305,322 research outputs found
Experimentally-derived Ca-Na partitioning between plagioclase and clinopyroxene : a new geobarometer for mantle rocks
No full textThe crystallization of plagioclase-bearing equilibrium assemblages in mantle peridotites is commonly considered witness of lithospheric mantle exhumation at shallow depth (e.g. Rampone et al., 1993; Ozawa & Takahashi, 1995; Newmann et al., 1999). Experimental works have pointed out that at subsolidus conditions plagioclase lherzolite assemblages are stable up to 1 GPa. Subsolidus experimental data in the complex chemical system TiO2-Cr2O3-Na2O-FeO-CaO-MgO-Al2O3-SiO2 on depleted and fertile lherzolite compositions (Borghini et al., 2010) have documented systematic compositional variations in coexisting minerals at decreasing pressure within the plagioclase stability field, similar to what observed in natural equilibrated plagioclase peridotites. In these experiments, Ca-Na partitioning between plagioclase and clinopyroxene is strictly dependent on pressure, with plagioclase composition varying significantly (An=59-83) in a narrow range of pressure. In a recent paper, Borghini et al. (2011) have defined the anorthite isopleths in plagioclase as a function of P and T in a specific fertile lherzolite composition, and they have demonstrated that plagioclase-facies equilibrium pressures can be estimated by comparing experimental data on a fertile lherzolite and microstructural-chemical observations in natural samples with the same bulk composition. This method represents a first-order empirical tool to trace the decompressional evolution of the lithospheric mantle up to very low-pressure and it is potentially applicable to natural plagioclase peridotites of different origin. Nevertheless, the composition of plagioclase at variable bulk Na2O/CaO ratios has been not fully discerned yet, making this approach directly applicable to a limited bulk composition range. Here, we present the results of new experiments on a Na-enriched lherzolite (bulk Na2O/CaO ratio = 0.13), representative of many refertilized lithospheric peridotites at extensional settings, thus enlarging significantly our investigated compositional spectrum (Na2O/CaO = 0.08 - 0.13). The goal of this work is to provide a formulation for a geobarometer analysis based on Ca-Na plagioclase-clinopyroxene partitioning on a larger experimental data set which takes into account the effect of bulk Na2O/CaO ratio and is consequently applicable to a wider compositional range of mantle rocks. References: Borghini, G., Fumagalli, P., Rampone, E. (2010): J. Petrol., 51, 229-254; Borghini, G., Fumagalli, P., Rampone, E. (2011): Lithos, in press; Newman, J., Lamb, W.M., Drury, M.R. & Vissers, R.L.M. (1999): Tect., 303, 193-222; Ozawa, K. & Takahashi, N. (1995): Contrib, Min. Pet., 120, 223-248; [5] Rampone, E., Piccardo, G.B., Vannucci, R., Bottazzi, P., Ottolini, L. (1993): Contrib, Min. Pet., 115, 1-17. AGU Fall meeting, San Francisco, Calif., 5-9 Dec., 2011. Section: Volcanology, Geochemistry, Petrology. Session: Mineralogical Signals as Keys to Understanding Petrological Processes II Posters. Abstract V11A-251
Xilografías de Alberto J. Rampone para los Cantares de Cuyo : ocho melodías sobre poesías populares, recopiladas por Juan Draghi Lucero ; música de Julio Perceval
No full textFil: Rampone, Alberto J.
