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Mécanismes et quantification de la génération d'hydrogène naturel en contexte intracratonique : le cas du Mid-Rift System (Kansas, USA)
No full textNatural hydrogen (H2) has been associated, for a long time, with the serpentinization of ultramafic and mafic rocks located at current lithospheric plate boundaries, in mid-oceanic ridges (MOR) and ophiolitic contexts. Such hydrogen is also found on the continent and is located within intracratonic areas that were not subjected to any significant magmatic or tectonic events over the last hundreds of millions of years. As the exploitation of hydrogen emitted at the MOR is excluded because of its location, intracratonic hydrogen could be considered more attractive. However, the lack of knowledge is still too high for this H2 to be considered a reliable energy source.Kansas (right in the middle of the USA) is home to H2-emitting wells where hydrogen was previously characterized as a flux and associated with the underlying Precambrian basement rocks. The Kansas Precambrian basement was intruded 1.1 Ga ago by the Mid-Rift System (MRS), an aborted rift with a kilometric-scale accumulation of iron-rich rocks being potential H2-generating rocks. The rift is buried below Paleozoic sediments in Kansas et extends over more than 2000 km, up to the Lake Superior Province (Minnesota, USA), where the basement rocks are outcropping.To overcome the global lack of knowledge on intracratonic H2, a mineralogy study on rock samples from the Kansas part of the MRS was conducted. The aim was to identify the potential mechanisms responsible for hydrogen generation. Subsequently, a multimodal and multiscale workflow to quantify hydrogen generation by combining EPMA analysis, a mass transfer evaluation, and X-ray microtomography was proposed. Finally, a field study was conducted in the Minnesota part of the MRS to acquire additional data, including the sampling of emitted gas and their associated waters on which geochemistry analyses were performed.Indeed, the Kansas Precambrian basement in the vicinity of the H2-emitting wells is made of fayalite-bearing monzo-gabbros with evidence of, at least, two events of water-rock interactions (WRI): (1) a deuteric alteration of fayalites during a late magmatic episode, (2) a late episode of fluid circulation at lower temperatures. They both could have led to hydrogen generation. In the Minnesota part of the MRS significant contents of methane (CH4), helium (He), carbon dioxide (CO2), heavier hydrocarbons, and H2 up to 500 ppm are found in dissolved gas and free-gas phases. They have complex isotopic signatures, and it is difficult to distinguish the different isotopic trends. They are, however, associated with reduced (negative Eh) and basic waters typical of WRI such as serpentinization. These results suggest that a part of this hydrogen is generated in the subsurface by serpentinization of the iron-rich rocks of the MRS and consumed with CO2 to produce CH4.This work provides new information on hydrogen related to the Mid-Rift System as well as key elements to better understand the more global subject of intracratonic hydrogen.L'hydrogène naturel (H2) a longtemps été associé uniquement à la serpentinisation des roches ultrabasiques et basiques en contexte de limites de plaques lithosphériques (rides médio-océaniques ou massifs ophiolitiques). Un tel hydrogène a aussi été identifié au milieu des continents, dans des zones qualifiées d'intracratoniques, et caractérisées par une quasi-absence d'activité tectonique et magmatique depuis plusieurs millions d'années. L'exploitation de l'hydrogène généré au niveau de dorsales océaniques étant exclu, l'hydrogène continental, et plus particulièrement intracratonique, pourrait être considérer comme plus attractif. Cependant, l'état actuel des connaissances scientifiques sur cet hydrogène est relativement limité et ne permet pas d'assurer une production à moindres risques et moindres coûts.Le Kansas abrite d'actuels puits émetteurs d'hydrogène naturel. Cet H2 a été, lors de précédentes études, caractérisé comme un flux et associé aux roches sous-jacentes appartenant au socle Précambrien. Ce socle a été intrudé, il y a 1.1 milliards d'années, par le Mid-Rift System (MRS), un rift avorté associé à une accumulation kilométrique de roches riches en fer et potentiellement génératrices d'H2. Ce rift qui est enfoui