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Comment on the paper “Late exhumation stages of the Alpujarride Complex (western Betic Cordilleras, Spain): new thermochronological and structural data on Los Reales and Ojen nappes” by Marc Sosson, Anne-Claire Morillon, Jacques Bourgois, Gilbert Féraud, Gérard Poupeau, Pierre Saint-Marc
Tectonophysics 331 (2001) 413±417
Discussion
www.elsevier.com/locate/tecto
Comment on the paper ªLate exhumation stages of the Alpujarride Complex (western Betic Cordilleras, Spain): new thermochronological and structural data on Los Reales and Ojen nappesº by Marc Sosson, Anne-Claire Morillon, Jacques Bourgois, Gilbert FeÂraud, GeÂrard Poupeau, Pierre Saint-Marc C. Sanz de Galdeano a,*, B. Andreo b, A.-C. LoÂpez-Garrido a a
Instituto Andaluz de Ciencias de la Terra, Facultad de Ciencias, Universidad de Granada (CISC), 18071 Granada, Spain b Departamento de GeologõÂa, Facultad de Ciencias, 29071 MaÂlaga, Spain Received 10 November 1999; accepted 1 November 2000
We would like to make several comments on this paper, not about the thermochronological data, but on the structural ones, particularly on the strike-slip fault referred to by the authors as Cartama-Istan Fault, which is used to support their ®nal model to explain the tectonic evolution of the region. In our opinion, the trend of this fault and the left-lateral separation that they attribute to it, according S-C microstructures and shear bands, are not correct. TubõÂa (1988) described a major dextral strike-slip fault from IstaÂn to Monda, called the Albornoque Fault (Fig. 1), which, in the area of IstaÂn, separates the Sierra Blanca marbles from the schists and gneisses, all of these belonging to the Alpujarride complex. Farther to the northeast, this fault separates these marbles from the rocks of the Malaguide complex. Later, Sanz de Galdeano and LoÂpez Garrido (1991), Andreo and Sanz de Galdeano (1994) and Sanz de Galdeano and Andreo (1995), extended this * Corresponding author. Fax: 134-9-58-243384. E-mail addresses: [email protected] (C. Sanz de Galdeano), [email protected] (B. Andreo), [email protected] (A.-C. LoÂpezGarrido).
fault along the northern border of Sierras Blanca and Mijas (Fig. 1) and not to the northern border of Sierra de CaÂrtama as indicated by Sosson et al. (1998), not crossing, but bordering, the Malaga Basin. We have reviewed the area and made many measurements of microstructures associated with this large fault (Figs. 1 and 2). These measurements have been specially made near Monda (on the road from CoõÂn to OjeÂn), more westwards, in the forest track situated just at the north of Sierra Blanca up to IstaÂn. Similarly, the areas N of the Sierra de Mijas, Sierra Chica, Sierra Grande (the last two situated to the NE of CoõÂn) and CaÂrtama have been reviewed. Figs. 1 and 2 show the sites of measurements, located by GPS (precision of 50±100 m, Table 1). In these measurements we used the striae, the ®bres of calcite, the associated S-C structures and the displacement of bed surfaces or foliations. The results expresed in the diagrams of Fig. 2 and Table 1 are clear: the N(060)070-100 microfaults, parallel to the Albornoque Fault, are consistently dextral. At the same sites there are another two sets of conjugated faults, generally much less abundant: microfaults with NE±SW to N±S direction, which are sinistral,
0040-1951/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0040-195 1(00)00283-3
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Fig. 1. (A) Location of the study area. (B) Simpli®ed geologic map of the area surrounding the Albornoque Fault. The numbers 15±20 correspond to sites of measurements indicated in Table 1. In the circles, the average direction of the most abundant set of microfaults is indicated by a thick line, the second by a thin line and the third by a broken line. In every case the numbers correspond to the average direction obtained and the number of measurements are signaled in brackets. The position of Fig. 2 is marked.
