PHD INPL 2005 Marrocchi

Abstract

The origin of the meteoritic organic matter and associated noble gases is poorly constrained. Experiments have been performed during this thesis in order to better constrain the possible environments of formation. Low pressure adsorption reproduces the concentration and elemental pattern of noble gases in the temperature range 80-100 K, but cannot explain the significant retention of noble gases within the organic structure. In addition, Rayleigh-type distillation experiments induced by adsorption do not show measurable isotopic fractionation. A solvation experiment carried out on insoluble organic matter of Orgueil (CI) reveals the volume trapping of P1 noble gases. This result suggests a mechanical trapping of P1 noble gases in the organic structure. Two syntheses have been carried out in order to reproduce these characteristics. Sublimation- condensation experiments under an ionizing xenon atmosphere reproduces the isotopic fractionation observed for P1 noble gases compared to the solar composition. This result shows that the P1 composition can be generated from a nebula of solar composition. However, this condensation process does not allow the diradicaloids observed by electron paramagnetic resonance to be reproduced. This result strongly suggests an interstellar origin of insoluble organic matter and associated P1 noble gases. Then, the second mechanism was tested : the transformation of nanodiamonds to carbon onions. Nanodiamonds represent an important part of the interstellar carbon and could undergo change to carbon onions under heating or irradiation conditions. Nanodiamonds heating experiments have been carried out. They reveal significant retention of trapped xenon with the maximum temperature release occurring at 800°C. This characteristic, coupled with the detection of carbon onions in primitive meteorites and their genetic link with nanodiamonds, strongly suggests that this structure could be advocated as the P1 noble gas carrier in meteorites.

keywords

;mots-clés en anglais : noble gases; xenon; organic matter, solar system; solar nebula; meteorites, adsorption