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1.
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2.
Atmospheric noble gases (e.g., 22Ne, 36Ar, 84Kr, 130Xe) in crustal fluids are only sensitive to subsurface physical processes. In particular, depletion of atmospheric noble gases in groundwater due to boiling and steam separation is indicative of the occurrence of a thermal event and can thus be used to trace the thermal history of stable tectonic regions. We present noble gas concentrations of 38 deep brines (~ 0.5–3.6 km) from the Michigan Basin. The atmospheric noble gas component shows a strong depletion pattern with respect to air saturated water. Depletion of lighter gases (22Ne and 36Ar) is stronger compared to the heavier ones (84Kr and 130Xe). To understand the mechanisms responsible for this overall atmospheric noble gas depletion, phase interaction models were tested. We show that this atmospheric noble gas depletion pattern is best explained by a model involving subsurface boiling and steam separation, and thus, consistent with the occurrence of a past thermal event of mantle origin as previously indicated by both high 4He/heat flux ratios and the presence of primordial mantle He and Ne signatures in the basin. Such a conceptual model is also consistent with the presence of past elevated temperatures in the Michigan Basin (e.g., ~ 80–260 °C) at shallow depths as suggested by previous thermal studies in the basin. We suggest that recent reactivation of the ancient mid-continent rift system underneath the Michigan Basin is likely responsible for the release of both heat and mantle noble gases into the basin via deep-seated faults and fracture zones. Relative enrichment of atmospheric Kr and Xe with respect to Ar is also observed, and is interpreted as reflecting the addition of sedimentary Kr and Xe from associated hydrocarbons, following the hydrothermal event. This study pioneers the use of atmospheric noble gases in subsurface fluids to trace the thermal history of stable tectonic regions.  相似文献   

3.
The authors conducted a Rn222 survey in wells of the Larderello geothermal field (Italy) and observed considerable variations in concentrations. Simple models show that flow-rate plays an important part in the Rn222 content of each well, as it directly affects the fluid transit time in the reservoirs. Rn222 has been sampled from two wells of the Serrazzano area during flow-rate drawdown tests. The apparent volume of the steam reservoir of each of these two wells has been estimated from the Rn222 concentration versus flow-rate curves.List of symbols Q Flow-rate (kg h–1) - Decay constant of Rn222 (=7.553×10–3 h–1) - Porosity of the reservoir (volume of fluid/volume of rock) - 1 Density of the fluid in the reservoir (kg m–3) - 2 Density of the rock in the reservoir (kg m–3) - M Stationary mass of fluid filling the reservoir (kg). - E Emanating power of the rock in the reservoir (nCi kg rock –1 h–1). - P Production rate of Rn222 in the reservoir: number of atoms of Rn222 (divided by 1.764×107) transferred by the rock to the mass unit of fluid per unit time (nCi kg fluid –1 h–1). - N Specific concentration of Rn222 in the fluid (nCi kg–1) - Characteristic time of the steam reservoir at maximum flow-rate (=M/Q)  相似文献   

4.
A general formula for the Dieterich-Ruina friction constitutive law with rate and state (n-state variables,n=1, 2,...) dependences has been obtained and discussed under the assumption that the slip acceleration a varies ion a linearly with the slip displacement , namelya = a 0 + (-0). Wherea 0, 0 are initial constants, is the acceleration rate and constant.a 0 and may be arbitrary constants (positive, negative or zero).The extreme value of frictional resistance and the existence condition of the extreme value, which are very important and govern to some degree the motion process of a frictionally slipping mechanical system, have been analyzed. A critical value c which is the measure of the velocity weakening and velocity strengthening of the mechanical system, and its properties and the relationship to the extreme problem have been studied. Again, according to the critical value c, the concepts of light or strong velocity weakening (or strengthening) are introduced.A possibly new phenomenon that frictional resistance may vary in some kind of decayed oscillation is found. Finally, the condition for the smallest frictional resistance for a slipping mechanical system with nonuniform acceleration has been obtained.  相似文献   

