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1.
Fourier-amplitude spectrum is one of the most important parameters describing earthquake ground motion, and it is widely used for strong ground motion prediction and seismic hazard estimation. The relationships between Fourier-acceleration spectra, earthquake magnitude and distance were analysed for different seismic regions (the Caucasus and Taiwan island) on the basis of ground motion recordings of small to moderate (3.5≤ML≤6.5) earthquakes. It has been found that the acceleration spectra of the most significant part of the records, starting from S-wave arrival, can be modelled accurately by the Brune's “ω-squared” point-source model. Parameters of the model are found to be region-dependent. Peak ground accelerations and response spectra for condition of rock sites were calculated using stochastic simulation technique and obtained models of source spectra. The modelled ground-motion parameters are compared with those predicted by recent empirical attenuation relationship for California.  相似文献   

2.
The so-called “Graded Unit” comprises 17.2 m of the core from the research borehole Nördlingen 1973 and is thought to represent fall-back material, which has been sorted similar to tephra. Samples from six levels of these air-borne impact debris sediments in the Ries Crater have been analyzed for Ir, Ni, Co, Cr and Fe. The concentrations of these elements are negatively correlated with average grain size and accordingly the depth of the samples indicating the presence of a surface correlated component and are hence consistent with vapour deposition of meteoritic material on small dust grains. The largest Ir concentration found is 230 pg/g, a factor of 28 higher than the indigenous concentration. Enrichment factors in the uppermost layer of the “Graded Unit” are about 28 for Ir, approximately 2 for Fe, Co, Ni and 1.5 for Cr. If the enrichment of all elements determined were of meteoritic origin, then the “net meteoritic composition” is most closely matched by aubrites as suggested previously. However, it seems more likely that the observed concentration trends of Cr, Fe, Co and Ni are due to mineral sorting. Therefore the only as yet certain indication of meteoritic material is the presence of Ir, which is not sufficient to further constrain the nature of the projectile.  相似文献   

3.
Kettle holes are glacially created, small, shallow, depressional wetlands collecting their water from internal or closed catchments in young moraine landscapes. Their water body is defined by having a maximum of 1 ha in extent. Mostly they undergo a wet-dry circle. In North-East Germany, kettle holes are widely spread, mostly on arable land. They are characterised by large differences in hydroperiod (HP), size, shape and edge steepness. They also have a high potential for both, geomorphic structural diversity and biological species diversity. However, kettle holes are subject to pollution, drainage and structural reduction that result from intensive land use practices.Although kettle holes in Germany are protected by law, protection strategies are not specific enough with respect to the variability of kettle holes, especially of HP. Therefore, the study objective was to characterise hydrogeomorphic (HGM) kettle hole types to create a basis for a decision support system with regard to the selection of the type dependent conservation and management measures.In three agricultural landscapes in North-East Germany, geomorphological and hydrological variables of 268 kettle holes (HP, shore overflow tendency, depth, area, form, shore width and slope) as well as those of their catchments (area, wetland to catchment area ratio, relief) were investigated from 1993 to 2003. By statistical analysis of datasets of 144 kettle holes, 10 HGM kettle hole types were defined. The basic types are “silted fen type” and “open-water type”. Basic subtypes of the latter type are “storage type”, “shore overflow type” and “puddle type”. Differences in spreading of kettle hole types in dependency on landscape relief were found.  相似文献   

4.
The medium shallow lake Grimnitzsee (maximum depth: 9.9 m; mean depth: 4.6 m; area: 7.7 · 106 m2) which is situated in the biosphere reserve “Schorfheide-Chorin” in northern Brandenburg (Germany) was studied in 1994 and 1995. A bathymetric map of Grimnitzsee is given for the first time. The lake is usually polymictic although in 1994 and 1995 relatively long summer stratification was observed due to very high global radiation input. Nutrient concentration, light climate, oxygen status, phytoplankton biomass and the species composition of littoral diatoms characterize the lake as eutrophic. Special features deducible from the lake's polymictic character were the multiple development of aerobic or anaerobic strata above the sediment, the fast recovery of silicon concentration in the water column after diatom sedimentation, the importance of resuspension for the success of planktonic diatom populations, and an only moderate correlation between chlorophyll a concentration and light attenuation as well as seston dry weight probably due to the influence of suspended particles.  相似文献   

