First C and O isotopic data for the Piedras de Afilar Formation (Tandilia Terrane, Uruguay): their bearing on its correlation and age

PAMOUKHAGHLIAN, KARINA; GAUCHER, CLAUDIO; BOSSI, JORGE; SIAL, ALCIDES; POIRÉ, DANIEL

Uruguay

Simposio; Southamerican Symposio of Isotope Geology; 2006

Sociedad Uruguaya de Geología

The Piedras de Afilar Formation (PAFm) crops out in the Departamento de Canelones, southern Uruguay (Fig. 1). Type area and stratotype were located by Jones (1956) in the Cerros Piedras de Afilar. The unit occurs as an erosional relict preserved only in the newly defined Tandilia Terrane (Bossi et al., 2005; Fig. 1). Its northern boundary has been recognized as the Colonia Shear Zone (Bossi et al., 2005), which separates the Tandilia Terrane from the Piedra Alta Terrane (Bossi et al., 1993). Both terranes are mainly made up of Transamazonian (ca. 2200 to 1900 Ma) supracrustal belts and granite-gneiss areas. The basement of the PAFm comprises amphibolite-facies metasedimentary rocks of the Montevideo Formation (Pando Belt), as well as the Soca rapakivi Granite (Oyhantçabal et al., 1998). This intrusion yielded an UPb SHRIMP zircon age of 2054 ± 11 Ma (Hartmann et al, 2001). The PAFm rests with erosional and angular unconformity on the mentioned basement units. In this contribution, we report preliminary C and O isotopic analyses performed on limestones at the top of the PAFm, and discuss their bearing on the age and correlations of the unit.