GEOCHRONOLOGY AND ND ISOTOPIC DATA OF GRENVILLE-AGE ROCKS IN THE COLOMBIAN ANDES - NEW CONSTRAINTS FOR LATE PROTEROZOIC EARLY PALEOZOIC PALEOCONTINENTAL RECONSTRUCTIONS OF THE AMERICA

New U-Pb zircon crystallization ages and Ar-40/Ar-39 cooling ages from the Colombian Andes confirm the existence of rocks metamorphosed duri ng the Orinoquian Orogenic Event (ca. 1.0 Ga) of northern South Americ a. epsilon(Nd) (t = 1.1 Ga) for these rocks range from -3.9 to +0.91, which is interpreted as a mixture of Late Archean-Early Proterozoic cr ust with juvenile material produced during the 1.1 Ga orogenic event. The Colombian Grenville age rocks are part of a much longer metamorphi c pericratonal belt, sporadically exposed along the Andes, in western- central Peru, southern Bolivia and northern Argentina. In addition, Nd model (T-DM) ages for the Colombian rocks range from 1.9 to 1.45 Ga, similar to those obtained in the Grenville Province of the eastern U.S . and in the Mexican basement, placing constraints on Late Proterozoic -Early Paleozoic paleocontinental reconstructions. (C) 1997 Elsevier S cience B.V.