Cordillera Penibética

The Penibética mountain range is the southernmost of the Betic mountain ranges, and runs along the southern coast of Spain, from the province of Cádiz to that of Alicante. A little further north, behind the so-called intermediate units (a set of depressed areas, called holes, among which are the Hoya de Baza and Guadix), are the Subbética and Prebética Mountain Ranges.

The main mountain ranges that make it up, from west to east, are Sierra de Grazalema, Sierra de las Nieves, Sierra de Tejeda, Sierra de Almijara, Sierra Nevada, Sierra de la Contraviesa, Sierra de Gádor, Sierra de Baza, Sierra of the Filabres and Sierra de Las Estancias.

From a structural point of view, it is made up of a very complex stacking of landslide sheets that overlap one another, distinguishing three: the Alpujárride, the Nevado-Filábride and the Maláguide sheets. The Alpujarride mantle and the Filabride-Nevado mantle outcrop in Sierra Nevada, constituting a tectonic window where highly metamorphosed materials outcrop, predominantly Paleozoic micaschists.

Situation

It constitutes the fundamental axis of the Betic mountain ranges. It is located to the south of the Subbético, we could say that it is separated by the Intrabético Furrow from the Subbético. It extends parallel to the coast from the Strait of Gibraltar to Almería, to continue through Murcia. It is an elongated set of SE-NE although in the easternmost part it adopts a W-E layout. It is formed by two different alignments parallel to each other and to the coast and above all these alignments appear up to the Guadalfeo river, from this and towards Gibraltar we can speak of an alignment although on some occasions they appear double. Thus, the Alpujarra syncline is occupied by two valleys: the Guadalfeo and the Andarax, which separate the Sierra Nevada from the Lújar and Gádor mountains. The chain as a whole appears quite close to the sea, but at its two ends the main alignments are separated a little further from the coast:

• In the Granada sector the alignment appears very close to the sea; from Nerja to Adra the coast is rocky and cliffs appear where the mountains sink their roots directly into the sea. The small existence of plains corresponds to deltas of the rivers that flow into this area like the Guadalfeo; this means a lack of space for agriculture, tourism and the construction of communication channels.
• In the stretch of Nerja to Gibraltar the mountains are located near the sea, but there are areas where they are further away as the valley of the Guadalhorce, forming wider plains.
• In the Almeria section we find wider plains such as the Campo de Dalías the Andarax valley or the Campo de Níjar.

Lithological and structural characteristics

The internal Betic zone presents a series of lithological and structural characteristics that define it. Something that differentiates it from the others is the presence of materials from the Paleozoic base forming part of these mountains. These materials have been affected by a pre-alpine metamorphism to which is added a metamorphism coinciding with the orographic movement itself. This means that it has constituted an important reserve of different types of minerals (iron, lead, copper, as well as marble, which are linked to metamorphic processes.

Another characteristic of the Penibética mountain range is the appearance in certain parts of endogenous rocks that emerged with the force of folding —Serranía de Ronda— and there are also materials of volcanic origin —Cabo de Gata—.

We must also highlight the almost absolute lack of Post-Triassic sedimentary materials that only appear in the so-called Maláguide complex; Logically, post-orogenic materials are abundant and have been produced from the erosion of mountain cores. There are Miocene sedimentary materials in the form of a halo, Pliocene, Plioquaternary - transition between the Tertiary and the Quaternary - and also at the foot of the mountains there are very late Quaternary materials deposited around the river deltas.

The last feature that defines it is the fact that all the lithological complexity is accentuated by a great complexity of the tectonic structures: forming large mantles of displacement several tens of kilometers, subjected to strong erosive processes due to the great slopes, giving rise to tectonic windows as is the case of the central core of Sierra Nevada.

Topography

The Mulhacén seen from Las Alpujarras.

Topographically, the Penibética mountain range has a great continuity of high altitudes compared to those of the outer one -Mulhacén, Veleta-. It presents a greater continuity and is only interrupted by the appearance of two passes that are the Fiñana corridor and the Lecrín valley, as well as the Guadalhorce valley. These steps usually have a double origin:

• Tectonic, responds to flaws that have occurred as a result of the readjustments with the formation of the bottom folds.
• Isostatic adjustment, produced by the lifting of the blocks that lose weight and the sinking of those who gain weight.

Morphology

In general, the Penibetic morphology is quite contrasted; in front of very wild reliefs produced by this deep embedding of the rivers when overcoming a great unevenness: like the Calar area -of limestone origin- that we find at an altitude of about 2000 m or the Trevenque. This contrasts with the hilly and smooth areas that usually coincide with the highest areas of the thrust sheets above 3000 m altitude, which is due to three factors:

• The structure in corrimiento blankets, which is composed of horizontal layers, so by destroying a stratum, the next one will continue to maintain horizontality.
• The existence of soft materials as slates.
• The glacial modeling that has helped soften the forms with the creation of wide valleys.

