Geochemistry of Neoproterozoic-Cambrian metasedimentary rocks of the Caucete Group, Sierra de Pie de Palo, Argentina: Implications for their provenance

摘要

The Caucete Group is a low-grade metasedimentary sequence of probable late Neoproterozoic-Cambrian age. It is exposed on the western flank of the Sierra de Pie de Palo, a basement block of the Cuyania terrane from western Argentina. The geochemical composition (major, trace and rare-earth elements, and Sm-Nd isotopes) of the El Quemado, La Paz, El Desecho, and Angacos formations (Caucete Group) was used to characterize the sedimentary provenance. We recognized two types of sources: A felsic source (crustal signature) and another mafic source with juvenile signature. Provenance is interpreted to be the mixing between Paleoproterozoic felsic rocks and Mesoproterozoic－Neoproterozoic juvenile rocks sources. This is supported by previous geochronological studies. The Cuyania basement is interpreted to be the Mesoproterozoic and Neoproterozoic juvenile component defined in the Caucete Group (e.g.: ophiolite assemblage of Sierra de Pie de Palo). The Cuyania basement is also considered to be the felsic source (paragneisses and meta-greywackes of the Pie de Palo Complex). We do not consider Gondwana as a provenance source based on the discrepancies in the Sm－Nd isotopic signatures and the detrital zircon provenance ages between the Caucete Group and the surrounding units that are considered to be autochthonous to the southern margin of Gondwana. The Caucete Group Laurentian Sm－Nd isotopic signature suggests that this sector could have been part of the source area. Hence an allochthonous origin for the Caucete Group (Cuyania terrane), derived from southern Laurentia, is supported for the geochemical results presented in this contribution.