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Unravelling carbonatite–silicate magma interaction dynamics: A case study from the Velay province (Massif Central, France)

Abstract : Mechanisms of interaction between a carbonatite magma and a silicate magma are inferred on the basis of the textural and geochemical features of a carbonate-bearing tuff from the Massif Central, characterized by the presence of carbonatite globules within a silicate glass matrix. A two-fluid dynamical model is proposed in order to constrain the formation of the carbonatite globules that underwent no geochemical re-equilibration with the trachyte magma due to rapid thermal re-equilibration and crystallization of dolomite. It is suggested that a viscous fingering instability occurred simultaneously with the injection of a carbonatite magma into a chamber filled with a more viscous trachytic magma. Instantaneous fragmentation of the fingers, induced by the action of gradient stresses, resulted in the formation of a magmatic emulsion. The replenishment event triggered immediate evacuation of the magma chamber such that interaction between the two magmas occurred over a short time scale and large-scale mixing was prevented. The exsolution of volatiles, perhaps as a consequence of the recharge event shortly before the eruption, drove a metasomatic event that produced the subtle chemical variations observed at the interface between carbonatite globules and silicate matrix.
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Submitted on : Tuesday, February 8, 2011 - 11:54:42 AM
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Luca Valentini, Kathryn Ruth Moore, Gilles Chazot. Unravelling carbonatite–silicate magma interaction dynamics: A case study from the Velay province (Massif Central, France). Lithos, Elsevier, 2010, 116 (1-2), pp.53-64. ⟨10.1016/j.lithos.2010.01.002⟩. ⟨insu-00564211⟩

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