Deciphering tectonic- and erosion-driven exhumation of the Nevado–Filábride Complex (Betic Cordillera, Southern Spain) by low temperature thermochronology

Deciphering tectonic- and erosion-driven exhumation of theNevado–Filabride Complex (Betic Cordillera, Southern Spain) bylow temperature thermochronology

Mercedes Vazquez,1 Antonio Jabaloy,1 Luis Barbero2 and Finly M. Stuart3

1Departamento de Geodinamica, Facultad de Ciencias, Universidad de Granada, Fuentenueva, s ⁄n 18002 Granada, Spain; 2Departamento de

Ciencias de la Tierra, Facultad de Ciencias del Mar y Ambientales, Universidad de Cadiz, 11510 Puerto Real (Cadiz), Spain; 3Isotope

Geosciences Unit, Scottish Universities Environmental Research Centre, Scottish Enterprise Technology Park, East Kilbride G75 OQF, UK

Introduction

The Betic Cordillera in south-eastSpain forms the westernmost end ofthe Alpine mountain belt. It is formedby a stack of metamorphic complexes(the so-called Internal Zones orAlboran Domain), which were thrustonto unmetamorphosed flysch units.The latter are superimposed onunmetamorphosed sediments of theSouth Iberian palaeomargin (Balanyaand Garcıa-Duenas, 1987). The pile ofmetamorphic complexes in the Inter-nal Zones is formed from bottom totop by the Nevado–Filabride, theAlpujarride and the Malaguide com-plexes.The Sierra Nevada and Sierra de los

Filabres mountains in the centralBetic Cordillera are antiformal ridgesresulting from large-scale uprightfolding with E–W to NNE–SSW foldaxes (Fig. 1A). In both the ranges, theNevado–Filabride rocks crop out inthe footwall of the Mecina Fault, abrittle detachment fault which definesa core-complex like-structure roofedby the Alpujarride complex (Galindo-Zaldıvar et al., 1989; Jabaloy et al.,

1993; Martınez-Martınez et al., 1997).The Mecina Fault shows a top-to-the-WSW sense of movement (Garcıa-Duenas and Martınez-Martınez,1988; Galindo-Zaldıvar et al., 1989).The Nevado–Filabride rocks aregrouped into an upper unit with highpressure (HP) metamorphism and alower unit with lower pressure condi-tions, separated by the Filabres Fault,a brittle detachment with top-to-the-West sense of movement (Martınez-Martınez et al., 2002, 2004) (Fig. 1A).How and when the Sierra Nevada

and Sierra de Filabres were exhumedis still a matter of debate. ZirconU ⁄Pb SHRIMP and garnet Lu ⁄Hfdating suggest that exhumation andcooling of the Nevado–Filabride com-plex started immediately after the HPmetamorphic peak in the upper unitat 18–15 Ma (Lopez-Sanchez-Viz-caıno et al., 2001; Gomez-Pugnaireet al., 2004; Platt et al., 2006). Apatiteand zircon fission track (AFT andZFT) ages in most of the Nevado–Filabride rocks support rapid coolingfrom 300 to 100 �C at 12–8 Ma(Johnson et al., 1997), while AFTdata in the western Sierra Nevadainclude ages that are younger than5 Ma. Figure 1(B) shows an isoagecontour map of available AFT cool-ing ages (Johnson, 1997; Johnsonet al., 1997; Reinhardt et al., 2007;Clark and Dempster, 2009; this

work). Johnson et al. (1997) proposedthat cooling was linked to the top-to-the-WSW movement of the MecinaFault, starting at c. 12 Ma in the eastand ending at 9–8 Ma in the west(Fig. 1B). To explain young (c. 4 Ma)AFT ages and a negative age-eleva-tion correlation in the western SierraNevada (Fig. 2A), Johnson (1997)proposed the exhumation of a palaeo-apatite partial annealing zone (PAZ)that was folded and eroded in thePliocene. Reinhardt et al. (2007)obtained a similar age-elevationpattern (Fig. 2A) and, in contrast,explained it by fault-controlled exhu-mation that involved unroofing viaextensional detachments above theNevado–Filabride core and localisedrapid denudation of the upland. Clarkand Dempster (2009) presented addi-tional AFT ages from the westernSierra Nevada that failed to corrobo-rate the age-elevation correlation(Fig. 2A). These authors proposedthree denudation events at 9, 7 and4 Ma: the 9 Ma event was related tothe movement of the Mecina Fault,the 7 Ma event was related to theformation of a rolling-hinge anticlinerecognised by Martınez-Martınezet al. (2002, 2004), and the third eventwas linked to a rapid cooling event at4 Ma generated by rotation of thebasement block around an east–westaxis.

