Aragonite and magnesite in eclogites from the Jæren nappe,SW Norway: disequilibrium in the system CaCO3–MgCO3 and petrological implications     

M. A. SMIT  M. BRÖCKER  E. E. SCHERER 《Journal of Metamorphic Geology》2008,26(9):959-979

Eclogites from the Jæren nappe in the Caledonian orogenic belt of SW Norway contain aragonite, magnesite and dolomite in quartz‐rich layers. The carbonates comprise composite grains that occur interstitially between phases of the eclogite facies assemblage: garnet + omphacite + zoisite + clinozoisite + quartz + apatite + rutile ± dolomite ± kyanite ± phengite. Pressure and temperature conditions for the main eclogite stage are estimated to be 2.3–2.8 GPa and 585–655 °C. Published ultrahigh pressure (UHP) experiments on CaO‐, MgO‐ and CO₂‐bearing systems have shown that equilibrium assemblages of aragonite and magnesite form as a result of dolomite breakdown at pressures >5 GPa. As a result, recognition of magnesite and aragonite in eclogite facies rocks has been used as an indicator for UHP conditions. However, petrological testing showed that the samples studied here have not experienced such conditions. Aragonite and magnesite show disequilibrium textures that indicate replacement of magnesite by aragonite. This process is inferred to have occurred via a coupled dissolution–precipitation reaction. The formation of aragonite is constrained to eclogite facies conditions, which implies that the studied rocks have experienced metasomatic, reactive fluid flow during their residence at high pressure (HP) conditions. During decompression, the bimineralic carbonate aggregates were overgrown by rims of dolomite, which partially reacted with aragonite to form Mg‐calcite. The well‐preserved carbonate assemblages and textures observed in the studied samples provide a detailed record of the reaction series that affected the rocks during and after their residence at P–T conditions near the coesite stability field. Recognition of the HP mechanism of magnesite replacement by aragonite provides new insight into metasomatic processes that occur in subduction zones and illustrates how fluids facilitate HP carbonate reactions that do not occur in dry systems at otherwise identical physiochemical conditions. This study documents that caution is warranted in interpreting aragonite‐magnesite associations in eclogite facies rocks as evidence for UHP metamorphic conditions.  相似文献   

The 73-day periodicity of the flare index during the current solar cycle 22     

Atila Özgüç  Tamer Ataç 《Solar physics》1994,152(1):318-318

The flare index of the current solar cycle 22 is analysed to detect intermediate-term periodicities from Sep. 1, 1986 to Dec. 31, 1991. Power spectral analysis of the time series of solar flare index data reveals a periodicity around 73 and 53 days. We find that a periodicity of 73 days was in operation from 1988 November to the end of 1991 December. We also find that when the 73-day periodicity or the 154-day periodicity is in operation, the flare index is well correlated with the relative sunspot numbers. As a conclusion, we do not expect to see a resumption of the 154-day or 73-day periodicity, but we do expect only one of the periodicity near the integral multiples of 25^d.8 in the next solar cycles.  相似文献   

Rb-Sr systematics of Permian volcanites in the Schwarzwald (SW-Germany)     

Helmut Schleicher  Hans Joachim Lippolt  Ingrid Raczek 《Contributions to Mineralogy and Petrology》1983,84(2-3):272-280

Rb-Sr mineral ages and Sr isotopic ratios were determined for several Permian rhyolites of the Schwarzwald, mainly by using mica-apatite pairs. Extrusion ages between_307+5 and 286+7 Ma were found ( _Rb=1.42· 10^–11 a^–1, 2). The initial Sr isotopic ratios range from 0,710 to 0.7125, with one exception (St. Märgen: 0.706). The Rb-Sr age of the granite porphyry Schweighof in the Southern Schwarzwald is 323+4 Ma.Thus the subsequent volcanic activity of the Hercynian orogeny lasted nearly 20–30 Ma, starting in the Late Carboniferous and culminating in the Early Permian. The volcanic activity moved in time from South to North. In the Southern as well as the Northern Schwarzwald a hiatus of about 20 Ma exists between late orogenic plutonism and subsequent volcanism. The initial ratios lie on the crustal evolution line of Schwarzwald basement and favour, with the St. Märgen porphyry as exception, a crustal provenance of the volcanic magmas.  相似文献   