and microfaults of NW±SE direction and dextral movements. Therefore, a dextral strike-slip displacement should be ascribed to the Albornoque Fault. Moreover, a normal component is necessary to explain the position of the Malaguide complex in contact with the marbles of Sierra Blanca and the thickness of the Neogene sedimentary ®lling the Malaga basin, which in some parts can reach 1000 m, according to geophysical data. This fault, near Monda, affects the VinÄuela Formation of early Burdigalian age (GonzaÂlezDonoso et al., 1982) and probably moved during the late Burdigalian and the middle Miocene. The NE± SW and NW±SE conjugated microfaults were formed
possibly from the Tortonian, as happened in other parts of the Betic Cordillera, when an approximately N±S compression affected it (Ott d'Estevou and Montenat, 1985; Sanz de Galdeano, 1990). The dextral displacement of the Albornoque fault is equally displayed by other larger geologic features. The ®eld data and the aerial photography show the existence of large drag structures in the N border of Sierra Blanca, 3±6 km W of Monda, pointed out by the surfaces of foliation of the marbles (Sanz de Galdeano and Andreo, 1995) as can be seen schematically in Fig. 2. The continuity of the Albornoque Fault from CoõÂn to CaÂrtama does not seem justi®ed. In the N of Sierra
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415
Fig. 2. Points of measurements of microfaults obtained along the Albornoque Fault, corresponding to sites 1±14 of Table 1. The key of the circles is similar to that of Fig. 1. In Sierra Blanca, to the WSW of Monda, the dotted lines indicate the surfaces of foliation, dragged by the dextral displacement of the Albornoque Fault and affected by smaller dextral strike-slip faults.
Blanca, this fault continues to the E more than 2 km south of CoõÂn (Fig. 1). From the SE of CoõÂn, the possible prolongation of this fault towards the N of the Sierra de CaÂrtama seems clearly forced by Sosson et al. (1998) and therefore it is necessary to change its strike and cross the Pliocene basin without forming the slightest relief. On the contrary, its prolongation along the N border of Sierra de Mijas (Fig. 1), certainly partially interrupted to the W of AlhaurõÂn El Grande, does not cut the Pliocene basin, gives strong relief and needs no major in¯ection in its strike. This long fault, going from the N of Sierra de Mijas to IstaÂn is cut locally by younger and smaller faults of NNE±SSW and NNW±SSE directions. In any case, we have reviewed the Sierra de CaÂrtama and its possible continuity to the W, in the small sierras, Grande and Chica, situated to the NE of CoõÂn (Fig. 1). There, the results of the microstructures are similar but poorer than those obtained in the Albornoque Fault. The N of Sierra de CaÂrtama and these two small sierras are affected by E±W to ENE±
WSW faults, situated several kilometres to the N of the Albornoque Fault, and are also dextral. Other aspects of the paper being commented on could be mentioned; for instance, the lithologic series of Sierra Blanca (OjeÂn nappe) can be seen in much more detail in Sanz de Galdeano and Andreo (1995). The lithologic series cited in Sosson et al. (1998) of the OjeÂn nappe is not accurate, although this lack of precision is also evident in other papers. Thus, the marbles are over the garnet micaschists and do not interlay this type of micaschist. Also, in the marbles, it is possible to distinguish clearly several formations, which cartography enables us to determine the internal structure of the Sierras Blanca and Mijas. Consequences of the Albornoque fault being dextral The model used by Sosson et al. (1998) to explain the evolution of the exhumation is not correct as long
416
C. Sanz de Galdeano et al. / Tectonophysics 331 (2001) 413±417
