Crustal extension in the northern Apennines: The transition from compression to extension in the Alpi Apuane Core Complex

Abstract

An interpretation of Northern Apennine geology is presented which relates the temporal and spatial occurrence of both compressional and extensional deformation features in terms of the changing dynamic evolution within an accretionary wedge, after a model proposed by Platt [1986], followed by the initiation and development of continental rifting. During Cretaceous to Eocene time an accretionary wedge formed as remnant Tethyan oceanic crust subducted beneath the rotating Corsica‐Sardinia microplate. Microplate collision during the Oligocene was characterized by the rapid imbrication of buoyant continental crust of the Italian continental margin, the record of which is preserved within the duplex structure geometry of the Alpi Apuane region. The overthickened wedge geometry returned to a more stable configuration by developing extensional features during the Miocene: both listric normal faults at upper‐crustal levels and shear zones indicating evidence of distributed ductile extensional strain at mid‐crustal levels are recorded. It is proposed that large‐scale regional extension with associated volcanism beginning in the Messinian was represented by the intrusion of asthenospheric material from the subducted plate into the already attenuated accretionary complex. Further rifting, perhaps aided by subduction and back arc processes in the Southern Apennines, led to the formation of the Tyrrhenian Sea as an oceanic basin. Both the Apennines and North American core complexes record evidence of crustal thickening followed by crustal thinning, and finally of continental rifting. This suggests that the similar histories of these regions with vastly different plate tectonic settings may both be explained by processes linked to the changing internal dynamics of accretionary wedges.

Late Miocene remagnetization within the internal sector of the Northern Apennines, Italy

“…1). It is unclear whether exhumation of the Middle Tuscan Ridge was due to isostatic unroofing in a regional extensional setting (e.g., Carmignani and Kligfield, 1990) or to syn-collisional exumation processes (Jolivet et al, 1998).…”

Clay minerals in cave sediments and terra rossa soils in the Montagnola Senese karst massif (Italy)

“…The collisional phase was re lated to the con ver gence be tween Eu rope and the Adria. The extensional post-collisional phase started in the Early-Mid dle Mio cene with the de vel op ment of low-an gle normal faults (Carmignani and Kligfield, 1990;Jolivet et al, 1991;Elter and Sandrelli, 1994), which caused a crustal stretch ing of 120% or more (Carmignani and Kligfield, 1990). The extensional re gime per sisted up to re cent times (Early Plio cene to Qua ter nary) re sult ing in the de vel op ment of high-an gle normal and transtensional faults, that caused a less sub stan tial stretch ing (about 10%) but that strongly in flu enced the present-day mor pho log i cal set tings of the In ner North ern Appennines (i.e., the "horst and graben" struc ture, Carmignani et al, 2001;Brogi, 2003).…”

Geological 3D modeling for excavation activity in an underground marble quarry in the Apuan Alps (Italy)

“…The Apuan Alps metamorphic complex, composed of two major units, the Massa unit and 65 the Apuan unit (Fig. 1), represents the largest tectonic window in the inner Northern Apennines where 66 deep levels of the belt are exposed (Carmignani and Kligfield, 1990;Elter, 1975;Molli, 2008). block and the Adria plate, and was followed by the D2 extensional event that led to a isostatic rebalance 86 (Carmignani and Kligfield, 1990).…”

“…1), represents the largest tectonic window in the inner Northern Apennines where 66 deep levels of the belt are exposed (Carmignani and Kligfield, 1990;Elter, 1975;Molli, 2008). block and the Adria plate, and was followed by the D2 extensional event that led to a isostatic rebalance 86 (Carmignani and Kligfield, 1990). During the D1 event, stacking took place of the tectonics unit 87 belonging to the Tuscan and Ligurian domains, with development of a progressive deformation in two 88 stages , the main of these represented by greenschist foliation (Sp) which is 89 axial plane of isoclinal micro-to kilometric-scale folds.…”

“…During the D2 event, the previously formed structures 93 were reworked and developed different generations of folds and locally high strain zones associated with 94 exhumation and vertical shearing (Molli, 2012). The result of this second deformative phase is a complex 95 mega-antiform with Appenninic trending axis (NW-SE) (Carmignani and Kligfield, 1990). This trend is Their axial direction runs from NE to SW and is sub-parallel to the stretching lineation which, in the entire 130 Apuan complex, shows a N60-80 trend.…”