Devenir des éléments métalliques en milieu hydrothermal profond : partition dissous-particulaire effective et spéciation dans le mélange fluide hydrothermal-eau de mer précoce

Abstract : Forty years after the discovery of deep hydrothermal circulation, chemical processes occurring in the early mixing between hydrothermal vent fluids and deep seawater are still not fully constrained. This thesis, whose the originality lies on the systematic use of in situ filtration, report on the partitioning of major metals (mainly Fe, Cu, Zn, Ba and Ca) between the dissolved (< 0.45 μm) and particulate (> 0.45 μm) phases in the early mixing of several black and clear smokers from the Lucky Strike vent field (37°N, MAR). The behavior and the speciation of Cu in the dissolved fraction are then deeper explored by performing ligands competition and voltammetric measurements. Our results first demonstrate the importance of the in situ filtration to restrict the bias induced by precipitation reactions or particles redissolution potentially occurring postsampling.The examination of the fluids collected at several occasions and on a wide range of smokers (240 samples) shows a spatial variability of chemical signatures along the east-west axis of the hydrothermal field. Among metals studied, most of Fe, Ca and Ba are measured as dissolved species whereas Cu and Zn are mainly found as particles. In the initial part of the mixing (50-150°C, dMn > 50 μM), the particulate pool is dominated by sphalerite (or wurtzite) and chalcopyrite, with generally lower amount of pyrite. In this zone, chemical changes seem kinetically limited and fluids collected display a chemical signature close to that of the end-members. However, as the hydrothermal fluid progressively mixes with seawater (4-50°C, dMn < 50 μm), the partitioning of some alkali and alkaline earth metals (Ca, Ba, Mg and Sr) between the two phases is deeply affected by precipitation of sulfates. Unlike thermodynamic predictions, precipitation of anhydrite, barite and potentially caminite is observed in the colder part of the mixing (4-50°C). The large increase of pH in this area also drives the beginning of Fe oxides precipitation. Finally, the dissolved Cu-ligands detected seem to be mainly inorganic sulfides originating from the hydrothermal fluid.
Document type :
Theses
Complete list of metadatas

Cited literature [292 references]  Display  Hide  Download

https://tel.archives-ouvertes.fr/tel-01780170
Contributor : Abes Star <>
Submitted on : Friday, April 27, 2018 - 11:29:06 AM
Last modification on : Saturday, April 28, 2018 - 1:17:55 AM
Long-term archiving on : Tuesday, September 25, 2018 - 5:15:08 PM

File

These-2017-SML-Chimie_marine-C...
Version validated by the jury (STAR)

Identifiers

  • HAL Id : tel-01780170, version 1

Collections

Citation

Laura Cotte. Devenir des éléments métalliques en milieu hydrothermal profond : partition dissous-particulaire effective et spéciation dans le mélange fluide hydrothermal-eau de mer précoce. Autre. Université de Bretagne occidentale - Brest, 2017. Français. ⟨NNT : 2017BRES0116⟩. ⟨tel-01780170⟩

Share

Metrics

Record views

164

Files downloads

231