Conclusions

Alboran peridotites have been emplaced in the crust by means of a complex process that comprised at least two main contractional events: the first one recorded by HP mineral assemblages on crustal and mantle rocks, and a second one expressed by the superposition of units (incuding the peridotite slab) and large recumbent folds. Between the main contractional events there was vertical lithospheric thinning contemporary with the rise of the peridotites through the mantle to the bottom of a thin crust (4-6 kbar, ca. 15-20 km).

All the Alboran peridotite bodies were emplaced as a single slab, probably farther east from the present position, forming an intra-Alpujarride suture during the early Miocene-Oligocene. Destabilisation of this second contractive event, or roll-back of a subducting lithosphere slab, generated considerable extension that affected the former peridotite slab. Initial fragmentation in the early Miocene was caused by ductile N-S lineated shear zones that individualized the main peridotite bodies and produced nearly continuous serpentinite slices between them. Middle to late Miocene brittle fault systems finalized the separation of the bodies to the current location.

Total accumulative N-S extension can be estimated from the reconstruction of the former peridotite slab (Fig. 6), of at least 1.4 to 2 (Fig. 2). Thus, paradoxically, N-S extension is one of the most patent features of the Alboran orogen in an N-S plate convergence setting.