A summary of sulfur dioxide emission rate measuremnts from Guatemalan volcanoes

Measurements of the sulfur dioxide (SO₂) emission rate from three Guatemalan volcanoes provide data which are consistent with theoretical and laboratory studies of eruptive and shallow magma chamber processes. In particular, unerupted magma makes a major contribution to the measured SO₂ emission rates at Santiaguito, a continuously erupting dacitic volcanic dome. Varying shallow magma convection rates can explain the variations in SO₂ emission rates at Santiaguito. At Fuego, a basaltic volcano currently in repose, SO₂ emission rate measurements are consistent with a high level magma body that is crystallizing and releasing volatiles. At Pacaya, a continuously erupting basaltic volcano, recent SO₂ emission rate measurements support laboratory simulation studies of strombolian eruptions; these studies indicate that the majority of gas escapes during eruptions and little gas escapes between eruptions.Average SO₂ emission rates over the last 20 years for Santiaguito, Fuego and Pacaya are 80, 160 and 260 Mg/d, respectively. On a global scale, these three volcanoes account for 1% of the annual global volcanic output of SO₂. Santiaguito and Pacaya, together, emit 6% of the total annual SO₂ emitted by continuously erupting volcanoes.Even though SO₂ measurements at these volcanoes have been made infrequently and by different investigators, the collective data help to establish a useful baseline by which to judge future changes. A more complete record of SO₂ emission rates from these volcanoes could lead to a better understanding of their eruption mechanisms and reduce the impact of their future eruptions on Guatemalan society.     

Determination of crustal movements in Turkey by terrestrial geodetic methods

In Turkey, neotectonic activity originated from the collision of the Arabian and Anatolian land masses during the Middle Miocene. As a result of the collision, westward escape of the Anatolian block introduced E-W compression in Western Turkey which began to be relieved by N-S extension. The North Anatolian Fault (NAF) is the major active strike-slip fault that was formed under the neotectonic regime. The rates of the motion along this fault estimated by several authors are in the range of 0.4–2.9 cm/a according to kinematic data. In Turkey, the first studies of crustal movements by geodetic methods were started in the west section of the NAF in 1972. So far, individual activities and studies coordinated by multidisciplinary projects have been realized in this region. The results obtained from available geodetic data indicate the motion of the Anatolian block relative to Eurasia.     

2.8-Ma ash-flow caldera at Chegem River in the northern Caucasus Mountains (Russia), contemporaneous granites, and associated ore deposits

Diverse latest Pliocene volcanic and plutonic rocks in the north-central Caucasus Mountains of southern Russia are newly interpreted as components of a large caldera system that erupted a compositionally zoned rhyolite-dacite ash-flow sheet at 2.83 ± 0.02 Ma (sanidine and biotite ⁴⁰Ar/³⁹Ar). Despite its location within a cratonic collision zone, the Chegem system is structurally and petrologically similar to typical calderas of continental-margin volcanic arcs. Erosional remnants of the outflow Chegem Tuff sheet extend at least 50 km north from the source caldera in the upper Chegem River. These outflow remnants were previously interpreted by others as erupted from several local vents, but petrologic similarities indicate a common origin and correlation with thick intracaldera Chegem Tuff. The 11 × 15 km caldera and associated intrusions are superbly exposed over a vertical range of 2,300 m in deep canyons above treeline (elev. to 3,800 m). Densely welded intracaldera Chegem Tuff, previously described by others as a rhyolite lava plateau, forms a single cooling unit, is > 2 km thick, and contains large slide blocks from the caldera walls. Caldera subsidence was accommodated along several concentric ring fractures. No prevolcanic floor is exposed within the central core of the caldera. The caldera-filling tuff is overlain by andesitic lavas and cut by a 2.84 ± 0.03-Ma porphyritic granodiorite intrusion that has a cooling age analytically indistinguishable from that of the tuffs. The Eldjurta Granite, a pluton exposed low in the next large canyon (Baksan River) 10 km to the northwest of the caldera, yields variable K-feldspar and biotite ages (2.8 to 1.0 Ma) through a 5-km vertical range in surface and drill-hole samples. These variable dates appear to record a prolonged complex cooling history within upper parts of another caldera-related pluton. Major W-Mo ore deposits at the Tirniauz mine are hosted in skarns and hornfels along the roof of the Eldjurta Granite, and associated aplitic phases have textural features of Climax-type molybdenite porphyries in the western USA. Similar ⁴⁰Ar/³⁹Ar ages, mineral chemistry, and bulk-rock compositions indicate that the Chegem Tuff, intracaldera intrusion, and Eldjurta Granite are all parts of a large magmatic system that broadly resembles the middle Tertiary Questa caldera system and associated Mo deposits in northern New Mexico, USA. Because of their young age and superb three-dimensional exposures, rocks of the Chegem-Tirniauz region offer exceptional opportunities for detailed study of caldera structures, compositional gradients in volcanic rocks relative to cogenetic granites, and the thermal and fluid-flow history of a large young upper-crustal magmatic system.     

