641

Geologische Rundschau 74/3 ] 641-655 ] Stuttgart 1985

A strike-slip fault corridor within the Alpujarra Mountains (Betic Cordilleras, ) By C. SANZ DE GALDEANO, J. RODRIGUEZ-FERNANDEZ & A. C. LOPEZ-GARRIDO, *)

With 6 figures

Zusammenfassung calculate. Evidence of considerable vertical movement can be found locally. In einem langen Korridor in der Internzone der Beti- These strike-slip displacements have essentially occurred schen Kordilleren, der im Norden durch die Sierra Nevada since the middle Miocene period and might still be taking und im Siiden von den Sierren Lujar, Contraviesa und Ga- place. dor begrenzt wird, sind zwei Streifen mit Blattverschie- bungen zu beobachten. Sic streichen etwa E-W und sind R~sum~ gut entlang des 85-km-langen Giirtels aufgeschlossen. Die charakteristischen Merkmale yon Blattverschiebun- Dans un long couloir situ6 dans la zone interne des Chal- gen wie etwa kataklastische Gesteine mit verschiedenen nes B&iques et limit~ au Nord par la Sierra N&ada et au texturierten Verwerfungsbrekzien, welche auch bis zu Sud par les Sierras de Lujar, Contraviesa et Gador, s'obser- mehreren Metern grol~e Gesteinsblrcke enthalten, begin- vent deux trains de failles de d&rochements. Ces trains ont nende Schieferung und Harnischbildung, zeigen die dex- une direction ~t peu pr& E-W et sont bien expos& tout au trale Natur der Bewegung. Daneben treten NW-SE und long des 85 Km de cette zone. NNE-SSW streichende St6rungen auf, die offensichtlich Les traits caract~ristiques des d&rochements, tels que ca- nach der Bildung der E-W verlaufenden Blattverschiebun- taclasites, br&he de faille avec fragments de roches jusqu'~t gen entstanden sind. Das Ausmaf~ des lateralen Versatzes ist plusieurs m&res de longueur, schistosit~ naissante et stria- schwer abzusch~itzen. tion, d~montrent la nature dextre du drplacement. I1 existe Diese Bewegungen linden seit dem mittleren Mioz~in aussi des fractures de direction NW-SE et NNW-SSW qui statt und sind mrglicherweise immer noch aktiv. se sont vraisemblablement form&s postrrieurement aux failles E-W. La valeur du d~placement lat&al est difficile estimer. On r~l&e localement des indices de mouvements Abstract verticaux importants. Ces d&rochements se sont produits essentiellement In a long ,,corridor~, in the internal zone of the Betic Cor- partir du Miocene moyen et peuvent encore se poursuivre dilleras, bounded to the north by the Sierra Nevada and to aujourd'hui. the south by the Sierras Lujar, Contraviesa and Gador, two discernible bands of strike-slip faults exist: These bands lie in an approximately E-W direction and are well exposed KpaTKOe coAep~aHRe throughout and beyond the 85 km long belt. The characteristic features of strike-slip faults, such as ca- Bo BHyTpeHHeH 3OHe BeTCI~HX Kop~2H;Ibep B ~FIHHHOM taclastic rocks composed of variously textured fault brec- KOp,~ope, oFpaHHqeHHOM Ha ceBepe CHeppo~I HeBa- cia, which also include fragments of rocks up to several aoI~, a Ha lore CHeppofi 5Itoxap, CHeppo~ KoHxaBelp3a H metres in size, incipient foliation, and striation demonstrate CHeppofi Fa~op, yCTaHHBHml ~ma I-OpH3OHTaYlBHblX the rightqateral nature of the displacement. There are also fractures which run in a NW-SE and NNE-SSW direction, caBHra. OHH npocTrlparOTC~ npHMepHo B E-W Har/paB- and apparently originated after formation of the E-W ~eHHH I4 xopoRIO O(SHa)KeHbl B~OYlb rlo~lca B 85 KM. Xa- faults. The magnitude of lateral displacements is difficult to paKTepHblMH qepTaMH FOpH3OHTaYlbHblX C~IBHFOB ~IB- ;I~IeTC~I TO, qTO B HHX orpa3ylOTC~l KaTaK;IaCTHqeCKHe cez214MeHTbl C 6peKqH~MH crpOCOB, HMeK)ttlHX pa3JlHq- *) Author's addresses: C. SANZ DE GALDEANO, Departa- HylO TeKCTylpy H B KOTOpblXBI(;IIOqeHbI 6YIOKH IIOpO~ Be- mento de Geologla, Facultad de Ciencias, Granada, FIHqHHOt~I B HeCKO.rlBKO MeTpOB. Ha I/oBepXHOCTH 9THX Spain, J. RODRIGUEZ-FERNANDEZ, Departamento de 6FIOKOB BH~Ha HaqHHatOIRa~/c~I CYlaHLIeBaTOCTBH LUTpH- Estratigrafia, Facultad de Ciencias, Granada, Spain and XOBKa, KOTOpble yKa3blBarOT Ha HanlgaB~eHrle gIBH>KeHH~ A. C. LOPEZ-GARRIDO, Departamento de Investigacio- 3THX 6~OKOB BrIpaBo. KpoMe TOrO 3~tecb yCTaHOB.~eHO nes Geol6gicas, C. S. I. C. Universidad de Granada, npocx~ipamte cTpyKTypHblX 3~eMeHTOB B NW-SE H Spain. NNE-SSW HaHpaB~eHHH rlO~BHBtHeec~ ~IBHO HOCTIe 642 C.S. DE GALDEANOet al. oOpa3oBaHl4~l FopH3oHTaflbHOFO C~BHFa, rlpOCTH- coarse detritic material. On top of these and discor- pa~oLLIeroc~ Ha E-W. O6"beM 6OKOBOFO CMeUleHH~t oue- dantly in the Western Sector there appears a conti- HHTB Tpy;IHO. 3TH ;/BI+I~eHI+I91 rlaua~nc~/3 cpe;IHeM MHO- nental sequence beginning with reddish and grey de- IieHe H, BO3MO>KHO, aKTHBHM H HO ce!