Use of magnetic hysteresis properties and electron spin resonance spectroscopy for the identification of volcanic ash: a preliminary study

This initial study investigates the possible use of hysteresis parameters and electron spin resonance (ESR) spectroscopy to identify and correlate volcanic ash. ESR and hysteresis properties are sensitive to characteristics such as the chemical composition, mineralogy, and grain size and shape. These characteristics are determined by the tectonic setting of the volcano and by the magmatic and eruptive history of the volcanic ash. Hysteresis properties and ESR spectra, therefore, should be distinct for each ash eruption and may help to identify the eruptive source of the ash and to correlate ash from unknown sources. We conducted ESR spectroscopy at room temperature and magnetic hysteresis measurements on 19 samples of a single ash, the 1974 October 14 eruption of the Fuego volcano, Guatemala, and on single samples of ash obtained from eight different volcanoes. The Fuego ash samples were obtained at increasing distances from the volcano. For the single Fuego ash, ESR spectra and hysteresis parameters become increasingly similar as the distance from the volcano increases. At distances greater than 30 km, ESR spectra and hysteresis properties are uniform. The variability of magnetic and ESR properties with distance from Fuego is due to the preferential fall-out of phenocrysts closer to the volcano. At large distances, the ash is more uniform, containing more glass and microcrystals. All eight ash samples from the different volcanoes can be distinguished from the distal Fuego 1974 October 14 ash using ESR spectra and hysteresis parameters. These results suggest that ESR and hysteresis measurements have a potential to be used as tools to identify distal ash when used in conjunction with geochemical, mineralogical and/or other types of data.     

Fluid inclusion, stable isotope and Ar-Ar evidence for the age and origin of gold-bearing quartz veins at Mont Chemin, Switzerland

Summary A new Swiss gold occurrence at Mont Chemin, comprising gold-bearing quartz veins, displays many characteristics that are typical of mesothermal gold deposits within the Alps and globally. The most notable of these features are: i) the presence of NaCl-H₂O-CO₂-bearing fluid with an XCO₂ of approximately 0.016 and NaCl equivalents in the range 4.6 to 10.6 weight percent, ii) greenschist formational temperatures and pressures in the range 265-285 °C and 700-1400 bars; and iii) the proximity of the occurrence to the Rhone-Simplon Line, a deep crustal structure in the Swiss Alps.Corrected Ar-Ar data for hydrothermal adularia, considered to be contemporaneous with mineral deposition from the gold-bearing fluid, yields an age of 9.9 ±1.0 Ma. Geothermal gradients and uplift rates derived from the Ar-Ar age data and the geothermometry are in agreement with existing data for this region, and indicate that the hydrothermal activity at the Mont Chemin gold occurrence records one of the last Alpine metamorphic events in the northeastern Mont Blanc massif.Temperature estimates from fluid-muscovite-quartz-feldspar equilibrium and oxygen isotope thermometry of coexisting adularia and quartz are combined with the fluid inclusion isochores to derive depositional pressures. These data yield geothermal gradients on the order of 50 °C/km and uplift rates of 0.44 mm/a for the NE portion of the Mont Blanc massif.

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Evidenz aus Flüssigkeitseinschluß-, stabilen Isotopen- und Ar- Ar Daten fü r das Alter und den Ursprung Gold führender Quarzgänge am Mont Chemin, Schweiz

Zusammenfassung Ein neues Schweizer Goldvorkommen am Mont Chernin, es handelt sich um Goldführende Quarzgänge, zeigt viele Charakteristika, die für mesothermale Goldlagerstätten der Alpen und weltweit typisch sind: i) Die Anwesenheit von NaCl-H₂O-CO₂ Fluiden mit einem XCO₂ von ca. 0.016 und NaCl zwischen 4.6 und 10.6 Gew. % Äquiv.ii) Grünschieferfazielle Bildungstemperaturen und -drucke von 265-285°C bzw. 7001400bar. iii) Die Nähe der Vorkommen zur Rhone-Simplon Linie, einer tiefgreifenden Struktur in der Kruste der Schweizer Alpen.Korrigierte Ar-Ar Daten von hydrothermalem Adular, der als zeitgleich mit den Minerallagerstätten gebildet, angesehen wird, ergaben ein Alter von 9.9 ± 1.0 Ma. Die aus aus den Ar-Ar Daten bestimmten geothermalen Gradienten und Hebungsraten und die Ergebnisse der Geothermometrie stimmen mit bisher existierenden Daten aus dieser Region überein und zeigen, daß die hydrothermale Aktivität in den Goldvorkommen des Monte Chemin eines der letzten alpidischen metamorphen Ereignisse im nordöstlichen Mont Blanc Massiv darstellt.Temperaturabschätzungen aus Fluid-Muscovit-Quarz-Feldspat Gleichgewichten und Sauerstoffisotopen-Thermometrie an koexistierendem Quarz und Adular werden mit den Isochoren der Flüssigkeitseinschlüsse kombiniert, um die Bildungsdrucke abzuleiten. Diese Daten ergeben geothermische Gradienten in der Größenordnung von ca. 50 °C/km und Hebungsraten von 0.44 mm/Jahr für den Nordostteil des Mont Blanc Massives.

