Alto Apa (basamento más antiguo del país)

In the north of the Eastern Region, in the so-called Alto Apa, outcrops include metamorphosed limestone, granites, metasediments, mafic gneisses and granitic and pegmatitic intrusions of Late Proterozoic age. It is usually considered the southern tip of the Central Brazilian (or Guaporé) Shield, and is the crystalline base on which the rocks of the Itapucumí Group, at Vallemí, were laid down. Its basement is described as Paleoproterozoic in age and is associated with the Río Apa Craton.

There is a second ancient core much farther south, the Alto Caapucú, which belongs to the Río de la Plata Craton. Paraguay sits right at the borderzone between several cratons.