Abstract

This study concerns the internal delphino helvetic zone (dauphinois realm), the Bréches de Tarentaise and Niélard zones (external penninic realm) from side to side of the Frontal Penninic Overthrusting (France).

Two kinds of breccia - the Quermoz azoic carbonate breccia and the Tarentaise azoic carbonate flysch (Bréches de Tarentaise zone) - were specially studied. Comparison of oxygen isotopic values between well dated breccia in Niélard zone and poorly dated breccia in Bréches de Tarentaise zone were used for indirect stratigraphy. The Tarentaise flysch is tertiary and certainly priabonien. The Quermoz breccia are dated of Dogger period.

Comparative séquence stratigraphy analysis of the dauphinois and the penninic external realms.

• A pre-rift stage (Triassic period) is marked by:
• four stratigraphic sequences in the alpine sea (Bréches de Tarentaise and Niélard zones)
1. - a Permian-Upper Anisian sequenÏ.
2. - a Ladinian-Carnian sequence.
3. - a Norian sequence.
4. - a Rhetien sequence.
• -only the three upper ones in the germanic sea (delphinohelvetic zone).
• A rifting stage (Lias and Dogger periods) is marked by the born of the european passive continental paleomargin with two areas:
• the dauphinois basin (delphinohelvetic and subbriançonnais zones).
• the occidental plate-form of briançonnais continent (Bréches de Tarentaise and Niélard zones).

In these areas, we have described two stratigraphic sequences:
1. -an Hettangian-Aalenian sequence containing three minor sequences (Lower Lias, middle Lias and Upper Lias-Aalenian).
2. - a Bajocian-Tithonic sequence marked by breccia sedimentations in pull-apart basins (Brèches de Tarentaise zone) and by turbidites near distensive faults (subbriançonnais zone).

• A post-rift stage (Malm and Cretaceous periods) (for memory).

• A flysch basin stage (Priabonien-Lower Oligocene ?) is characterized by sinistral faulting between old mesozoic realms. An only flysch basin is emplaced on dauphinois basement (Albiez unit) and briançonnais basement (Cheval Noir unit, Brèches de Tarentaise and Niélard zone).

Detritic sediments have a dauphinois origin in Albiez unit and a briançonnais origin in Cheval Noir unit and Bréches de Tarentaise, Niélard zones.

During Upper Priabonien time, the flysch basin goes to closure in Tarentaise area while it subsists in Pelvoux area to Lower-middle Oligocene.

In carbonates, isochimic and metasomatic metamorphisms are discribed. We have characterized six tectonic events:

• - first cleavage event only known in the Bréches de Tarentaise zone;
• - second cleavage event, under green schist facies conditions;
• - third cleavage event (crenulation) also under green schist facies conditions;
• - dextral hults in agreement with a North-South compression;
• - sinistral faults in agreement with a West-East compression;
• - late folds and faults born during the ENE-WSW actual compression.

_{UNIVERSITE DE SAVOIE  TRAVAUX DU DEPARTEMENT DES SCIENCES DE LA TERRE  ISSN 0758-749X}

N° 10- 1989 Jean-Pierre GELY: Stratigraphie, tectonique et métamorphisme comparés de part et d'autre du front pennique en Tarentaise (Alpes de Savoie, France). Premières applications cristallochimiques, géochimiques et isotopiques dans les reconstitutions paléogéographique et géodynamique régionales.343 p.+ annexes. (250 francs ou 38,11 euros, + port). ISBN 2-904431-19-5. Résumé français

Cet ouvrages est diponibles auprès de Andre.Paillet@univ-savoie.fr