Geological Evolution of the Iberian Peninsula
Precambrian Era
The Iberian Peninsula was located between the African (Gondwana) and European (Laurasia) continental plates, separated by the Tethys Sea. Orogenic movements during this era had minimal impact, primarily affecting the Galician-Leonese Massif, the western Asturian-Leonese Massif, and parts of the Toledo Mountains and Central System.
Paleozoic Era
The Hercynian orogeny, characterized by strong lateral pressures, began during the Carboniferous period. This resulted in the formation of mountain ranges aligned northwest-southeast (e.g., Galicia and the Guadalquivir Valley). Erosion during the Paleozoic created a peneplain, a flat surface of eroded rock. Intense magmatic activity marked the end of this cycle, with granitic outcrops in the western sector.
Mesozoic Era
A tectonically quiet period, the Mesozoic saw significant erosion of the Hercynian mountains. Vertical movements (subsidence and elevation) caused changes in sea levels. Deep ocean trenches, or geosynclines, formed in the areas of the Pyrenees and Betic Mountains, accumulating sedimentary and organic materials, including carbonate rocks.
Cenozoic Era (Tertiary)
The Alpine orogeny compressed and uplifted sediments in the Pyrenees and Betic Mountains, while the northeastern part of the Paleozoic massif subsided, forming the Ebro Basin. The Iberian Massif tilted towards the Atlantic, influencing river orientation. Folding, fracturing, and faulting of Paleozoic materials created the mountainous relief. The Galician-Leonese Massif is characterized by a fracture system susceptible to erosion. Collapsed areas formed the northern and southern sub-mesetas (plateaus).
Quaternary Era
Post-Alpine tectonic movements finalized the westward tilt of the Meseta, directing most rivers towards the Atlantic. Epirogenic movements caused fluctuations in sea levels, shaping coastlines and gulfs. This period also saw the final establishment of river systems.
Lithological Variety
Siliceous
Located in the oldest areas (Precambrian and Paleozoic), siliceous landscapes are formed by granite, gneiss, quartzite, and shale. Erosion shapes rounded forms. In colder areas, water freezing in cracks contributes to rock fragmentation. This type of landscape is common in western Iberia.
Calcareous
Primarily Mesozoic marine sedimentary formations, calcareous landscapes feature karst topography. Water dissolves calcium carbonate, creating features like crevasses, gorges, canyons, caves, chasms, and poljes.
Clay
Formed by sediments from the late Tertiary and Quaternary, clay landscapes are generally flat, horizontal, and easily eroded due to the softness of the rock. These are found in southeastern Iberia and the Ebro Valley.
Volcanic
Volcanic landscapes are primarily found in the Canary Islands, with active volcanoes from the Miocene to the present.
Differential Erosion
Erosion acts differently depending on the terrain type.
Principal Morphostructural Units
The Iberian Peninsula’s morphology is shaped by orogenic forces and subsequent erosion and tectonic activity.
Ancient Massifs
The most extensive massif is the Hercynian block forming the Meseta. The eastern edge of the Meseta experienced a collapse, forming a depression. Other remnants of the Hercynian orogeny include the Catalan-Balearic, Ebro-Aquitaine, and Betic-Rifan massifs. The Ebro Basin subsided due to isostatic adjustment. These structures are composed of metamorphosed and granitized rocks, primarily siliceous, resulting in rigid materials and gentle peaks.
Folded Mountain Ranges
Located in the eastern half of the peninsula, these younger, high-altitude mountains formed during the Tertiary. Their formation is partly due to pre-existing massifs and partly due to the folding of materials deposited in the Mesozoic geosyncline. Examples include the Iberian System, Coastal-Catalan Range, and Pyrenees.
Sedimentary Basins
Formed during the Tertiary and Quaternary, these basins are filled with sediments. They are located in concave depressions of the Paleozoic Meseta (e.g., Douro, Tagus, and Guadiana basins) and in grabens formed during the Alpine orogeny (e.g., Ebro and Guadalquivir valleys).