Search for evolutionary changes in Cepheid periods using the Harvard plate collection: NSV 9159

We have obtained 530 photographic magnitude estimates for the long-period classical Cepheid NSV 9159 (P = 39^d) in the plate collections of the Harvard Observatory and the Sternberg Astronomical Institute. Together with the currently available CCD observations from the ASAS-3 catalog, our data have allowed us to construct an O-C diagram spanning a time interval of 119 years. The O-C diagram has the shape of a parabola, which has made it possible to determine for the first time the quadratic light elements and to calculate the rate of evolutionary decrease in the period, 314.4 (±7.3) s yr^?1, in agreement with the results of theoretical calculations for the second crossing of the instability strip. The available data reduced by the Eddington-Plakidis method do not reveal any noticeable random fluctuations in the period.     

Distribution,behavior, and transport of inorganic and methylmercury in a high gradient stream

Concentrations of Hg remain elevated in physical and biological media of the South River (Virginia, USA), despite the cessation of the industrial use of Hg in its watershed nearly six decades ago, and physical characteristics that would not seem to favor Hg(II)-methylation. A 3-a study of inorganic Hg (IHg) and methylmercury (MeHg) was conducted in physical media (soil, sediment, surface water, porewater and soil/sediment extracts) to identify non-point sources, transport mechanisms, and potential controls on Hg(II)-methylation. Data collected from surface water and sediment indicate that the majority of the non-point sources of IHg to the South River are within the first 14 km downstream from the historic point source. Partitioning data indicate that particle bound IHg is introduced in this reach, releasing dissolved and colloidal bound IHg, which is transported downstream. Extraction experiments revealed that floodplain soils released a higher fraction of their IHg content in aqueous extractions than fine-grained sediment (FGS). Based on ultrafiltration [<5000 nominal molecular weight cutoff (NMWC)] the majority of soil IHg released was colloidal in nature, providing evidence for the continued evolution of IHg for Hg(II)-methylation from soil. Strong seasonal patterns in MeHg concentrations were observed in surface water and sediment. The highest concentrations of MeHg in surface water were observed at moderate temperatures, suggesting that other factors limit net Hg(II)-methylation. Seasonal changes in sediment organic content and the fraction of 1 N KOH-extractable THg were also observed and may be important factors in controlling net Hg(II)-methylation rates. Sulfate concentrations in surface water are low and the evidence suggests that Fe reduction may be an important Hg(II)-methylation process. The highest sediment MeHg concentrations were observed in habitats with large amounts of FGS, which are more prevalent in the upper half of the study area due to the lower hydrologic gradient and agricultural impacts. Past and present land use practices and other geomorphologic controls contribute to the erosion of banks and accumulation of fine-grained sediment in this section of the river, acting as sources of IHg.     

Vulnerability and resilience: Coalescing or paralleling approaches for sustainability science?

Vulnerability and resilience constitute different but overlapping research themes embraced by sustainability science. As practiced within this science, the two research themes appear to coalesce around one of the foundational pivots of sustainability, the coupled human–environment system. They differ in regard to their attention to two other pivots, environmental services and the tradeoffs of these services with human outcomes. In this essay I briefly review the emergence of sustainability science and the three foundational pivots relevant to vulnerability and resilience. I outline the distinctions and similarities between the two research themes foremost as practiced within sustainability science and especially in regard to the attention given to the three pivots. I conclude with the observation that improvement in the capacity of vulnerability and resilience research to inform sustainability science may hinge on their linkages in addressing tradeoffs.     

Proterozoic low-sulfidation epithermal Au-Ag mineralization in the Mallery Lake area, Nunavut, Canada

