1,721,115 research outputs found
Chromosome analysis of Eoleptestheria ticinensis and Leptestheria dahalacensis (Branchiopoda, Spinicaudata)
No full textChromosome analysis of Italian populations of Spinicaudata, Eoleptestheria ticinensis and Leptestheria dahalacensis (Leptestheriidae), shows 2n = 10 chromosomes, like as the other Spinicaudata, Limnadia lenticularis (Limnadiidae). Some male meiotic metaphase I with 2 univalents probably suggest a male heterogamy as evidenced in Anostraca. Haploid chromosome number of Spinicaudata appears very similar with those of well investigated Notostraca genus and comparable with those of Anostraca and Cladocera ones
Residence time analysis of active volcanic systems:Rb-Sr isotope study of Ischia and Pantelleria
No full textNumerous active and potentially high-risk volcanoes do occur in the Italian peninsula and therefore understanding their dynamics is crucial for volcanic hazard assessment. Here we present a study on the active volcanic systems of Ischia and Pantelleria, representing two high-silica volcanoes emplaced in subduction related and within-plate geodynamic settings, respectively.
Ischia has erupted in a subduction-related setting and it is characterised by a continuous transition from trachy-basalt to phonolite. The geochemical and radiogenic isotope data of its volcanic products demonstrate a two-step evolutive process: the first step, controlled by fractional crystallization plus crustal assimilation (AFC), drives magma composition from trachy-basalt to moderately differentiated trachyte; the second step, controlled only by fractional crystallisation (FC), drives the magma composition to the more differentiated products (phonolite) determining very low Sr (a few ppm) and high Rb (>500 ppm) contents due to extreme plagioclase and K-feldspar fractionation.
Pantelleria is located in a witin-plate setting and it is characterised by a bimodal magmatism of alkali-balsalt and differentiated products passing from trachyte to peralkaline ryolite (i.e. Pantellerite), through FC processes. Pantelleritic rocks also show extremely low Sr and high Rb contents.
The active volcanic systems of Ischia and Pantelleria, although belonging to different geodynamic settings, are characterized by the occurrence of strongly differentiated products with high Rb/Sr and anomalously high Sr isotope compositions that cannot be justified by the assimilation of crustal material.
This characteristic could be explained by 87Sr in-growth in long-lived magma chambers. To explore this hypothesis we carefully screened a number of evolved samples from Ischia and Pantelleria, on which we separated their rock-forming minerals (sanidine and clinopyroxene) and glass to determine Rb and Sr content by isotope dilution, along with Sr isotope composition. The extremely low diffusion coefficients of Sr in feldspar and clinopyroxene makes them perfect candidates to estimate the timing of crystallisation and, by inference, the magma residence time. The calculated crystallization times are here discussed in terms of the chemical and physical characteristic of the magmas
Geochemical modeling of acid–basic magma interaction in the Sardinia–Corsica Batholith: the case study of Sarrabus, southeastern Sardinia, Italy
No full textThe Hercynian intrusive rocks outcropping in the Sarrabus area, southeastern Sardinia, Italy, consist of microgranular mafic enclave (MME)-bearing granites (>95%) associated with coeval stratified gabbroic complexes and basic septa (BS) (<5%). The coexistence of partially molten magmas of contrasting composition offers the opportunity to study interaction processes in intrusive environments and the geochemical characteristics of hybrid products. In this paper we present a petrogenetic model for the differentiation of basic magmas injected into coeval, partially molten, granite magmas, on the basis of field, petrographic and geochemical data. Samples from the stratified basic complex of Capo Carbonara (CCB) and BS were grouped into outer and inner facies based upon the sampling sites close to, or far away (a few meters) the host granite contact. MME were grouped according to their composition: gabbro-diorites and tonalites. The inner facies of the basic complex and BS represent cumulus of amphibole+clinopyroxene+plagioclase with trapped intercumulus liquid. The calculated chemical composition of the parental magma is well within those calculated for the Hercynian basic magmas of the Sardinia–Corsica Batholith. The geochemical features of the MME and the outer facies of the basic complex and BS establish an origin by mixing/mingling mechanisms controlled by fractional crystallisation and contamination (CFC) of the parental magma of the inner gabbroic facies. Additional refinements of the model, addressed in this paper, establish the occurrence of a filter pressing process operating during the CFC evolution of the basic magma injected into the acid magma
Residence Time Analysis of the Active Volcanic System of Ischia, Italy.
