Estudios geol., 43: 435-443 (1987)

STRIKE-SLIP FAULTS IN THE SOUTHERN BORDER OF THE VERA BASIN (ALMERIA, BETIC CORDILLERAS)

C. Sanz de Galdeano (*)

ABSTRACT

The Southern border of the Vera basin is affected by a dextral fault (Cortijo Grande fault) trending N70E. This is crossed by other faults trending NNE-SSW, and particulary at the Eastern end where it is severely bent by the Palomares fault. The movements of the Cortijo Grande fault started at the latest during the Serravallian with compression trending from N80W to N60W wich steadily turned to N20W during the Messinian-Pliocene. Fault displacements affect Quaternary deposits in many occasions. Neogene sediments clearly show deformations contemporary to the deposit.

Key words: Strike-slip Jaults. Neogene, BelÍc Cordilleras.

RESUMEN

El borde sur de la depresión de Vera está afectado por una falla dextrorsa (falla de Cortijo Grande) de dirección N70E. Esta ha sido cortada por otras fallas de dirección NNE-SSW, en especial en su terminación oriental donde está fuertemente flexionada por la falla de Palomares. Los movimientos de la falla de Cortijo Grande se han producido al menos desde el Serravallicnse con compresiones según la dirección N80W a N60W que progresivamente rotaron a N20W en el Messiniense - Plioceno. Los desplazamientos de las fallas llegan a afectar en muchos casos a sedimentos cuaternarios. Los del Neógeno muestran claramente estas deformaciones coetáneas con el depósito.

Palabras clave: Fallas de desgarre. Neógeno, Cordilleras Bélicas.

Introduction bote (1963). Nevertheless, they are large strike­ slip faults which belong to the most important system of the Betic Cordilleras. (Sanz de Ga1dea­ On thc SE part of the Iberian Peninsula, within no, 1983). the Betic Cordilleras, there are important strike­ Here, features of these fractures in the north of slip faults. Some of these are trending NE-SW to Sierra Cabrera and their relationship with those NNE-SSW and have been described on many oc­ trending NE-SW are described. casions: Bousquet and Philip (1976), Ott d'Este­ From a geological point of view this sector is si­ vou and Montenat (1985), Rutter et al (1986), tuated to the east and south of the Sorbas and Weijermars et al (1985) or cited in the context of Vera basins respectively, within the interna1 Zü• thc Betic Cordilleras: Groupe de Recherche Néo­ nes of the Betic Cordilleras (fig. 1). tectonique (1977), Sanz de Galdeano (1983), In the basement of the Sierra Cabrera the Ne­ Boccalctti et al (1985), Sanz de Galdeano et al vado-Filabride is mainly constituted by dark (1985), etc. Howcver, fractures trending N6ÜE to schists and micaschists with garnet, quartzites and E-W on the northern flanks of the Sierras Cabre­ only in very few places by carbonate rocks and ra and Alhamilla have not been studied or have tourmaline gneises. However, in the Sierra de at most been described as faults without any ot­ Sedar (fig. 2), carbonate rocks, gneisses and me­ her specification or as reverse faults with local tabasites are much more common, although mi­ strike-slip components: Durand-Delga and Font- caschists are also presento

(*) Instituto Andaluz de Geología Mediterránea. e.S.Le. y Opto. de Geodinámica. Fac. de Ciencias. Universidad de Granada. 18071, Spain. .¡... w o- ········ D~: :. :,,:'.: :::..: Inlernal zones O Edernal lones

•• Forelands D•••··

Main faulls o o • o o o o Probable fautls o o o o o o o o Gravity slidings o o o o o • o o • o • J~ -N-"1/

