Geology of The Iberian Peninsula - Intrusions

Intrusions

During the Hercynian cycle, some plutons were formed in the peninsula. Gabbro appeared in northwest Galicia as Monte Castelo Gabbro, and also at Beja in Portugal. Two different kinds of granite occur. One comes from the middle crust and is high in felspar and low in Calcium, and the other kind comes from the lower crust mixed with mantle magmas, and is a calcalkaline granite.

The first kind of granite is subdivided into granodiorites and muscovite-biotite leucogranite. (two mica granites). The granodiorite can be found at Finisterre, western Salamanca, Zamora, Gredos, Aracena. The two mica leucogranites can be found at Friol, Porto-Viseu, Moncorvo-Vila Real, Vigo, Finisterre, Gil Ibarguchi, La Guardia and also near Salamanca. Most of the granites are 318 Ma to 319 Ma. But some are from 340 Ma.

The calcalkaline granites were intruded at two times. The older one consists of granodiorite and adamellite with inclusions of tonalite, diorite, and gabbro. In western Galicia they are 316 Ma.

The younger calcalkaline granites mostly have coarse crystals, they are biotite and hornblende granodiorites. These have intruded later than the two mica granites and are frequent in northern and central Portugal. The radiometric age is around 300 Ma. Some of the batholiths of this mixed type of granite are in Cabeza de Araya, Forgoselo, Ponferrada and Boal, and La Runa.