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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
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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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Watershed morphometric analysis of Wadi Baish Dam catchment area using integrated GIS-based approach
The integration of Remote Sensing (RS) and Geographic Information Systems (GIS) constitutes a powerful tool for the evaluation of watershed morphometric parameters. The benefits of this integration include saving time and effort as well as improving the accuracy of the analysis. Moreover, this technique is appropriate for describing the watershed and its streams. In this study, a detailed morphometric analysis of the Wadi Baish catchment area has been performed using the Shuttle Radar Topography Mission (SRTM). The performed morphometric analysis includes linear, areal, and relief aspects. The results of the morphometric analysis reveal that the catchment can be described as of eighth stream order and consists of an area of 4741.07 km2. Additionally, the basin is characterized by a relatively high mean value of bifurcation (4.012), indicative of the scarcity of permeable rocks with high slope in the area. This value of bifurcation ratio is consistent with the high drainage density value of 2.064 km/km2 and confirms the impermeability of the subsurface material and mountainous relief. The hypsometric integral of the catchment is 47.4%, and the erosion integral of the catchment is 52.6%, both were indications of a mature catchment area. 相似文献
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Corey A Cohn Christopher E Pedigo Shavonne N Hylton Sanford R Simon Martin AA Schoonen 《Geochemical transactions》2009,10(1):8-9
Background
Given the importance of highly reactive oxygen species (hROS) as reactants in a wide range of biological, photochemical, and environmental systems there is an interest in detection and quantification of these species. The extreme reactivity of the hROS, which includes hydroxyl radicals, presents an analytical challenge. 3'-(p-Aminophenyl) fluorescein (APF) is a relatively new probe used for measuring hROS. Here, we further evaluate the use of APF as a method for the detection of hydroxyl radicals in particle suspensions. 相似文献10.
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