SEA o 50 100Km ! ! ! MEDliERRANEAN o »C/) z N mO a » r Fig. I.-The faults of the Setie Cordilera. O »tT1 z o '"..., e: 7' tTI r.f, r -o ."» e Slrikt-slip foult Reverse fault Normol fault Indifferenlialed or probable foult ~ (/) z [] ..., ::J: tTI (/) O e..., ::J: tTI ;c Z ce O ;c o rn ;c O ."..., ::J: rn < tTI ;c » »Q:l ~ r,""~ r , Nevado- Filabride Phyllites and quartzites Martlres and Iimestones Canolomertl19s and clays Canglamerafes t~~ K~q 0p~ i ~ '?-~~ 11_ loo : O] ~t'?- Tortonian?- Messinian Messinian Pliocene - Quafernary Tyrrhenion .i;)\ , A'- ~, Clays and maria Sills Alluvial and playa deposits Sondstones Marls and silts GYP8um I¿¿¿¿¿I Conolamerotes 1-=--==--:I ~ 1".""." "1 l·····1 I o I

Fig. 2.-Geological map of the are investigated.

... '"-..J C. SANZ DE GALDEANO

The Alpujarride complex, overlies the Nevado­ to 4) passes through the Colorado and Pilica hills Filabride and is formed by triassic bluish grey south of Turre. phyllites (although in other arcas there are schits This fault is a set of almost parallel fracturc li­ under them) and quartzites with some metahasits nes affecting the Alpujarride and Neogene sedi­ and, over them, some carbonate rocks, here with ments within a zone lOO m to 1.500 m thick (fig. very linle metamorphism. The Malaguide appear 3). This zonc IS characterized by bands of intense in vcry small outcrops, whose description can be cataclasis of a few metres to over 30 m of thick­ secn in Rondeel (1965) and Garcia-Monzon et al ness, to he observed particularly within the Alpu­ (1974), included in this articIe together with the jarride phyllites. These bands show incipient ver­ Alpujarride complex. tical foliation. Furthermore, phyllites, quartzites The oldest neogene scdimcnts apart the Burdi­ and, sometimes even carbonate beds suddenly galian that form very linle outcroops, are those appear in vertical position with thcir edges para­ of the Serravallian-Lower Tortonian. They are llel to the direction of the bands. Also, there are formed by marine conglomerates, sands and silts many tectonic fragments specially formed by car­ several hundred meters thick. One of their cha­ bonate and quartzite materials and by Mioccne racteristics is that they do not have boulders from rocks included within the phyllites or vice vcrsa. the Nevado-Filabride but from the Alpujarride These fragments range from less than I m to and the Malaguide. more than 1 or 2 km in length (e.g. the Colora­ C1early discordant. some marine conglomerates do and Pilica hills). The edges of this tectonic are deposited, with boulders of up to several cu­ fragments, generally totally c1eancut, are striated. bic metres, containing thin beds of sanstones and The striae are in general subhorizontal and para­ in some places silts and c1ays. Thc boulders are lid to foliation bands and are interpreted as indi­ mostly formcd by the Nevado-Filabride rocks, cators of movement directions. They are very and of particular interest is the great amount of spectacular in some places, as in the Judio hill, tourmaline gneisses and metabasites. The thick­ however they are present throughout the fault, ness of this sediments varies very much, ranging from the vicinity of Mojacar to the village of La from 300-400 m thick near Cerro Colorado to al­ Huelga. In general, striae are parallel to the di­ most nil to the East near the sea. Their age is rection of the fault because the tectonic frag­ Upper Tortonian-Messinian? Their characteris­ ments themselves are elongated in this direction tics and age c10sely resemble those of the Block­ and only two class of deviation are found: at the Formation of the Granada basin (Viennot, 1930). ends of the fragments where faces are not parallel Over this, gradually, and at times laterally, ap­ to the direction of the fault and in very small pear silts, c1ays and marls. Their thickness varies fragments. In the first case, striae may have very greatly, reaching here about 300 m Their age is different directions. However, pianes associated Upper Tortonian?-Messinian. to the faults, even if not vertical, usually maintain Above this sediments and slightly discordant, the direction of the striae. Very small tectonic there are sandstones, sandly limestones and mari­ fragments can be rotated and the striae are adap­ ne conglomerates of varying thickness: 80-100 m ted surrounding the surfaces of the boulder. in this sector and towards Mojacar much less. On It has to be stressed that some large surfaces, top of these, there are marls and silts. They are sometimes of over 150 m, contain different sets, about lOO m thick, although laterally they also of subhorizontal as well as locally subvertical decrease considerably. Their age is Messinian. striae. The striae, calcite and gypsum fibers and To the SW of Mojacar, SE and SSE of Turre, lunate tectoglyphs, indicate that the Cortijo there are sediments formed by porous silts with Grande faults is dextral. This interpretatíon is scattered gypsum, with structures which resemble also supported by the great number of small tec­ small pipes, perhaps algae. They may correspond tonic fragments with sigmoidal tails. Furthermo­ to the Pliocene or Lower Quaternary. re, there are fractures oblique to the bands of ca­ There are also deposits to the Tyrrhenian age taclastic rocks with dextral displacements, with near to, or even on, the coast and other Quater­ could be considered as Riedel fractures (R). nary sedíments such alluvial and colluvial depo­ Miocene sediments, especially older ones, and sits. even those considered as Pliocene or Quaternary, are also affected by these bands. Cataclasis in Tectonics Miocene sediments is less intense, but the beds are vertical in places and severe fracturing, rather An important fault, the Cortijo Grande fault, than foliation, is frequent. on the Northern border of Sierra Cabrera (figs. 1 The Cortijo Grande fault is limited to both E STRIKE-SLlP FAULTS IN THE SOUTHERN BORDER OF THE VERA BASIN 439

