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排序方式: 共有185条查询结果,搜索用时 218 毫秒
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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
154.
地理信息系统中时空多维数据可视化技术研究 总被引:23,自引:0,他引:23
将科学可视化技术应用于地理信息系统之中,增强地理信息系统对时空多维数据的显示,处理胆当前的研究热点之一。通过对现有地理数据组织,显示简便概述的基础上,提出一种基于体素的时空多维数据组织方式。并通过二维,三维显示及动画形式的研究,从技术上对科学可视化与地理信息系统的结合进行初步的探索。 相似文献
155.
基于瑞典条分法的应变软化边坡稳定性评价方法 总被引:6,自引:0,他引:6
引入简化的应变协调方程,基于瑞典条分法的基本原理,提出一个新的能够考虑土的剪应力-应变关系的应变软化边坡稳定性简化分析方法。推导了该方法的计算公式,提出了具体算法并编制了计算程序,分析了不同应变软化特性的边坡稳定性。实际应用表明,该方法简单可靠、效率较高,计算所采用的分条数量和初始滑裂面位置对计算结果精度的影响均很小。应变软化边坡的安全系数介于基于峰值强度和残余强度的极限平衡条分法计算结果之间,具体数值不仅取决于土的抗剪强度指标,还与其剪应力-应变关系密切相关。 相似文献
156.
粗粒土与结构接触面三维本构关系及数值模型 总被引:4,自引:1,他引:3
基于试验结果,探讨了粗粒土与结构接触面的三维力学特性,该接触面在三维剪切时两个方向上的剪应力-应变关系表现出较强的耦合特性,但其主剪应变的大小只与主剪应力的大小有关。基于提出的接触面弹塑性损伤理论,建立了描述三维条件下接触面力学特性的本构模型及其数值格式。编制了有关程序,采用该模型对接触面的力学响应进行了预测。预测结果表明,建立的接触面三维本构关系及数值模型是合理和可行的,能够较好地反映包括剪切耦合特性在内的接触面主要力学特性。 相似文献
157.
于1990年10月 - 1992年7月在室内条件下测定黄河中游乌拉特前旗、包头黄河大桥及清水河地段水体中天然配体与铜、铅、锌、镉反应的络会容量(C?C),计算总条件稳定常数(K)和络合容量指数(I)。实验证明:乌拉特前旗水体中络合客量最大,包头和清水河相近。络合容量顺序为:Cu>Zn>Cd>Pb,和可溶性有机碳及碳酸盐分析结果一致。总条件稳定常数为:KPbL最大,KCuL,KZnL,KCdL相近。和长江水做了比较。络合容量指数在IgK相近情况下,随络合容量增大而增大。 相似文献
158.
Agnieszka Gałuszka 《Environmental Geology》2007,52(5):861-870
One of the most crucial issues of recent environmental sciences is the topic of background concentrations of elements and
organic compounds in various abiotic and biotic systems. The relationship between natural and anthropogenically altered concentrations
of chemical species is a question that involves many implications in the geosciences, environmental and biological sciences,
toxicology, and other related disciplines. This is especially important when interpreting geochemical and biogeochemical anomalies
of toxic elements and/or organic compounds in various media. To better understand the potential impact of hazardous substances
in the environment, we must become more familiar with their spatial and temporal distribution and with their behavior under
different physico-chemical and biotic conditions. This review presents an assessment of the geochemical background concept
as used by various authors. Different assumptions and approaches to this topic are presented, including direct, statistical,
and integrated methods. Based on the results derived from geochemical and biogeochemical studies performed in selected forest
ecosystems of Poland, an integrated method is presented. As a consequence of data processing, a normal distribution of data
points was obtained using an iterative 2σ-technique. This method of estimating geochemical background is feasible and can
be used for setting environmental quality standards or for studying the impact of anthropogenic pollution sources on the environment. 相似文献
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Gold occurs in a number of different ore types in the Fennoscandian Shield ranging in age from Late Archean to Late Proterozoic. Until recently, the metal was exploited primarily as a byproduct in volcanogenic massive sulphide deposits but during the 1980s more gold mines have been opened than during any other episode in the mining history of northern Europe. The occurrence of gold in the Fennoscandian Shield is reviewed in the context of the major tectonostratigraphic units:
These metallogenic features, deposit modelling and economic properties of the known occurrences suggest that the potential for new gold discoveries is highest in Late Archean to Early Proterozoic greenstone belts and in Early Svecofennian tonalite plutons. The gold potential of the Sveconorwegian Domain is also worth further consideration. 相似文献
1. | In the Karelian Province, gold is hosted by greenstone belts of the Archean basement complex e.g. at Ilomantsi, eastern Finland. Greenstone belts of the Nordkalott Province, which are interpreted as part of an Early Proterozoic cover sequence, contain gold deposits associated with copper (Bidjovagge, Saattopora and Pahtohavare). Gold is also associated with cobalt in the metasomatically altered Early Proterozoic cover in north-eastern Finland (Meurastuksenaho and Juomasuo). |
2. | In the Svecofennian Domain, the major gold deposits were generated during the emplacement of 1.92–1.87 Ga old accretional magmatism. These deposits occur in the northeastern part of the Svecofennian Domain, close to the Archean-Proterozoic boundary. They comprise two major types: (a) the porphyry-type and shear-zone gold hosted by tonalite at Tallberg, Laivakangas, Kopsa and Osikonmäki; (b) as a component of volcanogenic massive sulphide deposits (e.g. Holmtjärn, Boliden and Pyhäsalmi). Other types are: (c) gold-bearing quartz-alumina alteration zones formed during the 1.92–1.87 Ga magmatic period (Enåsen); (d) gold in massive sulphide and iron ore deposits in Bergslagen. |
3. | Gold associated with 1.84–1.54 Ga granites has been reported from several sites in the Shield, including quartz veins and contact-metasomatic deposits. In addition, shear-zone-related gold deposits post-dating these granites have been identified in southeastern Sweden (Ädelfors). |
4. | In the Sveconorwegian Domain, the gold deposits at Bleka, Eidsvoll, Glava and Hamas are associated with shear zones which developed penecontemporaneously with the intrusion of late (1.0–0.9 Ga) granites. |