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921.
High resolution climate simulations over the Arctic 总被引:1,自引:0,他引:1
Annette Rinke Klaus Dethloff Arne Spekat Wolfgang Enke Jens Hesselbjerg Christensen 《Polar research》1999,18(2):143-150
The regional atmospheric climate model HIRHAM has been applied to the Arctic. Simulations for the whole year 1990 and for an ensemble of winter months (January of 1985-1995) have been performed. The comparison of the simulations with observational data analyses shows that the general spatial patterns are in good agreement with the data, in both the vertical structure and the annual cycle. For an additional validation of the model results, a multivariate classification of large-scale circulation patterns has been applied to the January ensemble model simulations. 相似文献
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923.
Gaël Cazes David Fink Alexandru T. Codilean Réka-Hajnalka Fülöp Toshiyuki Fujioka Klaus M. Wilcken 《地球表面变化过程与地形》2020,45(2):424-439
We use cosmogenic 10Be and 26Al in both bedrock and fluvial sediments to investigate controls on erosion rates and sediment supply to river basins at the regional scale in the Kimberley, NW Australia. The area is characterised by lithologically controlled morphologies such as cuestas, isolated mesas and extensive plateaus made of slightly dipping, extensively jointed sandstones. All sampled bedrock surfaces at plateau tops, ridgelines, and in the broader floodplain of major rivers over the region show similar slow lowering rates between 0.17 and 4.88 m.Myr-1, with a mean value of 1.0 ± 0.6 m.Myr-1 (n=15), whilst two bedrock samples collected directly within river-beds record rates that are one to two orders of magnitude higher (14.4 ± 1.5 and 20.9 ± 2.5 m.Myr-1, respectively). Bedrock 26Al/10Be ratios are all compatible with simple, continuous sub-aerial exposure histories. Modern river sediment yield lower 10Be and 26Al concentrations, apparent 10Be basin-wide denudation rates ranging between 1.8 and 7.7 m.Myr-1, with a median value of 2.6 m.Myr-1, more than double the magnitude of bedrock erosion rates. 26Al/10Be ratios of the sediment samples are lower than those obtained for bedrock samples. We propose that these depleted 26Al/10Be ratios can largely be explained by the supply of sediment to river basins from the slab fragmentation and chemical weathering of channel gorge walls and plateau escarpments that result in diluting the cosmogenic nuclide concentration in river sediments measured at the basin outlets. The results of a mass-balance model suggest that ~60–90% of river sediment in the Kimberley results from the breakdown and chemical weathering of retreating vertical sandstone rock-walls in contrast to sediment generated by bedrock weathering and erosion on the plateau tops. This study emphasises the value of analysing two or more isotopes in basin-scale studies using cosmogenic nuclides, especially in slowly eroding post-orogenic settings. © 2019 John Wiley & Sons, Ltd. 相似文献
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The transition from porphyry- to epithermal-style gold mineralization at Ladolam, Lihir Island, Papua New Guinea: a reconnaissance study 总被引:8,自引:0,他引:8
Daniel Müller Klaus Kaminski Stephan Uhlig Torsten Graupner Peter M. Herzig Steve Hunt 《Mineralium Deposita》2002,37(1):61-74
The exceptionally large gold resource at Ladolam (>1,300 metric tons of gold), Lihir Island, resulted from the transition of an early-stage, low-grade porphyry gold system to a low-sulfidation epithermal gold event. This transition was probably triggered by rapid decompression during the partial slope failure of Luise stratovolcano and accompanied by the ingress of seawater. The original porphyry stage is indicated by remnant hydrothermal breccia clasts of strongly biotite-magnetite altered monzodiorite with disseminated pyrite - chalcopyrite and poorly developed pyrite - quartz stockwork veins. The breccias are overprinted by biotite-magnetite alteration and their matrix is strongly mineralized with disseminated auriferous pyrite. The breccias are cut by late-stage epithermal quartz-chalcedony-illite-adularia-pyrite veins and associated illite-adularia alteration that locally contain bonanza gold grades of up to 120 g/t. Isotope data suggest a magmatic source of sulfur in the gold-bearing fluids at Ladolam. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s00126-001-0230-y 相似文献
926.