Abstract.

Materials of ophiolitic suture zones can be used to restore the key steps of the evolution of fossil oceanic areas and of their margins.
This study deals with the different components of a part of the Tethyan suture in the north-western French-Italian Alps. It concerns more precisely the lithostratigraphic and structural analysis of the so-called Schistes lustrés complex.

The main studied area is the French-Italian border close to the Mont-Cenis pass (the Susa area in the Piemont Region, Italy and the Lanslebourg area in Savoy, France). The northern part of the peridotitic Lanzo massif (north of Torino, Italy) within its limits with the pre-alpine basement massif of Sesia, the klippe of the «ÝSchistes lustrés du Mont JovetÝ» (Moûtiers area, France), and finally the Valaisanne zone within the Bourg Saint Maurice area (France) were also examined.

Essentially qualitative, this work takes into account the known petrologic, metamorphic and radiochronologic data.

The Schistes lustres complex is resolved into three different lithostructural sets of units.
The two lower ones, born of the European palaeo-margin for the lowest and of the palaeo-oceanic realm or Tethys for the other, are made of calcschists and marbles labelled by syn-orogenic detrital deposits of composite origin, oceanic and continental. The mass and the height of the reworked materials, ophiolitic or not, notably decrease from the lowest oceanic units to the highest ones. Although the determinations of the rare fossil traces are always in debate, the ages found and the radiochronological intervals of the alpine metamorphic assemblages of the Schistes lustrés lead to a single conclusion : the primary sedimentary rocks belong to the Upper Cretaceous. They represent Upper Cretaceous flyschs.
The upper one, not identified within our field study, is made of very late Cretaceous gritty flysch without reworked ophiolitic materials [Deville, 1986].
All these Upper Cretaceous deposits are explained as the sedimentary consequences of two major stages of the closure of the Tethyan ocean during the late Cretaceous.

The Schistes lustres of the Lanzo area and the peridotitic Lanzo massif on one hand and the Schistes lustres of the Mont Jovet klippe on the other hand, can be combined with the previous pattern. The first ones indeed are connected to the Schistes lustres of the structurally oceanic lowest units and the second to the schistes lustres of the highest ones. Also a lithospheric sketch is proposed in which the Lanzo massif is disconnected with the south-alpine mantle, as it was previously interpreted.
The valaisanne zone in France in the Bourg Saint Maurice area finally is reexamined. The valaisan Flysch stratigraphically lies  upon the «ÝRoches vertes du VersoyenÝ», a primary volcanogenic complex. The new discovery of microfaunas, which complete the previous ones, leads to give to this Flysch a post Barremo-Aptian age. Moreover, the «ÝRoches vertes du VersoyenÝ» are interpreted as essentially a volcanogenic complex, born of a thinned shield realm becoming partially oceanic along the western limit of the Briançonnaise zone. If these metabasites were really emplaced during cretaceous times, if their 60-70 Ma metamorphism is evidenced, and if the valaisan Flysch has experienced the same metamorphic conditions at the same time, then this Flysch is finally an Upper Cretaceous Flysch.
In conclusion, all of the data of the studied transect allowed us to describe the different steps of the evolution of the Tethyan suture within the Alps of Savoy.

Key-words. French-Italians Alps, Schistes lustres complex, Lithostratigraphy, Petrology, Structural analysis, Mont Cenis Pass, Mont Jovet Massif, Lanzo Massif, Valaisanne Zone.

Résumé français, italien. Extrait, Conclusions générales, , se lit avec Acrobat (R) Reader

* LGHAM, Université de Savoie, Campus Scientifique, 73376 Le Bourget du Lac cédex.

Cet ouvrage (thèse d'Etat) a été publié par le Laboratoire de Géologie de l'Université I de Grenoble (Laboratoire de Géodynamique des Chaines Alpines), dans la série "Géologie Alpine", Mémoire HS n° 29, 1998, ISSN 0993-796X et peut être acquis au prix de 275 F + port ou 41,92 euros + port auprès de : Andre.Paillet@univ-savoie.fr
Cet ouvrage format A4 comporte 310 pages, 6 planches hors texte, dont une carte géologique en couleur.

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