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21.
Volker J. Dietrich Wolfgang Frank Kaspar Honegger 《Journal of Volcanology and Geothermal Research》1983,18(1-4)
The Ladakh Mesozoic ophiolite belt (western Himalaya) contains a pile of volcanic thrust sheets (Dras unit) which differ significantly in structure and composition from the ophiolitic mélange zones. The Dras unit is composed of pillow lavas, doleritic sills, very irregular basaltic (?basaltic andesites) and dacitic flows intercalated with pyroclastics, volcanoclastic sediments and radiolarian cherts. According to fossil evidence, this volcanism must have been active between Upper Jurassic and Upper Cretaceous.The presence of relict primary minerals, such as magnesiochromite, clinopyroxene, hastingsitic hornblende and Ti-magnetite as well as distinctive bulk chemistries, suggests that the volcanics belong to island arc tholeiite and to calc-alkaline rock series, typical of present island arcs in the Caribbean and Pacific.Model calculations incorporating probed phenocryst phases indicate that in addition to olivine, clinopyroxene and plagioclase, amphibole and titanomagnetite are crucial fractionating phases in the development of the dacites from a primitive tholeiitic melt. The latter process must have taken place at about 1000°C and at moderate depth of 5–15 km within or underneath the island arc. Today, hornblende-bearing mafic cumulates appear in the vicinity of Kargil within and close to the Dras volcanics.In a Sr-evolution diagram, the Dras volcanics have yielded a “pseudo-isochron” with a low initial
ratio of 0.7035 ± 0.0003, which is in the same range as the mean of modern island arc volcanics. However, a geologically unrealistic age of 263 m.y., is obtained from the slope of this isochron.The upper mantle is regarded as the source material for the island arc tholeiitic magmas. Enrichment in K, Ba, Sr and LREE supports the involvement of components derived from dehydration or incipient melting of subducted Tethyan oceanic crust in the mantle. 相似文献
22.
Geospatial data are now widely available to the general public thanks to geoportals and online mapping platforms. However, creating a map involves more than just combining data layers. Thus we develop cartographic functions for geoportals to support better visual hierarchy in user map mashups. This includes a couple of preparatory steps followed by a smart cartographic background symbolization derived from the original layer style. We evaluate different approaches to background symbolization: greyscale, desaturation, and smart background. The different background symbolization methods are analysed with two concrete map examples and evaluated with a survey. The smart background symbolization developed in this work improves the visual hierarchy of the map mashup by reducing the visual importance of the background layers. 相似文献
23.
Bernhard Jenny Tom Patterson Lorenz Hurni 《International journal of geographical information science》2013,27(11):1687-1702
The design of new map projections has up until now required mathematical and cartographic expertise that has limited this activity to a small group of specialists. This article introduces the background mathematics for a software-based method that enables cartographers to easily design new small-scale world map projections. The software is usable even by those without mathematical expertise. A new projection is designed interactively in an iterative process that allows the designer to graphically and numerically assess the graticule, the representation of the continents, and the distortion properties of the new projection. The method has been implemented in Flex Projector, a free and open-source application enabling users to quickly create new map projections and modify existing projections. We also introduce new tools that help evaluate the distortion properties of projections, namely a configurable acceptance index to assess areal and angular distortion, a derived acceptance visualization, and interactive profiles through the distortion space of a projection. To illustrate the proposed method, a new projection, the Cropped Ginzburg VIII projection, is presented. 相似文献
24.
We investigate the relative timing between hard X-ray (HXR) peaks and structures in metric and decimetric radio emissions
of solar flares using data from the RHESSI and Phoenix-2 instruments. The radio events under consideration are predominantly
classified as type III bursts, decimetric pulsations and patches. The RHESSI data are demodulated using special techniques
appropriate for a Phoenix-2 temporal resolution of 0.1 s. The absolute timing accuracy of the two instruments is found to
be about 170 ms, and much better on the average. It is found that type III radio groups often coincide with enhanced HXR emission,
but only a relatively small fraction (∼20%) of the groups show close correlation on time scales < 1 s. If structures correlate,
the HXRs precede the type III emissions in a majority of cases, and by 0.69 ± 0.19 s on the average. Reversed drift type III
bursts are also delayed, but high-frequency and harmonic emission is retarded less. The decimetric pulsations and patches
(DCIM) have a larger scatter of delays, but do not have a statistically significant sign or an average different from zero.
The time delay does not show a center-to-limb variation excluding simple propagation effects. The delay by scattering near
the source region is suggested to be the most efficient process on the average for delaying type III radio emission. 相似文献
25.
Kaspar Arzner 《Astrophysics and Space Science》2003,284(3):1113-1113
26.
Phytoplankton species composition, biomass, and rates of primary production were determined at two sites within Kenepuru Sound, New Zealand, in spring, summer, and autumn of 1982–83. Microflagellates and ultraplankton (< 5–10 μm) were numerically very abundant on each occasion and small gymnodinoid nanno‐planktonic (< 10–15 μm) dinoflagellates were likewise always a common component of the populations. The dinoflagellate, Prorocentrum gracile, made a substantial contribution to the total biomass in summer. The diatom community changed from mainly small chain forming species (Chaetoceros spp., Leptocylindricus spp.) in spring to small solitary centric and pennate forms (Nitzchia longissima, Coscinodiscus spp.) in summer, to a diversity of larger taxa (Coscinodiscus concinnus, Eucampia zoodiacus) in autumn. The autotrophic ciliate Mesodinium rubrum was a particularly important member of the autumn photo‐autotrophic assemblage. Both phytoplankton biomass and productivity increased from spring to autumn. In situ rates of primary production ranged from 15 to 1420 mgC m‐2h‐1 and chlorophyll a concentrations ranged from 6.9 to 258.5 mgChl a m‐2. A gross primary production rate, in summer, was estimated at 0.57 gC m‐2 d‐1. Phytoplankton production and biomass appeared to be related to dissolved inorganic nutrient concentrations as a result of variations in the freshwater inflow. A tentative comparison between the rates of phytoplankton and cultivated mussel production is made. 相似文献