Oboe
No full textDurante el transcurso del s. XIX constructores franceses aplicaron sucesivas innovaciones al diseño del tubo y del mecanismo de llaves del oboe. Dichas innovaciones cristalizaron hacia 1880 en un modelo que, con ligeras variantes, se conserva en los instrumentos actuales. A su vez debe consignarse un fenómeno bastante frecuente en la historia de los instrumentos: un número considerable de ejecutantes se resistieron a adoptar las nuevas propuestas y continuaron utilizando modelos conservadores. El ejemplar de la firma Frat. e Cugino Rampone se enrola en esta categoría. Su datacíón es cercana a 1900. Sin embargo sus características principales, con influencias tanto francesas como austríacas, pertenecen a un período anterior.In the 19 th. c , the oboe key mechanism and tube designs were successively modified by French makers. By 1880, such modifications originated a model which is found with slight variations in the instruments at present. A great number of players refused to adopt the new designs and continued using the old ones. This has been a frequent attitude throughout the history of instruments. The model of the specimen belonging to the firm Frat. e Cugino Rampone is old fashion. Although it dates from ca. 1900, its main features, which how both French and Austrian influence, are those of an earlier period.Perteneciente a la firma Frat. e Cugino Rampone (Milano) su creación data del 1900 aproximadamente.Museo de Instrumentos Musicales Dr. Emilio Azzarin
Postcumulus processes in oceanic-type olivine-rich cumulates: The role of trapped melt crystallization versus melt/rock interaction
No full textCombined microstructural and geochemical investigations on MORB-type primitive olivine-rich cumulates intruded in the Erro-Tobbio (ET) mantle peridotites (Voltri Massif, Ligurian Alps, Italy) revealed that significant chemical changes in minerals were caused by postcumulus crystallization. This is indicated by the occurrence of accessory interstitial minerals (Ti-pargasite, orthopyroxene and Fe-Ti oxides) and by systematic chemical zoning in intercumulus clinopyroxene, resulting in marked trace element (e.g. REE, Ti and Zr) enrichment at constant high Mg-numbers (0.88-0.91) and LREE depletion. Geochemical modelling shows that low trapped melt amounts (<5%) are sufficient to produce the observed trace element enrichments. Chemical zoning in large (mm-size) clinopyroxenes was dominantly caused by in situ fractional crystallization of trapped interstitial liquid rather then porous flow migration of externally derived evolved melts. Zr enrichment relative to REEs in vermicular clinopyroxene and pargasitic amphibole point to small-scale migration and interaction between residual evolved low melt fractions and the olivine cumulus matrix at final stage of crystallization
Melt migration and intrusion in the Erro-Tobbio peridotites (Ligurian Alps, Italy): insinghts on magmatic processes in extending lithospheric mantle
No full textThe Alpine/Apennine ophiolites are largely thought to represent lithosphere sectors mostly formed at an ocean/continent transition and allow the direct observation of petrologic and geodynamic processes in extensional systems evolving from continental rifting to ultraslow spreading. The Alpine/Apennine peridotites experienced multiple melt/ rock interaction and melt intrusion events occurred at different lithospheric depths, thus providing insights on mantle dynamics and lithosphere-asthenosphere interactions during progressive lithosphere extension. Here we present an overview of this multi-stage melt migration and intrusion history, as recorded in the Erro-Tobbio (ET) peridotites (Ligurian Alps, Italy). In the ET spinel peridotites, the oldest intrusion event is documented by the diffuse occurrence of cm-scale folded pyroxenite bands. They display variably fractionated REE spectra, marked by LREE depletion and absent EUN anomaly. Unusual trace element signature (high Sc,V contents and low MREE/HREE ratios) in clinopyroxenes from one pyroxenite layer is witness of a precursor garnet-bearing magmatic assemblage. Spinel pyroxenites likely originated as high-P (> 15-20 kbar) intrusions that preceded the extension-related peridotite exhumation. In the spinel peridotites, field, textural and chemical evidence (e.g. olivine embayment replacing pyroxene porphyroclasts, increasing modal olivine at constant bulk Mg values), points that they experienced open-system melt migration by reactive porous flow, subsequent to pyroxenite intrusion and folding. Melt/rock interaction (causing olivine crystallization and pyroxene dissolution) occurred at high melt volumes at deep lithospheric levels. At shallower lithospheric depths, the ET peridotites were impregnated by melts causing significant plagioclase enrichment and crystallization of poikilitic orthopyroxene replacing mantle olivine and clinopyroxene. Reacted clinopyroxenes preserve strong LREE depletion, indicating that impregnating melts originated as depleted melt fractions. After impregnation, peridotites underwent multiple gabbroic intrusion events. Structural and