CUCAR billBJ Sondstones. Messinion N13W 513E Silts, morla } A ond 50nds Tortonion ·¿,::·:::..¡ ::.::;.·0·.·. Conglomerotes ri." ." .. ~ Red conglomerotes 000 ~ 5ilts. serrovollion - Lower Tortonion ARRAEZ I 919m) carbonate Sl3E Ib:ks}Alpujorride NI3W Phyllit8s B l\'}DisPlocement {E. movement o Sense W. movement

111111 Foult gouge

NI3W 513E CORTIJO GRANDE e

MEZQUITA I 960m) N13W SI3E

o

2Km e!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!5;¡¡¡¡;;¡¡¡¡;;¡¡¡¡;;¡¡¡¡;¡;¡j1

Fig. 3.-Geological cross-sections of Cortijo Grande fault. and W by faults trending NNE. To the East, the E-W trending fault. This situation is interpreted Palomares fault, complex and diversified, is parti­ as two active crass-cutting systems. cularly important. Geological and photogeologi­ To the West, the NNE trending faults which cal studies show that it is formed by a set of faults pass thraugh La Huelga and to the East of the and not by a single surface. A description is given Sierra de Alcornia (East of Sierra de Bedar) have by Bousquet and Philip (1976) and Weijermars et c1early sinistral components and a vertical compo­ al (1985). nent of over 200 m. These faults cut the Cortijo Of particular interest are the effects of this Grande fault and represent its western termina­ fault on the Cortijo Grande fault: the latter turns tion. into parallelism with the NNE direction of the A third system of fractures is trending NW-SE, Palomares fault. AIso, Alpujarride and Neogene and unlike other sectors in the Betics, does not racks have been turned forming a vertical drag fram large fractures but are present at micra and fold. The Cortijo Grande fault reappears to the mesotectonic levels. east of the Palomares fault, which is crassed by The Cortijo Grande fault also presents vertical 440 e SANZ DE GALDEANO or subvertical striae and other intermediate ones In Mojacar, at the Western road, the directions but those with rakes between O and 20 are much obtained in the Messinian sediments for (TI are more common. Therefore it can be deduced that N24 E, N5E and N25W (fig. 5, disgram 11). Two the throw is not very important with regard to the of these, N24E and N5E, without any real signi­ heave. However, the latter cannot be calculated ficance 01' somehow unreliahle, since this is a sec­ directly, although the Cortijo Grande accident tor in which materials have rotated more that 50" may reach easily tens of km while that of Palo­ due to the drag effect of the Palomares lines of mares, taking into account the displacement cxis­ faults. The direction N25W coincides with other ting between the sierras Cabrera and Almenara, mentioned previously. reaches 60 km approximately. In Pliocene-Ouaternary (?) deposits there are joints which would be compatible with N20W and N70E compressions (fig. 4). Microtectonics Directions of tensional fractures in conglome­ rate pebbles (in Serravallian-Lower Tortonian se­ More than a thousand of measurements of diments outcropping near Cortijo Grande) have faults and joints were carried out. Many of this also been mcasured (121 measures). Their poles faults appear in well defined conjugated sets, 379 have one maximum in the dircction N58E and had strie and in 178 of these the direction of mo­ another Icss important one in N35E (fig. 5, dia­ vement could be deduced. gram 12). Measurements cover the whole area, which could be subdivided into 12 sectors. The results are shown in figs. 4 and 5. Cronology of deformations It has to be pointed out that fractures trending NW-SE