Structural and metamorphic evolution of the Camughera – Moncucco, Antrona and Monte Rosa units southwest of the Simplon line,Western Alps     

Lukas M. Keller  Maurus Hess  Bernhard Fügenschuh  Stefan M. Schmid 《Eclogae Geologicae Helvetiae》2005,98(1):19-49

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Formation of dykes,feeder-dykes,and the intrusion of dykes from magma Chambers   总被引：1，自引：0，他引：1  

A. Gudmundsson 《Bulletin of Volcanology》1984,47(3):537-550

The paper discussed the formation of dykes, and applies the results to Iceland. It is postulated that dykes follow the pathway of least work and of least tensile strength and thereby intrude the subvertical joints in lava flows. It is suggested that dykes form in magma pulses, where each dyke is split in two by the next magma pulse and so on. In Iceland the estimated time between successive magma pulses is of the order of several hundred days. Statistical considerations indicate that in Iceland the probability of seeing dykes end upwards is only 1–2%, which agrees with observations. It is concluded that many and probably the majority of dykes are non-feeders. This, together with the low probability of finding the connection between feeder and lava flow, explains the scarcity of observed feeder-dykes. It is concluded that overpressure in shallow magma chambers needed to drive magma through crustal fractures in Iceland is usually smaller than the tensile strength of the host rock (several MPa), which thereby is the critical factor in dyke intrusion.  相似文献   

Form and dimensions of dykes in eastern Iceland     

Agust Gudmundsson 《Tectonophysics》1983,95(3-4)

A study was made of about 700 dykes in eastern Iceland. The majority of these belong to three swarms. About 73% dip within 10° of the vertical. Most strike between 10° and 40°NE. The strike of the dykes within the southernmost swarm (Alftafjordur) changes along its trace, from almost N at the north end to NNE-SSW southward along the swarm. The average thickness of the dykes is about 4.1 m, and the thickness does not change notably along the Alftafjordur swarm. The thinner dykes tend to have smaller grains than the thicker dykes. Of five dykes followed laterally, the longest is over 22 km. The thickness of individual dykes changes irregularly along their length, and the dyke is often offset where its thickness changes. Many dykes appear to be completely discontinuous, but some parts are connected by veins. Where the dykes end in a vertical section, most of them simply taper away. Only about 10.5% of the dykes occupy faults. The mechanical and thermal effects of the dykes on the country rock are small. Many of the dykes appear to be non-feeders, i.e. dykes that never reached the surface to feed lava flows. Using the length/width ratio, the depth of origin of three dykes has been estimated. The maximum depth of origin of these three dykes is 7.5 km, 9 km and 10 km below the original surface.  相似文献   

Scale dependency of regional climate modeling of current and future climate extremes in Germany     

Merja?H.?T?lleEmail authorView author&#;s OrcID profile  Lukas?Schefczyk  Oliver?Gutjahr 《Theoretical and Applied Climatology》2018,133(3-4):829-849

A 26-year simulation (1980–2005) was performed with the Weather Research and Forecast (WRF) model over the Volta Basin in West Africa. This was to investigate the ability of a climate version of WRF to reproduce present day temperature and precipitation over the Volta Basin. The ERA-Interim reanalysis and one realization of the ECHAM6 global circulation model (GCM) data were dynamically downscaled using two nested domains within the WRF model. The outer domain had a horizontal resolution of 50 km and covered the whole of West Africa while the inner domain had a horizontal resolution of 10 km. It was observed that biases in the respective forcing data were carried over to the RCM, but also the RCM itself contributed to the mean bias of the model. Also, the biases in the 50-km domain were transferred unchanged, especially in the case of temperature, to the 10-km domain, but, for precipitation, the higher-resolution simulations increased the mean bias in some cases. While in general, WRF underestimated temperature in both the outer (mean biases of ?1.6 and ?2.3 K for ERA-Interim and ECHAM6, respectively) and the inner (mean biases of ?0.9 K for the reanalysis and ?1.8 K for the GCM) domains, WRF slightly underestimated precipitation in the coarser domain but overestimated precipitation in the finer domain over the Volta Basin. The performance of the GCM, in general, is good, particularly for temperature with mean bias of ?0.7 K over the outer domain. However, for precipitation, the added value of the RCM cannot be overlooked, especially over the whole West African region on the annual time scale (mean biases of ?3% for WRF and ?8% for ECHAM6). Over the whole Volta Basin and the Soudano-Sahel for the month of April and spring (MAM) rainfall, respectively, mean bias close to 0% was simulated. Biases in the interannual variability in both temperature and precipitation over the basin were smaller in the WRF than the ECHAM6. High spatial pattern correlations between 0.7 and 0.8 were achieved for the autumn precipitation and low spatial correlation in the range of 0.0 and 0.2 for the winter season precipitation over the whole basin and all the three belts over the basin.  相似文献   

Two‐layer scree/snow‐avalanche triggered by rockfall (Eastern Alps): Significance for sedimentology of scree slopes     

Diethard Sanders  Lukas Widera  Marc Ostermann 《Sedimentology》2014,61(4):996-1030

Rockfalls that trigger scree‐laden snow avalanches are common in mountain ranges, but the resulting avalanche development and its role in understanding the sedimentology of scree slopes are rarely described in detail. On Riepenwand (2774 m above sea‐level, Kalkkögel range, Alps), on 6 May 2011 a 5800 m³ rockfall of dolostone detached from the flank of a gorge in the upper part of the mountain. After first collapsing into the gorge, the fragmented rock mass fell down freely for 150 m onto a talus covered by coarse‐granular snow. Rockfall impact triggered a medium‐scale avalanche that developed: (i) a lower layer A of entrained, pure snow; and (ii) an upper layer B of clay‐sized to boulder‐sized fragments mixed with snow. This ‘two‐layer scree/snow avalanche’ halted in the distal slope segment of the talus. Boulders within layer B mainly came to rest in the distal part of the avalanche deposit. Fragments smaller than cobble‐size grade did not show obvious downslope segregation. With snowmelt, the rockfall fragments dispersed in layer B were concentrated to a clast‐supported veneer that was draped over the older talus surface upon slower melting of avalanche layer A. In the grain‐size fraction ≤16 mm, a mean of 5 wt% matrix (silt‐sized to clay‐sized grains) of the rockfall‐derived scree of layer B is similar to a mean matrix content of 7 wt% within stratified talus slopes of the Kalkkögel range. This similarity suggests that a major share of matrix – widespread in stratified talus – stems from rockfalls. The characteristics of the scree veneer as melt‐lag of a scree‐laden snow avalanche will be blurred with time. Fossil talus successions may contain a substantial proportion of scree carried down by snow avalanches. The formation of a distinct sedimentary facies of snow avalanche‐deposited scree is impeded by processes of redeposition and deposit modification on talus.  相似文献