ABSTRACT

New apatite (U-Th) ⁄ He and fission-track data from the Nevado–Filabride complex in the Sierra Nevada of southern Spain areused to constrain the Neogene exhumation history. Apatite(U-Th) ⁄ He ages are close to fission-track ages in western SierraNevada indicating that rapid cooling occurred at 8–6 Ma,consistent with exhumation due to extension along the MecinaFault. The western Sierra de los Filabres cooled rapidly atc. 12 Ma, while the central Sierra de los Filabres experienced

less rapid cooling at 8 Ma. The age distribution in the Sierra delos Filabres can be explained by exhumation due to flexuraluplift to the south-west of the footwall of the Mecina Fault. Thelower cooling rates in the central Sierra de los Filabres suggestthat folding and erosion were the main exhumation processesduring the Late Tortonian.

Terra Nova, 23, 257–263, 2011

Correspondence: Dr Mercedes Vazquez

Vılchez, Geodynamic Department, Faculty

of Science, Fuentenueva s ⁄n 18071 Gra-

nada, Spain. Tel.: +34958243351; fax:

+34958248527; e-mail: [email protected]

� 2011 Blackwell Publishing Ltd 257

doi: 10.1111/j.1365-3121.2011.01007.x

(A)

(B)

Fig. 1 (A) Tectonic map of the Internal Zones of the central and eastern Betic Cordillera. The yellow hexagon (El Hoyazo) marksthe location where Cesare et al. (1997) and Acosta-Vigil et al. (2010) determined the geothermal gradient mentioned in the text. (B)Hand-drawn isocontours of AFT cooling ages for the Nevado–Filabride rocks based on the result of applying a kriging method onpublished (Johnson, 1997; Johnson et al., 1997; Reinhardt et al., 2007; Clark and Dempster, 2009) and our data. Only sampleswith 20 apatite grains and more measured and v2 > 5% were plotted. The colour map shows the cooling ages from brown (oldestages c. 15 Ma) to yellow (youngest ages c. 3 Ma). Left inset in B: tectonic map showing the main tectonic domains of the peri-Alboran orogenic system: (1) Neogene basins; (2) Betic External Zones (3) Riphean External Zones; (4) Flysch Trough unit; (5)Internal Zones.

Deciphering tectonic- and erosion-driven exhumation • M. Vazquez et al. Terra Nova, Vol 23, No. 4, 257–263

.............................................................................................................................................................

258 � 2011 Blackwell Publishing Ltd

We present herein first apatite(U-Th) ⁄He (AHe) and new AFT agesfrom the Nevado–Filabride Complexin the Sierra Nevada and Sierra deFilabres to determine: (i) the timing offinal exhumation, (ii) the linkagebetween regional extensional tectonicsand exhumation and (iii) a discrimina-tion between exhumation processescontrolled by tectonics and ⁄or erosion.

Sampling and analytical methods

We have collected 56 samples from theNevado–Filabride Complex alongthree N–S transects perpendicular tothe large-scale fold trend. Apatitesfrom most samples lack the qualitynecessary to obtain AHe ages. Eightsamples were selected for AHe agedeterminations: 7 orthogneisses (SN-1,

SN-2, SN-4, SN-28, SN-30, SN-40,SN-54) and 1 metapsammite (SN-45).All samples are located in the upperNevado–Filabride units. SN-1, SN-2,SN-4 and SN-30 are close to theMecina Fault, while SN-28, SN-40,SN-45 and SN-54 are at more than1 km distance from the fault(Table 1). Apatite was separated usingstandard procedures and individualcrystals were hand-picked under abinocular microscope at 218· magni-fication. Crystal dimensions weremeasured with a calibrated graticule.One to two grains were loaded intostandard Pt foil tubes and analysedusing procedures published previously(Foeken et al., 2006). The alpha-emis-sion correction (Ft) is based on emis-sion from all surfaces (Balestrieriet al., 2005) (see Table 1 for details).

