STRUCTURE OF THE ALPUJARRIDES ON THE SOUTHERN AND EASTERN BORDER OF THE SIERRA DE LUJAR

The Alpujarride complex located to the South of the Sierra Nevada and extending between Motril and Adra is formed of five nappes, which in ascending order are: Lújar, Cástaras, Alcázar, Murtas and Adra. These five nappes display a structure that is the result of several overlapping events. Firstly, they reflect a process of ductile shearing associated with a mylonitic foliation and a mylonitic lineation with a N4ü E average orientation. Following this, an episode of translation towards the North has been recorded; this occurred under more superficial conditions and developed gouges and fault breccias. Associated with this episode are locally developed folds, which did not give rise to a mineral blastesis. Afterwards, the late deformations occurred, affecting the whole ofthe ensemble. Ofthese, the most important are those that originated folds with a N-S axis, verging towards the West and the normal faults. The extensional faults towards the South would be encompassed in this section.


Introduction
The rocks oí the Betic zone located to the South oí the Sierra Nevada have been the object oí study since almost the beginning oí the present century.However, it was only since the work oí F. Aldaya, towards the end oí the sixties, that the units compri-sing the Alpujarride nappes have been studied individually; such studies have been based on lithological, metamorphic and tectonic criteria.
The present work, oííers an overview oí the data obtained since then, basing the considerations on a detailed microstructural study and on new lithological and metamorphic data.These have led us to mo-dify the cartography of the area encompassed between Motril and Adra to a considerable extent.The principal controversies that have arisen in recent years concerning the Alpujarrides in this sector can be summarized as follows: (1) the existence and interpretation of sorne of the units dealt with individually by Aldaya, (2) the tectonic (Aldaya, 1981) or sedimentary (Estévez el al., 1985) nature of sorne of the contacts among the calcareous and pellitic formations on the southern and eastern border of the Sierra de Lújar, and (3) the existence, relative age and tectonic significance of the large recumbent folds observed in this sector and, in general, in the Alpujarride domain (Balanyá el al., 1987; Campos and Simancas,  1989).From the viewpoint of the authors, in most works dealing with this area no general review has been made of the whole of the structure of the AIpujarride complex; neither has any work been done to compile a new map and neither, as far as the authors are aware, have any microtectonic studies of sufficient amplitude been carried out.As a whole, the work that has been carried out only covers small sectors, and has attempted to extrapolate from these generalized interpretations based almost exclusively on the data of Aldaya for the rest of the area.
The present work therefore attempts to deal with all the foregoing problematic aspects, at the same time offering a critical review of the work published up to the present.Aldaya (1969Aldaya ( , 1979Aldaya ( , 1981Aldaya ( , 1983) ) has differentiated the following Alpujarride nappes south of the Sierra Nevada in ascending tectonic order: Lújar, Cástaras, Alcázar, Murtas and Adra.According to the data collected by the authors in the neighbourhood of the Sierra de Lújar (Fig. 1), the Lújar nappe is restricted exclusively to the carbonate formation within the study area and forming most of the range.In the southeastern and eastern sector of this range, schists, quartzites and marbles of the Cástaras nappe rest over the carbonate formation of the Lújar nappe.

Geological setting
The lithological succession of the Cástaras nappe (Fig. 2) is formed of dark micaschists bearing chlorite and biotite in the lowest levels.Towards the top, the metamorphism of the sequence decreases considerably, as shown by the appearance of grey fillites intercalated with decimetric bands of white quartzites or of yellow calc-schists.Above this outcrops the carbonate formation, formed of highly crystalline banded marbles, sometimes micaceous, with centimeter-thick intercalations of pellitic levels; these marbles are specially well represented in the Sierra de la Joya, within a complex syncline structure (Estévez el al., 1985).
The Alcázar nappe rests directly over the Lújar nappe on the southern border of the Sierra de Lújar and over the Cástaras nappe on the eastern border.At its base, the Alcázar nappe (fig.2) shows grey fillites, with porphyroblasts of chlorite that may have arisen from an alteration of chloritoid.These rocks are overlaid by green fillites and yellow calc-schists that, laterally, pass to levels of black micritic limestones and lenses of gypsum.At different levels on this lithological succession there are layers of conglomerates and of vulcanoclastic rocks.Finally, the carbonate formation is well developed in Cerro Escalate, but poorly represented in the eastern sector: there are sorne outcrops to the East of Bargís and on the road from Alcázar to Torvizcón.
The Murtas nappe, with brown hues, displays an important colour contrast with the foregoing nappes.The lowest rocks (fig.2) of the Murtas nappe are brown quartz schists with garnet that are intercalated with thin layers of marbles with nodules of quartz.Above, the metamorphism decreases progressively from quartz schists with biotite, levels of fillites and finally marbles with associations of talc and tremolite on the upper part, whose best represented outcrops are seen to the Northwest of Castell de Ferro, on the road to Gualchos.
The Adra nappe is located at the highest position.To the east of the Sierra de Lújar this nappe displays (fig.2) micaschists with sillimanite and kyanite and, in more eastern sectors, such as the Rambla de Melicena, it exhibits migmatites at their base.Like the other Alpujarride nappes, it also has a schist succession with a metamorphism that decreases upwards, reducing to mica schists with biotite/chloritoid on the upper part.In this sector there is no carbonate formation, as has been described to the East of Adra (Aldaya et al., 1979a) in the form of scanty and very thin outcrops.

