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Ž .Geomorphology 30 1999 259–272

Nature and impact of the Neotectonic deformation in thež /western Sierra Nevada Spain

Carlos Sanz de Galdeano ), Angel Carlos Lopez-Garrido´( )Facultad de Ciencias, Instituto Andaluz de Ciencias de la Tierra CSIC UniÕersidad de Granada , 18071 Granada, Spain

Received 10 August 1998; received in revised form 1 March 1999; accepted 16 March 1999

Abstract

The current high relief of the western sector of the Sierra Nevada was practically nonexistent before the Tortonian, asattested by the marine Late Neogene outcrops that reach a height of 1830 m, which would easily surpass 2000 m if not forerosion. The significant uplift produced, over 3500 m, has caused considerable thinning, detachments and gravitational slidesin the Alpujarride units. The general displacements of these movements are towards the WNW to SSW. On the whole, themorphology is fan-like, adapting itself to the border of the Sierra Nevada. This border contains normal conjugate NW–SEand N–S to NNE–SSW faults, the latter also with sinistral strike–slip character. These faults have accommodated the upliftof the Sierra Nevada within an almost N–S compressive context and linked E–W extension. This sector coincides with thewestern boundary of the Nevado-Filabride complex and, in its southern continuation, with the western limit of the lower

Ž .Alpujarride units, seeming to indicate a fault or faults reaching deep into the basement. Uplift has taken place unevenlyover the last few million years, with three noteworthy periods: during the deposition of the Block Formation in the LateTortonian, towards the Early?–Middle Pleistocene, and in the Middle?–Late Pleistocene. This has resulted in considerabledeepening of the fluvial net surrounding Sierra Nevada at the present time. q 1999 Elsevier Science B.V. All rights reserved.

Keywords: neotectonics; Sierra Nevada; Betic Cordillera; uplift; gravitational collapse; faults

1. Introduction

The western part of the Sierra Nevada, locatedŽ .East of Granada Fig. 1 , is formed of diverse units

of the Betic Internal Zone. There are significantoutcrops of Upper Miocene to Quaternary depositsŽ .belonging to the Granada basin unconformably

) Corresponding author. Fax: q34-958-243384.Ž .E-mail address: [email protected] C. Sanz de Galdeano

overlying or in tectonic contact with these units,especially on the border of the Sierra. There are alsoNeogene–Quaternary outcrops on the slopes of SierraNevada, some almost 2000 m in height.

The Betic Internal Zone comprises three al-lochthonous complexes, tectonically superimposed,that from bottom to top are: the Nevado-Filabride,

Žthe Alpujarride and the Malaguide Sanz de.Galdeano, 1997 complexes. In the western Sierra

Nevada, the Nevado-Filabride complexes can befound occupying the nucleus of the Sierra Nevada,

0169-555Xr99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved.Ž .PII: S0169-555X 99 00034-3

( )C. Sanz de Galdeano, A.C. Lopez-GarridorGeomorphology 30 1999 259–272´260

Ž . Ž .Fig. 1. Situation of the study area. A General situation in the Betic Cordillera. B Geological outline of the central part of the BeticCordillera. The location of Fig. 2 is marked.

and the Alpujarride complex, forms a fringe aroundit.

The Alpujarride complex presents rocks from theLower to Upper Triassic age which, as in theNevado-Filabride complex, were metamorphosedduring the Alpine orogeny. Its reliefs comprise the

Trevenque, Alayos and Silleta peaks among others,in which the Triassic materials are placed in threedifferent overthrust units that, from bottom to top,are the Viboras, Trevenque and Fuente-Piedra unitsŽ .Fig. 2 . This structural development took place dur-ing the Alpine orogeny and finished during the Late

Ž . Ž . Ž .Fig. 2. Simplified geological map of the study area. 1 Nevado-Filabride complex, 2 Alpujarride complex, 3 Serravallian, conglomeratesŽ . Ž . Ž . Ž .and marls, 4 Basal Tortonian, conglomerates and calcarenites, 5 Tortonian–Messinian, marls, 6 Late Tortonian, Block Formation, 7

Ž .Pleistocene, Alhambra and other equivalent formations, 8 Pleistocene–Holocene, a.—alluvial fan, b.—peat, c.—conglomerates, sands andŽ .clays, 9 Late Pleistocene–Holocene, alluvial deposits. The position of cross-sections of Fig. 5 is marked.

