Deltas in the Abisko area, northern Sweden: the Abiskojokka delta in lake Torneträsk     

Hans Andrén  Christer Jonasson  & Johan Ottosson 《Geografiska Annaler: Series A, Physical Geography》2002,84(3&4):151-156

  相似文献   

Deltas in the Abisko area, northern Sweden: the Abiskojokka delta in lake Torneträsk     

Hans Andrén  Christer Jonasson  & Johan Ottosson 《Geografiska Annaler: Series A, Physical Geography》2002,84(3-4):151-156

  相似文献   

Controls on magmatism in an island arc environment: study of lavas and sub-arc xenoliths from the Tabar–Lihir–Tanga–Feni island chain, Papua New Guinea     

George D. Kamenov  Michael R. Perfit  Paul A. Mueller  Ian R. Jonasson 《Contributions to Mineralogy and Petrology》2008,155(5):635-656

The Tabar–Lihir–Tanga–Feni (TLTF) islands of Papua New Guinea mainly comprise high-K calc-alkaline and silica undersaturated alkaline rocks that have geochemical features typical for subduction-related magmatism. Numerous sedimentary, mafic, and ultramafic xenoliths recovered from Tubaf seamount, located on the flank of Lihir Island, provide a unique opportunity to study the elemental and isotopic composition of the crust and mantle wedge beneath the arc and to evaluate their relationships to the arc magmatism in the region. The sedimentary and mafic xenoliths show that the crust under the islands is composed of sedimentary sequences and oceanic crust with Pacific affinity. A majority of the ultramafic xenoliths contain features indicating wide spread metasomatism in the mantle wedge under the TLTF arc. Leaching experiments reveal that the metasomatized ultramafic xenoliths contain discrete labile phases that can account for up to 50% or more of elements such as Cu, Zn, Rb, U, Pb, and light REE (rare-earth elements), most likely introduced in the xenoliths via hydrous fluids released from a subducted slab. The leaching experiments demonstrated that the light REE enrichment pattern can be more or less removed from the metasomatized xenoliths and the residual phases exhibit REE patterns that range from flat to light REE depleted. Sr–Nd isotopic data for the ultramafic residues show a coupled behavior of increasing ⁸⁷Sr/⁸⁶Sr with decreasing ¹⁴³Nd/¹⁴⁴Nd ratios. The labile phases in the ultramafic xenoliths, represented by the leachates, show decoupling between Sr and Nd with distinctly more radiogenic ⁸⁷Sr/⁸⁶Sr than the residues. Both leachates and residues exhibit very wide range in their Pb isotopic compositions, indicating the involvement of three components in the mantle wedge under the TLTF islands. Two of the components can be identified as Pacific Oceanic mantle and Pacific sediments. Some of the ultramafic samples and clinopyroxene separates, however, exhibit relatively low ²⁰⁶Pb/²⁰⁴Pb at elevated ²⁰⁷Pb/²⁰⁴Pb suggesting that the third component is either Indian Ocean-type mantle or Australian subcontinental lithospheric mantle. Geochemical data from the ultramafic xenoliths indicate that although the mantle wedge in the area was extensively metasomatized, it did not significantly contribute to the isotopic and incompatible trace element compositions of TLTF lavas. Compared to the mantle samples, the TLTF lavas have very restricted Pb isotopic compositions that lie within the Pacific MORB range, indicating that magma compositions were dominated by melts released from a stalled subducted slab with Pacific MORB affinity. Interaction of slab melts with depleted peridotitic component in the mantle wedge, followed by crystal fractionation most likely generated the geochemical characteristics of the lavas in the area. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

A holocene zinc orebody formed by supergene replacement of mosses     

Ian R. Jonasson  Lionel E. Jackson  Donald F. Sangster 《Journal of Geochemical Exploration》1983,18(3):189-194

