A Strike-Slip Fault Corridor Within the Alpujarra Mountains (Betic Cordilleras, Spain) by C
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641 Geologische Rundschau 74/3 ] 641-655 ] Stuttgart 1985 A strike-slip fault corridor within the Alpujarra Mountains (Betic Cordilleras, Spain) By C. SANZ DE GALDEANO, J. RODRIGUEZ-FERNANDEZ & A. C. LOPEZ-GARRIDO, Granada*) 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 Guadix 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.