Crustal reflections and structure in the Alborán basin: preliminary results of the ESCI-Alborán survey

Resum

The ESCI-Alb survey explores the crust beneath the Albarán Sea and the South-Balearic basin. Both extensional basins developed in the westernmost Mediterranean during the Neogene collision of the Eurasian and African plates. The ESCI-Alb profiles (Alb1 and Alb2) reveal shallow tectonic structures, and basins (filled mainly by Middle-to-Late Miocene to Recent sediments) located between fault-bounded highs of metamorphic basement and/or volcanic edifices. Profile ESCI-Alb1 sampled the Spanish margin and shows an extensional mid-Miocene basin deformed by later compressional structures, including folds and tectonic reversal of normal faults. The age of this compressional deformation spans up to the Late Pliocene. In the East Albarán and South Balearic basins, Late Miocene (?) rifting processes resulted in tilting and faulting of basement blocks (profile ESCI-Alb2). Structurally-induced bathymetric changes in the seafloor, either by extension or by compression, denote recent or present-day tectonic activity in the surveyed area. In profile ESCI-Alb1, a conspicuous package of dipping reflections (6-8 s TWT) could represent a detachment surface within the crust in the northern Albarán margin. Further South, a 60 km long zone from 6 to 9 s shows a distinctive layered lower crust where the lower boundary is interpreted as the reflective Moho. Scarce deep reflections are imaged at the ESCI-Alb2 profile; however, some single reflections might be ascribed to the reflection Moho of a possible transitional or oceanic crust in the South-Balearic basin.