1,721,051 research outputs found
Ca-distribution between almandine-rich garnet and plagioclase in pelitic and psammitic schists from the metamorphic basement of north-eastern Sardinia
No full textGarnet and plagioclase pairs from fourteen selected samples, from garnet to sillimanite zones, collected along a NS traverse throughout the metamorphic basement of NE Sardinia, have been analyzed by microprobe. Beyond the garnet isograd, plagioclase has albitic composition and the garnet (a Ca-rich almandine) shows Ca/ Ca+Mg+Fe ratios of about 0.35-0.30, fairly constant from core to rim. Towards the North, still in the garnet zone, when on the large albitic core of plagioclase a thin and discontinuous oligoclasic rim (An22-An18) formed, we observe in the garnet edge an abrupt decrease of the Ca/Ca+Mg+Fe ratio (0.27-0.16). In the staurolite and sillimanite zones garnet does not show significant Ca-zoning and it is characterized by low Ca content (Ca/Ca+Mg+Fe<0.1); the coexisting plagioclase has oligoclasic (An16-An27) composition. The chemical data and the microstructural evidence on growth time indicate that the garnet and plagioclase had a strong mutual interference in determining the relative Ca distribution. The most relevant reactions are discussed and, in particular, the antipathetical Ca-zoning, recorded by garnet and plagioclase in the garnet zone, is considered as the evidence of temperature increase during growth of the two minerals. It is also suggested that the sharp variation of Ca content at the garnet edge was controlled by the discontinuous nature of plagioclase solid solution in the "peristeritic" range. The order of appearance of garnet and oligoclase in the basement of NE Sardinia is also discussed in comparison with other well known metamorphic sequence (Vermont, New Zealand and Dalradian). It is concluded that the different order of appearance is controlled other than the different nature of the calcic phases in the lower grade zones also by the {Mathematical expression} in the fluid phase. © 1982 Springer-Verlag
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
Regional metamorphism and P-T evolution of the Ross Orogen in northern Victoria Land (Antarctica): a review
No full textThe main focus of this paper is on the petrological evolution of medium- to high-grade metamorphic units in the Wilson Terrane, the westernmost lithotectonic unit of the Ross Orogen in northern Victoria Land. The petrological data set is reviewed for all areas where P-T-t paths have been reconstructed and geochronological data are sufficiently complete to provide an overview of the regional metamorphic evolution of a ca. 600 km long segment of the Ross Orogen, from its termination along the Pacific coast to the Eisenhower Range near the Ross Sea coast. Petrological evidence reveals that different lithological units of the Wilson Terrane equate with distinct lithotectonic metamorphic complexes with partly independent P-T-t histories. In spite of the wide range of estimated peak metamorphic conditions, and variability in both shape of the P-T path (clockwise or counter-clockwise) and type of retrograde evolution (isobaric cooling or cooling/unloading), the reviewed P-T-t trajectories consistently support a setting of evolving subduction and accretion in the context of a Palaeozoic cordilleran-type active margin
Ultra high pressure metamorphism in felsic rocks: the garnet – phengite gneisses and quartzites from Lanterman Range (Antarctica)
No full textMesostructural and microstructural relations between eclogitic boudins and country gneisses in the Ross Orogen of the Lanterman Range (Northern Victoria Land, Antarctica) are in some areas characterized by interlayering with sharp contacts on a cm scale, which indicate that the two rock-types underwent a common metamorphic evolution. Contrary to many other UHP felsic rocks that only preserve a poor record of the HP stage, the studied rocks have recorded a metamorphic history ranging from initial prograde amphibolite facies through the eclogite facies to the retrogressive amphibolite facies. The prograde amphibolite stage is documented by garnet relics preserving prograde zoning and bearing biotite, plagioclase, muscovite, phengite and rutile inclusions. The eclogite stage is characterized by the coexistence of phengite with pyrope-grossularite rich garnet, the latter containing phengite and paragonite inclusions, and by radial fractures within garnet around quartz pseudomorphs after coesite. Symplectites have formed during the amphibolite-facies retrogression. They consist mainly of biotite + plagioclase around phengite and garnet; muscovite, biotite and plagioclase grew along the main foliation. The reconstructed metamorphic evolution, involves a steep prograde and retrograde PT path as well as a HP-T peak. Along with the geochronological evidence of fast exhumation, this supports a model of arc-continent collision, with the HP rocks belonging to the over-riding plate. Their exhumation is mainly controlled by extension related to renewed "rollback" of subduction in front of the orogenic zone
Sudoite, a rock-forming mineral in Verrucano of the Northern Apennines (Italy) and the sudoite-chloritoid-pyrophyllite assemblage in prograde metamorphism
No full textSudoite, the di-trioctahedral chlorite with ideal composition (Mg2Al)(Al2)(Si3Al)O10(OH)8 is a widespread rock-forming mineral in meta-siltstones and psammites of the Verrucano sequence of the Northern Apennines. Sub-ellipsoidal aggregates, probably derived from muscovite clasts, consisting of sudoite, pyrophyllite and muscovite, are common; sudoite may also occur as thin blades in the rock matrix. The co-existence of sudoite, Ferich chloritoid and pyrophyllite, reported here for the first time, has been observed in specimens from the M. Argentario and Monticiano-Roccastrada areas. This three-phase assemblage, diagnostic of a specific metamorphic facies, may be a tool for detailed zonation of low-grade terranes
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