segunda-feira, 14 de novembro de 2016
Seminário LabSis de 17/11/2016
Dando continuidade a série de seminários de 2016, nesta quinta-feira, dia 17/11, às 15:30h, no auditório do Módulo REUNI do Departamento de Geofísica, será proferido o décimo primeiro seminário do LabSis, do ciclo de 2016. O palestrante será o Professor Dr. Jordi Julià Casas, do Departamento de Geofísica (DGEF) e do pós-graduação da Programa de Pós-graduação em Geodinâmica e Geofísica (PPGG).
Título: Passive-Source Seismology in the Borborema Province of NE Brazil: Investigating Cenozoic Volcanism and Uplift
The Borborema Province of NE Brazil can be regarded as the remnant of a larger Proterozoic mobile belt that structured during the Brasiliano-Pan African orogeny at the end of the Neoproterozoic. The Province is scarred by a number of aborted rift basins resulting from extensional stresses related to the opening of the Atlantic ocean. After continental breakup, the Province was affected by episodes of intraplate volcanism and uplift, as expressed by the Macau-Queimadas magmatic alignment (93-7 Ma) and the high-standing Borborema Plateau (~1000 m). A number of models have been proposed to explain this intraplate activity, which invoke mantle plumes, small-scale convection cells, lateral crustal flow, and/or anomalous bodies in the lithospheric mantle. With the aim at discriminating among these competing models, the deep structure of the Province was investigated through analysis of seismic waves passively recorded at permanent and temporary seismic stations. At crustal levels, joint receiver function and surface-wave dispersion analysis revealed a 4-5 km thinning of the crust surrounding the southern Plateau, from 36-38 km to 30-32 km, along with the presence of a marked intra-crustal discontinuity accompanying the thin crust. Interestingly, the analysis also revealed the northern Plateau is a region of elevated thin crust. At upper mantle levels, SKS-splitting showed the mantle is surprisingly anisotropic at the heart of the Province, and body-wave tomography demonstrated the upper mantle under the northern half of the Province is markedly slower than that under the southern half. We propose the topographic variations are mostly the result of differential stretching during continental breakup - with Cenozoic uplift being restricted to the northern Plateau - while Cenozoic volcanism is likely to have resulted from lithospheric mantle sources. The lack of anisotropy in the mantle is harder to explain, and might have resulted from two layers with orthogonally oriented fast axes.
Jordi Julià, Rodrigo Luiz