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941.
The presence of ultrahigh-energy (UHE) cosmic rays results in an increase in the degree of ionization in the post-recombination Universe, which stimulates the efficiency of the production of H2 molecules and the formation of the first stellar objects. As a result, the onset of the formation of the first stars is shifted to higher redshifts, and the masses of the first stellar systems decrease. As a consequence, a sufficient increase in the ionizing radiation providing the reionization of the Universe can occur. We discuss the possible observational manifestations of these effects and their dependence on the parameters of UHE cosmic rays. 相似文献
942.
V. E. Strikha 《Geochemistry International》2006,44(8):791-807
Geochemical and isotopic data were used for a comparative analysis of Late Mesozoic (150–120 Ma) granitoids in various geological
structures of the upper Amur area. The granitoids are metaluminous high-potassic I-type rocks of the magnetite series. They
have variable alkalinity and consist of the monzonite-granite and granosyenite-granite associations. The monzonite-granite
association consists of calc-alkaline granitoids of normal alkalinity belonging to the Umlekan-Ogodzhinskaya volcanic-plutonic
zone and the Tynda-Bakaran Complex of the Stanovoy terrane. The rocks are characterized by negative anomalies of U, Ta, Nd,
Hf, and Ti (in patterns normalized to the primitive mantle), with Eu anomalies pronounced weakly in the granodiorites and
quartz and monzodiorites and more clearly in the granites: Eu/Eu* = 0.37–0.95, and (La/Yb)n = 7–24, Tbn/Ybn = 1.4–3.2. The granosyenite-granite association comprises of moderately alkaline rocks, which are subdivided into three groups
according to their geochemistry. The first group consists of phase-I granosyenites of the Uskalinskii Massif of the Umlekan-Ogodzhinskaya
zone with the highest concentrations of Sc, V, Cr, Co, Ni, Cu, Cs, Rb, Sr, Y, Zr, Yb, and Th; negative anomalies at Ba, Ta,
Sr, and Hf; Eu/Eu* = 0.50–0.58, (La/Yb)n = 15–16, and Tbn/Ybn = 1.8. The second group comprises of moderately alkaline granitoids of the Umlekan-Ogodzhinskaya zone and the Khaiktinskii
Complex of the Baikal-Vitim superterrane. Geochemically, the granitoids of this group are generally similar to the monzodiorite-granite
association and differ from it in having lower concentrations of REE and Y, Eu/Eu* = 6.2–1.0, (La/Yb)n = 28–63, and Tbn/Ybn = 2.1–4.5. The third group consists of granitoids of the Chubachinskii Complex of the Stanovoi terrane, which typically show
negative Cs, Rb, Th, U, Ta, Hf, and Ti anomalies; the lowest concentrations of V, Cr, Co, and Ni; and the highest contents
of Sr. The granosyenites of the first phase display clearly pronounced negative Eu anomalies (Eu/Eu* = 0.53–0.68), (La/Yb)n = 7–24, and Tbn/Ybn = 0.8–2.0. The granitoids of the second phase have (La/Yb)n = 51–84, no Eu anomalies, or very weak Eu anomalies (Eu/Eu* = 0.97–1.23). The silica-oversaturated leucogranites of the third
phase are characterized by elevated concentrations of REE, clearly pronounced Eu anomalies (Eu/Eu* = 0.48), and flat REE patterns
(Tbn/Ybn = 1.3). The diversity of the granitoids is demonstrated to have been caused largely by the composition of the Precambrian
source, which was isotopically heterogeneous. The rocks of the monzodiorite-granite association and first-group granosyenites
of the granosyenite-granite association of the Tynda-Bakaran Complex were supposedly derived from garnet-bearing biotite amphibolites.
In contrast to these rocks, the source of the second-group granites of the granosyenite-granite association was of mixed amphibolite-metagraywacke
composition. The third-group of granitoids were melted out of Early Proterozoic crustal feldspar-rich granulites of variable
basicity, with minor amounts of Archean crustal material. The granitoids were emplaced in a collisional environment, perhaps,
during the collision of the Amur superterrane and Siberian craton. This makes it possible to consider these rocks as components
of a single continental volcanic-plutonic belt.