( )C. Sanz de Galdeano, A.C. Lopez-GarridorGeomorphology 30 1999 259–272´ 261


Oligocene or perhaps at the beginning of the EarlyŽ .Aquitanian Early Miocene . However, the eventual

overthrusting was affected by later deformations,many of which are included in the neotectonic periodŽ .post Mid-Miocene .

The neotectonic aspects of the western sector ofthe Sierra Nevada have been studied to a greater or

Ž .lesser extent by several authors. Fontbote 1957´examined the various tectonic stages in the SierraNevada and indicated, apart from an initial stage ofoverthrusting, basal folding, bound to the formationof the huge vault of the Sierra Nevada since theMiocene, the formation of small, sharp folds, proba-bly related to the basal folding, and finally fracturetectonics during the Late Neogene to probably theQuaternary.

Ž .Sanz de Galdeano 1976 and Santanach et al.Ž .1980 describe the area of Padul–Durcal and esti-mate at least 800 m of fault throw in that sector sincethe Late Miocene. Later, Galindo-Zaldıvar and´

Ž .Gonzalez-Lodeiro 1988, 1990 , Galindo-Zaldıvar et´ ´Ž . Ž .al. 1989, 1991 and 1996 , Galindo-Zaldıvar 1993´

Ž .and Jabaloy et al. 1993 analysed the Neogenedeformations that took place in this and adjacentareas, considering them, in many cases, as prior tothe Late Miocene. However, Galindo-Zaldıvar et al.´Ž .1996 refer especially to modern deformations ofthe Alpujarride complex when it slid over theNevado-Filabride complex and associates them withthe important faults in the SW Sierra Nevada.

Ž .Riley and Moore 1993 used Digital ElevationModels to analyse the slopes controlled by faults inthe western and southern borders of the SierraNevada, emphasizing the Padul–Durcal sector. Theyestablished a correspondence among irregularities inthe relief, and break in the relief or spurs which arerelated to faults, and the formation of pedimentsrelated to recognizable tectonic stages in the GranadaBasin.

Ž . Ž .Sanz de Galdeano 1996 and Keller et al. 1996studied active tectonics in the Sierra Nevada, espe-cially in the Padul–Durcal sector and in its southernborder. They report uplift rates of over 0.6 mmryear,occasionally reaching 0.84 mmryear. The averagerate they obtain is approximately 0.4 mmryear sincethe beginning of the Tortonian. These values resultfrom the comparison of the different altitudes ofNeogene and Quaternary deposits affected by faults.

Ž .Keller et al. 1996 introduced geomorphologicalindices to study the relief and to determine the age ofits formation.

Ž .Johnson et al. 1997 , on the basis of apatite andzircon fission track analyses of the Nevado-Filabriderocks, indicate that the uplift of the Sierra Nevadabegan about 9–8 Ma ago, during the Tortonian.

Ž .Calvache et al. 1997 examined the alluvial fans ofthe Durcal sector and related the Pleistocene depositswith stages of uplift.

Finally, the revision of the structure of the Alpu-Žjarride complex Sanz de Galdeano and Lopez-Gar-´

.rido, in press have revealed new Neogene outcropson the slopes of the Sierra Nevada’s western sector,as well as separating with greater clarity the initialoverthrusting of the Alpujarride units from later phe-nomena.

The objective of the present paper is to presentthe main neotectonic features in the western part ofthe Sierra Nevada and the adjacent SE border of theGranada Basin. These data are then placed in a widercontext.

