Tectonic Implications
Middle - Late Devonian plutonism has been documented across the Eastern Sierras Pampeanas, with potentially correlative deformation restricted to local reactivation of existing fault zones (Dorais et al., 1997; Sims et al., 1998; Whitmeyer and Simpson, 2003). Mylonitic and ultramylonitic fabrics along the Tres Arboles fault zone and pseudotachylyte veins along the Los Tuneles fault zone strongly overprint earlier ductile deformation fabrics (Simpson et al., 2003). This suggests that the Late Devonian - Early Carboniferous ages reported here represent more extensive movement during fault zone reactivation than was previously thought. 40Ar/39Ar thermochronology of fault zone reactivation fabrics from this study suggest that ultramylonites of the Tres Arboles fault zone are likely correlative with brittle fault zone fabrics in the Los Tuneles zone but provide no constraints on earlier deformation in either area. These age results constrain the final juxtaposition of the Sierra de San Luis southwest of the Sierras de Córdoba to no later than Early Carboniferous, possibly as part of the Achalian orogeny of Sims et al. (1998) and possibly the accretion of the Chilenia terrane farther west (Davis et al., 1999). This event likely represents the last phase of the early to middle Paleozoic collisional sequence along the western margin of Gondwana, prior to the final assembly of Pangaea in the late Paleozoic.