Petrogenesis of Archaean Trondhjemites, Tonalites, and Granodiorites from Eastern Finland: Major and Trace Element Geochemistry   总被引：17，自引：4，他引：17  

MARTIN  HERV? 《Journal of Petrology》1987,28(5):921-953

The grey gneisses of eastern Finland form the basement on whichthe Archaean greenstone belts were developed. They are composedof orthogneisses emplaced during two distinct magmatic episodes:2.86 Ga (Kivij?rvi gneisses) and 2.65 (Naavala gneisses). Theirmodal and chemical compositions are those of trondhjemites,tonalites and granodiorites (TTG). Both suites show low-K₂Ocalc-alkaline differentiation trends (trondhjemitic). The aim of this study is to qualify and quantify the successionof different mechanisms by which the TTG series evolved. Theyoungest process was studied first, and the arguments then appliedin order to go back in time to the older ones. For each one,quantification was arrived at with the major elements, and theseresults provided a basis for calculation with the rare earthelements (REE). Finally the whole model was tested with othertrace elements. The petrogenetic model may be summarized as follows: meltingof the upper mantle to form a tholeiitic crust; melting of thesetholeiites transformed into garnet-bearing amphibolites to yieldthe parental magma of the TTG. The residue of the melt consistedof hornblende, plagioclase, clinopyroxene, and garnet with minoramounts of ilmenite and magnetite (10 < F < 30); and fractionalcrystallization of hornblende, plagioclase, and ilmenite withoccasional allanite and/or zircon in small amounts ((1-F) <40). No matter when they were emplaced during the Archaean, all theTTG of this part of the Baltic Shield arose from similar parentalmagmas. The petrogenetic study has shown that garnet and hornblendewere necessarily residual phases during the melting of the Archaeantholeiites. This constraint is very important, as it impliesthat the Archaean geothermal gradients occurring in subduction-zoneswere much higher than in modern times, thus allowing the partialmelting of the subducted oceanic crust.  相似文献   

Bar development in a fluvial sandstone (Westphalian 'A'), Scotland     

MARTIN KIRK 《Sedimentology》1983,30(5):727-742

The fluvial sandstone beneath the Mill Coal in the Westphalian ‘A’ of Scotland erosively overlies a lake mudstone. Slightly erosive surfaces within the sandstone, traceable for over 200 m, are used to divide it into two types of major sedimentary units termed type A and type B. Type A sand units are approximately 200 m wide, up to 7 m thick, convex upward, and lenticular in all directions. The constituent cosets overlap to the ENE and dip mainly at 1–2° downcurrent (NNW), but locally at 10–15°. Where thickest, type A sand units display a vertical facies sequence commencing with trough cross-bedded and massive sandstone, overlain by a thick zone of ripple cross-lamination, a thin zone of trough cross-beds, and a variably eroded silt drape up to 0.4 m thick. Attenuated lateral margins are dominated by flat bedded sandstone with primary current lineation. Type A sand units are interpreted as deposits which were accreted on to a large fluvial bar during successive flood events. The bar is thought to have had a similar topographic significance to sand waves described from the Brahmaputra and slip face bounded bars observed in the South Saskatchewan river. Palaeocurrents measured from trough cross-bed sets 0.3–1.0 m thick within type B sand units indicate flow to the WSW, perpendicular to the palaeoflow direction measured from type A units. In sections perpendicular to the WSW flow direction type B units are lenticular, and in ENE-WSW trending sections they can be traced for over 80 m at a constant thickness. Type B sand units are interpreted as the product of low stage channels which flowed across bar fronts and tops. The sandstone described herein is interpreted as a braided-type river deposit but is atypical, because it is fine grained and has an internal structure dominated by ripple cross-lamination and upper phase plane beds. The palaeoriver is thought to have been of low sinuosity, 7–10 m deep, with a high suspended load and large rapidly fluctuating discharge. At low stage a braided-type flow pattern developed around submerged bars. The regime of the palaeoriver was probably controlled by the fine sediment grain size and humid tropical climate.  相似文献   

Lichenometry in dating recent glacial landforms and deposits, southeast Iceland   总被引：1，自引：0，他引：1  

