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The varicoloured shales of the External Ligurian Units of the Emilia Apennines and the varicoloured shales of the southern Abruzzo are they the expression of an original, unique paleogeographic domain?
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Double décollement zone bordering the subduction channel in an ancient erosive subduction complex: implications for seismogenesis
No full textInsights into the deformation of an underthrust tectonic mélange from the Northern Apennines, Italy.
No full textThe Sestola-Vidiciatico Tectonic Unit (SVTU) in the Northern Apennines is an underthrust tectonic mélange presently sandwiched between the Tuscan-Umbrian foredeep “flysch” units and the overlying Ligurian/Subligurian thrust-nappe. The SVTU has been generated during the collision between the European and the Adria plates and now it separates the oceanic accretionary wedge from the underlying fold–and-thrust belt formed by Adria sedimentary units. The collision caused an eastward migrating foredeep basin and the overthrusting of the frontal part of the Ligurian/Subligurian thrust-nappe/accretionary prism on the subducting Adria margin. Part of the inner lower-slope and marginal sediments of the migrating foredeep basin have been unconformably deposited on a newly developed frontal prism formed by material already accreted in the Ligurian/Subligurian prism and gravitationally and tectonically reworked. The frontal prism and its sedimentary cover have been progressively dragged down along the plate boundary zone generating the Sestola-Vidiciatico tectonic mélange on top of the underthrust turbidites. The mélange has been generated under conditions ranging from the shallow diagenetic environment at the toe of the prism to temperatures of around 120°C. The research has been focused on the younger component of the mélange that has been deposited on the frontal prism generated by the tectonic and sedimentary reworking of the former Ligurian accretionary wedge. The underthrust lower-slope sediments incorporated in the mélange, as they were not completely lithified,, show a long deformation history ranging from continuous and pervasive soft-sediment deformation to brittle deformation concentrated along faults strongly controlled by the lithological proprieties of the components and by the cyclical evolution of the fluid pressure.In the first deformational stage the marly component has been pervasively sheared until the loss of the primary bedding, whereas the shaly component developed a penetrative scaly fabric. The sandstone beds have been cut crossed by hydroplastic conjugate shear bands with no grain breakage evolving to breaking concentrated on a sharp surface. During the last structural stage the mélange has been penetratively cross-cut by a spaced network of shear surfaces coated by calcite slikenfibres showing a characteristic crack-and-seal growth. The final state of strain of the mélange results in a stretching both parallel and perpendicular to the main direction of tectonic transport
Deformation in a subduction channel: anatomy of the shallow portion (T< 150°C) of an ancient analogue in the Northern Apennines of Italy
No full textIn the Northern Apennines of Italy, an underthrust tectonic mélange represents the ancient analogue of a shallow subduction channel. This mélange (the Sestola Vidiciatico Tectonic Unit) has been formed during the collision between the European and the Adria plates and it is presently sandwiched between the former oceanic accretionary wedge – Ligurian thrust nappe - and the underlying fold–and-thrust belt formed by Adria sedimentary units. It has a thickness of about 500 m and it is representative of a portion ranging from the shallow diagenetic environment to temperatures of around 150°C, a critical temperature recognized in most of the subduction zones as coincident with the up-dip limit of seismogenesis. The main portion of the material forming the subduction channel is the product of frontal erosion taken place at the toe of the Ligurian prism, including its sedimentary cover, reworked through sedimentary and tectonic processes (i.e. frontal prism). Basal erosion is represented by blocks of Ligurian prism tectonically incorporated in the subduction channel and found in the upper part of the mélange.The younger deformation phase, as defined by cross-cutting relationship, is characterised by a strong difference in lithification of the various components which causes a clear partitioning of the deformation. The softer, less lithified components at the time of entrance in the subduction channel record the whole deformation evolution showing clear evidence of continuous and pervasive soft-sediment deformation passing to discontinuous brittle deformation concentrated along faults at deeper levels. Instead the components already hard at the time of entrance in the subduction channel show only the last and brittle stage of deformation. The latter developed when lithification of the softer blocks became as such that the mélange started to show a homogeneous behaviour as shown by the deactivation of the blocks’ boundaries as detachment surfaces. The strain regime in the shallow part of the subduction channel is extensional suggesting a very weak nature of the plate boundary. This character seems to be controlled by the presence of fluid and, for the deeper part, by the cyclical variation of the fluid pressure (fault-valve behaviour)
Sediment instability triggered by gas hydrate dissociation: what can we learn from the fossil Northern Apennines ocean margin ?
No full textGas migration and gas hydrate
Mechanism of deformation in a subduction channel at the transition between subduction and collision: The Sestola Vidiciatico Example, Northern Apennines (Italy)
No full textInternal structure and tectonic evolution of an underthrust tectonic mélange: the Sestola-Vidiciatico tectonic unit of the Northern Apennines, Italy
Full text linkThe Sestola-Vidiciatico Tectonic Unit (SVTU) in the Northern Apennines is an underthrust tectonic melange presently sandwiched between the Tuscan-Umbrian foredeep units and the overlying Ligurian/Subligurian thrust-nappe. The SVTU has been generated during the collision between the European and the Adria plates and now it separates the former oceanic accretionary wedge -Ligurian/Subligurian thrust nappe-from the underlying fold-and-thrust belt formed by Adria sedimentary units. The collision caused an eastward migrating foredeep basin and the overthrusting of the frontal part of the Ligurian/Subligurian thrust-nappe on the subducting Adria margin. Part of the inner lower-slope sediments of the migrating foredeep basin have been unconformably deposited on a frontal prism formed by material already accreted in the Ligurian/Subligurian prism gravitationally and tectonically reworked. The frontal prism and its sedimentary cover have been progressively dragged down along the plate boundary zone generating the SVTU. The lower-slope sediments have been incorporated in the melange as they were not completely lithified, and they show a long deformation history ranging from continuous and pervasive soft-sediment deformation to discontinuous brittle deformation concentrated along faults and mainly controlled by cycles of fluid pressure as testified by the presence of crack-and-seal texture and implosion breccia in the veins
Inherited structures and lateral variability along a plate boundary shear zone in a convergent margin: The Sestola-Vidiciatico Tectonic Unit and the Subligurian Units of the Northern Apennines of Italy
No full textRelation between soft sediment and brittle deformation in a melange formed at the transition from subduction to collision
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