Die Entstehung der Schichtung in rhythmisch geschichteten Evaporiten

Zusammenfassung Das wesentliche Merkmal rhythmisch geschichteter Evaporite ist der regelmäßige Wechsel von schwerer und leichter löslichen Schichten. Er ist nur mit entsprechenden rhythmischen Konzentrationsschwankungen, speziell in der Oberflächenlösung erklärbar. Diese Schwankungen sind aber nicht durch Temperaturschwankungen, sondern durch Strömungsvorgänge verursacht. Sie sind bei speziellen Annahmen über die hydrodynamischen Auswirkungen des Klimas mit der Barrentheorie bei kontinuierlichem Nachfluß vereinbar. Die Jahresschichtungshypothese ist aber nur begrenzt gültig. In den Endstadien der Salzausscheidung treten gewöhnlich nur noch diskontinuierliche Überflutungen auf, so daß auch keine angenäherte Zeitbestimmung mehr möglich ist.

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Stratification in rhytmic evaporites is expressed in solubility-degrees of the individual laminae. It can be explained by corresponding changes in concentration of surface solutions. Such changes are not created by temperature changes but by sea-currents. Thus, the Bar-theory appears acceptable if certain presumptions as to the hydrodynamic effects of climate are made. The validity of the hypothesis of seasonal stratification, however, is limited since towards the end-stages of salt precipitation, discontinuous brine floods mask the time record.

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Résumé Le caractère essentiel des évaporites formant des couches rythmiques est constitué par l'alternance régulière de couches facilement et difficilement solubles. Celle-ci ne peut s'expliquer que par des variations rythmiques correspondantes de la concentration particulièrement dans la solution superficielle. Ces variations ne proviennent pas de variations de température, mais de phénomènes dus au courant. Elles peuvent être reliées, en partant de considérations spéciales sur les effets hydrodynamiques du climat avec la théorie des barres sous écoulement continu. Cependant l'hypothèse de stratification annuelle n'est valable qu'à un degré limité. Dans les phases terminales de la précipitation du sel il se produit généralement des submersions discontinues de sorte qu'on ne peut plus parvenir à une évaluation approximative du temps.

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Petrology and Age of the Pre-Otavi Basement Granite at Franzfontein, Northern South-West Africa

Chemical, spectrographic, and isotopic analyses are presentedfor the Franzfontein alkali granite and constituent minerals.This rock has the chemical character of granties produced byliquid crystal equilibrium. Dated at 1, 700?70m.y. by the constituentzircon, its crystallization formed part of a major period (theHuabian episode) of batholithic granite emplacement in northernSouth-West Africa. The occurrence of these crystalline rocksin the core of the Huab anticline defines the maximum possibleage of the overlying Otavi Facies sediments, precluding theircorrelation with the Transvaal System of South Africa. The imprint of the Damara metamorphism (Damaran episode) isreflected in the Sr/Rb age (560?30 m.y.) obtained for the biotite:the inversion of biotite to stilpnomelane and chlorite probablyrepresents the mineralogical effects of that metamorphis. Isotopicdata indicate that changes in the relative concentrations ofRb and Sr differed significantly in plagioclase and microcline;such data from feldspars in metamorphic rocks should, therefore,be interpreted with caution.     

Influence of image forces on combination in aerosols

Summary The effect of electrostatic image forces on the combination of small ions with uncharged aerosol nuclei and the self-combination of charged and uncharged nuclei is examined. In the ion-nucleus case a formula for the combination coefficient is derived for very small nuclei. This formula applies also to atmospheric nuclei and tends to the familiar 4ad form for large radii. For the case of the self-combination of nuclei the effect of the image force when one of the combining nuclei is charged, is shown to be small in the size range of atmospheric nuclei but not negligible if smaller sizes are considered; a table is included of the magnitude of the effect as a function of size.