5.
40Ar/39Ar age spectra have been obtained from 85 sanidine separates from 36 ignimbrites and one rhyolitic lava in the latest Eocene-Oligocene Mogollon-Datil volcanic field of southwestern New Mexico. Of the 97 measured age spectra, 94 yield weighted-mean plateau ages each giving single-spectrum 1 precision of±0.25%–0.4% (±0.07–0.14 Ma). Replicate plateau age determinations for eight different samples show within-sample 1 precisions averaging ±0.25%. Plateau ages from multiple (n=3–8) samples of individual ignimbrites show 1 within-unit precision of ±0.1%–0.4% (±0.04–0.13 Ma). This within-unit precision represents a several-fold improvement over published K-Ar data for the same ignimbrites, and is similar to the range of precisions reported from single-crystal laser fusion studies. A further indication of the high precision of unit-mean 40Ar/30Ar ages is their close agreement with independently established stratigraphic order. Two samples failed to meet plateau criteria, apparently due to geologic contamination by older feldspars. Effects of minor contamination are shown by six other samples, which yielded slightly anomalous plateau ages. 40Ar/39Ar plateau ages permit resolution of units differing in age by 0.5% (0.15 Ma) or less. This high resolution, combined with paleomagnetic studies, has helped to correlate ignimbrites among isolated ranges and has allowed development of an integrated timestratigraphic framework for the volcanic field. Mogollon-Datil ignimbrites range in age from 36.2 to 24.3 Ma. Ignimbrite activity was strongly episodic, being confined to four brief (<2.6 m.y.) eruptive episodes separated by 1–3 m.y. gaps. Ignimbrite activity generally tended to migrate from the southeast toward the north and west.  相似文献   

6.
Noble gas concentrations and isotopic compositions have been determined for four submarine volcanic glasses from the Valu Fa Ridge (VFR) in the southern Lau Basin. The samples are the least differentiated ones from this area, and they display enrichments in fluid-mobile elements similar to the nearby island arc. 3He/4He ratios are slightly below average MORB (6.8–7.8 times atmospheric), whereas Ne, Ar, Kr, and Xe have isotopic compositions very similar to air. Together with previously published data from the Valu Fa Ridge and other spreading segments in the Lau Basin, our data show a systematic latitudinal variation of increasing Ne, Ar, Kr, and Xe abundances from north to south as well as Ne and Ar isotopic compositions changing from MORB-like to atmosphere-like in the same direction. Moreover, isotopic compositions and noble gas abundances of the lavas correlate strongly with Ba/Nb ratios and H2O concentrations. Based on these observations and mass balance arguments, we propose that the atmospheric noble gases come from the subducting oceanic crust and are not due to shallow contamination with air dissolved in seawater or assimilation of old crust. Our data suggest that the noble gases released from the subducting slab are atmospheric and thus contain little or no solar He and Ne. In addition to the fact that ratios of He to heavy noble gases are small in aged ocean crust, He has possibly fractionated from the other noble gases due to its higher diffusivity, and thus He transport from the subducting slab into the mantle wedge is probably insignificant. We propose that the 3He/4He ratios lower than MORB observed in the VFR lavas result from radiogenic ingrowth of He in a highly depleted, and hence degassed, mantle wedge after the enrichment of U and Th released from the downgoing slab.  相似文献   

7.
Fifteen submarine glasses from the East Pacific Rise (CYAMEX), the Kyushu-Palau Ridge (DSDP Leg 59) and the Nauru Basin (DSDP Leg 61) were analysed for noble gas contents and isotopic ratios. Both the East Pacific Rise and Kyushu-Palau Ridge samples showed Ne excess relative to Ar and a monotonic decrease from Xe to Ar when compared with air noble gas abundance. This characteristic noble gas abundance pattern (type 2, classified by Ozima and Alexander) is interpreted to be due to a two-stage degassing from a noble gas reservoir with originally atmospheric abundance. In the Kyushu-Palau Ridge sample, noble gases are nearly ten times more abundant than in the East Pacific Rise samples. This may be attributed to an oceanic crust contamination in the former mantle source.There is no correlation between the He content and that of the other noble gas in the CYAMEX samples. This suggests that He was derived from a larger region, independent from the other noble gases.Except where radiogenic isotopes are involved, all other noble gas isotopic ratios were indistinguishable from air noble gas isotopic ratios. The3He/4He in the East Pacific Rise shows a remarkably uniform ratio of (1.21±0.07)×10?5, while the40Ar/36Ar ranges from 700 to 5600.  相似文献   

