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The Putumayo Orogen of Amazonia: A Synthesis
By Mauricio IBANEZ–MEJIA
Paleogeographic reconstructions of Amazonia in the Meso– and Neoproterozoic indicate that this cratonic block played an important role in the assembly of Rodinia, and that its incorporation into this supercontinent led to continent–continent collision(s) with the Grenville Orogen of Laurentia and the Sveconorwegian Orogen of Baltica. The Sunsás–Aguapeí belt of SW Amazonia has traditionally been regarded as the geological evidence of such interactions, although it is becoming increasing clear that the metamorphic and tectonic history of this margin does not match the grade and timing that would be expected from interactions with the (near)–Adirondian margin of the Grenville and/or the Sveconorwegian margin of Fennoscandia. Massifs of amphibolite– to granulite–grade basement of roughly late Mesoproterozoic age have been known to occur in the northern Andes for many decades, but an authochtonous late Meso– to early Neoproterozoic orogenic belt in the western Guiana Shield that is un–remobilized by Andean tectonics, was unknown. The discovery of such a belt hidden under the Putumayo Foreland Basin allowed, for the first time, to directly link the basement inliers of the Colombian Andes with the western Guiana Shield. Furthermore, the improved geochronologic database of some cordilleran inliers and Putumayo Basin basement, using high–spatial–resolution U–Pb methods, permited a more complete reconstruction of their evolution to be deciphered. This orogenic belt, which owing to its geographical location obtained the name 'Putumayo Orogen', holds key information about Amazonia's Meso– to early Neoproterozoic tectonics and is of great geodynamic significance to understand the role of this craton during amalgamation of the Rodinia supercontinent. This chapter provides a brief overview of the currently available geochronology and hypothesized tectonic evolution of the Putumayo orogenic cycle, making particular emphasis on its reconstruction within a dynamic framework of Laurentia–Amazonia–Baltica interactions in the second half of the Proterozoic and during Rodinia supercontinent accretion.
Keywords: Amazonia, Putumayo Orogen, Rodinia, Proterozoic tectonics, collisional orogenesis.