2. Main characteristics of the Neogene and Qua-ternary sediments in this sector

The older Neogene deposits of this sector areSerravallian conglomerates, sands and marls. Torto-nian deposits, comprising conglomerates and cal-carenites at the base, lie unconformably over thebasement or on the Serravallian sediments. Theypresent shallow-marine facies with abundant faunaand extremely variable thickness, from a few metresto more than 50 m. Above appear Tortonian–Mes-sinian marls, with some beds of sands and conglom-erates, several hundred metres thick. Particularly inthe northwestern sectors of Guejar-Sierra and¨

ŽMonachil a thick formation corresponding to marinedeposits in the bottom, passing progressively to flu-

.vial sediments has developed, containing large peb-bles inherited from the Nevado-Filabride complex,i.e., the nucleus of the Sierra Nevada. These de-

Žposits, whose age is Uppermost Tortonian Dabrio.and Ruiz-Bustos, 1979 , were termed the Block For-

Ž .mation by Viennot 1930 .Remains of all of these Tortonian sediments are

found at diverse heights on the slopes of the Sierra


Nevada, particularly two outcrops located betweenthe Trevenque and Niguelas, at 1755 and 1830-m¨

Ž .a.s.l. Fig. 2 .Unconformably overlying the Tortonian marls,

and locally on the conglomerates of the Block For-mation, is the Alhambra Formation, of Pleistocene

Ž .age Aguirre, 1957; Ruiz Bustos et al., 1992 . It

extends from Monachil towards the north. It is con-stituted by reddish conglomerates, sands, silts andclays, with some interbedded paleosol levels. Thepebbles of this formation are mainly inherited fromthe Nevado-Filabride and Alpujarride materials. Sim-ilar equivalent formations occur to the south, in thePadul–Durcal sector.

Fig. 3. Gravitational slides and other associated structures in the Alpujarride units. The positions of the cross-sections in Fig. 4 are indicated.


More modern Quaternary sediments form the setof alluvial fans bounding the Sierra Nevada. Amongthem, the La Zubia alluvial fan stands out, formedalmost exclusively of dolomites from the AlpujarrideTrevenque unit. This fan is no longer active as itsoriginal source area is now drained by the Huenesand Dilar rivers which constitute incised valleys atboth fan margins.

3. The relief in the Sierra Nevada’s western partat the end of the Middle Miocene and beginning

(of the Late Miocene start of the sensu lato neo-)tectonic period

At the beginning of the late Miocene, in theTortonian, almost none of the Sierra Nevada’s pre-sent high relief was evident. The base of the Ser-ravallian deposits in the western part of the SierraNevada are formed of conglomerates with pebblesinherited from the Malaguide and Alpujarride com-plexes that, to the top, pass to marine marls. Pebblesfrom the Nevado-Filabride complex first appear dur-

Ž .ing the Tortonian Block Formation . Until this time,the Nevado-Filabride complex core of Sierra Nevadahad not been exposed to erosion and only smallislands with low relief existed.

The heights of some Tortonian outcrops on theslopes of the Sierra Nevada support this conclusion.There is a large outcrop at 1755 m formed of micro-conglomerates and calcarenites, about 2 km longŽ .Sanz de Galdeano, 1996 . There is another, smaller,outcrop where, besides the calcarenites, are also

Ž .remains of marls and sands 2 m and of the BlockFormation. This outcrop is located in the Alayosarea, near the Puntal del Tigre peak, at 1830 m in

Žheight see Fig. 2, where only the calcarenites are.marked owing to the small size of the outcrop . In

spite of exhaustive searches, no higher outcrops havebeen located. There are numerous outcrops at 1600–1500 m and other lower ones, down to those of theGranada Basin, with minimum values of about 700-m

Ž .a.s.l. Considering that marls now missing weredeposited, and that at their time of deposition theywere laid down at greater depths than the calcaren-ites, then, without erosion, the Tortonian depositswould now be found at a height of over 2000 m. Inaddition, taking into account that the Alpujarrideunits, on which rest the higher Neogene outcropsdescribed, have gravitationally slid hundreds of me-

Ž .tres as discussed below , the result would be that theminimum uplift of the Sierra Nevada was about 3000m since the Late Miocene. At the present the maxi-mum height is 3480 m, in the Mulhacen peak, not farfrom its western border. In other words, before theTortonian the relief in the Sierra Nevada area wasslight and therefore the different processes involvedin the build up of the present mountain range would

Žhave occurred during the neotectonic period Torto-.nian to Present .