The AFT ages of these samples(Table 2) have been determined byEDM method (Gleadow, 1981; Hur-ford and Green, 1982) using a zetavalue (LB, after Hurford and Green,1983) of 337.8 ± 5 for dosimeterCN-5. Cf irradiation (Donelick andMiller, 1991) was used to increase thenumber of measurable confined tracklengths. All fission track ages exceptone pass the v2 test (Galbraith andLaslett, 1993), indicating single agepopulations. Fission track data fromSN-28 (v2 < 1.0) is not consideredany further in this study. Samples SN-30 and SN-45 showed too many dis-locations for reliable track counting.For this reason we have used the AFTages of Johnson et al. (1997) instead;SP-921 (12.1 ± 2.4 Ma) was sampledwithin 2–3 m of SN-30, and SP-29(11.9 ± 1.4 Ma) was sampled within500 m of SN-45.Modelling of thermal histories

based on the AFT and AHe datawas performed using HeFTy software(Ehlers et al., 2005). Cooling historiesfrom the AFT data were determinedaccording to the Ketcham et al. (2007)annealing model using Dpar as kineticparameter and c-axis projection foretching conditions of 5.5 M HNO3.Quoted mean track lengths for mod-elling correspond to projected lengthsand are therefore different from thoselisted in Table 2.

Results

The AHe ages from multiple aliquotsgenerally replicate well, with theexception of sample SN-54. IndividualAHe ages are between 13.5 and5.0 Ma (Table 1). Mean AHe ages ofthe Sierra Nevada samples vary from8.8 to 6.2 Ma, while those from theSierra de Filabres vary from 12.9 to8.7 Ma. AFT ages in the easternSierra Nevada and the Sierra de losFilabres vary from 15.6 to 6.4 Ma.The western Sierra Nevada hasyielded younger AFT ages (8.7–6.4 Ma; Table 2). Mean track lengthsare long, often >15 lm, and shownarrow distributions and low disper-sion. Mean Dpar values are similar inall samples and vary from 1.45 to1.70 lm (Table 2).The AHe (9.7–5 Ma) and AFT ages

(8.7–6.4 Ma) of western Sierra Neva-da samples are essentially identical,indicating rapid exhumation in Late

Age (Ma)

0

400

800

1200

1600

2000

0 5 10 15 20

(B)

Ele

vatio

n (m

)E

leva

tion

(m)

Ele

vatio

n (m

)

Tem

pera

ture

(°C

)Te

mpe

ratu

re (°

C)

Tem

pera

ture

(°C

)

Age (Ma)

Age (Ma)

Age (Ma)

0

1000

2000

3000

4000

0 5 10 15 20

(A) (D)

Age (Ma)

0

500

1000

1500

2000

2500

0 5 10 15 20

(C)

(F)

2070

120170220270320370

(E)

2070

120170220270320370

50 10 15

50 10 15

Age (Ma)0 5 10 15

700

600

500

400

300

200

100

0

Fig. 2 (A–C): Apatite fission track and (U-Th) ⁄He ages of the Nevado–FilabrideComplex plotted vs. elevation: (A) fission track ages from the western Sierra Nevada,(B) fission track ages from the Sierra de los Filabres, and (C) (U-Th) ⁄He ages plottedvs. sampling elevation of the Nevado–Filabride rocks. For legend of different agesources, see Fig. 1B. (D) T–t diagram for sample SN-4 with data from Gomez-Pugnaire et al. (2004) added as dark blue square. (E) and (F): Representative coolinghistories of the Nevado–Filabride rocks. (E) Western Sierra Nevada mountains:samples SN-1, SN-2, SN-4 and SN-40, and (F) Sierra de los Filabres: SN-30 plottedas red stars (through line) and SN-45 plotted as blue stars (hatched line).

Terra Nova, Vol 23, No. 4, 257–263 M. Vazquez et al. • Deciphering tectonic- and erosion-driven exhumation

.............................................................................................................................................................


Miocene times. The new AFT agesshow no clear correlation with eleva-tion (Fig. 2A,B), while the AHe agesshow neither clear spatial variation norcorrelation with elevation (Fig. 2C).Thermal models of the westernmost

Sierra Nevada using data from SN-1and SN-2 apatite are characterised byrapid cooling at around 6–7 Ma and7.5–9.5 Ma, respectively, with a dis-tinct decrease of cooling rate at

�50 �C, followed by a second coolingepisode at around 3–4 Ma for sampleSN-1 and a less well-defined period inSN-2, that bring the samples to sur-face temperatures (Fig. 3). SN-40apatites appear to have cooled rapidlyto 40 �C at 11–9 Ma, followed bysubsequent slow cooling to surfacetemperatures. For sample SN-54 fromthe Sierra de los Filabres only accept-able fits to the FT data could be

modelled. Modelled cooling is charac-terised by a fast cooling episode at 17–13 Ma followed by subsequent slowcooling to surface temperatures.

