Campo de Calatrava volcanic area
The volcanic area of Campo de Calatrava , together with the volcanic regions of the Garrotxa near Olot in the province of Girona and the Cabo de Gata in the province of Almería, is one of the three most important zones with young volcanism on the Iberian Peninsula . It is located near the city of Ciudad Real in the autonomous region of Castile-La Mancha .
The volcanic activity took place between 1.75 and 8.7 million years ago in the Pliocene and Quaternary . This makes it a geologically very young volcanism. For this reason, the volcanic buildings have largely been preserved in their original form, and the deposits they created can still be observed today.
The volcanic region covers an area of more than 5,000 km² and includes over 300 different volcanic buildings. Some of the main towns that are in the volcanic area are Ciudad Real, Almagro , Daimiel and Bolaños de Calatrava . Puertollano is located near the southern limit of the volcanic area, with the volcanoes closest to Almadén being La Bienvenida and Cabezarados .
Morphological and genetic aspects
The morphology of the Campo de Calatrava region is due to the existence of a series of Pliocene-Quaternary depressions that represent trenches delimited by Paleozoic quartzite ridges . In the trenches, the relief is modified by the existence of volcanic buildings, which create a characteristic and striking surface shape. The degree of preservation of these terrain forms depends on various factors:
- Age of the eruption (the youngest volcanoes are best preserved)
- original shape of the volcano
- Volume of material ejected
- Type of material ejected
- Place of origin (depressions or quartz backs)
- Existence of mining areas on the volcanoes
All of these factors can make it difficult to identify the volcanic nature of the landform in question.
The eruption mechanisms that create the terrain can basically be assigned to two types: Strombolian and phreatomagmatic volcanism . Hawaiian-type volcanoes are absent, even if a number of Strombolian volcanoes have discharged not inconsiderable amounts of lava . It is also quite common in the region for phreatomagmatic and strombolian volcanism to follow each other in the same eruption center.
Strombolian volcanism
Strombolian volcanism produces small volcanic cones, which today have been eroded into rounded hills, depending on the degree of erosion, from a truncated conical to hemispherical shape. The diameters are between 100 and 2,000 m and the heights are 20 to 120 meters. Volcanic crater- type depressions can only rarely be identified. From these volcanoes, lava flows of various dimensions can emanate, which can reach a length of up to 7 kilometers. Examples of this type of volcano are the volcanoes La Yezosa near Almagro and the Cerro Gordo near Valenzuela de Calatrava .
Phreatomagmatic volcanism
Phreatomagmatic volcanism is the most common in the region and created the very characteristic volcanic type of maar . This volcanic shape is difficult to identify as such in the terrain. It reaches a diameter of up to 1.5 km, one of the most typical representatives of this type of volcano is the Hoya del Mortero near Poblete .
Petrography
The volcanic rocks ejected by the volcanoes of the volcanic area of Campo de Calatrava belong petrographically to the basalts in the broader sense. They can be distinguished both by their composition and by texture . The composition ranges from melilite, rich in olivine , to limburgite , olivine- nephelinite , basalt, basanite and olivine- leucitite . The texture gives rise to a distinction between three types: massive porphyry varieties, pyroclastic slag varieties and phreatomagmatic deposits.
Massive porphyry varieties
The massive porphyry varieties have the eponymous porphyry texture and are formed exclusively from olivine or from olivine with pyroxene in a microcrystalline to glassy matrix. This basic mass consists of augite , iron titanium oxides ( magnetite - ilmenite ) and olivine. In addition, plagioclase , foide , melilite and volcanic glass can occur in different proportions, which allows the fine petrographic subdivision mentioned above.
Rocks of these varieties are used as paving stones for road paving . They are also used as building blocks, as broken aggregates and especially as ballast for the Tren de Alta Velocidad high-speed train . One of the largest quarries in these rocks is that of Morrón de Villamayor .
Pyroclastic slag varieties
The pyroclastic slag varieties are rocks with numerous cavities, which can be composed of material of very different grain sizes . This variety includes rocks made of very fine and even powder-like individual components through agglomerations of large blocks to fragments of very different sizes ( lapilli ) with isolated volcanic bombs.
This rock is mined in various quarries in the region, its main use is the production of pozzolans . It was also widely used as a building block, for example in the Castillo of Calatrava la Nueva or in the Gothic chapel Virgen de Zuqueca .
Phreatomagmatic deposits
The phreatomagmatic deposits are usually well- layered tuffs , whereby planar layers can be distinguished from oblique layers . In addition, blocks of non-volcanic material, especially quartzite, are found in the tuffs. The tuffs are to be considered as lithic or lithic crystal tuffs , poor in volcanic rocks associated with the respective volcanic eruption, little solidified and of different grain sizes.
The tuffs are used exclusively as classified aggregate.
geochemistry
From a geochemical point of view, the rocks of the volcanic region are to be addressed as alkaline intraplate basalts, which come from magma chambers of the upper mantle . The magmas are primary, as shown by the low nickel content and the low ratio of MgO to MgO + FeO. Due to its geochemical characteristics, the rise of the magmas is attributed to crustal expansion and the existence of mantle hotspots.
Accompanying mineral deposits
A number of mineral deposits are associated with magmatism, which can be divided into two large groups:
From a mineralogical point of view, the minerals found in the ore deposits are complex oxides and hydroxides of manganese (especially cryptomelane and lithiophorite ). These minerals are earth-like, micro- to cryptocrystalline and therefore of little interest to mineral collectors. In some occurrences of such crusts have become rain water during transport Pisolith formed ores.
Mining the ores associated with volcanism is not worthwhile, as they are not found in minable quantities, but their composition makes them unique in the world.
Individual evidence
- ↑ Volcanic area of Campo de Calatrava in the Global Volcanism Program of the Smithsonian Institution (English)
- ↑ a b J. López Ruiz, JM Cebriá, M. Doblas, R. Oyarzun, M. Hoyos and C. Martín: Cenozoic intra-plate volcanism related to extensional tectonics at Calatrava, central Iberia. Journal of the Geological Society London, Vol. 150, No. 5, pp. 915-922, 1993. ( Abstract )
Coordinates: 38 ° 52 ′ N , 4 ° 1 ′ W