General structure
The structure of Alpujarride nappes of this zone is the result of difierent events: 1) a first stage of thrusting under ductile conditions with a top-to-the-NE motion 2) a second stage under fragile conditions, with a movement of the upper block towards the north; this is fairly well represented in this sector, and 3) several late stages of deformation that affected the foregoing structures.

The thrusting towards (he N E
The Alpujarride complex as a whole exhibit structures linked to the translation under ductile conditions towards the NE and related with the metamorphic evolution of several nappes (see Tubía, 1984); this initial process of thrusting of the Alpujarride nappes led to a final result of the nappes with the highest degree of metamorphism being placed over others with a lower degree of metamorphism.This process 10- cally affected the lithosphere as shown by the subcontinental peridotite massifs forming the base of the  Los Reales nappe (Navarro-Vilá and Tubía, 1983;Tubía, 1985).The age of this process is post-Triassic, since both this metamorphic event and the associated deformations are recorded in the carbonate formations dated as belonging to (or attributed to) the Middle and Upper Triassic (Delgado et al., 1981).
In this sector structures associated with this stage are not very abundant, although they can be recognized in: a) the mylonitic rocks of the contact between the Cástaras nappe and the Lújar nappe on the eastern border of the Sierra de Lújar (figs.3B and C).These were formed in the intercalated quartzitic bands and in the marbles located in the upper part of the Cástaras nappe.These mylonites show a stretching minerallineation verging N30-N4Ü"E; b) the conglomeratic levels of the Alcázar nappe, with a very constant N4Ü"E stretching lineation that coincides with the stretching mineral lineation of the more metamorphic nappes; c) the mylonitization of the schists with kyanite and sillimanite of the Adra nappe, situated to the South of Rubite, and d) the decimetric folds of the Sierra de la Joya, ori-' ginated during the synmetamorphic structuring of the Cástaras nappe (Estévez et al., 1986) which in fact are second-phase folds (Cuevas, 1988).
AH these structures have been highly modified by later processes and it is therefore difficult to assign their true nature to a given contact in a given sector, although at regional or broad-sector scale the types of contact are reasonably weH known (ductile with ENE vergence, ductile-fragile with N vergence, extensional with SE -or other-vergence) as is their relative chronology.

