Metamafic rocks of the Tana Belt, Kola Peninsula: Isotopic age and PT conditions     

L. L. Perchuk  J. D. Kramers  V. O. Yapaskurt  A. V. Krotov 《Doklady Earth Sciences》2006,408(4):623-626

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Catastrophic debris flows near Machu Picchu village (Aguas Calientes), Peru   总被引：2，自引：0，他引：2  

V. Vilímek  J. Klimeš  J. Vlcko  R. Carreño 《Environmental Geology》2006,50(7):1041-1052

Slope movements together with intensive river erosion and the following accumulation are the leading processes in the landscape evolution in the area of Machu Picchu village (former Aguas Calientes), which is located close to the Machu Picchu Sanctuary. Debris flows affect not only the bottoms of valleys or canyons, but also debris fans at the termini of the drainage basins, which are heavily inhabited at some places. The most recent event in the Machu Picchu village occurred in April 2004, but several others were documented in a broader area in the last 50 years. The field inspections at Machu Picchu (May and September 2004; June and September 2005) together with oral testimony revealed the nature and behavior of the debris flow. Machu Picchu village can be assessed as a zone with high landslide risk in relation to its urban development. Despite that, the village recorded a rapid growth (threefold population increase) without urban control within the past two decades. Precipitation, which is the main triggering factor of the debris flows, and natural hazard management of the Machu Picchu village are discussed in this paper.  相似文献   

P-T paths and problems of high-temperature polymetamorphism     

L. L. Perchuk  T. V. Gerya  D. D. van Reenen  C. A. Smit 《Petrology》2006,14(2):117-153

Many Precambrian granulite-facies metamorphic complexes contain so-called straight gneisses, which are massive rocks with a clearly pronounced blastomylonitic texture, lineation, and gneissosity. These rocks occur exclusively in high-temperature ductile shear zones, which can develop either during the primary exhumation of rock complexes or during the overprinting by high-temperature dynamometamorphism. The main criterion for distinguishing between these two types of straight gneisses is the configuration of their P-T trajectories, which are recorded in the mineral assemblages in these rocks and their host gneisses. Ductile shear zones developed in Archean granulite gneisses simultaneously with their exhumation, and, hence, their P-T trajectories are segments of decompression and/or isobaric cooling paths. Straight gneisses in Proterozoic polymetamorphic complexes commonly compose high-temperature ductile shear zones overprinted on Archean granulite complexes, and the P-T paths of these rocks are Z-shaped. This means that, at a constant pressure in the middle part of the continental crust, the T _min of the older P-T trajectory corresponded to T _max of the younger trajectory, and often T _max–T _min > 100°C. Such ductile shear zones commonly have a strike-slip morphology and can be easily seen in aerial photographs and discerned during structural geological surveying. These zones can overprint older gneisses without any notable thermal effect on the latter. Relations of this type were identified in the granulite complexes of Limpopo in South Africa, Sharyzhalgai in the southwestern Baikal area, and Lapland in the Kola Peninsula. The results of our research propose a solution for the well-known problem of the significant discrepancies between the isotopic ages in high-temperature-high-pressure complexes and the partial or complete distortion of radiogenic isotopic systems under the effect of a newly inflowing metamorphic fluid. The application of geochronologic techniques to these situations is senseless, and only P-T trajectories provide insight into the actual age relations between the discrete tectono-metamorphic stages. It is thus expedient to conduct not only structural studies of metamorphic complexes but also their detailed petrological examination and the calculation of their P-T paths before geochronologic dating.  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

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Geodynamic setting of gold ore deposits of the neoproterozoic bodaibo trough     

M. I. Kuz&#;min  V. V. Yarmolyuk  A. I. Spiridonov  V. K. Nemerov  A. I. Ivanov  G. L. Mitrofanov 《Doklady Earth Sciences》2006,407(3):397-400

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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

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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   

Isotopic signatures of deposition and transformation of Lower Cambrian saliferous rocks in the Irkutsk Amphitheater: Communication 3. Carbon and oxygen isotopic compositions in carbonates     

V. I. Vinogradov  G. A. Belenitskaya  M. I. Bujakaite  V. N. Kuleshov  M. A. Minaeva  B. G. Pokrovskii 《Lithology and Mineral Resources》2006,41(3):271-279

In previous communications based on the study of sulfur and strontium, we showed that Lower Cambrian rocks of the Irkutsk Amphitheater underwent a significant epigenetic transformation. All postsedimentary alterations of rocks are related to the influence of water solutions that provoke the direct (physical) dissolution of material and its chemical transformation. In particular, an appreciable portion of anhydrites disappeared from the section due to reduction. Probably, these processes took place several times in the past and they are continuing at present. A similar conclusion was deduced from the strontium isotopic composition of carbonate rocks. Their strontium isotopic composition is usually shifted relative to the primary composition, although the prevalence of sulfate and carbonate rocks in the section promotes the stability of strontium isotopic composition with respect to secondary alterations. The carbon isotope system is even more stable due to the abundance of carbonate rocks in the section. This circumstance is probably responsible for the incapacity of isotope data to serve as obvious evidence of the epigenetic transformation of carbonates. The major elements of the evolution of carbon isotope signature could be retained since the sedimentation stage.  相似文献   

Precious metal and telluride mineralogy of large volcanic-hosted massive sulfide deposits in the Urals     

I. V. Vikentyev 《Mineralogy and Petrology》2006,87(3-4):305-326

Summary The study focuses on the mode of occurrence of Au, Ag and Te in ores of the Gaisk, Safyanovsk, Uzelginsk and other volcanic-hosted massive sulfide (VHMS) deposits in the Russian Urals. Minerals containing these elements routinely form fine inclusions within common sulfides (pyrite, chalcopyrite and sphalerite). Gold is mostly concentrated as ‘invisible’ gold within pyrite and chalcopyrite at concentrations of 1–20 ppm. Silver mainly occurs substituted in tennantite (0.1–6 wt.% Ag). In the early stages of mineralization, gold is concentrated into solid solution within the sulfides and does not form discrete minerals. Mineral parageneses identified in the VHMS deposits that contain discrete gold- and gold-bearing minerals, including native gold, other native elements, various tellurides and tennantite, were formed only in the latest stages of mineralization. Secondary hydrothermal stages and local metamorphism of sulfide ores resulted in redistribution of base and precious metals, refining of the common sulfides, the appearance of submicroscopic and microscopic inclusions of Au–Ag alloys (fineness 0.440–0.975) and segregation of trace elements into new, discrete minerals. The latter include Au and Ag compounds combined with Te, Se, Bi and S. Numerous tellurides (altaite, hessite, stützite, petzite, krennerite etc.) are found in the massive sulfide ores of the Urals and appear to be major carriers of gold and PGE in VHMS ores.  相似文献