The Gibraltar Arc: An Orogenic Float Modified by Late Transpression

Abstract

Seismic data, supplemented by field observations, indicate the presence of an accretionary complex in the frontal part of the Gibraltar arc. The complex can be subdivided into an inner complex represented by the classical Flysch units, and an outer complex made up by the Guadalquivir allochthonous units in the Betics and the Preifaine Nappe in the Rif. The inner complex records Upper Cretaceous to Paleocene accretion, and the outer complex registers Neogene accretion related to the westward escape of the Alboran domain. Upper Miocene extensional collapse in the wedge is coeval with frontal thrusting and back-arc extension in the Alboran back-arc basin. Extensional basins parallel to the arc are overprinted at right angles by a second set of half garbens. This radial extension could be related to oroclinal bending of the arc. Late Pliocene-Quaternary compression and transpression resulted in basement- and platform-involved, deep-seated tectonics. This late event is associated with Iberia-Africa northsouth convergence and is responsible for the seismicity and neotectonics of the Azores-Gibraltar-Alboran region. A number of satellite extensional and compressional basins, in the past interpreted as thrust sheets, developed piggyback on the accretionary complex. These basins reflect the westward accretion and late transpression that have affected the Gibraltarmore » arc since the Paleogene. The hydrocarbon potential of the satellite basins located on the accretionary complex will be evaluated.« less