An extensive deposit of secondary zinc minerals has been formed at Howard's Pass, Yukon by replacement of mosses and as a cement within talus. The deposits are of Holocene age (younger than 9610 yr. B.P.) and occur in blanket peat bogs percolated by zinc-rich springwaters. Buried moss strata undergo cell by cell replacement forming zincian clacite, smithsonite and hemimorphite. The last is the most important secondary mineral in both mosses and talus.  相似文献   

Eisbedeckung und hypolimnische Sauerstoffanreicherung im Greifensee von 1950 bis 1980     

Prof. Dr. Eugen A. Von Thomas  Dr. Christer G. Örn 《Aquatic Sciences - Research Across Boundaries》1982,44(1):117-148

Hypolimnetic oxygen in the highly eutrophic Swiss lake Greifensee (area 8 km², maximum depth 33 m) was almost entirely depleted during summer stratification. We found a strong empirical relation between wind action across the lake surface and hypolimnetic reoxygenation in the cold half year. Long periods of ice cover severely limited anemogenic reoxygenation.   相似文献   

Do leptites represent precambrian island arc rocks?     

Christer Löfgren 《Lithos》1979,12(2):159-165

Comparison of 172 analyses of Recent to Mesozoic volcanic rocks from New Zealand and 122 analyses of Svecofennian volcanic rocks (leptites) from the Swedish Precambrian (1,700–2,200 my), reveal strong similarities between these rock types. This suggests that the leptites form an island are suite of calc-alkaline rocks, ranging from basalt to rhyolite in composition and that they represent a well-defined rock type containing little or no sedimentary material. Probably they originated at a Precambrian subduction zone.  相似文献   

The airborne transport of Saharan dust: A review     

Christer Morales 《Climatic change》1986,9(1-2):219-241

The extent of the short and long-range transport, and the atmospheric residence time of airborne Saharan dust are dependent on factors like the initial size distribution of the dust and the type of weather systems raising dust and creating different kinds of dust storms.The paper discusses these factors. It further reviews a number of investigations of long-range transport of Saharan dust out from the Sahara, and shows how eolian dust can be monitored with the help of meteorological SYNOP and METAR observations.  相似文献   

Geo–ecology and management of sensitive montane landscapes     

John E. Gordon  Igor J. Dvorák  Christer Jonasson  Melanie Josefsson  Milena Kociánová  & Des B.A. Thompson 《Geografiska Annaler: Series A, Physical Geography》2002,84(3-4):193-203

Montane (alpine) areas are generally of high value for nature conservation. Such environments and the habitats they support are dynamic and often fragile. They are vulnerable to disturbance from a range of human activities and are responsive to climate changes over short and long timescales. Biodiversity and conservation values are closely linked to geological history, geomorphological processes and soils, and it is crucial that management systems are based on understanding these links.
There are many similarities between the Cairngorm Mountains (Scotland), the Giant Mountains (Czech Republic) and Abisko Mountains (Sweden) in terms of geology, geomorphology, ecology, links with biodiversity and high conservation importance. Comparable pressures and management issues involve, to varying degrees, a history of human use and impacts from deforestation, pasturing, grazing, recreation and atmospheric pollution. Landscape change therefore involves a complex interplay between natural and anthropogenic factors. Managing such change requires better understanding of the geo–ecological processes involved and the factors that determine landscape sensitivity. This is illustrated through a simple framework and examples from the three areas. Comparison of landscape sensitivity between similar montane areas, but in different geographic locations and climatic environments, should allow more informed management planning and a precautionary approach in advance of further changes in human activity and from predicted global warming scenarios.  相似文献   

Three-component modelling of C-rich AGB star winds – IV. Revised interpretation with improved numerical descriptions     

Christer Sandin 《Monthly notices of the Royal Astronomical Society》2008,385(1):215-230

  相似文献   

Evapotranspiration and crop coefficient for a temperate desert steppe ecosystem using eddy covariance in Inner Mongolia,China   总被引：2，自引：0，他引：2  

Feng Zhang  Guangsheng Zhou  Yu Wang  Fulin Yang  Christer Nilsson 《水文研究》2012,26(3):379-386

  相似文献