An automatic system for continuous monitoring of CO2, H2S, SO2 and meteorological parameters in the atmosphere of volcanic areas

An automatic system for the continuous monitoring of CO₂, H₂S, SO₂ and meteorological parameters in atmosphere has been developed. The system has been tested in the laboratory in order to verify the stability and reliability of each sensor and of the whole system. A field test for a period of one month, at the Solfatara of Pozzuoli has also been carried out. The acquired data during the field test reveal a correlation between the wind speed and the concentrations of CO₂, H₂S, and SO₂ in the atmosphere. With a wind speed of over 4 ms^-1 the concentration of the three gases reached constant background values of 600 ppm for CO₂ and about 2 ppm vol. for H₂S and SO₂. The different ratios of H₂S/SO₂ measured in the fumaroles (~100) and in the atmosphere (1–0.1) clearly indicate that H₂S is oxidized to SO₂ during the transport.     

Structural Setting of Strong Earthquakes in the Huabei Area of China

— Using P and S arrival times, which occurred within the Huabei seismic network, we carried out a tomographic inversion and compared results with the earthquake catalogue of the last 1000?years in the area. The results are as follows:¶1) The hypocenters of most of the strong shocks are distributed in the transitional zones between high- and low-velocity areas in the crust, especially at edges of high-velocity blocks.¶2) Strong shocks predominantly lie above low-velocity blocks, or in transitional zones between low- and high-velocity areas, in the lower crust.¶3) The tectonic settings for the Tangshan and the Sanhe-Pingu earthquakes are similar. Both are not known near large fault belts, and in zones with a sharp lateral velocity gradient.¶4) The Ninghe, Tangshan and Luanxia earthquakes are located in high-velocity blocks that differ in size and depth. This difference can explain the focal depth distribution of the Tangshan earthquake sequence, i.e., earthquakes are shallower in the northeastern Luanxian area but deeper in the southwestern Ninghe area.     

Acoustic stratigraphy and hydrothermal activity within Epi Submarine Caldera,Vanuatu, New Hebrides Arc

Geological and geophysical surveys of active submarine volcanoes offshore and southeast of Epi Island, Vanuatu, New Hebrides Arc, have delineated details of the structure and acoustic stratigraphy of three volcanic cones. These submarine cones, named Epia, Epib, and Epic, are aligned east-west and spaced 3.5 km apart on the rim of a submerged caldera. At least three acoustic sequences, of presumed Quaternary age, can be identified on single-channel seismic-reflection profiles. Rocks dredged from these cones include basalt, dacite, and cognate gabbroic inclusions with magmatic affinities similar to those of the Karua (an active submarine volcano off the southeastern tip of Epi) lavas.     

Capture of Helium and Other Volatiles during the Growth of Olivine Phenocrysts in Picritic Basalts from the Juan Fernandez Islands

Olivine crystals in basalt contain helium that can be extractedfor isotopic analysis. Helium-bearing olivine phenocrysts inpicritic tholeiites from the Juan Fernandez Islands, SE Pacific,crystallized from moderately differentiated liquids. None arexenocrysts of mantle peridotite. The helium occurs in cavitiesor bubbles in inclusions best seen at high magnification inthe olivine. The olivine grew around spinel, sulfide, and bubblesthat preferentially nucleated on crystal surfaces. Inclusionswithin these phases range from large cavities to tiny, facetedpits arranged in rows. Many crystals contain curving trainsof inclusions along annealed features. The inclusions formedduring mixing between cooler differentiated magma and hotterolivine-charged magma, which accelerated vesiculation. Bubblesnucleated on the olivine as they do on ice when stirred in carbonatedwater. Mixing also induced thermal stress fracturing, like thecracking of ice dropped into water. Cracking, irregular extinction,and subgrain formation occurred when faceted crystals collidedwith each other or with conduit walls. Boundary layer meltsand bubbles were drawn quickly into the fractures. Thus fewinclusions contain equilibrium proportions of minerals and vapor.Mantle-derived helium clearly permeated into shallow storagereservoirs, including rift zones where magmatic differentiation,mixing, and vapor exsolution were fairly extensive. KEY WORDS: Juan Fernandez; volatiles; inclusions; olivine; picrite     

