Crustal Structure of the Ionian Basin and Eastern Sicily Margin: Results From a Wide‐Angle Seismic Survey

Abstract

In the Ionian Sea (central Mediterranean) the slow convergence between Africa and Eurasia results in the formation of a narrow subduction zone. The nature of the crust of the subducting plate remains debated and could represent the last remnants of the Neo‐Tethys ocean. The origin of the Ionian basin is also under discussion, especially concerning the rifting mechanisms as the Malta Escarpment could represent a remnant of this opening. This subduction retreats toward the south‐east (motion occurring since the last 35 Ma) but is confined to the narrow Ionian basin. A major lateral slab tear fault is required to accommodate the slab roll‐back. This fault is thought to propagate along the eastern Sicily margin but its precise location remains controversial. This study focuses on the deep crustal structure of the eastern Sicily margin and the Malta Escarpment. We present two two‐dimensional P wave velocity models obtained from forward modeling of wide‐angle seismic data acquired onboard the R/V Meteor during the DIONYSUS cruise in 2014. The results image an oceanic crust within the Ionian basin as well as the deep structure of the Malta Escarpment, which presents characteristics of a transform margin. A deep and asymmetrical sedimentary basin is imaged south of the Messina strait and seems to have opened between the Calabrian and Peloritan continental terranes. The interpretation of the velocity models suggests that the tear fault is located east of the Malta Escarpment, along the Alfeo fault system.

Geology of the Ionian Basin and Margins: A Key to the East Mediterranean Geodynamics

“…The transition from the Malta platform to the Ionian Basin across the Malta escarpment is based on our calibration work (Figure a) and previous observations (Cernobori et al, ; Chamot‐Rooke, Rangin, et al, (); Minelli & Faccenna, ; Polonia et al, . The crustal structure of the Malta escarpment is mainly constrained by the refraction seismic profile shown by Dellong et al (). The interpretation across the Ionian Basin is based on lines 2 and 34 from the ARCHIMEDE survey presented in Chamot‐Rooke, Rangin, et al () and Gallais et al ().…”

“…Following many others, and based on our age calibration, we conclude that the thin Ionian crust shows similarities with old oceanic crust (Lower to Middle Jurassic), at least where ESP data are located. Results from recent wide‐angle seismic experiments (Dannowski et al, ; Dellong et al, ) confirm the oceanic nature of the Ionian crust, discarding the continental crust hypothesis east of the Malta escarpment and north of the Medina Seamount where they interpret the location of the ocean‐continent transition.…”

“…No refraction data are available on the Apulian side, but the abrupt linear trend of the margin, despite reshaping during the Messinian erosion, is preserved. Refraction data of Dellong et al () also image a sharp ocean‐continent transition and the tabular architecture of the Ionian crust. Our section runs south of the Alfeo‐Etna fault system (Figures and ; Polonia et al, ) commonly interpreted as a STEP fault (Cernobori et al, ; Hirn et al, ; Argnani et al, ; see review in Gallais et al, ) and consequently does not show it.…”

Geometry of the Deep Calabrian Subduction (Central Mediterranean Sea) From Wide‐Angle Seismic Data and 3‐D Gravity Modeling

“…The escarpment was originally interpreted to be a passive margin originating from the initial opening of the Ionian Sea. Later studies proposed this to be a transform margin (Catalano et al, ; Dellong et al, ; Frizon de Lamotte et al, ; Gallais et al, ), which is in good agreement with an opening at the Late Triassic/Early Jurassic of the Ionian Basin (Frizon de Lamotte et al, ). Other studies propose ages ranging from early Late Triassic (220 Ma; Speranza et al, ) to Late Jurassic to Early Cretaceous (Catalano et al, ).…”

“…CROP‐M3 MCS profile is coincident to DY‐P4 (Figure ; Polonia et al, ). Bathymetry from Gutscher et al () (after Dellong et al, ). Yellow‐shaded area marks the supposed extension of tectonically thickened evaporites in the Calabrian accretionary wedge.…”