~I 2IeHb. tritic rocks that pass upwards into pebbles and boul- ders derived from the Nevado-Filabrides. Towards the Eastern Sector these deposits change into silts and I. Introduction sands with interbedded conglomerates, containing a This article describes the long band of strike-slip marine fauna of Late Tortonian=Messinian age. faults wich are present in a corridor of the Alpujarra In the Neogene deposits one finds numerous and mountains, and the effects of these faults on both the considerable changes in facies, indicating consider- older metamorphic rocks and the more modern able tectonic activity. Neogene and Quaternary deposits. In many places there appear other discordant de- The Alpujarran corridor lies within the Betic Cor- posits. These are made up of very thick, red and grey dilleras to the south of the Sierra Nevada and north of conglomerate sequences containing thick beds of red the Sierras Lujar, Contraviesa and Gador, and forms clays. These are similar to the continental a narrow depression flanked by mountains, appro- Formation of Pliocene and Quaternary age, from the ximately 85 km long and between 2 to 6 km wide (fig. north side of the Sierra Nevada. 1). There are also very well developed alluvial-fan de- Geologically almost the whole mass of the Sierra posits along the boundary between the Central-Ea- Nevada belongs to the Nevado-Filabride complex stern and the Eastern Sectors, which are affected by and is made up of schists, quartzites and, to a lesser several fractures and show slight folds parallel to extent, marbles, dating from the Triassic, the Paleo- these fractures. Their age is probably Pliocene(?)- zoic or even older. Quaternary. On the lower slopes of the Sierra Nevada, thrust Finally, there appear other continental deposits of over the Nevado-Filabrides, are found rocks of the Pliocene to Quaternary age, mostly in the form of Alpujarride complex, extending southwards to the piedmonts and ancient river beds, some of which are sea. This complex is made up of schists, phyllites and topographically much higher than the level of the quartzites of Paleozoic and Triassic age and of ma- present hydrographic network. rble and more or less metamorphosed dolomitic li- Both the Nevado-Filabride and the Alpujarride mestone of the Triassic period. The metamorphism complexes have been studied by numerous geologists shown by this complex, just as that of the Nevado- and it is not the intention of this report to give an ex- Filabrides, is of alpine origin. haustive description of them. Suffice it to refer to the The Neogene deposits appear normally at the lo- work of PucA (1971) and the maps, to scale 1:50.000, west points of the depression overlying the Alpujar- drawn by ALDAYA et al. (1979 and in the press) and ride complex, although locally they may be in direct DIAZ DE FEDERICO et al. (1981), whick contain refe- contact with the Nevado-Filabrides. The oldest rences to previous works. Neogene rocks are marls of Early Burdigalian age. The Neogene deposits have been investigated by They precede the formation of the corridor and oc- several geologists. DURAND DELGA & FO>~TBOTE cur in isolated localities at its western end. On top of (1960) describe the area around Ugfjar and refer to these, or sometimes lying directly on Alpujarride Neogene beds which have been considerably affected rocks, there appear transgressive marly calcareous by reverse faults in an area to the east of the Alpujar- deposits which contain a pelagic fauna of Middle ran corridor, in the Sierra de Alhamilla. It is also Miocene age (Serravallian). The next, Serravallian- worth mentioning the works of RODRIOUEZ-FERNAN~ basal Tortonian rock unit is, again, discordant and DEz (1982), GoNzaLEz-DoNoSO et al. (1983) and OTT consists of reddish detritic materials in its lower, and D'eSTEVOU (1980). restricted shallow-water facies in the upper part. SANZ DE GALDEANO(1983) and SANZDE GALDEANO This can be seen in various outcrops, near Cadiar for et al. (1984) describe the essential features of post-al- example. These rocks outcrop extensively and are pine fracturing at the western end of the corridor in frequently highly tectonised. question and those of the Betic Cordilleras in gene- Above these deposits directly upon Alpujarride ral. Finally ALDAYAet al. (1984) report the existence rocks, is found a discordant sequence of Early Tor- of the Mecina fault, which extends along the contact tonian age, beginning with bioclastic limestones, between the Alpujarride and Nevado-Filabride passing into silts and marls. These silts and marls in- complexes and which they describe as being a trans- clude levels of turbidites and channel deposits of very tensive feature. t~ a. ?