5.
Thermal state, rheology and seismicity in the pannonian basin, Hungary   总被引：1，自引：0，他引：1  
On the basis of data on crustal structure and terrestrial heat flow, a 3-D geothermal model for the lithosphere in the Pannonian basin, Hungary, has been calculated. This model, together with information on crustal composition, laboratory data on rock friction, and certain assumptions about fluid conditions and strain-rate levels within the lithosphere, has been used to construct a rheological model of the area.The results obtained show a layered rheological structure where an aseismic part of the crust is “sandwiched” between an upper and a lower seismogenic crustal layers. According to the proposed rheological model, seismic activity in the upper crust may be expected down to depths of 10–12 km, which is confirmed well by the observed depth distribution of seismicity. The model also predicts a lower crustal seismogenic layer down to 20–22 km. Because of infrequent occurrences of deep earthquakes and/or a generally small number of reliable hypocenter depth determinations in the study area, this seismogenic zone is less constrained by observations.The depth of the different rheologic horizons within the crust is governed mainly by thermal conditions. The lower boundary of both seismogenic layers appears isothermal. Brittle-ductile transition in the upper crust coincides with the ˜200 °C isotherm, while in the lower crust it coincides with the ˜ 375 °C isotherm. The lowermost crust and the upper mantle beneath Hungary show ductile behavior, thus the possibility of siesmic activity at these horizons can be excluded.  相似文献   

6.
Rare earth element (REE) and other trace element compositions of 16 lavas from all historic and 2 prehistoric eruptions on 5 islands of the Azores Archipelago show notable intra-and inter-island differences. Fe enrichment and “compatible” element depletion due to fractional crystallization have been superimposed on variations established in the source area. Fractionation of La/Sm, U/Th, K/Na and “large ion lithophile” (LIL) element abundances are probably related to variable fusion of a source peridotite whose LIL element distribution cannot be exactly specified in view of its possible heterogeneity. Relative light-REE enrichment in basalt appears greatest on the “potassic” island São Miguel, the more sodic island Fayal and one lava from Pico, and least in basalts from the “sodic” islands Terceira, São Jorge and Pico. This variation is matched by most other LIL elements, although P shows unexpected enrichment in Terceira lavas, otherwise the least LIL element-enriched and most heavy-REE-enriched. Upper mantle phase chemistry is probably critical in establishing the patterns. In particular, P—REE covariance may reflect phase stabilities of apatite and (P-bearing) garnet in the upper mantle. Distribution patterns of REE in the historic lavas are similar to those of basalts from the Atlantic median rift at the crest of the Azores “platform”. Transition to light-REE-depleted rift-erupted basalts to the southwest is believed to be step-wise with increasing water depth, possibly indicating retention of a light-REE-rich phase in the residue from partial fusion as intersection of geotherm and peridotite solidus occur at lower pressures. The source mantle for the Azores basalts is probably light-REE- and LIL element-enriched but we find no evidence so far to suggest its emplacement by thermal “plume” activity.  相似文献   

