Geochemistry and hydrothermal alteration of the Kern Mountains plutonic complex,White Pine County,Nevada and Juab County,Utah

The Kern Mountains plutonic complex is composed of multiple intrusions referred as the Cove, Tungstonia and Hoodoo Canyon plutons, whose emplacement was structurally controlled. The plutons are members of the calc-alcaline granite series, leucogranite type that are relatively alkali rich. The complex is of epizone (4–10 km) and was emplaced during Jurassic time into the carbonates and quartzite of Paleozoic age. Trace and major element data indicate that the complex was derived from the partial melting of rocks similar to Canadian Shield rocks. Analysis of variance of chemical data suggets that hydrothermal solutions carried K₂O, Na₂O and SiO₂ and raised the levels of original oxides in the plutons. Hydrothermal activity is evidenced by the occurrence of second generation muscovite, potassium feldspar and quartz in the complex and tungsten and sulphide mineralization in the area.

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Zusammenfassung Der plutonische Komplex des Kerngebirges besteht aus mehrfachen Instrusionen, genannt Cove-, Tungstonia- und Hoodoo Canyon-Pluton, deren Platznahme tektonisch kontrolliert wurde. Die plutonischen Gesteine gehören zu den Kalkalkaligraniten; sie sind leucogranitisch und damit ziemlich alkalireich. Der Komplex ist epizonal (4–10 km), er drang während des Jura in die Karbonate und Quarzite des Paläozoikums ein. Spuren- und Hauptelementmeßwerte zeigen an, daß der Komplex von aufgeschmolzenen Gesteinen abgeleitet werden kann, die den Gesteinen des Kanadischen Schildes ähneln. Die Analyse der Variation von chemischen Meßwerten deutet an, daß hydrothermale Lösungen K₂O, Na₂O und SiO₂ enthielten, die das Niveau der ursprünglichen Oxide in den plutonischen Gesteinen erhöhten. Die hydrothermale Tätigkeit wird durch das Vorhandensein von Muskowit, Kaliunifeldspat und Quartz der zweiten Generation innerhalb des Komplexes und durch Wolfram- und Sulfidmineralisation in der Umgebung bewiesen.

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Résumé L'ensemble plutonique des montagnes de Kern, consiste en de nombreuses intrusions dénommées plutons du »Cove«, de »Tungstonia«, et du »Hoodoo Canyon« dont la mise en place a été tectoniquement controlée. Ces plutons font partie de la série granitique calco-alkaline; ce sont des leucogranites relativement riches en alcali. L'ensemble est épizonal (4–10 km), et s'est mis en place au cours du Jurassique dans des Calcaires et quartzites d'âge paléozoique. Les données analytiques relatives aux élements majeurs et en trace indiquent que cet ensemble peut provenir de la fusion partielle de roches similaires à celles du Bouclier Canadien.L'analyse de la variation des données chimiques suggère aussi que l'enrichissement de ces plutons en K₂O, Na₂O, et SiO₂ s'est fait à partir de solutions minéralisantes hydrothermales, comme en témoignent non seulement la présence d'une deuxième génération de muscovite, de feldspath potassique et de quartz, mais aussi par la mineralisation en tungstène et en minerais sulfurés à leur voisinage.

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Do Spur-Throated Grasshoppers, <Emphasis Type="Italic">Melanoplus</Emphasis> spp. (Orthoptera: Acrididae), Exert Top-Down Control on Smooth Cordgrass <Emphasis Type="Italic">Spartina alterniflora</Emphasis> in Northern New England?

Recently, strong top-down (consumer) control of cordgrass (Spartina alterniflora) has been demonstrated. Here, we manipulated the densities of cordgrass consumers, acridid grasshoppers (Melanoplus bivittatus and Melanoplus femurrubrum), to examine their impact on cordgrass in the Plum Island Estuary (PIE), MA, USA. After 1 month, there was no detectable effect of grasshopper density on S. alterniflora biomass and grasshoppers at the highest densities (34 individuals per square meter) consumed only ~14% of the standing stock biomass. However, significant impacts of grasshopper density on grazing damage were seen. For example, plant damage and scarring length increased by 160% and 6,156%, respectively, at the highest grasshopper densities relative to exclusion (zero grasshoppers) densities. Plant height was significantly reduced with increasing grasshopper densities, although this may be a function of leaf tip removal instead of reduced plant growth. No other strong consumers of cordgrass (e.g., Littoraria irrorata, Prokelisia marginata) were observed in PIE and we suggest that consumer regulation of cordgrass is weak in this system.     