Table 1 Sites of measurements of microfaults and associated structures, located by UTM coordinates (in brackets). Their positions are marked in Figs. 1 and 2. In every site the average direction of the three sets of microfaults is displayed and the number of measurements is signaled in brackets. Different sets of microfaults: (A) microfaults approximately parallel to the Albornoque Fault (generally ranging from N60 to E±W and with a dextral character); (B) microfaults ranging generally from N±S to NE±SW and with a sinistral character; (C) microfaults generally NW±SE, with a dextral character, and conjugates with (B). Most of the microfaults are vertical or nearly vertical (In the road from CoõÂn to OjeÂn, S of Monda). In marbles. Site 1. (336.87E±4055.32N). (A) N78 (10). (B) N08 (4). (C) 120 (1). Site 2. (336.50E±4055.22N). (A) N74 (6). (B) N33 (3). Site 3. (334.95E±4054.49N). (A) N84 (16). (B) N29 (15). (C) 150 (1). In the forest track to IstaÂn, along the northern border of Sierra Blanca). In the Malaguide rocks, in serpentinites and in gneisses, schists and quarzites of the Alpujarride Complex. Site 4. (333.74E±4054.78N). (A) N72 (18). Site 5. (333.62E±4054.70N). (A) N64(2). (B) N23 (3). Site 6. (332.95E±4054.51N). (A) N83 (7). Site 7. (332.69E±4054.20N). (A) N70 (3). Site 8. (332.30E±4054.13N). (A) N57 (20). Site 9. (331.26E±4053.53N). (A) N69 (4). (C) N160 (1). Site 10. (330.57E±4053.37N). (A) N67 (4). (B) N40 (1). Site 11. (329.96E±4052.83N). (A) N58 (8). (B) N35 (2). Site 12. (327.56E±4052.16N). (A) N70 (11). Site 13. (326.39E±4050.76N). (A) N50 (1). (B) N14 (6). Site 14. (326.28E±4050.62N). (A) N54 (7). (B) N60 (2). North of the Sierra de Mijas. In marbles within quarries. Site 15. (364.89E±4058.15N). (A) N94 (16). Site 16. (359.99E±4057.39N). (A) N94 (15). (B) N22 (2). (C) N149 (5). Site 17. (355.33E±4057.11N). (A) N84 (7). (B) 25 (4). North of Sierra Chica (NE of CoõÂn) in the Malaguide Complex and serpentinites. Site 18. (345.27E±4060.21 N). (A) N78 (4). (B) N25 (2). South of Sierra Gorda (NE of CoõÂn) in peridotites and serpentinites. Site 19. (346.75E±4060.07N). (A) N75 (1). (B) N33 (6). (C) N152 (8). North of Sierra de CaÂrtama in marbles and pelites. Site 20. (354.37E±4064.02N). (A) N74 (5).
as it closely involves the Albornoque fault (de IstaÂnCaÂrtama) with a sinistral relative movement (Fig. 13 of Sosson et al., 1998). Considering it is sinistral, they interpret the upper Alpujarride units (of OjeÂn and Los Reales) and the Malaguide complex to have moved extensionally southwestwards, with the movement taking place on the Albornoque fault while the Blanca unit rose, accommodating the extension and exhumation that doubtless occurred in the Betic Cordillera. However, the Albornoque fault is dextral, and therefore cannot be used in Sosson et al.'s model. Signi®cance of the Albornoque fault. The Sierras Blanca and Mijas originally constituted a single unit, although at present their formal continuity is truncated. Fig. 1 shows that these sierras have practically an E±W trend, while the western border of the
Sierra Blanca is almost N±S. In this western sector, as opposed to the central eastern part of Sierras Blanca and Mijas, where the folds are E±W, the folds become preferentially N±S, at the same time resulting in clear interference structures (Sanz de Galdeano and Andreo, 1995). Both in this commentary and in the paper of Sosson et al. (1998), it is accepted that the Internal Betic±Rif Zone moved throughout the early Miocene and at least during part of the middle Miocene, with a major westerly component. In this context, we interpreted the most western part of the Blanca unit to have adapted to the form of the Gibraltar Arc, an arc that is generally admitted to be tectonic and not palaeogeographical in origin. This adaptation occurred both in the External Betic and Rif Zones, as well as in the
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417
move more than others), it was progressively and rapidly exhumed, although uplift was subordinate to the horizontal displacement. It is within this framework that we interpret the occurrence of the rapid exhumation mentioned by Sosson et al. (1998). Subsequent movements, such as those of the normal fault of IstaÂn, have contributed, as indicated by Sosson et al. (1998), to the uplift and ®nal exhumation of the Internal Betic±Rif Zone.
References
Fig. 3. Main trends of the structures in the arc of Gibraltar area. The Blanca-Mijas units stand out.