Original Russian Text ? V.E. Strikha, 2006, published in Geokhimiya, 2006, No. 8, pp. 855–872. 相似文献
943.
An 11-month observation of dissolved and particulate organic matter, chlorophyll a(Chl a), C18 Sep-Pak extractable hydrophobic dissolved organic matter (hDOM) fraction and associated dissolved trace metals (Cd,
Cu, V, Co, Ni, Mo, U) was performed in the Lot–Garonne River system. This system includes the Riou Mort, the Lot River and
the downstream reaches of the Garonne River and represents the fluvial transport path of trace metals between the major point
source of polymetallic pollution, located in the Riou Mort watershed and the Gironde estuary. Spatial and temporal variations
of dissolved and particulate organic carbon and Chl areflect the presence of different types of organic matter and their relation with the hDOM fraction. Maximum Chl a/POC ratios (up to 0.03), indicate intense phytoplankton production from March to May. In the Lot River (Temple), DOC and
POC concentrations were clearly higher and mean Chl a concentration (2.8 mg g−1) was about three times higher than those of the other sites. High Chl a/POC ratios suggest high phytoplankton activity with maxima in spring and late summer. In the Riou Mort River, very high POC
concentrations of up to 40 (mean: 20) occurred, whereas Chl a concentrations were relatively low indicating low phytoplankton activity. High, strongly variable DOC and POC concentrations
suggest important natural (Carboniferous soils, forests) or anthropogenic (e.g., former coal mines, waste areas, agriculture,
sewage) carbon sources within the small Riou Mort watershed. Despite high DOC concentrations in the Riou Mort River, hDOM
metal fractions were generally lower than those at the other sites. The general order of decreasing binding strength between
metals and the organic hydrophobic phase (Cu, U > Co, Ni > V, Mo > Cd) at all four sites was in good agreement with the Irving–William
series of transition element affinity towards organic ligands. Accordingly, the role of the hydrophobic phase in dissolved
Cd transport appeared to be negligible, whereas the hDOM–Cu fraction strongly contributed to dissolved Cu transport. 相似文献
944.
The aim of this work is the joint application and integration of non-invasive geoelectrical methods for studying the landfill of Savoia di Lucania (Southern Italy). This landfill for its engineering features and small dimensions (70 m × 30 m × 6 m) represents an optimal test site to assess a geophysical survey protocol for municipal solid waste landfills investigation and monitoring. The landfill of Savoia di Lucania has been built with a reinforced concrete material and coated with a high-density polyethylene (HDPE) liner. Three electrical resistivity tomographies (ERT), two self-potential (SP) map surveys and one induced polarization (IP) section have been performed, both in the surrounding area and inside the waste landfill. The geophysical investigations have well defined some buried boundaries of the landfill basin and localized the leachate accumulation zones inside the dumpsite. Comparison of our results with other engineering and geological investigations could be the key for evaluating the integrity of the HDPE liner. Finally, the joint use of the ERT, IP and SP methods seems to be a promising tool for studying and designing new monitoring systems able to perform a time-lapse analysis of waste landfill geometry and integrity. 相似文献
945.
A. M. Larin E. B. Sal’nikova A. B. Kotov L. B. Makar’ev S. Z. Yakovleva V. P. Kovach 《Stratigraphy and Geological Correlation》2006,14(5):463-474
Early Proterozoic granitoids are of a limited occurrence in the Baikal fold area being confined here exclusively to an arcuate belt delineating the outer contour of Baikalides, where rocks of the Early Precambrian basement are exposed. Geochronological and geochemical study of the Kevakta granite massif and Nichatka complex showed that their origin was related with different stages of geological evolution of the Baikal fold area that progressed in diverse geodynamic environments. The Nichatka complex of syncollision granites was emplaced 1908 ± 5 Ma ago, when the Aldan-Olekma microplate collided with the Nechera terrane. Granites of the Kevakta massif (1846 ± 8 Ma) belong to the South Siberian postcollision magmatic belt that developed since ~1.9 Ga during successive accretion of microplates, continental blocks and island arcs to the Siberian craton. In age and other characteristics, these granites sharply differ from granitoids of the Chuya complex they have been formerly attributed to. Accordingly, it is suggested to divide the former association of granitoids into the Chuya complex proper of diorite-granodiorite association ~2.02 Ga old (Neymark et al., 1998) with geochemical characteristics of island-arc granitoids and the Chuya-Kodar complex of postcollision S-type granitoids 1.85 Ga old. The Early Proterozoic evolution of the Baikal fold area and junction zone with Aldan shield lasted about 170 m.y. that is comparable with development periods of analogous structures in other regions of the world. 相似文献
946.
