Geochemistry of Li isotopes in basalts - Geochemistry of MORB from the South Pacific

This work is divided in two independent parts which concerns respectively: the geochemistry of lithium isotopes and the geochemical variability in South Pacific MORB. The use of lithium isotopes in the Earth sciences is firstly addressed through the study of lavas from the Chaîne des Puys. Samples f...

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Bibliographic Details
Main Author: Hamelin, Cédric
Other Authors: Domaines Océaniques (LDO), Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Observatoire des Sciences de l'Univers-Institut d'écologie et environnement-Centre National de la Recherche Scientifique (CNRS), Université de Bretagne occidentale - Brest, Jean-Alix Barrat(barrat@univ-brest.fr)
Format: Doctoral or Postdoctoral Thesis
Language:French
Published: HAL CCSD 2008
Subjects:
Géochimie isotopique
isotopes stables
Lithium
Chaîne des Puys
AFC
MORB
hétérogénéités mantelliques
[SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry
Antarctic
Pacific
Antarc*
Online Access:https://theses.hal.science/tel-00344949
https://theses.hal.science/tel-00344949/document
https://theses.hal.science/tel-00344949/file/These_Cedric_Hamelin.pdf
Description
Summary:This work is divided in two independent parts which concerns respectively: the geochemistry of lithium isotopes and the geochemical variability in South Pacific MORB. The use of lithium isotopes in the Earth sciences is firstly addressed through the study of lavas from the Chaîne des Puys. Samples from this intraplate volcanic suite can provide constraints on the values of Li isotopic composition in the lower continental crust and in the HIMU mantle beneath the Massif Central. The second study examines the behavior of Li isotopes during the cooling of lavas. In situ analysis of the isotopic composition of Li has been performed through olivine phenocrysts in a picrite sample. These analyses, conducted by ion probe, have highlighted an isotopic fractionation induced by chemical diffusion of Li into the crystals during the cooling time. The second part of this work presents the results of the PACANTARCTIC2 cruise. Major, trace element and Sr-Nd-Pb-Hf isotope data in basalts collected along the Pacific Antarctic ridge axis between 53 and 41°S, far from any hotspot influence, reveal tight coherent geochemical variations within the depleted mantle. This along ridge geochemical variability illustrates the mantle heterogeneity at different scales. These variations are closely related to the morphological segmentation of the ridge. Ce travail est constitué de deux volets indépendants qui s'intéressent respectivement à la géochimie isotopique du lithium et à la variabilité géochimique des MORB du Pacifique sud. L'utilisation des isotopes du lithium en Sciences de la Terre est abordée dans un premier temps au travers de l'étude des laves de la Chaîne des Puys. Les échantillons de cette série volcanique intraplaque permettent d'apporter des contraintes sur les valeurs de la composition isotopique du Li dans la croûte continentale inférieure et dans le manteau d'affinité HIMU sous le Massif Central. La deuxième étude s'intéresse au comportement du Li lors du refroidissement d'une lave. Pour cela, des analyses in situ de la ...

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