Post-Rift Compressional Deformation on the Passive Margin of a young Mediterranean Backarc Basin (Eastern Sardinian Margin, Tyrrhenian Sea)

Abstract:

Compressional deformation has been reported on many passive margins, mostly attributed to thin-skinned tectonics in response to gravity gliding or spreading from viscous layers (overpressured shales, salt décollement). However some of the reported structures are obviously related to regional stress and also affect the basement, not only the upper sedimentary cover. Such deformation has been documented and discussed in the last decade mainly from the northern Atlantic margins (Doré et al., 2008 ; Pereira et al., 2011, & ref. herein). The compressional structures on passive margins have been notably considered as linked to tectonomagmatic and active asthenospheric upwelling, post-breakup compression and compactional stresses.

The western margin of the Tyrrhenian Sea (Central Mediterranean) is a passive margin formed during the late Miocene opening of a back-arc basin in relation with the roll-back and retreat of the Ionian subducting lithosphere (African Plate). From our new data, we can show evidence for compressional features that developed in the Pliocene, shortly after the main rifting period on the western Tyrrhenian Sea (Middle to Late Miocene) and beginning of oceanic spreading (Earliest Pliocene). We could describe such structures across the inner margin onshore, from field analysis, as well as offshore, from newly acquired seismic data (METYSS 1 & 3; Gaullier et al. 2014).

The characters and distribution of such compressional deformation, occurring very shortly after the onset of oceanic spreading in the deep basin (earliest Pliocene), allow us to discuss the possible interactions between breakup processes and inversion episodes on passive margins.

Doré A.G., Lundin E.R., Kusznir N.J., & Pascal C., 2008. Potential mechanisms for the genesis of Cenozoic domal structures on the NE Atlantic margin: Pros and cons and some new ideas. Geol. Soc. London Spec. Pub., 306, 1-26.

Gaullier V., Chanier F., et al., 2014. Salt tectonics and crustal tectonics along the Eastern Sardinian margin, Western Tyrrhenian : New insights from the « METYSS 1 » Cruise. Tectonophysics, 615-616, 69-84.

Pereira R., Alves T.M. , & Cartwright J., 2011. Post-rift compression on the SW Iberian margin (eastern North Atlantic): a case for prolonged inversion in the ocean-continent transition zone. J. Geol. Soc., 168, 1249-1263.