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[en] Pliocene-Pleistocene basaltic rocks from Transdanubia, Hungary were dated by the K/Ar method. In evaluating the radiometric data the geological position and petrographic type and character of the samples were taken into account. Besides the conventional K/Ar ages, the 40Ar/36Ar-K/36Ar isochron ages were calculated for presumably cogenetic samples. According to the present determinations the age of the basalts erupted near Pula at the end of the middle part of the Upper Pannonian Formation is 4.15+-0.17 m.y. The basalts of Szentgyoergy-hill, Badacsony, Laz-hill (Uzsa-quarry) and the quarries near Suemegpraga and Bazsi can be considered to belong to the upper part of the Upper Pannonian Formation. The average K/Ar age of the Pleistocene basic volcanic rock (jumillit) at village Bar is 2.02+-0.14 m.y. and its isochron age is 2.11+-0.17 m.y. (author)
[en] On the basis of measurement of total β- and γ-activity of rocks, mineral depositions and zones of present outflows of vapour-gas jets on the thermal field of caldera of Uzon volcano a material testifying to the elevated radioactivity of local sections with newly deposited sulphur is obtained. A supposition is made on the existence of newly formed sulphur of ephemeral radioactive compounds on the surface of new formations
[en] Conditions for formation of uranium mineralization in volcanic graben are considered. It is shown that volcanic structures of basin type are the most important ore-controlling structures of continental volcanic belts. Volcano-tectonic basins differing by maximum ore saturation are formed on granite-gnessic domes subjected to multievent tecmtono-magatic activization at essential participation of ore-preparatory metasomatosis. Prospects for uranium content of volcano-tectonic basins are determined by geotectonic regim of basement bloc s and petrogeochemical specialization of components of their formation complexes, position of relatively deep fractures, conditions of formation, composition and geochemical peculiarities of products of volcano-plutonic magmatism. Development of volcano-plutonic formations took place under discontinuous functioning of pallial, crustal and peripherical magmatic focuses
[en] Complete text of publication follows. In 2008, we acquired long period electromagnetic data with a high data quality up to periods of 100.000 seconds along a profile running across the Leinegraben near Goettingen to the western Eifel, crossing the Rhenish massif. The Eifel as well as the region around Goettingen saw at different times intercrustal volcanic activity. Previous studies found big, highly conductive crustal anomalies located under the Eifel and near Goettingen. Between those anomalies, the conductivity of the mantle is raised in the east-west direction. Our data are complementing a large data set that is giving good spatial coverage of the area. Using geomagnetic depth sounding, we aim to improve the understanding of the structure of the crustal conductivity anomalies on both ends of the profile and will investigate their relationship with the upper mantle anisotropy in the area. One hypothesis is that the anomalies could have been produced by a single mantle plume.
[en] Trace elements have been determined in samples of the mid-atlantic ridge which were taken during FAMOUS and MIDLANTE missions of the CNEXO and in samples of the volcanic islands of Azores taken for the INAG programme studies. A quantitative interpretation of the results is made, using hydromagmatophile elements properties (Th, U, Zr, Hf, Nb, Ta, rare earths). The following points are discussed: different differentiated volcanic rock series are distinguable in Azores and on the mid-atlantic ridge, showing important fractional crystallization process with different proportions of olivines, plagioclases, pyroxenes, magnetites phases; the different series correspond to different primary magmas which are generated by a partial melting process of the mantle; the partial melting curve drawn for the mid-atlantic ridge samples allow us to calculate the mantle composition wich is characterized by a flat chondritic rare earths distribution curve in Masuda-Coryell-Winchester plot
[fr]Une analyse de la distribution des elements en traces dans les echantillons preleves sur la dorsale medio-atlantique au cours des campagnes MIDLANTE et FAMOUS du CNEXO et aux Acores dans le cadre de l'A.T.P. Geodynamique de l'I.N.A.G., est effectuee en s'appuyant sur les proprietes des elements hydromagmatophiles (Th, U, Zr, Hf, Nb, Ta, terres rares). Cette analyse permet de degager les resultats suivants: l'importance des processus de cristallisation fractionnee individualisant plusieurs series differenciees aux Acores et sur la zone de la dorsale etudiee et qui se caracterisent par un role preponderant des olivines, plagioclases, pyroxenes, magnetites, cristallisant dans des proportions variables; ces series correspondent a des liquides primaires de compositions differentes et dont la genese s'explique par un processus de fusion partielle de degre variable d'une zone du manteau de composition chimique homogene pour la zone FAMOUS; la composition du manteau calculee a l'aides des courbes de fusion partielle est caracterisee par une courbe de distribution des lanthanides plate et d'ordonnee 1.3 dans un diagramme Masuda-Coryell-Winchester
[en] Intermediate and basic volcanic rocks from the northern part of the Tokaj Mts., Hungary, were dated by the K/Ar method. The majority of the samples were collected from the vicinity of Telkibanya. The majority of the radiometric data are in accordance with the geological results and indicate that the volcanic activity started in the Upper Badenian and terminated in the Pannonian. The K/Ar ages of some opacitized samples proved to be younger than expected geologically. It has been confirmed that the basalt near Sarospatak uncovered by borehole Sp-10 is of Pannonian age. (author)
[en] A structural analysis is presented of mare ridges in an area of about 360 000 km2 in the southeastern part of Oceanus Procellarum just north of Mare Humorum. Mare ridges can be regarded as the result of large-scale natural tectonic deformation experiments coupled with and extended by volcanic phenomena. The old lunar crust has evidently retained part of the Moon's original tectonic elements throughout major exo- and endogenic events. Those structures which in places were flooded by mare lavas were also the first flaws to yield and to extend during younger tectonic and volcanic activity. Linear mare ridges may thus have formed at the activated and re-activated junctures of lunar crustal plates. Implications for the tectonics of mare ridges evidently show that one global stress field cannot account for all lunar tectonics but that global and areal variations in the lunar stress system have probably occurred. (Auth.)
