The Grenvillian basement of the Precordillera/Cuyania Terrane and the Famatinian mobile belt. A-3 Field trip guide.

BALDO, E., CASQUET C., DAHLQUIST, J., VAN STAAL, C.R., VUJOVICH, G.I. (LEADERS IN ALPHABETICAL ORDER)

Mendoza

Conferencia; Gondwana 12 "Geological and Biological Heritage of Gondwana"; 2005

Academia Nacional de Ciencias

The A3 pre-conference field trip is aimed at visiting key areas of Western Sierras Pampeanas (WSP, Fig 1) where much geological research has been made over the past few years. The WSP became notorious when Grenvillian age rocks were discovered in the Sierra de Pie de Palo. This fact led support the Precordillera (or Cuyania) terrane hypothesis that was put forward in the late 1980´ and developed in the 1990´. According to this hypothesis the Precordillera (or Cuyania) terrane was a fragment of Laurentia that detached from it in the Late Neoproterozoic to Early Cambrian to eventually collide with the western margin of pre-Andean Gondwana to produce the Famatinian orogeny in the Ordovician (Fig. 1). The exotic Precordillera terrane consisted of a long enigmatic Cambrian to Early Ordovician carbonate platform sequence which outcrops in the Argentine Precordillera, to the west of the area dealt with in this field trip. In this hypothesis the WSP Grenvillian age rocks represented the basement of the platform carbonate sequence and were accordingly correlated with Grenvillian rocks of the Appalachian margin of Laurentia, i.e., the Ouachita embayment. The Precordillera (or Cuyania) terrane hypothesis estimulated further research in the WSP by different groups. The research was focused mainly on the Sierras de Pie de Palo, Maz, Espinal and Umango that were taken by many as a part of the Famatinian lower-plate, and in the Sierras de Valle Fértil and Famatina where an Early to Middle Ordovician Famatinian upper-plate magmatic arc developed. A wealth of new information has since been gathered that has led to a better understanding of many issues. Some of these issues will be dealt with in this field trip. We underline the following: i) the nature and extension of the Grenvillian basement, ii) the evolution of the WSP during the Neoproterozoic, iii) the boundaries between the alleged Famatinian upper and lower plates, and the problem of the allocthony vs autocthony of the Precordillera terrane, and iiii) the processes involved in the Famatinian magmatic arc preceding and during continental collision in the Ordovician.