Data di Pubblicazione:
2005
Abstract:
The nappe pile presently cropping out in the
central sector of the Ligurian Alps, is represented by
some principal groups of tectonic units. Starting from
the foreland, the outer and lower, weakly metamorphic
(up to 0.3 GPa) Brianc¸onnais units support the highpressure
(up to 1.3 GPa) ensemble of inner Brianc¸onnais
nappes, in turn overridden by the Prepiedmont units,
sourced from the European continental margin. Prepiedmont
units form two superposed groups. The lower
is composed only of a pre-Namurian basement (Alpine
metamorphism up to 0.6 GPa); and the upper is mainly
composed of a slightly metamorphic (greenschist facies)
post-Namurian cover. At the top lie the high-pressure
metamorphosed (up to 0.8 GPa in the sector here considered)
ophiolitic units. The group of the non-metamorphic
Helminthoid Flysch nappes (original
stratigraphic cover of the ophiolitic units) has travelled
the greatest distance and is presently mainly set onto the
outer part of the chain. Only events up to the stacking of
the nappe pile are discussed, disregarding late-stage
deformation. As the examined sector is located at a
considerable distance from the collisional zone, late
processes did not change the overall order of superposition
formerly acquired. The model proposes the
development of two major, subhorizontal detachment
surfaces. The first, shallower one confines at the base a
very thin-skinned set of nappes, nearly totally made up
of Prepiedmont sedimentary covers that are bounded at
their top by the Helminthoid Flysch units. Both these
groups underwent a mainly horizontal outwards transport.
In contrast, the underlying Prepiedmont crust and
the adjoining Brianc¸onnais inner sector (separated by
the second, deeper major detachment surface) were
progressively dragged into the subduction zone under
the ophiolitic units and duplexes were generated.
Exhumation of the metamorphic units occurred along
the subduction channel, as did stacking of the nappe
pile.
central sector of the Ligurian Alps, is represented by
some principal groups of tectonic units. Starting from
the foreland, the outer and lower, weakly metamorphic
(up to 0.3 GPa) Brianc¸onnais units support the highpressure
(up to 1.3 GPa) ensemble of inner Brianc¸onnais
nappes, in turn overridden by the Prepiedmont units,
sourced from the European continental margin. Prepiedmont
units form two superposed groups. The lower
is composed only of a pre-Namurian basement (Alpine
metamorphism up to 0.6 GPa); and the upper is mainly
composed of a slightly metamorphic (greenschist facies)
post-Namurian cover. At the top lie the high-pressure
metamorphosed (up to 0.8 GPa in the sector here considered)
ophiolitic units. The group of the non-metamorphic
Helminthoid Flysch nappes (original
stratigraphic cover of the ophiolitic units) has travelled
the greatest distance and is presently mainly set onto the
outer part of the chain. Only events up to the stacking of
the nappe pile are discussed, disregarding late-stage
deformation. As the examined sector is located at a
considerable distance from the collisional zone, late
processes did not change the overall order of superposition
formerly acquired. The model proposes the
development of two major, subhorizontal detachment
surfaces. The first, shallower one confines at the base a
very thin-skinned set of nappes, nearly totally made up
of Prepiedmont sedimentary covers that are bounded at
their top by the Helminthoid Flysch units. Both these
groups underwent a mainly horizontal outwards transport.
In contrast, the underlying Prepiedmont crust and
the adjoining Brianc¸onnais inner sector (separated by
the second, deeper major detachment surface) were
progressively dragged into the subduction zone under
the ophiolitic units and duplexes were generated.
Exhumation of the metamorphic units occurred along
the subduction channel, as did stacking of the nappe
pile.
Tipologia CRIS:
1.1 Articolo in rivista
Keywords:
Alpine tectonics; Ligurian Alps; Duplex; Subduction; Exhumation
Elenco autori:
Seno, Silvio; Dallagiovanna, Giorgio; Vanossi, Mario
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