Flexural isostatic response of the Alps to increased Quaternary erosion recorded by foreland basin remnants,SE France

We test the hypothesis that flexural isostatic compensation of the mass removed by enhanced Quaternary erosion is responsible for uplift of the Western European Alps and their forelands. We use two well‐preserved and well‐dated (1.8 Ma) abandonment surfaces of foreland basin remnants in SE France (the Chambaran and Valensole plateaux) as passive benchmarks for tilting of the foreland. Estimating their initial slope from morphometric scaling relationships, we determine bulk post‐depositional tilting of 0.5–0.8% for these surfaces. The calculated isostatic response of the Alpine lithosphere to erosional unloading, using the method recently proposed by Champagnac et al. [Geology 35 (2007) 195–198] , yields a predicted tilting of 0.3–0.4% in the considered areas, explaining approximately half of the determined post‐depositional tilting. Such long‐term deformation being insensitive to cyclic loading/unloading because of glaciations, we suspect the other half to be related to as yet undetermined long‐wavelength and long‐lived tectonic process(es).     

Processes controlling precipitation of carbonate cement and dissolution of silica in reef and near-reef settings

Carbonate cementation in the surface layer of reefs and beachrock eliminates porosity and partially replaces detrital quartz grains. The uptake and release of CO₂ by photosynthesis and respiration in reef communities cause a shift in the carbonate buffer system of seawater. Field studies and experimentation simulating the natural settings show minimum values of CO₂ (1.9 mmoles 1^?1) and HCO₃^? (2.4 meq 1^?1) in association with maximum values of pH (9.8) and O₂ (> 100% oxygen saturation) in waters covering corals and algae prior to sunset. The converse is true for these variables prior to sunrise, when minimum values of pH (7.6) and O₂ (<66% oxygen saturation) occur with maximum values of CO₂ (2.7 mmoles 1^?1) and HCO₃^? (2.7 meq 1^?1). Experimental tanks containing plain seawater showed almost no diurnal variability in pH (a constant 7.5–7.6) or O₂ (80–90% oxygen saturation) measurements. Seawater adjacent to reef biomass, with elevated pH and supersaturated with calcium carbonate, is periodically pumped into the underlying reef and beach sediments due to pressure-buildups between the reef framework or algal zones and open waters. Carbonate precipitation and quartz dissolution follow. As the system equilibrates, pH values progressively decrease.     

Constraints on the thermal evolution of continental lithosphere from U-Pb accessory mineral thermochronometry of lower crustal xenoliths,southern Africa

U-Pb isotopic thermochronometry of rutile, apatite and titanite from kimberlite-borne lower crustal granulite xenoliths has been used to constrain the thermal evolution of Archean cratonic and Proterozoic off-craton continental lithosphere beneath southern Africa. The relatively low closure temperature of the U-Pb rutile thermochronometer (~400-450 °C) allows its use as a particularly sensitive recorder of the establishment of "cratonic" lithospheric geotherms, as well as subsequent thermal perturbations to the lithosphere. Contrasting lower crustal thermal histories are revealed between intracratonic and craton margin regions. Discordant Proterozoic (1.8 to 1.0 Ga) rutile ages in Archean (2.9 to 2.7 Ga) granulites from within the craton are indicative of isotopic resetting by marginal orogenic thermal perturbations influencing the deep crust of the cratonic nucleus. In Proterozoic (1.1 to 1.0 Ga) granulite xenoliths from the craton-bounding orogenic belts, rutiles define discordia arrays with Neoproterozoic (0.8 to 0.6 Ga) upper intercepts and lower intercepts equivalent to Mesozoic exhumation upon kimberlite entrainment. In combination with coexisting titanite and apatite dates, these results are interpreted as a record of postorogenic cooling at an integrated rate of approximately 1 °C/Ma, and subsequent variable Pb loss in the apatite and rutile systems during a Mesozoic thermal perturbation to the deep lithosphere. Closure of the rutile thermochronometer signals temperatures of 𙠂 °C in the lower crust during attainment of cratonic lithospheric conductive geotherms, and such closure in the examined portions of the "off-craton" Proterozoic domains of southern Africa indicates that their lithospheric thermal profiles were essentially cratonic from the Neoproterozoic through to the Late Jurassic. These results suggest similar lithospheric thickness and potential for diamond stability beneath both Proterozoic and Archean domains of southern Africa. Subsequent partial resetting of U-Pb rutile and apatite systematics in the cratonic margin lower crust records a transient Mesozoic thermal modification of the lithosphere, and modeling of the diffusive Pb loss from lower crustal rutile constrains the temperature and duration of Mesozoic heating to 𙡦 °C for ₞ ka. This result indicates that the thermal perturbation is not simply a kimberlite-related magmatic phenomenon, but is rather a more protracted manifestation of lithospheric heating, likely related to mantle upwelling and rifting of Gondwana during the Late Jurassic to Cretaceous. The manifestation of this thermal pulse in the lower crust is spatially and temporally correlated with anomalously elevated and/or kinked Cretaceous mantle paleogeotherms, and evidence for metasomatic modification in cratonic mantle peridotite suites. It is argued that most of the geographic differences in lithospheric thermal structure inferred from mantle xenolith thermobarometry are likewise due to the heterogeneous propagation of this broad upper mantle thermal anomaly. The differential manifestation of heating between cratonic margin and cratonic interior indicates the importance of advective heat transport along pre-existing lithosphere-scale discontinuities. Within this model, kimberlite magmatism was a similarly complex, space- and time-dependent response to Late Mesozoic lithospheric thermal perturbation.     

