Porrinas threshing-floor | Geositios de Extremadura

LOCATION AND ACCESS

To reach the geosite, take a forest track that leaves the EX-118 to the right in the direction of Bohonal de Ibor, at kilometre 37; this corresponds to the Casitas de Papel y del Castañar de Ibor geological route. The Geosite is 10.5 km from the start of the route, after following a small path of 125 m that goes off to the right of the main path. This last stretch must be covered on foot, as a fence prevents access by car.

State of access/difficulty: The path is a dirt forest track which in some sections is impracticable if you are not on all-terrain vehicles. The path to be followed on foot presents no difficulties.

ATTRACTIONS OF THE VISIT

At this point, known as Era de Porrinas, there are also goatherds’ houses, which are now abandoned. They are built with fine slabs of the silurian slate that can be found in the surrounding area, which also make up Geosite 49 (Casitas de Papel) and are arranged in an orderly fashion in the form of dry stone to build the walls. Also visible is the circular paving in the vicinity of the structure, which would have been part of an ancient threshing floor.

As it is located very close to Geosite No. 47, its landscape features are similar. There is an abundance of a wide variety of plant species, including junipers and ash trees, alders, laurel, honeysuckle and riparian flora accompanying the Endrinal stream.

Relevant biotic elements: Medium-sized horseshoe bat, Egyptian vulture and Bonelli’s eagle.

GEOLOGICAL INTERPRETATION

Read Geological Interpretation

This point is located in the core of the Guadarranque-Gualija syncline, at the southwestern end of the metamorphic contact caused by the magmatic intrusion that gave rise to the Berrocal de Peraleda. This intrusion was produced by the ascent of a granitic magma through pre-existing fractures in the earth’s crust, until it became emplaced in a zone of greater permeability, forming the batholithic body itself as it cooled. During its ascent, the magma came into contact with the pre-existing rocks, in this case silicic shales, which, due to the effect of the magmatic heat, underwent a series of transformations in their texture and mineralogical composition, becoming slates. It is a phenomenon known as contact metamorphism, or thermal metamorphism, as it occurs due to the high temperatures to which the rocks were subjected. The transformations are produced by recrystallisation, with a new regrouping and orientation of the minerals in the shales which, generating new minerals, give rise to different metamorphic rocks depending on the degree of pressure and temperature received, which will be more intense as one moves towards the contact with the magmatic intrusion. This zone is called the “contact aureole” or “metamorphic aureole”.