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

NÓBILE, JULIETA; COLLO, GILDA; DÁVILA, FEDERICO M.; WEMMER, KLAUS

Congreso; XXIII International Lateinamerika-Kolloquium, Alemania.; 2014

The Argentine northern broken foreland has been the subject of continuous research to determine the uplift and exhumation history of the region. High-elevation mountains have been uplifted by N-S reverse faults resulting from the Andean tectonic compression scenery that disrupted a W-E Miocene foreland basin. We performed K?Ar dating on fault gouge related clay minerals samples (illite) collected along a transect within the Sierra de Ambato. K-Ar ages (3 samples) range from Late Devonian to Late Triassic (~ 360 to 220 Ma) and become older with increasing grain-size (~ 360-311 Ma for 2-1 µm grain size fraction, ~326-286 Ma for 1-0.2 µm and ~291-219 Ma of <0.2 µm). The reverse faults of Sierra de Ambato offset Neogene sedimentary rocks (Aconquija Fm., ~ 9 Ma, Nóbile, 2013). Faults affect the basement comprising Paleozoic metamorphic 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, Dalquist et 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 illite forming event at 220 Ma can be interpreted. According to our data, the Neogene reactivation would not have affected the K-Ar system.