Model studies of physical properties of mineral matter in high-pressure-temperature experiments     

T.S. Lebedev 《Physics of the Earth and Planetary Interiors》1980,23(4):292-303

Data derived from experimental model studies of the elastic properties of rocks of various compositions under high pressures and temperatures inherent in the thermobaric regimes of the upper lithosphere are generalized. The geophysical implications of the data are discussed. New results of experimental studies of the electrical characteristics of metamorphic rocks of ultrabasic composition at P ? 20 kbar and T ? 1000°C are presented.  相似文献   

Radiation from flexural vibrations of the baseplate and their effect on the accuracy of traveltime measurements     

A. Lebedev  I. Beresnev 《Geophysical Prospecting》2005,53(4):543-555

We analyse the problem of radiation of seismic waves by a vibroseis source when the baseplate is subject to flexure. A theoretical model is proposed to account for baseplate flexure, generalizing the well‐known model of the vibroseis source of Sallas and Weber, which was developed for a rigid plate. Using the model proposed, we analyse the effect of flexure on the properties of seismic waves. We show that the flexure does not contribute to the far‐field and mainly affects the readings of the reference accelerometer that is used to measure the force applied to the ground; these readings generally become dependent on the location of the sensor on the plate. For muddy and sandy soils, the effect of flexure on baseplate‐acceleration measurements is nonetheless pronounced at the high end of the vibroseis frequency band only (～100 Hz), and is negligible at all frequencies for stiffer soils. The corresponding phase lags introduced by the flexural vibrations at high frequencies lead to errors in the traveltime measurements (through the cross‐correlation function) of up to 0.6 ms for muddy soils and less for denser soils. We show the existence of an optimal position of the reference sensor on the baseplate and also propose a general method of eliminating the phase lag due to the baseplate flexure in acceleration measurements.  相似文献   

Centennial-to-millennial fluctuations in July temperatures in North Finland as recorded by timberline tree rings of Scots pine   总被引：1，自引：0，他引：1  

Maxim Ogurtsov  Markus Lindholm 《Quaternary Research》2005,63(2):182-188

A tree-ring proxy of summer temperature anomalies for northern Finland for the past 7500 yr was analyzed using Fourier spectrum and wavelet approaches. Multicentennial (250-450 yr) variability is present in the proxy record during most of the time range. This variability is suggested to reflect low-frequency variability in the North Atlantic Oscillation. Century-scale (90-130 yr) variation is another important feature of the tree-ring proxy data during the Holocene and may be attributed to Glessberg solar activity variations. In addition, an approximately 2000-yr quasi-period is found in this temperature proxy data, similar to the millennial-scale variability, present in many climate records from the North Atlantic region. The results point to the importance of multiple forcings underlying significant Holocene climatic fluctuations.  相似文献   

K-Ar dating of quaternary volcanics: Methodology and interpretation of results     

I. V. Chernyshev  V. A. Lebedev  M. M. Arakelyants 《Petrology》2006,14(1):62-80

The K-Ar method and its modifications play a unique role in the geochronology of young volcanic rocks, which has important fundamental and economic aspects. This method provides an opportunity for dating Quaternary rocks, from the oldest (1–2 Ma) to the most recent ones (<30 ka). This paper discusses physical and geochemical prerequisites for the use of the K-Ar method in the solution of this problem. The key factor providing favorable proportions of radiogenic and nonradiogenic ⁴⁰Ar for the K-Ar system in volcanic rocks is the low solubility of argon (0.n–0.0n ppb) in silicate melts and crystallizing rocks and minerals. The sources and controlling factors of errors in the K-Ar dating of young rocks were evaluated in detail. The main analytical problem in the K-Ar dating of young rocks is concerned with the conditions and methods of measurements of very low (0.0n–0.00n ppb) contents of radiogenic ⁴⁰Ar accompanied by much higher (by a factor of 3–10 or even more) contents of nonradiogenic ⁴⁰Ar. The main stages in the development of the K-Ar method in Russia and other countries that provided a solution to this problem are described. We describe the analytical mass spectrometer system and method designed in the Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences, which allowed us to carry out for the first time in Russia systematic studies on the geochronology of Quaternary volcanics up to late Pleistocene-Holocene age. The main characteristics of the method are the absolute sensitivity of measurements (5 × 10^?3 A/Torr) and background signal levels for argon isotopes (3 × 10^?3 ng ⁴⁰Ar and 1 × 10^?5 ng ³⁶Ar). The problems of excess radiogenic argon and variations in the initial ⁴⁰Ar/³⁶Ar ratio in young volcanics are discussed. The results of an investigation of the distribution of K-Ar isotopes among various constituents of young volcanics and the corresponding approach to the choice of material (geochronometer) for analysis are presented. This approach is illustrated by the example of geochronological results for three volcanic centers of the Caucasus differing in the time of occurrence and duration of the active phase: Elbrus, Samsari, and Aragats. A tentative regional time scale was proposed for Neogene-Quaternary magmatic events. This scale generalized the available data for the Greater and Lesser Caucasus and embraces the period from the late Miocene (8.5 Ma) to the late Neopleistocene-Holocene (<35 ka). An interesting feature of the young magmatism of the Caucasus is the synchronous occurrence of distinctive types of volcanic activity in particular volcanic areas. An important prognostic aspect related to the proposed time scale of the young magmatism of the Caucasus is the evidence that the most recent stage of volcanic activity, the youngest occurrences of which were dated at a few thousands to tens of thousands of years, is not yet finished.  相似文献   

