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The geologic positions and geochemical and isotope parameters of the Ordovician-early Silurian and Early-Middle Devonian continuous volcanic series of the Minusa basin and its mountainous framing are compared. Both series are composed mostly of moderately alkaline rocks with variations in SiO2 contents from 45 to 77 wt.%. The Ordovician-early Silurian series differs from the Early-Middle Devonian one in lower contents of TiO2 (< 1.7 wt.%) and Fe2O3tot and higher contents of Al2O3 in all rock varieties and in the more fractionated REE patterns of trachybasalts. The compositions of both series reflect two simultaneous mechanisms of magma evolution. The main process was fractional crystallization leading to the formation of rocks from trachybasalts to trachyrhyodacites. The accessory mechanism was the contamination of fractionated melts by crustal material, anatectic melting of crust, and mixing of deep-seated magmas with crustal melts. These processes had specifics at each stage and were controlled by the composition of the sources of parental melts. Their geochemical and isotopic parameters (high alkalinity, high contents of lithophile elements, negative anomalies of Nb, Ta, and Ti, and enrichment in radiogenic Sr) point to the interaction of mantle plumes with the lithospheric mantle that was metasomatically transformed during the preceding Vendian-early Cambrian subduction processes. 相似文献
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I. W. Roxburgh S. V. Vorontsov 《Monthly notices of the Royal Astronomical Society》2006,369(3):1491-1496
The basic properties of acoustic wave propagation in stellar interiors can be analysed from the autocorrelation function (ACF) of intensity (or velocity) observations without measuring the resonant p-mode frequencies. We show how the strength of acoustic wave refraction in the stellar core, or forward acoustic amplitude, can be measured from a modulation in the ACF. This is the basic physical quantity which governs the so-called 'small frequency separations', and its measurement from the ACF can be used for determining the small frequency separations when the data is of insufficient quality for a reliable identification of the stellar p-mode frequencies. 相似文献
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A. A. Vorontsov V. V. Yarmolyuk G. S. Fedoseev A. V. Nikiforov G. P. Sandimirova 《Petrology》2010,18(6):596-609
Based on the systematic investigation of the geochemical and isotopic (Sr and Nd) characteristics of basic rocks from various
volcanic areas of the Devonian Altai-Sayan rift system, the compositions of mantle magma sources were characterized, and the
geodynamic scenarios of their entrainment into rifting processes were reconstructed. It was found that the titanium-rich basic
rocks (2.5 < TiO2 < 4.2 wt %) of this region are enriched in lithophile trace elements, including the rare earth elements, compared with N-MORB
and are similar in composition to intraplate subalkali basalts of the OIB type. In contrast, moderate-titanium basic rocks
(1.1 < TiO2 < 2.5 wt %) are mainly depleted in the highly charged incompatible elements Th, U, Nb, and Ta (La/Yb = 1.2−2.2) and, to a
lesser extent, in Zr, Hf, and LREE ((La/Yb)N < 7), but are enriched in Ba. With respect to these characteristics, the moderate-titanium basites are similar to rocks formed
in subduction environments. The geochemical parameters of the basites are strongly variable, which probably reflects the heterogeneity
of the mantle sources that contributed to the formation of the rift system. In particular, the most notable variations in
rock composition related to an increase in the contribution of an OIB-type source to magma composition were observed in the
eastern direction, i.e., inland from the paleocontinent margin. The isotopic composition of the basites is relatively stable
within individual rift zones and significantly variable at a comparison of rocks from different zones of the region. Based
on the isotopic characteristics of the rocks, three melt sources were identified. One of them is chemically similar to the
PREMA and is a common component in all observed trends of isotopic variations, irrespective of the position of the particular
assemblage in the structure of the region. This component dominates the composition of the titaniumrich basalts with geochemical
signatures of the derivatives of enriched mantle reservoirs of the E-MORB and OIB types and is considered as a plume source.