4. Neotectonic deformations affecting the Alpujar-ride units of the western Sierra Nevada

The Alpujarride complex, previously structured inŽ .three overthursted units Fig. 3 , later underwent

Žconsiderable tectonic thinning Sanz de Galdeano.and Lopez-Garrido, in press . The original strati-´

graphic sequence of each one of the units was over1000 m thick, but the nearer the units are to theNevado–Filabride contact, the more thinned theyare. In some sectors, the Viboras unit is almostcompletely thinned and the Trevenque unit is nomore than 200 m thick. The cross-sections in Fig. 4show this thinning of the Alpujarride units near thecontact with the Nevado-Filabride complex. Theoriginal thrust surfaces were strongly affected duringthis event.

Detachments at different levels, slip surfaces af-fecting individual Alpujarride units, or others cuttingthe former thrust planes, also occurred during thisgravitational event. Nevertheless, all these newlydeveloped structures resemble overthrust surfaces

Fig. 4. Simplified geological cross-sections showing the thinning of the Alpujarride units and the gravitational collapse structures. Theirpositions are marked in Fig. 3.


since they partially or completely repeat the units oreven change the original superposition of the units.The Viboras unit presents a duplication near itscontact with the Nevado-Filabride complex. Thereare also several tectonic superpositions inside theTrevenque unit, which disappear towards the outerborder of the Sierra Nevada.

The slip vectors observed in the detachment sur-Ž .faces and the sheets Fig. 3 point towards the W

Ž .and even NW in the most northern part and SSW.This last direction was previously reported by

Ž .Galindo-Zaldıvar et al. 1996 and is observed from´the sector of Trevenque peak towards the south, bothin low-angle faults, dipping 5 to 158S, and in typicalnormal faults dipping 30 to 608. Well-developedstriae are usually observed on these surfaces, someof which are spectacular, as for example to the N ofthe Torrente ravine, to the NNE of Niguelas. This¨same direction of displacement is observed in theNW border of the Sierra Nevada, close to Monachil,in the surface-contact of the Trevenque and Fuente-Piedra units with the Neogene deposits of the GranadaBasin.

In the northern sector N–S to NNE–SSW anticli-Ž .nal and synclinal folds can be observed Fig. 3 ,

which are congruent with the cited westward dis-placements of the slides. Generally, the fold axes aresub-horizontal, with the exception of the N sector,near Guejar-Sierra, where they dip about 158N, fol-¨lowing the mountain slope.

All of the aforementioned structures present afan-like array delineating the western border of the

Ž .Sierra Nevada Fig. 3 . This structural arrangementcan be related to its own genesis. From the analysisof the detachment displacements, and fold orienta-tions, a centrifugal pattern in relation to the Nevado-Filabride core of the Sierra Nevada is observed. Asimilar situation occurs in relation to the thinning ofthe Alpujarride units. From these data it seems to beevident that, as a whole, the Alpujarride units over-riding the Nevado-Filabride complex in the westernsector of the Sierra Nevada underwent a large-scalegravitational slide in response to the uplift of thissierra. The entire studied sector has been uplifted andthe Alpujarride units have slid repeatedly, eventuallyaffecting the Nevado-Filabride materials.

The height of some of the Tortonian deposits,unconformably overlying the Alpujarride, indicates

that the elevation of the Sierra Nevada and most ofthe gravitational slide structures recorded in theAlpujarride units must be developed during Torto-nian and post-Tortonian times. Therefore, accordingto the evidence displayed at this border of SierraNevada, it is probable that part of the stages offragile deformation, previously reported for the Ser-

Ž . Žravallian Middle Miocene Garcıa-Duenas et al.,´ ˜.1992 took place in the Late Miocene onwards. They

were generated by gravitational sliding in responseto the uplift of the Nevado-Filabride core of theSierra Nevada.