7.
The centroid-moment tensor solutions of more than 300 earthquakes that occurred in the Himalayas and its vicinity regions during the period of 1977–1996 are examined. The resultant seismic moment tensor components of these earthquakes are estimated. The Burmese arc region shows prominent east–west compression and north–south extension with very little vertical extension. Northeast India and Pamir–Hindu Kush regions show prominent vertical extension and east–west compression. The Indian plate is subducting eastward beneath the northeast India and Burmese arc regions. The overriding Burmese arc has overthrust horizontally with the underthrusting Indian plate at a depth of 20–80 km and below 80 km depth, it has merged with the Indian plate making “Y” shape structure and as a result the aseismic zone has been formed in the region lying between 26°N–28°N and 91.5°E–94°E at a depth of 10–50 km. Similarly, the Indian plate is underthrusting in the western side beneath the Pamir–Hindu Kush region and the overriding Eurasian plate has overthrust it to form a “Y” shape structure at a depth of 10–40 km and below 60 km depth, it has merged with the Indian plate and both the plates are subducting below 60–260 km depth. Further south, the overriding Eurasian plate has come in contact with the Indian plate at a depth of 20–60 km beneath northwest India and Pakistan regions with left lateral strike slip motion.  相似文献   

8.
Five microearthquake seismographs were used at 11 sites in northern Sinai in the period February 1987 to February 1988 to study the microseismicity of the area around the Maghara coal mine for mine-development studies. A total of 270 events were recorded on 850 records. The magnitude, epicenter and depth of each event were calculated using suitable software for an Egyptian Geological Survey and Mining Authority's (EGSMA) XT computer. The interpretation of the seismic activity in the area is given in view of plate tectonics, the Sinai subplate boundary follows the Gulf of Aqaba and the Dead Sea. The plate and subplate boundaries are presently active, and there seems to be a diffuse zone of deformation between “NW Africa” and “Nubia” affecting the Cairo-Suez district.  相似文献   

9.
The Latera field (Vulsini volcanic complex, Latium, Italy) is one of the geothermal areas of the peri-Tyrrhenian belt along which a regional, high thermal anomaly has been detected. So far nine deep wells have been drilled within the Latera caldera and four of them have been productive. The geothermal reservoir is located within the fractured carbonatic rocks of the Tuscan nappe; the overlying volcanic units, sealed by hydrothermal minerals (mainly calcite and anhydrite), act as an impervious cover.The fluid produced by the wells comes from a deep aquifer (about 1000–1500 m depth) which at present is not connected with the shallow aquifer in the volcanoclastic units. Fluid temperatures range between 200 and 230°C; in-hole temperatures as high as 343°C at 2775 m depth have been measured in dry wells.The study of the newly formed mineral assemblages from both volcanic and sedimentary units as sampled from the geothermal wells can be used to reconstruct the thermal evolution of the geothermal field. The intrusion of a syenitic melt, up to a depth of about 2000 m, dated 0.86 Ma, represents the major thermal event for the units in the area and is assumed to represent the first step in the geothermal evolution of the Latera system.The above mentioned newly formed mineral assemblages can be divided into three groups: (a) “contact-metasomatic”: calcite, anhydrite, diopsidic pyroxene, grossularitic garnet, phlogopite, wollastonite or monticellite; (b) “high-temperature hydrothermal”: calcite, anhydrite, K-feldspar, vesuvianite, melanitic garnet, tourmaline, amphibole, epidote, sulphides; (c) “low-temperature hydrothermal”: calcite, anhydrite, K-feldspar, clay minerals, sulphides. Group (a) minerals are now relics. Part of (b) and all of (c) group are still in equilibrium with the existing conditions in different parts of the geothermal system.Thermodynamic calculations on the observed mineral assemblages permitted estimates of the P, T conditions and gas fugacities.  相似文献   

10.
Possible effects of signal reception from different electrojet heights in a skewness of auroral coherent spectra are studied assuming that the “inherent” spectral line due to plasma turbulence is of type-2 and symmetrical. For reasonable ionospheric parameters, the altitude integrated spectra are expected to be skewed negatively for positive mean Doppler shift, in agreement with radar observations at small aspect angles. However, the spectra could be skewed positively if the turbulent layer or the electron density profile is shifted to high altitudes of \sim120 km. This change of spectral shape will not be observed experimentally if, at the same time, either the electron collision frequency is enhanced or the “inherent” spectral width is increased. Observational results are discussed in view of the predictions given.  相似文献   