The overridings towards the North
Within the translation phase of the nappes towards the north are structures that have been described by Aldaya in the Betic zone (1969, and later works) and that have later been recognized throughout the chain.Initially, this episode was questioned (see publications of Paquet (1974) among others) although its existence is no longer debated.
The process is strongly evidenced by the structural record of the study area, particularly on the S and SE borders of the Sierra de Lújar (fig.4).It has given rise to subhorizontal contacts deformed by later NW-SE striking folds.Near to these contacts the general schistosity displays inflections and even folds that have not developed any schistosity, although they may have a spaced set of fractures parallel to the axial planeo The fault rocks associated with such contacts are mainly dark gouges and fault breccias.At the major contacts, corresponding to those exhibiting the greatest degree of displacement, the zone of gouges and fault breccias is usuaHy more than 10 m -;;::::==... • w ...  thick.In the immediately neighbouring zones of the contacts to the N the original rocks are highly transformed, with an important enrichment in hydrated minerals (sericite, chlorite), oxides of iron and manganese, and have numerous veins of white quartz.These features point to an important circulation of fluids in the contact zones.
The fault rocks indicate a deformation in the fragile-ductile transition (Cuevas et al., 1986): pressure was between 0.3-1 Kb and temperature lower than 150" C (Cuevas, 1988).These translations produced a strong extension towards the North of the Alpujarride nappes (Navarro-Vilá, 1976)  6B the North.Thus, the present contacts between the Cástaras and Alcázar nappes to the north of Rubite; between the Alcázar and Murtas nappes, to the west of the Conjuro vertex and between the Murtas and Adra nappes, to the south of Rubite, belong to this episode, like the contacts between nappes towards the north and to the east oí Bargís.
Related to the translation of the whole of the AIpujarride ensemble with a N100W trend, the Alcázar nappe on the southern border of the Sierra de Lújar has a N-verging anticlinal structure (fig.4); this is perfectly visible on the map owing to the use oí the reference Ievels of yellow calc-schists and black micritic limestones.Thus, it is possible to observe that at the contact with the Lújar nappe, the Alcázar nappe displays an inverted limb with a thickness of sorne 100 m, as measured perpendiculary to S2' This inverted limb displays a crenulation cleavage, dipping sorne 4Ü" to the S, whereas the dip towards the south of S2' on the same inverse limb, is more pronounced.The east-west axial direction of the minor folds associated with this structure, the basal shearing of the fold (fig.4) on the southern border of the Sierra de Lújar and their clearly post-metamorphic nature are highly suggestive of the relationship between this antiform and the shearings towards the North (Cuevas, 1988).In this case, the compressional character of the antiform within a global context of extension towards the North requires further explanation.A mechanical solution for the problem would be to consider that the structure would have been due to a lateral ramp on the southern border of the Sierra de Lújar or to a normal fault older than the emplacement of the Alpujarride nappes towards the north.The earlier event would explain why the general process of extension due to the emplacement towards the north would have produced a local compression and would also account for the reduced thickness of the inverted limb of the N-verging anticlinal in the fillites of the Alcázar nappe, situated on the southern border of the Sierra de Lújar.To a certain extent, this situation is similar to what occurred to the South of the Turón tectonic window, in the zone of Las Fuentes de Marbella, 9 km to the north of Adra (see F.m in figure 1).The contact here is particulary controversial; in it the carbonate formation of the Lújar nappe outcropping in the Calares de Turón tectonic window enters into contact with the fiHites and quartzites of the Alcázar nappe.This contact has been interpreted as belonging to the system of overridings towards the north (Aldaya, 1969;Cuevas, 1988) and as an inverted stratigraphic contact (Gervilla et al., 1985) on the inverted limb of a N-verging syncline several kilometers in length (Balanyá et al., 1987;Campos and Simancas, 1989).
Our data suggest that one is clearly dealing with tectonic contact.This is characterized by the existence, both in the limestones and dolomites of the Lújar nappe and in the fillites and quartzites of the Alcázar nappe located aboye, of a highly developed stretching lineation paraHel to the axis of folds with frequent curved hinges.The lineations and axes of these folds range in direction between N-S and N16Ü"E with a maximum of around N5Ü"E.The characteristics are not consistent with those of a typical contact towards the North since they are associated with certain structures suggestive of conditions of greater ductility.The authors' opinion is that such structural characteristics point to the existence of a lateral ramp belonging to the system of ductile overridings towards the NE, that was later modified by the shearings towards the north.The ramp dips towards the SE; and would corresponds to the lineament formed by the Cerrón and Calares de Turón tectonic windows.Below the Las Fuentes de Marbella contact, the limestones and dolomites of the Lújar nappe display an inverted So, as pointed out by Gervilla et al., (1985), with respect to the microfracturing generated in the contact.

Later deformations
The most striking structure, recently described, to the South of the Sierra de Lújar is undoubtedly a set of large late folds, with as NNW-SSE axis, that affected the earlier structures (fig.4).In particular, detailed mapping has allowed these structures to be appreciated: at the core of the formation of fillites and quartzites, the levels of yeHow calc-schists and their intercalations of black micritic limestones, form large anticlinal folds separated by narrow synclines, verging W, with the W limb vertical or slightly inverted (see fig. 4).These large folds are responsible for the variations in the general schistosity, S2, of the Alcá• zar nappe, which varies from a mean orientation of N12Ü"E to the NE of Motril to a N-S orientation to the NW of Motril and to the SW of the Conjuro de Gualchos vertex; they have also led to marked variations in the orientations of the F 2 and F 3 folds of the Alcázar nappe, which from mean orientations of N6Ü"E pass to orientations close to N-S, which are anomalous in the region between Motril and Adra.
The contacts between nappes have been affected by this late episode of folding, as can be seen aH along the contact between the Murtas and Alcázar nappes to the West of the Conjuro vertex (fig.1).This kind of structure has led sorne authors (Balanyá et al., 1987) to assume the existence of two mineral lineations in this region: one with a mean orientation consistent with the general shearing phase towards the NE of the Alpujárrides nappes (N4Ü"-N6Ü"E), and another close to the N-S orientation.However our data clearly show that they correspond to the same mineral lineation modified by the effect of the large late folds.As minor structures related to these folds, it is only possible to recognize the existence of small vergent folds associated with the inverse limb and the local development, in the more pellitic, rocks, of a very spaced cleavage (fig.5) with no associated neoformation of minerals (fig.6).
As has been reported, this region contains important low-angle, normal faults that originated during an important extensional tectonic stage of Miocene age.The best known of these is the «Mecina fault» (Aldaya el al., 1984) that gave rise to the current contact between the Alpujarride and the Nevado-Filábrides to the south of the Sierra Nevada.Above this level and at the core oC the Alpujarride pile other faults oC the same type have been described, although they are much less important.
In this sector we have observed minar struclures associated with contacts between units or belween formations oC Ihe same unit (e.g. at the contact between limestones and dolomiles and the fillites and quartzites of the Alcázar nappe, immediately to Ihe North of Motril).These structures indicate a movement lowards Ihe SW of blocks situaled on surCaces dipping lowards the SW or W, although there seem to be no important extensional Caults towards the South.Neither are there criteria, in the zones where certain units or formations are very thin, for aUribut ing an important parl oC the thinning to these extensional faults.In general the structures in the rocks Finally, it should be noted that at a local scale the role played by late fractures can be very important.Essentially, this can be seen in the network of normal fauits wilh N120"E and N6O"E orienlations Ihat have sunk the southern block and that havc affecled the earlier structures.There are also gentle folds with an E-W axial orientation that are responsible for the Lújar and Contraviesa ranges having an antiCorm structure.The general schistosity, 52, and structures linked to emplacemenl towards Ihe N dipping towards the N on the northem border and towards Ihc south on the southern border.