Rapid XRD determination of the chrysotile/lizardite ratios in asbestos-bearing serpentinites

Summary The quantitative XRD determination of the most common serpentinite minerals, e.g. lizardite and chrysotile, is hampered by strongly overlapping reflections. Reconnaissance investigations indicated that the reflections 204 of lizardite and 008 of chrysotile are best suited for quantitative XRD. These lines are not interferred by other minerals such as brucite, magnesite, chlorite or talc, which are common in serpentinites. A calibration curve for the determination of the chrysotile/lizardite ratios in natural serpentinites has been constructed by means of synthetically prepared chrysotile/lizardite standards. Using this method serpentinites of the Msauli Chrysotile Asbestos Mine, South Africa, were investigated for their relative chrysotile contents. It was found, that the total amount of chrysotile in the ore zone is considerably higher than the amount of extractable chrysotile asbestos fibre.

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Die röntgenographische Bestimmung der Chrysotil/Lizardit-Verhältnisse in asbesthaltigen Serpentiniten

Zusammenfassung Die quantitative röntgenographische Bestimmung der beiden häufigsten Serpentinminerale, Lizardit und Chrysotil, ist wegen der Überlagerung ihrer stärksten Reflexe erschwert. Aufgrund von Voruntersuchungen konnte jedoch festgestellt werden, daß die Reflexe 204 von Lizardit und 008 von Chrysotil für die quantitative Bestimmung geeignet sind. Diese Reflexe werden nicht überlagert von denen anderer häufig in Serpentiniten vorkommender Minerale, wie z.B. Brucit, Magnesit, Chlorit oder Talk. Eine Eichkurve zur Bestimmung der Chrysotil/Lizardit-Verhältnisse in natürlichen Serpentiniten wurde mit Hilfe synthetisch hergestellter Standardmischungen aufgestellt. Serpentinite der Msauli Chrysotilasbest Mine, Südafrika, wurden aufgrund der hier vorgestellten Methoden auf ihren relativen Chrysotilanteil untersucht. Es ergab sich, daß der totale Gehalt an Chrysotil in der erzführenden Zone deutlich größer ist als der Gehalt an ausbringbaren Chrysotilasbestfasern.

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With 4 Figures     

New insights into the size and timing of the Lawn Hill impact structure: relationship to the Century Zn – Pb deposit

The Lawn Hill circular structure in northwest Queensland contains unambiguous evidence of an extraterrestrial impact, including planar deformation features in quartz, impact diamonds, widespread shatter cone formation and impact melt breccia in the Mesoproterozoic basement. The question of its relevance to ore genesis is investigated because the world-class Century Zn – Pb deposit is situated at the conjunction of the 100+ km Termite Range Fault and the previously defined margin of the impact structure. The impact structure is considered to be a 19.5 km wide feature, this constrained in part by the outer margin of an annulus of brecciated and highly contorted limestone. New evidence is presented indicating impact into this Cambrian limestone, including: (i) ‘dykes’ of brecciated Cambrian limestone extending hundreds of metres into the Mesoproterozoic basement; (ii) highly contorted bedding in the limestone annulus compared with essentially undeformed limestone away from the impact site; as well as (iii) a 1 Mt megaclast of Mesoproterozoic Century-like ore suspended in the limestone. Through aerial photograph analysis, large-scale convoluted flow structures within the limestone are identified, and these are interpreted to indicate that parts of the Cambrian sequence may have been soft or only semi-consolidated at the time of impact. This highly contorted limestone bedding is suggested to represent slump-filling of an annular trough in response to impact-induced partial liquefaction of a sediment veneer. The age of impact is therefore considered to be concurrent with limestone formation during the Ordian to early Templetonian, at 520 – 510 Ma. Formation of the Century deposit is found to be unrelated to impact-generated hydrothermal activity, although some minor hydrothermal remobilisation of metals occurred. However, there was macro-scale remobilisation of gigantic ore fragments driven by impact-induced lateral and vertical injection of limestone into the Proterozoic sediments. The limestone-filled annular trough surrounds a 7.8 km diameter central uplift, consistent with formation of a complex crater morphology.