1,721,086 research outputs found
Mineral chemistry of the calcalkaline lavas from Marsili Seamount (southeast Tyrrhenian Sea): some magmatological and geodynamic considerations
No full textMineral chemistry data from lavas recovered over a large depth interval of the deep-water volcano of Marsili (Aeolian back-arc, SE Tyrrhenian Sea) are presented. The volcano is built up by products of calcalkaline affinity with the only exception of one outcrop of sub-alkaline, within plate basalts in the crestal area. On the whole, the calcalkaline lavas of Marsili have bimodal composition, and consist of basalts and andesites with, respectively, calcalkaline and high-K serial affinity. The andesites mark a change in the geodynamic conditions that is reflected by the clockwise rotation of the seamount rifting from the early NNE-SSE orientation, associated with the extrusion of the basalts, to a dominant tensional regime trending almost NE-SW. This evolution is discussed in the context of some magmatic-structural features in the southest Tyrrhenian volcanic area. -from Author
Mineralogy, petrography and evolution of Triassic magmatites of the Cima Pape Complex, eastern Dolomites
No full textMiddle Triassic magmatic products in the Cima Pape area (Eastern Dolomites) are examined. Stratigraphically the volcanic rocks are placed between the Livinallongo formation and the "Conglomerato della Marmolada' formation. The succession starts with the "agglomerati' (a tabular sheet of chaotic deposits derived from submarine slidings) followed by pillow lavas, pillow breccias and small subvolcanic bodies. A thick hyaloclastite sequence marks the end of volcanic activity. A sill varying in thickness from 50 to 300 m is injected inside the Livinallongo formation and controls the distribution of the overlying volcanics. The sill has undergone important differentiation. The chemical characteristics of the volcanic rocks show a clear affinity with shoshonitic series. The rocks could be derived from high alumina basalt primary magmas by high-pressure fractional crystallisation near the base of a thick crust. The "Conglomerato della Marmolada' is a thick conglomeratic sequence made almost exclusively of volcanic elements. This formation marks the end of an upper-Ladinian tectonic phase with extensive uplifting, faulting and erosions. -from English summar
Calc-alkaline magmatism and rifting of the deep-water volcano of Marsili (Aeolian back-arc, Tyrrhenian Sea)
No full textGeochemistry and mineral chemistry data indicate that new lava samples recovered from a large depth interval of Marsili volcano (southern Tyrrhenian Sea) are calc-alkaline. The deep to intermediate portions of the volcano are made up by calc-alkaline basalts, whereas the summit consists of high-potassium calc-alkaline andesites. The contents of MgO, CaO, total iron, Cr, Ni and V decrease with increasing silica, while K2O, Rb, Ba, Th, Nb and LREE exhibit the opposite behavior. The andesite lavas of the top, at waterdepth shallower than about 800 m, are younger than 0.2 Ma. Composition of the basalts varies with the waterdepth; overall, the deepest products of Marsili are geochemically more mafic than those erupted in the higher physiographic positions. Geochemical features suggest the existence of a mantle source that was modified by metasomatic acquirement of subduction-derived incompatible elements. The seamount lies on oceanic crust which formed above subducting lithosphere not earlier than about 2 Ma ago. It is currently undergoing extension along linear faults. The major distensional fractures trend N-S to N15°E paralleling the physiographic elongation of the volcano. At the summit, later faults have an oblique NE-SW orientation which is associated with the eruption of high-potassium andesites. The transition from basalts to high-potassium andesites is discussed as a possible response to the extension and rapid subsidence that dominate the volcano and surrounding region. © 1994
The acquired immunodeficiency syndrome (AIDS): Insights into the immunopathogenesis of the pulmonary involvement.
