Tertiary metallogenesis in the Eastern Alps: the Waldenstein hematite deposit (Austria)

The specularite deposit at Waldenstein is an epigenetic replacement/vein-type hematite mineralization with distinct alteration zones. It is situated in highly metamorphosed schists and, gneisses of the Koralm Crystalline Complex. Sericitization and chloritization are strictly bound to this alteration and occur within a few meters of the hematite veins. Radiometric dating of the sericitization and the implicity of the mineralization yield a Middle Eocene age. Petrographic evidence proves an early, relatively reduced paragenesis (magnetite, ilmenite) being partly replaced by hematite and chlorite during the main phase of ore formation. Fluid inclusion and stable isotope investigations indicate that formation temperatures were approximately 300°C during the main stage and decreased to 200°C in the latest stage of the hydrothermal event. The H-isotope compositions of chlorites and of fluid inclusions in quartz indicate the influence of seawater. This also explains the high salinities determined by fluid inclusion studies (20–30% NaCl equiv.). According to the genetic model presented in this paper the hydrothermal activity started when the deformation accompanying the uplift of the Koralm Crystalline Complex passed from a ductile to brittle regime (Middle Eocene). The brittle faults acted as channelways for rising, deep fluids, probably of metamorphic origin. Temperature differences between the different uplifting crustal segments supported fluid circulation. Precipitation of the ore occurred at shallow crustal levels where the hydraulic regime was dominated by seawater, and oxidation of the original reducing fluids took place.     

Application of multivariate analyses in studies of the organization and structure of fish and invertebrate communities

Ecological studies often attempt to link observed effects to multiple causal factors which may be operating simultaneously. Although in situ randomized experiments in which factor levels are controlled may be a powerful means for disentangling causal relationships, an experimental approach is not always feasible or even a desirable first step in the analysis, particularly when there is insufficient background knowledge of the system. In such cases, analysis of survey data, reflecting natural (co)variation in the putative causal factors and their direct and indirect effects, can be a practical and useful alternative to experiments. When set in the proper statistical framework, survey data can be used to assess whether a given factor has a detectable effect once the effect of other factors has been accounted for statistically (by partialling), and to estimate what proportion of the effect can be attributed to each factor (by variance decomposition). This analysis can help establish whether a particular causal model is consistent with the data at hand, and should be viewed as preliminary to a mechanistic approach, providing support and guidance for the investigation of more realistic variables. Here, we use three examples based on survey data from fish and invertebrate lacustrine communities to illustrate the application of partialling and variance decomposition in a multivariate setting. The first example shows that variation in the abundance and size structure of cladoceran taxa is still associated with fish species composition when potentially confounding effects of abiotic variables are accounted for by partialling. In the second and third examples, variance decomposition is used to determine the relative contribution of the environmental and spatial components to variation in the community structure of littoral zoobenthos and in the diet of a freshwater fish species.Contribution of the Group for Interuniversitary Research in Limnology (G.R.I.L.).     

磁纬20°以下地区哨声多台宽带定向观测及其初步结果

武汉大学哨声组与日本名古屋大学空电研究所合作于1988年1月在我国南方进行了哨声多台宽带定向测量。利用近两年研制的宽带数字化频率追踪定向分析系统,首次获得了磁纬20°以下地区哨声波出口区与偏振状态的实验结果。初步分析发现,在湛江附近(磁纬约10°N)存在一个比较稳定的哨声路径出口区,三台同时接收到的哨声大多从这同一出口区透射出来;有时存在两个出口区,一个仍位于湛江附近,另一个位于桂林和武昌之间;沿两条不同路径传播的同源哨声具有几乎相同的色散。本文所做的非导管射线追踪计算能比较满意地解释定向实验结果。另外,此次观测中还发现一些新的有意义的现象,如记录到近百例两跳、三跳及五跳回波等,这在低纬地区是非常少见的。     

Non-Linear, Microscale Modelling of the Flow Over Askervein Hill

The flow solver “3DWind” is used to explore new aspects of the Askervein hill flow case. Previous work has investigated sensitivities to the grid, the inflow boundary profile, the roughness and the turbulence model. Several different linear and non-linear numerical models have also been validated by means of the Askervein hill case. This analysis focuses on the flow sensitivity to the grid spacing, the incident wind direction and the vertical resolution of topographic data. The horizontal resolution is found to be fine enough to cause only minor differences compared to a grid where every second node is removed. The vertical resolution dependence is mainly attributed to the wall functions. Simulations are performed for wind directions 200°, 205°, 210° and 215° at the reference station. The smallest directional biases compared to experimental values along a line through the hilltop are found for the directions 200° and 205°. There are larger wind direction changes along this line through the hilltop in the 200° case than in the 215° case. Still the simulation results give less veering than found in the experimental results, and this is maybe caused by a slightly stable atmosphere. The sensitivity to the vertical resolution of the topographical data is found to be particularly high close to the ground at the top of the hill; this is where the speed-up is most important. Differences decrease with the height from the ground. At higher levels the speed-ups are smaller and caused by terrain formations with larger scales.     