have displaced both dextrally and sinis­ During the Serravallian and Lower Tortonian trally depending on whether (JI was closer to N-S there was not important erosiono since in their se­ 01' to E-W. Similarly, the whole set of fractures diments there is not any detrital material inheri­ has not been formed by only one system of stres­ ted from the Nevado-Filabride. ses, but at least two systems are necessary to ex­ Without any doubt, after the deposit of the Se­ plain its movements and the conjugated sets rravallian-Lowcr Tortonian sediments and before which are clearly observed. the upper Tortonian, a strong pulsation took pla­ In the Alpujarride rocks we have obtained the ce, as is shown by the faet that the Upper Torto­ approximate direction of N8üW-N5üW, depen­ nian-Messinian sediments are clearly discordant ding the sector, as predominat for (JI' A direction even over the Alpujarride. There are detrital ma­ close to N20W is also deduced (fig. 5, diagrams 1 terials from the Nevado-Filabride, in large boul­ to 4). ders in many plaees, but apparently thcy come In the Serravallian-Tortonian sediments the di­ from the Sierra de los Filabres (in this case. its reccion of N80W is deduced to the North of the Southeastern spur which is called Sierra de Bedar Pilica and Colorado hillocks and in the Cortijo and Sierra Alcornia) and apparently before Sierra Grande sectors. The direction N50W is deduced Cabrera had risen sufficiently. to the south of Judio hillock. The direction On the whole, it seems that the predominant N20W, approximately, is also deduced in this se­ direction of (JI ranged from N80W to N55W for diments with small changes from sector to sector the Serravallian (and earlier) and Tortonian ages. (fig. 5, diagrams 5 to 8). These stresses seem to have continued during the The direction N20W is the only one obtained Messinian, although a turn in the direction of (JI' in the Messinian outcrops at the bridge over the which steadily becomes N30W-N20W, can be de­ river Aguas and in the Alfaix sector (N27W and duced. At the same time, NNE-SSW faults must N15W respectively) (fig. 5, diagrams 9 and 10), have moved a great deal, whilst in this sector were there are also numerous normal faults al­ NW-SE faults are not very important, although most parallel to the deduced direetion of (Jl' This quite numerous at meso and microstructural le­ faet is particularly evident in the river Aguas ve\. The NNE-SSW faults may have had an older where there are a great number of normal eonju­ history, although movements older that the Mes­ gated faults with N27W as their average strike. sinian, when they already had vertical displace­ So, it is possible to think that the formation of ments of at least 200, are not observed. On the strike-slip and normal faults is almost eontempo­ SE edge of the Sierra Alcornia they formed a c1iff rary, with a clear tension perpendicular to the di­ on the base of which beach-like Messinian mate­ reetion of (Jl' rials were deposited. ~ c: 7' m V, r ;; , , 'T1 I .....,., .... 1'1..... _wuas : ... ",'~:' > I ,I pOSin _----,----... ,/\ \ e s..\,_~:::~~ i _---'••.. ,l \ :" I i "era \ \/ ,',./ \ c¡ ,',"', \ Vl 5 • l' I ., ~ ,/: ~, ;/~ I ...... \ .. , ¡/' / ~/: "-"', '..," \' ~' ~ , - ,~,' '- "\ ...., ~ ~~)7 :t .--:::~~ m 60 ..... ,' 'b,/ VJ O ~ ,- r.::\...... : •• -/": ~.>/ e...., , ;", :t , ~ m ,, :;¡;;l ,, '" ce --o O :;¡;;l tl m :;¡;;l O 'T1 ...., :t m e::·,: m-< :;¡;;l :J!-~; > ...... ce Vl> Z \ ,', , ' I / / / rerO CA b /( Sierra ~N/- o 1 2Km :...... I

