuznetsov A. B. Stein R. Gerland S. 《Doklady Earth Sciences》2018,479(2):534-538
Doklady Earth Sciences - The isotope-geochemical characteristics (LaN/YbN, Sm/Nd, εNd(t), 207Pb/206Pb, and 87Sr/86Sr) of ice-rafted sediments in several areas of the Western Arctic (Fram... 相似文献
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A. V. Maslov V. N. Podkovyrov E. Z. Gareev Yu. L. Ronkin 《Stratigraphy and Geological Correlation》2014,22(2):160-174
The Grenvillian orogeny (～1250 to 980 Ma) was one of the most significant Riphean events. It determined the formation of many structures observable now in North and South America, northwestern Europe, South Africa, Western Australia, Antarctica, and other regions. Nevertheless, its reflections in the most complete and relatively well investigated Upper Precambrian sedimentary sections of northern Eurasia such as the Riphean stratotype (Bashkir meganticlinorium) and hypostratotype (Uchur-Maya region) still remain unknown. This is primarily true of the petrographic and chemical compositions of terrigenous rocks. This work is dedicated to the analysis of peculiar features in variations of the whole-rock chemical composition of sandstones and fine-grained clastic rocks (shales, mudstones, fine-grained clayey siltstones) that constitute Middle-Upper Riphean boundary layers of the Bashkir meganticlinorium, Kama-Belaya aulacogen, and Uchur-Maya region. The analysis reveals no tendency for the decrease in the degree of the chemical and, consequently, mineralogical maturity in the upward direction through the Middle-Upper Riphean sections in the above-mentioned regions. The whole-rock compositions of fine-grained clastic rocks associated with sandstones correspond mostly to that of “common” Upper Precambrian clayey rocks. The formation of practically the entire Yurmatinian-Karatavian succession in the Bashkir meganticlinorium proceeded under relatively stable TDM and ?Nd(T) values. The period of 1250 to 980 Ma in the central and eastern parts of the Siberian Platform was marked by repeated rifting episodes alternating with accumulation of mature platformal sediments, although repercussions of Grenvillian collisional processes are missing from this region as well. The performed analysis provides grounds for the conclusion that contribution of the Grenvillian events to the formation of most complete Riphean successions in northern Eurasia was insignificant. 相似文献
166.
N. M. Fedorova N. M. Levashova J. G. Meert A. V. Maslov M. T. Krupenin 《Doklady Earth Sciences》2014,456(1):512-516
The latest concepts about the Earth’s paleogeography for the period of 700–500 million years are quite contradictory. Reliable paleomagnetic data are quite scarce for the Ediacaran-Cambrian of the majority of continental plates, which means that making any reliable global paleogeographic and paleotectonic reconstructions is impossible. According to various authors, Baltica within this time, for example, could have been located at any latitudes from the South Pole to the equator. Making correct reconstructions requires new paleomagnetic data; however, almost all objects that are applicable for such studies within Baltica have already been studied. A possible solution is to study the deformed margins of the plate, in particular, the western megazone of the Middle Urals, where the lower and upper Ediacaran volcanogenic-sedimentary and sedimentary sections are known within the Kvarkushsko-Kamennogorskii anticlinorium [1, 2] (Fig. 1). This paper presents the first paleomagnetic results obtained for the sedimentary rocks of the Upper Ediacaran Chernokamenskaya suite. They are consistent with the group of six poles of the same age [3–7], by which Baltica was located at the subequatorial latitudes at the end of the Educarian. 相似文献
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168.
The analysis of lithogeochemical data on the Upper Riphean and Vendian sandstones from the Bashkirian anticlinorium showed
that sandstone associations formed in a passive sluggish tectonic regime in the middle Late Vendian were replaced by associations
accumulated in the more active tectonic settings. This is well seen in the SiO2-K2O/Na2O and (Fe2O3* + MgO)-TiO2 diagrams reflecting the particular and median compositions of psammites. The lithochemical characteristics of sandstones
were examined to determine the compositional variation of rock complexes eroded on paleodrainage areas. Quartz-rich sedimentary,
metasedimentary, and metamorphic rocks, as well as felsic igneous rocks prevailed in the paleodrainage areas throughout the
entire Late Riphean and Early Vendian, while the main sources of clastic material in the Late Vendian were igneous intermediate
and basic rocks. With allowance made for the previous comparative-lithological data and some other materials, significant
similarity in the position and orientation of compositional fields of psammites from the middle and upper levels of the Asha
Group (Bashkirian anticlinorium) with fields of psammites from different syncollisional (flysch and molasse) basins in the
SiO2-K2O/Na2O, K2O/Na2O-SiO2/Al2O3, F1–F2 and other diagrams suggests that the middle Late Vendian (beginning from the Basa level) was marked by a variation
in tectonic/geodynamic settings of sandstone accumulation and in composition of the eroded paleodrainage systems. The revealed
trend agrees well with concept of the existence of the Late Riphean-Vendian Pechora paleocean. 相似文献
169.
I. A. Maslov 《Astronomy Letters》2000,26(7):428-432
We propose to use a global (wide-angle, of the order of several degrees) distribution of linearly polarized emission over the sky to detect light echoes of historical supernovae exploded in our Galaxy. The echo emission must be polarized tangential to the direction of the supernova explosion site, and its degree of polarization must exhibit a characteristic dependence on angular distance. The near infrared is an optimum spectral range for detection. A spotted structure in the shape of a ring ～5° in diameter and ～3° in width with a total brightness of ～12–13m in polarized light with a tangential orientation of the electric vector must be currently seen in the direction where Tycho Brahe observed a supernova explosion in 1572. A comparison of the expected intensity of the echo with the intensities of the zodiacal light and the atmosphere shows that it can be detected in principle during long-term observations from space and, under favorable conditions, even from the ground. 相似文献
170.