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31.
Granulite facies amphibole and biotite equilibria,and calculated peak-metamorphic water activities 总被引:2,自引:0,他引:2
Samples located near the Oregon Dome anorthosite massif in the south-central Adirondack Mountains, New York contain the fluid-buffering mineral assemblages: amphibole + clinopyroxene + orthopyroxene + quartz or biotite + quartz + orthopyroxene + K-feldspar. These rocks were metamorphosed under granulite-facies conditions (T=725°–750°C, P=7.5 kbar) during the Grenville orogeny. The Mg-rich nature of amphiboles, micas, and pyroxenes allow accurate calculation of water activities because corrections for the effects of solid solution are relatively small. The activity of water was low during the peak of granulite-facies metamorphism, with H2O0.15±0.14. Wollastonite occurrences indicate that the CO2 was low (<0.3) in nearby rocks, demonstrating that large quantities of CO2 did not infiltrate in a pervasive manner. The combination of low H2O with low CO2 is consistent with the hypothesis that magmatic processes were dominant, generating dry, fluid-absent conditions.Abbreviations
fi
Fugacity of species i in a fluid
-
Xi
mole fraction of component i in a phase
-
T
temperature
-
P
lithostatic pressure
-
P
F
fluid pressure
-
i
x
activity of component i phase X 相似文献
32.
Oxygen isotope analyses of 101 samples from the Marcy Anorthosite Massif (61 from this study, 40 from Taylor 1969), indicate that two major and distinct processes of crustal contamination have affected the massif. Ninety percent of the 93 samples with over 65% plagioclase are enriched in 18O by 2.6 relative to normal anorthosites or gabbros: the average 18O for 83 enriched samples is 9.5 Depletions in 18O occur in 8% of the samples which have values ranging from 3.0 to 5.8 Only 2 of the samples fall within the normal magmatic range for anorthosites.Low 18O values of 3.0 to 5.8 in the anorthosite occur only near contacts, and a gradient in 18O occurs near the contact within the border zone of the massif. Low 18O values in both the anorthosite and adjacent wollastonite skarns (with 18O down to –1.3) were probably caused by isotopic exchange with heated meteoric water when the anorthosite intruded at shallow levels, prior to Grenvilleage ( 1.1 by) granulite facies metamorphism.The 18O-enrichment was ascribed to exchange between anorthosite and 18O-rich marble by means of a pervasive, H2O-CO2 fluid during the regional metamorphism by Taylor (1969). However, a number of lines of evidence argue against this hypothesis: 1) the preservation of premetamorphic low 18O values in anorthosite from the border zone as well as preserved gradients in 18O from a number of localities, 2) mass balance calculations of the amount of marble necessary to produce the 18O enrichment 3) metamorphic phase equilibria which buffer
and
to low values, and, 4) recent oxygen isotope analyses show homogeneity which indicates that magmatic oxygen isotope compositions have been preserved. We evaluated the importance of magmatic assimilation of country rock at the present level of intrusion as an alternative cause of the 18Oenrichment. Samples from 2 distinct lobes of the massif were analyzed: the NE lobe where xenoliths of metasedimentary country rock are common, and the NW lobe, where xenoliths are scarce and the country rock is dominantly granitic. The mean values of 18O for these two lobes are 9.6 in the NE and 9.3 in the NW. Thus, magmatic assimilation at the present level of exposure probably had only localized and relatively minor effects on the oxygen isotope composition of the massif. This conclusion is supported by Rb/Sr data: variations in Rb content and (87Sr/ 86Sr)i show that such crustal contamination is localized, generally occurring only in samples near the border zone. All of the available results suggest that the 18O-enrichment is a magmatic feature, acquired prior to intrusion at the present level of exposure. 相似文献
33.
Radan Květ 《GeoJournal》1994,34(4):365-370
34.
Vladimír Schenk Vít Kárník Zdeňka Schenková Reviewer A. Zátopek 《Studia Geophysica et Geodaetica》1982,26(2):132-144
Summary The distribution of earthquake foci in the crust and the upper mantle indicates the position of mobile zones. Comparing epicentral maps of Central and Eastern Europe, known tectonic lines, results of deep seismic sounding and gravimetric survey enables a scheme of potential seismogenic zones, which correspond to active fault zones separating plates and blocks in the area, to be compiled. The level of earthquake activity varies along the investigated boundaries and can be considered as a measure of the intensity of the present geodynamic processes.Paper presented at the joint symposium AlO of the XVIIth General Assembly of the European Seismological Commission and of the 7th Annual Meeting of the European Geophysical Society, Budapest (Hungary), Aug. 21. – 29., 1980. 相似文献
35.
