Kornerupine in Mg-Al-rich gneisses from Namaqualand,South Africa: mineralogy and evidence for late-metamorphic fluid activity

Three kornerupine occurrences are reported in distinctive SiO₂-poor, MgO- and Al₂O₃-rich paragneisses from the Namaqualand Metamorphic Complex in South Africa. Kornerupine coexists stably with phlogopite, cordierite, orthopyroxene, gedrite, sapphirine, sillimanite and plagioclase and, in sapphirine-free rocks, with spinel and corundum. Tourmaline of a texturally older generation than kornerupine is commonly present in the same samples.Ten analysed kornerupines show a variation in total Fe as FeO from 1.8 to 10.9 weight per cent. B₂O₃ contents are estimated from x-ray data and a few spectrochemical analyses to range from 0.9 to 3.5 weight per cent. There is a strong inverse correlation between B³⁺ and Al³⁺. Total iron content has a strong and systematic effect on refractive index, colour and dispersion. Fe and Mg are systematically partitioned with the other minerals, and Mg/(Mg+Fe) ratios increase as follows: spinel 相似文献   

Sedimentology and kinematics of a large, retrogressive growth-fault system in Upper Carboniferous deltaic sediments, western Ireland

Growth faulting is a common feature of many deltaic environments and is vital in determining local sediment dispersal and accumulation, and hence in controlling the resultant sedimentary facies distribution and architecture. Growth faults occur on a range of scales, from a few centimetres to hundreds of metres, with the largest growth faults frequently being under‐represented in outcrops that are often smaller than the scale of feature under investigation. This paper presents data from the exceptionally large outcrops of the Cliffs of Moher, western Ireland, where a growth‐fault complex affects strata up to 60 m in thickness and extends laterally for ≈ 3 km. Study of this Namurian (Upper Carboniferous) growth‐fault system enables the relationship between growth faulting and sedimentation to be detailed and permits reconstruction of the kinematic history of faulting. Growth faulting was initiated with the onset of sandstone deposition on a succession of silty mudstones that overlie a thin, marine shale. The decollement horizon developed at the top of the marine shale contact for the first nine faults, by which time aggradation in the hangingwall exceeded 60 m in thickness. After this time, failure planes developed at higher stratigraphic levels and were associated with smaller scale faults. The fault complex shows a dominantly landward retrogressive movement, in which only one fault was largely active at any one time. There is no evidence of compressional features at the base of the growth faults, thus suggesting open‐ended slides, and the faults display both disintegrative and non‐disintegrative structure. Thin‐bedded, distal mouth bar facies dominate the hangingwall stratigraphy and, in the final stages of growth‐fault movement, erosion of the crests of rollover structures resulted in the highest strata being restricted to the proximity of the fault. These upper erosion surfaces on the fault scarp developed erosive chutes that were cut parallel to flow and are downlapped by the distal hangingwall strata of younger growth faults.     

Trace element distributions in aquatic sediments of Danang – Hoian area, Vietnam

 Distribution of the trace elements Cr, Cu, Ni, Pb and Zn in surficial sediments of the river/sea environment in Danang – Hoian area (Vietnam) was investigated to examine the degree of metal pollution caused by anthropogenic activities. Point sources from domestic and industrial wastes are identified as dominant contributors of trace element accumulation. Surficial sediments of Hoian River show extremely high total concentrations of Cu (Average Concentration 295 μg/g), Ni (AC 112 μg/g), Pb (AC 396 μg/g) and Zn (AC 429 μg/g) that exceed assigned safety levels ER-M. Similarly, the sediments of Han River show high Pb (AC 188 μg/g) and Zn (AC 282 μg/g) contents. In marine sediments of Thanhbinh beach Pb is also enriched (138 μg/g) above guideline levels. In contrast the sediments of the Cude River are dominated by trace element concentrations close to background values. Received: 17 December 1998 · Accepted: 6 May 1999     

Towards medium-term (order of months) morphodynamic modelling of the Teign estuary, UK

The main objective of this paper is to address the principal mechanisms involved in the medium-term (order of months to years) morphodynamic evolution of estuaries through the application of a process-based numerical modelling. The Teign estuary (Teignmouth, UK) is the selected site. The system is forced by the macrotidal semi-diurnal tide in the English Channel and is perturbed to a minor extent by high river discharge events (freshets). Although waves have a definite influence on the adjacent coastal area, Wells (Teignmouth Quay Development Environmental Statement: Changes to Physical Processes. Report R.984c:140. ABP Marine Environmental Research Ltd., Southampton, 2002b) suggested that swell waves do not enter the estuary. Hence, wave effects are neglected in this study, as only tides and the river discharge are taken into account. The sediment grain size is highly variable, but mainly sandy. Within the frame of the COAST3D project (), four bathymetric surveys of the adjacent coastal area were carried out at a nearly weekly intervals. The outer estuary and the adjacent coastal area were also surveyed every 6 months as part of the COASTVIEW project (). Based on these data and on continuously measured parameters, such as water level, waves, wind and river discharge, numerical modelling of the morphodynamic processes can be tested. To replicate the morphological changes in the medium-term within a feasible simulation time, forcing conditions are reduced through the use of an input reduction method (called ensemble technique). In this study, simulations are based on the coupling between Telemac-2D and its non-cohesive sediment transport module, Sisyphe (version 5.3 for both modules). Three different sediment transport formulae were tested: (1) Engelund and Hansen (A monograph on sediment transport in alluvial streams, 3rd edn. Technological University of Denmark, Copenhagen, 1967) including the modifications proposed by Chollet and Cunge (J Hydraul Eng 17(1):1–13, 1979); (2) Bijker (Mechanics of sediment transport by the combination of waves and current. In: Design and reliability of coastal structures. 23rd international conference on Coastal Engineering, pp 147–173, 1968) and (3) Soulsby (Dynamics of Marine Sands. A manual for practical applications. HR Wallingford, Wallingford, p 142, 1997) modified version of van Rijn [J Hydraul Eng 110(10):1431–1456, 1984a, J Hydraul Eng 110(11):1613–1641, 1984b] formulation. Both a qualitative (i.e. visual comparison) and a quantitative tool [Brier Skill Score (BSS); described in Sutherland et al. in Coast Eng 51:917–939, 2004b] are applied to assess the similarity of simulations when compared to model predictions and observations. Tests confirmed the reliability and time efficiency of the ensemble technique, since it reproduced very well the results of a reference run, a computation based on the observed boundary conditions. For the spring-neap cycle modelled, the BSS was of 0.91 (a perfect modelling would have a BSS of 1), with a reduction in the simulation time on the order of 80%. For the 6-month-period simulation, results were also excellent: BSS=0.92 and a computer time reduction of 85%. In principle, this method has the advantage of being applied to any process-based numerical model.     