     

Mechanisms Controlling Turbulence Development Across A Forest Edge

In this paper we discuss the development of turbulence back from the transition fromopen moorland to a forest. Data from a field study and a wind-tunnel experiment arepresented. These show that the variance in the streamwise velocity begins to adjust tothe new surface between 2 to 4 tree heights downwind of the transition. This is soonerthan either the vertical velocity variance or the shear stress, both of which begin to adjust in a zone 3 to 5 tree heights downwind of the edge. Key terms in the prognostic equations for streamwise and vertical velocity variance are evaluated in order to explain these differences. The flow distortion caused by the forest edge, which extends to 4 tree heights downwind of the forest edge, is shown to be crucial in the delayed turbulence development. Initially the shear production term, which is the dominant source for the streamwise velocity variance, is counteracted by a sink in the vertical advection term. After the flow levels out the pressure redistribution (return-to-isotropy) term becomes the main sink of streamwisevelocity variance and feeds energy into the vertical velocity component. Therefore, thedevelopment of the vertical velocity variance and shear stress cannot begin until afterdevelopment of an increase in the streamwise velocity variance. Results are comparedwith other experiments, including the flow across shelterbelts, and large-eddy simulations of forest flow.     

Rigorous transformation of variance–covariance matrices of GPS-derived coordinates and velocities

With the advances in the field of GPS positioning and the global densification of permanent GPS tracking stations, it is now possible to determine at the highest level of accuracy the transformation parameters connecting various international terrestrial reference frame (ITRF) realizations. As a by-product of these refinements, not only the seven usual parameters of the similarity transformations between frames are available, but also their rates, all given at some epoch t _k . This paper introduces rigorous matrix equations to estimate variance–covariance matrices for transformed coordinates at any epoch t based on a stochastic model that takes into consideration all a priori information of the parameters involved at epoch t _k , and the coordinates and velocities at the reference frame initial epoch t ₀. The results of this investigation suggest that in order to attain maximum accuracy, the agencies determining the 14-parameter transformations between reference frames should also publish their full variance–covariance matrix. Electronic Publication     

L1-norm pre-analysis measures for geodetic networks

 Several pre-analysis measures which help to expose the behavior of L ₁ -norm minimization solutions are described. The pre-analysis measures are primarily based on familiar elements of the linear programming solution to L ₁-norm minimization, such as slack variables and the reduced-cost vector. By examining certain elements of the linear programming solution in a probabilistic light, it is possible to derive the cumulative distribution function (CDF) associated with univariate L ₁-norm residuals. Unlike traditional least squares (LS) residual CDFs, it is found that L ₁-norm residual CDFs fail to follow the normal distribution in general, and instead are characterized by both discrete and continuous (i.e. piecewise) segments. It is also found that an L ₁ equivalent to LS redundancy numbers exists and that these L ₁ equivalents are a byproduct of the univariate L ₁ univariate residual CDF. Probing deeper into the linear programming solution, it is found that certain combinations of observations which are capable of tolerating large-magnitude gross errors can be predicted by comprehensively tabulating the signs of slack variables associated with the L ₁ residuals. The developed techniques are illustrated on a two-dimensional trilateration network. Received: 6 July 2001 / Accepted: 21 February 2002     

Comparison of analyses of Dst variations

At present no straightforward way exists of comparing independent analyses of storm-time variations, D_st. A method based on the properties of a distortion-free filter allows some comparison to be made. The method produces the best constant response ratio, α, that fits the data, and allows the morphology of each storm to be compared. Results have been obtained for various analyses of D_st, and efforts to establish bounds on the conductivity profile within the Earth are discussed.     

Sphalerite geobarometry of deformed sulphide ores from the C. S. A. Mine,Cobar, Australia

The C. S. A. Mine is located near Cobar, central New South Wales. The copper-zinc-lead ores occur in Early Devonian rocks of the Cobar Super-Group. Lower greenschist (slate-grade) metamorphism has developed elongate lenticular ore systems parallel to the extension (down-dip) lineation in cleavage. FeS contents of sphalerites coexisting with pyrite and pyrrhotite outside and inside pressure shadows indicate much higher pressures (7.7 to 9.0 kbar) than those inferred from stratigraphic reasoning and the low metamorphic grade. The homogeneous distribution of Fe in sphalerites suggests equilibration with pyrite-pyrrhotite; and concentrations of Co and Ni in iron sulphides, and Mn, Cd and Cu in sphalerite are too low to have influenced phase relations in the FeS-ZnS pseudobinary system. The anomalously high pressures are therefore ascribed to reequilibration of sphalerite compositions with a monoclinic pyrrhotite-pyrite buffer. The FeS contents of the reequilibrated sphalerites apparently reflect the differing mean stress domains that exist outside and inside pressure shadows. This suggests that reequilibration occurred under the same stress distribution as produced the original pressure shadows, and implies FeS dissolution during the decay of the cleavage-producing structuro-metamorphic event. The commonly observed scatter of sphalerite compositions in low grade assemblages appears to record micro-scale mean stress domains, and thereby testifies to the pressure sensitivity of the mole percent FeS contents.     

Seasonal phytoplankton composition in the lower Chesapeake Bay and old plantation Creek,Cape Charles,Virginia

During a 14-month phytoplankton study in the lower Chesapeake Bay, there was a bi-modal pattern of population peaks with fall and spring maxima. The phytoplankton was dominated bySkeletonema costatum and other diatoms similar to major dominants found on the continental shelf. The composition in an inlet adjacent to the Bay was similar throughout most of the period, but differed from Bay populations during the summer months when larger concentrations and diversity of phytoflagellates and small sized diatoms occurred. Seasonal phytoplankton assemblages characteristic for the lower and entire Chesapeake Bay are given with the seasonal appearances noted for 219 phytoplankters. The importance of nanophytoplankters, both diatoms and the phytoflagellates, to the total phytoplankton composition is also emphasized.