Time constraints on the tectonic evolution of the Pampean Conlara Metamorphic Complex, Sierra de San Luis, Argentina .

LOPEZ DE LUCHI, M.G.; CERREDO, M.E.; STEENKEN, A.; SIEGESMUND, S.; WEMMER, K.

Rio Cuarto

Simposio; 14 Reunion de Tectonica; 2009

Universidad de Rio Cuarto-Com-Tec AGA

A new garnet PbSL age of 564 ± 21 Ma for M2 metamorphism of the banded schists of the CMC (Siegesmund et al. 2009) confirm that D1/2 history took place during the Pampean orogeny (cf. Steenken et al., 2005, 2006, 2007). Petrological investigations indicate that the PT conditions were sufficiently high in order to reset the garnet and/or inherited monazites (López de Luchi et al. forthcoming). Even though the error is relatively high, a metamorphic evolution starting at 530 Ma is excluded. Constraints on the depositional history indicate a pre- 566 Ma deposition of the sediments (Steenken et al. 2006, Drobe et al. 2009). D3 is constrained by pervasively solid-state deformed granitoids like the Early Ordovician (497 ±8 Ma) the El Peñón batholith (Steenken et al. 2005, 2007) which exhibits folded xenoliths of the D2 banded schists. D4 deformation is bracketed between the 450-420 cooling ages of muscovite booklets of pegmatoids, the closure temperature of which is comparable with the thermal requirements for biotite recrystallization (Steenken et al. 2008). The restricted low greenschist facies overprint is comparable (both in strike and composition) to the mylonitic paragenesis characteristic of Río Guzmán Shear Zone (Sims et al. 1997). This age of the Devonian event which closely matches the regional biotite cooling ages within de CMC would have been responsible for final unroofing of the Complex.