2. Geological setting

The southwest boundary of Gondwana in South America is the counter-part of the Cape fold belt of South Africa [8]. It is extended from Sierras Australes-Claromecó Basin in the Buenos Aires province to the San Rafael Block in the Mendoza province (Figure 2). This fold and thrust belt [9], known as Gondwanides [8], was subject to deformation during the Paleozoic.

Ramos (1984) propose [10] an ocean closed by subduction toward the northern boundary of Patagonia at the southern margin of Gondwana, and generated a collision during the late Paleozoic. However, the geological evolution of this region is still a subject of debate and doubts remain about the origin of Patagonia and the age of the main deformation and if it is related or not with this collision. Now there are new proposals that include collisional and intra-continental deformation mechanisms (Ref. [11]). According to some researchers, the deformation occurs in one phase during the late Permian-Triassic, instead other authors propose that it began in the late Devonian-early Carboniferous and continued up to the Permian [12].

With the aim of regionally analyze the magnitude of the deformation regionally, the stress directions that acted in the different geological moments and the time-space relations between the different localities of the Gondwanides, AMS studies were making along its margin. Rocks of different lithologies and ages ranging from Cambrian to Permian-Triassic were studied in different localities along this belt (Figure 2), from the Sierras Australes-Claromecó Basin, Chadileuvú Block (Carapacha Basin, Los Viejos Hill and Sierra Chica) and San Rafael Block (Agua Escondida).
