The best exposure of the higher Alpujárride units is found in this region, corresponding to the Jubrique and Blanca Groups (Balanyá et al., 1997; Tubía et al., 1992), located respectively above and below the peridotite massifs (Fig. 1, Fig. 2).
The Jubrique Group (Fig. 2) consists of the Jubrique Unit and the overlying Benarraba imbrications (Balanyá et al., 1997). The metamorphic isograds display parallel to Sp foliation in all these units. This general parallelism was produced during the above-mentioned extensional event 2 (Loomis, 1972; Torres-Roldán et al., 1979; Balanyá et al., 1993); at the same time, the Jubrique Unit thinned to probably one-third its original thickness and the lower crust disappeared entirely (Balanyá et al., 1997).
Specifically, the Jubrique Unit (Balanyá, 1991; Balanyá and García-Dueñas, 1991) contains a 5-km-thick metamorphic succession of, from bottom to top (Fig. 3), garnet gneiss, migmatite gneiss, staurolite-bearing schists, chloritoid-bearing schists, fine-grained schists, quartzites, calc-silicate, and carbonate rocks. It has upward-decreasing metamorphic zoning, with isograds subparallel to the lithologic contacts. The surprisingly complete lithologic sequence of the Jubrique Unit roughly corresponds to a segment of condensed middle-upper crust (Balanyá et al., 1993; Balanyá et al., 1997). It grades from metapelitic granulites at the bottom to Triassic carbonate formations at the top, with little or no evidence of recrystallization. Each of the Benarraba imbrications (Fig. 2, Fig. 3) consists of lithologic sequences similar to the upper third of the Jubrique Unit, normally comprising chloritoid-bearing schists up to the formation of carbonates and, more locally, staurolite-bearing schists in a lowermost position.
The Blanca Group consists of, in ascending order, the Ojen and Guadaiza Units (Fig. 2, Fig. 3, Fig. 4), both predominated by high-grade metamorphic rocks intruded by variably sized granitic bodies (Navarro-Vilá and Tubía, 1983; Tubía, 1985).
The Ojen Unit, which underlies the Alpujata peridotite massif, is a large-scale recumbent syncline whose reverse limb crops out at the Sierra Blanca in the core of a late superimposed Miocene anticline (Fig. 2). The recumbent synclinal core contains thick marbles (Triassic protoliths) and the limbs contain high-grade schists, amphibolites, and gneissic rocks. Minor folds (Fig. 5C) and a penetrative axial-plane cleavage (Sc) overprint the Sp foliation. The Ojen lithologic sequence consists of the following members in ascending stratigraphic order (Fig. 3): migmatite and garnet gneiss (Fig. 5A), high-grade schist and gneiss with intercalated metabasites, and marbles, the latter attributed to the Triassic (Mollat, 1968; Westerhof, 1975). An abundance of metabasite intercalations, with eclogite relics in the lowest ones, is a characteristic feature of the Ojen Unit (Tubía and Gil Ibarguchi, 1991; Sánchez-Gómez, 1997).
The Guadaiza Unit contains a monotonous sequence of quartzites, high- and medium-grade schists, gneiss, and minor amounts of metabasites. Marble bodies are included within a thick fault zone overlying the unit; however, it is impossible to determine whether or not they form part of the unit.
The Montemayor tectonic slices lie beneath the Bermeja and Alpujata major peridotite bodies, but overlie the Guadaiza and Ojen Units (Fig. 2, Fig. 3). They are formed from alternating slices of peridotites or Blanca Group-type rocks, associated with abundant granitic rocks (Lundeen, 1978; Sánchez-Gómez et al., 1995). The Montemayor peridotite slices are generally undifferentiated in Figure 2 because of their extreme thinness (<10 m at times). Nevertheless, some Montemayor ultramafic slices are laterally continuous with the thick slabs forming the Ronda peridotite massifs, as is the case of the northeastern thinning of the lower of the two outcropping peridotite slabs 7 km north of Estepona (Fig. 2). The boudinlike structure of the Alpujata peridotite massif, emplaced between the overlying Jubrique Unit and the underlying Ojen Unit (Fig. 2), is an illustrative example of lateral thinning produced by northeast-southwest stretching. Nearly northwest-southeast extension can be seen throughout cross section A-A´ in Figure 4.
Migmatitic and intrusive granitic rocks (granite and granodiorite), normally rich in cordierite and xenoliths, commonly appear in the Blanca Group units and in the Montemayor slices and less commonly in the Jubrique Unit. Relationships with the other lithologies are varied and complex. These rocks occur as large sheetlike bodies associated with a wide shear zone that includes the lower peridotite boundary; they occur also as variably sized dikes cutting across most of the ductile structures (Fig. 5F).
The granitic rocks are subdivided in turn into three main lithologic sets according to their petrologic characteristics: diatexitic granitoids, porphyritic granitoids, and leucogranites, from oldest to youngest (Sánchez-Gómez, 1997). The radiometric ages of these rocks varies from 19 to 22 Ma (Priem et al., 1979; Zeck et al., 1989, 1992; Monié et al., 1994).
The superposition of extensional fault systems with transverse stretching during the Alboran Miocene rifting (event 4) gave rise to mega-chocolate tablet structures, a well-known regional feature in the tectonic units of the Alboran Domain Complexes (García-Dueñas et al., 1992; Comas et al., 1992; Crespo-Blanc et al., 1994; Crespo-Blanc, 1995). The extensional fault systems of this interference pattern dismembered the Alpujárride units and separated the peridotite massifs from the mantle lithosphere slabs that had presumably been emplaced during nappe-forming event 3. After extension, the main peridotite bodies were connected only by thin discontinuous sheets of serpentinized peridotites.