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TRANSITION FROM PROTOMYLONITE TO ULTRAMYLONITE IN THE VARISCAN LEUCOGRANITE FROM MONTE GRIGHINI COMPLEX, WEST-CENTRAL SARDINIA: PRELIMINARY PETROGRAPHIC AND PETROPHYSICAL DATA
No full textMonte Grighini Complex is a NW-SE elongated dome-shaped metamorphic complex which outcrops in central Sardinia in the eastern side of Campidano graben. This Complex consists of a pile of variscan Nappe. From top to bottom they are: Gerrei Unit, Castello Medusa Unit, M. Grighini Unit.
Gerrei Unit (Upper Unit) crops out along the Flumendosa antiform and consists of Porfiroidi auct. (Middle Ordovician), metasandstone, metavolcanics, Upper Ordovician-Silurian sedimentary succession and Devonian limestones (Carmignani et al., 2001). In the Monte Grighini area, the Gerrei Unit is made up of porphiroids, phyllites and mylonitic granitoids outcropping in the south-west of the complex (Musumeci 1991). This Unit has been affected by polyphasic Variscan tectonic events (D1,D2) followed by a late D3 shear deformation. D1 gives rise to NW-SE isoclinals folds with sub-horizontal axial plane schistosity (S1). D2 event causes prevailing simple shear deformation which results in structure and microstructure related to NE-SW compressional event (Carosi et al., 1990).
The Castello Medusa Unit crops out in tectonic windows along the Flumendosa antiform. It consists of a sedimentary succession made up of metasandstones to shales and limestones of Cambrian-Carboniferous age.
The Monte Grighini Unit (Lower Unit), located in the north-east side of the complex, shows the higher metamorphic grade represented by mostly mylonitic micaschist and gneiss of amphibolite facies.
In this Unit, a D2 deformational event gave rise to a pervasive S2 schistosity deforming previous D1 structures and transposing the S1 schistosity.
Monte Grighini Unit is also intruded by a suite of granitoids, mostly monzogranite and leucogranite (Musumeci 1992). Rb/Sr and Ar/Ar radiometric data give an age of about 305-300 Ma (Carmignani et al., 1987; Laurenzi et al., 1991).
Along the southern side, the granitoids are overlained by Upper Unit with the contact marked by a cataclastic fault zone. The leucogranite can be found mostly close to the cataclastic fault zone. Granitoids follow the regional trend (NW-SE) and show a pervasive subvertical schistosity and mineralogical lineation related to the late D3 deformation event.
Several outcrops show a rapid change in the intensity of mylonitic deformation. One of these has been investigated in some detail. The studied outcrop in 1.5 metres shows a transition from slightly to strongly deformed leucogranite. On the basis of granulometric, chromatic and schistosity morphology, five layers have been identified from each of which were taken some samples. The layer subdivision follow the pervasive foliation that affects the entire outcrop with N162°-N170° direction and 60°-65° W dipping.
The firs layer (L1) consists of about 40 cm of massive, coarse-grained, leucocratic rock with just a mild foliation and a moderate alteration grade. At the outcrop scale, it is possible to recognize plagioclase and K-feldspar phenocrysts and dark biotite layers parallel to the main foliation.
Moving toward NW there is a sharp transition to a thin (4 cm) strongly foliated, very fine-grained rock layer (L2). This layer consists of very thin dark- and light-colored alternating levels.
Layer L3, 10 cm in thickness, is similar to the previous one but shows a more spaced foliation and a coarser grain size. The color becomes darker than L2, due to millimetric trails and lenses of mafic minerals (biotite). In this layer the foliation envelopes the millimetric crystals aggregates.
Layer L4 (70 cm thick) is light-colored as compared to layer L3 and the alternating levels appear to be thicker. In this Layer grain size increases again, several minerals can be observed at the naked eye and foliation appears less pervasive than the previous layer L3.
In Layer 5, (30 cm thick) millimetric-thick very fine grained levels alternate with prevailing medium grained ones. Coarse-grained portion appear as a microcrystalline matrix with lens and levels of mafic minerals.
Several thin sections has been realized for each level for microstructural, mineralogical, and petrographic analyses.
Mylonitic granitoid consists of the following paragenesis: quartz, k-felspar, plagioclase, muscovite, biotite, iron oxides and ± tourmaline, ± apatite, ± zircon, ± epidote.
Almost all samples are characterized by k-feldspar phenocrysts within a quartz + phyllosilicate-rich matrix. k-felspar porphyroclasts sometimes show antithetic microfaults.
Generally quartz has typical fabric of dynamic recrystallisation: relics of large old quartz grain pass laterally into domains of recrystallised small grains (50- 100 μm).
L1 is characterized by k-feldspar, quartz and plagioclase phenocrysts, floating in a matrix of microcrystalline quartz and phillosilicate-rich levels (protomylonite). k-feldspar phenocrysts are generally fractured and sometimes show albite exsolutions (perthite). Quartz occurs mostly as microcrystalline lenses and bands which follow the weak foliation. Plagioclase range in composition between albite and oligoclase.
Phyllosilicates (largely biotite and muscovite) occur in thin trails and sometimes submillmetric crystals arranged along the foliation. Towards the ultramylonitic zone, muscovite content decreases up to its almost complete disappearance.
Based on its average porphyroclast/matrix ratio of about 60/40, the rock can be classified as protomylonite (Higgins, 1971).
Layer 2 is characterized by a strong shift to ultramylonitic conditions with a porphyroclast/matrix ratio of 2/98. In this layer it is not possible to distinguish any mineral except some strongly fractured k-feldspar relics.
In Layer 3 porphyroclast/matrix ratio decreases up to 30/70 whereas the grain size increase. This sample can be classified as mylonite. In this layer clusters of euhedral tourmaline (?) crystals not following the pervasive rock foliation have been found. Muscovite has been rarely found.
In layer L4 the texture is again protomylonitic, characterized by increasing grain size and phenocrists abundance (60/40 porphyroclast/matrix ratio); micas are well visible in these samples with a local intergrowth of biotite and muscovite.
Layer L5 again shows that porphyroclast/matrix ratio varying from 40/60 to 25/75 therefore it can be classified as mylonite. Fractures are filled by euhedral and microcrystalline quartz. In this levels locally occurs millimetric ultramylonitic trails.
Field observations and petrographic analyses suggest that protomylonite, mylonite and ultramylonite repeteadly alternate at the centrimetric to decimetric scale
Re-equilibration history of retrogressed eclogites hosted in the medium- grade metamorphic Complex from north-central Sardinia
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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
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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