8.
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9.
Fluid infiltration into fault zones and their deeper-level counterparts, brittle-ductile shear zones, is examined in diverse tectonic environments. In the 2.7 Ga Abitibi greenstone belt, major tectonic discontinuities, with lateral extents of hundreds of kilometres initiated as listric normal faults accommodating rift extension and acted as sites for komatiite extrusion and locally intense metasomatism. During reverse motion on the structures, accommodating shortening of the belt, these transcrustal faults were utilised as a conduit for the ascent of trondhjemitic magmas from the base of the crust and of alkaline magmas from the asthenosphere and for the discharge of thousands of cubic kilometres of hydrothermal fluids. Such fluids were characterised by 18O=+6±2, D=–50±20, 13C=–4±4, and temperatures of 270 to 450°C, probably derived from devolatilisation of crustal rocks undergoing prograde metamorphism. Hydrothermal fluids were more radiogenic (87Sr/86Sr=0.7010 to 0.7040) and possessed higher than did contemporaneous mantle, komatiites or tholeiites, and thus carried a contribution from older sialic basement. A provinciality of87Sr/86Sr and 13C is evident, signifying that fault plumbing sampled lower crust which was heterogeneous at the scale of tens of kilometres. Mineralised faults possess enrichments of large ion lithophile (LIL), LIL elements, including K, Rb, Ba, Cs, B, and CO2, and rare elements, such as Au, Ag, As, Sb, Se, Te, Bi, and W. Fluids were characterised by XCO 20.1, neutral to slightly acidic pH, low salinity 3 wt-%, K/Na=0.1, they carried minor CH4, CO, and N2, and they underwent transient effervescence of CO2 during decompression. Clastic sediments occupy graben developed at fault flexures. The40Ar/39Ar release spectra indicate that fault rocks experienced episodic disturbance on time scales of hundreds of millions of years.At the Grenville front, translation was accommodated along two mylonite zones and an intervening boundary fault. The high-temperature (580°C) and low-temperature (430 to 490°C) mylonite zones, formed in the presence of deep-level crust-equilibrated fluids of metamorphic origin. Late brittle faults contain quartz veins precipitated from fluids with extemely negative 18O (–14 per mil) at 200 to 300°C. The water may have been derived from downward penetration into fault zones of precipitation of low18O on a mountain range induced by continental collision, with uplift accommodated at deep levels by the mylonite zones coupled with rebound on the boundary faults.Archean gneisses overlie Proterozoic sediments along thrust surfaces at Lagoa Real, Brazil; the gneisses are transected by brittle-ductile shear zones locally occupied by uranium deposits. Following deformation at 500 to 540°C, in the presence of metamorphic fluids and under conditions of low water-to-rock ratio, shear zones underwent local intense oxidation and desilication. All minerals undergo a shift of –10 per mil, indicating discharge of meteoric-water-recharged formation brines in the underlying Proterozoic sediments up through the Archean gneisses, during overthrusting; 1000 km3 of solutions passed through these structures. The shear zones and Proterozoic sediments are less radiogenic (87Sr/86Sr=0.720) than contemporaneous Archean gneisses (0.900), corroborating the transport of fluids and solutes through the structure from a large external reservoir.Major crustal detachment faults of Tertiary age in the Picacho Cordilleran metamorphic core complex of Arizona show an upward transition from undeformed granitic basement through mylonitic to brecciated and hydrothermally altered counterparts. The highest tectonic levels are allochthonous, oxidatively altered Miocene volcanics. This transition is accompanied by an increase of 12 per mil in 18O, from +7 to +19, and a 400°C decrease in temperature. Lower tectonic levels acted as aquifers for the expulsion of large volumes of higher-temperature reduced metamorphic fluids and/or evolved formation brines. The Miocene allochthon was influenced by a lower-temperature reservoir inducing oxidative potassic alteration; mixing occurred between cool downward-penetrating thermal waters and the hot, deeper aqueous reservoir.In general, flow regimes in these fault and shear zones follow a sequence, from conditions of high temperature and pressure with locally derived fluids at low water-to-rock ratios, during initiation of the structures, to high fluxes of reduced formation or metamorphic fluids along conduits as the structures propagate and intersect hydrothermal reservoirs. Later in the tectonic evolution and at shallower crustal levels there was incursion of oxidising fluids from near-surface reservoirs into the faults. In general, magmatism, tectonics, and fluid motion are intimately related.  相似文献   

