Thèse de Emilie Thomassot | INSTITUT DE PHYSIQUE DU GLOBE DE PARIS

Twitter

Aller au compte twitter

Research Departments

Stable isotope geochemistry

  Thèse de Emilie Thomassot

Origine et formation des diamants et de leurs inclusions de sulfure : contribution à l’étude des processus géochimiques, des cycles (C, N et S) et de leur évolution dans le manteau supérieur terrestre.
Encadrant (et co-encadrant) : 
Résumé: 











The aim of this thesis was to better understand the origin and speciation of carbon in metasomatic fluids that give rise to diamonds. It included an analysis of diamonds from a same xenolith , polycrystalline diamonds and three suites of sulfide-bearing inclusion diamonds. This work was conducted in close collaboration with, among others , Dr. Jeff Harris ( University of Glasgow ) for the selection and characterization of samples and Dr. Marc Chaussidon and Dr Claire Rollion Bard ( CRPG -Nancy ) for implementation of the first analyses of    33S/32S  and  34S/32S isotopic compo sitions on the 1270-irms at CRPG. 

 

 

This work has led to several conclusions. First, the existence of reduced mantle fluids (ie methane-bearing) has been demonstrated. Finally, several opposite conclusions derived from previous studies have been clarified by the systematic analyses of C-, N, S- isotopic compositions of diamonds and their sulfide inclusion.

This work has confirmed the superficial origin of sulfur (Δ33S ≠ 0 per mille) of sulfide inclusions yet with diamonds mantle signatures ( δ13C and δ15N ~ -5 per mille). The data support a model of metasomatic formation of diamond by precipitation of mantle fluids including a pre- existing sulphide.

 

 

The main implications of this work relates to our understanding of diamond crystallisation ages. Metasomatic diamond formation encapsulating a pre-existing mineral implies
that diamond genesis ages inferred from the the study of diamond inclusions may not necessarily reflect the age of diamond precipitation.

Furthermore , this study shows significant differences between diamonds with an inclusion of sulfide compared to those with a silicate inclusion , suggesting that the “ages” of diamond formation inferred from either silicate or sulfide inclusion can not be generalized to diamonds from this locality.

 

Date de soutenance: 
Thursday 07 December 2006 - 10:30
Jury: 
Prof. Claude Jaupart – Prof. P7(Président du Jury), Dr Marc Chaussidon – DR-CNRS CRPG-Nancy (Rapporteur), Dr Olivier Alard – CR-CNRS Université de Montpellier (Rapporteur), Dr Jean-Pierre Lorand DR-CNRS MNHN (Examinateur), Pr Marc Javoy – Prof. P7 (Co-directeur de thèse), Dr Pierre Cartigny - CR-CNRS IPGP (Co-directeur de thèse)