[en] Complete text of publication follows. The three-dimensional (3-D) analysis should be adopted to clarify the actual structure of volcanoes, because the topography and specific structure of volcanoes can be considered as the 3-D geometry. In this study, we carried out the magnetotelluric survey at Tarumai Volcano, which is an active volcano located at the southwestern Hokkaido, NE Japan, and then estimate the structure using the 3-D analysis. The measured MT data included small impedance phases in the low frequency band, and thus could be affected by the regional structure. The measured induction vectors also suggested the effect by the ocean and sedimentary rocks which is called as Ishikari Plain. We evaluated this regional effect, with the aid of the 3-D forward modeling calculation code developed by Fomenko and Mogi (2002). The calculated induction vectors were well explained by the regional effects, and the calculated impedance phase showed the same tendency as the observed one. This fact indicates that the MT impedance is strongly affected by the regional conductive structure. We also estimated the effect due to the 3-D topography of the volcano. The results showed that the apparent resistivity decreased to maximum 20 Ωm (-80 %) at the top of the topography, while the impedance phase increased to maximum 55 deg (+20 %) there. Finally, we carried on a 3-D modeling based on the MT data, fixing the regional structure and topography. The final model showed the great resistivity boundary dividing the Shikotsu caldera and Ishikari Plain. This feature suggests that Tarumai Volcano was generated along the regional structural boundary which might be also related with the formation of the Shikotsu caldera. Low frequency earthquakes, which suggest the degassing from a magma chamber, occurred at the sea level beneath Tarumai Volcano. Although the magma chamber including the partial melt can be found generally as a conductor, no conductor at such a depth was found in our model. Since the high temperature gas tends to show high resistivity, there can be not the magma chamber but the gas reservoir at the depth.
[en] Tertiary felsic volcanics of the Sierra Pena Blanca in Mexico host potentially economic uranium deposits, and of Meseta Los Frailes in Bolivia contain interesting U anomalies but no significant deposits. A comparative study of the two uranium districts reveals differences that may explain the different degrees of U concentration. The host ignimbrite in Mexico, namely the Nopal Formation dated at 44 Myr. ago, is potassic alkaline rhyolite which is poorly compacted and contains phenocrysts of quartz, orthoclase, ilmenite and magnetite, totalling < 15% of the rock. The 16-Myr. old host tuffs in Bolivia on the other hand, are rhyodacites of calc-alkaline character, and contain phenocrysts of plagioclase, biotite and accessory minerals, amounting to > 30% of the rock. Vapour phase crystallization is well developed in the Mexican tuff, and has led to a primary concentration of labile U not tied up in refractory accessory minerals, as shown by fission-track studies. The Bolivian tuffs lack such vapour phase primary concentration of U. Subsequent hydrothermal alteration, in particular kaolinization is intense in the Mexican district, but is relatively less intense in the Bolivian one. It is postulated that an intense hydrothermal activity, probably of prolonged duration, in rocks displaying primary enrichment of labile U, is essential to form volcanogenic U deposits of the type found in Mexico. 26 refs.; 13 figs.; 3 plates; 3 tabs
[en] We present a new local Bouguer anomaly map of the Central Volcanic Complex (CVC) of Tenerife, Spain. The high-density core of the CVC and the pronounced gravity low centred in the Las Canadas caldera (LCC) in greater detail than previously available. Mathematical construction of a subsurface model from the local anomaly data, employing a 3-D inversion enables mapping of the shallow structure beneath the complex, giving unprecedented insights into the sub-surface architecture of the complex, and shedding light on its evolution.