Interaction dorsale-point chaud : relations entre les processus tectoniques et magmatiques à l'axe de la dorsale Est Pacifique, 16°N

Abstract : The 16°N segment of the East Pacific Rise (EPR) is the most over-inflated and shallowest of this fast -spreading ridge, in relation with an important magma flux due to the proximity of the Mathematician hotspot. The goal of this thesis is to analyze in detail the magmatic and tectonic processes along this segment in regards to the influence of the hotspot. The study of these processes is based on a morpho-structural and chronological analysis of the segment between 15°36.N and 15°53.N using bathymetric data (1,10 and 40 m resolution) and Nautile dive photos and videos of the French PARISUB (.PAnach Ridge SUBmerssible.) cruise. The characterization of the faults and fissures geometry (e.g., vertical throw, dip, length, depth, width) and their orientation reveled that tectonic processes occur more than 750 m of the ridge axis. Lateral and abyssal grabens formed by fault, less developed than in other EPR segments would be the consequence of a warmer and thinner lithosphere. At the axis, the existence of two parallel and contiguous Axial Summit Troughs (ASTs) over a distance of about 20 km and above a wide magma lens, indicate a wide zone of diking and thus a poor localization of magmatic processes. This poor localization, and the highly segmented and global “en echelon” shift of the ASTs that progressively accommodate the bow shape of the axial dome in the direction of the hotspot, revealed the importance of the Mathematician hotspot influences on spreading processes. This hotspot also influences, although indirectly lava flows morphologies.Indeed, it is at the origin of the formation of a wide sub-horizontal plateau that results in the formation of inflated sheet and pillow flows. That flows covering about one third of the plateau allows us to develop theoretical and conceptual models to investigate lava flow dynamics. Models revealed that inflated sheet and pillow flows may emplace during the same long-live (few hours to 20 days) eruption, with sheet flows erupted at the end.
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Morgane Le Saout. Interaction dorsale-point chaud : relations entre les processus tectoniques et magmatiques à l'axe de la dorsale Est Pacifique, 16°N. Géomorphologie. Université de Bretagne occidentale - Brest, 2015. Français. ⟨NNT : 2015BRES0019⟩. ⟨tel-02272300⟩

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