Sr, C and O-isotope geochemistry of carbonates from the area of Sierra de Pie de Palo, Argentina: stratigraphy and constraints on the origin of the Western Sierras Pampeanas

GALINDO, C.; CASQUET, C.; RAPELA, C.W.; PANKHURST, R.J.; BALDO, E.; SAAVEDRA, J.

PRECAMBRIAN RESEARCH

Elsevier

Año: 2004 vol. 131 p. 55 - 71

0301-9268

Sr, C and O isotope data are presented for carbonate rocks from the Sierra de Pie de Palo and other neighbouring crystalline rocks. These are used to distinguish three groups of rocks of quite different ages within the nappe pile that constitutes the Sierra de Pie de Palo. Carbonates from the Grenville-age ophiolitic unit at the bottom of the pile probably resulted from the interaction between hot seawater and contemporaneous oceanic crust. They are tentatively classified as ophicalcites. Carbonates from the Difunta Correa Sedimentary Sequence are part of a cover sequence to a Grenvillian basement, together forming the upper nappes. Isotope stratigraphy suggests a middle to late Neoproterozoic age (580 to 720 Ma) for these carbonates. This cover, which is recognized here for the first time, might be correlated with cover sequences to the Archean and early to middle Proterozoic cratons that are well preserved over large areas of Brazil. This fact, together with the absence of an equivalent Neoproterozoic carbonate – bearing cover in Laurentia, suggests that the Western Sierras Pampeanas, formerly considered part of the exotic Argentine Precordillera terrane of allegedly Laurentian derivation, could be autochthonous or para-autochthonous to Gondwana. The Caucete Group carbonates underlie the nappe pile and are separated from it by a first order thrust (the Pirquitas thrust). The latter carbonates are  Cambrian in age and isotopically similar to the carbonate platform of the  Precordillera. We thus conclude that the Pirquitas thrust is the boundary between the exotic Precordillera terrane and the autochthonous or para-autochthonous Western Sierras Pampeanas.       Keywords: Isotope stratigraphy, Neoproterozoic, Cambrian, terrane, Gondwana.