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

Abstract

Mineral chemistry,40 Ar/ 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 40 Ar/ 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 40 Ar/ 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.

Retrogressive fabric development during exhumation of the Voltri Massif (Ligurian Alps, Italy): arguments for an extensional origin and implications for the Alps–Apennines linkage

“…This interpretation in part coincides with the kinematic scenario proposed by Hoogerduijn , whom related the contact between the TPB and the Voltri Massif to a NW shearing, although framed during late thrusting. The lower bound for the timing of extension (ductile evolution) is uncertain, since the age of the metamorphic peak in the HP-units is still debated, ranging between 48 and 45 Ma (Barbieri et al 2003;Federico et al 2005Federico et al , 2007b and 33.6 ± 1.0 Ma (Rubatto and Scambelluri 2003). Nevertheless, these arguments are sufficient to propose the Late Eocene-Early Oligocene boundary as the time interval to place the activation of the extensional detachment tectonics in the Voltri Massif.…”

The early stages of the Alpine collision: an image derived from the upper Eocene–lower Oligocene record in the Alps–Apennines junction area

“…Recently, this approach has been applied successfully to clastic sediments deposited in the southern part of the Piedmont Tertiary Basin (TPB) in northwestern Italy ( Fig. 1; Barbieri et al, 2003;Carrapa et al, , 2004.…”

New data for the kinematic interpretation of the Alps–Apennines junction (Northwestern Italy)

“…The Alps are a double-verging pile of oceanic and continental units that were partially subducted, affected by HP metamorphism, stacked and exhumed before the Oligocene (e.g. Hunziker et al 1992;Rubatto and Hermman 2001;Barbieri et al 2003;Mosca et al 2005;Ford et al 2006;Malusà et al 2006). The Apennines (here regarded in their northern sector, i.e.…”