A new active tectonic model for the construction of the Northern Apennines mountain front near Bologna (Italy)

Abstract

[1] We integrate existing and new geologic data [REtreating TRench, Extension, and Accretion Tectonics (RETREAT project)], particularly on the origin, growth, and activity of the mountain front at Bologna, Italy, into a new model that explains Apennine orogenesis in the context of a slab rollback -upper plate retreat process. The Bologna mountain front is an actively growing structure driving rock uplift $1 mm/year, cored by a midcrustal flat-ramp structure that accommodates ongoing shortening driven by Adria subduction at a rate of $2.5 mm/year. The data we use are assembled from river terraces and associated Pleistocene growth strata, geodesy including releveling surveys, reinterpretation of published reflection lines, and a new high-resolution reflection line. These data constrain a simple trishear model that inverts for blind thrust ramp depth, dip, and slip. Apennine extension is recognized both in the foreland, as high-angle normal faults and modest stretching in the carapace of the growing mountain front, and in the hinterland, with larger normal faults that accomplish some crustal thinning as the upper plate retreats. This coevolution of extension and shortening shares some notable characteristics with other basement-involved collisional orogens including the early Tertiary Laramide orogeny in the American West and the Oligocene to Miocene evolution of the Alps. We propose a possible relationship between underplating and the development of the Po as a sag basin as a Quaternary phenomenon that may also apply to past periods of Apennine deformation (Tortonian). Continued shortening on the structure beneath the Bologna mountain front represents by far the most important and underappreciated seismogenic source in the front of the northern Apennines.

Recent and active tectonics of the external zone of the Northern Apennines (Italy)

“…1b) and a complex deformation pattern resulting from an active stress field characterised by predominant extension in the Tyrrhenian (internal) side and compression in the Adriatic (external) sector of the chain (e.g., Mariucci et al 1999). Consequently, normal faulting is the dominant active deformation style in the Tyrrhenian area, whereas the active tectonics of the Adriatic sector is accommodated by folding and thrusting (Benedetti et al 2000(Benedetti et al , 2003Burrato et al 2003;Vannoli et al 2004;Boccaletti et al 2004;Basili and Barba 2007;DISS Working Group 2007;Picotti and Pazzaglia 2008;Wilson et al 2009). Active shortening is well constrained by the analysis of earthquake fault plane solutions (e.g., Gasparini et al 1985;Boccaletti et al 1985;Anderson and Jackson 1987;Frepoli and Amato 1997;Selvaggi et al 2001;Pondrelli et al , 2004Lavecchia et al 2004;Chiarabba et al 2005;Piccinini et al 2006;Boncio and Bracone 2009), stress analysis (e.g., Mariucci et al 1999;Mariucci and Muller 2003;Montone et al 2004), and geodetic measurements (e.g., Battaglia et al 2004;Serpelloni et al 2005;D'Anastasio et al 2006).…”

“…Active shortening is well constrained by the analysis of earthquake fault plane solutions (e.g., Gasparini et al 1985;Boccaletti et al 1985;Anderson and Jackson 1987;Frepoli and Amato 1997;Selvaggi et al 2001;Pondrelli et al , 2004Lavecchia et al 2004;Chiarabba et al 2005;Piccinini et al 2006;Boncio and Bracone 2009), stress analysis (e.g., Mariucci et al 1999;Mariucci and Muller 2003;Montone et al 2004), and geodetic measurements (e.g., Battaglia et al 2004;Serpelloni et al 2005;D'Anastasio et al 2006). However, the knowledge of the main recent and active structures remains limited to scattered areas (e.g., Benedetti et al 2003;Burrato et al 2003;Vannoli et al 2004;Piccinini et al 2006;Picotti and Pazzaglia 2008;Picotti et al 2009;Wilson et al 2009). In this paper, we aim to fill this gap by presenting a comprehensive study of the active tectonics of the external part of the Northern Apennines.…”

Estimation of Subsidence in Po Delta Area (Northern Italy) by Integration of GPS Data, High-Precision Leveling and Archival Orthometric Elevations

“…Carminati et al [14] indicated the downflexure of the Adria plate as one cause of movement, at a maximum rate of 2.5 mm/year. The possible effects of tectonic activity along the northern Apennine thrust front buried under quaternary sediments was thoroughly discussed in [20]. More sophisticated measurements now show that the recent deformation pattern of the Apennine belt and Po Plain is due to the northward movement of the Adria plate [21].…”

Appraisal of active tectonics using DEM-based hypsometric integral and trend surface analysis in Emilia-Romagna Apennines, northern Italy

“…With reference to the Po Plain, all of the northern Apennines belt is actively being uplifted at rates ranging from 0.1 to 2 mm/year (Spagnolo and Pazzaglia, 2005). The northern Apennines mountain front and its adjacent foothills are riddled with geomorphic and geologic evidence of recent tectonics such as active folds and faults (Picotti and Pazzaglia, 2008). However, information on the recent and active structures remains limited to scattered areas (Piccinini et al, 2006;Picotti and Pazzaglia, 2008;Picotti et al, 2009;Wilson et al, 2009).…”

“…The northern Apennines mountain front and its adjacent foothills are riddled with geomorphic and geologic evidence of recent tectonics such as active folds and faults (Picotti and Pazzaglia, 2008). However, information on the recent and active structures remains limited to scattered areas (Piccinini et al, 2006;Picotti and Pazzaglia, 2008;Picotti et al, 2009;Wilson et al, 2009). The study area is characterized by complex structures showing the presence of different fault systems of tectonic origin Panini et al, 2002aPanini et al, , 2002bPlesi et al, 2002aPlesi et al, , 2002bSeveri et al, 2002aSeveri et al, , 2002bBalocchi, 2003;Boccaletti et al, 2004b).…”