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The fate of melts within the slow-spreading lower oceanic crust : New insights from Atlantis Bank (Southwest Indian Ridge)

Abstract : Magmatic processes that govern crustal accretion at mid-ocean ridges still need to be better constrained. Among the processes potentially involved in the evolution of the lower crust magma reservoirs, reactions associated with reactive porous flow through crystal mushes tend to be considered as one of the predominant processes together with simple crystallization of magmas. The share of these processes during magma differentiation is dependent on the modes of melt migration and is thus correlated to the geometry of the reservoirs considered. By combining high-resolution structural, petrographic and geochemical studies of in situ sections drilled in an oceanic core complex of the Southwest Indian Ridge, I was able to bring new constraints on the formation and evolution of magmatic reservoirs involved in crustal accretion. All or part of the igneous reservoir model developed herein can be applied to other sections of lower oceanic crust. This model, together with additional constraints obtained by the coupled experimental petrology study of crystallization processes, paves the way for new quantifications of the involvement of melt-rock reactions in the differentiation of gabbroic lithologies, and more generally in the evolution of melts within the oceanic crust. Those developments are consistent with the constant evolution in recent decades of the understanding of crustal magmatic systems, which shifted from melt-filled magma chambers to igneous reservoir models mostly composed of crystal mushes.
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Marine Boulanger. The fate of melts within the slow-spreading lower oceanic crust : New insights from Atlantis Bank (Southwest Indian Ridge). Earth Sciences. Université de Lorraine, 2020. English. ⟨NNT : 2020LORR0030⟩. ⟨tel-02929290⟩

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