ORIGIN OF THE BETIC-RIF MOUNTAIN BELT

In recent years, the origin of the Betic-Rif orocline has been the sub ject of considerable debate. Much of this debate has focused on mechan isms required to generate rapid late-orogenic extension with coeval sh ortening. Here Me summarize the principal geological and geophysical o bservations and propose a model for the Miocene evolution of the Betic -Rif mountain belts, which is compatible with tie evolution of the res t of the western Mediterranean. We regard palaeomagnetic data, which i ndicate that there have been large rotations about vertical areal and earthquake data, which show that deep seismicity occurs beneath the Al boran Sea, to be the most significant data sets. Neither: data set is satisfactorily accounted for by models which invoke convective removal or delamination of lithospheric mantle. Existing geological and geoph ysical observations are, however, entirely consistent with the existen ce of a subduction zone which rolled or peeled back until it collided with North Africa. We suggest that this ancient subducting slab conseq uently split into two fragments, one of which has continued to roll ba ck, generating the Tyrrhenian Sea and forming the present day Calabria n Arc. The other slab fragment rolled back to the west, generating the Alboran Sea and the Betic-Rif orocline during the early to middle Mio cene.