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Characterization of different crustal domains in the Central Tyrrhenian Sea from wide-angle and near vertical seismics and gravity modelling

Manel Prada, Valentí Sallarès, César R. Ranero, Montserrat Guzman, Nevio Zitellini, Ingo Grevemeyer, and Roberto de Franco

We use coincident wide-angle seismic data (WAS), multichannel seismic reflection (MCS) images and gravity data acquired during the MEDOC cruise in 2010 to characterize the tectonic structure of the Central Tyrrhenian basin. The ~450km-long, E-W-trending transect that we present, crosses the entire basin from Sardinia (40N) to the Campanian margin (Italy). The WAS data, recorded on 26 OBH/S (Ocean bottom hydrophones/seismometers) and 5 land stations, were modelled to obtain a P-wave velocity model of the basin and the Moho geometry by joint refraction and reflection travel-time tomography. The velocity-derived density modelling was used to infer the composition of domains that fit gravity data being consistent with the velocity model. On the basis of the velocity gradients the model shows four different crustal domains. The westernmost domain, in Sardinia, displays a ~23±2km-thick continental crust with a mean velocity of 6.5±0.3km/s. Eastwards from this domain the crust thins to 10±1 km in ~140 km. This domain is interpreted as a highly extended continental crust, containing numerous faults that are consistently imaged in the coincident MCS profile. In the central part of the profile, the third domain is characterized by the lack of crustmantle reflections in both WAS and MCS data, and a strong vertical velocity gradient, similarly to what has been described in regions of mantle exhumation like the West Iberian Margin. In this region there are also several isolated velocity anomalies with low velocity roots associated with the presence of well-known volcanic bodies, probably in the form of magmatic intrusions that occurred after the mantle exhumations. In the Easternmost segment of the profile, beneath the Campanian margin, the crust-mantle boundary is well-defined and very similar to the conjugate margin in the velocity field and crustal thickness, showing a progressive thickening of the continental crust towards mainland. We conclude that, in this part of the Tyrrhenian basin, and especially in the central part, extension occurred slowly enough to exhume mantle rocks without producing enough synchronous magmatism to generate a well-defined oceanic crust.

AAPG Search and Discovery Article #90161©2013 AAPG European Regional Conference, Barcelona, Spain, 8-10 April 2013