The generation and shape of feeder dykes from mantle sources     

Sven Maaløe 《Contributions to Mineralogy and Petrology》1987,96(1):47-55

The criterion for fracture propagation suggests that the primary magma generated in the mantle ascends in a stepwise fashion. Initially a pulse of magma forms a dyke above the mantle source and ascends for some distance, whereafter it stops. A subsequent pulse of magma joins the first one, and the ascent of the accumulating body of magma continues for some distance each time a new pulse of magma reaches the body of magma situated in the top of the dyke. In this manner a dyke is formed that may extend either partly or the whole way from the mantle source to the surface. This model may explain the large pressures, up to 2000 bars, that prevail during basaltic eruptions. The calculated shape of the ascending pulses of magma suggests that their heights and widths are similar.  相似文献   

Turbulent exchange above a pine forest,I: Fluxes and gradients     

Ulf Högström  Hans Bergström  Ann-Sofi Smedman  Sven Halldin  Anders Lindroth 《Boundary-Layer Meteorology》1989,49(1-2):197-217

Measurements of gradients of wind, temperature and humidity and of the corresponding turbulent fluxes have been carried out over a sparse pine forest at Jädra»s in Sweden. In order to ascertain that correct gradient estimates were obtained, two independent measuring systems were employed: one system with sensors at 10 fixed levels on a 51 m tower and another with reversing sensors for temperature and humidity, covering the height interval 23 to 32 m. Turbulent fluxes were measured at three levels simultaneously. Data from three field campaigns: in June 1985, June 1987 and September 1987 have been analyzed. The momentum flux is found on the average to be virtually constant from tree top level, at 20 to 50 m. The average fluxes of sensible and latent heat are not so well behaved. The ratio of the non-dimensional gradients of wind and temperature to their corresponding values under ideal conditions (low vegetation) are both found to be small immediately above the canopy (about 0.3 for temperature and 0.4 for wind). With increasing height, the ratios increase, but the values vary substantially with wind direction. The ratios are not found to vary systematically with stability (unstable stratification only studied). The ratio of the non-dimensional humidity gradient to the corresponding non-dimensional potential temperature gradient (equivalent to k _h /k _w ) is found to be unity for (z – d)/L _v less than about –0.1 and about 1.4 for near neutral stratification, but the scatter of the data is very large.  相似文献   

Technical Note Estimation of the Joint Roughness Coefficient (JRC) by Visual Comparison   总被引：2，自引：0，他引：2  

A. J. Beer  D. Stead  J. S. Coggan 《Rock Mechanics and Rock Engineering》2002,35(1):65-74

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Development of a hydrogeological model description of intrusive rock at different investigation scales: an example from south-eastern Sweden     

Ingvar Rhén  Hans Thunehed  Carl-Axel Triumf  Sven Follin  Lee Hartley  Jan Hermansson  Carl-Henric Wahlgren 《Hydrogeology Journal》2007,15(1):47-69

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Problems associated with luminescence dating of Late Quaternary glacial sediments in the NW Scottish Highlands   总被引：2，自引：0，他引：2  

Sven Lukas  Joel Q.G. Spencer  Ruth A.J. Robinson  Douglas I. Benn   《Quaternary Geochronology》2007,2(1-4):243-248