11.
Crustal earthquakes near Ruapehu and Ngauruhoe fall into two classes, each of which can be subdivided. On the one hand, there are high-frequency events ( 3 Hz) with sharp, well-defined phases, mainly concentrated beneath Ruapehu Crater Lake. Low-frequency events (< 2 Hz), on the other hand, are common at shallower depths under both volcanoes. These are usually emergent multiple events, and are often closely associated with eruptions.The low-frequency events resemble Minakami's B-type and explosion earthquakes, but sometimes occur where no vent exists and rather deeper than his formal definition (< 1 km) permits. More importantly, they lack reliable criteria (wave-form or magnitude differences) to distinguish between his two groups. Whether or not they accompany an eruption (Minakami's definition of explosion earthquake) appears to depend on whether the volcanoes are in a “closed-” or “open-vent” condition. The high-frequency earthquakes are similar in wave-form to Minakami's A-type. However, many at Ruapehu (here designated “roof-rock” earthquakes) originate at shallower depths than the B-type earthquakes, which is contrary to Minakami's definition.Difficulty in applying Minakami's classification rigorously, and the fact that low frequencies may be due to abnormal attenuation of higher frequencies along the path, rather than to their suppression or absence at the source, has led to reclassification of earthquakes near the volcanoes into two broad groups, tectonic and volcanic. The former includes all high-frequency earthquakes, and those discrete events in which dominant low frequencies are due to path effects. The latter includes multiple and emergent events which show evidence of prolonged or repetitive source mechanism. Dominant low frequencies are ascribed to occurrence in heat-weakened material, and high frequencies to instantaneous source mechanisms operating in competent rock. The term volcano-tectonic describes tectonic earthquakes within some arbitrary distance of a volcano.At Ngauruhoe and Ruapehu, volcanic earthquakes accompany explosive, vent-clearing eruptions. Subsequent “open-vent” degassing and ash emission, however, although often powerful and prolonged, usually occurs without earthquakes. Such activity is, however, frequently accompanied by volcanic tremor. At Ruapehu, under “closed-vent” conditions, when lake temperature is low, low-frequency earthquakes up to magnitude ML = 3.4 have occurred without any eruption.Five types of phreatic eruptions are identified at Ruapehu, each having a distinctive seismic pattern. The three most explosive types appear to be generated by a chain reaction process, and all involve flashing of water to steam; the first by failure of the roof, with little precursory seismicity, after a “closed-vent” period, during which lake temperature decreases; the second, after prolonged heating of the lake and much preliminary volcanic tremor, interpreted as due to rising magma; and the third, under “open-vent” conditions in the wake of one of the two preceding types. A fourth probably occurs in wet sediments near the base of the lake, as a result of upward migration of hot gas, and a fifth, aseismic, or accompanied by very weak volcanic tremor, is associated with convective overturn within Crater Lake.  相似文献   

12.
The patterns of variation of TiO2 conent during magmatic evolution are different in the so called “orogenic” and “anorogenie” basic associations; these last terms, which are the cause of much misunderstanding, can be replaced by the terms “isotitaniferous” and “anisotitaniferous”.  相似文献   

