While rifting was occurring in the southern portion of Gondwana, the margin further west (along the proto-Andean belt) was experiencing a compressional regime that introduced several allochthonous terranes to the western margin of South America. The first of these, the Pampean orogeny (mentioned above), resulted in the accretion of the Pampia terrane. This was followed by the formation of the Famatina-Eastern Puna magmatic arc during the Famatinian orogeny in the Ordovician period, which culminated in the accretion of the Cuyania (Precordillera) terrane. Paleomagnetic evidence suggests that this Cuyania terrane is of Laurentian origin, and it has been hypothesized that the terrane may have been a plateau attached to Laurentia which was involved in the Cambrian rifting event and later accreted during collision between Laurentia and Gondwana. Geochronological evidence shows that the Famatinian magmatic belt extends south from the Andean margin into the North Patagonian massif, and paleomagnetic studies of these rocks indicate that separation between these bodies has not occurred at least since the Devonian, both lending support to the theory of an autochthonous component of Patagonia. Subduction continued along this margin, and in the late Devonian resulted in the collision and accretion of the Chilenia terrane to the western border of the Precordillera.