JOHN E. GORDON  MARTIN SHARP 《Boreas: An International Journal of Quaternary Research》1983,12(3):191-200

Lichenometry curves were derived for the glacier forelands of Breidamerkurjokull and Skalafellsjökull using measurements of the collective species, Rhizocarpon geographicum , from independently dated surfaces deglaciated during the period since the late-19th century ice maximum episode in the area. The form of the curves appears to be linear. Several methods of predicting the ages of undated surfaces were compared for specific test examples, including single lichenometry curves, families of curves and multiple curves based on randomly selected largest lichens. The last method provided a useful means of assessing the reproducibility of predicted ages. Where substrate conditions were highly variable, a lichenometry curve based on single largest lichens provided a preferred result.  相似文献   

The visualization of socio-economic GIS data using virtual reality tools     

DAVID MARTIN  GARY HIGGS 《Transactions in GIS》1996,1(4):255-266

This paper addresses two issues: the use of 'realistic' environments for the visualization of socio-economic data, and the use of virtual reality tools for the exploration of data from existing GIS databases. 'Realistic' is here used in a narrow sense to imply the reconstruction of real-world scenes in which major components of the physical environment are reconstructed to facilitate geographical visualization. A review of visualization techniques for geographically-referenced 3-D data is presented, and the translation of an existing urban GIS database into virtual reality modelling language (VRML) demonstrated for a study area in Cardiff, UK. This work shows that the export of conventional 2-D GIS data into virtual reality toolkits can be relatively straightforward, and offers exciting new avenues for visualization and exploration. We argue that some of the parameters of the true scene such as colour, building shape, and texture may be directly modified in order to represent otherwise unobservable socio-economic characteristics, in the spirit of exploratory data analysis. These issues are of particular importance in the context of current advances towards the dynamic linkage of GIS and virtual reality modelling.  相似文献   

STUDY OF CORONAL TRANSIENTS IN UV LINE EMISSION     

MARTIN  RENATO  MACCARI  LISA  NOCI  GIANCARLO 《Solar physics》1997,172(1-2):215-223

We investigate the expected emission from coronal transients in the following spectral lines observable with the Ultraviolet Coronagraph Spectrometer (UVCS) on board SOHO: Hi L 1216 Å, Ovi 1032–1037 Å, Nv 1239–1243 Å, Mgx 610–625 Å, Sixii 499–521 Å, and Fexii 1242 Å. We calculate line intensities and profiles for typical CME conditions, and we analyse their relation with the properties of the perturbed coronal region. We find that significant changes in UV line intensities are produced during a coronal transient. An overall decrease of the Hi L intensity is found, which is mainly due to the Doppler dimming produced by the increase in plasma outflow velocity. The emission from heavy ions is instead mainly affected by variations in plasma density and temperature. We expect to compare these results with the future UVCS observations of coronal transients.  相似文献   

SEISMIC REFRACTION MEASUREMENTS IN THE BALTIC SEA*     

ELIZABETH T. BUNCE 《Geophysical Prospecting》1969,17(1):28-35

Seismic refraction measurements were made in two areas of the Baltic Sea in June 1967. The refraction data were obtained in the course of the transmission measurements program of Operation MILOC BALTIC 67. Three profile pairs were obtained, two in the area south of Öland Island, Sweden, the third to the east, north of the peninsula of Hel, Poland. The water depths vary from 60 to 90 meters between the areas. The receiving positions for the two profiles south of Oland Island are only 46 km apart but the structures differ markedly. The northern section, only 500 m thick, shows a rather thin sedimentary cover above 350 m of 3.7 km/sec material that in turn overlies 5.6 - 5.9 km/sec velocity material. The southern section, almost 2 km thick, has an equivalent amount of low velocity material, and a layer about 1 km thick having velocity 4.8 km/sec that overlies 6.0 km/sec velocity material. The eastern profile shows high velocity material, 5.6 km/sec, at 2.5 km depth. Correlation of the layers determined by seismic refraction with nearby geology suggests that the structural change south of Öland Island may represent the boundary of the Sarmatian Shield in this region.  相似文献   

Seismic and volcanic hazards in Peru: changing attitudes to disaster mitigation   总被引：1，自引：0，他引：1  