Vít Kárník Zdeňka Schenková Vladimír Schenk Reviewer K. Pěč 《Studia Geophysica et Geodaetica》1982,26(1):42-58
Summary The time development of three large sequences, Friuli 1976, Thessaloniki 1978 and Monte Negro-Albania 1979, was investigated by analysing the characteristics of the time distribution of magnitudes of the events, M(t), of average magnitudes,
(t), and of the number of events, n(t), as well as the strain release curves and the magnitude-frequency relations, N(M). The existence of time gaps and of an anomalous decay of the numbers of shocks before major events, as well as the oscillation of
( const b–1) may be considered as precursory phenomena. The clustering of events has been tested by the Poisson and negative binomial laws.Communication presented at the XVIIth General Assembly of the European Seismological Commission in Budapest, 21–29 August, 1980 under the title Properties of Seismic Regime and Recent Earthquake Sequences in Europe. 相似文献
36.
A structural model for the seismicity of the Arudy (1980) epicentral area (Western Pyrenees, France)
Noalwenn Dubos-Sallée Bertrand Nivière Pierre Lacan Yves Hervouët 《Geophysical Journal International》2007,171(1):259-270
The Western Pyrenees presents a diffuse and moderate ( M ≤ 5.7) instrumental seismicity. It nevertheless historically suffered from strong earthquakes (I = IX MSK). The seismic sources of these events are not yet clearly identified. We focus on the Arudy (1980) epicentral area ( M = 5.1) and propose here the reactivation of early Cretaceous normal faults of the Iberian margin as a potential source. The late Cretaceous inversion of this basin, first in a left-lateral strike-slip mode and then in a more frontal convergence, resulted in a pop-up geometry. This flower structure attests of the presence of a deep crustal discontinuity.
The present-day geodynamic arrangement suggests that this accident is reactivated in a right lateral mode. This reactivation leads to a strain partitioning between the deep discontinuity that accommodates the lateral component of the motion and shallow thrusts, rooted on this discontinuity. These thrusts accommodate the shortening component of the strain. The distribution of the instrumental seismicity fits well the structural model of the Arudy basin. Whatever the compressive regional context, the structural behaviour of the system explains too the extensive stress tensor determined for the Arudy crisis if we interpret it in terms of strain ellipsoid. Indeed numerical modelling has shown that this concomitant activity of strike-slip and thrust faulting results in an extensive component that can rise 50 per cent of the finite strain.
We identify too a 25–30 km long potential seismic source for the Arudy area. The size of the structure and its potential reactivation in a strike-slip mode suggest that a maximum earthquake magnitude of ∼6.5 could be expected. The extrapolation of this model at the scale of the Western Pyrenees allows to propose other potential sources for major regional historical earthquakes. 相似文献
The present-day geodynamic arrangement suggests that this accident is reactivated in a right lateral mode. This reactivation leads to a strain partitioning between the deep discontinuity that accommodates the lateral component of the motion and shallow thrusts, rooted on this discontinuity. These thrusts accommodate the shortening component of the strain. The distribution of the instrumental seismicity fits well the structural model of the Arudy basin. Whatever the compressive regional context, the structural behaviour of the system explains too the extensive stress tensor determined for the Arudy crisis if we interpret it in terms of strain ellipsoid. Indeed numerical modelling has shown that this concomitant activity of strike-slip and thrust faulting results in an extensive component that can rise 50 per cent of the finite strain.
We identify too a 25–30 km long potential seismic source for the Arudy area. The size of the structure and its potential reactivation in a strike-slip mode suggest that a maximum earthquake magnitude of ∼6.5 could be expected. The extrapolation of this model at the scale of the Western Pyrenees allows to propose other potential sources for major regional historical earthquakes. 相似文献
37.
38.
Vít Kárník 《Studia Geophysica et Geodaetica》1958,2(4):400-401
Резюме Приводятся результаты анализа записей двух камерных взрывов, имевших место 15-го Февраля 1958 г. в Баварии. Взрывы были регистрированы
двумя вертикальными электродинамическими сейсмографами, иаготовленными в Геофизическом институте ЧСАН и назначенными для регистравии
слабых тектонических толчков.
Address: Boční II, Praha 13-Spořilov. 相似文献
Address: Boční II, Praha 13-Spořilov. 相似文献
39.
40.
Karel Prikner Jaroslav Střeštík Karel Dobeš Reviewer M. Hvoždara 《Studia Geophysica et Geodaetica》1972,16(3):262-270
Summary The spectral analysis of samples of beating-type pc3 pulsations, recorded at the Budkov Observatory during the summer months of 1968 and 1969 was carried out in the frequency interval10 mHz100 mHz. The average limits of the pulsation frequency range are roughly20 mHz60 mHz. The centre of the occurrence frequency graphs for both components is at the frequency fg 41 mHz. The analysis of three separated daily intervals showed a very slight tendency to a systematic decrease in the frequency of the centre from the morning to the afternoon. The study of the sense of rotation of the pulsation disturbance vector in the (X, Y)-plane showed an overall predominancy of L over R-types during daytime, particularly during the morning. 相似文献