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PETROLOGY OF BASIC AND INTERMEDIATE OROGENIC GRANITOIDS FROM THE SILA MASSIF (CALABRIA, SOUTHERN ITALY) RID A-1229-2011
No full textHercynian gabbroic, dioritic and tonalitic rocks crop out in the neighbourhood of Rovale (Sila Grande, Calabria). They make up a crude rectangular outcrop with the western part consisting of gabbroic rocks and the eastern of dioritic and tonalitic rocks. They come into contact with medium to high grade metapelites on the western side and with heterogeneous granodiorites on the other sides. In the gabbroic body both opx +/- ol bearing cumulates and amphibole differentiates occur and are characterized by the widespread presence of brown pargasite. Sporadic magmatic to subsolidus corona textures between olivine and plagioclase or orthopyroxene and plagioclase can be observed and their preservation clearly suggests a post-tectonic emplacement for the gabbroic magma. Diorites and tonalites display hypidiomorphic textures free of olivine and orthopyroxene and bearing green Mg-hornblende. The granitoids, on the basis of chemical data, display orogenic features of the continent-continent collision type. The gabbroic rocks have high Al tholeiitic composition and fractionation of orthopyroxene and plagioclase played an important part in their evolution. The Rb/Sr isochron method did not give a precise emplacement age for the granitoids as a whole. Initial Sr-87/Sr-86 ratios (at 290 Ma) are higher in the gabbroic body (0.7091-0.7095) than in diorites and tonalites (0.7083-0.7092). Thus gabbroic rocks appear more displaced than diorites and tonalites towards crustal isotopic composition. The epsilonNd data seem to confirm this feature, thus suggesting that the gabbroic rocks and diorites derived from distinct mantle magma batches. Interestingly, small isotropic gabbroic masses occur within the diorites and show general features that allow them to be considered as possibly parental with respect to the host diorites. The evolution to the dioritic composition might have occurred through fractionation and minor mixing with a more acidic component such as the northern granodiorites. Geochemical, Sr and Nd isotopic data indicate a scenario of a composite plutonic body formed by distinct magma batches of mixed crust and mantle origin
PETROGENESIS OF HERCYNIAN PERALUMINOUS GRANITES FROM THE CALABRIAN ARC, ITALY RID A-1229-2011
No full textThe Capo Rasocolmo (CR) and Villa San Giovanni (VSG) granitoids, in the Southern Calabrian Arc (CLA), form post-tectonic unzoned intrusions in migmatitic paragneisses. They are strongly peraluminous (two-mica aluminosilicate-bearing), showing significant small-scale mineralogical and chemical heterogeneities with compositions ranging from leucotonalite to monzogranite. The CR and VSG granitoids are characterized by SiO2 contents varying from 67 to 75%, low mafics (TiO2 + FeO(t) + MgO < 3.9%) and high Al2O3 (A/CNK = 1.201. 40) with low Rb and high Ba contents and strongly fractionated REE patterns (La(n)/Yb(n) = 34 and Yb(n) = 3.7, on average). They show broad trends in major and trace element compositions which define linear regressions on variation diagrams. The granitoids have an ''S''-type signature in terms of their enclaves, mineralogy and zircon typology, whereas their geochemical characteristics are similar to those of late- to post-collision granites. Initial Sr isotopic ratios (0.7094 - 0.7107) are lower than that of the regionally exposed basement rocks and similar to that of the coeval hybrid calc-alkaline granitoids; is-an-element-of NdI values range from -6.7 to -9.1. Petrographic and geochemical evidence indicate a crystal-liquid unmixing process as the dominant mechanism involved in granitoid evolution. A two-stage model was tested on the CR granitoids, involving fractional crystallization plus assimilation followed by partial solid-liquid segregation during the emplacement of the granite magma; the model accounts very well for the observed geochemical and isotopic variations. The ultimate origin of the CR and VSG granitoids investigated in the present study. A direct derivation from shale-like protoliths, suggested by field data, mineralogy, is consistent with REE patterns and experimental melting data, but is not supported by Ba-Rb decoupling and the Sr isotopic data. A comparison with the classical S-type granites of the Lachlan Fold Belt also excludes an S-type source for the CR and VSG granitoids. A direct derivation of the CR and VSG granitoids from a coeval calc-alkaline suite, through low pressure fractionation processes, is not consistent with the geochemical trends and REE patterns. An origin from a distinct calc-alkaline magma batch, involving both crustal and subcrustal components, is favoured as the most realistic petrogenetic model