No full textThe lung is involved in more than 50 per cent of patients with the acquired immune deficiency syndrome (AIDS), and pulmonary abnormalities can be easily investigated using the bronchoalveolar lavage (BAL). Besides providing information on the type of infecting microorganism, BAL has been used to characterize immunocompetent cells from the lower respiratory tract in these patients. This allows new insights into the immunopathogenetic mechanism involved in the persistence of opportunistic pulmonary infections and in the uncontrolled viral replication. This paper emphasizes the value of BAL evaluation as a simple and useful method for investigating the involvement of the distal respiratory tract in AIDS patients. A particular attention is payed on the immunological pulmonary abnormalities of this epidemic immunodeficiency syndrome
Fe-Mn carbonate concretions in the Reno-Limentra fluvial deposits near Vergato (Bologna province, Northern Apennines): A petrographic and geochemical study
No full textFerromanganese carbonate concretions of extremely variable compositions mineralogical, petrographic and geochemical features. The obtained results lead to a genetic model by which concretions appear to be diagenetic rather than hydrogenic or hydrothermal. This origin is particularly supported by trace metal concentrations, REE patterns and stable isotope compositions
Monte Cavaloro: Small differences in outcrop lithology (Fe-Ti-P diorite) of a complex olistolith (Apennines Bologna)
No full textAt Monte Cavaloro near Bologna, outcrops a small olistolith of the ophiolite sequences of the Northern Apeninnes. This small outcrop is known in the geological literature as Bombicci (1868) find out a new type of rock which he named "oligoclasite". Cappellini (1878) studying the same outcrop, named the rock "Cavalorite". These two terms are still present (although obsclete) in the geological nomenclature. The same outcrop was studied by various authors which gave contrasting description of the mineralogy and recognized different rock types, from oligoclase bearing gabbro to quartzdiorite. The last study was by Gazzi (1961) who recognized the presence of stilpnomelane and classified the rock as stilpnomelane-oligoclase bearing gabbro. The present work lead us to the finding of several litothypes in the Monte Cavaloro olistolith: Fe-gabbros, Fe-gabbrobrodiorites, Fe-Ti-P diorites, Fe-Ti-P meladiorites, quartzdiorites and amphibole bearing albitite dikes. The Fe-Ti-P diorites are made up by oligoclase, ferroaugite, ferrohortonolite, ferrosilite, apatite, titanomagnetite and Fe-edenite and appear to be the product of cumulus processes from Fe-rich andesitic magmas which concentrate Fe-Ti oxides when apatite appeared as a liquidus phase. The other associated rocks are genetically linked through flow differentiation processes which generated the Fe-Ti-P meladiorites and the zircon rich quartzdiorites. The differentiation processes, took place in a closed system under low oxygen fugacity; during the late magmatic stages the high volatile content promoted the formation of hydrous minerals (mainly amphiboles) and the peculiar association biotite, cummingtonite-grunerite, stilpnomelane, chlorite. Stilpnomelane is variable in composition and in spite of its chemical features, it may correspond to that find in late stage granophyre of the Skaergaard pluton. This fact is a clear indication of the highly evoluted nature of our stilpnomelane bearing rock in keeping with the presence of stilpnomelane relics in the quartzdiorites. REE and trace elements abundances and composition of apatites and titano-magnetites agree with this genetic interpretation. Liquid immiscibility, as responsible of Fe-Ti-P rock, would seem to be not a viable genetic mechanism. The amphibole bearing albitite dikes represent a late injection of a slightly evolved gabbric magma
Glass chemistry in volcaniclastic sediments of ODP Leg 107, Site 650, sedimentary sequence: provenance and chronological implications
No full textA detailed chemical investigation of volcanic glass fragments from volcaniclastic strata (6 tephras, 1 volcanic debris flow, 12 volcanic turbidites) of ODP Leg 107, Site 650, sedimentary sequence, leads to a varied pattern in terms of both provenance and age constraints. The six analyzed tephra strata indicate a provenance from at least three different volcanic provinces: Aeolian, Campanian, and Sicilian Channel (Pantelleria Island). The older tephra strata (021, 018, 012) have a large amount of "orogenic" rhyodacite/rhyolite deposits that may be attributed to the Aeolian province, although no subaerial coeval volcanic activity of similar composition has so far been documented in the Aeolian Arc. Tephra 007 is related to the Pantelleria Island activity and, particularly, to an ignimbrite episode dated circa 130 ka. Tephra strata 005 and 003, have a clear Campanian provenance, and are correlated with analogous tephra layers, observed in the Tyrrhenian and Ionian seas, dated circa 107 and 60 ka respectively. In the oldest portion of the sequence (from 1.3 to 0.13 Ma), the volcaniclastic sediments were only derived from the Aeolian domain whereas in the latest 130 ka, the Campanian influx becomes much more predominant. Therefore, a general K-enrichment trend is observed in the temporal sequence of all the analyzed samples (almost 700 point analyses) which may be related both to a variation in the source area and to the specific Pleistocene magmatic evolution of the peri-Tyrrhenian volcanic provinces. © 1994
Trioctahedral smectites and zeolites as transformation products of the Cala Pozzolana di Ponente pyroclastic rocks (Linosa Island - Italy)
No full textOn Linosa Island the pyroclastites of Cala Pozzolana di Ponente have been affected by post depositional alteration phenomena. Field and laboratory study point out that this pyroclastic deposit was affected by hydrothermal circulation with formation of secondary minerals like smectite, zeolites, calcite. The transformation processes were accomplished in two stages; a first one was brought about by the circulation of abundant hydrothermal fluids that reacted with the glass fragments producing a thin regular crust of smectite surrounding glass fragments and a second one, responsible for the zeolite growth, was accomplished by fluids enriched in alkalis and calcium released by the altered glass, in conditions of decreasing fluid circulation and falling temperature. -from Author
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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