Internal Zone (in this case common to Betic and Rif Mountains) (Fig. 3). In particular, in the Betic Cordillera, the units of the western front of the Internal Zone are clearly adapted to the form of the arc as happen in the unit of Los Reales (Fig. 3) and, as we indicated, also in the western part of the Blanca unit. In this interpretation, the Albornoque dextral fault facilitated the westward movement of one segment of the Internal Betic±Rif Zone, which occurred with other various segments of the Internal Zone (Sanz de Galdeano, 1996). In this context, as the Internal Zone moved westwards (and within it, some segments
Andreo, B., Sanz de Galdeano, C., 1994. Stratigraphy and structure of the Sierra de Mijas (Alpujarride Complex, Betic Cordillera). Ann. Tectonicae 8 (1), 23±35. GonzaÂlez-Donoso, J.M., Linares, D., Molina, E., Serrano, F., Vera, J.A., 1982. Sobre la edad de la FormacioÂn de La VinÄuela (Cordilleras BeÂticas, provincia de MaÂlaga). Bol. R. Soc. Esp. Hist. Nat. (Geol.) 80, 255±275. Ott d'Estevou, P., Montenat, C., 1985. Evolution structurale de la zone beÂtique orientale (Espagne) du Tortonien a l'HoloceÁne. C. R. Acad. Sci. Paris 300 SeÂrie 2(8), 363±368. Sanz de Galdeano, C., 1990. Geologic evolution of the Betic Cordilleras in the Western Mediterranean, Miocene to the present. Tectonophysics 172, 107±119. Sanz de Galdeano, C., 1996. The E±W segments of the contact between the External and Internal Zones of the Betic and Rif Cordilleras and the E±W corridors of the Internal Zone (a combined explanation). Estud. Geol. 52, 123±136. Sanz de Galdeano, C., Andreo, B., 1995. Structure of Sierra Blanca (Alpujarride Complex, west of the Betic Cordillera). Estud. Geol. 51, 43±55. Sanz de Galdeano, C., LoÂpez Garrido, A.C., 1991. Tectonic evolution of the Malaga basin (Betic Cordillera). Regional implications. Geodinam. Acta 5, 173±186. Sosson, M., Morillon, A.C., Bourgois, J., FeÂraud, G., Poupeau, G., Saint-Marc, P., 1998. Late exhumation stages of the Alpujarride Complex (western Betic Cordilleras, Spain): new thermochronological and structural data on Los Reales and Ojen nappes. Tectonophysics 285, 253±273. TubõÂa, J.M., 1988. Estructura de los AlpujaÂrrides occidentales: cinemaÂtica y condiciones de emplazamiento de las peridotitas de Ronda. Parte IV: Deformaciones de las peridotitas de Sierra Alpujata. Bol. Geol. Min. 99 (5), 71±103.
Discussion
www.elsevier.com/locate/tecto
Comment on the paper ªLate exhumation stages of the Alpujarride Complex (western Betic Cordilleras, Spain): new thermochronological and structural data on Los Reales and Ojen nappesº by Marc Sosson, Anne-Claire Morillon, Jacques Bourgois, Gilbert FeÂraud, GeÂrard Poupeau, Pierre Saint-Marc C. Sanz de Galdeano a,*, B. Andreo b, A.-C. LoÂpez-Garrido a a
Instituto Andaluz de Ciencias de la Terra, Facultad de Ciencias, Universidad de Granada (CISC), 18071 Granada, Spain b Departamento de GeologõÂa, Facultad de Ciencias, 29071 MaÂlaga, Spain Received 10 November 1999; accepted 1 November 2000
We would like to make several comments on this paper, not about the thermochronological data, but on the structural ones, particularly on the strike-slip fault referred to by the authors as Cartama-Istan Fault, which is used to support their ®nal model to explain the tectonic evolution of the region. In our opinion, the trend of this fault and the left-lateral separation that they attribute to it, according S-C microstructures and shear bands, are not correct. TubõÂa (1988) described a major dextral strike-slip fault from IstaÂn to Monda, called the Albornoque Fault (Fig. 1), which, in the area of IstaÂn, separates the Sierra Blanca marbles from the schists and gneisses, all of these belonging to the Alpujarride complex. Farther to the northeast, this fault separates these marbles from the rocks of the Malaguide complex. Later, Sanz de Galdeano and LoÂpez Garrido (1991), Andreo and Sanz de Galdeano (1994) and Sanz de Galdeano and Andreo (1995), extended this * Corresponding author. Fax: 134-9-58-243384. E-mail addresses: [email protected] (C. Sanz de Galdeano), [email protected] (B. Andreo), [email protected] (A.-C. LoÂpezGarrido).
