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Karin Högdahl Jaroslaw Majka Håkan Sjöström Katarina Persson Nilsson Stefan Claesson Patrik Konečný 《Contributions to Mineralogy and Petrology》2012,163(1):167-188
Monazite in melt-producing, poly-metamorphic terranes can grow, dissolve or reprecipitate at different stages during orogenic
evolution particularly in hot, slowly cooling orogens such as the Svecofennian. Owing to the high heat flow in such orogens,
small variations in pressure, temperature or deformation intensity may promote a mineral reaction. Monazite in diatexites
and leucogranites from two Svecofennian domains yields older, coeval and younger U–Pb SIMS and EMP ages than zircon from the
same rock. As zircon precipitated during the melt-bearing stage, its U–Pb ages reflect the timing of peak metamorphism, which
is associated with partial melting and leucogranite formation. In one of the domains, the Granite and Diatexite Belt, zircon
ages range between 1.87 and 1.86 Ga, whereas monazite yields two distinct double peaks at 1.87–1.86 and 1.82–1.80 Ga. The
younger double peak is related to monazite growth or reprecipitation during subsolidus conditions associated with deformation
along late-orogenic shear zones. Magmatic monazite in leucogranite records systematic variations in composition and age during
growth that can be directly linked to Th/U ratios and preferential growth sites of zircon, reflecting the transition from
melt to melt crystallisation of the magma. In the adjacent Ljusdal Domain, peak metamorphism in amphibolite facies occurred
at 1.83–1.82 Ga as given by both zircon and monazite chronology. Pre-partial melting, 1.85 Ga contact metamorphic monazite
is preserved, in spite of the high-grade overprint. By combining structural analysis, petrography and monazite and zircon
geochronology, a metamorphic terrane boundary has been identified. It is concluded that the boundary formed by crustal shortening
accommodated by major thrusting. 相似文献
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Anders Wästfelt Katarina Saltzman Elisabeth Gräslund Berg Annika Dahlberg 《Geoforum》2012,43(6):1171-1181
Contemporary European agriculture has a number of additional aims beside of food production, such as safeguarding environmental services and conservation values. Substantial efforts at official levels are aimed towards sustainable development but also towards maintaining values of what may be termed vanishing landscapes. Selected areas and landscape features are set aside for protection or restoration. Individual efforts of this type have a long history in Sweden, and the issue has recently received increased attention, primarily due to more ambitious government goals concerning biodiversity conservation and Sweden’s ratification of the European Landscape Convention. This has resulted in an increased scientific and official interest in vanishing values in the rural landscape, where parts of Eastern Europe, such as the Maramures district in Romania, have been used as model examples of land use regimes which in the past was common in Sweden. In this context, the dilemma of romanticizing peasants’ use of land is highlighted and discussed more than has hitherto been done. This paper sheds light on some paradoxes inherent in official policies in relation to land use practices concerning the management of rural landscapes in Sweden, and relates the Swedish situation to a contrasting example of landscape practice in Romania. We discuss the concept of landscape care in relation to the construction and perception of landscape values and valuable landscapes through the lenses of rural realities and official policies. When Swedish authorities engage in the promotion of landscape care, they tend to work with slices of land, specific predefined values and individual farmers, and they often disregard the need to treat the landscape as a socio-ecological complex dynamic in space and time. We discuss how environmental policy generally could be improved through the adoption of a more inclusive and flexible approach towards aiding the different aims inherent in multifunctional rural landscapes. 相似文献
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Karin Holmgren Julia A. Lee-Thorp Gordon R. J. Cooper Katarina Lundblad Timothy C. Partridge Louis Scott Riashna Sithaldeen A. Siep Talma Peter D. Tyson 《Quaternary Science Reviews》2003,22(21-22):2311-2326