Chronicle of the Sixth Conference “Physicochemical and Petrophysical Studies in Earth Sciences” (Moscow,October 3–5, 2005)     

E. B. Lebedev  Yu. S. Genshaft  A. V. Zharikov 《Geochemistry International》2006,44(12):1250-1256

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K-Ar age and Sr-Nd characteristics of subalkali basalts in the Central Georgian Neovolcanic region (Greater Caucasus)     

V. A. Lebedev  I. V. Chernyshev  A. V. Chugaev  O. Z. Dudauri  G. T. Vashakidze 《Doklady Earth Sciences》2006,408(4):657-661

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A step ahead of time: design, allocation and preservation of private open space in the 1920s––the case of a garden suburb in Israel     

Naftaly Goldshleger  Irit Amit-Cohen  Maxim Shoshany 《GeoJournal》2006,67(1):57-69

In the course of the last 50 years, the landscape in Israel has undergone major changes, due to accelerated urbanization following population growth. These processes had increased the pressure on the open land, especially in areas of urban expansion. Recognizing that Governments and local Municipalities had failed to stop the consequent loss of public open spaces, not only in Israel but worldwide, had lead recently many communities to adopt new solutions in the form of private open spaces. In this article we present a “step ahead of time”: a case of privately owned land, set aside as public green area during the 1920s in a neighborhood called “Ahuza Herbert Samuel” (Herbert Samuel, the first High Commissioner of Palestine under the British Mandate), located in the City of Haifa, in Northern Israel. The roots of this unique phenomenon during the 1920s could be linked to several sources of influence: Colonial town planning concepts, the emergence of garden cities and garden suburbs and most importantly to concepts brought in by the leaders of the immigrant community coming from Rumania. Photogrammetric and GIS analysis of this phenomenon had revealed that it had prevailed throughout 75 years of constant and massive increase in the demand for built-up areas in Israel in general and in Ahuza neighborhood in particular. The success in preserving these open areas gains current relevance in view of recent trends in the Western world of allocating privately owned green areas for public use.  相似文献   

Reconnaissance paleomagnetism of Late Triassic blocks, Kuyul region, Northern Kamchatka Peninsula, Russia     

William Harbert  Sergei Sokolov  Maxim Alexutin  Kirill Krylov  Vladimir Grigoriev  Alexander Heiphetz   《Tectonophysics》2003,361(3-4):215-227

The northernmost Kamchatka Peninsula is located along the northwestern margin of the Bering Sea and consists of complexly deformed accreted terranes. Progressing inland from the northwestern Bering Sea, the Olyutorskiy, Ukelayat and Koryak superterranes (OLY, UKL and KOR) are crossed. These terranes were accreted to the backstop Okhotsk-Chukotsk volcanic-plutonic belt (OChVB) in northernmost Kamchatka. A sedimentary sequence of Albian to Maastrichtian age overlaps the terranes and units of the Koryak superterrane, and constrains their accretion time. A paleomagnetic study of blocks within the Kuyul (KUY) terrane of the Koryak superterrane was completed at two localities (Camp 2: λ=61.83°N, φ=165.83°E and Camp 3: λ=61.67°N, φ=164.75°E). At both localities, paleomagnetic samples were collected from Late Triassic (225–208 Ma) limestone blocks (2–10 m in outcrop height) within a melange zone. Although weak in remanent magnetization, two components of remanent magnetization were observed during stepwise thermal demagnetization at 32 sites. The A component of magnetization was observed between room temperature and approximately 250 °C. This magnetic component is always of downward directed inclination and shows the best grouping at relatively low degrees of unfolding. Using McFadden–Reid inclination-only statistics and averaging all site means, the resulting A component mean is I_opt=60.3°, I₉₅=5.0° and n=36 (sites). The B magnetic component is observed up to 565 °C, at which temperature, most samples have no measurable remanent magnetization, or growth of magnetic minerals has disrupted the thermal demagnetization process. Combining sites with Fisher estimates of kappa (k-value)≥13 and n (sites)≥3, where bedding orientation differs within a block, most of these sites show the best grouping of B component directions at 100% unfolding, and two of the blocks display remanent magnetizations of both upward and downward directed magnetic inclination. Combining sites with Fisher estimates of kappa (k-value)≥13 and n (sites)≥3, the resulting overall B component paleolatitude and associated uncertainty are λ_obs=30.4°N or S, λ₉₅=8.9° and n=19 (sites). When compared with the expected North America paleolatitude of λ_{APWP expected}=57.9°N, our data support a model in which blocks within the Koryak superterrane are allochthonous and far travelled.  相似文献   

