Evolution of stress fields in the Por’ya Guba dike field (Kandalaksha Gulf, White Sea)     

T. I. Vasil’eva  E. S. Przhiyalgovskii 《Geotectonics》2006,40(1):53-63

The tectonic evolution of the Por’ya Guba segment of the White Sea Rift System began in the late Paleoproterozoic, i.e., soon after completion of the Svecofennian collision. The fracture system that controlled localization of the lamproite dike complex was formed under conditions of horizontal compression combined with shear. Subsequently, this system predetermined the location of a rift-graben segment that formed as a result of simple shear. The reactivation of the rift system in the Middle Paleozoic proceeded in two stages. The first stage, when strike-slip movements along previously formed faults predominated, resulted in formation of quartz-carbonate veins bearing base-metal mineralization. The veins that filled the shear fractures opened owing to local reorientation of the stress field. The second stage fitted the transtension conditions, and the Late Devonian alkaline ultramafic dikes of this stage introded into the already existing fracture system, which was oriented at a roughly right angle to the predominant stress orientation.  相似文献   

International Viewpoint and News     

Philip E. LaMoreaux  Jörg Matschullat 《Environmental Geology》2006,51(1):171-171

  相似文献   

Detection of spectral variability of the optical component of the IR source IRAS 20508+2011     

V. G. Klochkova  V. E. Panchuk  N. S. Tavolzhanskaya  G. Zhao 《Astronomy Reports》2006,50(3):232-248

Our high-resolution spectral observations have revealed variability of the optical spectrum of the cool star identified with the IR source IRAS 20508+2011. We measured the equivalent widths of numerous absorption lines of neutral atoms and ions at wavelengths 4300–7930 Å, along with the corresponding radial velocities. Over the four years of our observations, the radial velocity derived from photospheric absorption lines varied in the interval V _r⊙ = 15–30 km/s. In the same period, the Hα profile varied from being an intense bell-shaped emission line with a small amount of core absorption to displaying two-peaked emission with a central absorption feature below the continuum level. At all but one epoch, the positions of the metallic photospheric lines were systematically shifted relative to the Hα emission: ΔV _r = V _r(met) ? V _r(Hα, emis) ≈ ?23 km/s. The Na D doublet displayed a complex profile with broad (half-width ≈ 120 km/s) emission and photospheric absorption, as well as an interstellar component. We used model atmospheres to determine the physical parameters and chemical composition of the star’s atmosphere: T _eff = 4800 K, log g = 1.5, ξ_t = 4.0 km/s. The metallicity of the star differs little from the solar value: [Fe/H]_⊙ = ?0.36. We detected overabundances of oxygen [O/Fe]_⊙ = +1.79 (with the ratio [C/O] ≈ ?0.9), and α-process elements, as well as a deficit of heavy metals. The entire set of the star’s parameters suggests that the optical component of IRAS 20508+2011 is an “O-rich” AGB star with luminosity M _v ≈ ?3^m that is close to its evolutionary transition to the post-AGB stage.  相似文献   

Channel water balance of the Lena River Cascade system     

N. E. Kosheleva  E. B. Karabanov  N. S. Kasimov  A. G. Kositskii  V. A. Bychinskii  D. Williams  S. Armstrong 《Doklady Earth Sciences》2006,411(9):1452-1456

  相似文献   

The early cretaceous collisional granite-leucogranite association of the Stanovoi Terrane: New geochronological, geochemical, and isotope-geochemical data     

V. E. Strikha  N. I. Rodionov 《Doklady Earth Sciences》2006,406(1):107-111

  相似文献   

Hydrogeology of thermal waters in Viterbo area, central Italy     

V. Piscopo  M. Barbieri  V. Monetti  G. Pagano  S. Pistoni  E. Ruggi  D. Stanzione 《Hydrogeology Journal》2006,14(8):1508-1521

A conceptual hydrogeological model of the Viterbo thermal area (central Italy) has been developed. Though numerous studies have been conducted on its geological, geochemical and geothermal features, there is no generalized picture defining the origin and yield of the hydrothermal system. These latter aspects have therefore become the objectives of this research, which is based on new hydrogeological and geochemical investigations. The geological setting results in the coexistence of overlapped interacting aquifers. The shallow volcanic aquifer, characterized by fresh waters, is fed from the area around the Cimini Mountains and is limited at its base by the semiconfining marly-calcareous-arenaceous complex and low-permeability clays. To the west of Viterbo, vertical upflows of thermal waters of the sulphate-chloride-alkaline-earth type with higher gas contents, are due to the locally uplifted carbonate reservoir, the reduced thickness of the semiconfining layer and the high local geothermal gradient. The hot waters (30–60°C) are the result of deep circulation within the carbonate rocks (0.5–1.8 km) and have the same recharge area as the volcanic aquifer. The upward flow in the Viterbo thermal area is at least 0.1 m³/s. This flow feeds springs and deep wells, also recharging the volcanic aquifer from below.  相似文献   

