La lithosphère océanique de la Téthys ligure : etude du magmatisme et des minéralisations associées dans les ophiolites du Queyras ( zone piémontaise des Alpes occidentales)

Abstract : The mesozoïc ophiolite sequence of Queyras (piemont zone, Western Alps) is characterised in several small overthrusted massifs scattered within the piemont "Schistes lustres" (Mont Viso). Their study allows to the reconstruction of the early structure of at least a part of the Tethyan oceanic basement. Nevertheless several field observations lead to distinguish the succession of two distinct magmatic events (the peridotite-gabbro, then the basalts), the petrological and geochemical study show strong similarities with the Apenninic and Corsican ophiolites. Thewhole sequence exhibits a tholeïtic differentiation trend. The typologic study of the zircons populations from the acid rocks well agrees with this model. The traces elements, Y, Ti, Zr, Nb, show a cogenetic and comagmatic origin between basic and evolved petrologic facies. The mineral phases which control the fractional cristallization and the valuation of the partial melting, suggest an attenuated-crust tectonic and a magmatism close to the occidental Mediterranean ophiolites (magmatism type I). Granitic clasts of a sedimentary breccia located between the oceanic basement and under the basal tic flows, show a calc-alcaline tendency. These facts require the proximity and break-up of a continental crust during the early spreading stage. Hydrothermalism is responsible for the spilitisation and the mineralization observed on the seafloor in contact with thesurrounding sediments: the stratiform sulphide deposit of Viafiorcia (Val Germanasca, Italy) is an example.
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Applied geology. Universite Scientifique et Medicale de Grenoble, 1986. French


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Patrick Saby. La lithosphère océanique de la Téthys ligure : etude du magmatisme et des minéralisations associées dans les ophiolites du Queyras ( zone piémontaise des Alpes occidentales). Applied geology. Universite Scientifique et Medicale de Grenoble, 1986. French. <tel-00523836>

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