Full text linkThe Italian peninsula hosts numerous active and potentially high-risk volcanoes, therefore understanding their dynamics is fundamental for volcanic hazard assessment. Here we present a study on the active volcanic system of Ischia, whose products have a potassic affinity with a subduction-related signature.
Volcanic rocks are characterised by a continuous transition from trachy-basalt to trachyte and minor phonolite. Geochemical and radiogenic isotope (Sr, Nd, Pb, Hf) data are consistent with a closed-system, two-step crystal fractionation process: the first step, drives magma composition from trachy-basalt to moderately differentiated trachyte; the second step drives the magma composition to the more differentiated products (trachyte and minor phonolite) determining very low Sr (a few ppm) and high Rb (>500 ppm) contents due to extreme plagioclase and K-feldspar fractionation.
A number of these highly differentiated trachytes have, along with high Rb/Sr, anomalously high Sr isotope composition that cannot be justified by assimilation of crustal material.
This characteristic could be explained by 87Sr in-growth in a long-lived magma chamber. To explore this hypothesis we carefully screened a number of evolved samples on which we analysed feldspar-glass pairs through Rb-Sr isotope dilution method. The extremely low diffusion coefficients of Sr in feldspars makes them perfect candidates to estimate the timing of crystallisation and, by inference, the magma residence time. The calculated crystallisation times are here discussed in terms of magma chamber dynamics
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
Reproductive cycle of the common sole Sole vulgaris Quensel, 1806, in the northern Adriatic Sea
No full textAnatomical and cytotogical modifications of the ovary of Solea vulgaris Quensel from the northern Adriatic Sea were studied over a one-year period. Seven stages of ovarian development were observed. The gonadosomatic index increased rapidly during the reproductive season from December to March, when the majority of oocyte growth (>20010-6m in diameter) occurred. Hydrated oocytes immediately before spawning reach 136010-6m. During spring, summer and autumn (from April to November) previtellogenic oocytes (<20010-6m) occurred
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
Mo and stable U isotopes as tracers for subduction components in the Quaternary West-Mediterrean potassic and ultrapotassic magmatism
No full textThe central-western Mediterranean is one of the most important areas on Earth for studying subduction-related potassic and ultrapotassic magmatism. In a very restricted area, leucite-free (lamproite) and leucite-bearing (kamafugite, leucitite, and plagioleucitite) ultrapotassic rocks have been emplaced and are associated with shoshonites and high-K calc-alkaline volcanic rocks.
Despite their alkaline characteristics, the least evolved Italian ultrapotassic rocks associated with destructive plate margins invariably show a strong depletion of Nb and Ta along with the highest levels of incompatible trace elements ever seen in any volcanic arc. These characteristics are thought to be derived through the recycling of sediments via subduction within the mantle wedge, and their extreme trace element enrichments make them unique for understanding the roles of different subduction-related metasomatic agents (e.g. silico-clastic vs carbonate). In fact, the variable compositions of the sedimentary materials, subducted along the Adriatic slab and transported into the overlying mantle forming a vein network, could explain the distinct geochemical signature of each Italian magmatic region (Avanzinelli et al., 2009).
We propose to investigate this issue considering two stable isotopic systematics that are perceptive to redox condition-related isotopic fractionation. We measured Mo and stable U isotopes with the high-resolution MC-ICP-MS (Neptune), using a double-spike technique, on selected volcanic rocks from three Italian magmatic provinces and representative samples of subducting sediments.
Molybdenum has seven stable isotopes, which have been shown to fractionate during the incorporation into oceanic sediments. Under oxic conditions, Mo adsorbs to particles into the sediment, particularly when Fe-Mn oxides are present, producing lighter isotopic composition (δ98Mo/95Mo), whilst is quantitatively removed in anoxic conditions, leaving sediments with a heavier isotopic signature. The recently observed variability in natural 238U/235U values (different from the widely used “consensus” value of 137.88) due to isotopic fractionation during the redox transition between the U(IV) and U(VI) oxidation states, produces as well as Mo isotopes, a lighter isotopic composition (δ238U/235U) in oxic sediments compared to a heavier composition in anoxic sediments. We interpret those results in order to recognize the U and Mo isotopic signature of sediments, with different lithology and chemical composition, recorded into the selected volcanic rocks, and to set new constraints on the metasomatic agents responsible for the transition from silica oversaturated lamproite-like to strongly silica undersaturated HKS magmas
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