New data on hydrocarbons in auriferous conglomerates of the Witwatersrand ore region, Republic of South Africa     

A. A. Kremenetsky  I. E. Maksimyuk 《Lithology and Mineral Resources》2006,41(2):102-116

Genesis of deposits in the world’s largest Witwatersrand auriferous region (South Africa) remains a debatable issue over several decades. Based on geological and mineralogical-geochemical investigations, we previously proposed a sedimentary-exhalative hypothesis for its origin. In the present communication, we have attempted to develop and scrutinize this concept based on the study of organic matter in ore and nonore conglomerates, quartz in conglomerate pebbles, and fluid inclusions in quartz from pebbles and cement of ore and nonore conglomerates.  相似文献   

Different-depth xenoliths from Devonian intrusions of the Kola peninsula: Key to deciphering paleogeodynamic settings of alkaline magmatism     

A. S. Baluev  E. N. Terekhov 《Doklady Earth Sciences》2006,407(2):167-171

  相似文献   

Lower Miocene sediments of central and western Ciscaucasia     

A. S. Stolyarov  E. I. Ivleva 《Lithology and Mineral Resources》2006,41(2):174-186

The composition, structure, and geochemical properties of the thickest, relatively deep-water Lower Miocene sediments developed in western Ciscaucasia are considered. Of particular interest are materials from the Kuban superdeep borehole SG-12000 that recovered the uppermost layers of the Maikop Group at 3148–3961 m in the central Indol-Kuban Trough west of Krasnodar. However, the borehole did not penetrate the whole Lower Miocene section of the Maikop Group. Therefore, characteristics of the Maikop Group are supplemented with new materials from several other boreholes drilled in the eastern Kuban region. Thus, the typical (reference) Lower Miocene section of central and western Ciscaucasia has been sufficiently well described.  相似文献   

Equation of state of MgGeO3 perovskite to 65 GPa: comparison with the post-perovskite phase     

C. E. Runge  A. Kubo  B. Kiefer  Y. Meng  V. B. Prakapenka  G. Shen  R. J. Cava  T. S. Duffy 《Physics and Chemistry of Minerals》2006,33(10):699-709

The equation of state of MgGeO₃ perovskite was determined between 25 and 66 GPa using synchrotron X-ray diffraction with the laser-heated diamond anvil cell. The data were fit to a third-order Birch–Murnaghan equation of state and yielded a zero-pressure volume (V ₀) of 182.2 ± 0.3 Å³ and bulk modulus (K ₀) of 229 ± 3 GPa, with the pressure derivative (K′₀ = (?K ₀/?P) _T ) fixed at 3.7. Differential stresses were evaluated using lattice strain theory and found to be typically less than about 1.5 GPa. Theoretical calculations were also carried out using density functional theory from 0 to 205 GPa. The equation of state parameters from theory (V ₀ = 180.2 Å³, K ₀ = 221.3 GPa, and K′₀ = 3.90) are in agreement with experiment, although theoretically calculated volumes are systematically lower than experiment. The properties of the perovskite phase were compared to MgGeO₃ post-perovskite phase near the observed phase transition pressure (～65 GPa). Across the transition, the density increased by 2.0(0.7)%. This is in excellent agreement with the theoretically determined density change of 1.9%; however both values are larger than those for the (Mg,Fe)SiO₃ phase transition. The bulk sound velocity change across the transition is small and is likely to be negative [?0.5(1.6)% from experiment and ?1.2% from theory]. These results are similar to previous findings for the (Mg,Fe)SiO₃ system. A linearized Birch–Murnaghan equation of state fit to each axis yielded zero-pressure compressibilities of 0.0022, 0.0009, and 0.0016 GPa^?1 for the a, b, and c axis, respectively. Magnesium germanate appears to be a good analog system for studying the properties of the perovskite and post-perovskite phases in silicates.  相似文献