Contractional and extensional tectonics in Flysch and Penibetic units (Gibraltar Arc, SW Spain):: new constraints on emplacement mechanisms

The Aljibe Unit (Flysch Trough Complex), which can be described as a thin-skinned contractional belt, represents a major element of the Gibraltar Are accretionary prism. It is shown that this unit underwent WNW-ESE shortening during the Miocene, as did the underlying Penibetic units. The organization of the Aljibe unit suggests a push-from-behind emplacement mechanism during this first contractional event. By contract, the current boundary between the Penibetic and Aljibe units is found to be a normal, low-to-moderate angle fault that was later folded. This extensional faulting occurred between two compressional pulses (Lower-to-Middle and Upper Miocene in age) with similar shortening directions. (C) 2000 Academie des sciences / Editions scientifiques et medicales Elsevier SAS.