Evolución tectónica de la cuenca de Cañadón Asfalto (zona del Valle Medio del Río Chubut)

• Main Author: Figari, Eduardo G.
• Other Authors: Ramos, Victor
• Format: Doctoral or Postdoctoral Thesis
• Language: Spanish
• Published: Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales 2005
• Subjects: Argentina; Chubut; Falla; mar de Weddell; Weddell; Weddell Sea; Mar de Weddell
• Online Access: https://hdl.handle.net/20.500.12110/tesis_n3896_Figari; http://repositoriouba.sisbi.uba.ar/gsdl/cgi-bin/library.cgi?a=d&c=aextesis&d=tesis_n3896_Figari_oai

La Formacion Canadon Asfalto es un conjunto de depositos volcanicos, bioquimicos, piroclasticos y epiclasticos que aflora en la zona central y norte de la Provincia de Chubut, pero que fueron descritos inicialmente en la region del Valle Medio del rio Chubut. Las principales incognitas sobre esta unidad se planteaban sobre la geometria, extension y genesis de la cuenca que la albergo, asi como sobre los esfuerzos posteriores que la habrian deformado. El estudio de campo en detalle de la estratigrafia, distribucion, geometria, discontinuidades, y elementos tectonicos que controlaron la depositacion de la Formacion Canadon Asfalto (sensu lato) demostro que bajo este nombre se han considerado distintas unidades litoestratigraficas que deberian en realidad formar parte de formaciones distintas (Formaciones Canadon Calcareo, Estratos de Almada, etc.). Sin embargo por motivos conceptuales y de simplicidad, se decidio mantener el nombre generico de Formacion Canadon Asfalto y adoptar una nomenclatura descriptiva, evitando crear nombres formales nuevos. Los estudios estructurales y tectosedimentarios presentados en esta tesis doctoral permitieron reconocer que la clasica Formacion Asfalto representaba, ademas, el registro de etapas diferentes dentro de la evolucion de cuencas de hemigraben. Estas cuencas se desarrollaron como depocentros aislados sobre un area mas extensa que la conocida hasta el momento, habiendose encontrado numerosos afloramientos previamente mal asignados desde el punto de vista temporal, pero que en realidad pertenecen al mismo gran evento. Se definio entonces la existencia de un sistema de rift elongado en direccion noroeste que se desarrollo desde el Jurasico Medio hasta el Cretacico Temprano, constituido por un conjunto de hemigrabenes vinculados entre si por zonas de acomodacion, que recibe el nombre de Cuenca de Canadon Asfalto. Estos resultados se integraron a la evolucion tectonica de la parte sur del continente americano teniendo en cuenta su relacion temporal y espacial, en especial con la orientacion de los esfuerzos, de la apertura del Mar de Weddell. Esfuerzos compresivos durante el Neogeno de orientacion principal oeste-este provocaron la inversion tectonica parcial de la cuenca, principalmente en su borde occidental. La actitud diferencial que ha tenido la fracturacion preexistente frente a esta compresion regional, se justifica a partir de la orientacion de esas fallas ante al esfuerzo maximo compresivo (sigma 1). De esa manera, se produjo la reactivacion de esos planos de falla previos con desplazamiento inverso u oblicuo o su no reactivacion. The Canadon Asfalto Formation is a succession of volcanic, biochemical, pyroclastic and epiclastic deposits which are exposed in the central and northern regions of the province of Chubut. These sequences were only originally described in the region of the Middle Valley of the Chubut River. The main uncertainties over this unit, before the present studies, were its geometry, distribution, and genesis of the basin, which controlled its deposition, as well as the stress field that later deformed its sediments. The detail field studies on the stratigraphy, distribution, geometry, discontinuities, and tectonic elements that constrain the deposition of the Canadon Asfalto Formation (sensu lato) showed that under this denomination have been grouped different litostratigraphic units, which could be considered as independent formations such as Canadon Calcareo Formation, the Almada beds, and so on. However, based on conceptual and simplicity reasons it was decided to keep Canadon Asfalto Formation as a generic name and to adopt a descriptive nomenclature avoiding creating new formal names. The structural and tectosedimentary studies in this doctoral thesis allowed recognizing that the classic Canadon Asfalto Formation represented a record of different stages in the evolution of a rift system that was controlled by halfgraben basins. These basins were developed as isolated depocentres over a more extensive area that was previously known. Several outcrops have been identified, whose ages were wrongly interpreted, and were part of a single great event. This reconsideration allowed defining a rift system a with a north-western trend that occurred between the Middle Jurassic up to the Early Cretaceous, formed by a series of halfgrabens linked among them by accommodation zones, which have received the name of Canadon Asfalto Basin. These results have been integrated to the tectonic evolution of the southern part of South American continent, and based on the temporal and space distribution, it was related to the main orientation of the stress field during the opening of the Weddell sea in Middle Jurassic times. Compressive stresses during the Neogene with a main east-west trend were responsible of the partial tectonic inversion of the basin, mainly along its western margin. The differential response that have been observed in the pre-existing fractures, it is explained by the orientation of these faults in relation to the maximum compressive stress (sigma 1). This fact, explains why this reactivation occurred by reverse or oblique displacements or in some cases by no reactivation of the previous faults. Fil:Figari, Eduardo G. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.