Data from stalagmites in the Makapansgat Valley, South Africa, document regional climatic change in southern Africa in the Late Pleistocene and Holocene. A new TIMS U-series dated stalagmite indicates speleothem growth from 24.4 to 12.7 ka and from 10.2 to 0 ka, interrupted by a 2.5 ka hiatus. High-resolution oxygen and carbon stable isotope data suggest that postglacial warming was first initiated 17 ka, was interrupted by cooling, probably associated with the Antarctic Cold Reversal, and was followed by strong warming after 13.5 ka. The Early Holocene experienced warm, evaporative conditions with fewer C4 grasses. Cooling is evident from 6 to 2.5 ka, followed by warming between 1.5 and 2.5 ka and briefly at AD 1200. Maximum Holocene cooling occurred at AD 1700. The new stalagmite largely confirms results from shorter Holocene stalagmites reported earlier. The strongest variability superimposed on more general trends has a quasi-periodicity between 2.5 and 4.0 ka. Also present are weaker 1.0 ka and 100-year oscillations, the latter probably solar induced. Given similarities to the Antarctic records, the proximate driving force producing millennial- and centennial-scale changes in the Makapansgat record is postulated to be atmospheric circulation changes associated with change in the Southern Hemisphere circumpolar westerly wind vortex. 相似文献
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Gilbert‐type deltas recording short‐term base‐level changes: Delta‐brink morphodynamics and related foreset facies 
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下载免费PDF全文 Gilbert‐type deltas are sensitive recorders of short‐term base‐level changes, but the delta‐front record of a base‐level rise tends to be erased by fluvial erosion during a subsequent base‐level fall, which renders the bulk record of base‐level changes difficult to decipher from the delta‐front deposits. The present detailed study of three large Pleistocene Gilbert‐type deltas uplifted on the southern coast of the Gulf of Corinth, Greece, indicates a genetic link between the delta‐front morphodynamic responses to base‐level changes and the delta‐slope sedimentation processes. Sigmoidal delta‐brink architecture signifies a base‐level rise and is accompanied by a debrite‐dominated assemblage of delta foreset deposits, thought to form when the aggrading delta front stores sediment and undergoes discrete gravitational collapses. Oblique delta‐brink architecture tends to be accompanied by a turbidite‐dominated assemblage of foreset deposits, which are thought to form when the delta‐front accommodation decreases and the sediment carried by hyperpycnal effluent bypasses the front. This primary signal of the system response to base‐level changes combines further with the secondary ‘noise’ of delta autogenic variation and possible allogenic fluctuations in fluvial discharge due to regional climatic conditions. Nevertheless, the evidence suggests that the facies trends of delta foreset deposits may be used to decipher the delta ‘hidden’ record of base‐level changes obliterated by fluvial topset erosion. Early‐stage bayhead deltas may be an exception from the hypothetical model, because their narrow front tends to be swept by river floods irrespective of base‐level behaviour and their subaqueous slope deposits are thus mainly turbidites. 相似文献
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Ljubomir Tashkov Katarina Manova Lidija Krstevska Mihail Garevski 《Bulletin of Earthquake Engineering》2010,8(4):995-1018
The ALSC base isolation system was investigated by testing a church model to the scale 1/3.5 on the two-component shaking
table at the IZIIS’ Laboratory, Skopje, Macedonia. The investigation was performed within the frames of the European FP6 project
PROHITECH, related to seismic protection of historical buildings by innovative and reversible mixed technology systems. This
system was originally developed in 2001 and applied on a model of a steel reservoir. The church model was tested twice: with
an active base-isolation system and fixed to the base. The effectiveness of the base-isolation system was investigated by
the transfer function/floor response spectra technique. Special software for calculation of the transfer functions and floor
response spectra based on experimental data, referred as “SPECTRA”, was developed by the authors of this paper. The main objective
of the investigations presented in this paper was evaluation of the effectiveness of the ALSC floating sliding base-isolation
system by using the Response Spectra approach. Comparison of the Floor Response Spectra was done for two cases a fixed base
model and a base-isolated model. The base response spectrum was calculated from the input time history of the Montenegro earthquake
compressed 3.5 times (geometry scale of the model). The Transfer Functions and the Floor response Spectra at a particular
