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Modélisation numérique 3D des caractéristiques physiques des segments de dorsale lente

Abstract : I developed 3D thermal and physical numerical models of the slow-spreading ridge segments to investigate whether the presence of a hot zone beneath the segment center may account for off-axis and along-axis geophysical observations and determine the characteristics of such a hot zone. Observations from the Mid-Atlantic Ridge show along-axis variations of geophysical characteristics from segment center to ends. Off-axis observations show the existence of rhomb-shaped patterns suggesting that a segment lengthens then shortens through time over a period of 3-9 My. In my model the thermal structure is controlled by the geometry and the dimensions of a permanent hot zone imposed beneath the segment center, where is simulated the adiabatic ascent of magmatic material. The physical processes at the origin of such a hot zone are not considered. From the thermal structure, geophysical parameters (gravity anomalies, magnetic anomalies, maximum depth of earthquakes, and along-axis variation of crustal thickness) are simulated and compared to the observed ones to identify the particular geometries and dimensions of the hot zone which reproduces geophysical observations. Thermal structures of different types of segment, characterized by different length, are determined in such a way. The models show that, with her parameters remaining equal, the lengthening of the hot zone is sufficient to account for the varying characteristics of the different segment types. This simple evolution of the hot zone suggests that the different "segment types" indeed represent different phases in the evolution of a unique segment type. In order to test whether such an evolution can account for off-axis observations I modeled this evolution of the hot zone and the resulting thermal structure and evolution. Such a evolution accounts for off-axis observations if the hot zone progressively lengthens for 3 My then shortens for 3 My.
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Contributor : Sébastien Gac <>
Submitted on : Monday, March 21, 2005 - 5:00:50 PM
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Sébastien Gac. Modélisation numérique 3D des caractéristiques physiques des segments de dorsale lente. Géologie appliquée. Université de Bretagne occidentale - Brest, 2002. Français. ⟨tel-00008837⟩

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