MARTIN R DEGG  DAVID K CHESTER† 《The Geographical journal》2005,171(2):125-145

Over the last 15 years there have been dramatic shifts in the consensus over how best to cope with natural hazards in economically developing regions such as South America. One very positive outcome of the United Nations sponsored International Decade for Natural Disaster Reduction (IDNDR 1990–2000) has been that there is now greater interchange between the work of earth scientists examining the processes and mechanics of hazard occurrence and impact, and social scientists exploring the causes of human vulnerability to hazard – and thereby disaster. This paper traces the development of this new understanding with reference to earthquakes and volcanic eruptions in Peru, one of the most hazardous countries in South America. Particular focus is placed on the excellent progress currently being made by scientists in better understanding the physical dimensions of natural hazard exposure, and the ground-breaking work by social scientists in promoting new approaches to understanding and mitigating human vulnerability to disaster. The paper concludes by emphasizing the need to build on this research to produce more inclusive, incultured and unified strategies of disaster mitigation at the local, national and international levels.  相似文献   

Silicate, Hydrous and Carbonate Metasomatism at Lherz, France: Contemporaneous Derivatives of Silicate Melt-Harzburgite Reaction   总被引：4，自引：0，他引：4  

BODINIER  JEAN-LOUIS; MENZIES  MARTIN A.; SHIMIZU  NOBUMICHI; FREY  FREDERICK A.; McPHERSON  ELAINE 《Journal of Petrology》2004,45(2):299-320

Complex multi-stage models involving silicate, hydrous and carbonatemelts of distinct provenance have been invoked to explain themetasomatism observed in mantle rocks. In contrast, relativelysimple models requiring polybaric crystallization of alkalinesilicate melts have been proposed to explain the occurrenceof veined mantle rocks. To address the spatial and temporalrelationships between veins and wall-rocks, a sequence of drillcores was obtained from Lherz, France. In outcrop the vein (amphibole–garnetpyroxenite dyke) is spatially associated with hornblendite veinlets(lherzite), and proximal amphibole-bearing and distal apatite-bearingwall-rock peridotite. Considerable elemental and isotopic heterogeneityexists in these wall-rock peridotites, in many instances equivalentto, or greater than, that observed in mantle xenoliths fromworldwide localities. A single stage of reactive porous flowbest explains the elemental and isotopic heterogeneity in thewall-rock. In essence it is proposed that emplacement of thesilicate melt (dyke) was inextricably linked to chromatographicfractionation/reaction of derivatives which led to the coexistence,in space and time, of silicate, hydrous and carbonate melts.This model elegantly and simply describes the formation of complexmetasomatic aureoles around mantle veins and negates the need,in the case of basalt-hosted (and kimberlite-hosted) xenoliths,for complex multi-stage models involving several episodes ofmelt influx with each melt being of different provenance. KEY WORDS: mantle metasomatism; trace-element enrichment; isotopic contamination; wall-rock peridotite; Lherz peridotite  相似文献   

Moved by the Company - International Migrants and Transnational Organisations     

MARTIN PERRY 《New Zealand geographer》2003,59(2):54-63

Labour markets are generally thought to have become more integrated across international boundaries. Employees that move between branches of transnational organisations are a potential contributor to this integration. Interviews with human resources managers in 33 New Zealand‐based organisations indicate that the number of employees transferred is small and likely to decrease as corporate functions are transferred from New Zealand to regional offices.  相似文献   

IDENTITY AND ASSIMILATION AMONG YOUNG ETHIOPIAN IMMIGRANTS IN METROPOLITAN WASHINGTON*     

ELIZABETH CHACKO 《Geographical review》2003,93(4):491-506

ABSTRACT. Ethiopians are a recent immigrant group in the United States, having entered the country in significant numbers during the 1980s and 1990s. This preliminary study examines the ethnic and racial identities of children of first‐generation Ethiopian immigrants living in the Washington, D.C. metropolitan area. The results of twenty in‐depth interviews demonstrate that race is a much more fluid and contested form of identification than is ethnicity to the young immigrants, who equate the latter unilaterally with their Ethiopian heritage. Immigrants also adopt different subject identities in various locales, favoring those that are most in accordance with their needs and sense of self.  相似文献