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1.
Liparitic volcanism is a typical feature of the orogenic phase giving rise to the Kazakhstan, Middle Asia and Caucasus folded systems. The main characteristics of the liparitic volcanism common to these three regions are the following:
  1. Geo-structural zonation of the volcanic structures.
  2. Dismembered Moho surface within the volcanic structures.
  3. Synchronous, yet independent evolution of liparitic and andesitic volcanisms.
  4. Ignimbritic character of the liparitic volcanism.
  5. Lateral petrochemical zonation with some features common to the liparitic and andesitic rock series.
Geo-structural and petrochemical zonations are likely governed in the regions studied by a deep-seated plutonic body.  相似文献   

2.
The paper gives a summary of geophysical aspects of man-made electromagnetic noise in the Earth as follows:
  • - EM distortion effects of man-made constructions below and over the Earth's surface defined as ‘passive-noise’,
  • - field observation of EM disturbances due to ‘active’ man-made sources,
  • - EM source mechanism of some important active sources from a geophysical point of view,
  • - efforts in order to improve the signal-to noise ratio by instrumental, methodological and dataprocessing ways,
  • - application of man-made EM noise for geophysical prospecting.
  • The paper is based on world-wide EM noise survey studies published mainly in geophysical journals.  相似文献   

    3.
    Steam samples from six wells (Colombaia, Pineta, Larderello 57, Larderello 155, Gabbro 6, and Gabbro 1) in a south to north section across the Larderello geothermal field have been analyzed for inorganic and hydrocarbon gases and for oxygen-18 and deuterium of steam. The wells generally decrease in depth and increase in age toward the south. The steam samples are generally characterized by
    1. Total gas contents increasing south to north from 0.003 to 0.05 mole fraction;
    2. Constant CO2 (95±2 percent); near constant H2S (1.6±0.8), N2 (1.2±0.8), H2 (2±1), CH4 (1.2±1), and no O2 in the dry gas;
    3. Presence of numerous, straight chain and branched C2 to C6 hydrocarbons plus benzene in amounts independent of CH4 contents with highest concentrations in the deeper wells;
    4. Oxygen-18 contents of steam increasing south to north from ?5.0‰ to ?0.4‰ with little change in deuterium (?42±2‰).
    These observations are interpreted as showing:
    1. Decreasing gas contents with amount of production because the proportion of steam boiled from liquid water increases with production;
    2. Synthesis of CH4 from H2 and CO2 with CO2 and H2 produced by thermal metamorphism and rock-water reactions;
    3. Extraction of C2 to C6 hydrocarbons from rock organic matter;
    4. Either oxygen isotope exchange followed by distillation of steam from the north toward the south (2 plates at ~220°C) or mixture of deeper more-exchange waters from the north with shallow, less-exchanged recharging waters from the south.
      相似文献   

    4.
    Origin of rhyolites by anatectic melting of granitic crustal rocks   总被引:1,自引:0,他引:1  
    Rhyolitic pumice deposits on some East Aegean Islands are the remnants of a tuff sheet which covered formerly more than 2500 km2. The rhyolites originated by melting of granitic crustal rocks. The petrological properties leading to this conclusion are as follows:
  • -mineralogical composition of the pumice being 60 wt % of glass and 40 % of relictic granitic minerals (quartz, plagioclase, potash feldspar, biotite) in «phenocrysts» up to 1 cm Ø.
  • -phenomena of strong corrosion, resorption and melting of all light colored «phenocrysts» in the rhyolitic pumice.
  • -mineralogical and chemical identity between pumice and granitic xenolites found in great quantity in the pumice tuff.
  • -structurally transitional types between pumice and the granites in different state of melting.
  • -eutectic composition of the pumice glass for a pressure of 2 kb.
  •   相似文献   

    5.
    For most previous geomagnetic surveys, the time variations of the observatory closest to the site of observation have been used for reduction. The accuracy of repeat station measurements depends upon the distance between the station and the observatory. Nowadays, the requirements for the accuracy of repeat station measurements are much higher, especially with respect to local secular variation anomalies. On the other hand, transportable variograph stations are available, by means of which time variations can be recorded closer to the station site. The reduction steps for this method are:
    1. Reduction of measured values to the base-line of the nearby variograph station;
    2. Computation of the nearest quiet night value using the baseline of the variograph;
    3. Computation of the difference between this value and the corresponding one at the observatory.
    The problems are:
  • - the stability of the base-line values of the variographs;
  • - the question as to what degree a quiet night value represents the normal value at that time (e.g. influence of aD st field and/or other fields).
  • A repeat station survey of the Federal Republic of Germany was carried out in 1982. During the same time, eleven stations recorded the time variations in that area. We discuss the aforementioned aspects by way of an example taken from this survey.  相似文献   

    6.
    Results obtained by means of an ultrasonic current meter in the plume of the Rhone river are summarized as follows:
    1. Currents of Rhone river water entering the lake were clearly discernible up to a distance of about 1 km from the river mouth. The interflow was observed at depth of 10 to 30 m.
    2. Interflow velocities decreased with increasing distance from the river mouth: from 40cm/s at a distance of 350 m to about 15 cm/s at 1 km.
    3. Short-term variations of current velocities and directions documented the highly turbulent nature of the interflow.
    4. The entering river water (inflow direction to the NNW) interfered with a persisting northeastward current of the lake water. At a distance of 1–2 km from the mouth the interflow gradually assumed the same direction, possibly due to deflection by Coriolis forces.
    5. Current velocities showed considerable variations within a time scale in the order of hours at the same measuring position. The reasons for these fluctuations remain unclear. Possible causes may be lateral oscillations of the entering river water or its deviation by river mouth bars during periods of reduced river discharge. Variations of the discharge alone cannot explain these current fluctuations.
      相似文献   

