Abstract

The Cretaceous-Eocene Formations of the Tuscan Nappe ("Maiolica" and "Scaglia Toscana" Fms.) cropping-out on the western side of Monte Amiata, in the Monte Aquilaia-Monte Buceto ridge, were affected by syn-sedimentary normal faults and by extensional calcite veins, perpendicular to bedding-parallel stylolitic joints. These structures were developed during the pre-collisional convergence of the Northern Apennines, suggesting a more recent extensional tectonic phase than that already documented in the Jurassic successions of the Tuscan Domain and linked to the opening of the Tethys (Gelmini et alii, 1967; Giannini & Lazzarotto, 1970; Giannini et alii, 1971; Lazzarotto & Mazzanti, 1978; Bernouli et alii, 1979; Bettelli, 1985; Fazzuoli et alii, 1988; Costantini et alii, 1993 cum bibl.). Differences in orientation of the syn-sedimentary normal faults have been detected in the "Maiolica" and "Marne del Sugame" Fms. In particular, in the Cretaceous "Maiolica" Fm. and in the transitional lithofacies with the "Argilliti di Brolio" member ("Scaglia Toscana" Fm.) the faults show a main NE-SW direction (N degrees 40-N degrees 60); in the Eocene "Marne del Sugame" member ("Scaglia Toscana" Fm.) the faults show a main N-S to NNE-SSW direction (N0 degrees -N30 degrees ). The difference in orientation may be related to the variation of the stress field orientation during the Cretaceous and Eocene. The presence of extensional structures affecting the Cretaceous-Eocene deposits of the Tuscan Nappe reveals very important analogies between the tectonic evolution of the Tuscan and the outer Umbro-Marchigian Domain and could be related to the tectonic evolution of the Apennine Chain-foredeep-foreland system.

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