P~ 2. I:L o

Fig. 1.a. Location within the Betic Cordilleras of the study area.

Fig. 1. b. Overall plan of the Alpujarran Corridor. The precise position can be seen in A. Numbers for the inset frames 2, 3, 4 and 5 refer to subsequent figures of the same number. 644 C.S. DE GALDEANOet al.

II. Fracturing II-l-b. The West-Central Sector. Alpine structuring of the Betic Zone began during In this sector, in the Alpujarride complex on the the Eocene, or perhaps earlier (Upper Cretaceous?) slopes of the Sierra Nevada, fracture lines can be seen and lasted until the Early Miocene. This does not outcropping clearly and at times dramatically. Such mean that there were no later stages of important de- is the case with the great dolomitic limestone scarp formation, as will be seen. During this period occur- which runs from a little to the west of Castaras, pas- red metamorphism of the internal zone and its mo- ses through Nieles and Timar and ends in the proxi- vement westwards relative to the external Betic and mity of Cadiar. This scarp is not only of great geolo- Rifean zones. It was this movement that caused the gical interest when studied in detail, but also very internal zone to wedge itself between the external spectacular when seem as a whole from a distance. ones (ANDRIEUXet al. 1971). The contact between the Here one can find an enormous number of very well internal and external zones was clearly formed in the preserved horizontal striations, which clearly and Burdigalian, although there had been movements without doubt indicate the right-lateral nature of the prior to this age. This contact trended approximately strike-slip. But, as shown in figs. 3 and 4 (cross sec- in a N70E sense and was essentially a right-lateral tion A-A'), it is not the only fracture in this area. In transcurrent event with a relative displacement of fact it is part of a fault zone of over 500 m in width. In perhaps 300 kin. Other parallel faults were formed its southern part the superficial rocks affected by the both in the internal and external zones (SANz D~ fault are Alpujarride metapelites. Bands of crushed GALDEANO 1983, and SMET 1984). Further fractures rocks, which are darker than the surrounding, un- appeared, trending in a more E-W direction, but as crushed rocks, have been formed. These bands of ca- part of the fault system as a whole which moved in a taclastic rocks are, in general fault breccias or fault right lateral sense. It were these E-W strike-slip gouges but they also show foliations subparallel to faults which created the Alpujarran corridor. the slip, containing numerous fragments of lense- shaped rocks, whose trails serve to indicate the sense of the movement. Locally there are large, exotic, tec- II-1. A description of the E-W to tonic limestone lenses, the presence of which would N70E faults be inexplicable unless it is assumed that they have These faults are clearly visible throughout the been tectonically transported along the strike-slip length of the corridor (fig. 1-6). They form two large fault. They can be up to 50 m in length with long, ho- groups of fracture lines, though in places they merge rizontal or nearly horizontal striations parallel to the sufficiently to make it difficult to distinguish clearly fault, and the lenses themselves are aligned in the di- between the two groups. rection of the fault. Tortonian marine conglomerates In order to describe the characteristics of the frac- are also found among the crushed and striated ele- tures it is convenient to divide the corridor into four ments of the fault breccia. Still further to the south in sectors: the western sector from around Beznar to the area of there appears another band of frac- Orgiva, the west-central sector from Orgiva to Cadi- tures in which, if less spectacular, the Neogene depo- at, the east-central sector from Cadiar to Laujar de sits are better preserved. The Serravallian-basal Tor- Andarax (with Ugijar in the middle) and the eastern tonian rocks are clearly truncated and the fault zone sector to around Alhama de Almerla. in the adjacent Alpujarrides has a width of more than 30 m. In the Neogene deposits horizontal striations II-l-a. The Western Sector. occur. Nearby possible late Tortonian-Messinian deposits are found which partly cover the fault tra- In this sector fracture lines occur on the southern ces, but elsewhere these deposits can be observed cle- flank of the Sierra Nevada as well as on the northern arly affected by the wrench-slips. The wrench faults flank of the Sierra de Lujar, but it is difficult to find have also created some tectonic windows of lower sufficient evidence to determine the sense of move- Alpujarride units and the dolomitic limestones thus ment. Where they can be observed there seem to be revealed are elongated in the direction N80E. Hori- several types of faulting, such as normal and reverse zontal striations can also be seen. There is a good faults, which obscure the strike-slip movements. In example of such a window on the road to Lobras. some places, however, horizontal striation is pre- sent. Aerial photographs reveal some possible lines II-l-c. The East-Central Sector. of strike-slip fractures but in the field it is usually not possible to establish their existence with any cer- This sector is indubitably the most geologically in- tainty (fig. 2). teresting of the four. The formation of cataclastic A strike-slip fault corridor 645

