U/Pb and 207Pb/206Pb ages on detrital zircons from El Quemado Quartzite (Caucete Group), Sierra de Pie de Palo, San Juan Province.

NAIPAUER, M., MCCLELLAND, W.C., VUJOVICH, G.I., CINGOLANI, C.A., ELLIS, J.R.

La Plata

Congreso; XVI Congreso Geológico Argentino; 2005

Asociación Geológica Argentina

The Caucete Group (Borrello, 1969) is composed of a low-grade metasedimentary sequence of siliciclastic-carbonate composition that outcrops on the western flank of the Pie de Palo range (Fig. 1).  The group was originally subdivided into four units: Puntilla Blanca Schists, Angacos Limestone, El Quemado Quartzite, and Pie de Palo Formation and assigned them to the Neoproterozoic. Recently Vujovich (2003), defined a new stratigraphic column consisting: El Quemado Quartzite, La Paz Formation, El Desecho Formation and Angacos Limestone on the basis of detailed mapping (van Staal et al., in prep.). The absence of diagnostic fossils and/or stratigraphic relationships do not permit assigning a precise chronostratigraphic position to the different formations. Since the beginning of the last century, the limestone units have been assigned to the Lower Paleozoic and compared with the carbonate sequences of the Precordillera due to similarities in lithology  (Schiller, 1912; Groeber, 1948). On the basis of C and O stable isotope data, Linares et al. (1982) concluded that the carbonate of the Caucete Group is similar in origin to the Cambrian limestone of the Precordillera. This interpretation is supported by Galindo et al. (2004) who also consider the group equivalent to the Cambro-Ordovician carbonate platform of the Precordillera on consideration of 87Sr/86Sr, d13C and d18O isotope values. Detrital zircons from metasedimentary schists that resemble those from the Difunta Correa Sedimentary Sequence (Baldo et al., 1998) produced three groups of U/Pb ages: 1160-1150 Ma, 1080-1050 Ma and 665 Ma, allowing the assignment of a maximum depositional age in the Neoproterozoic (van Staal et al., 2002; Vujovich et al., 2004). The Caucete Group is structurally overlain along the Las Pirquitas thrust by the Pie de Palo Complex (Schiller, 1912; Vujovich and Ramos, 1994). The Pie de Palo Complex is composed of middle to high grade metamorphic rocks which yield ages between 1.0 to 1.2 Ga (Vujovich et al., 2004; and others therein).  Both the Caucete Group and the Pie de Palo Complex form the eastern extent of the Precordillera terrane (Astini et al., 1995) or Cuyania composite terrane (Ramos, 1995; Ramos et al., 1998), which has been interpreted as an allochthonous terrane to Gondwana and derived from the Ouachita embayment in southeastern Laurentia since the pioneer works of Ramos et al. (1986), Dalla Salda et al. (1992), Astini et al. (1995), Dalziel (1997) and Ramos et al. (1998). Alternatively, other studies made by Aceñolaza et al. (1988), Baldis et al. (1989) and more recently by Aceñolaza et al. (2002) and Finney et al. (2003) argue that this terrane has a para-autochthonous origin and that it obtained its current position by strike-slip displacement along the southern Gondwana margin. The main objective of this work is to present preliminary results on the morphology and U/Pb ages obtained by the LA-ICP-MS method on detrital zircons of the El Quemado Quartzite (Caucete Group). We discuss the maximum depositional age and the provenance of these metasediments and compare them with data from different studies from the Cambrian sequences of the eastern Precordillera.