fault along the northern border of Sierras Blanca and Mijas (Fig. 1) and not to the northern border of Sierra de CaÂrtama as indicated by Sosson et al. (1998), not crossing, but bordering, the Malaga Basin. We have reviewed the area and made many measurements of microstructures associated with this large fault (Figs. 1 and 2). These measurements have been specially made near Monda (on the road from CoõÂn to OjeÂn), more westwards, in the forest track situated just at the north of Sierra Blanca up to IstaÂn. Similarly, the areas N of the Sierra de Mijas, Sierra Chica, Sierra Grande (the last two situated to the NE of CoõÂn) and CaÂrtama have been reviewed. Figs. 1 and 2 show the sites of measurements, located by GPS (precision of 50±100 m, Table 1). In these measurements we used the striae, the ®bres of calcite, the associated S-C structures and the displacement of bed surfaces or foliations. The results expresed in the diagrams of Fig. 2 and Table 1 are clear: the N(060)070-100 microfaults, parallel to the Albornoque Fault, are consistently dextral. At the same sites there are another two sets of conjugated faults, generally much less abundant: microfaults with NE±SW to N±S direction, which are sinistral,
0040-1951/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0040-195 1(00)00283-3
414
C. Sanz de Galdeano et al. / Tectonophysics 331 (2001) 413±417
Fig. 1. (A) Location of the study area. (B) Simpli®ed geologic map of the area surrounding the Albornoque Fault. The numbers 15±20 correspond to sites of measurements indicated in Table 1. In the circles, the average direction of the most abundant set of microfaults is indicated by a thick line, the second by a thin line and the third by a broken line. In every case the numbers correspond to the average direction obtained and the number of measurements are signaled in brackets. The position of Fig. 2 is marked.
and microfaults of NW±SE direction and dextral movements. Therefore, a dextral strike-slip displacement should be ascribed to the Albornoque Fault. Moreover, a normal component is necessary to explain the position of the Malaguide complex in contact with the marbles of Sierra Blanca and the thickness of the Neogene sedimentary ®lling the Malaga basin, which in some parts can reach 1000 m, according to geophysical data. This fault, near Monda, affects the VinÄuela Formation of early Burdigalian age (GonzaÂlezDonoso et al., 1982) and probably moved during the late Burdigalian and the middle Miocene. The NE± SW and NW±SE conjugated microfaults were formed
possibly from the Tortonian, as happened in other parts of the Betic Cordillera, when an approximately N±S compression affected it (Ott d'Estevou and Montenat, 1985; Sanz de Galdeano, 1990). The dextral displacement of the Albornoque fault is equally displayed by other larger geologic features. The ®eld data and the aerial photography show the existence of large drag structures in the N border of Sierra Blanca, 3±6 km W of Monda, pointed out by the surfaces of foliation of the marbles (Sanz de Galdeano and Andreo, 1995) as can be seen schematically in Fig. 2. The continuity of the Albornoque Fault from CoõÂn to CaÂrtama does not seem justi®ed. In the N of Sierra
C. Sanz de Galdeano et al. / Tectonophysics 331 (2001) 413±417
415
Fig. 2. Points of measurements of microfaults obtained along the Albornoque Fault, corresponding to sites 1±14 of Table 1. The key of the circles is similar to that of Fig. 1. In Sierra Blanca, to the WSW of Monda, the dotted lines indicate the surfaces of foliation, dragged by the dextral displacement of the Albornoque Fault and affected by smaller dextral strike-slip faults.