Fig. 2. Western Sector of the Alpujarran Corridor. Thin lines indicate probable fractures. (Taken from SANZD~ GALDE- ANO et al. 1984.) rocks both in the Neogene and Alpujarride deposits component of the displacement must be at least and even in the Nevado-Filabrides is much more 200 m, but many horizontal striations are found wide-spread than in the westerly sectors. Two along the fault traces. The road, which runs north- groups of faults that correspond exactly to the fault ward cuts across two more bands of crushed rock. In lines in the previous sectors can be clearly distinguis- one of these there are boulders of several cubic met- tied. res with superficial striations, clearly demonstrating that they have been rolled around during displace- ment. These curved striations follow horizontal pla- The northern group of faults (fig. 3, nes. In this fault zone there is evidence of incipient cross-section B-B' to G-G' and fig. 5) foliation. Here the Castaras-Cadiar fractures continue. To the north of Ugijar, between Yegen and Laro- From the location where the secondary road to Yator les, the Miocene deposits are notably affected by branches off the main road through the Alpujarran wrench-faults. 3 km to the north of Ugijar there ap- corridor just north of Cadiar, till 1 km to the west the pears a band of completely fractured Alpujarride rocks are very finely crushed (cross section B-B'). phyllites and quartzites which also contains fractu- The resulting breccia (or gouge) is composed of A1- red Serravallian-basal Tortonian rocks. The fault pujarride phyllites and also contains highly striated zone is very steep in this area. This band splits into :rocks of the Serravallian-basal Tortonian sequence. two branches in a westward direction. The southern This fault runs eastward towards Yator and here ver- branch, locally dipping to the south gradually loses tical Tortonian deposits can be seen. The vertical the phyllites and finally the fault breccia consists o,x

(2

63 ;>

)- o

~a

Fig. 3. West-Central Sector of the Alpujarran Corridor. Tectonic windows produced by strike-slip faults are indicated as asterisks. Zones of intense crushing are indicated by cross-hatching. A strike-slip fault corridor 647 only of crushed Neogene deposits. The crushed of brecciation and incipient foliation in the fault zo- Neogene rocks are clearly visible, even from a di- nes, which include Neogene rock fragments within stance of some kilometres, owing to common efflo- the crushed schists and phyllites as well as striated rescences of gypsum, which impart a light color to boulders following the flow-line of the displace- the terrain. There are also severe deformations in the ment. Striations are abundant and clearly indicate rocks adjacent to the fault. right-lateral movement. The fault lines are almost The northern branch of the fault continues in a al- completely rectilinear. Locally normal or reverse most straight line and shows severely deformed faulting appears. Neogene deposits are of lower Tor- Neogene rocks. At the point where the two branches tonian-Messinian age, similar to those found to the separate several inclusions of Neogene deposits are east of Cherin. found within the phyllites. There is one outstanding II-l-d. The Eastern Sector outcrop visible from the road (km. 57, UTM co-or- dinates: VF 944936), where the Miocene appears dis- On the northern side of the corridor the fault lines cordantly above the Mpujarrides and is in turn over- described in the above sector continue from Laujar thrust by Alpujarride rocks which, at first sight, de Andarax to Alboloduy. Between Laujar and Can- might even be interpreted as a gravitational slide to- jayar the bands of crushed rock occur in the Alpujar- wards the south. However, this is not the case. On rides and in the Miocene deposits. The contact bet- climbing the Neogene hillock it can be clearly seen ween the Alpujarride and the Nevado-Filabride that these rocks are vertically embedded in the phyl- rocks bends northward in this area and appears to be lites. Its flat top comprises an area of more than 200 unaffected by the transcurrent movements. sq.m., is distinctly striated and cut by channels in a The fault traces are clearly visible in two localities. direction N80E (fig. 4, sketch E). A similar structure One is 2 km WSW of Beires (km 35.8 on road 332, is found in the vicinity of Yator and to the south of see fig. 6 and cross-section H-H' of fig. 4) and the ot- Yegen, where large dolomitic limestone boulders oc- her on the same road where it passes over Capitan hill cur, completely covered by striations indicating the (fig. 6). In both these localities bands of crushed direction of displacement. These two sites are men- rocks with foliation and long horizontal striation li- tioned because of their clarity and ease of access, but nes can be seen. Locally they might appear to be re- further examples can be found both to the east and verse faults but in fact are right-lateral strike-slip west of the Yegen area. The band of crushed rock re- faults. flecting the strike-slip character of the fault continues From Canjayar onwards, the fault line follows the westward for several kilometres. The phyllites con- contact between the Nevado-Filabrides on one hand tain large quantities of Neogene rocks in the form of and the Alpujarrides and the Miocene on the other. elongated lense-shaped boulders whose tails again Through the effects of the slip the Alpujarride rocks extend in the direction of displacement. They are of- are here restricted to a long, very narrow strip of out- ten completely contained within the phyllites and crops that locally disappears completely, so that the consequently are only visible in the sections of ,,bar- Miocene deposits are in direct contact with the Ne- rancos~, (steep-sided, eroded, stream beds). The op- vado-Filabride rocks. posite can also be seen, with bands of phyllites inclu- A little further to the west, along the old road to ded within Neogene deposits. Ohanes two huge Alpujarride dolomitic limestone Further to the north there is another band of crus- and phyllite blocks some 50 m in length occur within hed rocks at a point of contact between phyllites and the Miocene of the fault zone (cross section I-I' of Neogene deposits. Its characteristics are similar to fig. 4). Incipient foliation and horizontal striations those described above, though the fault splits into se- are clearly visible. veral branches within the phyllites and contains large The strike-slip faults continue until they reach a ,,fishes~, of dolomitic limestone whose sides are com- point a little to the east of Alboloduy, where the A1- pletely striated horizontally. A good example can be pujarride rocks disappear and the corridor as such found at the locality VF 9 19937. ends. To the north of Alboloduy some fault lines can still be seen, which, locally, have the appearance of The southern group of faults reverse faults but in fact show evidence of both hori- zontal fight-lateral movement and an element of ver- These faults, although somewhat less spectacular tical movement. The same can be seen in the Neva- than the northern group, are nevertheless very cle- do-Filabride complex, with bands of generally stee- arly visible from the air and in the field and show very ply inclined (60 degrees or more) crushed rock, al- distinct contrasts in colour. They also show evidence though locally these bands can show less inclination. s oo A ll Kin.27 R. Ouodolfeo Lobros T[mor N #8 W A 3 0

