INTERFERENCE PATTERN OF EXTENSIONAL FAULT SYSTEMS - A CASE-STUDY OF THE MIOCENE RIFTING OF THE ALBORAN BASEMENT (NORTH OF SIERRA-NEVADA, BETIC CHAIN)

In the Betic-Rif orogenic belt, in the westernmost part of the Mediterranean, early and middle Miocene crustal thinning of the upper part of the Alboran basement is well established by previous studies. In the Alboran domain of the central Betics, the present distribution of the Alpujarride units results from the extensional dismembering of a pre-Miocene nappe stack under brittle conditions. The interference of two subperpendicular and successive extensional fault systems can explain the current geometric pattern of the Alpujarride units: upper-Burdigalian-Langhian north-south extension was followed by west- to southwestward extension of Serravallian age. Northeast of Sierra Nevada, these two extensional systems have resulted in a spectacular chocolate tablet megastructure and the cropping out, at any one vertical sequence, of a varying number of extensional units belonging to the Alpujarride complex. This pattern can be considered representative of the middle Miocene tectonics of the entire Alboran domain in the Betics, and illustrates the development of rifting processes in the upper crust.