Patterns and Average Rates of Late Neogene–Recent Uplift of the Betic Cordillera, SE Spain

Geomorphology 50 (2003) 3–26 www.elsevier.com/locate/geomorph Patterns and average rates of late Neogene–Recent uplift of the Betic Cordillera, SE Spain Juan C. Braga a,*, Jose´ M. Martıń a, Cecilio Quesada b aDepartamento de Estratigrafıá y Paleontologıá, Facultad de Ciencias, Universidad de Granada, Campus de Fuentenueva s.n. 18002 Granada, Spain bIGME/Direccioń de Geologıá, Rıós Rosas 23, 28003 Madrid, Spain Received 1 September 2000; received in revised form 1 May 2001; accepted 15 July 2002 Abstract The facies distribution in the sedimentary units infilling a series of Neogene basins has been used to reconstruct the relief generation and uplift across the Internal Zone of the Betic Cordillera in southern Spain. Uplift amounts and average rates can be estimated using the current elevation of the outcrops of well-dated deposits indicative of ancient sea-level positions. Coral reefs and coastal conglomerates record the initial development of emergent Betic relief during the Langhian. Continental and marginal marine deposits indicate the existence of a large island centred on the present Sierra Nevada–Sierra de los Filabres chain by the end of the Middle Miocene. The precursor of the Sierra Nevada–Sierra de los Filabres chain, originally part of this large island, remained emerged whilst the surrounding areas were re-invaded by the sea during the early Tortonian. At the end of the Tortonian the inland basins (Granada and Guadix basins) became continental, while the Sierras de la Contraviesa, Sierra de Ga´dor and Sierra Alhamilla emerged, separating the Alborań Basin from the Alpujarra, Tabernas and Sorbas basins, which became narrow passages of the Mediterranean Sea. In contrast, the Sierra Cabrera emerged during the late Messinian, suggesting a progressive uplift from west to east of the sierras south of the Sierra Nevada–Sierra de los Filabres chain. During the Pliocene, only the low areas closest to the present-day coast remained as marine basins and progressively emerged throughout this stage. The highest average uplift rate recorded is 280 m/Ma for the Sierra de Ga´dor, although the average uplift rates of upper-Neogene coastal marine rocks since depositon have maximum values of approximately 200 m/Ma. Most of the uplift of the Betic mountains took place before the early Pliocene. The recorded uplift of Neogene rocks was highest at the margins of western Sierra Nevada, where peaks higher than 3000 m occur. The average rates of uplift were lower to the east of this major relief. The main sierras and depressions in the present-day landscape correspond respectively to the emergent land, in which uplift was concentrated, and to the marine basins that existed before the final emergence of the region. The altitude of the sierras reflects the time at which they became emergent, the highest mountains being the first to rise above sea level. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Uplift; Late Neogene; Palaeogeography; Betic Cordillera; SE Spain 1. Introduction * Corresponding author. Fax: +34-958-248528. E-mail addresses: [email protected] (J.C. Braga), [email protected] This is a study of the long-term landscape develop- (J.M. Martıń), [email protected] (C. Quesada). ment of the Internal Zone of the Betic Cordillera in 0169-555X/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII: S0169-555X(02)00205-2 4 J.C. Braga et al. / Geomorphology 50 (2003) 3–26 southern Spain (Fig. 1) as recorded by the sediments conditions prevailing in the modern landscape (Har- which have infilled the Neogene basins that formed vey, 2001). and evolved as the Betic mountains were emerging Within this paper, we describe the palaeogeo- and rising. The modern topographic configuration of graphic evolution of the area during the late Miocene southern Spain consists of a series of mountain and Pliocene as deduced from the spatial distribution ranges, with peaks higher than 3000 m in the Sierra of coastal marine deposits from successive time slices. Nevada, separated by depressions. The late-Neogene We also quantify the amounts and average rates of uplift history and sedimentary evolution of the region uplift since their deposition for rocks formed in largely pre-determined the present-day landscape, coastal environments at the basin margins. since the major extant ranges (sierras) and depressions Previous attempts to quantify relief generation in are the direct counterparts of the earlier emergent the Betic mountains are either localised to a specific basement highs and the intervening marine basins area (e.g. Weijermars et al., 1985) or focus only on the respectively. The general emergence of the region Plio/Quaternary evolution of the region (Mather, resulted in a change from marine to continental 1991; Viseras, 1991; Stokes, 1997; Garcia, 2001). deposition in the basins and, during the Quaternary, Several other papers have addressed the timing and continued uplift caused a switch to the net erosional amount of the exhumation of