Linking the timing of glacial episodes and behaviour to climatic shifts that are documented in ice and marine sedimentary archives is key to understanding ocean-land interactions. In the NW Scottish Highlands a large number of closely spaced (‘hummocky’) moraines formed at retreating glacier margins. Independent age control on one palaeo-glacier limit is consistent with the timing of Younger Dryas (YD) glaciation in the area, but adjacent glacier lobes have remained undated due to the lack of sites and material for ¹⁴C dating. Direct dating of ice-marginal moraines using optically stimulated luminescence (OSL) techniques has never been attempted before in Scotland, but if successful, they may be the most appropriate methods for constraining the age of sediment deposition in the absence of organic material. Coarse-grained quartz and K-feldspar minerals from supraglacial sheet flow deposits and glacilacustrine sediments within ice-marginal moraines were analysed using the single-aliquot regenerative-dose (SAR) protocol. Independent age control and clear geomorphological relationships indicate that all samples should yield YD or post-Last Glacial Maximum (LGM) ages. Quartz OSL shine down curves showed low luminescence sensitivity, significant medium-to-slow components, a weak fast component, and scattered SAR data; Linearly Modulated-OSL (LM-OSL) measurements confirmed that the fast component was weak or absent. In contrast, feldspar infrared stimulated luminescence (IRSL) was highly sensitive with excellent SAR data. However, SAR data from 3 mm diameter aliquots of feldspar (200 grains) give higher than expected equivalent doses (D_e) by an order of magnitude. SAR measurements of small clusters of feldspar grains (ranging from 1–8) considerably broaden the apparent D_e distribution, but even the lowest value is about 2–3 times the expected D_e. Two possibilities arise to explain the quartz and feldspar data: (1) that glacial sequences in the NW Highlands re-work inherited (older) glacial deposits and that some of the pre-Devensian existing glacial landforms have only been modified during Devensian glaciation; or (2) that the sedimentary processes operating in these ice-marginal environments are not conducive to adequate bleaching of quartz and feldspar grains. Our study implies that ice-proximal supraglacial sediments from this region in NW Scotland reflect older ages of deposition, but dating YD sediments has not been possible.  相似文献   

Comment on “Stable carbon isotopes in freshwater mussel shells: Environmental record or marker for metabolic activity?” by J. Geist et al. (2005)     

Bernd R. Schöne  David L. Rodland  Jens Fiebig  Sven M. Baier 《Geochimica et cosmochimica acta》2006,70(10):2658-2661

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Conductive structures in southernmost Africa: a magnetometer array study   总被引：1，自引：0，他引：1  

J. O. de  Beer D. I. Gough 《Geophysical Journal International》1980,63(2):479-495

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Magnetometer array studies and deep Schlumberger soundings in the Damara orogenic belt, South West Africa     

J. H. de  Beer  R. M. J. Huyssen  S. J. Joubert  J. S. V. Van  Zijl 《Geophysical Journal International》1982,70(1):11-29

Summary. A zone of concentrated induced electric currents crossing parts of Zimbabwe, Botswana and South West Africa was discovered during a magnetovariational study conducted in 1972. In 1977, a second study was made with 27 recording magnetometers distributed across the width of South West Africa between latitudes 19 and 22°S. Several geomagnetic disturbances were recorded with high recording efficiencies. Three of these time sequences were digitized for analysis. Magnetograms and Fourier transform amplitude and phase maps in the period range 22–128min were used to delineate the westward continuation of the conductive structure revealed by the earlier investigation. The conductive zone runs approximately east-west from the Botswana border (21°E) to 17°E longitude. From here to the Atlantic coast it trends in a NE—SW direction. Anomalous fields, normalized to the horizontal field at a station recording the normal field, were used to obtain maximum depth estimates of around 45 km for the induced currents. Several deep Schlumberger soundings were done over the anomalous zone and the results showed that the conductive structure is, in places, only 3 km from the surface and that it has a resistivity of less than 20 Ωm. The resistivity of the upper crust outside the structure ranges from 5000 to more than 20000 Ωm. Some 14 post-Karoo alkaline igneous complexes occur along the course of the resistivity anomaly. These intrusive complexes represent the youngest igneous activity in the Damara Orogenic Belt and were most probably emplaced along a line of weakness in the lithosphere. The resistivity anomaly would seem to delineate this line of weakness.  相似文献   

The planet in M4: implications for planet formation in globular clusters     

M. E. Beer  A. R. King  J. E. Pringle 《Monthly notices of the Royal Astronomical Society》2004,355(4):1244-1250

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A Magnetometer Array Study in Southern Africa     

D. I. Gough  J. H. de  Beer J. S. V. van  Zijl 《Geophysical Journal International》1973,34(4):421-433

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