The mass accommodation coefficient of ammonia on water

The mass accommodation coefficient of ammonia gas on water has been determined by measuring the absorption rate of 50–200 ppm NH₃ in one atm of air or helium into a liquid jet of 97 µm diameter as function of the exposed jet length, and comparing the results with numerical simulations which treat as the only free parameter. The model considers in detail transport of NH₃ by molecular diffusion, penetration of the gas/water interface, hydrolysis in the acidified water, and transport of the solutes from the surface into the jet. A correction is applied for the time evolution of the jet surface speed, using literature data on the fluid mechanics of liquid jets. The result of nine sets of independent measurements is

On the bogussing of tropical cyclones in numerical models: A comparison of vortex profiles

Summary At the resolutions currently in use, and with the sparse oceanic data coverage, numerical analyses cannot adequately represent tropical cyclone circulations for use in numerical weather prediction models. In many cases there is no circulation present at all. Most numerical weather prediction centers therefore employ a bogussing scheme to force a tropical cyclone vortex into the numerical analysis. The standard procedure is to define a synthetic data distribution based on an analytically prescribed vortex, which is passed to the analysis scheme as a set of high quality observations.In this study, four commonly used bogus vortices are examined by comparing resultant forecast tracks in an environment at rest, and in a background flow that simulates a typical monsoon trough-subtropical ridge structure. There are three main findings, each of which has significance for operational tropical cyclone track prediction. First, great care is needed in the choice of the characteristics of the bogus vortex, such as the radius and magnitude of the maximum wind. Second, the tropical cyclone trajectories can be very sensitive to their initial position in the idealised environment. Third, the bogus vortex can substantially influence the environment, especially over longer time periods and for vortices of larger size.With 9 Figures     

Daily rainfall domains in Mallorca

Summary A Pearson Product Moment Correlation matrix for four years of daily rainfall from 96 sites on the island of Mallorca has been used to derive and map correlation fields and construct composite correlation fields for different parts of the island based on previously defined daily rainfall affinity areas. Significant variations in rainfall organisation over the island are revealed. These reflect the dominance of uplift and exposure by upland areas in the generation of rainfall, evidenced in strongly anisotropic correlation fields. Further anisotropy along lowland coasts normal to the relief trend indicate the role of local rainfall generation along sea-breeze fronts. Near isotropic fields for central island locations highlight the importance of local convection and local convergence between opposing sea breeze systems and inland convection. Linear correlation distance-decay trends are determined for the island and for the predetermined rainfall affinity areas, including estimates of distance-decay rates along field axes. A suite of exponential cone functions is derived to model the empirically observed fields, representing their typical bidimensional structure. Use of the fitted cones to model a typical rainfall day, where the rainfall distribution mimics quite closely the longer term average, yields quite good results and suggests that their use may be more appropriate than applying more conventional general interpolation techniques in the mapping of spatial rainfall distributions.With 14 Figures     

Geology of the volcanic-hosted Brockman rare-metals deposit,Halls Creek Mobile Zone,northwest Australia. l. Volcanic environment,geochronology and petrography of the Brockman volcanics

Summary Rare-metals mineralization of the Brockman deposit (Halls Creek Mobile Zone, NW Australia) is hosted in a fluorite-bearing, rhyolitic volcaniclastic unit informally termed the Niobium Tuff. The Tuff, more correctly described as a tuffaceous volcaniclastic deposit, is the lowermost unit of a sequence of trachyte-to-rhyolite lavas, trachyandesite subvolcanic rocks, and volcaniclastic units of the Brockman volcanics located within the Halls Creek Group, a thick, early Proterozoic volcano-sedimentary sequence. High precision SHRIMP ion-microprobe zircon dating of the Niobium Tuff gives an eruption age of 1870 ± 4 Ma. Regional geochronological constraints indicate the Niobium Tuff was deposited about 15 Ma before major orogenic activity affected the area. Despite folding, faulting and low-grade metamorphism, the Brockman volcanics show excellent preservation of primary volcanological features, including pillow-lavas and pillow-breccias, that suggest a dominantly subaqueous, below-wave-base emplacement environment. The style of eruption products and magma volume constraints suggest the trachyte-dominated volcanics were erupted from a small shield volcanic complex probably in a rift-related basin in a shallow-marine setting. The tectonic setting was intraplate but differs from most Tertiary to recent trachyte volcanic complexes which are largely subaerial, are built on relatively thick continental crust, and show no post-eruptive orogenic history. Brockman-style rare-metal deposits are characterized by preservation of subaqueous volcanics beneath a thick sedimentary sequence, eruption of early incompatible-element enriched products followed by less differentiated magmas, and fine-grained mineralogy influenced by alteration processes. Prospects exist for discovery of analogous deposits, particularly in early Proterozoic mobile belts and Tertiary intraplate shield volcanic provinces.

