On the significance of aragonite occurrences in the Western Alps |
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| Authors: | P Gillet B Goffé |
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| Institution: | (1) Laboratoire de Minéralogie Physique, C.A.E.S.S. (CNRS), Université de Rennes, 1, Campus de Beaulieu, 35042 Rennes Cedex, France;(2) ER 224 (C.N.R.S.) Laboratoire de Géologie, Ecole Normale Supérieure, 24 rue Lhomond, F-75005 Paris Cedex, France |
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| Abstract: | Aragonite occurrences from two areas of the Western Alps are described. It is shown that aragonite has been formed under blueschist metamorphic conditions in the Western Vanoise, while it has been precipitated under sub-surface conditions in the Queyras region. An uplift (P, T) path of the aragonite-bearing rocks of the Western Vanoise is constructed using two independent methods: (1) temperature estimates using the Sr++ content of aragonite in the successive veins and (2) the kinetics of the aragonitecalcite solid-state transition. The uplift (P, T) path has an unusual shape with an important temperature decrease (100° to 150° C for a pressure decrease of 0.2 GPa) following blueschists metamorphism (P=0.7 GPa, T=300° C). Thermal models show that this unusual (P, T) path of the Western Vanoise can be explained if one maintains a low temperature (between 125° and 175° C) at the base of the tectonic unit containing the aragonite-bearing rocks during part of its burial history, followed by the whole of its exhumation. A tectonic scenario is proposed to account for the observed and modelled (P, T) path. |
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