Discussion and eondusions
The data offered in the present work inelude the novel report oC microtectonic data form structures hitherto unrecognized in the sector; also offered are importanl changes in the cartography, as well as a description of lithological members that complete the sequences of sorne of the nappes.AlI this has led to a redefinition of sorne of the nappes (such as the Cástaras nappe), and to a tectonie reinterpretation of Ihis sector.Of special relevance are the following points: 1) The large recumbent Colds that would be recognized both to the East ant lO the West of this sector, have been related by Balanyá el al., (1987) to the emplacemen: of nappes towards Ihe North.Nevertheless it should be taken into aceount that: -They inelude within the same group syn-metamorphie folds such as those of the Tejeda and Lújar ranges (which are equivalent to Ihe structure displa• yed by the Cástaras nappe in the Sierra de la Joya) and also post-metamorphic folds, such as that of the Capellanía syncline in the Herradura nappe (Avidad and García-Dueñas, 1981).Folds such as these later gave rise to limited inverse limbs, in general synform in the carbonatic rocks and antiformal in the metap ellites (e.g. the fillites of the Alcázar nappe to the south of the Sierra de Lújar).AIso, they fold the metamorphic isograds, and are hence later than the iso-e1inal Colds related to the emplacement oC nappes towards the NE or produced in earlier stages oC deformation.In this sense, along the Arroyo de la Miel section, it is seen that the Capellanía syneline oC the Herradura nappe has locally developed a spaced crenulation e1eavage, without mineral blastesis, contrary to what is stated by Balanyá et al., (1987), this syndine Colds the S~whose by the metamorphic rocks.
2) Regardmg the propasal of Estévez el al., (1985) oC omitting the Cástaras nappe and including the Alcázar nappe and the Lújar nappe within a broad er set designated as the Lújar Nappe, it should be noted that these authors were working under the assumption that the contact between the Alcázar or Cástaras nappes with the Lújar Nappe defined by AIdaya (1969) is stratigraphic.We believe that this is untenable, not only because the contacts between the nappes are marked with scattered outcrops of mylonitic rocks (fig.3), but also because over the limestones of the Lújar Nappe are found the upper mar-bIes, the quartzites or biotitic schists of the Cástaras Nappe; only where the Cástaras Nappe becomes layered, to the South of the Sierra de Lújar, does the Alcázar Nappe rest over that of Lújar, but in an inverted position and with the general structure clearly governed by the calc-schists layers (fig.4) described previously.
Additionally, in the cartographic scheme offered in the work of Campos and Simancas (1989) it is seen that at the southern and southeastern borders of the Sierra de Lújar the contact between fillites and carbonate rocks is interpreted as being transitional, while in fact, and independentIy of the nature of the contact, there are micaschists with chloritoid and biotite and mylonitic rocks that have been described as «fi-Hites» by these authors.
3) Finally, an important question relates to the interpretation of the inversions, because most of the units show two or three overlapping reference surfaces.This means that to speak genericaHy of «inversion» can only lead to confusion, unless one specifies which surface is inverted and with respect to what: So with respect to S2 or any of these surfaces with respect to the spaced cleavages developed in the large late folds.

Fig. 2 .
Fig.2.-Synthetic logs of the Alpujarride nappes differentiated in Fig.1.Note that the columns do not coincide with others lifted outside this sector for the same units.
reached in the previous stage oí ductile thrusting towards the NE.On the S and SE borders of the Sierra de Lújar, there are numerous contacs of this translation towards Fig. 4.-Structure of the Alcázar nappe on the southern border of the Sierra de Lújar.The leveIs of yellow calc-schists are represented in black.