Petrogenesis of the Monte Croce granitoids in the context of Permian magmatism in the Southern Alps, Italy RID A-1229-2011
No full textThe Monte Croce pluton (MCP), in the central-eastern Southern Alps, belongs to a large calc-alkaline magmatic association of Permian age also including the Bressanone, Ivigna, Cima d'Asta and Monte Sabion granitoid intrusions, as well as the Atesina volcanics. The MCP was intruded into the low-medium grade basement of the Southern Alps, at depths corresponding to a crystallization pressure of about 3.1 +/- 0.6 kbar. Rb/Sr biotite dating yields a value of 273 +/- 3 Ma for the intrusion age. The MCP consists of medium-grained to porphyritic biotite +/- hornblende granodiorite/monzogranite (GD) containing mafic microgranular enclaves (MME) of tonalitic to granodioritic composition. Field, petrographic and mineralogical evidence strongly supports a model of extensive interaction between partially crystallized mafic and felsic magmas, with incorporation, fragmentation and dispersal (i.e. mingling +/- mixing) of the mafic component into the granitic host magma. The occurrence of mafic enclaves having distinct textures and particular compositions for the Fe-rich biotite and amphibole, suggests that at least two pulses of hybridized intermediate magmas were involved in the petrogenesis of the Monte Croce granitoids. The GD and the hosted MME are metaluminous to weakly peraluminous granitoids with high-K calc-alkaline affinity, mostly following linear trends on Harker diagrams. On chondrite-normalized spider diagrams, both GD and MME show patterns with low HFSE/(LILE, LREE) ratios and distinct Ba, Nb, Sr, P, and Ti negative spikes, similar to those of orogenic suites. Initial Sr-87/Sr-86 ratios range from 0.7086 to 0.7114 in the GD, and from 0.7080 to 0.7099 in the MME. epsilon(Ndi) values range from -6.0 to -7.6 in the GD, and from -4.9 to -7.1 in the MME. Field and petrographic evidence, as well as geochemical trends and isotopic data, are all consistent with a complex petrogenetic model involving magma mingling/mixing coupled with chemical exchange, plus local crystal fractionation. The tectonic significance of the MCP granitoids is interpreted in the context of the Permian magmatism of the Southern Alps. Geochemical features, similar to those of are-related suites, point to an orogenic signature. Palaeogeographic restorations, however, do not show evidence of active subduction processes. Furthermore, geological and tectonic evidence, as well as the timing of intrusion, indicate that the magmatism is related to late/post-orogenic lithospheric extension. Therefore, the calc-alkaline affinity and the orogenic signature of these Permian granitoids might reflect the involvement of mantle source(s) modified by previous subduction processes
LOWER CRUSTAL GRANITE GENESIS CONNECTED WITH CHEMICAL FRACTIONATION IN THE CONTINENTAL-CRUST OF CALABRIA (SOUTHERN ITALY) RID A-1229-2011
No full textGranulite-facies rocks, of metasedimentary and metaigneous type are exposed in the Serre (Southern Calabria). They are representative of the intermediate - lower crust remaining after the Hercynian orogeny and exhumed during the Alpine orogeny. Huge masses of calc-alkaline and peraluminous granitoids intrude both the lower crust and the overlying shallower crustal levels. In this paper, we deal with the composition of the lower crust and its relationship with granitoids along the Serre section, on the basis of major, minor, trace elements, REE and Sr, Pb, Nd isotope systematics. The metapelites, which make up a large part of the lower crust section, have a restite character due to the extraction both of in situ crystallized