5. The normal faults of the western border of theSierra Nevada

This western border is bounded by relevant NW–ŽSE, N–S to NNE–SSW and E–W faults Figs. 2 and

.3 . The NW–SE faults are generally normal, withŽ .throws of several hundred metres Fig. 5 . Their

sense of displacement, towards the SSW, agrees withpart of the displacements displayed for the Alpujar-ride units, at least in the SW part of the study area.

In the N–S to NNE–SSW faults, two movementsare observed, one essentially of normal character and

Ž .the other in many cases the most important sinistralstrike–slip or oblique normal-sinistral, depending onthe specific orientation of the fault, with slip vectorsalso pointing towards the SSW. This set of faults andthe NW–SE one are conjugate structures. The E–Wfaults are more poorly represented in this sector andshow normal vertical movement.

Although most of these faults are placed in thewestern border of the Sierra Nevada, along the con-tact between the Alpujarride and the Granada Basinsediments, similar structures occur inside the moun-tain range. These structures usually cut the Alpujar-ride units, and in some sectors graben and horststructures were developed, affecting the aforemen-tioned detachments in some cases. It is a continuousprocess where new faults cut previous ones, setwithin the progressive uplift of the Sierra Nevada.

Several of these faults, especially the NW–SE set,extend to the N and S, particularly in the GranadaBasin. The faults that affect the Sierra Elvira and the

Ž .town of Granada Fig. 1 trend in the same directionand present throws of hundreds of metres. The same

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Ž . Ž .Fig. 5. Geological cross-sections in the Padul sector horizontal sc.s vertical sc. . Taken from Sanz de Galdeano 1996 . Their positions are marked in Fig. 2.


Fig. 6. Geological interpretation of the relationships among the Serravallian, the basal Tortonian, the Block Formation and the La ZubiaŽ .alluvial fan. It corresponds to the SE of Monachil, with two different planes joined to show the structure horizontal sc.svertical sc. .

situation holds for the faults of the Sierra Harana,NE of Granada. In Granada, the Alhambra Forma-tion and, further south, the La Zubia alluvial fan, areaffected by throws of over a hundred metres. In fact,these faults control the Neogene and Quaternaryevolution of the Eastern and Central part of theGranada Basin. In this way, all the reliefs existingbetween the city of Granada and the Sierra Harana

Ž .are produced by the throws more than 500 m ofthese faults. This set of faults continues towards theSE, in an area occupied by the Alpujarride complex,in the Alpujarran Corridor, S of Sierra Nevada,finally reaching the coast.

The N–S to NNE–SSW faults that flank part ofthe western border of the Sierra Nevada also affectthe Neogene sediments, not only in the contact withthe Alpujarride complex, where these deposits dipagainst the mountain slopes at numerous points, butalso in the Granada Basin itself. Thus, directly to theN of Monachil, a fault, seemingly antithetic with thatof the border of the Sierra Nevada at that point,crosses the valley and affects the Block Formation.These NNE–SSO faults continue both to the S and N

Ž .of the study area Sanz de Galdeano et al., 1982 .

Although the gravitational slides of the Alpujar-ride units are a secondary effect of the uplift of theSierra Nevada core, these faults have facilitated theelevation and not only cut the Alpujarride complexand the Neogene and Quaternary deposits, but alsoreach an even greater depth, also affecting the

ŽNevado-Filabride complex Sanz de Galdeano et al.,.1982; Vidal et al., 1982 .

6. The geodynamic situation that produced thedeformation and general interpretation

Since the Tortonian, the situation in the BeticCordillera and N Morocco has been compressive in aNNW–SSE to N–S direction, combined with an

ŽE–W extension Montenat et al.,1990; Aıt Brahim,ˆ.1991; Sanz de Galdeano and Vera, 1992 . This situa-

tion, perhaps combined with the isostatic rebound ofthe region, after the nappe stacking of the differentcomplexes of the Betic Internal Zone, finished dur-ing the early Miocene, gave rise to the formation ofthe Sierra Nevada antiform.