    7.
    This paper summarizes seismic and rockburst research activities related to South African deep-level gold mines over the period 1983 to 1987. It covers continued research in directions that were considered in the Seismicity in Mines Symposium in 1982 as well as in several new areas of research. Five broad areas are identified:
    1. Seismic data acquisition and processing. Improved seismic systems are being developed. Velocity models related to known stratigraphy are being used to provide more accurate estimates of seismic locations.
    2. Source mechanisms and near-source effects on seismic wave transmission. This work provides fundamental insights into seismicity and rock behaviour and is being applied in rockburst prediction research.
    3. Mine layouts. Excess shear stress is being investigated as a design parameter by analyzing mining configurations and resultant seismicity. In addition, better understanding of the behaviour of highly stressed remnants and pillars is also being obtained from seismic studies.
    4. Strong ground motion studies. Evaluation of the performance of support elements, including recently developed backfill materials, requires better knowledge of ground motion around underground excavations during seismic events and rockbursts.
    5. Rockburst prediction and control. Rockburst prediction research continues with some reported success. In addition, the feasibility of actively triggering fault slip or conditioning the rock ahead of the stope face to ameliorate the rockburst hazard is currently being investigated.
      相似文献   

    8.
    Concentrations in uranium, thorium and potassium were determined by gamma spectrometry in more than 100 samples of volcanic rocks from the material obtained during the French-Italian expedition in Dankalia (Afar-Ethiopia) (December 1967 – February 1968). These samples were taken from two geographically distinct areas:
    1. the danakile depression (Erta Ale range, Pierre Pruvost massif, Alayta, Afdera, Borawlu).
    2. Ethiopian high lands (Adigrate — Axum).
    The values we obtained give the following contents:

    Dash

  • in the Erta Ale range, for basalts, K: 0,5%, U: 1,3 ppm, Th: 3,3 ppm, Th/U: 2,6.
  • for alkaline rhyolites, U: 4,1 ppm, K: 2,3%, Th: 15,2 ppm, Th/U: 3,7.
  • in the Pierre Pruvost massif, for acid rocks, K: 3,9%, U: 3,6 ppm, Th: 13,5 ppm, Th/U: 3,8.
  • in the Borawlu centre, K: 2,8%, U: 4,6 ppm, Th: 14,7, Th/U: 3,4 for the rhyolites, K: 0,6%, U: 0,9 ppm, Th: 3,1 ppm for the basalts.
  • on the Ethiopian high lands, for the Adigrate basaltic trap rocks, K: 0,6%, U: 0,6 ppm, Th: 1,1 ppm, Th/U: 1,7 and for the Axum zone of phonolitic pinnacles, K: 3,9%, U: 2,7 ppm, Th: 14,9 ppm, Th/U: 4,9.
  • The Th/K and U/K ratios are particularly high compared with the usual data, except for the Pierre Pruvost massif which seems to be different from the others. The difference of Th/U ratios for basic rocks and acid rocks is meaningful. For the magma which gave the volcanism of the studied area, one can think of an evolution more especially connected with transfers of volatile elements. The strong correlations existing between potassium, uranium and thorium probably indicate the presence of groups which are distinct from a geochemical point of view in the Dankalia lavas.  相似文献   

    9.
    Data obtained from Lakes Baldegg and Sempach, two artificially mixed and oxygenated lakes, show that it is technically possible to significantly improve redox conditions, even in large eutrophic lakes. It is discussed why
  • - the well-known release of phosphorus from anoxic sediments does not necessarily result from an abiotic reduction of phosphorus containing iron compounds,
  • - net phosphorus retention by sediments is not simply linearly related to the phosphorus content of a lake,
  • - artificial oxygenation of a previously anoxic hypolimnion does not permanently increase phosphorus retention capacity of lake sediments.
  • From this it is concluded that improvement of hypolimnic redox conditions by lake internal measures such as aeration or oxygenation may accelerate the rate of recovery induced by a reduction of the external phosphorus loading, but that oxygenation per se will hardly be able to cause a reduction of trophic state.  相似文献   

    10.
    Characterization of and correction for cultural noise   总被引:2,自引:0,他引:2  
    Surveys of time varying electromagnetic fields result in time series consisting of signals and noise, the latter defined as that part of the data which cannot be explained by a theory. Man-made contributions to noise can be subdivided into active and passive sources and are complex in character. As Szarka has treated this topic extensively in a recent review paper (Szarka, 1988), only a few further examples are presented here. Following discussion of noise correction in transient electromagnetic investigations which consists mainly of sophisticated stacking and filter procedures, several aspects of its correction in magnetotelluric and geomagnetic depth sounding data are considered. These include:
    1. The methods of treatment of single time series in the presence of visible noise—its detection, removal and sometimes replacement by data predicted from undisturbed intervals.
    2. The investigation of time series interrelations. This is mainly coherence based and—if possible—takes advantage of remote reference techniques.
    3. The examination of the statistical properties of the time series by regression analysis. This leads to the weighting of time segments of data in order to achieve unbiased and minimum variance estimates based on identically and independently Gaussian distributed residuals.
    4. The application of constraints. These can further improve the estimates' quality.
    5. The use of simultaneously recorded multistation data. This can contribute remarkably to noise suppression as well as to the treatment of non-uniform source fields.
    6. Leveraging and confidence limits. Problems relating to the former have not yet been solved satisfactorily while the Jacknife method seems to be an easy way of determining the latter.
    Thanks to the modern processing techniques reviewed in this paper it should be possible to obtain a rather dense net of high quality data in spite of the world-wide increasing noise level. As most processing codes are widely accessible current problems are more related to availability of instruments, carrying out the measurements and reserving enough time for thorough data processing.  相似文献   

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