Grenville-age sources in Cuesta de Rahue, northern Patagonia: Constrains from U/Pb SHRIMP ages from detrital zircons

RAMOS, V.A, GARCÍA MORABITO, E., HERVÉ, F., FANNING, C.M.

Mar del Plata

Congreso; Geosur (International Geological Congress on the Southern Hemisphere); 2010

The northern part of Patagonia has scarce basement exposures. They are located in the south-eastern sector of the province of Neuquén along the foothills of the Patagonian Cordillera at 39º16’S latitude and 70º50’W longitude (see Fig. 1). These exposures were studied by Turner (1965) who mapped them as part of his Colohuincul Formation. This unit at that time was assigned to the Precambrian to early Paleozoic, based on regional correlations. Digregorio (1972) considered this basement as Precambrian, although in a later contribution followed the proposal of Turner (Digregorio and Uliana, 1979). The outcrops of Cuesta de Rahue, as well as other exposures of the Cordón de la Piedra Santa located few kilometers to the east, were included by Franzese (1995) in the Piedra Santa Complex. This author presents the first K/Ar ages of these metamorphic rocks which yielded values between 372 and 311 Ma with large errors, but that indentified a late Paleozoic age for the metamorphism. The first hard evidence that the rocks of the Colohuincul Formation could be of younger age was presented by Basei et al. (1999), whom found 345 ± 4.3 Ma old zircons in an amphibolite further south in the Cañadón de la Mosca near Bariloche. This finding  implies that these rocks were metamorphosed in late Paleozoic times. An age on U-Pb in titanite ca. 360 Ma together with the previous K-Ar ages, was interpreted as the cooling age of the metamorphic peak. The objective of this study was to know more about the age of these rocks in the Cuesta de Rahue section in order to constrain the age of the basement of the Neuquén Basin in its south-western margin.