Fig. 4.-The Cortijo Grande fault. In points are marked carbonate tectonic fragments in cataclastic bands within the Alpujarride. Letters and numbers show the positions of the cross-sections and the sectors of the diagrams of figs. 3 and 5 respectively. The arrows show directions of (J, deduced from joints in Pliocene-Quaternary? sediments.

..,. Pilica HiII Judio Hitl N

·r·

.:: JI.

(AlpulOrridel 2 (Alpujarricle) 3 N of Calofoclo Hill Cortijo Grande

00 .. "D1o 000 \ 00 R"

w E E

x x .. Xx x ~ ~ (Alpujarride) 4 (Serravallion - Tarta ion) 5 Serravallion - Tartanian) 6 S af Judio Hill R{a AQua, . , .0'

Xx NN NN N E w :. E A:6. '.A A •• ," '" o' • ......

5erravallian-Tartonían 8 (M..'inian) 9 w Mojácar N \e • •;. D\D : D~x X • 000....O••' • x ..-, • l': • E w E w E • N• •R • :

(MeSlmian¡ 10 11 (Torfonian) :=="12

Fig. 5.-Diagrams of tectonic measures. Points: Poles of strike-slip and reverse faults. Triangtes: Poles Ol normal faults. Crosses: Indifferentiated striae. D, S, R and N: Striae of dextral, sinistral, reverse and normal faults respectively. In many cases several measures are coincident in a determinated point. The arrows show the directions of (J", deduced, and their size is proportional to the importance of the directions obtained. Diagram 12: measures of poles of tensional joints in Lower Tortonian conglomerates. STRIKE-SLIP FAULTS 1 THE SOUTHERN BORDER OF THE VERA BASIN 44}