13.
A regional terrane map of the New Jersey Coastal Plain basement was constructed using seismic, drilling, gravity and magnetic data. The Brompton-Cameron and Central Maine terranes were coalesced as one volcanic island arc terrane before obducting onto Laurentian, Grenville age, continental crust in the Taconian orogeny [Rankin, D.W., 1994. Continental margin of the eastern United States: past and present. In: Speed, R.C., (Ed.), Phanerozoic Evolution of North American Continent-Ocean Transitions. DNAG Continent-Ocean Transect Volume. Geological Society of America, Boulder, Colorado, pp. 129–218]. Volcanic island-arc rocks of the Avalon terrane are in contact with Central Maine terrane rocks in southern Connecticut where the latter are overthrust onto the Brompton-Cameron terrane, which is thrust over Laurentian basement. Similarities of these allochthonous island arc terranes (Brompton-Cameron, Central Maine, Avalon) in lithology, fauna and age suggest that they are faulted segments of the margin of one major late Precambrian to early Paleozoic, high latitude peri-Gondwana island arc designated as “Avalonia”, which collided with Laurentia in the early to middle Paleozoic. The Brompton Cameron, Central Maine, and Avalon terranes are projected as the basement under the eastern New Jersey Coastal Plain based on drill core samples of metamorphic rocks of active margin/magmatic arc origin. A seismic reflection profile across the New York Bight traces the gentle dipping (approximately 20 degrees) Cameron's Line Taconian suture southeast beneath allochthonous Avalon and other terranes to a 4 sec TWTT depth (approximately 9 km) where the Avalonian rocks are over Laurentian crust. Gentle up-plunge (approximately 5 degrees) projections to the southwest bring the Laurentian Grenville age basement and the drift-stage early Paleozoic cover rocks to windows in Burlington Co. at approximately 1 km depth and Cape May Co. at approximately 2 km depths. The antiformal Shellburne Falls and Chester domes and Chain Lakes-Pelham dome-Bronson Hill structural trends, and the synformal Connecticut Valley-Gaspe structural trend can be traced southwest into the New Jersey Coastal Plain basement. A Mesozoic rift basin, the “Sandy Hook basin”, and associated eastern boundary fault is identified, based upon gravity modeling, in the vicinity of Sandy Hook, New Jersey. The thickness of the rift-basin sedimentary rocks contained within the “Sandy Hook basin” is approximately 4.7 km, with the basin extending offshore to the east of the New Jersey coast. Gravity modeling indicates a deep rift basin and the magnetic data indicates a shallow magnetic basement caused by magnetic diabase sills and/or basalt flows contained within the rift-basin sedimentary rocks. The igneous sills and/or flows may be the eastward continuation of the Watchung and Palisades bodies.  相似文献   

14.
Topographic and associated gravity signals often result from the interference of several phenomena. In the present paper, an admittance function for the superposition of several physical mechanisms acting in the same waveband is derived. If the processes are not phase related, the resulting admittance function is the average of the individual admittance functions weighted by the squared amplitude of the topography for each process.We use this concept of superposition of different processes to understand the compensation of the Atlantic ridge valley. Classical transfer function studies applied to slow-spreading ridges have concluded that the topography was emplaced on an elastic plate about 10 km thick. These analyses of gravity and topography seem to contradict the physical models explaining the median rift valley, which is thought to be due to dynamical effects and thus to be uncompensated. We obtain an “average axial valley” gravity and topography profile by stacking several profiles perpendicular to the Mid-Atlantic Ridge and subtracting a long-wavelength thermal effect. We find that the gravity over topography spectral ratio of the “average axial valley signal” is consistent with an uncompensated process. Our study thus confirms that the mode of formation of the axial valley of a slow-spreading ridge involves an uncompensated mechanism. The presence of an additional process characterized by low admittance values, uncorrelated from one profile to the other, is also suggested in order to explain the observed admittance function. The study of the long wavelength (λ > 300 km) gravity and topography signal leads us to invoke the cooling of the upper portion of the crust by water circulation and to exclude the presence of a large amount of partial melt at depth (more than 5% over a 20 km thick layer at a mean depth of 60 km).  相似文献   

15.
In the STAR/AQEM protocol microhabitats covering less than 5% of the sampling area were neglected. Driven by an ongoing discussion on the importance of these underrepresented microhabitats we tested the influence of sampling them. We investigated 48 streams representing 14 different stream types from all over Germany. Macroinvertebrates of underrepresented microhabitats were sampled in addition to the STAR/AQEM protocol. To ensure the method remains feasible in routine monitoring programmes the total sampling and sorting effort of additional sampling was limited to 20 min. Particularly those taxa were picked, which were not recognised during the routine STAR/AQEM sorting.To identify the effect of additional sampling on stream assessment results, we calculated the stream type-specific Multimetric Index (MMI) with the “main” and the “main+additional” data for each sample. The mean and median difference in MMI values between “main” and “main+additional” samples was 0.02 and 0.01, respectively. In seven of 48 samples (14.6%) a different ecological quality class was calculated with the “main+additional” dataset. Regarding common metrics within the MMI as well as intercalibration metrics differences between “main” and “main+additional” samples were analysed. The values differed most in richness metrics (e.g., number of EPTCBO Taxa, number of Trichoptera Taxa). The results of the present study show that additional sampling of underrepresented microhabitats could alter multimetric assessment results.  相似文献   