Discussion

We have estimated the minimum cool-ing rates by assuming closure temper-atures (tc) of 120 �C for AFT ages and60 �C for AHe ages, including the 1r

Table 1 Apatite (U-Th) ⁄He data from Nevado–Filabride rocks, southern Spain.

Sample

Elevation

(m)

Distance to

Mecina

Fault (m)

X

(UTM)

Y

(UTM)

4He

(10)10 cc)

238U

(ng)

232Th

(ng)

Number

crystals

Equivalent

radius (lm)*

Uncorrected

He age (Ma)

Corrected

He age

(Ma)�Mean

ages (Ma)

Sierra Nevada

SN-1 1952 85 461828 4107492 21 0.037 0.078 2 40 3.4 5.0 ± 0.3 6.2 ± 0.4

11 0.016 0.020 2 43 4.3 6.2 ± 0.5

3.1 0.358 0.520 2 58 5.7 7.3 ± 0.3

SN-2 2001 230 462409 4106953 1.5 0.124 0.307 2 64 6.6 8.2 ± 0.5 7.9 ± 0.5

22 0.023 0.028 2 44 6.6 7.5 ± 0.5

SN-4 2187 420 462648 4107920 61 0.054 0.060 2 65 7.7 9.7 ± 0.6 8.8 ± 0.5

34 0.344 0.498 2 101 6.8 7.9 ± 0.4

SN-28 2478 >1500 464563 4093739 0.7 0.098 0.044 2 57 5.0 6.6 ± 0.3 6.8 ± 0.3

7.1 1.073 0.123 2 105 5.3 7.0 ± 0.2

SN-40 1051 1400 521503 4113436 2.3 0.223 0.277 1 57 7.1 8.2 ± 0.3 7.6 ± 0.4

2.4 0.315 0.322 2 65 6.0 7.0 ± 0.3

2.2 0.235 0.246 2 75 6.8 8.0 ± 0.4

97 0.107 0.177 2 85 5.7 7.2 ± 0.4

Sierra de los Filabres

SN-30 1452 30 504868 4127801 73 0.042 0.115 2 57 9.7 12.5 ± 0.8 12.9 ± 0.7

0.8 0.339 5.130 2 65 10.4 12.6 ± 0.8

1.9 0.108 0.199 2 65 9.9 13.1 ± 0.6

6.4 0.342 0.732 2 85 10.2 13.5 ± 0.5

SN-45 588 >1500 558653 4110042 19 0.019 0.012 2 94 7.2 8.5 ± 0.9 8.7 ± 0.8

20 0.200 0.015 2 70 7.2 8.8 ± 0.7

19 0.021 0.010 2 61 6.8 8.7 ± 0.8

SN-54 523 1500 587605 4119057 33 0.048 0.045 2 61 4.8 6.3 ± 0.4 15.2 ± 0.8

1.4 0.073 0.089 2 65 12.4 16.5 ± 0.8

1.2 0.046 0.064 2 50 17.2 22.7 ± 1.2

*The equivalent radius is the weighted mean of the ratio of spheres with the same surface to volume ratios as the analysed crystals.

�Alpha emission correction for broken grains assumes that broken faces represent zero-loss. Ft is increased by a factor equal to the ratio of the total grain surface area

of the assumed emitting faces. This typically increases Ft by <10%. No systematic relationship between the fraction of broken grains and corrected ages has been

observed indicating that the correction method is robust.

Table 2 Fission track data from Nevado-Filabride rocks, southern Spain.

Sample

Rock

type

No. of

grains

CN-5 track density

(· 106 tracks cm)2)

(tracks counted)

Spontaneous

track density


(tracks counted)

Induced track density


(tracks counted) P(v2)

Fission track

central age

(± 1r) (Ma)

Mean track

length (lm)

(No. of tracks)

SD

(lm)

Dpar

(lm)

SN-1 O 25 0.982 (2974) 0.055 (84) 1.421 (2178) 67.47 6.4 ± 0.7 15.27 (65) 0.79 1.30

SN-2 O 28 0.979 (2966) 0.080 (274) 1.517 (3216) 65.05 8.7 ± 0.8 15.46 (66) 0.83 1.47

SN-4 O 24 0.977 (2959) 0.079 (127) 1.584 (2536) 45.14 8.3 ± 0.8 14.74 (1)