0 ' ' B t Km. NSW

B' Kin.36 Kin. 37 _~r.~~ c~ :> r- q

s

m i-- o 1Km. C o C I Km,IZ4 Cerro Cruz Rombte de Yegen Yegen Km, 49,2 516W , _ ~_. +. +. +. ~ NI6E + +. +" ~. ~-s..~. .

,-<

r~

lu I Kin. D' D Km,?de YGtor a Ugi]or Lomo de Pinto NSW SSE +. +- " +. +, +. ~~./ o i

> > 1. i l Km. u1 0 E s ; N

, t lOOmts. F N7W F'Luca~nena Kin. 4 6 +. ~/ e~ +. -t-. S TE +'+. +. ~~

o > I I I Km. G ? G' + S ~" S12E AIcpleo +. +~ N/2W f2~

Y 3 E I i I Kin.

H'Copi t dn H +. N3W II Ca- untigua Tojo Negro I o Ohones S2E .~ N2W

DISPLACEMENT SENSE OF STRIKE- SLIP FAULTS i i I Kin. I Kin. ~ ~ W MOVEMENT ~ SCHISTS E MOVEMENT ALPUJARRIDE NEVADO- FILABRIDE METAMORPHOSED DOLOMITIC LIMESTONES MIDDLE & UPPER PHYLLITES AND SCHISTS M|OCENE cN (3

>.

>.

0

Fig. 5. East-Central Sector of the Alpujarran Corridor. The thick parallel solid lines indicate areas of intensive crushing. A strike-slip fault corridor 651

To the south of this corridor sector there are fewer gene or Alpujarride deposits. This appears to be a re- bands of fracturing. These occur in many points of cent phenomenon, it is the result of lateral gravita- contact between the dolomitic limestones of the tional sliding, and presents no problem in the geolo- northern flank of the Sierra de Gador and the Torto- gical analysis of the fault corridor. nian deposits of the corridor itself. In places there has been vertical movement to the extent of 700 m. and II-l-f. Foliation vertical strations can be seen, for example at Alhama Materials principally encountered in the fault de Almeria. There are also, however, oblique displa- bands range from fault breccias through fault gouge cements and others with horizontal striations which to fault pug. At several points, however, marked fo- indicate pure strike slip. An example of this latter, liation can be seen in rocks which are not completely horizontal, movement can be seen in vicinity of Ra- coherent. This foliation is parallel or subparalM to gol (UTM WF 292945) in a small barranco, visible the direction of displacement and, locally, may be from the Ragol to Instincion road where the di- notably oblique. Normally there are also lenses or stinctly striated fault plane is visible. even large blocks with ,>tails<, stretching in the direc- In the basin interior there are also faults which may tion of the movement. seem to affect Neogene deposits. To the east of Padu- The foliation is generally in a vertical plane, al- les, for example, a vertical band of crushed rock ex- though where thrust sheets have been produced it tends in a E-W direction. In other places, between may progressively lose inclination until it lies almost Bentarique and Terque, the river Andarax follows flat (through the influence of older pre-existing sur- the trace of one of these faults. This appears clearly faces). Thus, where the schistosity of the phyllites, from the sharp change in lithology between the two schists or quartzites dips a few degrees and the folia- banks of the river. tion is less intense, the latter may have adopted the plane of the older surface. The same may occur in faults where the crushing has been less significant. II-l-e. Subsidiary thrust sheets These too may be controlled by older surfaces and develop with a preference towards levels of lower In the East-Central Sector, both to the north of cohesion, such as phyllite layers within quartzites. Cadiar and of Ugijar, several thrust sheets of Alpu- A clear loss of inclination can also be observed in jarride material are intercalated within the bands of the vicinity of large boulders which are at times in- the strike-slip faults. Neogene deposits are similary corporated in the faults. Close to the bottoms of affected. Thrusting varies between a direction paral- these boulders vertical foliation will twist rapidly and lel to the strike-slip and a angle of some 30~ but lo- align itself with the new surface; that is, adapt itself to cally it may be even more, attaining directions which the movement of the boulder. Large masses produce approximate NE-SW. In some cases, particularly in the same effect as boulders and the resultant foliation the western zone of this thrust-sheet area, the thrusts takes on the appearance of sheets. However, as men- appear to have had a northern sense and in others a tioned above, analysis of the striations clearly indica- south-eastern or even southern sense. tes the direction and sometimes the sense of the dis- These thrust-sheets are interpreted as being subsi- placement. diary to the strike-slip displacements, in the same manner as HARmNc (1974) and several later geolo- II-l-g. The limits of the Corridor gists have recorded in other regions. Furthermore, a real transition exists between the strike-slip bands At its western limit in the Lecrin valley the three and the thrust-sheets, in such a way that as the faults principal Betic Cordilleran systems of strike-slip change direction they decline from the vertical and fractures merge (SANz DE GALI~EANOet al. 1984, see gradually flatten out. Nevertheless, the predominant fig. 2) and the overall picture becomes somewhat direction of displacement identified in these thrust- more complex. Nevertheless, the E-W faults conti- sheets by the striations and foliation is the same as nue in a westerly direction to the vicinity of Zafar- that of the wrench fault. Thus in some places the raya-Colmenar, where they enter the point of con- sheets have the appearance of completely flat surfa- tact between the internal and external zones of the ces, but with clear evidence of an almost E-W displa- Betic Cordilleras. The epicentre of the disastrous cement. earthquake of Christmas 1884 was in the sector of One further detail is the occasional existence, on -. the slopes of the Sierra Nevada, of Alpujarride and At the eastern extreme, in the Almerfa, Tabernas even Nevado-Filabride rocks emplaced above Neo- and Sorbas basins it is difficult to see a distinct conti- t~

