Geology of Andorra

Andorra is located in the axial zone of the central Pyrenees. This means that it has intensely folded and thrusted rocks formed when the Iberian peninsula was rotated onto the European continent.Rocks from Cambrian or Ordovician occur in the form of conglomerate, limestone, phyllite, quartzite and
slate. Diapirs of slate from the Silurian Period are found in the Llavirsi syncline near Bixesarn (south west).
Gneiss and schist are found in the cores of anticlines in the north east of the country. This gneiss contains
muscovite. The antiforms are connected with near horizontal shear zones, containing nappes of metamorphosed sediments. Younger overlying Paleozoic metamorphosed sediments found over most of Andorra have also been steeply folded.

In the south east of the country is an alkaline granite from a batholith called Mt-Louis-Andorra Batholith. It extends into Spain and covers an area of 600 km². Different rock composition zones occur with monzogranite found at the centre, quartz diorite at the edge and granodiorite in intermediate parts. The batholith has caused metamorphism on its western edge. The base of the batholith is exposed in the east of Andorra.

During the Quaternary various glacial erosional features were formed, including U shaped valleys, cirques, arêtes and roche moutonnées. One major cirque was the Cirque de Pessons in the east. Santa Coloma has a glacial terminal moraine.

References

*"Andorra" by P. M. Oliver and E. M. Moores in Eldridge M. Moores, Rhodes Whitmore Fairbridge: "Encyclopedia of European and Asian Regional Geology", 1997 Springer, p26 .
*"Berga" 24 Mapa Geologico 1:200.000, 1970, Instituto Geologico Y Minero de Espana.