SN-30 O 39 0.972 (2944) 0.047 (200) 1.181 (4994) 9.84 6.9 ± 0.8

SN-45 M 39 1.350 (9414) 1.045 (78) 0.213 (98) 67.00 11.9 ± 1.4

SN-40 O 32 0.969 (2937) 0.066 (188) 1.231 (3520) 33.01 8.7 ± 0.8 15.37 (77) 0.83 1.34

SN-54 O 30 0.976 (2929) 0.096 (242) 1.034 (2612) 8.00 15.6 ± 1.9 15.63 (52) 0.64 1.70

Ages determined by EDM method using a zeta value (LB) of 337.8 ± 5 for dosimeter CN-5 (see text for further explanation about methodology). Number of Dpar

measured per sample varies between 250 and 400. O, Orthogneiss; M, Metapsammite.


.............................................................................................................................................................


uncertainties of the individual ages.We have also used ZFT ages by John-son et al. (1997) (tc = 240 ± 25 �C;Brandon et al., 1998) and U-PbSHRIMP ages (tc = 660 ± 55 �C;Gomez-Pugnaire et al., 2004). Theminimum cooling rates were calculatedas themaximum difference between theAFT and the AHe ages for the samesample. Converting cooling rates todenudation rates requires an estima-tion of the geothermal gradient duringexhumation. We have used geothermalgradients between 38 and 47 �C km)1,deduced by studying crustal anatexis inxenoliths from c. 9-Ma-old volcanicrocks (Cesare et al., 1997; Acosta-Vigilet al., 2010) in the easternmost SierraAlhamilla (see Fig. 1A for location).

Cooling and exhumation history of theSierra Nevada

The whole T–t path estimated for thewestern Sierra Nevada indicates rapidcooling from 660 to 60 �C between

c. 16.5 and 8–6 Ma (Fig. 2D). SN-1,SN-2 and SN-4, from the topmostrocks of the Nevado–Filabride com-plex close to the Mecina Fault, andSN-40 from the eastern Sierra Nevadahave average AHe ages from 8.8 to6.2 Ma and AFT ages from 8.7 to6.4 Ma (Tables 1 and 2). These agesare consistent with rapid cooling at 8–6 Ma (Figs 2D,E and 3). The mini-mum cooling rate from 120 to 60 �C is21–38 �C Ma)1 (Fig. 2E). The corre-sponding minimum denudation ratesare 0.5–1.8 mm year)1, in accordancewith the rates of 1.2–1.4 mm year)1

determined by Johnson (1997) andReinhardt et al. (2007). Furthermore,these ages indicate that 2–3.5 km ofcrust have been removed during thelast 8–6 Ma. After the 8–6 Ma coolingevent, denudation rates slowed downto 0.1–0.2 mm year)1, which corre-sponds to cooling rates <10 �CMa)1 (Fig. 2E).The period of rapid exhumation at

8–6 Ma cannot be explained by high

erosion rates because Tortonian sedi-ments are preserved at high altitudesin the western and southern SierraNevada (Sanz de Galdeano andLopez-Garrido, 1999; Braga et al.,2003; Reinhardt et al., 2007). The fastcooling rates are likely the result oftectonic rather than erosional exhu-mation. Extensional movement alongthe Mecina normal fault with a top-to-the-west sense of movement islikely to be responsible for the fastexhumation in agreement with John-son et al. (1997), because the brittlefault cuts and thins the hangingwallAlpujarride rocks and exhumes theNevado–Filabride rocks in its foot-wall. The movement must be sub-sequent to the HP metamorphismwithin the Nevado–Filabride rocksdated at 16.5 ± 0.4 Ma in this area(Fig. 2D and 4B).The apparent eastward AHe age

increase indicated by samples SN-1(6.2 ± 0.4 Ma), SN-2 (7.9 ± 0.5 Ma)and SN-4 (8.8 ± 0.5 Ma) can be

2E

2E2E

2E

2E2E

AFT: Track Length Distribution

m)

20181614121086420

Freque

ncy

0.60

0.55

0.50

0.45

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.00


Length ( m)

20181614121086420

Freq

uenc

y

0.60

0.55

0.50

0.45

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.00

0

2E

2E

2E

2E

2E2E



Length ( m)

2018161412108642

Frequ

ency

0.70

0.65

0.60

0.55

0.50

0.45

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.00

0

40

80

120

160

200

Tem

pera

ture

(ºC

)

20 15 10 5 0Time (Ma)

SN-1

SN-2

40

0

120

140

180

Tem

pera

ture

(ºC

)

20 15 10 5 0Time (Ma)

Length (µm)Length (µm)

0

40

80

120

160

200

Tem

pera

ture

(ºC

)SN-40

20 15 10 5 0Time (Ma)

Length (µm)

SN-540

40

80

120

160

200

Tem

pera

ture

(ºC

)

0102030Time (Ma)

Length (µm)

ModelAge (Ma) Length Meas. Model Meas.GOF GOF

6.57 6.42 0.89 16.05 15.88 0.86Model

Age (Ma) LengthModel Meas.GOF GOF Meas.

