Plio-Quaternary strike-slip tectonics in the Central Mallorca Depression, Balearic Promontory: Land–sea correlation

The Balearic Promontory (Spain) is of key importance to understand the tectonic kinematics of the westernmost Mediterranean, because its continued marine sedimentation has recorded the contrasting effects expected from competing geodynamic models proposed for the region. Near the center of this promontory, between the islands of Mallorca and Ibiza, the Miocene to Pleistocene stratigraphy of the Central Mallorca Depression presents an ideal record of the tectonic deformation that has received only limited attention. We use a widespread dataset of 2D seismic reflection profiles to identify, interpret and map the main prominent reflectors and extrapolate the thickness of the pre-Messinian and Pliocene-Quaternary sedimentary units. We then quantify the timing and style of deformation related to the various fault systems. Our results reveal for the first time a series of aligned small depressions bounded by extensional and strike-slip faults and filled with Plio-Quaternary sediment, perfectly aligned with the sub-basins of the onshore Mallorca Graben. A subsidence analysis confirms this correlation. We identify non-cylindrical deformation within the Plio-Quaternary unit that is remarkably similar to that observed onshore, suggesting continuous fault zones from the Central Mallorca Depression to Mallorca Island. We interpret an intra-PQ unconformity as the marker of a transition from extensional to strike-slip tectonic regime. The strike-slip stage is represented by both transpressional and transtensional structures, interpreted as restraining/releasing bends respectively and step overs along the faults. We show that these offshore faults in the Central Mallorca Depression overlap well with seismic epicenters and suggest major active strike-slip corridors that have an onshore continuity both until eastern Mallorca and in the southwestern Ibiza margin. The role of previous tectonic inherited structures (rifting, Betic thrusts, post-orogenic collapse) on the deformation reported here is discussed and we propose a tentative sketch that integrates our results in a Miocene to Present-day evolution at regional scale.
This research is partly carried out under the SALTGIANT ETN, a European project funded by the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement number 765256. SALTGIANT ESRs and PIs are all thanked for the numerous exchanged discussions and comments during workshops, courses and fieldtrips. We are grateful to Antonio Cap? and Juan Forn?s for inspiring discussions on arguments about the study area. Part of the seismic data covering the Balearic Promontory and shown in this work were provided courtesy of WesternGeco and Spectrum companies that we acknowledge. We acknowledge Schlumberger Company for providing the academic license of the seismic interpretation software Petrel. The authors are grateful to Guillermo Booth-Rea and Rob Govers whose reviews and suggestions greatly improved the original manuscript. This paper is dedicated to our colleague Guillem Mas who suddenly and dramatically passed away during the writing of the manuscript. He showed us the field in Mallorca in 2019, where the idea of this work came from.