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Matière organique et métamorphisme thermique dans les chondrites primitives

Abstract : The Organic Matter of primitive chondrites is inherited from the presolar cloud, but the chondritic
OM have suffered from secondary processes inside the proto-solar nebula and on their asteroidal parent
body (Aqueous Alteration, Thermal Metamorphism), that may erase or transform the initial characteristics.
The TM has been approached here from OM, which is irreversibly transformed by TM. More than
30 chondrites (CV3, CO3, UOC) have been studied : structure of the OM has been quantified by Raman
spectroscopy, the texture by HRTEM. Petrographic studies have also been done on each chondrite. A new
interclass metamorphic tracer is defined : consistent with other ones available in the litterature, independant
from the AA and sensitive to the Peak Metamorphic Temperature. For the most metamorphosed
chondrites, the PMT is evaluated from the structural grade of the OM : 330°C (Allende), consistent with
other available thermometers. The limitations of the commonly defined petrographic scale are shown
and a new one based on a Raman spectral parameter is defined. A precise evaluation of the metamorphic
grade of the chondrites allows to discriminate the nebular from the asteroidal effects induced on the
petrography. This work gives also some constraints to the models of formation of the chondritic OM. It
shows that the organic precursor from ordinary and carbonaceous chondrites are chemically and structurally
closed and that the understanding of the isotopic characteristics from the OM (D, 15N) requires to
take into account the effects induced by the secondary processes. This work favors an interstellar origin
of the precursor of the chondritic OM.
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Contributor : Lydie Bonal <>
Submitted on : Thursday, December 14, 2006 - 1:24:09 PM
Last modification on : Friday, November 6, 2020 - 4:13:28 AM
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  • HAL Id : tel-00120337, version 1




Lydie Bonal. Matière organique et métamorphisme thermique dans les chondrites primitives. Autre. Université Joseph-Fourier - Grenoble I, 2006. Français. ⟨tel-00120337⟩



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