Inherent gravitational instability of thickened continental crust with regionally developed low- to medium-pressure granulite facies metamorphism     

Taras V. Gerya  Walter V. Maresch  Arne P. Willner  Dirk D. Van Reenen  C.Andre Smit 《Earth and Planetary Science Letters》2001,190(3-4):221-235

Petrological arguments show that regionally developed low- to medium-pressure, high-temperature granulite facies metamorphism may critically enhance the lowering of crustal density with depth. This leads to gravitational instability of homogeneously thickened continental crust, mainly due to changes in mineral assemblages and the thermal expansion of minerals in conjunction with the exponential lowering of the effective viscosity of rocks with increasing temperature. It is argued that crustal processes of gravitational redistribution (crustal diapirism) contributing to the exhumation of granulite facies rocks may be activated in this way.  相似文献   

Population Belongs on the Johannesburg Agenda     

Wolfgang Lutz  Mahendra Shah  Richard E. Bilsborrow  John Bon-gaarts  Partha DasGupta  Barbara Entwisle  Günther Fischer  Brigida Garcia  Daniel J. Hogan  Arne Jernelöv  Zhenghua Jiang  Robert W. Kates  Sanjaya Lall  F. Landis MacKellar  P.K. Makinwa-Adebusoye  Anthony J. McMichael  Vinod Mishra  Norman Myers  Nebojsa Nakicenovic  Sten Nilsson  Brian C. O'Neill  Xizhe Peng  Harriet B. Presser  Nafis Sadik  Warren C. Sanderson  Gita Sen  Barbara Torrey  Dirk van de Kaa  Hans J.A. van Ginkel  Brenda Yeoh  Huda Zurayk 《Global Change & Human Health》2002,3(1):33-35

The forthcoming World Summit on Sustainable Development (WSSD) in Johannesburg (August 26-September 4, 2002) has been set by the United Nations to consider strategies toward sustainable development in all its dimensions. Hence, its mandate is broader than that of the Rio 1992 United Nations Conference on Environment and Development (UNCED). Population issues have so far been discussed in a separate series of World Population Conferences (Bucharest 1974, Mexico City 1984, Cairo 1994). With no new World Population Conference scheduled for 2004 and Johannesburg having a mandate that is stated to explicitly include social and economic aspects, population as a key component of sustainable development should figure prominently on the Johannesburg agenda. Yet, after the third of four preparatory meetings for Johannesburg (which ended in New York on April 5th), consideration of population is completely absent. The reasons for this are not entirely clear. We assume that they have to do with the fear of entering into political controversies over abortion. We are concerned that, despite its broader mandate, in most countries inputs to Johannesburg are being prepared mainly by environment ministries who have little experience in dealing with population questions. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Three-dimensional modelling of an isolated carbonate buildup (Triassic, Dolomites, Italy)   总被引：1，自引：0，他引：1  

Wolfgang Blendinger  Peter Brack†  Arne Kristoffer Norborg‡  Erik Wulff-Pedersen§ 《Sedimentology》2004,51(2):297-314

The Middle Triassic carbonate buildups of the Dolomites show facies similarities with mud mounds but display apparent architectural elements of flat‐topped carbonate platforms. In order to test whether the facies similarities to mounds are also reflected in the internal buildup architecture, a three‐dimensional modelling study of the Middle Triassic Monte Cernera buildup has been carried out. The Cernera buildup exhibits apparent geometries suggesting a mounded platform in the lower and uppermost part of the buildup, separated by an interval with apparent platform geometry and a retrogradational platform interior, which is difficult to explain with a flat top platform model. For this purpose, a number of three‐dimensional models were constructed using the three‐dimensional modelling programme petrel ^TM. Key geological horizons were constructed based on outcrop measurements, intermediate horizons were calculated in the modelling program, and the intersections of the modelled layers with a digital topography surface were displayed and compared with outcrop photographs. The models were refined stepwise until a best fit with the actual bedding architecture was achieved. The best fit model shows that the mounded geometries in the lower and uppermost part of the buildup are real architectural elements. The intermediate platform stage, about 1·5 km across, had probably retained a mounded top with a relief of up to 50 m, which is difficult to distinguish from an absolutely flat top, but necessary to explain the retrogradational platform interior. The present study shows that Monte Cernera was dominated by mounded geometries at all stages of platform development. The mounded geometry plus facies data suggest that the platform is a deep‐water accumulation, below the zone of intense wave energy, but within the photic zone. The Cernera represents a tropical buildup type, which did not have the capacity to grow into continuously wave‐swept environments because of the small size and the absence of a wave‐resistant energy barrier. Such buildup types are probably common after major crises in earth history, when reef organisms were virtually absent.  相似文献   