10.
Variations in D and 18O values with H2O contents and outlet temperatures indicate that the fumaroles of La Fossa crater have discharged mixtures of magmatic water and marine hydrothermal water, since 1979. The contribution of meteoric water was low in the period 1979–1982 and very low afterwards. The 18O values of the marine-hydrothermal component of +5 to +7.2 are due to isotopic exchange with the 18O-rich silicates of the rocks under high-temperature and low-permeability conditions. The 18O value of the magmatic end-member is generally +3.5 to +4.3, although values as high as +5.5 to +6.5 were reached in the summer of 1988, when magma degassing appears to have extended into the core of the magma body. The D values of the end-member were close to -20, typical of andesitic waters. Both the isotopic values and chemical data strongly support a dry model, consisting of a central magmatic gas column and a surrounding hydrothermal envelope, in which marine hydrothermal brines move along limited fracture zones to undergo total evaporation on approaching the conduits of magmatic fluids. The vents at the eastern and western boundaries of the fumarolic field are fed by fluids whose pressure is governed by the coexistence of vapor, liquid and halite, giving rise to a high risk of phreato magmatic explosions, should magma penetrate into these wet environments. Most La Fossa eruptions were triggered by an initial hydrothermal blast and continued with a series of phreatomagmatic explosions. The fluids discharged by the Forgia Vecchia fumaroles are mixed with meteoric water, which is largely evaporated, although subordinate loss of condensed steam may be responsible for scrubbing most of the acidic gas species. The temperatures and pressures, and the risk of a sudden pressure increase, are low. A boiling hydrothermal aquifer at 230° C is present underneath the Baia di Levante beach. This area has a minor risk of hydrothermal explosions.  相似文献   

11.
u u u u uu smu um ¶rt;um ¶rt; a, s¶rt;a ¶rt;a ¶rt;u suu (n — mn, k — n¶rt;): saumauo n u: n=2, k=0; n=2, k=2; n=3, k=0, 1, 2, 3; n=4, k=0; n=4, k=3; saumau n : n=2, k=0; n=2, k=2; saumau n a: n=2, k=0.

Dedicated to Prof. RNDr. Emil Buchar, DrSc., Corresponding Member of the Czechoslovak Academy of Sciences, on the Occasion of His 75th Birthday  相似文献   

12.
A number of processes may modify the noble gas composition of silicate liquids so that the composition of noble gases observed in glassy margins of deep-sea basalts is not that of the upper mantle. Differential solubility enhances the light noble gases relative to the heavier gases; however, we demonstrate that the observed abundance pattern cannot be attributed to solubility of noble gases with atmospheric proportions. Partial melting and fractional crystallization increase the noble gas content of all species relative to mantle concentrations, but do not fractionate their relative abundances. Noble gases may be lost from an ascending magma in various ways, the most important, however, may be exclusion of gas from crystals forming at the time of solidification, which is shown to result in marked loss of gas from the basalt. Small amounts of low-temperature alteration of solidified basalt can produce dramatic changes in the noble gas abundance pattern, since the adsorption coefficients for the different noble gas favor uptake of heavy species relative to the light species. Atmospheric contamination can account for observed variations in the 40Ar/36Ar ratio of oceanic basalts. The degree of crystallinity of glassy margins of deep-sea basalts may control the helium abundance of these samples; however, the uniform 3He/4He values reported apparently reflect a relatively constant proportion of radiogenic and primordial helium in the mantle.  相似文献   