The Mallery Lake area contains pristine examples of ancient precious metal-bearing low-sulfidation epithermal deposits. The deposits are hosted by rhyolitic flows of the Early Proterozoic Pitz Formation, but are themselves apparently of Middle Proterozoic age. Gold mineralization occurs in stockwork quartz veins that cut the rhyolites, and highest gold grades (up to 24 g/t over 30 cm) occur in the Chalcedonic Stockwork Zone. Quartz veining occurs in two main types: barren A veins, characterized by fine- to coarse-grained comb quartz, with fluorite, calcite, and/or adularia; and mineralized B veins, characterized by banded chalcedonic silica and fine-grained quartz, locally intergrown with fine-grained gold or electrum. A third type of quartz vein (C), which crosscuts B veins at one locality, is characterized by microcrystalline quartz intergrown with fine-grained hematite and rare electrum. Fluid inclusions in the veins occur in two distinct assemblages. Assemblage 1 inclusions represent a moderate temperature (Th=150 to 220 °C), low salinity (~1 eq. wt% NaCl, with trace CO₂), locally boiling fluid; this fluid type is found in both A and B veins and is thought to have been responsible for Au-Ag transport and deposition. Assemblage 2 inclusions represent a lower temperature (Th=90 to 150 °C), high salinity calcic brine (23 to 31 wt% CaCl₂-NaCl), which occurs as primary inclusions only in the barren A veins. Assemblage 1 and 2 inclusions occur in alternating quartz growth bands in the A-type veins, where they appear to represent alternating fluxes of dilute fluid and local saline groundwater. No workable primary fluid inclusions were observed in the C veins. The A-vein quartz yields '¹⁸O values from 8.3 to 14.5‰ (average=10.9ǃ.7‰ [1C], n=30), whereas '¹⁸O values for B-vein quartz range from 11.2 to 14.0‰ (average=13.0ǂ.9‰, n=12). Calculated '¹⁸O_H2O values for the dilute mineralizing fluid from B veins range from -2.6 to 0.2‰ (average=-0.8ǂ.9‰, n=12) and are consistent with a dominantly meteoric origin. No values could be calculated for the brine, however, because all A-vein quartz samples contain mixed fluid inclusion populations. However, the fact that A-vein quartz samples extend to lower '¹⁸O values than the B veins suggests that the brine had a lighter isotopic signature relative to the dilute fluid. Hydrogen isotopic ratios of fluid inclusion waters extracted from eleven quartz samples of both vein types range from 'D_FI=-56 to -134‰, but show no particular correlation with vein type. In most respects, the mineralogical and fluid characteristics of the Mallery Lake system are comparable to those of Phanerozoic low-sulfidation deposits, and although the presence of high salinity brines is unusual in such deposits, it is not unknown (e.g., Creede, Colorado). In addition, one of the few other examples of well-preserved, Precambrian, low-sulfidation epithermal deposits, from the Central Pilbara tectonic zone, Australia, contains a similarly bimodal fluid assemblage. The significance of these saline brines is not clear, but from this study we infer that they were not directly involved with Au-Ag transport or deposition.     

An experimental study of the application of kinematic-wave theory to overland flow

An experimental test to evaluate the accuracy of kinematic-wave theory as applied to overland flow over a rough, uneven surface is described. The depression storage, and the hydraulic roughness for flows without rain were measured in separate tests; the hydraulic roughness for flows under rain was calculated from the rising limbs of the runoff hydrographs from a series of simulated storms. Recession curves were calculated using kinematic wave theory. The close agreement between experimental and calculated recessions showed the accuracy of this theory in predicting the behaviour of flows over the rough uneven surface. Hysteresis was observed in the storage-discharge curves; this was also explained in terms of kinematic wave theory.     

A laboratory model of a replenished magma chamber

It has recently been suggested that periodic influxes of hot but heavy magma into the base of a basaltic magma chamber can remain isolated from the rest of the chamber while the new magma cools and crystallization proceeds. When thermal equilibrium is almost complete, the suspended crystals settle out and the residual, less dense liquid can then mix with the fluid above. In the present paper the basic fluid-dynamical processes underlying this model have been investigated in laboratory experiments using aqueous solutions. The lower layer was hot KNO₃ solution, for which saturated solutions become less dense as the temperature decreases. With a cold, deeper layer of less dense NaNO₃ or K₂CO₃ above the lower layer, there was strong convective transfer of heat through a sharp interface separating the layers, at a rate which is predicted here drawing on previous studies carried out with oceanographic applications in mind. Once crystallization began, non-equilibrium effects became important and the observed temperatures differ somewhat from those predicted. In the experiments crystals grew mainly from the bottom rather than while in suspension, but this is not an essential aspect of the model. The important fact is that the density of the residual liquid in the lower layer decreased until it became equal to that of the upper layer, and then the interface broke down so that the two layers mixed thoroughly together, leaving a layer of KNO₃ crystals at the base. No crystallization at all occurred when the hot input liquid was forced to mix initially with the cold solution already in the chamber.     

