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Contribution du flanc ouest des Andes du Nord du Chili aux stades précoces de l'orogenèse Andine : une étude de géologie structurale, thermochronologie et modélisation analogique
No full textLes chaînes de montagnes se forment le long des limites de plaques convergentes par raccourcissement et épaississement de la croûte, en particulier lorsque deux plaques continentales entrent en collision. A l'inverse, les zones de subduction ne sont généralement pas associées à des reliefs (hormis les volcans) et à de la déformation de la plaque supérieure. Il existe cependant des exceptions : le long de la marge ouest de l'Amérique du Sud, les Andes constituent en effet un exemple moderne et actif de telles chaînes, dites de subduction. La majeure partie de la convergence est dans ce cas absorbée le long de l'interplaque de subduction sous la forme de grands séismes, mais une petite fraction de cette convergence contribue à la déformation de la plaque continentale supérieure et à la formation de l'un des plus grands reliefs actuels : la Cordillère des Andes et le plateau de l'Altiplano-Puna. La formation de l'orogène andin a probablement débuté vers la fin du Crétacé - début du Cénozoïque le long du flanc ouest de la chaîne, à ~16'22ºS, et s'est poursuivie depuis par la propagation de la déformation vers l'est, donc vers l'intérieur du continent sud-américain. Si les structures du plateau de l'Altiplano-Puna et des chaînes Est-andins sont maintenant bien connues, celles du flanc ouest restent mal documentées et leur contribution à l'épaississement crustal mal comprise. De ces points émergent plusieurs questions majeures non résolues : Pourquoi les Andes, dans un contexte de subduction ? Où et quand l'orogenèse andine s'est-elle initiée, plus précisément ? Comment la déformation a-t-elle été accommodée le long du flanc ouest, en particulier lors des premiers stades ? Pour répondre à ces questions, la première partie de ce travail documente les structures géologiques formant le flanc ouest des Andes à ~20'22ºS, quantifie leur contribution au raccourcissement andin et apporte des contraintes temporelles sur leur déformation. Pour cela, de nouvelles coupes géologiques sont proposées à partir d'observations de terrain, d'images satellites, de données topographiques et de profils sismiques existants, au Nord du Chili. L'acquisition et la modélisation de nouvelles données thermochronologiques complètent le tableau en documentant l'âge et la durée de l'exhumation du socle. Les résultats indiquent que le raccourcissement multi-kilométrique a été accommodé par deux structures majeures à vergence ouest : l'Andean Basement Thrust (ABT) et le West Andean Fold-Thrust-belt (WAFTB). Le WAFTB a été actif principalement entre ~68'29 Ma (voire ~68'44 Ma), tandis que l'activité de l'ABT a été datée à ~100'45 Ma grâce aux données thermochronologiques. Ces résultats fournissent de nouveaux indicateurs sur les premiers stades andins à ~20'22ºS, et apportent de nouveaux éléments pour répondre à "où", "quand" et "comment" les Andes sont apparues. La deuxième partie de cette thèse étudie les conditions qui amènent au raccourcissement de la plaque continentale au-dessus d'une zone de subduction. Des modèles analogiques, basés sur un dispositif expérimental original, permettent d'explorer ces questions. Ils montrent que la déformation de la plaque chevauchante se produit lorsqu'un flux mantellique sous-jacent pousse la plaque océanique subductante contre le continent, lui-même fixé à une paroi. Pour la première fois à notre connaissance, un modèle analogique ressemblant aux Andes Centrales est proposé, dans lequel la localisation de la déformation est favorisée par une lithosphère continentale pré-structurée et faible. Ces expériences contribuent donc à comprendre "pourquoi" les Andes se sont formées dans un contexte de subduction, et ouvrent des perspectives prometteuses pour de futures études.Orogenic growth results from long-lasting plate convergence engendering tectonic shortening in association with crustal thickening. This process is, as such, well understood in collisional settings, where two continental plates collide. On the contrary, subduction zones most often do not produce any topographic building, except for volcanism, even if the general tectonic configuration is comparable: the convergence of two plates. However, there exist exceptions with mountain-building in the context of oceanic plate subduction. Along the western margin of South America, the Andes stand as one of the most active convergent plate boundaries and are a modern active caseexample of such subduction- (or Cordilleran-) type orogen. Here, the oceanic Nazca plate plunges beneath the South American continent. The major part of the convergence is absorbed by the subduction megathrust in the form of large earthquakes (magnitude Mw ≥ 8), but a small fraction of this convergence contributes to the deformation of the upper continental plate over millions of years and to the formation of one of the largest reliefs at the Earth’s surface: the Andean Cordilleras and the Altiplano-Puna plateau in between. Andean mountain-building initiated by Late Cretaceous to Early Cenozoic times along the western Andes at the level the Bolivian Orocline (between ~16–22°S), and proceeded since then with the progressive eastward propagation of deformation onto the South American continent. Most of the previous studies have essentially focused on the structures of the Altiplano-Puna plateau and on those of the various cordilleras to the east, whereas the structures of the western Andean flank remain under-studied and their contribution to the significant topographic relief and crustal thickness of this part of the orogen poorly understood. From these points emerge some major unresolved questions, which are addressed in this thesis work: Why did Andean orogeny initiate? Can we more precisely document where and when it initiated along the western flank of the Andes? Can we better resolve how deformation proceeded, in particular in the early stages? To solve these questions, the first part of this work aims at describing the geological structures forming the western Central Andes, quantifying their contribution to crustal shortening and better constraining their timing and kinematics. For that, a structural geology approach is first followed to build new cross-sections, based on field and satellite observations, combined with geomorphology and existing data on seismic profiles, along the West Andean flank in Northern Chili at ~20–22°S. The acquisition and modeling of new low-temperature thermochronological data from the same region in Northern Chile allows to better assess the timing of basement exhumation and from there the timing of initiation and ending of deformation. This work highlight that multikilometric shortening was accommodated by two major structural features within the West Andean flank at ~20–22°S, which are the Andean Basement Thrust (ABT) bringing Paleozoic basement over folded Mesozoic series, and the west-vergent West Andean Fold-and-Thrust-Belt (WAFTB) deforming Mesozoic and Cenozoic sediments. The period of main activity of the WAFTB has been determined between ~68–29 Ma (possibly ~68–44 Ma). The low-thermochronological study allowed for constraining the timing of the exhumation through the ABT, with its main activity between ~100–45 Ma, documenting as such the early stages of Andean orogeny along the West Andean flank at ~20–22°S, and brings new elements of answer to the questions of where, when and how the Andes arised. The second and last part of this thesis investigated the possible conditions that lead to compression and subsequent crustal shortening in the upper plate of a subduction zone. A short series of analog experiments, based on a novel experimental set-up, allowed to explore these questions. (…
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
Les séismes destructeurs du 6 Février 2023 en Turquie et en Syrie, un doublet sismique sur la zone de faille Est Anatolienne
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