Ionosphere and surface weather

Summary The author describes the pulsing ionospheric technique which since 1939 has been successfully employed for forecasting surface weather.     

Higher order analytical solutions of water table fluctuations in coastal aquifers

The groundwater response of coastal aquifers to tidal forcing is described by Laplace's equation coupled with the nonlinear phreatic-free surface boundary condition. Here we describe fluctuations in the water table using two small parameters, extending previous work by proposing an ansatz to compute higher order, semi-analytical solutions. The new solutions are compared with known lower order solutions. The relative difference between the linear solution and higher order solutions can reach up to 30% of the linear solution for shallow beaches. The new solutions exhibit a reduction in the over height of the groundwater fluctuations compared with the lower order solutions. In addition, the super elevation of the water table, both near shore and as the aquifer tends landward, is examined with the inclusion of higher order terms.     

Reaching critical mass? Theory, politics, and the culture of debate in children's geographies

A small but growing number of voices have begun to raise questions about the current direction of children's geographies as a subfield and its status within the wider discipline. This article intervenes in these emerging discussions to examine the status of debate itself within children's geographies. I argue that children's geographies over the past decade has operated primarily in a consensus-based mode, with a number of potential tensions and differences between practitioners masked as a result. I develop the example of notions of children's competent social agency, a core theoretical assumption that is rarely interrogated in much depth. In closing, I pose questions regarding several contemporary political issues concerning children's agency about which geographers have had surprisingly little to say. I suggest that explicitly addressing some of these vexing issues would contribute to a richer state of debate within children's geographies.     

The generation ofK indices from digitally recorded magnetic data

TheK index was developed by Bartels and is a measure of geomagnetic activity. The important feature of this index is that it is a measure of solar activity superimposed on the regular daily variation.It is the most used estimate of activity being of particular interest to researchers in ionospheric physics and telecommunications.In response to increased availability of digital data from magnetic observatories and their demand by the scientific community it becomes desireable to check whetherK indices produced from magnetograms plotted from digital data are consistent with those handscaled from La Cour charts.This paper presents results of these comparisons and also reports on several methods tested to produce theK index directly from the digital data.Handscaled indices from digital plots are suitable for producing theK index. Computations using digital data do not reproduceK as defined by Bartels precisely but do provide an equivalent index which is satisfactory for most user and research purposes.     

Scope for a small circumsolar annular gravitational contribution to the Pioneer anomaly without affecting planetary orbits

All proposed gravitational explanations of the Pioneer anomaly must crucially face the Equivalence Principle. Thus, if Pioneers 10 and 11 were influenced by anomalous gravitational effects in regions containing other Solar System bodies, then those bodies should likewise be influenced, irrespective of their shape, composition or mass. Although the lack of any observed influence upon planetary orbits severely constrains such explanations, here we aim to construct by computer modeling, hypothetical gravitating annuli having no gravitational impact on planetary orbits from Mercury to Neptune. One model has a central zone, free of radial gravitation in the annular plane, and an ‘onset’ beyond Saturn’s orbit, where sunward annular gravitation increases to match the Pioneer anomaly data. Sharp nulls are included so that Uranus and Neptune escape this influence. Such models can be proportionately reduced in mass: a 1 % contribution to the anomaly requires an annulus of approximately 1 Earth mass. It is thus possible to comply with the JPL assessment of newly recovered data attributing 80 %, or more, of the anomaly to spacecraft heat, which appears to allow small contributions from other causes. Following the possibility of an increasing Kuiper belt density at great ranges, another model makes an outward small anomalous gravitation in the TNO region, tallying with an observed slight indication of such an effect, suggesting that New Horizons may slightly accelerate in this region.     

Stratigraphy, Chronology, and Paleoenvironmental Reconstruction of the Quaternary Sedimentary Infilling of a Volcanic Tube in Fuerteventura, Canary Islands

La Cueva del Llano is a volcanic tube of Pleistocene age on Fuerteventura Island, in the Canary Islands. Part of it is infilled with sediments of external origin. These deposits are exceptional in stratigraphic complexity and thickness compared with other known tube infillings, and they comprise nine stratigraphic units deposited in five phases. In Phase I, which has not been dated, sedimentation of cinder from a nearby cone occurred. Phase II began ca. 16,830 ± 900 ¹⁴C yr B.P., whereas phase IV dates to 9280 ± 370 ¹⁴C yr B.P. The interpretation of sedimentary features shows that phases III and V correspond to a dry climate, similar to the present one, whereas the climate was much wetter during phases II and IV. This paleoclimatic sequence agrees with those suggested by the study of deposits formed in other sedimentary environments, not only in Fuerteventura but on other islands of the Canary group and the Sud-Maroc region.