K?Ar fault gouge dating in northern Argentine broken foreland.

NÓBILE, J.; COLLO, G.; DÁVILA, F.M; WEMMER, K.

Conferencia; 23rd Latin American Colloquium LAK 2014; 2014

The Argentine northern broken foreland has been the subject of continuous research to determinethe uplift and exhumation history of the region. High-elevation mountains have beenuplifted by N-S reverse faults resulting from the Andean tectonic compression scenery that disrupteda W-E Miocene foreland basin. We performed K?Ar dating on fault gouge related clayminerals samples (illite) collected along a transect within the Sierra de Ambato. K-Ar ages (3samples) range from Late Devonian to Late Triassic (~ 360 to 220 Ma) and become older withincreasing grain-size (~ 360-311 Ma for 2-1 μm grain size fraction, ~326-286 Ma for 1-0.2 μmand ~291-219 Ma of <0.2 μm). The reverse faults of Sierra de Ambato offset Neogene sedimentaryrocks (Aconquija Fm., ~ 9 Ma, Nóbile, 2013). Faults affect the basement comprising Paleozoicmetamorphic and igneous rocks that have been dated at ~477-470 Ma (migmatization age,Larroverre et al., 2011) to the north of Sierra de Ambato and ~340 Ma (crystallization age, Dalquistet al., 2006) to the south. If we consider all illite grains as associated to fault gouge formation,a long lasting brittle deformation history with a minimum age of ~360 Ma and a last illiteforming event at 220 Ma can be interpreted. According to our data, the Neogene reactivationwould not have affected the K-Ar system.