Some views on land ownership in urban planning and housing production in Sweden     

Ella Ödmann 《Geoforum》1973,4(1):31-41

Urbanisation is a functional change in land utilisation which requires a high degree of coordination in time and space. Swedish society has not considered it possible to entrust this coordination to the free market forces. A number of measures was introduced during the latter part of the sixties with a view to coordinating housing development by means of local authority-land ownership and preventing land speculation. In a recently published report of a Government Commission it is proposed that dwellings receiving Government housing loans (more than 90 % of building construction) shall only be built on land which is owned by the local authorities. The local authorities may then be assumed to be the only purchasers of land for housing development purposes. Their housing policy can be given a more short-term character and can be better adapted to urban planning. Urban development in Sweden during recent decades is characterised by a struggle between the two groups of our mixed-economy society, i. e., a social democratic government, and capitalistic enterprise. As far as the private individual is concerned, both parties are remote decision makers. The important question is whether an improvement in town environment may be expected before the private individual has been given a chance to influence planning. The relationship between housing development and land ownership in some Swedish towns over the period 1950–1970 is presented as an example of the realization of land policy.  相似文献   

Zur Tektonik im Bereich der Brennerlinie     

Dr. Hansgeorg FÖrster  Dipl.-Min. Annemarie Schmitz-Wiechowski 《International Journal of Earth Sciences》1970,59(2):637-648

Zusammenfassung Die Verfasser entwickeln aus den Ergebnissen ihrer feldgeologischen und petrographischen Untersuchungen — gestützt auf gesteinsmechanische Überlegungen und tektonische Experimente — ein neues geologisches Konzept für das Tauernwestende.

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A new concept about the geology of the Brenner region is developed from field observations, petrographic investigations, mechanic considerations and tectonic experiments.

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Résumé Les auteurs présentent une conception géologique nouvelle de la partie occidentale des Tauern d'après leurs observations géologiques sur le terrain et leurs recherches pétrographiques, en s'appuyant sur des considérations de la mécanique des roches et des expériences tectoniques.

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FrauSchmitz-Wiechowski (Wiechowski 1968) hat die Phyllitserie östlich des Brenner untersucht und tektonische Grenzflächen verfolgt.Förster bearbeitete hauptsächlich das Gebiet westlich des Brenner.  相似文献   

Zu Wärmehaushalt und Hydroklima der nordamerikanischen Deserts     

Prof. Dr. Ingrid Henning  Dr. D. Henning 《Theoretical and Applied Climatology》1984,34(4):341-352

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J.T. Houghton, L.G. Meira Filho, B.A. Callander, N. Harris, A. Kattenberg, and K. Maskell (eds.): Climate Change 1995, The Science of Climate Change     

CHRISTIAN-D. SCHÖNWIESE 《Journal of Atmospheric Chemistry》1997,27(1):105-106

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20th-CENTURY CHANGES OF TEMPERATURE IN THE MOUNTAIN REGIONS OF CENTRAL EUROPE     

RUDOLF O. WEBER  PETER TALKNER  INGEBORG AUER  REINHARD BÖHM  MARJANA GAJIĆ-ČAPKA  KSENIJA ZANINOVIĆ  RUDOLF BRÁZDIL  PAVEL FAŠKO 《Climatic change》1997,36(3-4):327-344