>

t~ o

Fig. 6. Eastern Sector of the Alpujarran Corridor. A strike-slip fault corridor 653 nuation of the fault. However, there are points, for Thus, there appear to have been two essential mo- example to the north of the Sierras Alhamilla and vements in the region: The first which wedged the in- Cabrera, where clear fractures bear witness to the ternal zones of the Betic Cordilleras between the ex- continuity of wrench-faults. The tectonic sedimen- ternal zones (a product of an eastward movement, of tary relationship of this area has been well described the Iberic block due to the widening of the Atlantic, by OTT D'~STEVOU (1980). and the second a product of the approximation of Africa to the Iberian peninsula. Both these move- 11-2. The NW-SE and NNE-SSW ments could have their origin in the displacement of fractures Africa and Europe to the east and to the north. Once the three original fracture systems had been The formation of these faults appears to have taken created, movements along the fault traces occurred place slightly after that of the N70E to E-W faults. according to the orientation of a stress at any particu- Although they appear abundantly as joints which af- lar moment. That is, the movements may have been fect the metamorphic and Neogene rocks, faults also various and recurrent during the time since their exist (SANz DE GALDEA>:Oet al. 1984 and in the formation. Furthermore, the existence of some frac- press). tures has affected the movement of those adjacent. It As mentioned above, at the western limit of the would seem from observations in the region that the corridor there exist NW-SE faults, continuations of predominant stress during the Quaternary has been which are clearly discernible in the vicinity of Gra- approximately N-S and that vertical readjustments nada. Others running NNE-SSW make up part of have also taken place during this period. One possi- the western edge of the Sierra Nevada (SANZDE Ga> ble results of this N-S stress can be seen to the east of DEANOet al. 1982). Further to the east several signifi- Orgiva where there exist a number of vertical fractu- cant examples of these faults define part of the pre- res which affect Pliocene-Quaternary deposits and sent hydrographic network, and at the eastern limit Alpujarride limestones. These take the form of joints of the corridor the existence of the Tabernes-Almeria running N30W and N20E and thus are apparently basin itself is partly a result of these same faults. conjugate. In general the NW-SE faults are right-lateral, However, not all the faults are of a strike-slip natu- while the NNE-SSW faults are left-lateral. Never- re. There are clearly discernible examples of normal theless, indisputable evidence has also been found for and oblique faults and, in fact, the corridor under left-lateral displacement in NW-SE faults: viz. rela- discussion owes its very existence to the vertical dis- tive displacements of N70E to E-W faults, the sense placements which delimit the northern and southern of striations, and the growth of minerals in the fault boundaries and form the walls of this complex ,,gra- plane. ben<,. In the Corridor the lateral distance of displace- ment is very difficult to calculate solely from field III. The Chronology and importance of the displacements evidence, as the present geological structure of the Betic Cordilleras runs in almost the same direction as The N70E to E-W faults appeared at the end of the the N70E to E-W fractures. Laterally displaced ele- Early Miocene or perhaps a little later, and were ap- ments thus often betray no recognisable signs of parently very active during the rest of the Neogene xmovement~. and even into the Quaternary. Deformation of the From data obtained in neighbouring areas one oldest deposits of the Serravallian-lower Tortonian might arrive at a tentative figure for lateral displace- formations are particularly important. ment in the E-W system of some tens of kilometres, The other two fault systems appear to be slightly but as yet there is no concrete evidence to support later in origin and reflect a separate set of stresses. this conjecture. In the other two systems in this cor- Thus the N70E to E-W faults were essentially for- ridor displacements in the order of some 500 m or med by a stress whose principal axis 61 would have less can be seen. At times, despite the fact that the vi- been in the direction WNW-ESE, while the other sible fracture is long, the movement involved would two fault groups (NW-SE, right-lateral and appear to be almost nil. NNE-SSW left-lateral) were the result of a stress axis The vertical displacements are very significant, ~1 almost N-S, slightly tending towards the west. both at the northern and southern edges of the corri- Left-lateral displacements of the NW-SE system cor- dor. In the neighbourhood of Lanjaron, for example, respond to a movement conjugated to the N70-100E the vertical movement has been at least 800 m. Prof. slip. Fernandez Rubio (pers. comm.) has recorded the re- 654 C, S. DE GALDEANO et al. sults of a test bore for water, carried out at the con- the diversity of the movement suggested. ALDAYA'S tact zone between the Alpujarride and Nevado-Fila- team also claims that the Medna fault changes direc- bride complexes in the village of Lanjaron. The bore tion at the extreme western end of the corridor, at reached a depth of 117 m where it encountered CO2 Nigiielas, to the northwest of Lanjaron. It appears at a pressure of 27 arms., resulting in a large quantity that, after continuing for some 80 km in a direction of material being expelled from the bore in a violent N70E to E-W, it abruptly changes course and runs explosion. This material included Miocene rocks for some 20 km in a direction N-S to NNE-SSW. which appear to be volcanic, though there is a total The present authors incline to the opinion (see also absence of any volcancic rock at superficial levels in SANZ DE GALDI~ANOet al. 1982) that this apparent this area. change in direction is merely the result of the