Relationship between shell weight and cadmium content in whole digestive gland of the Japanese scallop Patinopecten yessoensis (Jay)     

Belcheva NN  Zakhartsev M  Silina AV  Slinko EN  Chelomin VP 《Marine environmental research》2006,61(4):396-409

Seasonal and age-specific variations of cadmium (Cd) concentration in the digestive gland were investigated in the Japanese scallop Patinopecten yessoensis from Peter the Great Bay, Sea of Japan, with different degrees of Cd pollution. The seasonal changes in Cd concentrations of the digestive gland were inversely proportional to the dry weight of the gland. Concentrations of Cd and total Cd content (mug Cd per organ) increased with age (age-specific) to the same extent in contaminated and uncontaminated areas. There was also a strong positive correlation between Cd content in the whole digestive gland and shell weight and it is proposed that this relationship can be used as a new criterion for comparative evaluation of Cd levels in scallops from different areas We hypothesize that Cd is uptaken into scallops in proportion to the amount of calcium that absorbed through ion channels, and in addition, Cd in the digestive gland is in immobile forms (e.g. metal-rich granules) that accumulate with age. Moderate environmental pollution has no effect on the relationship between Cd content and shell size and the observed decrease in growth performance of the scallops from polluted areas may be due to other factors.  相似文献   

Across‐axis variations in petrophysical properties of the North Porcupine Basin,offshore Ireland: New insights from long‐streamer traveltime tomography     

Manel Prada  Franois Lavou  Muhammad Mudasar Saqab  Brian M. O'Reilly  Sergei Lebedev  John J. Walsh  Conrad Childs 《Basin Research》2019,31(1):59-76

The Porcupine Basin is a Mesozoic failed rift located in the North Atlantic margin, SW of Ireland, in which a postrift phase of extensional faulting and reactivation of synrift faults occurred during the Mid–Late Eocene. Fault zones are known to act as either conduits or barriers for fluid flow and to contribute to overpressure. Yet, little is known about the distribution of fluids and their relation to the tectono‐stratigraphic architecture of the Porcupine Basin. One way to tackle this aspect is by assessing seismic (V_p) and petrophysical (e.g., porosity) properties of the basin stratigraphy. Here, we use for the first time in the Porcupine Basin 10‐km‐long‐streamer data to perform traveltime tomography of first arrivals and retrieve the 2D V_p structure of the postrift sequence along a ~130‐km‐long EW profile across the northern Porcupine Basin. A new V_p–density relationship is derived from the exploration wells tied to the seismic line to estimate density and bulk porosity of the Cenozoic postrift sequence from the tomographic result. The V_p model covers the shallowest 4 km of the basin and reveals a steeper vertical velocity gradient in the centre of the basin than in the flanks. This variation together with a relatively thick Neogene and Quaternary sediment accumulation in the centre of the basin suggests higher overburden pressure and compaction compared to the margins, implying fluid flow towards the edges of the basin driven by differential compaction. The V_p model also reveals two prominent subvertical low‐velocity bodies on the western margin of the basin. The tomographic model in combination with the time‐migrated seismic section shows that whereas the first anomaly spatially coincides with the western basin‐bounding fault, the second body occurs within the hangingwall of the fault, where no major faulting is observed. Porosity estimates suggest that this latter anomaly indicates pore overpressure of sandier Early–Mid Eocene units. Lithological well control together with fault displacement analysis suggests that the western basin‐bounding fault can act as a hydraulic barrier for fluids migrating from the centre of the basin towards its flanks, favouring fluid compartmentalization and overpressure of sandier units of its hangingwall.  相似文献