the metamorphic com- Fig. 1. Geological schematic map of southeastern Spain. Unless specified, the basins are named after the main town in them. J.C. Braga et al. / Geomorphology 50 (2003) 3–26 5 plexes in the Internal Zone of the Betic Cordillera (i.e. Permian basement (Lonergan, 1993; Martıń-Martıń, Zeck et al., 1992; Johnson et al., 1997; Lonergan and 1996). Johnson, 1998; Platt and Whitehouse, 1999). These The upper Nevado–Fila´bride tectonic unit (Mulha- papers focus mainly on the tectonometamorphic evo- ceń Nappe, Puga, 1976) and the Alpuja´rride complex lution of the basement rocks following their exhuma- were affected by high-pressure metamorphism due to tion during the Early and Middle Miocene. In crustal thickening as a result of the convergence of the contrast, we concentrate on the growth of the Betic African and Eurasian plates. The radiometric dates mountains after the emplacement of the Betic meta- constraining the high-pressure metamorphism in the morphic complexes to shallow crustal levels. Nevado–Fila´bride Complex indicate that convergence The study area is limited to the central-eastern began at about 51 Ma (Monie´ et al., 1991), although portion of the Betics, roughly spanning the provinces earlier dates have also been suggested (De Jong, of AlmerıáandGranada(Fig. 1),inwhichthe 1991). A sharp decompression in the metamorphic stratigraphy, facies distribution and age of the deposits P–T path of the Nevado–Fila´bride and Alpuja´rride in the Neogene basins are well constrained. The late complexes (Vissers, 1981; Go´mez-Pugnaire and Fer- Neogene uplift history of the Cabo de Gata volcanic nańdez-Soler, 1987; Bakker et al., 1989; Garcıá-Casco province, along the major Carboneras strike-slip fault and Torres-Roldań, 1996) suggests rock exhumation system, is treated separately in another paper (Martıń due to crustal-scale extension during the Early and et al., 2003, although some references to Cabo de Gata Middle Miocene (Monie´ et al., 1991; Garcıá-Duenãs et and the External Zone are made below. al., 1992; Watts et al., 1993; Comas et al., 1999; Platt and Whitehouse, 1999). Thinning of the previously thickened crust took place (Platt and Vissers, 1989) as 2. Regional setting a result of the extension. The Mala´guide complex did not undergo Alpine metamorphism and, consequently, 2.1. Basement geology was probably never subducted (De Jong, 1991). The present contact with the underlying Alpuja´rride Com- The Betic Cordillera in southern Spain is the plex is marked by a thick mylonitic zone cut by normal westernmost segment of the European Alpine belt. faults (Aldaya et al., 1991). This cordillera has traditionally been subdivided into an External Zone and an Internal Zone (Fig. 1). The 2.2. Neogene basins External Zone represents the Mesozoic to Middle Miocene southern continental margin of the Iberian The Betic Neogene basins developed on both the Massif, which was divided by rifting into different Internal and the External Zones and underwent defor- domains (Garcıá-Hernańdez et al., 1980; Vera 1988). mation and were uplifted as they filled with sediments The Prebetic constitutes the external domain where (Sanz de Galdeano and Vera, 1992). Consequently, the continental and shallow-marine sedimentation pre- configuration, limits and sedimentary dynamics of vailed from the Triassic to the Middle Miocene, while each basin changed considerably over time, reflecting the Subbetic, to the south, became a pelagic basin both the regional and local tectonic evolution. A during the Early Jurassic. major basin, the Guadalquivir Basin, developed at The Internal Zone consists of three stacked com- the cordillera front and was open to the Atlantic plexes that, in ascending order, are the Nevado– Ocean. The intermontane basins located on the Exter- Fila´bride, Alpuja´rride and Mala´guide (Fig. 1). The nal Zones are either continental (Prebetic basins) or Nevado–Fila´bride Complex comprises Palaeozoic or marginal embayments of the Guadalquivir Basin and older (Go´mez-Pugnaire et al., 2000) metamorphic as such related to the Atlantic Ocean. The rest of the rocks. The Alpuja´rride tectonic units include a series intermontane basins of the cordillera were connected of Palaeozoic–Mesozoic metasediments (Delgado et to the Mediterranean Sea. Two main types of Medi- al., 1981; Martıń and Braga, 1987; Tubıá et al., 1992). terranean-linked basins can be distinguished. (a) Inner The Mala´guide complex consists of a non-metamor- basins (the most distant from the present-day Medi- phic Mesozoic to Cenozoic cover overlying a pre- terranean Sea) occur mainly at the contact between the 6 J.C. Braga et al. / Geomorphology 50 (2003) 3–26 External and Internal Zones. Although both the Gua- during the rest of the Miocene and, in some cases even dix-Baza and Granada basins belong to this type, we during the Pliocene, except for a short time-interval in have chosen the Granada Basin as the most represen- the Messinian during the so-called ‘‘Messinian Salin- tative example (Fig.

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