In the Alboran Domain, lithologic sequences formed mainly of high-grade schists, gneiss, and migmatites are found solely in the tectonic units belonging to the Jubrique and Blanca Groups of the Alpujárride Complex, located above and below the Ronda peridotite slabs, respectively (Fig. 2, Fig. 3). To the east of Málaga (Azañón et al., 1994; 1997), high-grade metamorphic rocks from the Jubrique Group units lie directly over Blanca Group units because of the absence of the Ronda peridotite slabs, which were thinned and moved southwest along extensional detachment faults (Balanyá et al., 1997).

Metamorphic and lithologic criteria are used to clarify whether the basement rocks recovered from Holes 976B and 976E formed part of any of the tectonic units belonging to the Blanca or Jubrique Groups. Partial PT conditions reached by the high-grade schists of the Alboran Sea basement are fairly similar to those of the high-grade schists from the Ojen Unit. In both cases, temperatures of 650°C were reached at ~4-5 kbar at the end of tectonometamorphic event 2 (see Fig. 6 and comments in text on the PT metamorphic conditions of the Alpujárride units and on the Alboran basement beneath Site 976). High-grade schists are found only adjacent to or near marble (probable Triassic protolith) in the Blanca Group units and in the cored basement from Holes 976B and 976E. In contrast, in the Jubrique Unit, phyllites and fine-grained schists stratigraphically close to Triassic carbonate rocks recorded a metamorphic evolution at temperatures of <500°C (Balanyá et al., 1997). The PT conditions of gneiss from the Jubrique and Ojen Units, and of the gneiss from the basement beneath Site 976, are similar.

The lithologic assemblages from the cored basement and the Ojen Unit are also similar. Alternating marble and high-grade schists appear in the Ojen Unit on both sides of the axial-plane of a major recumbent syncline formed during tectonometamorphic event 3 (see Fig. 3). Some of these alternations appear to of stratigraphic origin, but at least some of them are related to the second-order folds of the recumbent syncline.

The rocks recovered from Holes 976B and 976E are similar to those comprising the Ojen unit in the Ronda region. Nevertheless, structural considerations lead us to present the two tentative correlation proposals in Figure 3. It is possible that part of the rocks drilled at Site 976 were Guadaiza Unit schists or marbles and high-grade schists from one of the Montemayor slices. However, numerous fault rock zones were drilled, which suggests that the original thickness of the lithologic sequence was significantly reduced, with the consequent approximation of the lithologic boundaries.

The tectonic exhumation of rocks from the Blanca Group is partially contemporary with the deposition of lithoseismic unit 4 (Upper Serravallian-Tortonian; Comas et al., 1992) and this tectonic exhumation forms part of an extensional episode of the Alboran Basin rifting that had a direction of roughly northeast-southwest (García-Dueñas et al., 1992). Cross section B-B´ (Fig. 4) shows the structural relationship between the Alpujárride units of the Ronda region (cross section A-A´, Fig. 4) and the basement high beneath Site 976. Mud diapirs are related to the north-northwest-south-southeast extension episode that produced thinning and dismembering of the Alpujárride units located to the north of the Sierra Blanca (cross section A-A´). Superimposed northeast-southwest extension-generated faults, with a transport sense toward the southwest (García-Dueñas et al., 1992; Balanyá et al., 1997), probably reused the previous faults as ramps, with right-lateral slip (fault next to the shoreline) and left-lateral slip (fault north of the basement high).

Final positioning of the peridotite bodies around the Gibraltar Arc (Fig. 1) shows the result of the superposition of the two transverse extensional systems. The Ronda peridotite bodies could be connected to the Beni Bousera massifs of the Rif through a thin layer of serpentinized peridotites, visible at Ceuta (north-northwest-south-southeast extensional direction), in the same way that the Carratraca and Bermeja bodies are connected (northeast-southwest extensional direction; Fig. 2).