8.68 8.71 0.97 15.95 16.01 0.85

ModelAge (Ma) Meas. GOF Model

Age (Ma) Meas. GOF

LengthModel Meas. GOF

LengthModel Meas. GOF

9.58 9.59 0.90 15.30 15.30 0.99 16.04 16.10 0.2116.11 15.95 0.90

80

Fig. 3 Thermal models for samples SN-1, SN-2, SN-40 and SN-54. Green and purple areas mark envelopes of statisticallyacceptable and good fit, respectively, and thick lines correspond to the best fit thermal histories. The GOF (goodness-of-fit) givesan indication about the fit between observed and predicted values (values close to 1 are best; a value >0.05 is consideredacceptable; a value >0.5 is considered good).


.............................................................................................................................................................


explained by tilting of the MecinaFault and its footwall after 8 Matowards a lower dip (Wernicke andAxen, 1988). An alternative explana-tion is that sample SN-1 is closer tothe fault surface and the circulation ofhot fluids along this surface may haveheated the neighbouring rocks(Fig. 4).The AFT ages from the highest

peaks of the westernmost SierraNevada (c. 4 Ma; Johnson et al.,1997; Clark and Dempster, 2009) areyounger than AFT and AHe agesfrom samples SN-1, SN-2 and SN-4(Fig. 2A). These young AFT agesindicate that the core of the westernSierra Nevada was exhumed signifi-cantly later than the outer sectors(Figs 1B and 2E). This was explainedby late formation of the open NNE-SSW to E–W folds during Pliocenetimes (Johnson, 1997). Reinhardtet al. (2007) found similarly youngAFT ages at lower altitudes closer tothe Mecina Fault, suggesting that thecomplete palaeo-PAZ, that was estab-lished between 8 and 4 Ma, and theoverlying rocks, are no longerpreserved in the western Sierra Neva-da. The Filabres Fault and currentlyactive faults located along the westernand southern Sierra Nevada mountainfronts (Perez-Pena et al., 2010; andreferences therein) have likely causedthe thinning of the apatite PAZ.Neither the orientation of the foliationnor the orientation of the few normalfaults that crop out within the Neva-do–Filabride rocks in the Sierra Ne-vada support a late-stage rotation ofbasement blocks around an east–west

axis as proposed by Clark and Demp-ster (2009).

Cooling and exhumation history of theSierra de los Filabres

Sample SN-30, from the western endof the Sierra de los Filabres, has amean AHe age of 12.9 Ma and anAFT age of 12.1 Ma, while SN-45 inthe central Sierra de los Filabres has amean AHe age of 8.7 Ma and an AFTage of 11.0 Ma. The minimum coolingrates from 120 to 60 �C of SN-30 andSN-45 are 38 and 15 �C Ma)1, respec-tively (Fig. 2F). These correspond tominimum denudation rates of 0.8–0.7and 0.4–0.3 mm year)1. Denudationrates after 12 and 8 Ma are similar forboth samples (0.1 mm year)1) sug-gesting that the tempo of tectonicactivity has waned and erosional pro-cesses have dominated exhumation ofthe region.The cooling rate of SN-30 (Fig. 2F)

and SN-54 (Fig. 3) are similar tothose of the Sierra Nevada, thoughthis event occurred significantly ear-lier (13–12 Ma). The data seem toindicate that exhumation of theNevado–Filabride rocks started inthe Sierra de los Filabres (Fig. 1B).The initiation at 13 Ma in the Sierrade los Filabres and unroofing of theSierra Nevada at 8–6 Ma indicate thatthe exhumation was diachronous. Wepropose that continuous top-to-the-west extensional movements along theMecina Fault were responsible forthe diachronous exhumation of theNevado–Filabride rocks within theupper crust.

