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Your search keyword '"Chassé, A."' showing total 216 results
Start Over Author "Chassé, A." Publisher elsevier b.v.
216 results on '"Chassé, A."'

21. Multiscale processes controlling niobium mobility during supergene weathering.

Author

Bollaert, Quentin, Chassé, Mathieu, Allard, Thierry, Courtin, Alexandra, Galoisy, Laurence, Landrot, Gautier, Quantin, Cécile, Vantelon, Delphine, and Calas, Georges

Subjects
*NIOBIUM, *WEATHERING, *REGOLITH, *CHEMICAL speciation, *X-ray absorption, *X-ray spectroscopy, *TANTALUM
Abstract

Niobium (Nb) is one of the most immobile elements during supergene weathering, widely used for mass-balance calculations, despite elusive information on the mechanisms controlling its dynamics in the critical zone. Here, a multiscale approach, from weathering profile to atomic-scale, is developed to monitor Nb speciation along a thick (about 50 m) lateritic regolith formed over the Pitinga pluton (Amazonas, Brazil). In the A-type parent granite, Nb is mainly hosted in ilmenite (1.5–2 wt% Nb 2 O 5) and, to a lesser extent, in rutile (2–3 wt% Nb 2 O 5). A quantitative assessment of the average Nb speciation from the parent rock to the upper horizons has been carried out by combining spectroscopic and spatially-resolved chemical techniques. The contribution of Nb-bearing Ti oxides (2–6 wt% Nb 2 O 5) and Fe oxides (0.1–0.3 wt% Nb 2 O 5) in the average Nb speciation increases with the degree of weathering and reaches 80% in the most altered horizon. This unusual Nb speciation results from the nature of the primary Nb carriers, less resistant to weathering than common Nb ore minerals such as pyrochlore. X-ray absorption spectroscopy demonstrates that Nb released from the weathering of ilmenite substitutes for Fe and Ti in goethite and Ti oxides, respectively, providing atomic-scale evidence of the high affinity of Nb for these phases. Elemental mobility of Nb, Ta and Sn followed by geochemical mass-transfer calculations evidences lateral transport from Nb-Sn-enriched laterites developed over the surrounding Nb-enriched facies of the Pitinga granite to the studied profile. Elements such as Ti, Zr and Hf, often considered immobile, are leached or redistributed in the studied profile. Our results demonstrate Nb remobilization during intense weathering. Although Nb scavenging by secondary Fe and Ti oxides limits Nb mobility at the mineral scale, this work questions the unrestricted use of Nb as a chemical invariant during surficial alteration processes. [ABSTRACT FROM AUTHOR]

Published
2023
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29. Are young candidates "sacrificial lambs"? Evidence from the 2012, 2017, and 2022 French legislative elections.

Author

Gélix, Camille and Chassé, Philippe

Subjects
*YOUNG adults, *OLDER people, *POLITICAL parties, *OLDER men, *LAMBS
Abstract

The underrepresentation of young adults is widespread in the parliaments of Western democracies. Yet evidence suggests that voters do not have a negative bias towards young candidates. In this article, we focus on another factor that may contribute to youth underrepresentation: the level of competitiveness in districts where political parties nominate young people. Using data on all candidates who ran for a major political party/coalition in the 2012, 2017, and 2022 French legislative elections, we attempt to determine whether young adults tend to be nominated in districts where they have little or no chance of winning. To do so, we use three different measures of district competitiveness. Our results show that young people – and especially young women – are more likely than others to be "sacrificial lambs". Our analyses nevertheless indicate that men aged between 31 and 35 have become almost as competitive as older people in 2022. [ABSTRACT FROM AUTHOR]

Published
2024
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