leucosomes and of some of the late-Hercynian peraluminous granites which intrude the upper crust. The dominant calc-alkaline granitoids seem to require the contribution of hydrated basic lower crust and/or mantle-derived magmas for their genesis. As a result it appears that the melting processes which affected the lower crust about 300 Ma ago, at the same time as decompression, produced a crustal differentiation contributing to the generation of granitoids which migrated toward high crustal levels. The occurrence of some gabbroic rocks and microgranular mafic enclaves associated with the calc-alkaline plutonic rocks indicates that the mantle contributed both thermally and chemically to granitoid genesis. Nd model ages in granitoids (1.0 - 2.4 Ga) indicate significant addition of juvenile material in late Proterozoic - early Palaeozoic times
RELATIONSHIPS BETWEEN INTERMEDIATE AND ACIDIC ROCKS IN OROGENIC GRANITOID SUITES - PETROLOGICAL, GEOCHEMICAL AND ISOTOPIC (SR, ND, PB) DATA FROM CAPO-VATICANO (SOUTHERN CALABRIA, ITALY) RID A-1229-2011
No full textMajor, trace element and isotopic data are reported for Hercynian granodiorites and tonalites from Capo Vaticano, Calabria, with the aim of clarifying the relationships between acidic and intermediate lithologies in orogenic intrusive suites. These granodiorites (SiO2 = 70.5%-73.5%) are peraluminous, relatively depleted in Rb, U, Th, and Pb, and display a large variation in many geochemical and isotopic parameters. REE show fractionated, cross-cutting chondrite-normalized patterns with small but significant negative Eu anomalies. Initial (290 Ma) Sr and Nd, and present-day Pb isotope ratios are: (Sr-87/Sr-86)290 = 0.7105-0.7110; (Nd-143/Nd-144)290 = 0.51 175-0.51221; Pb-206/Pb-204 = 18.35-18.50; Pb-207/Pb-204 = 15.64-15.76; Pb-208/Pb-204 = 38.51-39.03. Pb isotope ratios determined for separated feldspars show similar Pb-206/Pb-204 and Pb-208/Pb-204 and higher Pb-207/Pb-204 ratios compared to the present-day values for the whole rock. The tonalites (SiO2 = 57.6%-67.3%) are typically calc-alkaline in composition and most of them are weakly peraluminous. They display large heterogeneities in trace-element abundances, REE patterns and Nd and Pb isotope ratios. both between and within individual intrusive units. Sr. Nd and Pb isotopic compositions display a range of values close to that of the associated granodiorites (Sr-87/Sr-86)290 = 0.7099-0.7111; (Nd-143/Nd-144)290 = 0.51185-0.51224; Pb-206/Pb-204 = 18.31-18.56; Pb-207/Pb-204 = 15.65-15.72, Pb-208/Pb-204 = 38.41-39.59. The obtained data indicate that the tonalites and granodiorites share many compositional features which point to a genetic linkage. Likewise, many petrological, geochemical and field data exclude the possibility that all the granodiorites derive from intermediate magmas by any common evolutionary process, such as crystal-liquid fractionation or assimilation-fractional crystallization (AFC), and point to a different genesis for the two rock types. An origin of the granodiorites by the mixing of two separate acidic melts, one of crustal anatectic origin and one probably derived from an intermediate magma by crystal/liquid fractionation or AFC, is suggested by the data presented. The tonalites appear to have been generated by interaction of a mafic magma with crustal end-member(s) with isotopic and geochemical signatures similar to those of the granodiorites. The large involvement of crustal material in the genesis of the Capo Vaticano granitoids is responsible for the many common compositional characteristics observed in the intermediate and acidic rocks. However, a contribution from mantle components is also indicated by petrological and geochemical data, as well as by the occurrence of mafic enclaves commonly present in the tonalites. Nevertheless, the geochemical and isotopic features of such a mantle component appear to be greatly diluted by a large quantity of crustal material involved in the genesis of the studied granitoids
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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Assessment of a shallow magmatic system: The case of the 1888-90 eruption, Vulcano Island, Italy
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