Ž . Ž .Fig. 7. Main canyons, gorges and ravines of the drainage net in the western Sierra Nevada area. 1 Nevado-Filabride complex, 2Ž . Ž . Ž . Ž .Alpujarride complex, 3 Upper Miocene sediments, 4 a.—Alluvial fans Pleistocene , b.—Pliocene–Quaternary sediments, 5 Canyons

Ž .and gorges, 6 ravines.


During the uplift of the Sierra Nevada theNevado-Filabride complex formed a huge antiformalstructure whose axis, on the whole E–W, is curved

Žtowards the SW in the western Sierra Nevada Fig.. Ž .1B , as Galindo-Zaldıvar 1993 indicates. This in-´

flection seems to correspond to a big drag foldlinked to a deep fault with a possible NNE–SSWdirection and a normal and sinistral character. Thisinterpretation is congruent with the SSW movementof the Alpujarride units situated in the SW of theSierra Nevada.

The slides to the W or WNW of the Alpujarrideunits in the western border of the Sierra Nevada areclearly controlled by gravity. The same happens withthe slides to SSW in the central and southern sectors,but these last movements also coincide with thedisplacement of the N–S to NNE–SSW faults, thataccommodate part of the uplift of the Sierra Nevadaon its W and SW borders.

Comparing the western sector of the Sierra NevadaŽand the adjacent SE area of the Granada Basin Fig.

.1 , although the entire sector has been uplifted sincethe Late Miocene, the Sierra Nevada has undergonemuch more significant uplift, with a relative verticalelevation of the order of 3000 m. In the footwall, thecompression triggered the formation of the citedantiform structure, although the concomitant upliftcaused gravitational collapse. In contrast, in theGranada Basin the effects of the compression areless obvious, showing instead more effects due to theE–W extension. It is possible that this importantvertical step between the two sectors was controlled

Ž .at depth by a fault or faults controlling the westerntermination of the Nevado-Filabride complex in theCordillera. Moreover, its probable southward prolon-gation, in the area of the Guadalfeo river, marks thewestern limit of the lower Alpujarride units, thisbeing one of the major neotectonic features of theBetic Cordillera.

7. Stages of creation of relief

At the beginning of the Tortonian, the BeticCordillera underwent significant marine transgres-sion that produced the deposition of the Tortoniansediments overlying a low-relief substratum. Duringthe Late Tortonian an important stage of uplift took

place in the Sierra Nevada. It was then that theNevado-Filabride core of the range was stronglyeroded, giving rise to the thick deposits of the BlockFormation, which contain large-sized blocks re-worked from the Nevado-Filabride substratum. Thisinterpretation agrees with the age of the uplift of the

Ž .Sierra Nevada reported by Johnson et al. 1997 fromŽ .fission-track analysis 9–8 Ma .

The Block Formation unconformably overlies theŽ .previous Tortonian sediments Fig. 6 , but locally it

also rest directly on the Alpujarride basement. In theoutcrop located at 1830 m, the Block Formation liesunconformably over the Tortonian calcarenites,which conserve some 10 m thickness. In the GranadaBasin and adjacent zones during the deposition ofthe Block Formation, a regression took place produc-ing the change from marine to continental sedimenta-

Ž .tion Dabrio and Ruiz-Bustos, 1979 . This indicatesthat the uplift, although very important in the SierraNevada, also affected a wider area, although not so

Ž .strongly. The Messinian 6.5 to 5.3 Ma sediments inthe Granada Basin are generally fine-grained andmainly composed by marls and lacustrine carbonates,indicating a period of tectonic quiescence.

During the Early Pleistocene, significant newcoarse detritic inputs coming from the Sierra Nevadawere deposited in the basins surrounding the sierra.These detritic events are especially represented bythe Alhambra Formation in the Granada Basin andby the deposits to the SW of the Sierra Nevada, inthe Padul sector. These deposits can be related to anew stage of important uplift, which took place in

Ž .the Pliocene Estevez and Sanz de Galdeano, 1983 .´From this renewed uplift, the Sierra Nevada progres-sively widened, incorporating former marginal sec-tors of the surrounding basins.

