Major ash eruptions of Barren Island volcano (Andaman Sea) during the past 72 kyr: clues from a sediment core record

Barren Island (Andaman Sea) is the northernmost active volcano of the Indonesian Arc. To construct the eruptive history of this little studied volcano, we measured ¹⁴C dates of inorganic carbon in sediment beds, and Sr and Nd isotopic ratios of seven discrete ash layers, in a marine sediment core collected from 32 km southeast of the volcano. The study reveals that the volcano had seven major ash eruptions at ~70, 69, 61, 24, 19, 15, and 10 ka. The ash layers erupted from 70 ka through 19 ka have highly uniform Nd isotopic composition, and since the ~15 ka eruption to the present the isotopic composition has been highly variable. Between ~24 ka and ~10 ka, the volcano had large ash eruptions spaced at 4,500 year intervals. Isotopically correlating the precaldera lavas and ash exposed on the volcano to the uppermost ash layer in the core, we infer that the caldera of Barren Island volcano is younger than 10 ka.     

Structural performance of a base-isolated reinforced concrete building subjected to seismic pounding

The effects of seismic pounding on the structural performance of a base-isolated reinforced concrete (RC) building are investigated, with a view to evaluate the influence of adjacent structures and separation between structures on the pounding response. In particular, seismic pounding of a typical four-story base-isolated RC building with retaining walls at the base and with a four-story fixed-base RC building is studied. Three-dimensional finite element analyses are carried out considering material and geometric nonlinearities. The structural performance of the base-isolated building is evaluated considering various earthquake excitations. It is found that the performance of the base-isolated building is substantially influenced by the pounding. The investigated base-isolated building shows good resistance against shear failure and the predominant mode of failure due to pounding is flexural. Copyright © 2012 John Wiley & Sons, Ltd.     

Anthropogenic sulphate aerosols and large Cl-deficit in marine atmospheric boundary layer of tropical Bay of Bengal

Our long-term study provides an unequivocal evidence for near-quantitative (80–100%) depletion of chloride from sea-salts in the marine atmospheric boundary layer (MABL) of tropical Bay of Bengal. During the late NE-monsoon (Jan-Mar), continental outflow from south and south-east Asia dominate the wide-spread dispersal of pollutants over the Bay of Bengal. Among anthropogenic constituents, SO ₄ ^2? (range: 0.6–35 μg m^?3) is the most dominant. The non-sea-salt SO ₄ ^2? (nss-SO ₄ ^2? ) constitutes a major fraction (55–65%) of the aerosol water-soluble ionic composition (WSIC), whereas contribution of NO ₃ ^? is relatively minor. The magnitude of Cl-deficit (with respect to its sea-salt proportion) exhibits linear increase with the excess-nss-SO ₄ ^2? (excess over NH ₄ ⁺ ). We propose that displacement of HCl from sea-salt aerosols by H₂SO₄ is a dominant reaction mechanism for the chloride-depletion. These results also suggest that sea-salts could serve as a potential sink for anthropogenic SO₂ in the downwind polluted marine environment. Furthermore, loss of hydrogen chloride, representing a large source of reactive chlorine, has implications to the oxidant chemistry in the MABL (oxidation of hydrocarbons and dimethyl sulphide).     

Relativistic model of radiating massive fluid sphere

In this paper we present a new class of nonsingular solutions representing time dependent balls of perfect fluid with matter-radiation in general relativity. The solution of the class is suitable for interior modeling of a quasar i.e. a massive radiating star. The interior solution is matched with a zero pressure Vaidya metric. From this solution we constructed a quasar model by assuming the life time of the quasar of ≈10⁷ year. We obtained a mass of the quasar of ≈10⁹ M _θ , linear dimension ≈10¹⁷ km and a rate of emission L _∞≈10⁴⁷ erg/s.     

Reconstruction of Last Glacial to early Holocene monsoon variability from relict lake sediments of the Higher Central Himalaya,Uttrakhand, India

Proglacial lake sediments at Goting in the Higher Central Himalaya were analyzed to reconstruct the summer monsoon variability during the Last Glacial to early Holocene. Sedimentary structures, high resolution mineral magnetic and geochemical data suggest that the lacustrine environment experienced fluctuating monsoonal conditions. Optically stimulated luminescence (OSL) dating indicates that the lake sedimentation occurred before 25 ka and continued after 13 ka. During this period, Goting basin witnessed moderate to strengthened monsoon conditions around 25 ka, 23.5 ka–22.5 ka, 22 ka–18 ka, 17 ka–16.5 ka and after14.5–13 ka. The Last Glacial phase ended with the deposition of outwash gravel dated at ～11 ka indicating glacial retreat and the onset of Holocene condition. Additionally, centennial scale fluctuations between 16.5 ka and 12.7 ka in the magnetic and geochemical data are seen.A close correspondence at the millennial scale between our data and that of continental and marine records from the Indian sub-continent suggests that Goting basin responded to periods of strengthened monsoon during the Last Glacial to early Holocene. We attribute the millennial scale monsoon variability to climatic instability in higher northern latitudes. However, centennial scale abrupt changes are attributed to the result of albedo changes on the Himalaya and Tibetan plateau.     

Investigation of bauxites with the help of electron-probe

Summary 25 representative karstic and lateritic bauxite samples from Europe, Asia and Africa were studied by a JEOL-JXA-5 electron-probe X-ray microanalyser. The main directions of the investigation were: determination of the microtextures and the distribution of the main elements in bauxite (Al, Fe, Ti, Si). Conclusions on the genesis of the textural constitution and on bauxitization are given. Further possibilities of using the electron-probe in solving different problems connected with bauxites are enumerated.