geochemical features of melt impregnation and melt intrusion products point to a progressive change in melt composition and dynamics. Peridotite impregnation was caused by diffuse migration of opx-saturated depleted melts, and is consistent with cooling and crystallization of migrating melts when the peridotites, due to lithosphere extension and thinning, became part of shallower and colder lithospheric environments. The subsequent intrusion events originated by MORB-type aggregated magmas that had not experienced significant compositional modifications during ascent. The transition from porous flow melt migration to emplacement of magmas in fractures reflects progressive change of the lithospheric mantle rheology, across the ductile to brittle transition, during extension-related uplift and cooling of the ET mantle
The heterogeneous tethyan oceanic lithosphere of the alpine ophiolites
No full textThe Alpine-Apennine ophiolites are lithospheric remnants of the Jurassic Alpine Tethys Ocean. They predominantly consist of exhumed mantle peridotites with lesser gabbroic and basaltic crust and are locally associated with continental crustal material, indicating formation in an environment transitional from an ultra-slow-spreading seafloor to a hyperextended passive margin. These ophiolites represent a unique window into mantle dynamics and crustal accretion in an ultra-slow-spreading extensional environment. Old, pre-Alpine, lithosphere is locally preserved within the mantle sequences: these have been largely modified by reaction with migrating asthenospheric melts. These reactions were active in both the mantle and the crust and have played a key role in creating the heterogeneous oceanic lithosphere in this branch of the Mesozoic Western Tethys
The Ligurian Ophiolites : a journey through the building and evolution of slow spreading oceanic lithosphere
No full textLe ofioliti liguri rappresentano una finestra geologica unica e accessibile per ricostruire le prime fasi di formazione ed evoluzione della litosfera oceanica a bassa velocità di espansione. Le ofioliti delle unità liguri interne sono formate da corpi gabbrici di dimensioni chilometriche all’interno di peridotiti di mantello impoverite e presentano chiare analogie con la litosfera oceanica delle dorsali oceaniche a bassa e ultra-bassa velocità di espansione. Le ofioliti delle unità liguri esterne sono associate a rocce di crosta continentale e includono sequenze di mantello di origine litosferica sottocontinentale. Questa escursione geologica consente l’osservazione di alcuni siti più rappresentativi su due associazioni gabbro-peridotitiche delle ofioliti delle unità
liguri interne:
i) l’ofiolite Bracco-Levanto, che contiene un corpo chilometrico di gabbro simile ai “core complexes” dei settori oceanici estensionali moderni (es. Atlantis Massif, Oceano Atlantico);
ii) l’ofiolite Scogna-Rocchetta Vara, che è caratterizzata dalla mancanza di basalti, come le sezioni non-vulcaniche degli oceani Atlantico e Indiano. Le peridotiti e i gabbri di entrambe queste ofioliti registrano una storia composita di deformazione e alterazione associata all’esumazione verso il fondale oceanico. L’escursione include inoltre alcuni corpi peridotitici delle ofioliti delle liguridi esterne, che rappresentano un eccellente esempio di mantello tipo MORB con diffuse pirosseniti.The ligurian ophiolites constitute an accessible and unique window to track the opening and evolution of slow-spreading oceanic lithosphere. The internal ligurian ophiolites consist of km-scale gabbroic bodies intruded into depleted mantle peridotites and bear remarkable structural and compositional similarities to oceanic lithosphere from slow and ultra-slow spreading ridges. The external ligurian ophiolites are associated with continental crust material and include mantle sequences retaining a subcontinental lithospheric origin. This field trip explores two gabbro-peridotite associations from the internal ligurian ophiolites:
i) the Bracco-Levanto ophiolite, which includes a km-scale gabbroic body recalling the oceanic core complexes from modern
spreading centres (e.g. the Atlantis Massif, Atlantic Ocean);
ii) the Scogna-Rocchetta Vara ophiolite, which lacks the basalt layer similar to the nonvolcanic sections from Atlantic and Indian oceans. The peridotites and the gabbros from both these ophiolites record a composite history involving deformation and alteration from high temperature to seafloor conditions. The field excursion also explores peridotite bodies from the external ligurian ophiolites, representing a nice example of MORB-type pyroxenite-bearing mantle
Recenti orientamenti della giurisprudenza costituzionale in materia di enti locali e finanza pubblica (gennaio - ottobre 2016)
No full textL'articolo analizza le pronunce della Corte costituzionale, relativamente al periodo gennaio-ottobre 2016, in tema di rapporto fra gli enti locali e la finanza pubblica
Tortura, tra abusi e tutela dei diritti fondamentali della persona nel sistema giuridico sovranazionale e nazionale
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