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Geologie der an Vulkanite gebundenen Seltene-Metalle-Lagerstätte Brockman, Halls Creek Mobile Zone, Nordwest-Australien. I. Vulkanologie, Geochronologie und Petrographie der Brockman-Vulkanite

Zusammenfassung Selten-Metall-Vererzung der Brockman-Lagerstätten (Halls Creek Mobile Zone, NW Australien) sitzt in einer Fluorit-führenden, rhyolitischen vulkanoklastischen Einheit auf, die informell als der Niob-Tuff bezeichnet wird. Es handelt sich hier um ein vulkanoklastisches Tuff-Sediment; dieses ist die unterste Einheit einer Abfolge vor Trachyt bis Rhyolit-Laven, trachyandesitischen Subvulkaniten and vulkanoklastischen Einheiten der Brockman Vulkanite innerhalb der Halls Creek Gruppe, einer mächtigen frühproterozoischen vulkanosedimentdren Abfolge. Prüzisionsdatierungen des Niob Tuffs mit der SHRIMP Ionen-Mikrosonde ergeben ein Eruptionsalter von 1870 +-4 Millionen Jahren. Regionale geochronologische Zusammenhänge zeigen, daß der Niob Tuff etwa 15 Millionen Jahre vor einer größeren Orogenese, die das Gebiet betroffen hat, abgelagert wurde. Trotz Faltung, Bruchtektonik and niedriggradiger Metamorphose zeigen die Brockman-Vulkanite einen hervorragenden Erhaltungszustand primärer vulkanologischer Erscheinungen. Diese urnfassen auch Kissenlaven und KissenBreckzien, die eine vorwiegend subaquatische Ablagerung in ruhigem Wasser erkennen lassen. Die Art der Eruptionsprodukte and das Magmavolumen zeigen, daß die Trachytdominierten Vulkanite von einem kleinen Schildvulkan stammer, wahrscheinlich in einem Becken in einer Rift-Situation im seichten marinen Milieu. Die tektonische Situation war intraplate, aber unterscheidet sich von den meisten tertiären bis rezenten trachytischen Vulkan-Komplexen, die hauptsächlich subaerisch sind, auf einer relativ mächtigen kontinentalen Kruste aufsitzen, and keine post-eruptive orogene Entwicklung zeigen. Seltene-Metalle-Lagerstatten des Brockman-Typs rind durch die Erhaltung subaquatischer-Vulkanite unterhalb einer machtigen sedimentdren Abfolge gekennzeichnet; welters durch frühe Eruptionsprodukte, die an inkompatiblen Elementen angereichert sind, auf die dann weniger differenzierte Magmen folgten, und schließlich durch einen feinkörnigen Mineralbestand, der vor Umwandlungsprozessen betroffen war. Es besteht die Möglichkeit der Entdeckung analoger Lagerstätten, besonders in frühproterozoischen mobilen Gürteln und in tertidren intraplate Schildvulkan Provinzen.

