Ionian Abyssal Plain: a window into the Tethys oceanic lithosphere

Anke Dannowski,David Graindorge,Anne Krabbenhoeft,Ingo Klaucke,Dirk Klaeschen,Heidrun Kopp,Marzia Rovere,Frauke Klingelhoefer,Cord Papenberg,Marc-André Gutscher,David Dellong

doi:10.5194/se-10-447-2019

Abstract

Abstract. The nature of the Ionian Sea crust has been the subject of scientific debate for more than 30 years, mainly because seismic imaging of the deep crust and upper mantle of the Ionian Abyssal Plain (IAP) has not been conclusive to date. The IAP is sandwiched between the Calabrian and Hellenic subduction zones in the central Mediterranean. A NNE–SSW-oriented 131 km long seismic refraction and wide-angle reflection profile, consisting of eight ocean bottom seismometers and hydrophones, was acquired in 2014. The profile was designed to univocally confirm the proposed oceanic nature of the IAP crust as a remnant of the Tethys and to confute its interpretation as a strongly thinned part of the African continental crust. A P-wave velocity model developed from travel-time forward modelling is refined by gravimetric data and synthetic modelling of the seismic data. A roughly 6–7 km thick crust with velocities ranging from 5.1 to 7.2 km s−1, top to bottom, can be traced throughout the IAP. In the vicinity of the Medina seamounts at the southern IAP boundary, the crust thickens to about 9 km and seismic velocities decrease to 6.8 km s−1 at the crust–mantle boundary. The seismic velocity distribution and depth of the crust–mantle boundary in the IAP document its oceanic nature and support the interpretation of the IAP as a remnant of the Tethys lithosphere with the Malta Escarpment as a transform margin and a Tethys opening in the NNW–SSE direction.

Highlights

IntroductionSeismicity and geodesy measurements show that strain is concentrated in narrow bands bounding the microplates that are moving independently from the overall convergent motion (Faccenna et al, 2014)
Starting back in the Cretaceous the ongoing convergence between the African and Eurasian plates results in a complex tectonic setting in the central Mediterranean Sea
Folds in the sedimentary units have been observed at different depth levels at the sea floor within the Plio–Quaternary unit and in the Messinian evaporites (Fig. 2); we do not interpret this as a result of deformation stepping back in time towards the north

Summary

Introduction

Seismicity and geodesy measurements show that strain is concentrated in narrow bands bounding the microplates that are moving independently from the overall convergent motion (Faccenna et al, 2014). The lithosphere of the Ionian Sea constitutes one of these microplates, for which the long-lasting contradictions in the interpretations of the nature of the Ionian Sea crust (“oceanic” vs “thinned continental”) result from a lack of conclusive imaging of the deep crust and upper mantle, preventing a clear characterization. Of special difficulty is the Messinian evaporite unit, which massively impedes seismic energy penetration and limits the data quality of geophysical imaging methods. The challenges in imaging have ignited a long-standing debate about the deeper structure and the nature of the crust and lithosphere of the Ionian Abyssal Plain (IAP). The interpretations range from continental or hyperextended continental lithosphere

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