Banca de DEFESA: MIRO FELICIANO DORING DOS SANTOS

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : MIRO FELICIANO DORING DOS SANTOS
DATE: 30/07/2021
TIME: 09:00
LOCAL: Videoconferência
TITLE:

Crustal structure of the Recôncavo-Tucano basin from joint inversion of seismic data

KEY WORDS:

Joint inversion; Crustal structure; Extensional tectonics; Recôncavo-Tucano Basin

PAGES: 100
BIG AREA: Ciências Exatas e da Terra
AREA: Geociências
SUMMARY:

The stresses that led to the opening of the South Atlantic were responsible for intracontinental extension and, consequently, for the formation of a number of aborted rift basins in Northeastern  Brazil. Extension began in the Neo-Jurassic, with the formation of an Afro-Brazilian depression south of the Patos Lineament, and continued in the Eoberriasian with rifting along two NS-trending deformation axes: Recôncavo-Tucano-Jatobá (RTJ) and Gabon-Sergipe-Alagoas (GSA). Rifting initiated north of the Pernambuco Lineament during the Neoberriasian – Eobarremian, later migrating to the West along the NE-SW Cariri-Potiguar (CP) trend. In the Neobarremian, approximately coinciding with the opening of the Equatorial Atlantic, rifting was aborted along the RTJ and CP axes and continued along the GSA trend, eventually resulting in the separation of the continents. The magmatic activity on the Brazilian continental margin seems to have been restricted to the north of the Patos Lineament, as represented by the dykes of the Rio Ceará-Mirim. The geological history of the continental rifting process in NE Brazil indicates the influence of different types of extensional stresses in the rifting styles of each sub-basin. In order to better understand the influence of these stresses on possible rifting models, 11 seismographic stations were installed in and around the RTJ rift in October 2018. The installation was funded by the national oil company Petrobrás and included both short-period and broadband stations. In addition, 10 more stations from the Rede Sismográfica do Nordeste (RSISNE) that were close to the study area were utilized. In this work, measurements of crustal thickness and Vp/Vs ratio obtained from the  joint analysis of receiver functions and surface wave dispersion, aided with the H-k stacking technique, are reported. The results show that the crust is 40 km thick below the Recôncavo and Tucano sub-basins and that it contains a thick layer (5-8 km) of high-velocity material (Vs > 4.0 km/s) below 35 km depth. These observations contrast with the structure immediately to the West (São Francisco Craton) and East (Borborema Province) of the basin, for which the crustal thicknesses are in the order of 44 km and 36 km, respectively, the lower crustal velocities are below 4.0 km/s, and local instances of crust as thin as 31 km are observed. Thus, we propose, according to the 'flexural cantilever' model, that the high- velocity layer that forms the lower crust of the basin resulted from mafic underplating after stretching and thinning during the syn-rift phase, restoring crustal thickness to pre-rift phase values (or greater) and providing the necessary buoyancy to initiate regional uplift. Furthermore, although not generalized, cases of thin crust along the footwall may be related to ‘rift flank’ erosion. We therefore conclude that, regardless of the mode of extension in the upper crust, our results favor basin formation models that involve the extension of the lower crust by pure shear

BANKING MEMBERS:
Presidente - 1863578 - JORDI JULIA CASAS
Interno - 350640 - FRANCISCO HILARIO REGO BEZERRA
Externo à Instituição - MARCELO SOUSA DE ASSUMPÇÃO - USP