sous des sédiments paléozoïques au Kansas, s'étend sur plus de 2000 km, jusqu'à la région des grands lacs (Minnesota) où les roches affleurent.Pour combler le déficit de connaissance concernant l'hydrogène intracratonique une étude minéralogique poussée des échantillons de roches provenant de la partie du rift situé au Kansas a été réalisée. L'objectif était d'identifier le mécanisme principal de génération d'H2. Ensuite, une méthodologie d'étude multi-échelle combinant données de microsonde, bilan de transfert de masse, et données de microtomographie par rayons X a été développée, dans le but de quantifier l'H2 généré. Enfin une mission d'échantillonnage d'eau et de gaz dans la zone nord du MRS (Minnesota) a été effectuée. L'objectif était d'acquérir des données additionnelles et de fournir des analyses géochimiques destinées à mieux comprendre le système H2 lié au MRS.Le socle Précambrien du Kansas, dans la zone des puits émetteurs d'H2, est composé de monzo-gabbros riches en fayalites portant des marques d'au moins deux évènements d'interactions eau-roche : (1) un épisode tardi-magmatique d'altération deutérique des fayalites, (2) un épisode tardif de circulation de fluide à plus basse température. Ces évènements pourraient avoir conduit, chacun, à une génération d'H2. Dans la partie du rift se situant au Minnesota, des quantités significatives de méthane (CH4), d'hélium (He), de dioxyde de carbone (CO2), d'hydrocarbures lourds, et d'H2 (jusqu'à 500 ppm) ont été mesurés dans des gaz dissous et des gaz libres. Leur signature isotopique est complexe et il est difficile de distinguer les différents pôles isotopiques. Il est important de noter que ces gaz sont associés, en partie, à des eaux réduites et basiques typiques des réactions eaux-roches comme la serpentinisation. Ainsi, ces résultats suggèrent qu'une partie de l'H2 est généré en subsurface par serpentinisation des roches riches en fer du rift puis consommé avec le CO2 présent pour produire du CH4.Ce travail de thèse a permis de produire de nouvelles données essentielles pour mieux comprendre la génération d'hydrogène dans le MRS mais aussi de manière plus générale dans les zones intracratoniques
Mechanism and quantification of natural hydrogen generation within intracratonic areas : the case of the Mid-Rift System (Kansas, USA)
No full textL'hydrogène naturel (H2) a longtemps été associé uniquement à la serpentinisation des roches ultrabasiques et basiques en contexte de limites de plaques lithosphériques (rides médio-océaniques ou massifs ophiolitiques). Un tel hydrogène a aussi été identifié au milieu des continents, dans des zones qualifiées d'intracratoniques, et caractérisées par une quasi-absence d'activité tectonique et magmatique depuis plusieurs millions d'années. L'exploitation de l'hydrogène généré au niveau de dorsales océaniques étant exclu, l'hydrogène continental, et plus particulièrement intracratonique, pourrait être considérer comme plus attractif. Cependant, l'état actuel des connaissances scientifiques sur cet hydrogène est relativement limité et ne permet pas d'assurer une production à moindres risques et moindres coûts.Le Kansas abrite d'actuels puits émetteurs d'hydrogène naturel. Cet H2 a été, lors de précédentes études, caractérisé comme un flux et associé aux roches sous-jacentes appartenant au socle Précambrien. Ce socle a été intrudé, il y a 1.1 milliards d'années, par le Mid-Rift System (MRS), un rift avorté associé à une accumulation kilométrique de roches riches en fer et potentiellement génératrices d'H2. Ce rift qui est enfoui sous des sédiments paléozoïques au Kansas, s'étend sur plus de 2000 km, jusqu'à la région des grands lacs (Minnesota) où les roches affleurent.Pour combler le déficit de connaissance concernant l'hydrogène intracratonique une étude minéralogique poussée des échantillons de roches provenant de la partie du rift situé au Kansas a été réalisée. L'objectif était d'identifier le mécanisme principal de génération d'H2. Ensuite, une méthodologie d'étude multi-échelle combinant données de microsonde, bilan de transfert de masse, et données de microtomographie par rayons X a été développée, dans le but de quantifier l'H2 généré. Enfin une mission d'échantillonnage d'eau et de gaz dans la zone nord du MRS (Minnesota) a été effectuée. L'objectif était d'acquérir des données additionnelles et de fournir des analyses géochimiques destinées à mieux comprendre