level were calculated from the Cross Power Spectra (CPS) and the Auto-Power Spectra. The obtained results showed that the
effect of the base-isolation system was considerable, with a low transmissibility of energy from shake table to the model. 相似文献
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Heleen A. de Wit Ahti Lepistö Hannu Marttila Hannah Wenng Marianne Bechmann Gitte Blicher-Mathiesen Karin Eklöf Martyn N. Futter Pirkko Kortelainen Brian Kronvang Katarina Kyllmar Jelena Rakovic 《水文研究》2020,34(25):4831-4850
Agricultural, forestry-impacted and natural catchments are all vectors of nutrient loading in the Nordic countries. Here, we present concentrations and fluxes of total nitrogen (totN) and phosphorus (totP) from 69 Nordic headwater catchments (Denmark: 12, Finland:18, Norway:17, Sweden:22) between 2000 and 2018. Catchments span the range of Nordic climatic and environmental conditions and include natural sites and sites impacted by agricultural and forest management. Concentrations and fluxes of totN and totP were highest in agricultural catchments, intermediate in forestry-impacted and lowest in natural catchments, and were positively related %agricultural land cover and summer temperature. Summer temperature may be a proxy for terrestrial productivity, while %agricultural land cover might be a proxy for catchment nutrient inputs. A regional trend analysis showed significant declines in N concentrations and export across agricultural (−15 μg totN L−1 year−1) and natural (−0.4 μg NO3-N L−1 year−1) catchments, but individual sites displayed few long-term trends in concentrations (totN: 22%, totP: 25%) or export (totN: 6%, totP: 9%). Forestry-impacted sites had a significant decline in totP (−0.1 μg P L−1 year−1). A small but significant increase in totP fluxes (+0.4 kg P km−2 year−1) from agricultural catchments was found, and countries showed contrasting patterns. Trends in annual concentrations and fluxes of totP and totN could not be explained in a straightforward way by changes in runoff or climate. Explanations for the totN decline include national mitigation measures in agriculture international policy to reduced air pollution and, possibly, large-scale increases in forest growth. Mitigation to reduce phosphorus appears to be more challenging than for nitrogen. If the green shift entails intensification of agricultural and forest production, new challenges for protection of water quality will emerge possible exacerbated by climate change. Further analysis of headwater totN and totP export should include seasonal trends, aquatic nutrient species and a focus on catchment nutrient inputs. 相似文献
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Mladjen Ćurić Dejan Janc Katarina Veljović 《Theoretical and Applied Climatology》2010,102(3-4):471-481
Convective precipitation is the main cause of extreme rainfall events in small areas. Its primary characteristics are both large spatial and temporal variability. For this reason, the monitoring of accumulated precipitation fields (liquid and solid components) at the surface is difficult to carry out through the use of rain gauge networks or remote-sensing observations. Alternatively, numerical models seem to be the most powerful tool in simulating convective precipitation for various analyses and predictions. Due to a lack of comparisons between modelled and observed precipitation characteristics over a long period of time, we focus our research on comparisons between observations and three model samples of accumulated convective precipitation over a particular study area. We use a numerical cloud model with two model schemes involving the unified Khrgian–Mazin size distribution of cloud drops and a model scheme involving a monodisperse cloud droplet spectrum and the Marshall–Palmer size distribution for raindrops, respectively. For comparison, we have selected a study area with a sounding site. Our analysis shows that the model version with the Khrgian–Mazin size distribution exhibits a better agreement with the observed mean, median and range of extreme values of accumulated convective precipitation. Model simulations with the Khrgian–Mazin size distribution most closely match observations, with a correlation coefficient of 0.91. Use of the Marshall–Palmer size distribution, on the other hand, systemically underestimates the observed precipitation and has the lowest correlation coefficient among the methods, 0.83. Such an investigation is crucial to improve predictions of accumulated convective precipitation for various climatological and hydrological analyses and predictions. 相似文献