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Deceased     

Efficient generation of conditional simulations by chebyshev matrix polynomial approximations to the symmetric square root of the covariance matrix

Consider the problem of generating a realization y₁ of a Gaussian random field on a dense grid of points ₁ conditioned on field observations y₂ collected on a sparse grid of points ₂. An approach to this is to generate first an unconditional realization y over the grid =_{1 2}, and then to produce y₁ by conditioning y on the data y₂. As standard methods for generating y, such as the turning bands, spectral or Cholesky approaches can have various limitations, it has been proposed by M. W. Davis to generate realizations from a matrix polynomial approximations to the square root of the covariance matrix. In this paper we describe how to generate a direct approximation to the conditional realization y₁, on ₁ using a variant of Davis' approach based on approximation by Chebyshev polynomials. The resulting algorithm is simple to implement, numerically stable, and bounds on the approximation error are readily available. Furthermore we show that the conditional realization y₁ can be generated directly with a lower order polynomial than the unconditional realization y, and that further reductions can be achieved by exploiting a nugget effect if one is present. A pseudocode version of the algorithm is provided that can be implemented using the fast Fourier transform if the field is stationary and the grid ₁ is rectangular. Finally, numerical illustrations are given of the algorithm's performance in generating various 2-D realizations of conditional processes on large sampling grids.     

Textures in a poikilitic olivine gabbro cumulate: Evidence for supercooling

Summary Supercooling of repeated influxes of high-MgO ( 13.5 wt% MgO) tholeiitic magma emplaced along the floor of the Kap Edvard Holm magma chamber led to the formation of fine grained, intraplutonic quench zones that define the bases of 12 macrorhythmic units. The quench zones grade upwards into poikilitic cumulates containing olivine dendrites, suggesting supercooling by 40°C. Supercooling led to early, precumulus crystallization of metastable, non-equilibrium plagioclase, followed by co-precipitation of cumulus plagioclase and olivine. Later nucleation of clinopyroxene followed by rapid growth led to crystallization of zoned oikocrysts during the cumulus stage, followed by postcumulus overgrowth and crystallization of discrete intercumulus grains. At least four generations of plagioclase crystals appear to be preserved.

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Gefüge in einem poikilitischen Olivingabbro-Kumulat: Hinweis auf Unterkühlung

Zusammenfassung Unterkühlung von mehrmals nachströmendem MgO-reichen (ca. 13,5 Gew.% MgO), tholeiitischen Magma, das sich am Boden der Magmenkammer vom Kap Edvard Holm sammelte, führte zur Bildung von feinkbrnigen Zonen mit Abschreckungsgefüge, die jeweils die Basis von 12 makrorhythmischen Einheiten bilden. Diese Zonen gehen im Hangenden in poikilitische Kumulate über, die Olivin-Dendriten enthalten, was auf eine Unterkühlung um ca. 40°C hindeutet. Die Unterkühlung führte zu einer frühen präkumulativen Kristallisation von metastabilem, nicht im Gleichgewicht befindlichem Plagioklas, gefolgt von gleichzeitiger Präzipitation von Kumulus-Plagioklas und -Olivin. Eine spätere Keimbildung von Klinopyroxen, die von raschem Wachstum abgelöst wurde, führte während der Akkumulation zur Kristallisation von zonierten Oikokrysten. Danach folgte eine postkumulative Überwachsung und die Kristallisation von Einzelkörnern in den Zwischenräumen. Zumindest vier Generationen von Plagioklaskristallen scheinen erhalten zu sein.

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Trace elements distribution and mineralogical composition in the < 2-μm size fraction of shales from the Southern Apennines,Italy

Summary Mineralogical composition and trace elements distribution in the < 2-m size fraction of Late Cretaceous-Oligocene shales from the Southern Apennines (Italy) are presented.The clay mineral assemblage consists of illite, smectite, kaolinite and minor chlorite. Analytical evidence points to a detrital micaceous precursor for illite and smectite. Accessory phases were also found. Chemical data, normalized with respect to the Post-Archean Australian Shales (PAAS), indicate depletion of Ba, Rb, Y, Zr and enrichment of Nb. PAAS-normalized REE-patterns exhibit a positive Eu anomaly and HREE depletion. A kaolinite-rich sample has high REE contents in contrast to smectite-rich fractions. A REE-pattern without appreciable Eu anomaly is displayed by the illite-rich sample.Statistical data processing indicates a link between Ti, P, Y, Zr, Nb and Yb, suggesting that accessory phases may play a role in controlling HREE and that the observed LREE/HREE fractionation may also be due to hydraulic sorting of these phases. An important La-kaolinite relationship accounts for the capability of this phase to host LREE. Smectite and, thus, adsorption mechanisms, appear to exert a limited role in distributing REE. The Eu anomaly is a source inherited feature, probably not determined solely by clay minerals.

