THE CUSHAMEN FORMATION AT SIERRA DE MAMIL CHOIQUE: DATING A BASEMENT SEPTA, SW MARGIN OF THE NORTH PATAGONIAN MASSIF

LÓPEZ DE LUCHI, M. G.; MARTÍNEZ DOPICO, C. I.; GRILLO VIDAL CAROLINA; MONTENEGRO, T.; ROSSELLO, E.

Pto Madryn, Chubut

Congreso; XXI Congreso Geologico Argentino; 2022

Asociacion Geologica Argentina

The Paleozoic metamorphic basement in NW Patagonia is represented by the Colohuincul Complex (CC) along the eastern foothills of the Andean Cordillera and by the Cushamen Formation (CF) along the western border of the North Patagonian Massif. The latter forms a poorly exposed NNW trending belt from 39º 45´S/ 70º 36´W to 42º 48´S/ 69º 30´W. U-Pb ages calculated based on concordant zircons (90-110%) yielded peaks at 229.2, 285.8, 514.8, 606, 667.2, 1089.6, 1285.2, 1785.1 Ma appear in the probability density diagram . The youngest peak is defined by three zircons with very low Th/U and lacks geological meaning since the U-Pb SHRIMP age of the intruding granite is ca 277 Ma (our own unpublished data). The RC74a spectra with a more prominent peak at the Grenvillian interval is similar to those exhibited by the zircons of the sample of Cuesta de Rahue and Estero El Loco (Herve et al. 2018), Arroyo Pescado schist (Uriz et al 2019) and in one example of CC at San Martín de los Andes (Serra Varela et al., 2016).