Transport of the hangingwall of theMecina Fault towards the west-south-west produced the flexural uplift of thefootwall. This model explains the AFTage pattern in the Sierra de los Fila-bres (Fig. 1B) and the homogeneousAHe ages found in the upper Nevado–Filabride unit. The mean AHe age of8.7 Ma indicates that after 8 Ma, theexhumation mechanism changed tofolding and high angle normal faultingcausing reduced erosion.

Acknowledgements

The authors acknowledge financial supportby Junta de Andalucıa (Research GroupRNM-148 and RNM-160), the SpanishResearch Project (CSD2006-00041) fromthe CONSOLIDER-INGENIO 2010,CGL2009-10858 ⁄BTE, CGL2008-03249 ⁄BTE funded by the Spanish Ministry forScience and Innovation. We thank LuigiaDiNicola for her help in the He thermo-chronology laboratory and Jenny Estu-pinan for her assistance in fission-tracksample preparation and processing. More-over, we thank Tim Dempster, FedericoRossetti and M. Rahn for their review ofthe manuscript and Antonio Azor for hishelpful comments.

References

Acosta-Vigil, A., Buick, I., Hermann,R.G., Cesare, B., Rubatto, D., London,D. and Morgan, G.M., 2010. Mecha-nisms of crustal anatexis: a geochemicalstudy of partially melted metapeliticenclaves and host dacite, SE Spain.J. Petrol., 51, 785–821.

Balanya, J.C. and Garcıa-Duenas, V., 1987.Structural trends of the Alboran Domainon both sides of the straits of Gibraltar.CR Acad. Sci. Paris, 304, 929–933.

Balestrieri, M.L., Stuart, F.M., Persano,C., Abbate, E. and Bigazzi, G., 2005.Geomorphic development of the escarp-ment of the Eritrean margin, southernRed Sea from combined apatite fission-tracks and U-Th ⁄He thermochrono-metry. Earth Planet. Sci. Lett., 231,97–110.

Braga, J.C., Martın, J.M. and Quesada, C.,2003. Patterns and average rates of theNeogene–Recent uplift of the BeticCordillera, SE Spain. Geomorphology,50, 3–26.

Brandon, M.T., Roden-Tice, M.K. andGarver, J.I., 1998. Late Cenozoicexhumation of the Cascadia accretionarywedge in the Olympic Mountains,northwest Washington State. GSA Bull.,110, 985–1009.

Cesare, B., Salvioli-Mariani, E. andVenturelli, G., 1997. Crustal anatexis

(A) (B)

Fig. 4 Cross-section (A) and geological map (B) of the Collado de Sabinas area,western Sierra Nevada, showing the location of SN-1, SN-2, SN-4 and samples fromthe literature. For legend, see Fig. 1B.


.............................................................................................................................................................


and melt extraction during deformationin the restitic xenoliths at El Joyazo(SE Spain). Min. Mag., 61, 15–27.

Clark, S.J.P. and Dempster, T.J., 2009.The record of tectonic denudation in anemerging orogen: an apatite fission-track study of the Sierra Nevada,southern Spain. J. Geol. Soc. London,166, 87–100.

Donelick, R.A. and Miller, D.S., 1991.Enhanced tint fission-track densities inlow spontaneous track density apatitesusing 252Cf-derived fission fragmenttracks—a model and experimentalobservations. Nucl. Tracks Radiat.Meas., 18, 301–307.

Ehlers, T.A., Chaudhri, T., Kumar, S.,Fuller, C.W., Willett, S.D., Ketcham,R.A., Brandon, M.T., Belton, D.X.,Kohn, B.P., Gleadow, A.J.W., Dunai,T.J. and Fu, F.Q., 2005. Computationaltools for low temperature thermochro-nometer interpretation. Rev. Min.Geoch., 58, 589–622.

Foeken, J.P.T., Stuart, F.M., Dobson,K.J., Persano, C. and Vilbert, D., 2006.A diode laser system for heating mineralsfor (U-Th) ⁄He chronometry. Geochem.Geophys. Geosyst., 7, Q04015.

Galbraith, R.F. and Laslett, G.M., 1993.Statistical methods for fission track ages.Nucl. Tracks, 21, 459–470.

Galindo-Zaldıvar, J., Gonzalez-Lodeiro, F.and Jabaloy, A., 1989. Progressiveextensional shear structures in a detach-ment contact in the western SierraNevada (Betic Cordilleras, Spain).Geodin. Acta, 3, 73–85.

Garcıa-Duenas, V. and Martınez-Martı-nez, J.M., 1988. Sobre el adelgazamientoMioceno del Dominio Cortical deAlboran: El despegue extensional deFilabres. Geogaceta, 5, 53–55.

