Tectonic domains in the NW Amazonian Craton from geophysical and geological data

Abstract

The Amazonian Craton is one of the largest cratonic areas in the world. In Colombia, a major portion of the Craton is covered by Paleozoic to Cenozoic sedimentary rocks and recent deposits. This, in addition to the difficulty of access and dense tropical rainforest, have made the geology of this area to remain relatively unexplored to this date. Most accepted models for the Proterozoic evolution of the Amazonian Craton indicate that it evolved via successive accretion of orogenic belts and crustal terranes around an ancient nucleus, and that tectonic provinces identified in the southern half of the craton, the Guaporé Shield, extend underneath the Amazon River Basin onto its northern exposure, the Guiana Shield. Nevertheless, recent geologic studies in the W Guiana Shield indicate that its evolution may have been different from the W Guaporé Shield, where these accretionary models were formulated. In this work, we used airborne gravity/magnetic geophysical datasets covering the NW portion of the Amazonian Craton, to better elucidate its structure and tectonic evolution. We apply a multiscale edge detection and 3D modeling to identify and delineate major crustal discontinuities and other geological features. Using this approach, we identified six primary geophysical lineaments that are interpreted as possible crustal boundaries. By combining our geophysical interpretation with all the geological, geochronologic and isotopic information available for the region, we propose the presence of the following tectonic domains: Ventuari-Tapajós, Rio Negro-Juruena (which we further subdivide into Atabapo and Vaupés Belts), Apaporis Graben, and Putumayo. Furthermore, a new U-Pb zircon crystallization age of 1227 ± 8/13 Ma obtained from volcanic rocks of the Piraparaná Formation indicates that extensional tectonics along the Apaporis Graben began at least in the late-Mesoproterozoic. This is significantly older than previously thought, and thus entirely transforms the tectonic significance of the Apaporis Graben structures. Our interpretation of structural limits is in excellent agreement with and provides a more accurate location for previously suggested boundaries, which were until now only loosely constrained by the sparse geological and geochronologic information available. This work provides the first regional reconstruction of crustal-scale features of NW South America, improving the understanding of the regional tectonic architecture of NW Amazonian Craton using geophysical methods.