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The interplay between deformation and metamorphism during Alpine eclogitisation of pre-Alpine amphibolites in the Sesia-Lanzo Zone (Italian Western Alps)
No full textStudio e caratterizzazione delle vernici negli strumenti musicali antichi: i mandolini Vinaccia (1769-1787)
No full textCl-rich amphiboles from continental and oceanic crust : a microstructural and microchemical study
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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
Metamorphic assemblages in layered amphibolites and micaschsist from the Dessent Formation (Mountaineer Range - Antarctica).
No full textTectonic significance of alpine eclogites
No full textA review of P-T peaks and paths of eo- and meso-Alpine eclogite facies rocks occurring along the axial part of the Alpine chain shows that rocks re-equilibrated under high- and low-T (group-B and -C eclogites), are, respectively, hosted within a lower and an upper tectonic level of the Penninic nappe system. If P-T estimates for eclogites are considered peak conditions the two crustal portions, otherwise undistinguishable, were sutured during the collision of the European and Adriatic continental plates, which corresponds to the latest tectonic mechanism of eclogitization. Before collision, formation and preservation of eclogitic rocks up to shallow levels was assisted by subduction of the cold oceanic crust. The two lithospheric processes of oceanic subduction and continental collision, though separated in time, contribute to continuous generation of eclogites under thermal conditions that evolve from higher to lower P-T ratios from the end of ocean consumption. Exhumation trajectories are characterized by low-or high thermal regimes in the same structural domain in different parts of the chain (Western and Eastern Austroalpine), in the same part of the chain (Penninic and ophiolites in Western, Central and Eastern Alps), or even within the same nappe (Dora-Maira, Gran Paradiso and Adula). Late orogenic collapse or slab breakoff processes may have caused late heating at very low pressure (0.3 GPa) during exhumation in some units of the Pennine nappes and ophiolites Mechanisms of nappe emplacement are demonstrably multiphase and inferences on palaeogeographic derivation of eclogitic units can be drawn from interpretation of P-T trajectories
Il ruolo della composizione chimica per gli studi di provenienza: confronto tra metodi petrografici e statistici
No full textGeochemical characteristics of Proterozoic post-orogenic magmatism in the Nagssugtoqidian Mobil Belt of southeast Greenland
No full textThe final event in the Nagssugtoqidian (NAG) Mobile Belt of East Greenland is represented by the post-orogenic intrusion of plutonic bodies into an Archaean-Proterozoic polymetamorphic basement. The petrogenesis of plutonic rocks and dykes, which make up the Ikasaulak Intrusive Complex, is interpreted on the basis of their major- and trace-element geochemistry.
The investigated intrusive complex consists of a lower ultramafic-mafic sequence and an upper-inter-mediate felsic sequence. A compositional gap exists at the 60-70% Si02 range. Silica-rich rocks, corresponding to a minimum-melt composition, are characterized by strong LREE enrichment and highly fractionated REE patterns, consistent with an origin by partial melting of a garnet-rich source, probably triggered by the intrusion of mantle-derived melts.
Most primitive mafic rocks show enrichment in LREE and large-ion lithophile elements and depletion in Nb and Ta. Although these data are suggestive of magmas generated at destructive plate margins, there is no geological reason for assuming a subduction-related origin of the melts. Thus trace-element compositions appear to be a feature of the mantle source, probably retaining the geochemical signature of the crust-generating processes occurring during the previous NAG ocean subduction (1920-1840 Ma).
Petrogenetic modelling of the major- and trace-element compositions indicates that fractional crystallization can only partially account for the compositional differences up to 60% Si02 and other mechanisms, such as concurrent assimilation and fluid activity, are involved.
The present data suggest that the final event in the mobile belt was the stabilization of the sub-continental mantle, which occurred at least 200-300 Ma after the subduction-related crust-generating processes
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