Mitigation of seismic and meteorological hazards to marine oil terminals and other pier and wharf structures in California

For the past 12 years, the California State Lands Commission has been involved in the operational monitoring, structural inspection and requalification of 45 marine oil terminals along California’s coast, which have an average age of about 50 years and plans to keep these structures in service for another 20–40 years. Having seen the port and harbor damage from the 1995 Kobe and 1999 Izmit earthquakes, the potential for a major disruption in petroleum product production is real. Losing the daily gasoline production for a period of weeks or months as a result of a moderate earthquake or tsunami could significantly affect the economic well being of California and much of the western United States. In addition, a major oil spill resulting from such an event could cause the closure of a major port for days or even weeks. Such a closure would further affect the economy of California and the United States. Most of these facilities were designed to primitive seismic standards and for vessels much smaller than those currently moored. Many of these structures have never had a comprehensive underwater inspection. Wind and current forces on large tank ships can cause mooring lines to break or cause serious structural damage to supporting structures. In California, non-regulatory progress has been made in the following areas: (i) underwater and above water inspections or audits; (ii) mooring analyses and structural/environmental monitoring in high velocity current areas; (iii) seismic analyses and structural rehabilitation with updated seismic hazard data; and (iv) accelerometers on marine structures. In addition, standards have been developed and are proposed to be regulatory by early 2004. The new standards include most of the items listed above, but also extend into many other areas. Along with the proposed regulations come many issues that raise economic and political questions. These issues are not unique to marine oil terminals and are applicable to other pier and wharf structures in harbors.     

地质环境质量评价的态势分析法

探讨了将SWOT态势分析法应用于地质环境质量评价中的具体步骤。通过长江江苏段过江隧道工程的地质环境质量等级评价的实例,从地质体本身的优势、劣势,外部条件的有利(机会)、不利(威胁)等4个方面对评价对象进行全面、系统、准确的研究,最后得出地质环境质量的评价等级。     

利用费希尔最优分割法划分临夏盆地早更新统地层孢粉带的初步研究

将费希尔（Fisher）最优分割法引入到临夏盆地早更新统东山组地层孢粉带的划分中，结合地层特征，共划分出了3个孢粉带。这3个孢粉带分别为：带Ⅰ（深度78．5～45．5m）柏科-禾本科组合带、带Ⅱ（深度45．5～12．5m）云杉属-榆属-禾本科组合带、带Ⅲ（深度12．5～0．5m）云杉属一禾本科组合带。孢粉带分带揭示，临夏盆地早更新世气候变化经历了干-湿-干3个阶段，这一结果同以往获得的粒度、碳酸钙和Cl-等无机指标高分辨率分析结果相一致。     

Postcumulus processes in oceanic-type olivine-rich cumulates: the role of trapped melt crystallization versus melt/rock interaction

Combined microstructural and geochemical investigations on MORB-type primitive olivine-rich cumulates intruded in the Erro–Tobbio (ET) mantle peridotites (Voltri Massif, Ligurian Alps, Italy) revealed that significant chemical changes in minerals were caused by postcumulus crystallization. This is indicated by the occurrence of accessory interstitial minerals (Ti-pargasite, orthopyroxene and Fe–Ti oxides) and by systematic chemical zoning in intercumulus clinopyroxene, resulting in marked trace element (e.g. REE, Ti and Zr) enrichment at constant high Mg-numbers (0.88–0.91) and LREE depletion. Geochemical modelling shows that low trapped melt amounts (<5%) are sufficient to produce the observed trace element enrichments. Chemical zoning in large (mm-size) clinopyroxenes was dominantly caused by in situ fractional crystallization of trapped interstitial liquid rather then porous flow migration of externally derived evolved melts. Zr enrichment relative to REEs in vermicular clinopyroxene and pargasitic amphibole point to small-scale migration and interaction between residual evolved low melt fractions and the olivine cumulus matrix at final stage of crystallization. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Earthquake fault rupture—shallow foundation interaction in undrained soils: a simplified analytical approach

The interaction between normal or reverse fault ruptures and shallow foundations resting on a homogeneous undrained soil layer is investigated. After performing a thorough set of non‐linear finite element simulations, three simple kinematic mechanisms are proposed to predict the conditions for the fault rupture to be diverted by the foundation. The results obtained by both numerical and analytical approaches are in good agreement, and support the adequacy of the proposed mechanisms. A relationship is established for assessing the minimum foundation bearing load needed for diversion of the fault rupture trace, either normal or reverse. This relationship is proved to be independent of the fault type and dip angle, so that it can be applied easily for engineering applications, even in the absence of specific tectonic information. Copyright © 2006 John Wiley & Sons, Ltd.     

Mitigation of the seismic motion near the edge of cliff-type topographies using anchors and piles

Concentration of damage of buildings near the edge of cliff-type topographies has been observed during a number of recent earthquakes and interpreted by numerical dynamic analyses that illustrate the amplification of the horizontal acceleration and the generation of parasitic vertical acceleration near the tip of slopes. The paper performs a detailed parametric numerical analysis to investigate the ability of mitigating this topographic effect using anchors and piles. A typical field case, the Aegion slope of Greece, is considered. Different input motions are applied. The results illustrated that anchors and piles can be effective in mitigating the topographic effect. The main issue is that if the part of the slope in which topographic amplification occurs is connected to that at larger depths, in which the acceleration is smaller, then the accelerations at the top of the slope have to become more uniform and smaller. For typical diameter and material properties of anchors/piles the effectiveness of the mitigation depends on the length, inclination, location and number of anchors/piles. An optimum configuration of anchors/piles mitigating the topographic effect is proposed.