Blanca, this fault continues to the E more than 2 km south of CoõÂn (Fig. 1). From the SE of CoõÂn, the possible prolongation of this fault towards the N of the Sierra de CaÂrtama seems clearly forced by Sosson et al. (1998) and therefore it is necessary to change its strike and cross the Pliocene basin without forming the slightest relief. On the contrary, its prolongation along the N border of Sierra de Mijas (Fig. 1), certainly partially interrupted to the W of AlhaurõÂn El Grande, does not cut the Pliocene basin, gives strong relief and needs no major in¯ection in its strike. This long fault, going from the N of Sierra de Mijas to IstaÂn is cut locally by younger and smaller faults of NNE±SSW and NNW±SSE directions. In any case, we have reviewed the Sierra de CaÂrtama and its possible continuity to the W, in the small sierras, Grande and Chica, situated to the NE of CoõÂn (Fig. 1). There, the results of the microstructures are similar but poorer than those obtained in the Albornoque Fault. The N of Sierra de CaÂrtama and these two small sierras are affected by E±W to ENE±
WSW faults, situated several kilometres to the N of the Albornoque Fault, and are also dextral. Other aspects of the paper being commented on could be mentioned; for instance, the lithologic series of Sierra Blanca (OjeÂn nappe) can be seen in much more detail in Sanz de Galdeano and Andreo (1995). The lithologic series cited in Sosson et al. (1998) of the OjeÂn nappe is not accurate, although this lack of precision is also evident in other papers. Thus, the marbles are over the garnet micaschists and do not interlay this type of micaschist. Also, in the marbles, it is possible to distinguish clearly several formations, which cartography enables us to determine the internal structure of the Sierras Blanca and Mijas. Consequences of the Albornoque fault being dextral The model used by Sosson et al. (1998) to explain the evolution of the exhumation is not correct as long
416
C. Sanz de Galdeano et al. / Tectonophysics 331 (2001) 413±417
Table 1 Sites of measurements of microfaults and associated structures, located by UTM coordinates (in brackets). Their positions are marked in Figs. 1 and 2. In every site the average direction of the three sets of microfaults is displayed and the number of measurements is signaled in brackets. Different sets of microfaults: (A) microfaults approximately parallel to the Albornoque Fault (generally ranging from N60 to E±W and with a dextral character); (B) microfaults ranging generally from N±S to NE±SW and with a sinistral character; (C) microfaults generally NW±SE, with a dextral character, and conjugates with (B). Most of the microfaults are vertical or nearly vertical (In the road from CoõÂn to OjeÂn, S of Monda). In marbles. Site 1. (336.87E±4055.32N). (A) N78 (10). (B) N08 (4). (C) 120 (1). Site 2. (336.50E±4055.22N). (A) N74 (6). (B) N33 (3). Site 3. (334.95E±4054.49N). (A) N84 (16). (B) N29 (15). (C) 150 (1). In the forest track to IstaÂn, along the northern border of Sierra Blanca). In the Malaguide rocks, in serpentinites and in gneisses, schists and quarzites of the Alpujarride Complex. Site 4. (333.74E±4054.78N). (A) N72 (18). Site 5. (333.62E±4054.70N). (A) N64(2). (B) N23 (3). Site 6. (332.95E±4054.51N). (A) N83 (7). Site 7. (332.69E±4054.20N). (A) N70 (3). Site 8. (332.30E±4054.13N). (A) N57 (20). Site 9. (331.26E±4053.53N). (A) N69 (4). (C) N160 (1). Site 10. (330.57E±4053.37N). (A) N67 (4). (B) N40 (1). Site 11. (329.96E±4052.83N). (A) N58 (8). (B) N35 (2). Site 12. (327.56E±4052.16N). (A) N70 (11). Site 13. (326.39E±4050.76N). (A) N50 (1). (B) N14 (6). Site 14. (326.28E±4050.62N). (A) N54 (7). (B) N60 (2). North of the Sierra de Mijas. In marbles within quarries. Site 15. (364.89E±4058.15N). (A) N94 (16). Site 16. (359.99E±4057.39N). (A) N94 (15). (B) N22 (2). (C) N149 (5). Site 17. (355.33E±4057.11N). (A) N84 (7). (B) 25 (4). North of Sierra Chica (NE of CoõÂn) in the Malaguide Complex and serpentinites. Site 18. (345.27E±4060.21 N). (A) N78 (4). (B) N25 (2). South of Sierra Gorda (NE of CoõÂn) in peridotites and serpentinites. Site 19. (346.75E±4060.07N). (A) N75 (1). (B) N33 (6). (C) N152 (8). North of Sierra de CaÂrtama in marbles and pelites. Site 20. (354.37E±4064.02N). (A) N74 (5).