Pollution characteristics of alluvial groundwater from springs and bore wells in semi-urban informal settlements of Douala,Cameroon, Western Africa

Alluvial groundwater from springs and bore wells, used as the major source of water for drinking and other domestic purposes in the semi-urban informal settlements of Douala, Cameroon, has been studied. Six representative springs, four bore wells and two hand dug wells, situated in the Phanerozoic basin were selected, from which a total of 72 water samples were analyzed for chemical characteristics and indicators of bacterial contamination. The results showed anthropogenic pollution, evident from high concentrations of organic (up to 94.3 mg NO₃/l nitrate) fecal coliform and fecal streptococcus detected in the springs and bore wells (with values of 2,311 and 1,500 cfu/100 ml, respectively). The pH ranged from 3.4–6.5, which is lower than the guidelines for drinking water. Groundwater samples from background upstream inland natural areas W1 and W2 had low electrical conductivity (54.2 and 74.8 μs/cm, respectively) and major ions, which increased downstream in the valleys, peaking in the more densely settled areas. An acceptable concentration of solutes was observed for the bore wells except for a single sample from B4. The bore-well sample B4 registered the highest microbial content (2,130 cfu/100 ml) and nitrate level(26 mg/l), which could be due to the bottom of this well lying just at or close to the zone of mixing between sewage and groundwater. The absence of a direct correlation between nitrate and fecal matter suggests multiple sources of contamination. The shallow alluvial aquifer consists of unconsolidated deposits of gravel, sand, silt and clay. The springs, therefore, receive direct recharge from the ground surface with limited contaminant attenuation, which leads to water quality deterioration, especially during the rainy season. This shows the urgent need to put basic service infrastructures in place. The local population should be sensitized to the importance of chlorinating and boiling drinking water to prevent health hazards.     

Evidence for the depletion of ammonia in the Uranus atmosphere

The theoretical disk brightness temperature spectra for Uranus are computed and compared with the observed microwave spectrum. It is shown that the emission observed at short centimeter wavelengths originates deep below the region where ammonia would ordinarily begin to condense. We demonstrate that this result is inconsistent with a wide range of atmospheric models in which the partial pressure of NH₃ is given by the vapor-pressure equation in the upper atmosphere. It is estimated that the ammonia mixing ratio must be less than 10^?6 in the 150 to 200°K temperature range. This is two orders of magnitude less than the expected mixing ratio based on solar abundances. The evidence for this depletion and a possible explanation are discussed.     

Protecting small cetaceans from coastal development: Impact assessment and mitigation experience in Hong Kong

Since the early 1990s, there has been an active program in Hong Kong to manage and protect local populations of small cetaceans from the effects of massive development in the area. This paper reviews the progress that has been made. Only two species regularly occur there: the Indo-Pacific humpback dolphin and the finless porpoise. Because most development has occurred in the western waters of Hong Kong, where generally only the humpback dolphin occurs, most of the work has been conducted on that species. Development of large infrastructure projects (such as airports, bridges, expressways, power plants, fuel facilities, and container ports) in Hong Kong often results in land reclamation, dredging and dumping of spoils, pipe and cable laying, percussive and bored piling work, underwater blasting, large increases in vessel traffic, and other impacts. Several mitigation measures have been used with varying levels of success, including bubble curtains/jackets, exclusion zones, ramping up of piling hammers, acoustic decoupling of noisy equipment, vessel speed limits, no-dumping policies, and silt curtains. Baseline, construction-phase, and operational-phase cetacean monitoring is often conducted to evaluate the success of conservation measures put into place. The Environmental Impact Assessment process in Hong Kong has involved cetaceans to a degree perhaps higher than anywhere else in the world, and much can be learned from studying the successes and failures of this situation.     

Inertial and hydrodynamic inertial loads on floating units

The analysis of the dynamic behavior of floating units usually employs a coordinate system with origin in the unit's center of gravity, which significantly simplifies the global mass matrix. Hydrodynamic coefficients are then computed considering the same coordinate system. However, to analyze other conditions of mass distribution and maintain the simplicity of a global mass matrix, it is necessary to determine again the hydrodynamic coefficients, thereby reducing the efficiency of the entire process. Another important point is that the geometries frequently used in floating units are such that the cross-terms of an added mass are relatively unimportant when compared with the main terms, and it is, therefore, common to use only some of them to analyze the unit's dynamic behavior. Recently, however, in the search for production systems suitable for water depths greater than 3000 m, other geometries have been considered in technical and economic feasibility studies. It is possible that for these new geometries all terms of the added mass matrix must be included in the analysis. This paper presents the full development used to determine the complete global mass matrix, the inertial and hydrodynamic inertial loads that make use of the added mass matrices considering any coordinate system and the six degrees of freedom, including all cross-terms.