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 Mediter ranean, 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-M iocene nappe stack under brittle conditions. The interference of two s ubperpendicular and successive extensional fault systems can explain t he current geometric pattern of the Alpujarride units: upper-Burdigali an-Langhian north-south extension was followed by west- to southwestwa rd extension of Serravallian age. Northeast of Sierra Nevada, these tw o 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 comp lex. This pattern can be considered representative of the middle Mioce ne tectonics of the entire Alboran domain in the Betics, and illustrat es the development of rifting processes in the upper crust.