The Lipari volcanic complex, situated in the central Aeolian sector, was constructed between c. 267 ka and medieval ages by various lava flows, scoriaceous deposits, lava domes (coulees) and pyroclastic products related to hydromagmatic and strombolian activities. The eruptive history of Lipari is described by nine Epochs of activity interrupted by dormant periods, volcano-tectonic phases and episodes of terrace formation during the Last Interglacial. Several partially overlapping volcanic edifices were active through time, mostly under control of the NNW–SSE and north–south (minor east–west) regional tectonic trends. The latest eruptive events of M. Pilato and Rocche Rosse occurred from AD 776 to 1220. Lipari rocks range from calc-alkaline basaltic andesites to rhyolites, with silicic rocks dominating during the last 43 ka. There is a clear increase in K2O and incompatible elements with time, with distinct trends for mafic-intermediate and silicic rocks. Sr, Nd and Pb isotope ratios are highly variable. Petrographic and geochemical data suggest AFC (assimilation plus fractional crystallization) and mixing as the main magma evolution processes, with important effects of crustal anatexis, in the context of a polybaric feeding system.DVD:The 10 000 scale geological map of Lipari is included on the DVD in the printed book and can also be accessed online at http://www.geolsoc.org.uk/Memoir37-electronic. Also included is a full geochemical data set for Lipari.
We applied the electrochemical atomic layer epitaxy ͑ECALE͒ methodology to obtain deposits of CdS and ZnS on Ag͑111͒ by alternate underpotential deposition of the elements forming the compounds. The amounts of the elements deposited, determined by stripping coulometry, always yielded a stoichiometric 1:1 ratio. The deposits were formed using an automated electrochemical deposition system, described here, making use of a simple distribution valve.Recent work in our group is devoted to the growth of thin-film compound semiconductors on silver single crystals by electrochemical atomic layer epitaxy ͑ECALE͒. Stickney and co-workers developed this method to obtain structurally well-ordered II-VI and III-V compound semiconductors on gold at low cost. 1-3 The method is based on the alternate electrodeposition of atomic layers of the elements making up a compound, at underpotential. Underpotential deposition ͑UPD͒ is a surface-limited electrochemical phenomenon that results in the deposition of an atomic layer. A monolayer of the compound is obtained by alternating the UPD of the metallic element with the UPD of the nonmetallic element in a cycle. The ECALE cycle can be repeated as many times as necessary to obtain deposits of practical thickness, and the thickness of the deposit is determined by the number of cycles.The method requires the definition of precise experimental conditions, such as potentials, reactants, concentrations, supporting electrolytes, pH, deposition times, and the possible use of complexing agents. These conditions are strictly dependent on the compound one wants to form and on the substrate used. We found the conditions to grow practically all II-VI compound semiconductors and are now beginning to study the III-V compounds. The substrate that has been used up to now is Ag͑111͒, a single crystal to ensure the maximum probability for the epitaxial growth.In a previous paper we described the experimental conditions needed to obtain up to five sulfur layers and four cadmium layers of CdS. Sulfur layers were obtained by oxidative UPD from sulfide ion solutions, 4-6 whereas cadmium layers were obtained by reductive UPD from cadmium ion solutions. 7 Both precursors were dissolved in pyrophosphate plus sodium hydroxide of pH 12. The high pH was used to shift the hydrogen evolution toward very negative potentials in order to evidence the whole underpotential oxidation process of sulfide ions which takes place between Ϫ1.35 and Ϫ0.8 V/SCE. A strong complexing agent such as pyrophosphate was used to keep cadmium ions in solution at this high pH. This paper describes the growth of thicker deposits of CdS, up to 150 deposition cycles, obtained using an automated system. The deposit morphology was examined by scanning electron microscopy ͑SEM͒. This paper also describes conditions to form ZnS.The experimental conditions for CdS and ZnS growth on silver are different from those required on gold. 8-10 ExperimentalMerck analytical reagent-grade 3CdSO 4 •8H 2 O and Aldrich analytical reagent-grade Na 2 S were used ...
The electrosorption valency l B of an adsorbed species is usually obtained from the slope of plots of the charge density on the metal against the surface concentration of the given species, at constant applied potential. Herein, two alternative procedures for the estimate of l B are proposed and applied to the formation of ordered overlayers of chloride, bromide, iodide, and sulfide on Ag(111). One of these procedures applies to strongly adsorbing anions, whose incipient adsorption turns out to be diffusion controlled under limiting conditions when stepping from a potential negative enough to exclude their specific adsorption. This procedure allows l B to be estimated as a function of the applied potential. Partial charge-transfer coefficients λ estimated from l B values on the basis of some modelistic assumptions decrease in the order sulfide ≈ iodide > bromide > chloride, namely in the order of increasing Pauling's electronegativity. Some direct procedures for the estimate of λ, which avoid the intermediate estimate of l B, are shown to lead to erroneous results.
Stratigraphic, structural, volcanological and geochemical data allow a detailed reconstruction of the geological history of the island of Salina (central Aeolian sector). Its subaerial volcanism (c. 244 ka to 15.6 ka) developed through six successive Eruptive Epochs interrupted by major quiescence periods, volcano-tectonic collapses and recurrent episodes of marine terrace formation during MIS 7 and MIS 5. Several stratovolcanoes were constructed by strombolian and effusive (Pizzo Capo, Monte Rivi, Monte Fossa delle Felci, Monte dei Porri) to hydromagmatic and subplinian (Monte dei Porri, Pollara) activity, with a general east–west shift of active vents, controlled primarily by the dominant NNW–SSE and minor NE–SW regional tectonic trends, and a progressive chemical differentiation of the erupted products from calc-alkaline basalts to rhyolites. The magma compositions and variations through time are the result of contamination of primary magmas derived from a subduction-modified mantle source with the Calabro–Peloritano lower crust and subsequent differentiation dominated by polybaric fractional crystallization. Magma mixing and mingling processes occurred during individual eruptions. The early basalts were fed from deep reservoirs located near the crust–mantle boundary, whereas the later andesitic to dacitic and, ultimately, rhyolitic magmas originated through combined assimilation and fractional crystallization processes in magma reservoirs at mid- to upper-crustal levels.DVD:The 10 000 scale geological map of Salina is included on the DVD in the printed book and can also be accessed online at http://www.geolsoc.org.uk/Memoir37-electronic. Also included is a full geochemical dataset for Salina.
The volcanic rocks of the Aeolian arc exhibit important within-island and along-arc compositional variations that testify to both geochemical heterogeneous mantle sources and different roles and intensities of shallow-level magmatic evolution processes. Calc-alkaline magmas are present on all islands, but dominate in the western arc and at Lipari and Panarea. Shoshonitic rocks are present on the central-eastern islands and are particularly abundant at Vulcano and Stromboli. Mafic and intermediate rocks comprise the bulk of older volcanic sequences for most islands. Rhyolites are restricted to younger activity of the central arc, and become particularly abundant at Lipari and Vulcano. Regional variations of incompatible trace element ratios and Sr-, Nd-, and Pb-isotope signatures in mafic-intermediate rocks document the variable composition of mantle sources, which were contaminated by different types of metasomatic fluids released from an oceanic slab in the western-central sectors and from oceanic slab plus sediments in the east. This metasomatism was superimposed over a heterogeneous mantle wedge, which had a mid-ocean-ridge basalt (MORB-) to ocean-island basalt (OIB)- type character passing from the centre to the margins of the arc. The OIB-type component in the external arc is attributed to asthenospheric mantle inflow from the Africa foreland, around the borders of a narrow slab during rollback.
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