Banca de QUALIFICAÇÃO: DIOGO LUIZ DE OLIVEIRA COELHO

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
DISCENTE : DIOGO LUIZ DE OLIVEIRA COELHO
DATA : 30/11/2017
HORA: 14:00
LOCAL: Labsis
TÍTULO:

Structural analysis of the Parnaíba basin through receiver functions and dispersion curves from earthquakes and ambient seismic noise

PALAVRAS-CHAVES:

Passive-source seismology, basin subsidence, receiver function, ambient noise.

PÁGINAS: 20
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Geociências
RESUMO:

The genesis and evolution of large basins in the stable interiors of continents is an important geological problem that is not easily understood within the Plate Tectonics paradigm. The Parnaíba basin is one of three large Paleozoic basins in stable South America - together with the Paraná and Amazon basins. The basin is commonly described as a large, sag-type cratonic basin, with a roughly circular shape and a depocenter reaching up to 3.5 km depth. The physical mechanism behind its subsidence and evolution, on the other hand, is more controversial. A number of basin-forming mechanisms have been proposed for this basin, but the knowledge about the deep architecture of this cratonic basin is still scarce. Owing to that, we propose to investigate the crustal and mantle architecture beneath of the Parnaíba basin through P-wave receiver functions and ambient noise tomography, in order to image deep and shallow structure, respectively. In the first part of our work, we present point estimates of crustal thickness and Vp/Vs ratio at 9 broadband stations in a 600 km-long transect crossing the central portion of the basin, along with detailed S-wave velocity-depth profiles obtained from the joint inversion of P-wave receiver functions and surface-wave dispersion velocities. Our analysis reveals the crust could be as thick as 44-45 km around the basin’s depocenter, and that it progressively thins to 39-41 km towards the edges, while bulk Vp/Vs ratios are in the 1.70-1.78 range along the transect, with larger values around the depocenter. The velocity-depth profiles confirm our previous crustal thickness estimates, and reveal a lower crustal layer below 18-22 km depth with S-velocities in the 3.7-3.8 km/s range, locally raising to 4.0-4.2 km/s near the depocenter. Our findings favor models invoking minimal stretching of the basin’s underlying crust and are found compatible with flexural bending by a deep load. However, the existence of a thick intrusive body pervading the lower crust is not supported by our results. We argue that deep convective processes in the asthenosphere might provide an alternative loading mechanism. The second part of our work consists of imaging the transition zone of the mantle with P-wave receiver functions to see how is the behavior of the asthenosphere beneath the basin, and the use of ambient seismic noise to image shallow crustal structure under the basin, with the goal of understanding the role of the Transbrasiliano lineament in the basin’s evolution.

MEMBROS DA BANCA:
Presidente - 1863578 - JORDI JULIA CASAS
Interno - 1451214 - ADERSON FARIAS DO NASCIMENTO
Interno - 1315614 - DAVID LOPES DE CASTRO