Elektrooptische entfernungsmessung     

Arne Bjerhammar 《Journal of Geodesy》1956,30(2):1-15

Ohne Zusammenfassung übersetzung von: Elektrooptisk avst?ndsm?tning,Svensk Lantm?teritidskr. 2 (1955).  相似文献   

Leaching of nitrate from arable land into groundwater in Sweden     

Arne Gustafson 《Environmental Geology》1983,5(2):65-71

The agricultural influence on the quality of the groundwater in Sweden is mostly associated with infiltration areas. The local conditions here determine the extent of the nitrate leakage. It is evident that certain combinations of factors in normal cropping can give unduly high nitrate concentrations in the groundwater.  相似文献   

Correlations between metamorphic events and Rb-Sr ages in metasediments and eclogite from Western Tasmania     

Arne Rheim  William Compston 《Lithos》1977,10(4):271-289

The Strathgordon area of low metamorphic grade (450±50°C, 4±1 Kb) and the eclogitebearing Lyell Highway-Collingwood River area, which is of higher grade (670±20°C, 11±1 Kb), have been studied by the Rb-Sr technique.

Three deformational events, D₁ to D₃ correlate in time with two important P,T events, here termed D₂₋₂ and D₃, D₁₋₂ reflects the continuous prograde P,T environment up to the metamorphic maximum of the two areas (D₂), while D₂ is a superimposed deformational event occuring at lower P,T conditions. According to stratigraphical constraints D₃ must have occured before or about 550 m.y. ago.

It is possible from rather complex Rb-Sr data to indicate ages for the D_1–2 and D₃ events. Two-point total rock+phengite (mica) ages together with total rock isochrons using closely spaced samples show that the main metamorphic event D_1–22 occurrred at about 800 m.y. in both areas. Similar data suggest that the superimposed event D₃ occurred between 550 and 630 m.y. ago, probably near the lower age limit. This deformation (crenulation cleavage) was responsible for the local resetting of total rock and mineral systems.

Consistent with later Palaeozoic events, the Cambrian-early Ordovician Jukesian Movement and the Devonian Tabberabberan Orogeny, which affected some Rb-Sr mineral systems (phengite, amphibole and chlorite), have ages of 500±20 m.y. and 385-350 m.y. respectively.

Due to dispersion of the eclogite total rock data points along secondary isochrons it is difficult to estimate an original age. The age of the original minerals must however have been set by the 800 m.y. D_1–2 event, as the P,T history of the eclogite is the same as that of the surrounding schists.  相似文献   

Secondary geologically meaningless Rb---Sr isochrons, low Sr/Sr initial ratios and crustal residence times of high-grade gneisses     

Dennis Field  Arne Rheim 《Lithos》1980,13(4):295-304

Dark green quartzo-feldspathic charnockitic ortho-gneisses from Arendal, southern Norway, have locally been decoloured in the vicinities of intrusive, undeformed granite sheets and pegmatite dikes. The result is a series of pink rocks which are macroscopically indistinguishable from primary augen granite gneisses. The main mineralogical changes associated with the secondary decolcuration occurred under relatively low-grade conditions, and mainly involved chlorite, serpentine ± actinolitic amphibole ± biotite growth. The alterations were initiated along narrow, irregularly spaced cracks. The primary ( 1540 m.y.) total rock Rb---Sr isotopic systems which relate to the charnockite mineralogy were disturbed, and sometimes reset, during the secondary event which occurred at 1060 m.y. Locality by locality, the decoloured samples yield linear arrays corresponding to 1457 ± 200 m.y., 1303 ± 50 m.y. and 1125 ± 185 m.y. The combined data (n = 19) give an apparent age of 1364 ± 43 m.y. with an ⁸⁷Sr/⁸⁶Sr initial ratio of 0.7011 ± 0.0018. This apparent age is unrelated to any geological event and there is no overlap at the 2δ level between the ⁸⁷Sr/⁸⁶Sr initial ratio and that defined by the primary event (0.70345 ± 0.00014). Any estimate of crustal residence time based on these decoloured samples would be in error. The weight of evidence is against significant involvement of Rb mobility in the isotopic resetting process which accompanied decolouration. A model involving modification of the ⁸⁷Sr/⁸⁶Sr ratios is preferred.  相似文献   