le système H2 lié au MRS.Le socle Précambrien du Kansas, dans la zone des puits émetteurs d'H2, est composé de monzo-gabbros riches en fayalites portant des marques d'au moins deux évènements d'interactions eau-roche : (1) un épisode tardi-magmatique d'altération deutérique des fayalites, (2) un épisode tardif de circulation de fluide à plus basse température. Ces évènements pourraient avoir conduit, chacun, à une génération d'H2. Dans la partie du rift se situant au Minnesota, des quantités significatives de méthane (CH4), d'hélium (He), de dioxyde de carbone (CO2), d'hydrocarbures lourds, et d'H2 (jusqu'à 500 ppm) ont été mesurés dans des gaz dissous et des gaz libres. Leur signature isotopique est complexe et il est difficile de distinguer les différents pôles isotopiques. Il est important de noter que ces gaz sont associés, en partie, à des eaux réduites et basiques typiques des réactions eaux-roches comme la serpentinisation. Ainsi, ces résultats suggèrent qu'une partie de l'H2 est généré en subsurface par serpentinisation des roches riches en fer du rift puis consommé avec le CO2 présent pour produire du CH4.Ce travail de thèse a permis de produire de nouvelles données essentielles pour mieux comprendre la génération d'hydrogène dans le MRS mais aussi de manière plus générale dans les zones intracratoniques.Natural hydrogen (H2) has been associated, for a long time, with the serpentinization of ultramafic and mafic rocks located at current lithospheric plate boundaries, in mid-oceanic ridges (MOR) and ophiolitic contexts. Such hydrogen is also found on the continent and is located within intracratonic areas that were not subjected to any significant magmatic or tectonic events over the last hundreds of millions of years. As the exploitation of hydrogen emitted at the MOR is excluded because of its location, intracratonic hydrogen could be considered more attractive. However, the lack of knowledge is still too high for this H2 to be considered a reliable energy source.Kansas (right in the middle of the USA) is home to H2-emitting wells where hydrogen was previously characterized as a flux and associated with the underlying Precambrian basement rocks. The Kansas Precambrian basement was intruded 1.1 Ga ago by the Mid-Rift System (MRS), an aborted rift with a kilometric-scale accumulation of iron-rich rocks being potential H2-generating rocks. The rift is buried below Paleozoic sediments in Kansas et extends over more than 2000 km, up to the Lake Superior Province (Minnesota, USA), where the basement rocks are outcropping.To overcome the global lack of knowledge on intracratonic H2, a mineralogy study on rock samples from the Kansas part of the MRS was conducted. The aim was to identify the potential mechanisms responsible for hydrogen generation. Subsequently, a multimodal and multiscale workflow to quantify hydrogen generation by combining EPMA analysis, a mass transfer evaluation, and X-ray microtomography was proposed. Finally, a field study was conducted in the Minnesota part of the MRS to acquire additional data, including the sampling of emitted gas and their associated waters on which geochemistry analyses were performed.Indeed, the Kansas Precambrian basement in the vicinity of the H2-emitting wells is made of fayalite-bearing monzo-gabbros with evidence of, at least, two events of water-rock interactions (WRI): (1) a deuteric alteration of fayalites during a late magmatic episode, (2) a late episode of fluid circulation at lower temperatures. They both could have led to hydrogen generation. In the Minnesota part of the MRS significant contents of methane (CH4), helium (He), carbon dioxide (CO2), heavier hydrocarbons, and H2 up to 500 ppm are found in dissolved gas and free-gas phases. They have complex isotopic signatures, and it is difficult to distinguish the different isotopic trends. They are, however, associated with reduced (negative Eh) and basic waters typical of WRI such as serpentinization. These results suggest that a part of this hydrogen is generated in the subsurface by serpentinization of the iron-rich rocks of the MRS and consumed with CO2 to produce CH4.This work provides new information on hydrogen related to the Mid-Rift System as well as key elements to better understand the more global subject of intracratonic hydrogen
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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