Paramirim Aulacogen: finite strain analysis and tectonic shortening, implications for the São Francisco craton evolution and its marginal orogen

• Autor(a) principal: Veloso, Raulindo Santana Silva
• Data de Publicação: 2023
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Biblioteca Digital de Teses e Dissertações da USP
• Texto Completo: https://www.teses.usp.br/teses/disponiveis/44/44141/tde-16062023-075319/
• topic: Aulacógeno de Paramirim; Cráton do São Francisco; Deformação finita; Encurtamento tectônico; Finite strain; Paramirim aulacogen; Partição de deformação; São Francisco craton; Strain partitioning; Tectonic shortening

This dissertation presents new findings and investigates issues regarding the Structural Geology of the Paramirim aulacogen region. The study area is understood as a system of intracontinental rifts developed in the São Francisco craton from the Statherian period onwards and includes Paleoproterozoic to Neoproterozoic metasedimentary rocks from the Espinhaço and São Francisco Supergroups. During the Brasiliano orogenic cycle, this system of rifts and sedimentary basins underwent tectonic inversion resulting in the development of two main fold-and-thrust belts with opposite tectonic vergences: the Northern Espinhaço Range and the Western Chapada Diamantina. The study includes quantification of finite deformation, modeling of deformation matrices, kinematic forward modeling and estimates of tectonic shortening for the area. The results estimate a tectonic shortening for the Western Chapada Diamantina of 17.0% 19.4%, and for the Northern Espinhaço Range of 13.5% 16.3%. Based on the finite strain ellipsoids X/Z ratios, both fold-and-thrust belts were subjected to a similar strain magnitude. However, the areas differ in their deformation regime, axial orientation and shape of the finite strain ellipsoids. The former displays mostly oblate ellipsoids, while the latter exhibits prolate-shaped ellipsoids. The Western Chapada Diamantina domain is compatible with a thrust regime and associated folding, while the Northern Espinhaço Range shows a combination of thrust and strike-slip tectonics, with the occurrence of strain partitioning. Furthermore, a numeric deformation matrix simulation suggests that a combination of sedimentary compaction followed by a thrust and strike-slip regime could explain the strain patterns obtained. Moreover, the estimates of tectonic shortening for the area highlight the nature of the region as a Neoproterozoic deformation zone, supporting the hypothesis of a zone of non-rigidity between the western and eastern segments of the São Francisco craton.