N70E Some of the natural springs in the area are also to E-W fractures intersection the NNE-SSW fault thermal. system. Abundant examples to support this view are These findings appear to confirm the hypothesis visible in the study area. that fracturing in this zone is very considerable and In summary the succesion of movements in the reaches great depths. Alpujarran Corridor may be roughly synthetized as At the northern edge of the Sierra de Gador verti- follows: during lower Burdigalian the Corridor did cal displacements can be in the order of some 700 m not exist as such. Even fracture movements during and the overall displacement, comprising a combina- middle Miocene (lower and middle Serravallian), tion of purely vertical and lateral slips with a vertical seem not to have individualized the Corridor, al- component, can cumulatively reach 1000 m or more, though the basin starts to restrict its length. even though each individual displacement is less. In this eastern extreme of the corridor the thermal Important horizontal movements and other verti- springs of Alhama de Almerfa occur. cal ones are produced at upper Serravallian - basal Moreover the Mecina fault described by ALDaYa et Tortonian, clearly individualizing the Corridor, that at the same time yields thick clastic wedges. As it was al. (1984) is worth mentioning. According to these pointed out, the deformation stage of lower Torto- geologists the contact zone between the Nevado-Fi- labrides and the Alpujarrides, the latter originally be- nian is very important, being of this age many of the movements previously described. The Corridor di- ing an overthrust complex, today represents a trans- vides itself in several sub-basins, with various sedi- tensive fault with right-lateral and right-oblique mo- mentations and subsidences. Thus in the sector ana- vement. The vertical displacement could be some lyzed in this work, marine series become substituted 2.000 m. The trend of striations is parallel or subpa- by a system of alluvial fans proceeding from Sierra rallel to one of the fault systems described in this pa- Nevada. These fans will eventually be covered by a per (N50-70E) and plunges WSW in fault planes which dip 200-30 ~ in direction N160-180E. new marine series during upper Tortonian - Lower Messinian. During middle Messinian the sea retreats One of the present authors (S. de G.) holds the itself from the Corridor at its eastern end, where new view that the extent of vertical displacement (appro- horizontal movements are also more evident. In ximately 2000 m) which ALDAYAet aI. (op. &.) base Pliocene and Quaternary, new vertical movements on the apparent disappearance of one of the Alpujar- took place, even though there are traits of horizontal ride nappes (Lujar nappe), is open to doubt. SANZDe GALDeANO'sopinion is that the Lujar nappe does not ones. disappear but continues in this area as the Castaras At regional level it is observed that fractures E-W nappe, identified by ALDAYAet al. as being a separate to N70E also appears, both at the Internal and Exter- feature. Furthermore, as described elsewhere in this nal zones (fig. 1 A). As a matter of fact, the contact paper, zones occur in which the contact with the Ne- between both zones is of N7OE general trend and is vado-Filabride complex is vertical and affected by essentially a transpressive accident, with a clockwise strike-slip faults which cut obliquely across the AI- movement. All moved practicaly during the same pujarrides and even across Neogene deposits. At stages except the contact accident between Internal other points of contact between the Alpujarride and and External zones, that seems to be older. Thus as Nevado-Filabride complexes and in the Nevado-Fi- early as the begining of Miocene it allowed the first labride complex itself there can indeed be seen evi- movements toward the West of the Internal Zones, dence of oblique movement, such as described by very separated at that time of its present position, ALDAYAet al. (op. cit.). This evidence is interpreted 300 km about. During the lower Burdigalian, the ac- as proof of the existence of other faults, subsidiary r~ cident between both zones was almost totaly blok- the system described here and a further indication of ked, and new others fractures of the same general A strike-slip fault corridor 655 trend such that of the Alpujarran Corridor contribu- d) Many of these fractures, moving again, produ- ted to this movements. ced important vertical movements and, are in great As a result of all those movements, the following part responsible for the rugged present relief. features were stamped in the Betic Cordilleras: e) Roughly, present superficial and middle depth a) A wedge movement of the internal zones toward seismicity, is essentialy located within these fracture the W created the Gibraltar arc, thus appearing as a lines. tectonic arc, and not a paleogeographic one. The Ex- ternal ones, not the Internal, are those that approxi- mately design the arc. b) Important displacement was caused toward the W and NW in the External zones and there some structures of approximately N - S direction occur- Acknowledgements red. Important rearrangement of its units took place in the Internal zones. We want to thank Prof. Hermes for his ideas and sugge- c) To a good extent they are responsible for the stions and for correcting the English text, and to H. G. Wilke for the abstract in German. formation of pull-apart basins, such as the Granada This study was carried out under the auspices of the De- basin can be considered, and other basins located ab- partamento de Investigaciones Geol6gicas del C. S. I. C., ove the strike- slip accidents, such as the Alpujarran Centro Coordinado con la Universidad de Granada, during Corridor. Therefore movements of these fractures a research project entitled: ,,Borde mediterr~neo espafiol: have conditioned the thickness and type of sediments Evoluci6n del Or6geno B&ico y Geodinftmica de las De- of Neogene and Quaternary materials. presiones Ne6genas.