The strong drags (over 2 km) and the f1exure 3. The (TI direction steadily rotates in timc caused by the Palomares faults on the Cortijo from N80W-N60W, in the Serravallian or even Grande fault clearly affect Upper Messinian sedi­ earlier, to N20W in the Messinian. This last pre­ ments which proves that the movements are quite dominant direction seems to have continued up moderno Furthemore, to the North in the Vera to the present, although are some very modern basin, in outcrops which are almost kilometrical movements which prove the existence of com­ in size, sediments, possibly from the Lower Qua­ prcssions, at least of a local and momentary natu­ ternary and affected by wrench faults trending re, with WNW-ESE directions. NNE-SSW are observed. One of these faults Study carried out through the 3184-83 C04-02 clearly affects tyrrhenian deposits in the village of projcct of the e.A.I.e.Y.T. and 79/84. C4 pro­ Garrucha. Also in the interior of Sierra Cabrera jcct of the e.A.Le.Y.T. and e.S.Le. sorne colluvial deposits are affectcd by strike mo­ vements (c1early seen due to the presence of gyp­ Referencias sum fibers), but on this occasion the fault trends N70E. Boccaletti. M .. Gclati. R. and Papani. R. (I'J84). Trascorrenze plio-'1uaternire nel settore hetico dell'Areo de Gibilterra. Aeta Even fault planes it the Cortijo Grande fault Nafllralia de /'Atelleo Pllnnellse. 20. 'J7-I05. are c1early affccted at several points, such as the Bous'luet. 1.C. and Philip. H. (1 \>7ó). Ohservations microlecto­ Judio hillock, where they are cut by NNE-SSW ni'lues sur la compression nord-sud '1uaternaire des Cordillc­ res bétiques orientales (Espagne méridionale-Are de Gihral­ faults. It should also be pointed out however that tar). B/I//. Soco Géo/. France (7). 28. 711-724. near Mojacar, almost E-W fault planes cut NNE­ Durand Delga, M. and Fontbote, 1.M. (1'Jó'J). Le problcme de SSW faults with decimetrical, dextral horizontal ráge des nappes alpujarrides ti"Andalousie. Ret'. Géogr. displacements. Phys. Céo/. Dy". (2), VIII. 181-187. García Monzón. G .. Kampschuur W. and Verburg. J. (''J74). In short, forces running N80W which steadily Ce%gica/ map of Sorbas (1031). 1:50.000. I.G.M.E., Ma­ changed to an average N45W were predominant drid. in this sector during the Serravallian and until the Groupe de Recherche néotectoni'lue de rarc de Gihraltar. (1 \>77). L'histoire tectonique récente (Tononien á Ouaternai­ Tortonian-Messinian. (TI rotation continued du­ re) de rArc de Gihraltar et des bordures de la mer d'Albo­ ring the Messinian-Pliocene until the approximate rano Bull. SoC. Géo/. Franee. (7). 19, 575-óI4. direction of N20W became predominant, as can Ott d'Estevou Ph. and Montenat Ch. (IW\5). Evolution structu­ rale de la zone béli'lue orienlale (Espagne) du Tortonien a be observed in the river Aguas. This compression I'Holocene. eR. Acad. Sc. Paris. 300. 11. 8. 3ó3-368. direction extends into the Quaternary, if not until Rondeel H. E. (1 (5). Ce%gica/ 11l1'esfigllfiolls ill tll(' "·e.\'Iem present. However, E-W movements still continue Sierra Cabrera and adjoilling Areas. SOlllh-Eastem Spllin. somehow, as is shown by the existence of defor­ Thesis, Amsterdam, lól p. Rulter E.H., Maddock R.H., Hall S.H. and Whitc S.H. (198ó). mations and sets of faults in Neogene and Qua­ Comparalive Microstructures of Natural and Expcrimcnlally ternary sediments compatible with WNW-ESE Produced C1ay-Bcaring Fault Gougcs. P//re & Applied Geop­ compressions. hysics, 124, 1/2. 2-30. Sanz de Galdcano. c., (1983). Los accidentes y fracturas princi­ pales de las Cordilleras Béticas. Estudios Ceo/. Madrid. 39. 157-165 Sanz de Galdeano. C. Rodríguez Fermíndez, 1. and López Ga­ Conclusions rrido. A.e. (1\>85). A Strike-slip Fault Corridor within the AI­ pujarra Mountains (Betic Cordilleras, Spain). Ceo/. R//nds­ chau. 74. 641-655. 1. The Northern border of Sierra Cabrera is Viennot, P. (1930). Observations géologiques dans la région de affected by a large dextral accident trending ap­ Grenade (Andalousie). Uvre ¡uhilaire Soco Céol. France. 11. proximately N70E: the Cortijo Grande fault. The 633-660. rocks adjacent to the fault contain cataclasite Weijermars. R., Roep. Th. B.. Van den Eeckhou!. B., Postma G. and Klcverlaan K. (]\>85). Uplift hislory of a Bctic fold bands and striations. nappe inferred from Neogene-Quaternary sedimentation and 2. The Cortijo Grande faults is cut both to the tcctonics (in the Sierra Alhamilla and Almeria. Sorbas and East (Palomares fault) and to the West, by NNE­ Tabernas Basins of the Betic Cordilleras, SE Spain). Ce%~~ en SSW faults. The Palomares faults provoked the Mijnho//w. 64, 397-411. f1exion and dragging of the Cortijo Grande fault Recihido el 25 de Noviembre de 19f17 with a displacement of over 2 km. Aceptado e/ 20 de Diciembre de 19f17