1,721,056 research outputs found
Ti solubility in diopsidic pyroxene from a suite of New South Wales leucitites (Australia)
No full textThe pyroxene chemistry from a suite of leucitites and related differentiates from New South Wales has been investigated with the aim of understanding the physico-chemical factors which may influence the Ti solubility in the pyroxene, relative to the chemistry of the host rocks. These are characterized by high and variable Ti (TiO2=3.9−8.0 wt.%) and a high agpaitic index, , combined with . The pyroxenes from this suite are notable in that they contain insufficient Al to complete the occupancy of the tetrahedron to 2.000 atoms per formula unit and Ti occurs both as TiIV and TiVI.
The Ti solubility in the investigated pyroxenes depends on the partitioning of Ti to TiIV and TiVI, TiIV being favoured in the early-crystallized (core) and TiVI in the late-crystallized (rim) compositions, relative to Al. Therefore, the well-known and common substitution couple TiVI-Al2IV is associated with the TiIV-Si substitution, predicted by T.F.W. Barth and later by E.R. Segnit from synthetic pyroxenes. Further, ti solubility in the New South Wales pyroxenes depends on the Ti/Al ratio of the liquid from which the pyroxene crystallized and not necessarily that corresponding to the bulk rock. Ti partitioning between pyroxene and coexisting magnetite varies significantly with temperature and fO2, increasing dramatically in favour of the coprecipitated pyroxene at relatively low temperature and higher fO2. However, the pyroxene Ti content is independent of tetrahedral Si, which remains high and relatively insensitive to variations in silica and silica saturation, respectively, in the host rock
Clinopyroxenes from Somma-Vesuvius:Implications of crystal chemistry and site configuration parameters for studies of magma genesis
No full textA clinopyroxene suite from Somma-Vesuvius clinopyroxenite cjecta and mcgacrysts has been investigated by single crystal X-ray diffraction combined with electron probe microanalysis. The aim of the study was to characterize the intracrystalline configuration of the clinopyroxenes and delineate their possible parental liquid(s). Vesuvius megacrysts and nodule clinopyroxenes show the initial ‘signature’ of the leucitite (sensu lato) magma while Somma clinopyroxenes are characteristic of leucite phonolite magma. The crystal chemical variations demonstrate that the specimens investigated had originated by shallow-level crystallization of leucitite and its derivatives, under reducing conditions. T-site (Si + Al) deficiency, typical of clinopyroxene from lamproites is reported in some specimens from the Roman Volcanic Region for the first time. Intracrystalline Mg-Fe2+ ordering in M1-M2 appears to be configuration-dependent, yielding the largest KD variation in the clinopyroxene from phonolite. This is contrary to expectation
Comin-Chiaramonti P., Cundari A., Gomes C.B., Carbonatitic Magmatism in the Paranà-Angola Mantle Plume (?) sistem: Petrological and Isotope-Geochemical Bering on the Source Mantle.
No full textExtension of the melilite-carbonatite province in the Apennines of Italy: the kamafugite of Grotta del Cervo, Abruzzo.
No full textA new occurrence of a rare kamafugite near L’Aquila, Abruzzo, is described in detail to characterize its paragenesis and to establish possible genetic links with similar alkaline mafic igneous rocks from the Oricola-Camerata Nuova (OC) volcanic field, ~20 km to the west. Both occurrences belong to the Umbria-Latium-Ultralkaline-District (ULUD), an igneous district represented by rare kamafugites and carbonatites and distinct from the much more voluminous Roman Region (RR) rocks. The new kamafugite was found in a cave known as Grotta del Cervo (GC), associated with epiclastic and pyroclastic rocks. In the latter, lapilli ash tuff, welded lapilli, ultramafic xenoliths, cognate lithics and pelletal lapilli have been identified. The mineralogy of the welded lapilli comprises, in order of decreasing abundance, diopside, leucite, haüyne, Mg-mica, andraditic garnet, apatite, magnetite, kalsilite and olivine. The rock is carbonate-free. Based on bulk-rock chemistry it is classified as a kamafugite, closely approaching the composition of ULUD kamafugites, according to Sahama’s (1974) criteria. Separate lapilli ash tuff, characterized by the same silicate mineralogy as that of the welded lapilli, plus modal carbonate exceeding 10 wt.%, is classified as a carbonatitic kamafugite. Bulk-rock and trace-element compositions confirm that the Grotta del Cervo rocks closely approach the ULUD analogues. The Grotta del Cervo occurrence partially fills the geographical and compositional gap between ULUD rocks and the rocks from the Vulture Complex, also a carbonatite and melilitite locality ~200 km south of GC, and adds considerably to the bulk of kamafugitic and related rocks lying along the Italian Apennines. The petrogenesis of these kamafugites rocks is discussed and possible mineralogical similarities with the Roman Region rocks are highlighted
Melilitite-carbonatite association in the Umbria-Latium Ultra-alkaline District (ULUD): first recorded occurence in Italy.
No full textNew mineral data from the kamafugite-carbonatite association: the melilitolite from Pian di Celle, Italy
No full textA detailed mineralogical investigation of a Pian di Celle sill rock (San Venanzo, Italy), classified as melilitolite and associated with venanzite and carbonatitic pyroclasts, revealed new and rare mineral parageneses, considered as characteristic of the kamafugite-carbonatite association. These are formed by several accessory minerals, including minerals of the cuspidine family, götzenite, khibinskite, minerals of the rhodesite- delhayelite- macdonaldite family, pyrrhotite, bartonite and (Fe, Ni, Co) monoarsenide, mostly optically and chemically identified also in fluid inclusions. The chemical composition of these minerals and their probable crystallisation succession, deduced from textural relationships, demonstrates extensive atomic substitutions, notably for Ca, Ti, Mg and alkali, essentially reflecting high concentrations of REE, Sr, Ba, Nb and Zr, which significantly varied during crystallisation. Molecular alkali excess over Al and high Ca content in (H2O, F, CO2)-rich, Si-undersaturated liquid(s) are considered the dominant factors in controlling the stability of disilicate-type minerals. Separation of the carbonatite liquid from the silicate magma, constrained by textural and fluid inclusion data, was fundamental in moving the residuum onto a strongly peralkaline trend which stabilised the sulphides under changed redox conditions
Regole di progetto specifiche e modalità di verifica per gli edifici in muratura ordinaria e armata
No full textIl volume "Fondamenti di tecnica delle costruzioni" nasce con l'intento di colmare una lacuna nel panorama italiano, ma anche internazionale, in cui manca un testo che fornisca una visione unitaria e organica dell'argomento, proponendo una trattazione sistematica dei diversi sistemi costruttivi. Il panorama progettuale, infatti, è oggi estremamente variegato e versatile, soprattutto in un'epoca in cui si guarda sempre di più all'ottimizzazione e all'integrazione delle prestazioni strutturali, energetiche e produttive, oltre che all'uso efficiente e sostenibile dei diversi materiali nell'edilizia corrente e specialistica. Il testo, aggiornato al D.M. 17 gennaio 2018 e relativa Circolare applicativa e pensato non solo per i corsi inseriti nelle lauree triennali di Ingegneria e Architettura, di cui presenta in maniera completa tutti i contenuti richiesti, ma anche come linea guida e punto di partenza per le discipline caratterizzanti le lauree magistrali, è contraddistinto da una spiccata prospettiva didattica. Per ogni argomento, infatti, vengono sviluppati gli elementi teorici di base, comprensivi dei richiami alla Normativa tecnica, e sistematici inquadramenti applicativi dei sistemi costruttivi e dei loro aspetti pratici e di cantiere
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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