947.
E. M. Chamorro Pérez I. Daniel J.-C. Chervin P. Dumas J. D. Bass T. Inoue 《Physics and Chemistry of Minerals》2006,33(7):502-510
High-pressure synchrotron infrared (IR) absorption spectra were collected between 650 and 4,000 cm−1 at ambient temperature for hydrous Mg-ringwoodite (γ-Mg2SiO4) up to 30 GPa. The main feature in the OH− stretching region is an extremely broad band centred at 3,150 cm−1. The hydrogen bond is strong for most protons and the most probable site for protonation is the tetrahedral edge. With increasing pressure, this band shifts downward while decreasing its integrated intensity until disappearance at a pressure of 25 GPa. Only one band at 2,450 cm−1 and an absorption plateau persist with a maximum wavenumber of 3,800 cm−1. This behaviour is reversible upon pressure release. We interpret this as a second-order phase transition occurring in hydrated Mg-ringwoodite at high pressure (beyond ∼ 25 GPa). This result is compatible with the observation by Kleppe et al. (Phys Chem Miner 29:473–476, 2002a) who suggested the presence of Si–O–Si linkages and/or partial increase in the coordination of Si. Beyond the phase transition, the protons are delocalized and their environment on the ringwoodite structure is probably quite different from that at low pressure. Data obtained in situ at high pressures and temperatures are needed to better understand the effect of protonation on the structure and to better constrain this phase transition. 相似文献
948.
Magma mingling: Tectonic and geodynamic implications 总被引:2,自引:0,他引:2
An attempt is made to consider the tectonic and geodynamic implications of the mingling of mafic and felsic magmas, particularly, the relationships between mafic and felsic igneous rocks in composite dikes and plutons. Magma mingling develops in suprasubduction, intraplate, and collisional settings. The attributes typical of each type of mingling are discussed with special emphasis on the magma mingling of the collisional type, which is related to synmetamorphic shearing and may be regarded as a direct indicator of synorogenic collapse of collisional structural features. This phenomenon is exemplified in the Ol’khon collisional system in Siberia. 相似文献
949.
Coastal fortifications in South East England have been continuously built and rebuilt over the centuries according to the ebb and flow of politics in Europe. This paper covers an extensive historical period from the influx of the Romans to the present day, detailing how landslides and coastal erosion have affected the numerous constructions along this stretch of coastline. Principal landslide-prone strata form extensive sections of this part of the coast with the tendency to be weak and highly susceptible to marine attack and cliff retreat. Fortifications have been built out of necessity in strategic positions without full consideration of the ground upon which they have been constructed. The continual construction of fortifications along this section of coastline constitutes an unparalleled archaeological record, but it is one that is under continuous threat from coastal erosion and landsliding. 相似文献
950.
Mercury speciation and mobilization in contaminated soils of the Valle del Azogue Hg mine (SE,Spain) 总被引:1,自引:0,他引:1
Hg mobilization from contaminated soils and mine wastes was the source of environmental contamination in the Valle del Azogue
mining area. We researched solid-phase speciation and aqueous mobility of Hg through Scanning electron microscopy-energy dispersive
X-ray spectroscopy and electron probe microanalysis analysis, solid-phase-Hg-thermo-desorption (SPTD) and laboratory column
experiments. We found that in contaminated soils and mine wastes, the predominant Hg species was cinnabar (HgS), mainly formed
from the weathering of Hg-rich pyrite, and metallic Hg (0) in the matrix, whereas in calcines and tailings the dominant species
was metallic Hg (0). The mobilization of Hg in the aqueous phase seems to have originated from the dissolution of elemental
Hg (0) present in soils and wastes, reaching concentrations of up to 67 μg l−1, and showing a higher long-term environmental potential risk, in addition to atmospheric emissions. 相似文献