Betics
The Betic Cordillera is a mountain range in southern and southeastern Spain, oriented in an ENE direction. It stretches from the Gulf of Cádiz to the Cabo de la Nao.
The Betic Cordillera was formed as a result of a complex interaction of the African Plate with Iberia. It consists of four parts, the internal Betics along the coast, the external Betics inland, the flysch units in the far south of Spain (and Gibraltar), and the foreland basin: the Guadalquivir River Basin. Formation happened with 250 km of north south convergence from mid-Oligocene to late Miocene. From 50 km West North West convergence.
The Betics are part of the Gibraltar Arc, which also includes the Rif in Morocco.
During Triassic and Jurassic times the Betic and Maghrebian margins were opposite each other.
The Internal Betics or Alboran Crustal Domain are found along the coast. They are metamorphosed basement rocks from prior to the Miocene. Three thrusts make up these mountains (first Nevado–Filábride was buried 50 to 70 km deep, then Alpujárride, and lastly Maláguide). The crust was substantially thickened and the lower thrust was high pressure metamorphosed. Within the Internal Betics there are many depressions that have created basins that have filled with sediments. They are called the Betic Neogene Basins, and some are forming even now.
The Maláguide thrust sheet contains rocks from Silurian to Oligocene. Although the Silurian rocks were deformed in the Variscan Orogeny, the rocks in this sheet have only low grade metamorphism. It can be found north and east of Málaga and in a strip along the border between the internal and external Betics. The rocks in the Maláguide thrust sheet include phyllite, metagreywacke, limestone, metaconglomerate. The Devonian and Early Carboniferous is represented by gray slates and conglomerate, with smaller amounts of limestone, chert, and radiolarite. There are some Permian to Triassic red beds, starting with conglomerate and thinning to sandstone and lutite.
The Alpujárride Thrust Sheet spreads from western Málaga province to Cartagena in the east. This layer has been more metamorphosed than the Maláguide thrust sheet. It was buried from 35 to 50 km deep. At its base is mica schist, with some gneiss and migmatite formed from sediments older than the Permian. Above this is a bluish grey schist from the Permain, and the next layer is carbonate from the Middle to Late Triassic. Above this is a black mica schist, and the top layers are a brown coloured metapelite and a quartzite.
The Triassic Mesozoic to Miocene deposits form the External Betics. Subbetic zone with deeper water deposits is in the southeast and the Prebetic zone to the northwest contains shallow water deposits. The Campo de Gibraltar Unit is a prism accreted from terrigenous deposits formed in the Oligocene.
The Fortuna Basin makes up the Eastern Betics. It is from Tortonian to Pliocene (younger than 11.6 Ma). The basin floor subsided rapidly at first. It started filling with marine sediments as it was connected with the Mediterranean Sea. Later it became isolated and evaporites started to appear. These were then covered with continental sediments by late Tortonian 7.2 Ma. The basin became isolated as the edges were tectonically raised. During the Messinian to lower Pliocene 7.2–3.6 Ma the basin floor was lowered another 1 km and continental sediments filled it. During the Pliocene the basin was compressed, sheared and uplifted.
Ronda Peridotites outcrop in the western Internal Betics in the Alpujárride thrust sheet. These have been partly serpentonized. The variety of peridotite is lherzolite. These were intruded at a pressure of 1 gigapascal (GPa). Beneath the Ronda Peridotites is an eclogite formed at a pressure of 1.5 GPa. Two massifs, Sierra Bermeja and Sierra Alpujata have been rotated by 40° to the west since their solidification, as has the western External Betics.
The Nevado–Filábride Thrust Sheet was buried 50 to 70 km deep. It contains rocks originally from the Paleozoic to the Cretaceous. It has undergone high pressure low temperature metamorphism. It consists of three units. The Ragua Unit consists of albite and graphite containing mica schist, and quartzite. The Calar Alto Unit has choritoid and graphite containing mica schist, from the Paleozoic, light coloured Permo-Triassic schist, and marble from the Triassic, which have been metamorphosed to upper greenschist level at up to 450 °C. The Bédar-Macael Unit was metamorphosed to the amphibolite level, and contains marble, serpentinite, and tourmaline gneiss, as well as the more common schist. This unit was heated to 550 °C.
At the west end of the Betics lies the Guadalquivir Basin. It unconformably overlies the South Portugal Zone, Ossa Morena Zone and Central Iberian Zone. It contains Neogene to Quaternary aged material.
The Betics were compressed about 300 km in the Tertiary.
In Late Miocene a sill (land bridge) formed in the Gibraltar arc, disconnecting the Mediterranean from the Atlantic Ocean several times. This caused the evaporation of the Mediterranean Sea.
The Rock of Gibraltar is a monolithic limestone promontory. The rock was created during the Jurassic period some 200 million years ago and uplifted during the Betic Orogeny.
Read more about this topic: Geology Of The Iberian Peninsula