16.
The Chilean lake district includes diverse lentic ecosystems along ca. 700 km of the country (36°–43°S), including the “Nahuelbutan lakes”, “Araucanian lakes” and “Chiloe lakes”. This area is recognized as an important “hot spot” of benthic freshwater biodiversity in Southern South America. In Chilean temperate lakes, increased nutrient loads of P and N caused eutrophication, particularly in the Nahuelbutan Lakes. The freshwater Hyriidae mussel Diplodon chilensis (Gray, 1828) which is one of the most abundant species in Chilean temperate lakes, is known to be very susceptible to eutrophication. This species presents a clear reduction in its geographic ranges and is considered to be a threatened species in many Chilean lakes. In this study, we used a correlative approach to determine how eutrophication-driven changes in the food supply and in geographical parameters of different Chilean lakes affected the shell growth rates of D. chilensis. The results obtained from sclerochronological analyses of the mussel shells suggest an association with a group of environmental variables, including geographical types (negative), such as latitude and altitude, and limnological types (positive), especially phosphorous and turbidity. However, the D. chilensis populations under extreme conditions of turbidity in eutrophic and hypertrophic lakes are extinct or nearly so. The high positive correlation of the mean D. chilensis growth rates with orthophosphate (R=0.76; P<0.05), in relation to dissolved inorganic nitrogen, suggests that P is the major limiting factor of the primary productivity in Chilean temperate lakes. We discuss some implications of our results in terms of the conservation of biodiversity in temperate lake ecosystems at different taxonomic levels.  相似文献   

17.
The concept of a time-depth correlation between tectonic earthquakes at depth beneath some volcanoes, and their eruptions, developed by the author since 1962, has been confirmed by new observations and successful prediction of renewed volcanic activity in New Zealand.Regular earthquake migrations are observed along the Benioff zone, and volcanic eruptions are found to be related to these seismic migrations beneath the volcanoes, as follows:
Full-size image (2K)
Therefore, in island arcs and continental margins, volcanic activity is the result of two processes occurring beneath the volcanoes: (1) a “tectonic process”, a migration of strain release along the downgoing lithosphere, of which the earthquakes are the manifestation; (2) a “magmatic process”, a relatively fast vertical ascent of magmatic material from the deep root of the volcano, where the observed shocks may be the starting signal from this level.The rate of migration of tectonic earthquakes increases with depth in the upper mantle.An empirical time relationship between the earthquakes occurring at depth beneath a volcano and its eruptions, has been successfully tested for renewed activity at White Island in New Zealand, over the period 1977–1978.  相似文献   

