The palaeogeographic position of Central Iberia in Gondwana during the Ordovician: evidence from zircon chronology and Nd isotopes

The abnormally elevated abundance of inherited zircon (locally up to 80-90% of zircon grains contain pre-magmatic cores) in the Cambro-Ordovician magmatic rocks of Central Iberia made possible an estimation of the distribution of ages of their source rocks. The comparison of inherited U-Pb ages and whole-rock Nd model ages with those of three main North African Neoproterozoic terranes reveals that the Iberian magmas can only have been generated from a crust similar to that of the East African Orogen west of the Arabian-Nubian Shield. Such crust is currently found in the three Precambrian inliers of the Western Desert of Egypt east of the Archaean terranes of Gebel Kamel. Palaeontological evidence also indicates that the Ordovician fauna of Central Iberia is similar to that of the region between eastern Algeria and Arabia; therefore, we conclude that during the Ordovician Iberia was not attached to north-west Africa near Morocco, as is usually assumed, but instead to the East African Orogen in northern Egypt.