Banca de DEFESA: FLODOALDO DE LIMA SIMOES NETO

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
DISCENTE : FLODOALDO DE LIMA SIMOES NETO
DATA : 28/02/2018
HORA: 14:30
LOCAL: Auditório do Departamento de Geofísica
TÍTULO:

Upper mantle structure under the Borborema Province from P-wave teleseismic tomography: Implications for intraplate volcanism and uplifit, and opening of the Equatorial Atlantic

PALAVRAS-CHAVES:

Intraplate phenomena; Seismic tomography; Borborema Province; Equatorial Atlantic

PÁGINAS: 150
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Geociências
RESUMO:

The Borborema Province is a geological and structural domain located in the Brazilian Northeast, which is limited to the South by the São Francisco craton, to the West by the Parnaíba basin, and to the North and East by a number of marginal basins. Its basement consists of Paleoproterozoic rocks and Archean nuclei, which underlay metamorphic supracrustal rocks with ages spanning the entire Proterozoic eon. Its structuration happened during the Brasiliano/Pan African orogeny, at the end of the Neoproterozoic, resulting in a complex orogenic system affected by ductile, metamorphic, and magmatic deformational processes. During the Mesozoic, the evolution of the Borborema Province was marked by extensional events that eventually led to continental breakup and the opening of the Atlantic Ocean. The separation formed a rift system in the Brazilian Northeast that was ultimately responsible for the formation of the marginal and interior basins that pervade the Province. After continental breakup, the evolution of the Province was characterized by episodes of intraplate volcanism along the Macau Queimadas Alignment 

(MQA) and tectonic uplift throughout the Borborema Plateau, which displays an elliptic topography and is located in the western half of the Borborema Province with maximum elevations of approximately 1200 m.

In order to understand the origin of the intraplate volcanism and uplift after the opening of the Atlantic Ocean, P-wave (and PKPdf) travel-times from teleseismic earthquakes were utilized to develop tomographic images of the upper mantle under the Borborema Province. About 120 events with magnitudes 5.5 and above, totaling over 1800 relative residuals, were used in the tomographic inversion. Those residuals were in turned mapped in 3D as P-wave velocity perturbations in the upper mantle under the recording seismic stations, through a tomographic inversion. Among the main features displayed by the tomographic images we find: (i) a relatively shallow low-velocity anomaly (< 150  km), located under the north easternmost corner of the continente and clos to the Cenozoic volcanism, and (ii) a high-velocity lithospheric mantle (<250 km) South of the Patos Lineament – approximately coinciding with the Southern half of the Borborema Plateau – when compared with the lithospheric mantle to the North. Those results suggest that the origin of the Cenozoic volcanism might be related to a relatively shallow termal at the corner of the continente, and that the Patos Lineament is a lithospheric-scale suture zone that separates contrasting mantle rheologies, with the more rigid rheolgy to the South of the Patos Lineament being responsible for the topographic elevation of the Borborema Plateau. The rigid lithosphere to the South of the Patos Lineament might also have affected the stress regime during the opening of the Equatorial Atlantic. The equatorial region marked the last phase of the continental breakup, contrasting with the stress regime in other segments of the Atlantic rift. A cold and rigid lithosphere at the Earth’s equator was independently postulated by other authors to explain the anomalous opening of the Atlantic Ocean in the equatorial region. However, theoretical calculations for the equatorial stress field developed in this work, demonstrate that a cold and rigid equatorial lithosphere would have resulted in a stress rotation opposite to that inferred from geological observations. Additionally, the pressence of a cold and rigid lithosphere contrasts with the tomographic results developed for the Borborema Province. Thus, a new tectonic model for the opening of the Atlantic Ocean in the equatorial region is proposed, in which Precambrian structures and lithospheric delamination – assisted by the St. Helena mantle plume – would have been responsible for stress transfer and rotation during the various rifting phases in the Equatorial region.

MEMBROS DA BANCA:
Interno - 350640 - FRANCISCO HILARIO REGO BEZERRA
Presidente - 1863578 - JORDI JULIA CASAS
Externo à Instituição - MARCELO PERES ROCHA - UnB
Externo à Instituição - VICTOR SACEK - USP
Interno - 349684 - WALTER EUGENIO DE MEDEIROS