18.
Dispersion and radial depth of investigation of borehole modes   总被引：2，自引：0，他引：2  
Sonic techniques in geophysical prospecting involve elastic wave velocity measurements that are performed by placing acoustic transmitters and receivers in a fluid‐filled borehole. The signals recorded at the receivers are processed to obtain compressional‐ and shear‐wave velocities in the surrounding formation. These velocities are generally used in seismic surveys for the time‐to‐depth conversion and other formation parameters, such as porosity and lithology. Depending upon the type of transmitter used (e.g. monopole or dipole) and as a result of eccentering, it is possible to excite axisymmetric (n= 0) , flexural (n= 1) and quadrupole (n= 2) families of modes propagating along the borehole. We present a study of various propagating and leaky modes that includes their dispersion and attenuation characteristics caused by radiation into the surrounding formation. A knowledge of propagation characteristics of borehole modes helps in a proper selection of transmitter bandwidth for suppressing unwanted modes that create problems in the inversion for the compressional‐ and shear‐wave velocities from the dispersive arrivals. It also helps in the design of a transmitter for a preferential excitation of a given mode in order to reduce interference with drill‐collar or drilling noise for sonic measurements‐while‐drilling. Computational results for the axisymmetric family of modes in a fast formation with a shear‐wave velocity of 2032 m/s show the existence of Stoneley, pseudo‐Rayleigh and anharmonic cut‐off modes. In a slow formation with a shear‐wave velocity of 508 m/s, we find the existence of the Stoneley mode and the first leaky compressional mode which cuts in at approximately the same normalized frequency ωa/VS= 2.5 (a is the borehole radius) as that of the fast formation. The corresponding modes among the flexural family include the lowest‐order flexural and anharmonic cut‐off modes. For both the fast and slow formations, the first anharmonic mode cuts in at a normalized frequency ωa/VS= 1.5 approximately. Cut‐off frequencies of anharmonic modes are inversely proportional to the borehole radius in the absence of any tool. The borehole quadrupole mode can also be used for estimating formation shear slownesses. The radial depth of investigation with a quadrupole mode is marginally less than that of a flexural mode because of its higher frequency of excitation.  相似文献   

19.
Five geothermal waters from the Mons area (southern Belgium) have been studied: one natural hot spring at Stambruges, one stagnant warm water from the “inclined tunnels” at Baudour, and three thermal waters from the drillholes at St. Ghislain, Ghlin and Douvrain, originating from the carbonate/anhydrite-bearing Visean strata, at depths of ca. 2600, 1550 and 1300 m, respectively.Multielement chemical analysis of the filtered water and its suspended matter > 0.4 μm) was carried out by instrumental neutron activation.Temperature in depth, calculated using the silica (chalcedony) chemical geothermometer, ranged from 75 to 88°C, in good agreement with experimentally determined values. Na/K and Na/K/Ca geothermometers yieilded erratic results, as expected from the geological environment in the aquifer.From the analytical data it can be calculated that the thermal waters of St. Ghislain, Ghlin and Douvrain are not only saturated with respect to chalcedony, but also to anhydrite, calcite, fluorite, barite, strontianite, and possibly zinc silicate, iron (III) hydroxide or siderite, albite, microcline, gibbsite and kaolinite. They are oversaturated with respect to muscovite. Data are also presented for the other thermal waters, and a cold spring water (Claire Fontaine, Stambruges).The similar trace-element composition of the thermal waters can be explained by percolation of the water in the same distant recharge zone, from where it descends, becomes heated at depth and rises along collapse breccia, and locally (Baudour, Stambruges) along fissures. The uptake of higher amounts of Ca, Mg, Sr and sulfate in St. Ghislain and Ghlin, as compared to Douvrain and Baudour is correlated with the boundary between the “non-dissolved” and “dissolved” evaporitic zones. This boundary is situated between St. Ghislain and Douvrain, and is roughly parallel with the direction of the groundwater flow (WNW).  相似文献   

20.
The different basalt types related to rift structure development have been investigated, starting from the pre-rift stage in the northern Ethiopian rift and its eastern escarpment and plateau.The basic volcanic rocks are represented mainly by transitional basalts, both in the pre-rift (plateau) and rift (escarpment and rift floor) stages. A striking feature is that although the plateau basalts show clear tholeiitic affinity and the rift basalts reveal a somewhat pronounced “alkaline” character, the REE and LILE element abundances, however, progressively decrease from the “tholeiitic” basalts of the plateau to the “alkaline” basalts of the rift.All data support the view that such contrasting features may be attributed to a continuous depletion of hygromagmatophile (REE, LILE) elements in the mantle source material, related to the large volumes of magmas produced in the early phase of rift structure development. The transition from “tholeiitic” (plateau) to “alkaline” (rift) transitional basalts is related to decreasing intensity of extensional movements.  相似文献   

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