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Theses

Recyclage du carbone et formation du diamant en zone de subduction : contraintes expérimentales

Abstract : In order to constrain the hypotheses of carbon recycling and diamond formation at subduction zones, experiments were carried out on a multi-anvil apparatus with a starting mixture composed of Fe-dolomite + quartz (contained in subducted sediments or due to the alteration of basalts) in pressure - temperature conditions from 4 to 14 GPa and 800 to 1600°C. Two studies were conducted : first, the stability of the mixture was constrained at intrinsic and reducing conditions; then, the interactions with the mantle wedge were studied by constraining, first, the exchange processes between a Fe-dolomite + quartz cylinder and a garnet peridotite cylinder, and then, phase equilibrium relations in mixtures of sediment + peridotite in various proportions. This study shows that a carbonated sediment (or eclogite) is destabilised at lower depth in the presence of iron. Moreover, the reducing conditions imposed by the mantle also lower their stability depth during subduction. A reaction zone composed mainly of clinopyroxene + Fe-magnesite forms at slab/mantle interface. Carbon infiltration in the mantle wedge is very fast and magnesite cristallizes. Thus, recycling of carbonates to high depth is unlikely. These experiments also show that graphite or diamond can form at the top of the subducted crust by the reduction of carbonates at low temperature.
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Submitted on : Tuesday, August 28, 2012 - 2:42:56 PM
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  • HAL Id : tel-00725967, version 1

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Audrey Martin. Recyclage du carbone et formation du diamant en zone de subduction : contraintes expérimentales. Pétrographie. Université Blaise Pascal - Clermont-Ferrand II, 2009. Français. ⟨NNT : 2009CLF21910⟩. ⟨tel-00725967⟩

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