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The pseudotachylyte-mylonite association: an insight into the mechanics of deep earthquakes
Full text linkThe aim of this thesis is to investigate the association of fault rocks formed by seismic deformation with coeval ductile deformation. The only recognised geological record of these two concurrent deformation mechanisms is represented by the relationship between coeval pseudotachylytes (quenched melts produced during seismic slip) and mylonites (high-‐strain rocks deformed in high-temperature ductile flow). The scientific importance of this association of rocks lies in the fact that their existence in rocks exhumed from below the long-‐term brittle/ductile transition is a compelling evidence that rheology of the deep crust cannot be treated simply in terms of brittle and ductile models. By investigating associations of coeval pseudotachylytes and mylonites we aim at giving an original and meaningful contribution to the understanding of the mechanisms involved in the interplay in space and time between seismic deformation and ductile flow.
A model proposed to explain such association of fault rocks is “self-‐localising thermal runaway”, assuming a spontaneous acceleration of localized slip in a ductile shear zone eventually leading to seismic slip and melting. This model is supported by numerical modelling, but its application to nature is disputed and speculative. We analyse a pseudotachylyte-ultramylonite association in exhumed lower crustal, quartz-‐rich metapelites from the Mont Mary nappe of the Western Italian Alps, representing a possible candidate for thermal runaway instability, to find evidence in support or against this process.
• We document by detailed electron backscatter diffraction (EBSD) analysis of quartz-‐rich layers, the progressive microstructural evolution, at nearly constant temperature conditions (550 °C), to high differential stresses (> 200 MPa) and high strain rates (10-‐9 s-‐1) within the most strongly deformed portions of the ultramylonite hosting the pseudotachylyte. This microstructural evolution is associated with a switch in deformation mechanism from grain-size-insensitive to grain-size-sensitive creep assisted by grain boundary sliding and creep cavitation. These latest recorded stages of deformation were still aseismic, as the rate-controlling process was precipitation of oriented biotite in cavitation pores.
• We calculate, by calibrated numerical models, the critical conditions for thermal runaway instability in quartz for a wide range of temperature/strain-‐rate combinations, and determine that deformation in the studied ultramylonite occurred close to the conditions for the instability to occur. At the same time, we estimate that deformation occurred proximal to brittle-ductile transition for such high strain rates.
• We conclude that the observed pseudotachylyte-mylonite association is best explained by transient downward propagation of seismic rupture from the nearby, overlying base of the seismogenic crust; or by earthquake nucleation below the long-term brittle/ductile transition permitted by the downward deflection of the transition after a large seismic event in the upper crust.
Based on the study of wall-rock garnet coseismic fragmentation in the Mont Mary pseudotachylyte-ultramylonite and on garnet preferential melting within the pseudotachylyte, we suggest a general process for garnet disappearance due to thermal shock fragmentation during co-seismic frictional heating. We show that garnet has the lowest thermal shock resistance between the host rock minerals (garnet, plagioclase, quartz, and sillimanite, in an increasing sequence of resistance), and thus underwent extreme comminution leading to total melting within the frictional melt. Our
analysis highlights the critical role of thermal shock as a general process in mineral comminution during the initial stages of co-seismic slip preceding (and promoting) extensive frictional melting.
We also present the preliminary results (mechanical and microstructural) of rotary shear experiments designed to reproduce the formation of Mont Mary pseudotachylytes in the lab.
We extend the study of deep crustal pseudotachylytes and pseudotachylyte-mylonite associations to the Calabrian lower crust (Southern Italy) in a preliminary study that aims at paving the way to a further in-depth analysis of Calabrian pseudotachylytes, which represent a unique information source about the rheology of the granulitic continental lower crust. We present microstructural
evidence for cyclic pseudotachylyte and mylonite development in the dry lower crust and document the first finding of low-‐p/high T, cordierite-bearing, peraluminous pseudotachylytes featuring sillimanite microlites
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
The fate of garnet during (deep-seated) coseismic frictional heating: the role of thermal shock
No full textGarnet stability in high-grade (deep-seated) pseudotachylytes may be obscured by the peculiar thermomechanical properties of garnet. Within garnet-rich high-grade mylonites, the supposedly coeval pseudotachylytes are commonly free or poor of garnet. Based on a study of amphibolite-facies mylonite-pseudotachylyte association of the Mont Mary unit (western Alps) we suggest a general process for garnet disappearance due to thermal shock fragmentation during coseismic frictional heating. We show that garnet has the lowest thermal shock resistance between the host-rock minerals (garnet, plagioclase, quartz, and sillimanite, in an increasing sequence of resistance), and thus underwent extreme comminution leading to total melting within the frictional melt, which was deprived of nuclei for growth of garnet microlites. Our analysis highlights the critical role of thermal shock as a general process in mineral comminution during the initial stages of coseismic slip preceding (and promoting) extensive frictional melting, though the process remains active during these later stages. Our finding has general implications for establishing the coeval development of pseudotachylytes and mylonites and, therefore, for recognizing the evidence of deep earthquakes in exhumed rocks
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
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