Banca de QUALIFICAÇÃO: ALANNY CHRISTINY COSTA DE MELO

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
DISCENTE : ALANNY CHRISTINY COSTA DE MELO
DATA : 06/07/2018
HORA: 14:00
LOCAL: Sala 1 - PPGG
TÍTULO:

REGIONAL GEOPHYSICAL MAPPING OF THE MESOZOIC-CENOZOIC MAGMATISM IN THE BORBOREMA PROVINCE, NE-BRAZIL

PALAVRAS-CHAVES:

Borborema Province; Aeromagnetic Data; Dyke Swarm

PÁGINAS: 28
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Geociências
RESUMO:

The Borborema Province comprises a vast geotectonic unit in the South American platform. It is a complex mosaic of crustal blocks of different ages, origin and evolution, that was amalgamated in the Brasiliano Orogeny, at the end of the Neoproterozoic and beginning of the Phanerozoic, in the context of the construction of the supercontinent Gondwana. The northern portion of the Borborema Province is recognized by the Cretaceous magmatic event called the Rio Ceará-Mirim Dyke Swarm (CDMS). The CDMS corresponds to a series of E-W trending diabase dyke swarms associated with the initial rift stage of the Potiguar Basin in Early Cretaceous. It has an extension of approximately 350 km in length, crosscutting the NE-SW oriented Precambrian fabric. To the west of the 39º W, the diabase dykes change their orientation to NE-SW direction, defining an arched geometric pattern for the entire CDMS, whose longitudinal extension reaches about 1000 km and an average lateral extension of 100 km. Two other sets of mafic dykes are also recognized in the Borborema Province. They are known as Riacho do Cordeiro Dyke Swarm (RCDS), approximately 700 km long, and Canindé Dyke Swarm (CDS), with about 260 km. The present study aims to promote a regional geophysical cartography of the Mesozoic dyke swarms, based on aeromagnetic data and field surveys, to propose models that explain the causes of this vast magmatism and its evolution in the Borborema Province geological setting. The airborne data were assigned by the Brazilian Geological Survey (CPRM), previously corrected for the diurnal variation of the geomagnetic field and removed its main component (International Geomagnetic Reference Field - IGRF). The Total Magnetic Intensity (TMI) map was obtained by interpolating the magnetic data using the Bi-directional Method, with cell size referring to half the spacing between the flight lines (500 m). Next, we applied the Reduction to Magnetic Pole (RTP) filter, aiming to centralize the magnetic anomaly on its source, using the magnetic declination and inclination as transformation parameters. For the interpretation of the aeromagnetic data and the correlation with the geology were used filters that highlight the magnetic signature. For this we apply a Matched Filter, to separate the magnetic anomalies in different spectral bands to obtain the geometry and the estimate of the depth of the sources of the anomalies. The mean depths of the magnetic sources calculated by the Matched Filter were 11.9 km for the longest wavelength anomalies, 3.0 km for the intermediate 1 anomalies, 1.1 km for the intermediate 2 anomalies, and 0.27 km for the shortest wavelength anomalies. Then the Analytical Signal Amplitude filter was applied to produce a maximum on the magnetic inflection points, highlighting the edges of the magmatic bodies. The mapping of the dykes was carried out from the qualitative interpretation of the geophysical maps, in which the magnetic patterns corresponding to the dykes were recognized due to the high contrast of magnetic susceptibility between the igneous bodies and their host rocks. The magnetic maps together with the field work allowed to delineate the dyke swarms more accurately. The spatial distribution of mafic dykes in the Borborema Province suggests that CMDS and CDS converge to form a triple junction, with the focus being situated in the western portion of the Potiguar Basin, suggesting that this magmatic set comes from the same Large Igneous Province (LIP). Based on these results we are proposing evolutionary models that explain the deep causes and the evolution of the Mesozoic magmatism in the Borborema Province.

MEMBROS DA BANCA:
Presidente - 1315614 - DAVID LOPES DE CASTRO
Interno - 349684 - WALTER EUGENIO DE MEDEIROS
Interno - 350630 - ZORANO SERGIO DE SOUZA