A third relevant event of creation and reorganisa-Žtion of the relief took place during the Early –Mid-

.dle? Pleistocene. Low areas in the borders of theSierra Nevada were raised and incorporated to themarginal zones of the range, undergoing subsequenterosion, recorded by large-scale alluvial fan deposits.This event is recorded in the western border of theSierra Nevada, where, from the Tortonian to thePliocene, only sediments almost exclusively made upof reworked Nevado-Filabride materials occur. Afterthis last event, this area began to supply very abun-dant coarse-grained sediments but now reworked


from Alpujarride materials. These materials wereinherited from the new outcrops of Alpujarride com-plex, situated in the western fringe of the SierraNevada, that suddenly were exposed to the erosion.This is the case of the La Zubia fan, which uncon-formably overlies the basement, the Neogene and,

Ž .partially, the Quaternary deposits Fig. 6 . At thatmoment, the products of the erosion of the Nevado-Filabride complex were mainly drained to the S, inthe Niguelas-Durcal area.¨

The La Zubia alluvial fan was in turn inactive andisolated from the drainage network by a later impor-tant incision of the rivers. The age of the La Zubiaalluvial fan is not known, but in any case, it isyounger than the Alhambra Formation, because theNE part of the La Zubia alluvial fan overlies thatformation. Fluvial incision promoted an early fanabandonment. On both of its margins, the Monachiland Dilar rivers have been deeply incised, producing,in the case of the Dilar river, the development of acanyon some 550-m deep, gouged out probably fromthe Middle?–Late Pleistocene. Spectacular canyonsand gorges reflect the uplift of the Sierra Nevada on

Ž .its W and SW borders Fig. 7 . This process ofincision continues at the present time.

In summary, the present high relief of the SierraNevada, developed mainly over a period of about 8Ma, was not a continuous process, but rather wascontrolled by pulses of tectonic uplift separated byperiods of relative quiescence.

Congruently with this uplift, there are significantvalues of vertical displacement presented by thefaults on the western border of the Sierra Nevada.The Durcal–Niguelas fault has a throw of over 800¨m, with similar and somewhat lower values obtainedfor other faults of this border. To its interior, throwsof several hundred metres are also observed.

Without doubt, the fundamental gravitational col-lapse took place in the contact between the Nevado-Filabride and Alpujarride complexes, the main de-tachment surface, but the Nevado-Filabride complexis also affected. This complex shows very well-de-veloped sets of NNW–SSE open joints and lesserNNE–SSW joints, parallel to the faults describedabove. It also presents faults, some with more than ahundred metres of throw and several of which proba-bly affect it in depth. The very fact that this sector isthe western limit of the Nevado-Filabride complex

and that, towards the south, the lower Alpujarrideunits disappear, seems to imply the existence of a

Ž .fault or faults deeply affecting the basement.

8. Conclusions

The present relief of the western sector of SierraNevada has been created since the Tortonian. Thisimplies an uplift process of over 3500 m in about 8million years, causing important detachments andgravitational collapse in the Alpujarride units, pro-ducing a great thinning of their series. The generaldisposition of these movements is fan-like, adaptingitself to the shape of the border of the Sierra Nevada.

The significant faults on this border have con-tributed to the uplift of the Sierra Nevada. Thissector coincides with the western limit of theNevado-Filabride complex and, in its southward pro-longation, with the western boundary of the lowerAlpujarride units. This fact seems to indicate the

Ž .existence of a fault or faults deeply cutting thebasement. All these deformations are inscribed withina setting of approximately N–S compression andnearly perpendicular extension.

The rates of uplift and erosion are high, especiallywith respect to the Quaternary, with an incision of550 m from the Middle?–Late Pleistocene. Thisdeepening of the fluvial net is a very clear feature ofthe relief in this sector.

Acknowledgements

This article was financed by projects PB97-1267-C03-01 and PB94-0050 of the DGICYT and of the

Žgroups RNM-0217 and RNM 0163 Junta de An-.dalucıa . Careful critical reviews by two anonymous´

referees greatly improved the article. We are in-debted to Christine Laurin for revising the Englishversion of the text.

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