Two other isotopic melt sources are related to subduction processes, which is indicated by their dominance during the formation
of the moderate-titanium basalts showing the geochemical signatures (primarily, Ta-Nb depletion) of typical volcanic-arc rocks.
These differences are consistent with the formation of the Altai-Sayan rift system in a complex geodynamic setting, which
developed under the influence of intraplate magma sources (mantle plume) on the region of melt generation in an active continental
margin (subduction zone). 相似文献
5.
I. W. Roxburgh S. V. Vorontsov 《Monthly notices of the Royal Astronomical Society》2007,379(2):801-806
The rapid variation of density with depth in a stellar core can distort acoustic wave propagation in stellar interiors, producing a reflected wave. The reflectivity can come from a rapid density change at the boundary of a convective core, or from the steep gradients established in a radiative core during chemical evolution. We analyse this wave reflection within the framework of wave scattering theory, and address the question of the detectability of the reflected wave in the autocorrelation function of stellar p-mode measurements. 相似文献
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V. V. Yarmolyuk D. A. Lykhin T. N. Shuriga A. A. Vorontsov A. M. Sugorakova 《Geology of Ore Deposits》2011,53(5):390-400
The Snezhnoe phenakite-beryl deposit is one of the highest-grade deposits in the Altai-Sayan beryllium province. This deposit
is spatially associated with the alkali granite of the Ognit Complex and localized in the apical part of the granitic pluton.
The trace element composition of granite, as well as of Be and Ta-Nb ores was studied. The Rb-Sr age of Be mineralization
estimated at 305 Ma is consistent with the time of formation of numerous rare-metal alkali granitic plutons in the Eastern
Sayan and the eastern Tuva. The region of these granitic plutons is outlined as the Late Paleozoic East Sayan rare-metal metallogenic
zone specialized for Nb, Ta, Be, Li, Zr, Th, and REE mineralization. The East Sayan zone is localized in the marginal part
of the Barguzin igneous province and is similar to the marginal zone of this province in composition of igneous associations
and metallogenic specialization. The formation of the Barguzin igneous province and the East Sayan metallogenic zone is related
to the evolution of the Late Carboniferous-Early Permian mantle plume. 相似文献
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The type of convergent boundaries forming in the area of mantle plumes is considered. These convergent boundaries (West Pacific type) are characteristic of the western margin of the Pacific. West Pacific-type boundaries are a regular succession of structures from ocean to continent: island arcs, marginal basins, rift basins, and associated OIB-type volcanics at the continental edge. The convergence zones are up to a thousand kilometers wide.Studies of the history of the part of the Central Asian Fold Belt forming the folded periphery of the Siberian continent have shown that the continent drifted above the African plume or corresponding low-velocity mantle province for most of the Phanerozoic (up to the Early Mesozoic inclusive). This fact determined the West Pacific type of convergent boundaries for the accretionary structures of the Central Asian Fold Belt. The drift of Siberia from African to Pacific province in the Late Cenozoic determined the structure and development of the convergent boundary in the western Pacific, including extensive intraplate magmatism in continental Asia in the Late Mesozoic and Cenozoic. 相似文献
10.
S. V. Vorontsov 《Monthly notices of the Royal Astronomical Society》2007,378(4):1499-1506
Accurate measurements of solar p-mode frequencies and frequency splittings at high degree l require an adequate theoretical knowledge of the effects of mode coupling, induced by the variation with latitude of the angular velocity of the solar internal rotation. Earlier results for expansion coefficients of composite solutions (coupling coefficients) are due to Woodard. In this paper, the analysis is extended to allow for the dependence of the differential rotation on depth, and the result is expressed in terms of measurable quantities (the rotational splitting coefficients), which makes it convenient for diagnostic purposes. The analysis is based on the approach of quasi-degenerate perturbation theory, and is extended further to address possible effects of mode coupling in the observational line profiles. It is shown, using approximations applicable at high degree l , that the expected line profiles of composite modes in the observational power spectra are not distorted by mode coupling. 相似文献