Gleadow, A.J.W., 1981. Fission trackdating methods: what are the real alter-natives? Nucl. Tracks Radiat. Meas.,5, 3–14.

Gomez-Pugnaire, M.T., Galindo-Zaldıvar,J., Rubatto, D., Gonzalez-Lodeiro, F.,Lopez-Sanchez-Vizcaıno, V. andJabaloy, A., 2004. A reinterpretation ofthe Nevado-Filabride and Alpujarridecomplex (Betic Cordillera): field,petrography and U-Pb ages fromorthogneisses western Sierra Nevada, SSpain). Schweiz. Mineral. Petrogr. Mitt.,84, 303–322.

Hurford, A.J. and Green, P.F., 1982. Ausers� guide to fission track dating. EarthPlanet. Sci. Lett., 59, 343–354.

Hurford, A.J. and Green, P.F., 1983. Thezeta age calibration of fission trackdating. Chem. Geol., 1, 285–317.

Jabaloy, A., Galindo-Zaldıvar, J. andGonzalez-Lodeiro, F., 1993. TheAlpujarride-Nevado-Filabride exten-sional shear zone, Betic Cordilleras, SESpain. J. Struct. Geol., 15, 555–569.

Johnson, C.J., 1997. Resolving denuda-tional histories in orogenic beltswith apatite fission-track thermochro-nology and structural data: an examplefrom southern Spain. Geology, 25,623–626.

Johnson, C.J., Harbury, N. and Hurford,A.J., 1997. The role of extension in theMiocene denudation of the Nevado-Filabride Complex, Betic Cordillera (SESpain). Tectonics, 16, 189–204.

Ketcham, R.A., Carter, A., Donelick,R.A., Barbarand, J. and Hurford, A.J.,2007. Improved modeling of fission-track annealing in apatite. Am. Min.,92, 799–810.

Lopez-Sanchez-Vizcaıno, V., Rubatto, D.,Gomez-Pugnaire, M.T., Tommsdorff, V.and Muntener, O., 2001. Middle Mio-cene high-pressure metamorphism andfast exhumation of the Nevado-FilabrideComplex, SE Spain. Terra Nova, 13,327–332.

Martınez-Martınez, J.M., Soto, J.I.and Balanya, J.C., 1997. Crustal

decoupling and intracrustal flow beneathdomal exhumed core complexes,Betics (SE Spain). Terra Nova, 9,223–227.

Martınez-Martınez, J.M., Soto, J.I. andBalanya, J.C., 2002. Orthogonal foldingof extensional detachments: structureand origin of Sierra Nevada elongateddome (Betics, SE Spain). Tectonics, 21,1–20.

Martınez-Martınez, J.M., Soto, J.I. andBalanya, J.C., 2004. Elongated domes inextended orogens: a mode of mountainuplift in the Betics (Southeast Spain). In:Gneiss Domes in Orogeny (D.L. Whitney,C. Teyssier and C.S. Siddoway, eds),pp. GSA Spec. Pap., Boulder, Colorado,243–266.

Perez-Pena, J.A., Azor, A., Azanon, J.M.and Keller, E.A., 2010. Active tectonicsin the Sierra Nevada (Betic Cordillera,SE Spain): insights from geomorphicindexes and drainage pattern analysis.Geomorphology, 119, 74–87.

Platt, J.P., Anczkiewicz, R., Soto, J.I.,Kelley, S.P. and Thirlwall, M., 2006.Early Miocene continental subduc-tion and rapid exhumation in thewestern Mediterranean. Geology, 34,981–984.

Reinhardt, L.J., Dempster, T.J., Shroder,J.F. and Persano, C., 2007. Tectonicdenudation and topographic develop-ment in the Spanish Sierra Nevada.Tectonics, 26, TC3001.

Sanz de Galdeano, C. and Lopez-Garrido,A.C., 1999. Nature and impact of theNeotectonic deformation in the westernSierra Nevada (Spain). Geomorphology,30, 259–272.

Wernicke, B. and Axen, G.J., 1988. On therole of isostasy in the evolution of nor-mal fault systems. Geology, 16, 848–851.

Received 16 June 2010; revised versionaccepted 3 May 2011


.............................................................................................................................................................


Documents

Deciphering tectonic- and erosion-driven exhumation of the Nevado–Filábride Complex (Betic Cordillera, Southern Spain) by low temperature thermochronology