On the foundation of collocation in physical geodesy     

Arne Bjerhammar 《Journal of Geodesy》1982,56(4):312-328

The boundary value problem in physical geodesy is nowadays mostly presented with the use of an advanced stochastic model by Krarup-Moritz. This model includes a primary Gauss-Markov model and an adjoining Wiener-Hopf model. Degenerations of the Wiener-Hopf section are found in thesingular auto-covariance matrix of the residuals. The non-singular inverse of the auto-covariance matrix of the signal is proved to be a generalized inverse of the singular auto-covariance matrix of the residuals. The joint model is given a non-stochastic evaluation for a case with spherical external surface (using a non-singular inverse). These findings will not prevent a successful application of the model, which has important merits, specially when using suitablea priori values for the stochastic parameters in the covariance functions. A method for quadratic unbiased estimation ofa priori variances is presented in an introductory section. It is meant to be of value when using a solution of the boundary value problem with the collocation technique based on the classical Gauss-Markov solution. (Bjerhammar (1963).)  相似文献   

Model analysis of the measured concentration of organic gases in the Norwegian Arctic     

Ivar S. A. Isaksen  Øystein Hov  Stuart A. Penkett  Arne Semb 《Journal of Atmospheric Chemistry》1985,3(1):3-27

A 2-D meridional model for the chemistry and transport in the troposphere is used to study the seasonal variation of the concentration of organic gases like C₂H₂, C₂H₆, C₃H₈, C₆H₆, C₇H₈. CHCl₃ and C₂Cl₄ at high latitudes. The anthropogenic sources for these species were estimated, and the temporal and latitudinal distribution of OH and O₃ was calculated using a complex photochemical reaction system. There is fair agreement between the calculated annual variation and the measured concentrations for C₂H₂, C₂H₆, C₃H₈, C₇H₈ and C₂Cl₄ at Spitsbergen during July 1982 and March/April 1983, with a distinct late winter maximum and summer minimum. For CHCl₃, the direct anthropogenic source is minor compared to indirect anthropogenic or natural sources. For benzene, emission in car exhaust is important, but other anthropogenic sources are required for the calculations to agree with the measurements. Measured C₂H₄ and C₃H₆ concentrations are much higher than the calculated ones based on anthropogenic emissions, and show opposite seasonal trends. This indicates biogenic sources for these compounds.A buildup of PAN (300 pptv) is calculated at high latitudes during winter. This makes it the dominant source for NO_x as the temperature increases in the spring. NO_x is found to be a limiting factor for O₃ production at high latitudes during spring.  相似文献   

Gas chromatographic/mass spectrometric (GC/MS) analysis of C_27–30-steranes     

Arne Steen 《Organic Geochemistry》1986,10(4-6)

Sterane analyses in petroleum geochemistry are normally based on mass spectrometric detection of major fragment ions. This method has limited specificity and is much improved by detection of parent or metastable transition ions. The latter provide a less complex picture and suggest a better analytical approach, although the technique has only limited mass resolution.Geochemical parameters calculated from mass spectrometric data are dependent on the method employed. Accepted values of these parameters will, therefore, show some variations with the techniques used.Internal standards are necessary for quantitative determination of components by mass spectrometry. A recommended approach is to use a stable isotope labelled analogue of the compound being determined with, in the case of deuterium, only three or four isotopic atoms introduced into the molecule. Too few isotopic atoms will result in interference from the natural isotopes and too many will give analytical deviations.  相似文献