The structure and evolution of the Northern Tyrrhenian Sea

Abstract

Field studies on the island of Elba and seismic lines from the Northern Tyrrhenian Sea, Italy, indicate that major extensional displacements were accommodated along east-dipping low-angle detachment faults. The rifting and subsidence in the Northern Tyrrhenian Sea basin have followed convergence and collision of the Corso-Sardinian block and the Apulian microplate. This collisional episode produced the Northern Apennines fold-and-thrust belt. Major extensional faults cut down-section through the stratigraphy and pre-existing west-dipping thrust faults. West-dipping thrusts can also be reactivated and form antithetic faults to the east-dipping detachments. Brittle deformation conditions predominated during the extensional phase. The geometry, internal structure and the fabrics (brittle and penetrative) associated with a wellexposed low-angle extensional detachment in Elba are presented in this paper. A geometrical model for the brittle extensional faulting is presented in which regional extension was accommodated on a system consisting of two sets of simultaneously active antithetic faults. The east-dipping detachment faults appear to have started at steeper angles, based on field and seismic observations, and rotated counter-clockwise to lower dips. Due to this rotation, and for space accommodation, antithetic west-dipping faults formed and rotated clockwise. A tectonic model is proposed whereby slowing of the convergence between Apulia and Corsica, as well as Tethys oceanic crust and Apulian crust subduction, led to the delamination of the Apulian lithospheric mantle away from the crust. Accompanying asthenospheric upwelling and intrusion at the crust-mantle interface beneath the Tyrrhenian Sea caused late orogenic crustal stretching in the Northern Apennines internal zone.

Development of interconnected talc networks and weakening of continental low-angle normal faults

“…1). Fault rocks currently exposed at the surface preserve evidence for deformation processes that occurred at <8 km depth, with a total fault offset in the range of 6-8 km (Keller and Coward, 1996;Collettini and Holdsworth, 2004). Geological data demonstrate that the fault accommodated extension as a gently dipping structure (Collettini and Holdsworth, 2004;Smith et al, 2007).…”

Early‐stage rifting of the northern Tyrrhenian Sea Basin: Results from a combined wide‐angle and multichannel seismic study

“…[39] The west-dipping sediment unit at the eastern edge of the Corsica Basin might be related to thrusting formed during the collisional phase between Corsica-Sardinia and the Apulian continental block [Keller and Coward, 1996]. Mauffret et al [1999] propose that the basin formed over a collisional prism in a forearc position between Corsica and the Adriatic plate, and that the thrusts are Alpine.…”

“…Possible weak regions in the Tyrrhenian might be inherited pre-existing tectonic features that can be reactivated. Field work on Elba Island shows that extensional features related to the opening of the Northern Tyrrhenian Sea overprint former compressional features [Keller and Coward, 1996]. Thus, the initial angle of the major normal faults may have been controlled by the reactivation of relatively high-angle thrust faults.…”

Neogene deformation and granite emplacement in the metamorphic units of northern Apennines (Italy): Insights from mylonitic marbles in the Porto Azzurro pluton contact aureole (Elba Island)

“…In the Alpi Apuane, early deformation (D 1 ) was realized at 27-20 Ma, whereas later synmetamorphic deformation (D 2 ) predated 11 Ma (Kligfi eld et al, 1986;Balestrieri et al, 2003).…”