References

ALDAYA, F., E. MARTINEZ, A. DIAZ DE FEDERICO, E. OTT D'ESTEVOU, PI-i. (1980): Evolution Dynamique du PUGA, V. GARCIA-DUENAS & F. NAVARRO-VILA bassin n4ogene de Sorbas (Cordill~res B6tiques Orien- (1979): Mapa geoi6gico de Espafia. Serie MAGNA. tales, Espagne). Docum. et tray. IGAL, Paris. n >_ 1, 1:50.000, (1.042). Lanjar6n IGME. 264. -, BAENA,J. & EWERT, K. (in press): Mapa geoi6gico de PUG& E. (1971): Investigaciones petrol6gicas en Sierra Espafia. Serie MAGNA. 1:50.000 (1.043). Ugijar. Nevada Occidental (Cordilleras B&icas). Thesis. 269. IGME. Univ. Granada. -, CAMPOS,J.; GARCIA-DUEI~AS,V.; GONZALES-LODEI- RODRIGUEZ-FERNANDEZ,J. (1982): E1 Mioceno del sector RO, F. & OROZCO M. (1984): E1 contacto Alpuj~rri- central de las Cordilleras B6ticas. Thesis. 379. Univ, des/Nevado-Filfibrides en la vertiente meridional de Granada. Sierra Nevada. Implicaciones Tect6nicas. Reuni6n del SANZ DE GALDEANO,C. (1983): Los accidentes y fracturas Proyecto del Borde mediterr~ineo espafiol. 18-20. principales de las Cordilleras B&icas. Estudios Geol. ANDRIEUX, J., FONTBOTE,J. M. & MATTAUER,M. (1971): 39, 157-165. Madrid. Sur un module explicatif de l'Arc de Gibraltar. Earth -, FERNANDEZ-RUBIO,R. & FERNANDEZ-LORCA, S. (in and planetary Science Letters 12, 191-198. press) : Fracturaci6n y fotointerpretaci6n en el sector de DIAZ De FEDERICO, A., BURGOS, J., ALMARZA, J. & Albufiol-La R~tbita. (Conjunto Alpuj~rride. Cordille- OROZCO, M. (1981): Mapa geol6gico de Espafia. Serie ras B&icas). MAGNA. 1:50.000, (1.028). . IGME. --, ESTEFEZ, A., LOPEZ-GARRIDO, A. C. & RODRIGUEZ- DURAND DELta, M. & FONTBOTE, J. M. (1960): Le pro- FERNANDEZ, J. (1984): La fracturaci6n tardia al SW de blame de l'~ge des Mappes Alpujarrides d'Andalousie. Sierra Nevada. (Terminaci6n occidental del Corredor Revue de G6ogr. Physique et de G~ol. Dyn. (2), III 4, de las , zona B&ica). Esmdios Geol. 40, 181-187. 183-192. GONZALEZ-DONOSO,J. M., RODRIGUEZ-FERNANDEZ,J., -, VIDAL,F. & DE MIGUEL,F. (1982): E1 sistema de frac- ESTEVEZ, A., LINARES, D., LOPEZ-GARRIDO,A. C., turas de direcci6n N 10-30 E del borde occidental de SANZ DE GALDEANO, C. & SERRANO, F. (1983): El Sierra Nevada (Cordilleras B6ticas). Estudios Geol. 38, Ne6geno del borde SE de la depresi6n de Granada y su 393-398. conexi6n con el Corredor de las Alpujarras. X. Congr. SMET, M. E. M., DE (1984): Investigations of the Crevil- Hal de Sedimentologia, 5, 33-34. Menorca, Spain. iente Fault Zone and its Role in the Tectogenesis of the HARDING, T. P. Petroleum trapps associated with wrench Betic Cordilleras, Southern Spain. Thesis. 174. Free faults. (1974): Bull. Am. Ass. Petrol. Geol. 58. University Press. Amsterdam. 1290-1304.