Distribution of regional Metamorphism in Africa

The preparation of the International Metamorphic Map of Africa has revealed a number of important trends in regional metamorphism across the orogenic belts of Africa. Relatively simple systematic increases in grade in some belts is in marked contrast to polycyclic metamorphism in others. Reworking of older sialic basement and the development of granulites are commonly recorded from belts. Archaean cratons are characterised by granitoids and high thermal metamorphism within a relatively low pressure environment. In late Precambrian belts regional metamorphism was more frequently of intermediate pressure type, the paired metamorphic belt regime not being recognised.

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Zusammenfassung Die Herstellung der internationalen Karte der regionalmetamorphen Zonen Afrikas hat eine Anzahl wichtiger Trends in Bezug auf regionalen Metamorphismus, der sich über Afrika erstreckenden orogenen Gürtel, aufgezeigt. Verhältnismäßig unkomplizierter, systematischer Metamorphoseablauf in einigen Gürteln stehen in scharfem Kontrast zu polyzyklischen Metamorphismus in anderen. Die Weiterbeanspruchung eines älteren sialischen Grundstratums und die Entstehung von Granuliten werden im allgemeinen in vielen Gürtel beobachtet. Archaische Kratone zeigen granitartige Charakteristiken und hohen thermalen Metamorphismus in ihrer Umgebung unter verhältnismäßig niedrigem Druck. In spät-praekambrischen Gürteln war regionaler Metamorphismus öfters von mittleren Drucken begleitet.

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Résumé La préparation de la carte internationale métamorphique de l'Afrique a révéle un certain nombre de tendances dans le métamorphisme régional des zones orogéniques de l'Afrique. Des accroissements systématiques relativement simples du degré métamorphique dans certains zones tranchent nettement avec le métamorphisme polycyclique dans d'autres. Le remainiement du vieux socle sialique et le développement de granulites sont couramment signalés dans nombreuses zones. Les cratons archéens se caractérisent par des granitoÏdes et par un métamorphisme thermique éllevé dans un environnement à pression relativement basse. Dans les zones précambriennes récentes le métamorphisme régional fut plus fréquemment du type à moyenne pression, la double Çeinture métamorphique n'étant pas connues.

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The geology and petrogenesis of a greenstone belt and related nickel sulfide mineralization at Yakabindie,Western Australia

Two major rock sequences, the Lower and Upper Greenstones, separated by an unconformity and associated conglomerate, are exposed in a narrow (5–30 km) elongate (130 km) greenstone belt in the Lawlers—Mt Keith area of the Eastern Goldfields of Western Australia. The Upper Greenstones, which contain zones of significant nickel sulfide mineralization, appear to have been emplaced in a graben which cuts across folded strata of the Lower Greenstones.Exposed portions of the Lower Greenstones consist of over 90% mafic and less than 10% felsic rocks, whereas the Upper Greenstones consist of approximately one third mafic and two thirds felsic rocks. The mafic rocks of the latter sequence all appear to belong to the komatiitic rock series.⁷ They are divided into two groups of flows and thin sills ranging in composition from peridotite to basalt and a number of strata-bound podiform dunitic bodies which are regarded as feeder chambers for some of the overlying flows. Mafic rocks of the Lower Greenstones include Fe-rich tholeiitic basalts, gabbros, komatiitic⁷ ultramafic rocks and some basalts which appear chemically to be transitional between the two rock series.At Yakabindie in the centre of the Lawlers—Mt Keith belt, Western Australia, the nickel sulfide mineralization occurs mainly within the dunite pods as large (in excess of 70·10⁶ tonnes) low grade (approx. 0.6 wt.% Ni) zones composed largely of disseminated pentlandite. Textures in much of the ore suggest that magmatic sulfides were trapped interstitial to olivine grains, although textures and chemical variations in some of the ore indicate that metals and sulfides have been redistributed during metamorphism or alteration of the host rocks.Chemical variations within the komatiites are consistent with their being the result of low pressure fractional crystallization of a liquid containing in excess of 33 wt. % MgO. In order to produce such a magnesian liquid, it is postulated that the source region of the mantle must have been melted twice, once to give rise to a basaltic liquid and again to give rise to the magnesian, komatiitic liquid. This would require diapiric ascent of mantle material from a depth of perhaps 200–250 km. Consideration of the melting curves of sulfides and mantle periodotite with pressure suggests that sulfides might have become concentrated at these depths, thus accounting for their almost universal association, in Western Australia, with very magnesian komatiites.