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Zusammenfassung Es wird der Effekt der elektrostatischen Bildkräfte auf die Vereinigung von Kleinionen mit ungeladenen Aerosolkernen und die Selbstvereinigung von geladenen und ungeladenen Kernen untersucht. Im Falle der Ionen und Kerne wird eine Formel für den Vereinigungskoeffizienten von sehr kleinen Kernen abgeleitet. Diese Formel ist auch für atmosphärische Kerne anwendbar und strebt für grosse Radien dem bekannten Ausdruck 4ad zu. Für den Fall der Selbstvereinigung der Kerne wird gezeigt, dass der Effekt der Bildkraft im Grössenbereich der atmosphärischen Kerne klein ist, wenn einer der sich vereinigenden Kerne geladen ist. Der Einfluss ist aber nicht vernachlässigbar, wenn kleinere Grössen in Betracht gezogen werden; es wird eine Tabelle mitgeteilt, welche den Betrag des Effektes als Funktion der Grösse gibt.

     

The metastability of natural and urban aerosols

Summary The principle of the sampling method of submicron aerosols with the Aerosol Spectrometer is briefly described and the analytic procedures for deriving the frequency-size distributionC _d (d) from photo-micrographic particle counts and microphotometric light scattering measurementsS _d (d) of identical areas of the particle deposit.After initial analysis the deposits were exposed to elevated temperature (80° C) for several hours and re-analyzed. Four representative aerosol types, originating from the high sea, the shore, vegetation, and metropolitan smog are analyzed in this manner for the range (0.2 d1.3 ). All show a very marked decrease, even disappearance of the smaller particles (d<0.5 ) and shrinkage of the larger particles (d<1 ). By far the largest effect is observed for the smog aerosols.This volatility appears to be caused by either evaporation of the particle substace or by the gradual oxidation of its organic components into more volatile products (CO₂, H₂O).     

Paläomagnetismus in den Rhombenporphyren von Oslo und in den Rhyoliten,Doleriten und Sedimenten des Estérel

Zusammenfassung Es werden einige Ergebnisse mitgeteilt über paläomagnetische Untersuchungen, die vom Mineralogisch-Geologischen Institut in Utrecht unter Mitarbeit des Königlich-Niederländischen Meteorologischen Instituts in de Bilt durchgeführt werden. Während der Entmagnetisierungsversuche zeigte es sich, daß viele Gesteinsproben neben einer ursprünglichen Magnetisierung, die wahrscheinlich während der Ablagerung entstanden ist, noch störende sekundäre magnetische Komponenten in der Richtung des heutigen Erdfeldes besitzen. Diese sekundären Komponenten kann man ganz durch teilweise Entmagnetisierung entfernen; die ursprüngliche Komponente des Magnetismus wird dabei auch kleiner, aber die Abnahme wird erst bedeutend bei Anwendung von hohen Temperaturen und sehr starken Wechselfeldern. Dadurch werden also auch diese Gesteine brauchbar für die Bestimmung des magnetischen Pols.     

Die C14-Methode

Zusammenfassung Die Altersreichweite der C¹⁴-Datierung von pflanzlichen und tierischen Stoffen beträgt 50 000, allenfalls 70 000 Jahre. Die Datierungsunsicherheit beläuft sich auf mindestens ± 100 Jahre. Bei einem Alter bis zu etwa 10 000 Jahren spielen individuelle Unterschiede im Anfangsgehalt contemporärer organischer Substanzen eine gewisse Rolle. Geringfügige Verzerrungen der C¹⁴-Zeitskala sind möglich und zum Teil nachgewiesen. Bei höherem Alter spielen diese Abweichungen praktisch keine Rolle, dafür wächst die Gefahr der Altersfälschung durch eine kleine Verunreinigung mit jüngerem, sehr viel mehr C¹⁴ enthaltendem Material. Eine fälschliche Verjüngung kann in dem Zeitbereich über etwa 30 000 Jahren zwar nie mit Sicherheit ausgeschlossen werden, als Mindestalter sind die Ergebnisse aber selbst an der Reichweitengrenze äußerst zuverlässig und wertvoll.Einige Meßmethoden werden kurz erläutert. Die Ergebnisse und Möglichkeiten der Methode werden an einigen typischen Beispielen besprochen.