Provenance of Oligocene synorogenic sediments of the Ligurian Alps (NW Italy): inferences on belt age and cooling history

• Published in: International journal of earth sciences : Geologische Rundschau 2003-10, Vol.92 (5), p.758-778
• Main Authors: Barbieri, Chiara, Carrapa, Barbara, Di Giulio, Andrea, Wijbrans, Jan, Murrell, Glen R.
• Format: Article
• Language: English
• Subjects: Chemistry; Geology; Mineralogy; Miocene; Oligocene; Pliocene
• ISSN: 1437-3254; 1437-3262
• DOI: 10.1007/s00531-003-0351-x

Mineral chemistry, ^sup 40^Ar/^sup 39^Ar geochronology on white micas and Apatite Fission Track Thermochronology (AFTT), are applied here to study the provenance of the synorogenic Molare Formation (lowermost unit of the Tertiary Piedmont Basin clastic sequence). The Molare Formation was deposited during transgression onto the Ligurian Alps nappe stack in the Early Oligocene. Depositional facies show that clastic distribution remained transversal, with local sources located just landward from the coastline. Phengite mineral chemistry together with ^sup 40^Ar/^sup 39^Ar data clearly shows two distinctive source areas, each one mirroring the composition of the basement directly beneath the clastic sequence. Amphibole mineral chemistry allows second order provenance distinctions within each sector, reflecting heterogeneous metamorphic evolution of the bedrock complexes. Integrated ^sup 40^Ar/^sup 39^Ar dating and AFTT suggest that, following a fast cooling/exhumation episode of the Ligurian Alps during the Oligocene, very little net uplift has since occurred. This is due to a period of general subsidence from the Oligocene-Late Miocene followed by comparable uplift from Late Miocene-Pliocene to the present. In general our data provide an image of the Ligurian Alps during the Oligocene, which is very similar to the present-day one.[PUBLICATION ABSTRACT]