Rifting of continental margins and evolution of conjugated margins in the Tyrrhenian Sea caused by subduction-related slab roll back
Final Report Abstract
The Tyrrhenian basin has been created during the extension of continental lithosphere driven by the retreat of the Ionian slab. The basin does not seem to be actively extending, but its preserved crustal structure provides information of the time evolution of the processes involved in rifting. Thus, seismic refraction/wide-angle (WAS) and multichannel reflection seismic (MCS) transects of the structure attained at different stretching (beta ß) factors provide information of the formation processes. Most interestingly, seismic stratigraphy calibrated with drill holes indicates that the north to south changes in structure are related mainly to changes in extension rates rather than on large changes in the age of rifting. The northern region stopped opening after a relatively low extension factor. Here, the rift structure is rather symmetric, ruling out that simple-shear is a major driving force generating rift asymmetries in young rifts with β~1.3 to 1.5 (total crust thinner from ~24 km under Corsica to 17 km in the northern basin). Towards the south extension increased. With increasing extension asymmetries were introduced at β~2,2. Rift-asymmetries are indicated by changes in crustal thickness (decreasing to ~11 km) and decreasing fault-block sizes, while the number of faults increases. Rift-asymmetries are suggested to be governed by the eastward migration of the axis of rifting. In the northernmost region, rifting stopped at a ~ factor of ~2.2. Farther south, increasing extension led to full crustal separation that produced mantle exhumation. Analysis of the WAS data has provided a characterization of the type of crust and its lateral distribution. Break-up was followed by formation of ocean crust in a back-arc setting. Faulting activity migrated and localized in a different region of the rift system and was followed by extensive mantle exhumation. The final structure displays two conjugate continental margins separated by an intervening region of ocean crust that laterally abruptly changes to exhumed mantle. The seismic stratigraphy indicates that the change from oceanic back-arc spreading to mantle exhumation occurred at fast opening rates, comparable to those of fast spreading centers. The lateral distribution of rock types and fast extension rates characterizing the time of mantle exhumation challenge current conceptual models of continental rifting. In contrast, the text-book example Iberia/Newfoundland indicated that the final stage of rifting caused widespread mantel exhumation at very low extension rates. Latter, oceanic crustal formation took over. Thus, we have to revise our conceptual models, suggesting that serpentinization and un-roofing of mantle is controlled by slow extension rates and cooled mantle conditions.
Publications
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(2013), Early-stage rifting of the northern Tyrrhenian Sea Basin: Results from a combined wide-angle and multichannel seismic study, Geochem. Geophys. Geosyst., 14, 3032-3052
Moeller, S., I. Grevemeyer, C. R. Ranero, C. Berndt, D. Klaeschen, V. Sallares, N. Zitellini, and R. de Franco
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Rifting in the northern Tyrrhenian Sea Basin: a multichannel and wide-angle seismic study, Dissertation, Christian Albrechts-Universität zu Kiel, pp. 205, 2013
Moeller, S.
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(2014), Crustal thinning in the northern Tyrrhenian Rift: Insights from multichannel and wide-angle seismic data across the basin, J. Geophys. Res., 119, Issue 3, March 2014, Pages 1655-1677
Moeller, S., I. Grevemeyer, C. R. Ranero, C. Berndt, D. Klaeschen, V. Sallares, N. Zitellini, and R. de Franco
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(2014), Seismic structure of the Central Tyrrhenian basin: geophysical constraints on the nature of the main crustal domains, J. Geophyis. Res., 119, Issue1, January 2014, Pages 52-70
Prada, M.,V. Sallares, C.R. Ranero, M.G. Vendrell, I. Grevemeyer, N. Zitellini, and R. de Franco
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Structure and Formation of the Tyrrhenian Basin in the Western Mediterranean Back-arc setting, Dissertation, Universitat de Barcelona, pp 294, 2014
Prada, M.
