THE GRENVILLE-AGE PUTUMAYO OROGEN OF NORTHWESTERN SOUTH AMERICA AND ITS IMPLICATIONS FOR PROTEROZOIC TECTONIC RECONSTRUCTIONS OF AMAZONIA WITHIN THE RODINIA SUPERCONTINENT

Tectonic reconstructions for the early Neoproterozoic supercontinent Rodinia predict collisional interactions between a Laurentia-Baltica-Amazonia triple-join along Grenville-age (s.l.) internal collisional belts. However, although the positions of Laurentia and Baltica are relatively well constrained, the role of Amazonia is still debated since few paleomagnetic poles are available and geochronological data from some key areas is scarce. A northward extension of the late Meso- to early Neoproterozoic collisional belt of the SW Amazon Craton, the Sunsas belt, has been commonly inferred by the presence of high-grade metamorphic inliers included within the northern Andes of Colombia, but the reworked nature of these blocks with respect to the stable South American platform casts doubts about their relation with the non-remobilized Precambrian crust that underlies the proximal foreland. We present the first geochronological evidence to support the existence of a Grenville-age orogenic segment buried underneath these basins. Altogether, more than ~1100 individual U-Pb ages in zircons from 18 samples of the cordilleran inliers, drilling-cores from the foreland basin basement and outcrops of the exposed stable shield, document the complex accretionary and collisional history that this margin underwent during the last stages of Rodinia assembly. Its evolution was characterized by mid to late Mesoproterozoic arc magmatism and arc-related sedimentation in a peri-Amazonian fringing-arc system, followed by arc accretion and metamorphism under amphibolite-facies conditions during the interval 1.07 to 1.01 Ga and final granulite-facies collisional metamorphism at ca. 0.99 Ga. This new geochronological evidence is inconsistent with collision against the Grenville orogen of Laurentia, and instead supports correlations with the Sveconorwegian province of Baltica and the central American Oaxaquian terranes at the heart of Rodinia.