Paleozoic crustal blocks of onshore and offshore central Argentina: New pieces of the southwestern Gondwana collage and their role in the accretion of Patagonia and the evolution of Mesozoic south Atlantic sedimentary basins

Abstract

The southwestern Gondwana basement block configuration in the central Argentinean offshore area was analyzed using gravimetric, magnetic and seismic data and existing onshore tectonic models. The resultant maps, the distribution of the Mesozoic and Cenozoic basins and Paleozoic structural features were used to validate the interpretations and to produce a new regional tectonic model. Pre-Carboniferous southwestern Gondwana of South America was interpreted as an open margin formed from east to west by the Dom Feliciano Belt, the Río de la Plata Craton, the Pampean Belt and the Pampia and Cuyania terranes. The collision of the Patagonia allochthonous terrane during the Late Paleozoic resulted in the development of the Ventania-Cape Fold Belt, which was mapped for the first time off the Argentinean coast out to 600 km from the shore. A strong change in the orientation of the Fold Belt is referred to as the Colorado Syntaxis, a mirror image of the Cape Syntaxis in South Africa. This change reflects the buttressing effect of the cratonic blocks that hamper the northward propagation of syncollisional deformation and resulted in a 180-km shift of the orogenic front. The Mesozoic basins and the basement block distribution were analyzed. The Pampean Belt, a deformed area produced by the Pampia accretion to the cratonic area, is the locus to two episutural basins, the General Levalle and Macachín basins. The Salado Basin was interpreted as an episutural basin controlled by a 2.1-2.0 Ga suture within the Rio de la Plata Craton. The Colorado Basin is composed of four segmented depocenters that reflect different emplacement controls: the location of the western Colorado Basin was controlled by the Upper Paleozoic orogen; the distributions of the central and eastern Colorado depocenters, orthogonal to the continental boundary, were also strongly influenced by the Upper Paleozoic structures and were offset by lineaments that reflect Dom Feliciano fabric; the Colorado Basin external depocenter that parallels the continental margin was also controlled by these lineaments. We interpret a time gap of some 50 Ma between the beginning of the evolution of the margin-orthogonal depocenters and the Atlantic breakup.