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Spurenelement-Verteilung und mineralogische Zusammensetzung der < 2m Fraktion von Schiefern aus dem südlichen Appenin (Italien)

Zusammenfassung Die mineralogische Zusammensetzung und die Verteilung der Spurenelemente in der < 2 m Fraktion von spät-kretazischen-oligozänen Schiefern aus dem südlichen Appenin (Italien) werden in Übersicht gebracht. Die Tonmineral-Vergesellschaftung besteht aus Illit, Smectit, Kaolinit und kleineren Mengen von Chlorit. Analytische Daten weisen darauf hin, daß Illit und Smectit aus einem detritischen Glimmermineral hervorgegangen sein dürften. Auch akzessorische Phasen kommen vor. Chemische Daten zeigen gegenüber post-Archaischen australischen Schiefern (PAAS) eine Verarmung in Ba, Rb, Y, Zr und eine Anreicherung von Nb. PAAS-normalisierte SEE-Verteilungsmuster zeigen eine positive Eu Anomalie und eine Verarmung an HSEE. Eine Kaolinit-reiche Probe zeigt hohe Gehalte an gesamten SEE im Gegensatz zu einer Smectit-reichen. Die Illit-reiche Probe zeigt ein SEE-Verteilungsmuster ohne deutliche Eu Anomalie.Statistische Verarbeitung der Daten läßt eine Verbindung zwischen Ti, P, Y, Zr, Nb und Yb erkennen; dies weist darauf hin, daß akzessorische Phasen einen Einfluß auf die HSEE-Verteilung haben und daß die beobachtete LSEE/HSEE Fraktionierung auch auf hydraulische Sortierung dieser Phasen zurückgehen könnte. Es gibt eine bedeutsame Beziehung zwischen La und Kaolinit und diese unterstreicht die Fähigkeit des Kaolinits für die Aufnahme von LSEE. Smectit und Adsorptionsmechanismen scheinen eine geringe Rolle für die Verteilung der SEE zu spielen. Die Eu Anomalie ist eine Erscheinung, die auf die Quelle der sedimentären Minerale zurückgeht und wahrscheinlich nicht ausschließlich durch Tonminerale bestimmt wird.

     

Sector collapse,sedimentation and clast population evolution at an active island-arc volcano: Stromboli,Italy

Sciara del Fuoco is the subaerial part of a partially filled sector-collapse scar that extends to 700 m below sea level on Stromboli volcano. The collapse occurred <5000 years ago, involved 1.81 km³ of rock and is the latest of a series of major collapses on the north-west flank of Stromboli. A north-east trending arc-axial fault system channels magmas into the volcano and has caused tilting and/or downthrow to the north-west. The slope of the partial cone constructed between the lateral walls of the collapse scar acts as a channelway to the sea for most eruptive products. From 700 m below sea level and extending to >2200 m and >10 km from the shore to the NNW, a fan-shaped mounded feature comprises debris avalanche deposits (>4 km³) from two or more sector collapses. Volcaniclastic density currents originating from Sciara del Fuoco follow the topographic margin of the debris avalanche deposits, although overbank currents and other unconfined currents widely cover the mounded feature with turbidites. Historical (recorded) eruptive activity in Sciara del Fuoco is considerably less than that which occurred earlier, and much of the partial fill may have formed from eruptions soon after the sector collapse. It is possible that a mass of eruptive products similar to that in the collapse scar is dispersed as volcanogenic sediment in deep water of the Tyrhennian basin. Evidence that the early post-collapse eruptive discharge was greater than the apparent recent flux (2kg/s) counters suggestions that a substantial part of Stromboli's growth has been endogenous. The partial fill of Sciaria del Fuoco is dominated by lava and spatter layers, rather than by the scoria and ash layers classically regarded as main constituents of Strombolian (cinder) cones. Much of the volcanic slope beneath the vents is steeper than the angle of repose of loose tephra, which is therefore rapidly transported to the sea. Delicate pyroclasts that record the magmatic explosivity are selectively destroyed and diluted during sedimentary transport, mainly in avalanches and by shoreline wave reworking, and thus the submarine deposits do not record well the extent and diversity of explosive activity and associated clast-forming processes. Considerable amounts of dense (non-vesicular) fine sand and silt grains are produced by breakage and rounding of fragments of lava and agglutinate. The submarine extension of the collapse scar, and the continuing topographic depression to >2200 m below sea level, are zones of considerable by-passing of fine sand and silt, which are transported in turbidity currents. Evidently, volcanogenic sediments dispersed around island volcanoes by density currents are unlikely to record well the true spectrum and relative importance of clast-forming processes that occurred during an eruption. Marine sedimentary evidence of magmatic explosivity is particularly susceptible to partial or complete obliteration, unless there is a high rate of discharge of pyroclastic material into the sea.     