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Bauxit-Untersuchungen mit der Elektronstrahl-Mikrosonde

Zusammenfassung Es wurden 25 typische Karst- und Lateritbauxite aus Europa, Asien und Afrika mit Hilfe einer JEOL-JXA-5 Elektronstrahl-Mikrosonde untersucht. Die Hauptrichtungen der Untersuchung waren die Bestimmung der Mikrostruktur und die Verteilung der Hauptelemente in den Bauxiten (Al, Fe, Ti, Si). Es wurden mehrere Schlüsse bezüglich der Entwicklung der Strukturelemente und der Bauxitbildung gezogen. Weitere Anwendungs-möglichkeiten zur Lösung verschiedener Bauxit-Probleme werden angegeben.

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With 30 Figures     

Development of magmas and igneous rocks in the tertiary volcanism of Hungary

In the Tertiary history of the Pannonian massif — typical example of median masses — the most remarkable features are the considerable thinning out and the increase of accessibility of the crust. Diversities of its behaviour with respect to ascending selective (ionic) currents — which are considered as primary causes of volcanism — are manifest in the distribution and characteristics of igneous products: on the culmination area (core) of the mantle dome Neogene volcanism is represented exclusively by huge ash-flow blankets (in three cycles) totalling 15,000 cu. kms in volume, while famous volcanic mountains of the border area consist of andesitic explosion, effusion and shallow intrusion products of much less (5000 cu. kms) extension. The two distinct trends of composition and petrogenetic features are explained by different conditions of ascent of the igneous material: 1. diffuse and extremely slow rise combined with intense contaminations yields ash-flow outpourings of rhyolitic composition; 2. speedy issue along chimneys controlled by the border fractures of the median mass feed normal andesitic volcanism.

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Zusammenfassung Das pannonische Massiv, ein typisches Beispiel für die Zwischenmassive, ist in seiner tertiären Entwicklung neben bedeutender Ausdünnung durch eine erhöhte Penetrierbarkeit der Kruste gekennzeichnet. Ihr verschiedenes Verhalten gegenüber emporsteigenden, selektiven ionischen Strömungen, die als Ursachen der vulkanischen Erscheinungen angenommen werden, kommt in der Verteilung und im Charakter der vulkanischen Produkte klar zum Audruck: das zentrale Kulminationsgebiet der Mantelwölbung wurde in drei Hauptzyklen von riesigen, rhyolithischen Ignimbritdecken überflutet (etwa 15 000 km³), an den Randpartien erhoben sich dagegen andesitische Vulkangebirge, bestehend aus explosiven, effusiven und seichtintrusiven Bildungen (etwa 5000 km³). Abweichungen der Zusammensetzung und Ausbildung werden mit Verschiedenheiten des Aufstiegs erklärt: 1. schwache Wegsamkeit, sehr langsames Emporsteigen, bis zur Oberfläche anhaltende Kontamination Rhyolith-Fluttuffe; 2. rascher Magmenaufstieg, durch Randbrüche gefördert normaler andesitischer Vulkanismus.

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Résumé Dans l'évolution tertiaire du massif pannonien — exemple le plus typique des « median mass » — c'est l'atténuation considérable de la croûte et l'augmentation de sa pénétrabilité qui sont les traits les plus remarquables. La résistance différentielle de l'écorce contre les courants ascendants (ioniques) sélectifs sortants des sources infracrustales (auxquels l'initiation du volcanisme est attribuée) vient d'être exprimée tout à fait nettement dans la répartition et faciès des produits ignés: au sommet de la protubérance du manteau (partie centrale) le volcanisme néogène consiste essentiellement en épanchements immenses (à trois reprises) du tuf rhyolithique soudé (ignimbrite) ( 15.000 km³), tandis qu'aux bords ce sont des montagnes « andesitiques » édifiées de produits d'explosion, d'effusion et de ceux d'intrusions peu profondes ( 5.000 km³). Les différences de composition et des caractères pétrogénétiques sont expliquées par les manières différentes de la montée des matériaux ignés: 1. pénétrabilité diffuse, soulèvement extrêmement lent, contaminations s'avançant jusqu'à la surface épanchements ignimbritiques à composition rhyolithique; 2. montée plus rapide par conduits le long des fractures marginales volcanisme habituel andesitique.

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Ignimbrites of Hungary with regard to their genetics and classification

Bulletin of Volcanology -     

Petrology, geochemistry and magnetic properties of Sadara sill: Evidence of rift related magmatism from Kutch basin, northwest India

Mafic volcanic rocks of the Mesozoic Kutch basin represent the earliest phase of Deccan volcanic activity. An olivine-clinopyroxene-plagioclase-phyric undersaturated basalt occurs as a sill near Sadara in the Pachham upland, Northern Kutch. The Sadara sill is deformed and emplaced along faults. The sill is alkaline in character and is transitional between basalt and basanite. Compared to primitive mantle, the Sadara sill is enriched in Sr, Ba, Pb and LREE but depleted in Nb, Cr, Y, Cs and Lu. Fractional crystallization of olivine and clinopyroxene from an alkaline mafic melt generated by low degree partial melting of mantle peridotite can explain the observed chemical variation in the sill.IRM and L-F test experiments and mineral analyses show titano-magnetite as the major remanence carrying magnetic mineral. AF and thermal demagnetizations of the Sadara sill yielded a mean ChRM direction as D=315.6°, I=−43.0° (α₉₅=9.78; k=25.38) and the corresponding VGP at 25°S; 114.6°E (dp/dm=6.58°/11.6°). The Sadara sill pole is significantly different from those of the Deccan (65 Ma) and the Rajmahal Traps (118 Ma) but is close to the Cretaceous poles of 85–91 Ma rock units from southern India. This suggests a pre-Deccan age for the sill.