13.
Summary The theory of methods of computing single- and inter-station transfer functions in both the spectral and time domains was developed in paper[1]. Both approaches are applied to the variation data recorded at field stations along two non-simultaneous profiles traversing the eastern margin of the Bohemian Massif, where a zone of anomalous induction seems to mark an important geological boundary of formations with different histories of development. The results of both analyses are found to coincide within reasonable bounds of 20–30% in the principal induction characteristics.
u m¶rt; ama ¶rt;-u -mau n¶rt;am u nma u am a ua am[1]. am nua m am a n¶rt;¶rt;a nu ¶rt; aaua ¶rt;aaum auau aumua a n mau ¶rt; u nu, nau m au aua,¶rt; aa a aa u¶rt;uu. a, u¶rt;u, mamau a¶rt;a ¶rt; ¶rt; ¶rt;uuau au umuu aumu. mam aau nma u am auam a 20–30% ¶rt; u¶rt;u naam.
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14.
Summary The convection in a rapidly rotating, electrically conducting, horizontal fluid layer, non-constantly stratified and penetrated by an inhomogeneous magnetic field, is studied. The convection is investigated for various ratios of the thickness of the stable and unstable stratified part of the layer. The thermal model of the layer, as well as the analysis of the results have been treated with regard to the physical conditions in the liquid core of the Earth.
am u¶rt;m u m aa mn¶rt; u¶rt;uma nm mamuuau, nua ¶rt;¶rt; aum n. u u¶rt;m ¶rt; a mu m u mu u mu mamuuuao amu . ua ¶rt; , a u aau mam, n¶rt;a anm uuu u u¶rt; ¶rt; u.
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15.
Summary Spatial and temporal variability of natural ELF-VLF phenomena field intensity has been studied using data from Interkosmos satellites with apogees below 2000 km. The results show a distinct dependence of the diurnal variation and latitudinal intensity distribution on the magnetic activity. The L-value at which the maximum of plasmaspheric noise occurs, e.g., correlates better with the Dst-index than with other indicies.
mama u a auau anmu n mm - u a ua a uu ¶rt;a uu m an u 2000 . mam naam m auum m ¶rt;a u um an¶rt;u uu m aum amumu. uua L-naama, a m nm au naa uu, um Dst-u¶rt; ¶rt;uu u¶rt;auaum amumu.
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16.
Summary The paper deals with the general theory of equivalent projection. By specifying the results derived, special cases may be treated. Examples of methods are described which enable free functions to be found in a general solution. A detailed procedure of solving the problem with a numerical example is given, taking into account the optimization according to the global criterton, established for extreme angular distortion.
aamuam a mu auu nu; ¶rt;am m am au. nu m¶rt;, nu amu ¶rt; uu uu. umam nmuauau n aamumu au, ma ¶rt; aua uau , u nuam n¶rt; m¶rt; u u nu.

Dedicated to Professor Frantiek Fiala on the Centenary of his Birthday  相似文献   

17.
n¶rt;m mu ¶rt; mu uau aumma. mu aum u mu u m u mu auauu m¶rt;a. u¶rt;m u naam nm nmmuna uau aumma.  相似文献   

18.
¶rt;m n¶rt;u nu nm n m . m¶rt; n¶rt;am nuuu am uma au muna (6) u (10). amua aumnu m m nn unam u u, m nmu ama mm (u. 2). uu nu nm ¶rt;u am mu n¶rt; uua 15mu anau u mu u nn uua mu anau. u unauu m nn ¶rt;u am mu n¶rt; uua ¶rt; 21 anau.

Dedicated to 90th Birthday of Professor Frantiek Fiala  相似文献   

19.
1) , 2) 3) .  相似文献   

20.
Summary Problems of occurrence of density inhomogeneities in the upper mantle are discussed and their gravitational effects in the region of Central Europe are investigated. Attention is namely devoted to the density contrast between the asthenosphere and the lower lithosphere, and its possible dependence on depth.
¶rt;am n nu nmm ¶rt;¶rt;m amuu u uaumau ¶rt;mu a mumuu ¶rt; n. uau ¶rt;m n¶rt; nmm mam ¶rt; am u um u auumu mu aau.
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