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641.
Adrian J. Boyce Paolo Fulignati Alessandro Sbrana Anthony E. Fallick 《Journal of Volcanology and Geothermal Research》2007
High-sulfidation (HS) epithermal systems have elements in common with passively degassing volcanoes associated with high T, acid fumarole fields or acid crater lakes. They are considered to form in two stages, the first of which involves advanced argillic alteration resulting from intense, strongly acidic fluid–rock interaction. The La Fossa hydrothermal system (Vulcano Island) represents a classic example of such an active HS system and can be considered as a modern analogue of this early stage of alteration, resulting in a core of intense silicic (90–95% pure SiO2) alteration surrounded by alunitic alteration zones. 相似文献
642.
Fungi in dung of the Arctic ground squirrel (Spermophilus parryii) collected near Dominion Creek, Yukon Territory, Canada, have a radiocarbon age of 12,200 ± 100 yr B.P. Most of the fungal remains are assignable to modern taxa, and most of these are either widespread saprobes or nonspecific coprophiles. However, specimens identified as Chaetomium simile and Thecaphora deformans represent fungi that may be more characteristic of rodent dung than that of other animals, inviting consideration of dung fungi as a potential source of paleontological data. 相似文献
643.
Potentiometric titrations were used to measure conditional stability constants of UO22+-fulvic acid and UO22+-humic acid complexes. Both 2:1 and 1:1 COO-:UO22+ binding were observed. With decreasing metal concentration (2.5·10−4-6.25·10−5 M) increasing amounts of UO22+ were in the form of 1:1 humate complexes and 2:1 fulvate complexes. Despite the high nitrogen content and the low acidic OH group content, the successive stability constant values were similar to those determined for divalent cations associated with fulvic and humic compounds isolated from soils. Stability constant values increase simultaneously with increasing ionization of the humic (or fulvic) acid polyelectrolytes and with decreasing metal concentration. 相似文献
644.
Adrian E. Scheidegger 《Journal of Structural Geology》1983,5(1):53-59
Thousands of linear elements (joint traces, river trends and photolinears) have been identified and statistically analysed in the Province of Alberta, Canada, from the U.S. border to the Fort McMurray area. A statistical evaluation was performed on the data by fitting Dimroth-Watson distributions to groups of them. It is suggested that the joints represent shear surfaces formed in a neotectonic stress field whose maximum compression is oriented normal to the front of the Rocky Mountains, at least in the vicinity of that range. Further to the northeast, the stress trajectories swing to E-W and N-S directions. The river courses in Alberta do not align themselves with the joints and are presumably controlled by the general slope of the land towards Hudson's Bay. The photolineaments are features of uncertain origin and age. 相似文献
645.
Adrian E. Scheidegger 《Journal of Hydrology》1973,20(3):193-215
A review of the current state of our knowledge of the mechanical effects caused by (liquid) water on the morphology of the Earth is presented. The mechanical interaction of surface water and groundwater with landscapes is described and the mechanical effects of the sea on coastal regions and on the ocean bottom are discussed. 相似文献
646.
Summary A previously noted analogy between certain transport equations and the heat conductivity equation is further analyzed. It is shown thatPrigogine's nonequilibrium formalism can be directly applied to statistical processes where there is a non-negative constant of the motion. If the total mass (of contaminant, tracer etc.) contained in a fluctuating system is taken as such a constant of the motion, a statistical theory of the corresponding transport process is obtained. 相似文献
647.
Dr. Adrian J. Lloyd 《International Journal of Earth Sciences》1964,53(2):551-580
Sonmartel forms part of the anticlinal Cornu-Foulets Chain of the Neuchâtel High Jura. The strata exposed in the district include much of the Malm (Argovien to Purbeckien), the Lower Cretaceous (Berriasien to Hauterivien) and some Tertiary rocks (Siderolithique, Helvetian Miocene). An outline account is given of the Mesozoic formations, the distribution of marker bands being shown on the map (Pl. 1). The structure of the area is discussed in terms of its constituent parts. The folding is concentric but due to erosion-breaching following the earliest movements, subsequent deformation of the Pre- and Post-Kimeridgien rocks differed. The former are gently diapiric, while the folding of the latter is, in part, a gravity effect. Faults normal to the fold axes are present everywhere. They originated as tension cracks but later permitted transcurrent movements. Tear faults are best developed in regions where the trend of the fold axes changes. Thrusts are restricted to the Grand Sonmartel area. The joint systems are thought to result from stresses due to bed-over-bed sliding during the folding. The different types of deformation combine to produce a rhomboidal pattern of dissected cross-folds. Each of these strain-phenomena show that the region has been subjected to stresses of two different orientations, with a third also affecting the vicinity of Grand Sonmartel. These owe their origins to relative movements of basement blocks beneath the area — thrusting during the Post-Stampian phase, the thrusts re-activated as sinistral shears during the Post-Pontian phases when they were joined by conjugate dextral shears. On this basis the Alpine Push theory for the origin of the Folded Jura must be rejected. The Wegmann hypothesis of basement shears accounts best for the structures observed. 相似文献
648.
We report REE and minor element distributions for perovskites from seven kimberlites (South Africa and U.S.A.). The REE (1.6–6.3 oxides wt.%) are always strongly light REE enriched, often with Ce > La (chondrite-normalized), and show an expected close correlation with whole-rock analyses. Where examined, perovskite contains far more REE than coexisting apatite, by about an order of magnitude. Calculations indicate that iron is mostly present as Fe3+ and is low (1.0–2.9 wt.% Fe2O3) compared with perovskite from carbonatite complexes such as Oka (4.4 wt.% FeO [3]). In addition to established Nb (0.3–1.7 oxide wt.%), geochemically interesting elements encountered include Zr (up to 1.5 oxide wt.%), Ba and Sr (up to 0.2, 0.4 oxide wt.% respectively). Specific geological applications suggest a possible genetic link between Wesselton pipe and Benfontein Sills kimberlites, and that carbonate-rich dikes in the Premier mine were derived from kimberlites. The overall similarities with incompatible element-rich titanates in veined mantle peridotites suggest a more direct link between kimberlite magmatism and mantle metasomatism. 相似文献
649.
650.
Adrian C. Armstrong 《地球表面变化过程与地形》1983,8(2):183-187
In structured clay soils, water levels in open auger holes (dipwells) respond to water movement through macropores and may mask the existence of drier zones either at depth or within peds. Variability between replicated dipwells expresses the small scale variation in the soil, and statements about soil water regimes should be made in statistical terms. Suitably replicated dipwells give sufficiently precise measurements of mean watertable position for studies of soil water regimes. 相似文献