Allochthoneity of the Argentine precordillera terrane: An alternative to current paleogeographical models

CASQUET, C.; RAPELA, C.W.; BALDO, E.G; PANKHURST, R.J; DAHLQUIST, J.A.; GONZÁLEZ-CASADO, J.M.; GALINDO, C.; FANNING, C.M; SAAVEDRA, J.

Oslo, Noruega

Congreso; 33th. International Geological Congress; 2008

The concept of the Argentine Precordillera terrane (or Cuyania), supposedly consisting of a Grenville-age (~ 1.0–1.2 Ga) crystalline basement with a Cambrian to Middle Ordovician sedimentary carbonate cover, introduced a radical hypothesis for the earlyPaleozoic evolution of the proto-Andean margin of SW Gondwana. Mainly on the basis of faunal and stratigraphical similarities to the coeval carbonate platform along the SE Appalachian margin of Laurentia, it was suggested that the Precordillera terrane drifted away from Laurentia in the Late Neoproterozoic or Early Cambrian and was subsequently accreted to the proto-Andean margin of Gondwana during the Middle Ordovician Famatinian orogeny. In one version the Precordillera terrane rifted from the Ouachita embayment and crossed the Iapetus Ocean before collision with SW Gondwana; in another the terrane initially formed the southern tip of Laurentia and was accreted to SW Gondwana after collision of the promontory during clock-wise rotation of Laurentia. The exotic origin implicit in these models has been challenged by claims for an alternative origin on the SW Gondwana margin to the south (present-day sense), with accretion by transcurrent displacement. U-Pb SHRIMP detrital zircon dating of the late Neoproterozoic Puncoviscana Formation of NW Argentina, along with other geological and chronological evidence, suggest that this largely turbiditic sequence, now bounded to the east by the Paleoproterozoic Rio de la Plata craton, is also a transcurrent terrane. Its location resulted from right-lateral movements along the SW Gondwana margin associated with the oblique subduction and subsequent collision of a continent from the southwest during the Pampean– Araguaia orogeny (555–515 Ma) following closure of the intervening Clymene ocean. The colliding continent is thought to have included the Western Sierras Pampeanas Grenville-age basement, Amazonia and the Arequipa–block, among other. This collage of Archean to Mesoproterozoic cratons was amalgamatedduring the Grenville orogeny and was formerly attached in the west to Laurentia according to diverse geological, geochemical and paleomagnetic evidence. Rifting from Laurentia started at ~775 Ma and opening of the Iapetus ocean by the Early Cambrian led to development of carbonate platforms on the conjugate continental margins. We suggest that the Argentine Precordillera carbonate platform may have formed on the eastern side of Iapetus. This hypothesis offers a new view of Proterozoic–Phanerozoicpaleogeographical links between SW Gondwana and Laurentia through a large intervening continental landmass.