The role of pre-existing thrust faults and topography on the styles of extension in the Gran Sasso range (central Italy)

Abstract

Structural analysis and field mapping together with simple geometrical and flexural elastic models, document that two styles of Quaternary extensional tectonics characterized the Gran Sasso range (central Apennines, Italy). In the western part of the range, extension took place on 10-15-km-long range-front normal faults with associated 600-1000-m-high escarpments showing evidence of Late Glacial-Holocene activity. This topography has been reproduced with a thin elastic plate subjected to the isostatic forces induced by the movement along high-angle (55º-65º) planar normal faults. In the eastern part of the belt extension occurred on shallow-dipping normal faults (30º-35º) which reactivated progressively deeper pre-existing thrusts. In this area antithetic 'domino' faults formed to accommodate the mechanical adjustment of the hanging-wall over a variably dipping major fault surface. The eastward increase in shortening, due to the earlier compressional phase, documented in the Gran Sasso belt by previous authors, accounts for the more developed zones of weakness and high topographic relief in the eastern sector. This setting could explain the different styles of extension and the more advanced northeastern limit of normal faulting in the eastern sector. This work suggests that normal faults can originate either with low-or high-angle geometry in the upper crust according to the pre-existing tectonic setting and that topography could be important in controlling the geometry and pattern of migrating normal faulting.

Transverse systems along the extensional Tyrrhenian margin of central Italy and their influence on volcanism

“…1998]. Along the Tyrrhenian margin of central Italy, active extensional tectonics migrated eastward, from the Tyrrhenian area (mostly during the Miocene-Pliocene) to the Apennines divide (Present), where the boundary between the extensional and compressional domains is approximately located (Figure 1) [D'Agostino et al, 1998;Ghisetti and Vezzani, 2002]. While the eastern part of the divide is characterized by active compression, the western part is presently marked by extension and associated with seismic activity due to NW-SE normal faulting [Montone et al, 1999;Valensise and Pantosti, 2001, and references therein; D' Agostino et al, 2001;Roberts and Michetti, 2004].…”

“…The NW-SE normal faults responsible for the extension of the area between the Tyrrhenian Sea and the Apennines divide are also responsible for the development of several subparallel Plio-Quaternary basins (Figure 1) [Mariani and Prato, 1988;Cavinato et al, 1994]. Many of the NW-SE normal faults reactivate preexisting thrust planes, mostly SW dipping, formed during the buildup of the Apennines D'Agostino et al, 1998]. Balanced cross sections from published works [e.g., Spadini and Podladchikov, 1996;Faccenna et al, 1997;Mele and Sandvol, 2003] permit estimation of the stretching factor b across the Tyrrhenian margin.…”

“…the NW-SE and NE-SW systems is related to the reactivation of preexisting compressional structures, such as NW-SE thrusts and NE-SW tear faults D'Agostino et al, 1998;Ghiestti andVezzani, 1997, 1999]). However, such a reactivation, when generating NW-SE strike-slip faults and NE-SW normal faults, has to take into account for the presence of minor stress variations along the margin.…”

“…In one case, the intersection between NE-SW and NW-SE structures increases the permeability of the crust and focuses the rise and emplacement of magmas. In the second case, the NW-SE normal faults along the volcanic chain are responsible for an overall crustal thinning of $5 km ($1.5 kbar): of these, $4 km are due to the westward shallowing of the Moho and $1 km is related to the difference in topography [Locardi and Nicolich, 1988;D'Agostino et al, 1998]. The multiple and widely spaced sets of NE-SW faults responsible for transverse basins also have a significant dip-slip component.…”

Evidence for detachment faulting on the NE Parnassos mountain front (Central Greece)

“…The role of pre-existing overthrusts is crucial, since they are suitable weakness planes that can potentially be reactivated under a new stress regime (e.g. D ' Agostino et al, 1998).…”