IDEAN   23403
INSTITUTO DE ESTUDIOS ANDINOS "DON PABLO GROEBER"
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
New age constrains for the Cenozoic deposits of the Patagonian Andes and the Sierra de San Bernando between 43º and 46º S
Autor/es:
VANESA LITVAK; LUCIA FERNÁNDEZ PAZ; ANDRES FOLGUERA; GUIDO GIANNI; VICTOR VALENCIA; ALFONSO ENCINAS; ANDRES ECHAURREN; RENÉ BOBÉ
Reunión:
Simposio; Primer Simposio de Tectónica Sudamericana; 2016
Resumen:
In order to understand the Cenozoic evolution of the Patagonian Andes and the Sierra de San Bernardo (Chile and Argentina, ~43-46°S), we carried out new geochronological (U-Pb, LA-ICP- MS analyses in zircons) and structural studies on Eocene to Miocene strata from these areas. We report the following results. At the Rivadavia Range, in the southern end of the El Maitén Volcanic Belt (~43°S), we obtained an age of 37.0 Ma from a tuff of the Ventana Formation. This volcanic succession unconformably overlies Mesozoic rocks and shows wedge-like geometries associated with inverted normal faults. At the Sierra de San Bernardo (~46°S) the Paleocene-Eocene fluvial deposits of the Río Chico Group overlie marine strata of the Danian Salamanca Formation and underlie continental pyroclastic deposits of the late Eocene to early Miocene Sarmiento Formation. We observed syntectonic growth-strata associated to the Grande-Funes anticline in beds of the Koluel-Kaike Formation (Río Chico Group). A tuffaceous sandstone from the top of this unit yielded an age of 43.9 Ma. In the same area, at the Codo del Senguer anticline, we dated a marine sandstone of the ?Patagoniense? that yielded a maximum depositional age of 17.4 Ma. At the head of the Cisnes River (44°30?S) a Miocene succession of siltstones, sandstones, and tuffs of the Río Frías Formation overlies Cretaceous volcanic rocks of the Divisadero Formation and underlies Miocene conglomerates of the Galera Formation. The Río Frías Formation contains abundant remains of vertebrate fossils that characterize the Friasense SALMA. We dated a tuff from the Río Frías Formation and obtained an age of 15.8 Ma. We observed syntectonic growth-strata in this unit. At the Meseta de Chalía (45°30?S) a succession of tuffs and tuffaceous siltstones was correlated with the early-middle Miocene Río Frías Formation by previous workers. The tuff succession overlies volcanic Cretaceous rocks of the Carrenleufú Formation and underlies middle-late Miocene fluvial conglomerates of the Pedregoso Formation. We observed growth-strata in the tuff unit but we could not discern whether they are related to extensional or compressive tectonics, or to sedimentologic causes. One tuff among these strata yielded an age of 39.9 Ma, which indicates that this unit cannot be correlated with the Río Frías Formation.