Styles and rates of deformation in the frontal accretionary wedge of the Calabrian Arc (Ionian Sea): controls exerted by the structure of the lower African plate

Giovanni Bortoluzzi (†), Alina Polonia (1), Luigi Torelli (2), Andrea Artoni (2), Mirko Carlini (2), Savino Carone (3), Gabriela Carrara (1a), Marco Cuffaro (4), Fabrizio Del Bianco (1b), Fabrizio D'Oriano (1a), Valentina Ferrante (1), Luca Gasperini (1), Roberta Ivaldi (3), Amedeo Laterra (3), Marco Ligi (1), Marina Locritani (5), Filippo Muccini (5), Paola Mussoni (2c), Flavio Priore (1b), Francesco Riminucci (1b), Stefania Romano (1) & Giuseppe Stanghellini (1)
(1) Institute of Marine Science CNR ISMAR-Bo, Via Gobetti, 101, 40129 Bologna, Italy. Tel: +39 051-6398888. Corresponding author: e-mail: alina.polonia@ismar.cnr.it.
(2) Department of Chemistry, Life Sciences and Environmental Sustainability.
(3) Istituto Idrografico della Marina, Passo Osservatorio, 4 -16134 - Genova.
(4) Istituto di Geologia Ambientale e Geoingegneria, CNR, c/o Dipartimento di Scienze della Terra, Sapienza Università di Roma, P.le A. Moro 5, I-00185 Rome, Italy.
(5) Istituto Nazionale di Geofisica e Vulcanologia, via di Vigna Murata 605, 00143 Rome, Italy.
(a) now: independent researcher.
(b) now: PROAMBIENTE S.c.r.l., Emilia-Romagna High Technology Network, Via P. Gobetti, 101 40129, Bologna, Italy.
(c) now: Eni S.p.A.- Upstream and Technical Services (GEOS).

The Calabrian Arc is a narrow subduction-rollback system resulting from Africa/Eurasia plate convergence. We analysed the structural style of the frontal accretionary wedge through a multi-scale geophysical approach. Pre-stack depth-migrated crustal-scale seismic profiles unravelled the overall geometry of the subduction complex; high-resolution multi-channel seismic and sub-bottom CHIRP profiles, together with morpho-structural maps, integrated deep data and constrained the fine structure of the frontal accretionary wedge, as well as deformation processes along the outer deformation front.
We identified four main morpho-structural domains in the western lobe of the frontal wedge: the proto-deformation area at the transition with the abyssal plain; two regions of gentle and tight folding; a hummocky morphology domain with deep depressions and intervening structural highs; a highstanding plateau at the landward limit of the salt-bearing accretionary wedge, where the detachment cuts through deeper levels down to the basement. Variation of structural style and seafloor morphology in these domains are related to a progressively more intense deformation towards the inner wedge, while abrupt changes are linked to inherited structures in the lower African plate. Our data suggest focusing of intense shallow deformation in correspondence of deeply rooted faults and basement highs of the incoming plate.
Back-arc extension in the Southern Tyrrhenian Sea has recently ceased, producing a slowdown of slab rollback and plate-boundary re-organization along trans-tensional lithospheric faults segmenting the continental margin. In this complex setting, it is not clear if the accretionary wedge is still growing through frontal accretion. Our data suggest that shortening is still active at the toe of the wedge, and uplift rates along single folds are in the range of 0.25-1.5 mm/yr. An unconformity within the Plio-Quaternary sediments suggests a discontinuity in sedimentation and tectonic processes, i.e. a slowdown of shortening rate or an increase in sedimentation rate, but not a real inactivation of frontal accretion, which still contributes to the migration of the outer deformation front towards the foreland.

Calabrian Arc, Accretionary wedge, African plate, frontal accretion, Basement structure