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S.V. Efremov S.I. Dril&#x; G.P. Sandimirova I.V. Sandimirov 《Russian Geology and Geophysics》2010,51(12):1257-1261
The validity of the Rb/Sr isotopic ages of Cretaceous granitoid complex in the central Chukchi region has been verified. The performed studies showed that the Rb/Sr isotopic ages of late-orogenic granitoids are not reliable. Their variation can be explained in terms of the mixing of primary mantle magmas with continental-crust matter. Most probably, the variation is due to the constant compositions of mixing components and their proportions. 相似文献
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V. A. Makrygina I. V. Sandimirov G. P. Sandimirova Yu. A. Pakhol’chenko A. B. Kotov V. P. Kovach A. V. Travin 《Geochemistry International》2010,48(10):979-987
The paper presents data on the Nd-Sr systematics of magmatic rocks of the Khaidaiskii Series of the Anginskaya Formation in
the Ol’khon region, western Baikal area, and rocks of the Talanchanskaya Formation on the eastern shore of Lake Baikal. Geochemical
characteristics of these rocks are identical and testify to their arc provenance. At the same time, the ɛNdtof rocks of the Khaidaiskii Series in the Ol’khon area has positive values, and the data points of these rocks plot near the
mantle succession line in the ɛNdt-87Sr/86Sr diagram, whereas the ɛNdt values of rocks of the Talanchanskaya Formation are negative, and the data points of these rocks fall into the fourth quadrant
in the ɛNdt-87Sr/86Sr diagram. This testifies to a mantle genesis of the parental magmas of the Khaidaiskii Series and to the significant involvement
of older crustal material in the generation of the melts that produced the orthorocks on the eastern shore of the lake. These
conclusions are corroborated by model ages of magmatic rocks in the Ol’khon area (close to 1 Ga) and of rocks of the Talanchanskaya
Formation (approximately 2 Ga). The comparison of our data with those obtained by other researchers on the Nd-Sr isotopic
age of granulites of the Ol’khon Group and metavolcanics in various structural zones in the northern Baikal area suggests,
with regard for the geochemistry of these rocks, the accretion of tectonic nappes that had different isotopic histories: some
of them were derived from the mantle wedge and localized in the island arc itself (magmatic rocks of the Anginskaya Formation)
or backarc spreading zone (mafic metamagmatic rocks of the Ol’khon Group), while others were partial melts derived, with the
participation of crustal material, from sources of various age (metagraywackes in the backarc basin in the Ol’khon Group and
the ensialic basement of the island arc in the Talanchanskaya Formation). 相似文献
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The problem of eutrophication of the surface water in the Arctic Regions is discussed. The natural hydrochemical indices of the trophic status of lakes are analyzed in connection with the landscape and physiographic features of the Kola Peninsula. The regular features of changes in the hydrochemical indices of the trophic status of lakes and the development of the process of eutrophication are analyzed in the case of subarctic Lake Imandra, which has been polluted with municipal and industrial (phosphorus-containing waste of the apatite production) wastewater for more than fifty years. Criteria are proposed for establishing and assessing water eutrophication in cold climate. 相似文献
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Water Resources - The effect of a large mining complex of Apatit JSC on the aquatic ecosystem of Lake Imandra is discussed. Hydrochemical data are given to characterize the pollution zone, and the... 相似文献
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In the east of the Tuvinian trough within the Kropotkin Ridge, the formation of Devonian volcanic associations was intimately conjugate with rifting on the southwestern framing of the Siberian Platform. The associations include picrite-like basalts, trachybasalts, basaltic trachyandesites, trachyandesites, trachytes, trachyrhyodacites, trachyrhyolites, comendites, and subvolcanic dolerites. The basic and normal-basic rocks are subdivided into two groups by TiO2 contents: high-Ti (TiO2 ～ 2.2–4.2 wt.%) and medium-Ti (TiO2 ～ 1.3–2.0 wt.%). Compared with the high-Ti basites, the medium-Ti ones are depleted in K, Rb, REE, Nb, Ta, Th, and U and have features of magmatic series of active continental margins. The high-Ti rocks are similar in composition to within-plate basalts. But in the isotopic compositions of Sr and Nd the above groups of basites are similar and correspond to mantle sources forming enriched within-plate basalts of the OIB type. This combination of within-plate and continent-marginal geochemical features in the basites localized in the same structure-geologic conditions might indicate the formation of rock associations in the rift zone at the rear of active continental paleomargin during the evolution of their common plume source. Its interaction with the suprasubductional lithospheric mantle determined the geochemistry of rocks. 相似文献
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S.V. Andryushchenko A.A. Vorontsov V.V. Yarmolyuk I.V. Sandimirov 《Russian Geology and Geophysics》2010,51(7):734-749
The Khambin volcanotectonic complex is a horst framing the Late Cretaceous Lake Gusinoe basin in the northwest. This complex is due to the intracontinental rift conditions which existed in western Transbaikalia in the Late Mesozoic. They gave rise to a system of subparallel grabens and horsts in present-day topography. The magmatic evolution of this complex spans from 159 to 117 Ma and is divided into three stages. The first stage (159–156 Ma) witnessed the formation of thick (up to 1500 m) volcanic masses of trachybasalts, basaltic trachyandesites, trachytes, trachydacites, trachyrhyolites, and pantellerites. The next two stages were the formation of isolated ancient volcanoes (127–124 Ma) composed of trachybasalts, basaltic trachyandesites, phonotephrites, tephriphonolites, and alkali trachytes and the formation of the Murtoi (Lake Gusinoe) essexite dike (122–117 Ma). The main trends for igneous associations from early to late stages are reduced magmatism and reduced rock diversity because of the decreasing portion of felsic volcanic rocks. Mafic rocks show an increase in total alkalinity, the content of incompatible elements (Th, U, K, Rb, Pb, Nb, Ta, Zr, Hf), total REE content, and the LREE/HREE ratio. The Sr–Nd isotopic composition of these rocks remained nearly constant and corresponds to that of OIB-EMII mantle sources. Compositional variations are attributed to a time-dependent decrease in the degree of partial melting of a similar magma source. 相似文献
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The interaction of natural and industrial waters with the rocks and apatite ores of the Khibiny alkaline massif was studied to estimate the extent of anthropogenic influence on natural processes. The abundance of the major rock-forming elements of the nepheline syenites and foidolites in the natural waters indicates that dissolution of nepheline and feldspathoids in natural water plays a significant role under the conditions of slow weathering in the Far North. Experiments showed that fine nepheline particles are transformed into amorphous phases at a fixed water volume at 18–20°C and pH 7.5–8.1. This process became observable already within the first day and continued for months. It is possible in stagnant reservoirs of natural waters and clearly expressed in industrial settling tanks. This is supported by the high content of amorphous phases enriched in Na, K, Al, and Si in the top layer of lacustrine sediments at the zone affected by the sewage of a concentrating mill. 相似文献
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