A sulfur isotope study of volcanogenic massive sulfide deposits of the Eastern Black Sea province,Turkey

Kuroko-type massive sulfide deposits of the Eastern Black Sea province of Turkey are related to the Upper Cretaceous felsic lavas and pyroclastic rocks, and associated with clay and carbonate alteration zones in the footwall and hangingwall lithologies. A complete upward-vertical section of a typical orebody consists of a stringer-disseminated sulfide zone composed mainly of pyrite and chalcopyrite; a massive pyrite zone; a massive yellow ore consisting mainly of chalcopyrite and pyrite; a black ore made up mainly of galena and sphalerite with minor amounts of chalcopyrite, bornite, pyrite and various sulfosalts; and a barite zone. Most of the deposits in the province are associated with gypsum in the footwall or hangingwall. The paragenetic sequence in the massive ore is pyrite, sphalerite, chalcopyrite, bornite, galena and various sulfosalts, with some overlap between the mineral phases. Massive, stringer and disseminated sulfides from eight kuroko-type VMS deposits of the Eastern Black Sea province have a ³⁴S range of 0–7 per mil, consistent with the ³⁴S range of felsic igneous rocks. Sulfides in the massive ore at Madenköy (4.3–6.1 per mil) differ isotopically from sulfides in the stringer zone (6.3–7.2 per mil) suggesting a slightly increased input of H₂S derived from marine sulfate with time. Barite and coarse-grained gypsum have a ³⁴S range of 17.7–21.5 per mil, a few per mil higher than the ³⁴S value of contemporaneous seawater sulfate. The deposits may, therefore, have formed in restricted basins in which bacterial reduction of sulfate was taking place. Fine-grained, disseminated gypsum at Kutlular and Tunca has ³⁴S values (2.6–6.1 per mil) overlapping those of ore sulfides, indicating sulfide oxidation during waning stages of hydrothermal activity.     

Powder- and single crystal Mössbauer spectroscopy on synthetic fayalite

Mössbauer measurements on synthetic iron orthosilicate Fe₂SiO₄ (fayalite) were carried out in the antiferromagnetic spin state below T _N 65 K. The Mössbauer parameters isomer shift , inner magnetic field H(0), angle between H(0) and the z-component of the electric field gradient (efg), quadrupole splitting QS and asymmetry parameter were determined as a function of temperature. These parameters could be attributed to the two crystallographic sites M1 and M2.The smaller isomer shift on M1 with respect to M2 displays the more covalent character of the Fe-O bond on M1, which is supported by previous neutron diffraction experiments. H(0) shows a Brillouin-type behaviour with different fields on the two crystallographic sites (stronger on M1) and a small discontinuity at T = 23 K which corresponds with previous magnetic measurements. The quadrupole splitting is equal on both sites within error bars, in agreement with previous theoretical results and in contradiction to previous Mössbauer refinements published elsewhere.