Large geological units

Within the Penibética mountain range, geologists have distinguished three large structural units or complexes: the Nevado-filábride, Alpujárride and Maláguide complexes, all three made up of a landslide mantle, although there are authors who defend the idea that there is more than one landslide blanket for each complex.

Nevado-Filábride Complex

It owes its name to the area where this complex is best represented. It is made up of rocks that have undergone strong metamorphic processes that have led to the existence of noble construction materials such as streamers, marble, etc., there are also iron works. It is possible to distinguish a preparatory plinth -materials prior to the Permian and Triassic-, a Permotriassic and Triassic cover and a whole series of Postalpine materials of a sedimentary nature. It is made up of three large units:

Sierra Nevada Unit

It is made up of materials from the Upper Carboniferous - Permian of a schistous nature -schistous graphites, micaschists or slates-; metamorphic intercalations also appear, such as amphibolites or serpentines -volcanic rocks that have subsequently been subjected to metamorphic processes-.

Unity of the Sabine Women

It is the mixing zone (mischungzone). There is a section occupied by quartzites and amphibolites and another section made up of marbles, gneisses and serpentines, which correspond to materials from the Upper Paleozoic and the Trias.

Boiler Unit

Formed by materials from an intense metamorphic process -plutonites- corresponding to the Permotriassic age.

Surrounding the complex are some phyllites that have allowed the displacement of the mantles. After this an area of limestone appears. Therefore we have:

• Lastra: zone of the nucleus formed by micaesquistos.
• Launa: surrounding the lastra and formed by filitas.
• Calar: surrounding the launa and formed by limes.

Later, Tertiary and Quaternary sedimentary materials appear, such as the Alhambra Conglomerate.

Alpujárride Complex

It takes its name from the fact that it reaches its maximum presence in the Alpujarra area. It is formed by micaschists that belong to the lower Paleozoic and/or Precambrian. There are also phyllites and micaschists from the lower Paleozoic and a powerful formation of limestone and dolomites belonging to the Upper Middle Trias.

Within this Alpujárride complex, a series of units and mantles can be distinguished that may correspond to as many orogenic impulses and that are identified in different areas of the Alpujarra:

• Lujar mantle.
• Adra mantle.
• Manto de Múrtas.
• Alcazar's mantle.
• Castaras mantle.

The problem is whether they are successive mantles or whether they have become individualized.

Málaguide Complex

It is made up of Paleozoic materials that either have not undergone metamorphic processes or these have been very light and are formed by materials from the Lower Devonian (limestone) and also by conglomerates, sandstones and dolomites from the Permotrias -in the transition from primary to secondary-. Jurassic limestone, Cretaceous marl limestone, Eocene marl and limestone, and Oligocene marl and sandstone appear on top of these Palaeozoic materials.

As in the Alpujárride and Nevado-Filábride complex, in this complex there are also different layers of landslides; these appear better defined in the Alpujárride. The problem they pose is that of their chronology. The beginning of these mantles goes back to the Cretaceous, where the first impulses that formed the Alpine folding manifest themselves. These continued during the tertiary era where a final stage of large deformations and development of these mantle structures occurs. The most active period coincides with the Eocene and the Oligocene; but still in the Miocene and Pliocene, the last movements took place that have no longer produced mantles of landslides but rather large bottom folds with a large radius of curvature, as well as faults and fractures on the previous structures that have contributed to breaking the unity of the entire planet. whole and has been used by erosion to form the different river valleys that descend from the heart of the Penibética towards the Mediterranean Sea. (An example of this is the series of existing faults in the Lecrín Valley).

Finally, and this is an element that remains in the air, since 1966 geologists began to speak of a third unit, which is what is known as the Betic ridge (limestone chain) that until At that time some geologists had included it in the Subbético, for others it was part of the Alpujárride complex; but since 1966 some geologists have argued that it is an independent unit. It is a set of limestone flakes located on the northern edge of the Penibetic and therefore on the southern edge of the Subbético strict census -Subbético of geologists-. This structure in scales and its own stratigraphy is different from what we found in the Penibético and in the Subbético strict census. It is made up of limestone and dolomites from the lower lees -beginning of the Triassic-, marly limestone from the upper leas and middle Eocene, and finally detrital formations and conglomerates from the Eocene and Oligocene. (eg Sierra de Harana).