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Sr, C and O isotope geochemistry and stratigraphy of Precambrian and lower Paleozoic carbonate sequences from the Western Sierras Pampeanas of Argentina: tectonic implications

Galindo Francisco, Mª del Carmen and Casquet, César and Rapela, Carlos W. and Pankhurst, R.J. and Baldo, Edgardo G. and Saavedra, Julio (2004) Sr, C and O isotope geochemistry and stratigraphy of Precambrian and lower Paleozoic carbonate sequences from the Western Sierras Pampeanas of Argentina: tectonic implications. Precambrian research, 131 . pp. 55-71. ISSN 0301-9268

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Abstract

Sr, C and O isotope data are presented for carbonate rocks from the Sierra de Pie de Palo and other crystalline outcrops of the
Western Sierras Pampeanas. 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. These carbonates 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 (580–720 Ma) for these
carbonates. This cover 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 apparently absence of an equivalent Neoproterozoic
carbonate-bearing cover in the Appalachian margin of Laurentia, suggests that the Western Sierras Pampeanas, which are
considered part of the exotic Argentine Precordillera terrane of allegedly Laurentian derivation, could be autochthonous or
para-autochthonous to Gondwana. Other geochemical and geological arguments reinforce this hypothesis. The Caucete Group
carbonates underlie the nappe pile and are separated from it by a first order thrust (the Pirquitas thrust). These 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-autochthonousWestern Sierras Pampeanas.

Item Type:Article
Uncontrolled Keywords:Isotope stratigraphy; Neoproterozoic; Cambrian; Terrane; Gondwana
Subjects:Sciences > Geology > Stratigraphic geology
Sciences > Geology > Geochemistry
ID Code:12082
Deposited On:25 Jan 2011 10:53
Last Modified:25 Jan 2011 10:53

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