as it closely involves the Albornoque fault (de IstaÂnCaÂrtama) with a sinistral relative movement (Fig. 13 of Sosson et al., 1998). Considering it is sinistral, they interpret the upper Alpujarride units (of OjeÂn and Los Reales) and the Malaguide complex to have moved extensionally southwestwards, with the movement taking place on the Albornoque fault while the Blanca unit rose, accommodating the extension and exhumation that doubtless occurred in the Betic Cordillera. However, the Albornoque fault is dextral, and therefore cannot be used in Sosson et al.'s model. Signi®cance of the Albornoque fault. The Sierras Blanca and Mijas originally constituted a single unit, although at present their formal continuity is truncated. Fig. 1 shows that these sierras have practically an E±W trend, while the western border of the
Sierra Blanca is almost N±S. In this western sector, as opposed to the central eastern part of Sierras Blanca and Mijas, where the folds are E±W, the folds become preferentially N±S, at the same time resulting in clear interference structures (Sanz de Galdeano and Andreo, 1995). Both in this commentary and in the paper of Sosson et al. (1998), it is accepted that the Internal Betic±Rif Zone moved throughout the early Miocene and at least during part of the middle Miocene, with a major westerly component. In this context, we interpreted the most western part of the Blanca unit to have adapted to the form of the Gibraltar Arc, an arc that is generally admitted to be tectonic and not palaeogeographical in origin. This adaptation occurred both in the External Betic and Rif Zones, as well as in the
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417
move more than others), it was progressively and rapidly exhumed, although uplift was subordinate to the horizontal displacement. It is within this framework that we interpret the occurrence of the rapid exhumation mentioned by Sosson et al. (1998). Subsequent movements, such as those of the normal fault of IstaÂn, have contributed, as indicated by Sosson et al. (1998), to the uplift and ®nal exhumation of the Internal Betic±Rif Zone.
References
Fig. 3. Main trends of the structures in the arc of Gibraltar area. The Blanca-Mijas units stand out.
Internal Zone (in this case common to Betic and Rif Mountains) (Fig. 3). In particular, in the Betic Cordillera, the units of the western front of the Internal Zone are clearly adapted to the form of the arc as happen in the unit of Los Reales (Fig. 3) and, as we indicated, also in the western part of the Blanca unit. In this interpretation, the Albornoque dextral fault facilitated the westward movement of one segment of the Internal Betic±Rif Zone, which occurred with other various segments of the Internal Zone (Sanz de Galdeano, 1996). In this context, as the Internal Zone moved westwards (and within it, some segments
Andreo, B., Sanz de Galdeano, C., 1994. Stratigraphy and structure of the Sierra de Mijas (Alpujarride Complex, Betic Cordillera). Ann. Tectonicae 8 (1), 23±35. GonzaÂlez-Donoso, J.M., Linares, D., Molina, E., Serrano, F., Vera, J.A., 1982. Sobre la edad de la FormacioÂn de La VinÄuela (Cordilleras BeÂticas, provincia de MaÂlaga). Bol. R. Soc. Esp. Hist. Nat. (Geol.) 80, 255±275. Ott d'Estevou, P., Montenat, C., 1985. Evolution structurale de la zone beÂtique orientale (Espagne) du Tortonien a l'HoloceÁne. C. R. Acad. Sci. Paris 300 SeÂrie 2(8), 363±368. Sanz de Galdeano, C., 1990. Geologic evolution of the Betic Cordilleras in the Western Mediterranean, Miocene to the present. Tectonophysics 172, 107±119. Sanz de Galdeano, C., 1996. The E±W segments of the contact between the External and Internal Zones of the Betic and Rif Cordilleras and the E±W corridors of the Internal Zone (a combined explanation). Estud. Geol. 52, 123±136. Sanz de Galdeano, C., Andreo, B., 1995. Structure of Sierra Blanca (Alpujarride Complex, west of the Betic Cordillera). Estud. Geol. 51, 43±55. Sanz de Galdeano, C., LoÂpez Garrido, A.C., 1991. Tectonic evolution of the Malaga basin (Betic Cordillera). Regional implications. Geodinam. Acta 5, 173±186. Sosson, M., Morillon, A.C., Bourgois, J., FeÂraud, G., Poupeau, G., Saint-Marc, P., 1998. Late exhumation stages of the Alpujarride Complex (western Betic Cordilleras, Spain): new thermochronological and structural data on Los Reales and Ojen nappes. Tectonophysics 285, 253±273. TubõÂa, J.M., 1988. Estructura de los AlpujaÂrrides occidentales: cinemaÂtica y condiciones de emplazamiento de las peridotitas de Ronda. Parte IV: Deformaciones de las peridotitas de Sierra Alpujata. Bol. Geol. Min. 99 (5), 71±103.