Hyper-extended rifted margin in the Tyrrhenian Sea, upper plate of the Ionian subduction zone

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Abstract

The Tyrrhenian Sea is a Miocene to Present back-arc basin developed in the upper plate of the Ionian subduction zone. Refraction seismic data indicate that the central sector of the Marsili Basin is a zone of thin crust ∼7 km thick compatible with its oceanic origin (Steinmetz et al., 1983). Conventional models rather define a Continent-Ocean Transition (COT) with normal oceanic crust (i.e. Finetti et al., 2005). This does not seem to be the case for the whole Tyrrhenian Basin. Serpentinized peridotites, emplaced during Pliocene, have been drilled at ODP Site 651 (Sartori et al. 2004). The W Calabria segment of the Tyrrhenian continental margin is peculiar as seismic data has excluded the presence of Miocene to Recent significant normal faults (Pepe et al., 2010). There is therefore a major question as to which structures were able to cause thinning and what does the oceanic domain look like. A possible answer is derived from the high-penetration Crop-M27 seismic line acquired along the COT of the W Calabria margin and the Marsili ocean itself. The most surprising result is the discovery of tilted fault-blocks located within the area Marsili Basin considered as floored by oceanic crust. The blocks are generally 2-4 km wide and are composed of an acoustic basement which corresponds to the top of the Kabilian-Calabrian units and of a sedimentary cover unit that on the basis of their geometry we consider as pre-rift. The overall style of the block is comparable to dominos. The deposits filling the depressions between blocks are partly syn-rift and, more dominant, post-rift. With a very few exceptions, the infill completely smoothes out pre-existing topography and explain the very flat sea floor in the area surrounding the Marsili Basin. Its age was estimated as young as 0.45 Ma (Kastens et al., 1988). A conceptual model for the evolution of the Marsili Basin was reconstructed along a NW-SE cross-section using seismic data and seafloor morphology (Marani & Gamberi, 2004). Extensional tectonics during the Early Pliocene was active in the area of the future Vavilov Basin while, towards the SE, tectonics is dominated by contraction with thrust and reverse faulting. Since ∼4.2 Ma, extensional tectonics jump in the area of the future Marsili Basin. Extension tectonics affected a sector of the Kabilian-Calabrian chain and resulting in the formation of normal faults, mostly trending NNE-SSW and dipping to the NNW. The early stage of emplacement of oceanic crust was dated at ∼1.8–2 Ma (Kastens et al., 1988). Extensional tectonics persisted until ∼0.5 Ma resulting in the formation of ∼80 km of oceanic crust and ∼30 km of Continent Ocean Transition Zone with a thickness ranging from ∼10 to less than ∼7 km. Normal faults were active before and after crustal separation. Extensional tectonics ended ∼0.5 Ma. However, this was not the end of the overall evolution of the Marsili Basin because from ∼0.78 Ma to ∼0.3Ma the Marsili seamount formed (i.e. Cocchi et al., 2009). The position of this volcano is not random and is probably controlled by deep transition between continental and oceanic lithosphere.
Lingua originaleEnglish
Numero di pagine1
Stato di pubblicazionePublished - 2011

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