Daily maximum and minimum temperatures from 29 low-lying and mountain stations of 7 countries in Central Europe were analyzed. The analysis of the annual variation of diurnal temperature range helps to distinguish unique climatic characteristics of high and low altitude stations. A comparison of the time series of extreme daily temperatures as well as mean temperature shows a good agreement between the low-lying stations and the mountain stations. Many of the pronounced warm and cold periods are present in all time series and are therefore representative for the whole region. A linear trend analysis of the station data for the period 1901–1990 (19 stations) and 1951–1990 (all 29 stations) shows spatial patterns of similar changes in maximum and minimum daily temperatures and diurnal temperature range. Mountain stations show only small changes of the diurnal temperature range over the 1901–1990 period, whereas the low-lying stations in the western part of the Alps show a significant decrease of diurnal temperature range, caused by strong increase of the minimum temperature. For the shorter period 1951–1990, the diurnal temperature range decreases at the western low-lying stations, mainly in spring, whereas it remains roughly constant at the mountain stations. The decrease of diurnal temperature range is stronger in the western part than in the eastern part of the Alps.  相似文献   

ON THE POSSIBLE CHANGES OF THE SOLAR DIFFERENTIAL ROTATION DURING THE ACTIVITY CYCLE DETERMINED USING MICROWAVE LOW-BRIGHTNESS-TEMPERATURE REGIONS AND Hα FILAMENTS AS TRACERS     

BRAJŠA  R.  RUŽDJAK  V.  VRŠNAK  B.  POHJOLAINEN  S.  URPO  S.  SCHROLL  A.  WÖHL  H. 《Solar physics》1997,171(1):1-34

The solar rotation rate obtained using the microwave Low-brightness-Temperature Regions (LTRs) as tracers in the heliographic range ± 55° from the years 1979–1980, 1981–1982, 1987–1988, and 1989–1991 varied from 3% to 4% in medium latitudes, and below 1% at the equator. Using H filaments as tracers at higher latitudes from the years 1979, 1980, 1982, 1984, and 1987, the solar rotation rate variation was between 2% and 8%. This represents an upper limit on the rotation rate variation during the solar activity cycle. Such changes could be caused by short-lived, large-scale velocity patterns on the solar surface. The Sun revealed a higher rotation rate on the average during the maxima of the solar activity cycles 21 and 22, i.e., in the periods 1979–1980 and 1989–1991, respectively, which differs from the rotation rates (lower on the average) in some years, 1981–1982 and 1987–1988, between the activity maximum and minimum (LTR data). Simultaneous comparison of rotation rates from LTRs and H filament tracings was possible in very limited time intervals and latitude bands only, and no systematic relationship was found, although the rotation rates determined by LTRs were mostly smaller than the rotation rates determined by H filaments. The errors obtained by applying different fitting procedures of the LTR data were analyzed, as well as the influence of the height correction. Finally, the north–south asymmetry in the rotation rate investigated by LTRs indicates that the southern solar hemisphere rotated slower in the periods under consideration, the difference being about 1%. The reliability of all obtained results is discussed and a comparison with other related studies was performed.  相似文献   

Temporal variations in the fractal properties of seismicity in the North Anatolian Fault Zone between 31°E and 41°E     

Ali Osman Öncel  Ian Main  Ömer Alptekin  Patience Cowie 《Pure and Applied Geophysics》1996,147(1):147-159

We investigate the nature of temporal variations in the statistical properties of seismicity associated with the North Anatolian Fault Zone between longitudes 31°–41°E during the instrumental period 1900–1992. Temporal variations in the seismicb value and the fractal (correlation) dimensionD _c of earthquake epicenters are examined for earthquakes of magnitudeM _S 4.5, using sliding windows of 100 consecutive events.b varies temporally between 0.6 and 1.0, andD _c between 0.6 and 1.4, both representing significant fluctuations above the errors in measurement technique. A strong negative correlation (r=–0.85) is observed betweenb andD _c , consistent with previous observation of seismicity in Japan and southern California. Major events early in this century (M _S 7) are associated with lowb and highD _c , respectively consistent with greater stress intensity and greater spatial clustering of epicenters—both implying a greater degree of stress concentration at this time.  相似文献