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Previous issue date: 2016-08-04 === Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico (CNPq) === A Bacia do Parna?ba ocupa uma imensa ?rea na por??o NE do territ?rio brasileiro, abrangendo
v?rios estados do Brasil. Ela ? uma sin?clise paleozoica, que contem registros desde a forma??o e
desagrega??o do supercontinente Gondwana. A bacia ? sustentada por um embasamento
cristalino desenvolvido ap?s a colis?o entre as plataformas Amaz?nica e Brasileira. Em um
contexto tect?nico de ruptura do megacontinente Pangeia no Mesozoico, que levou ? abertura do
Oceano Atl?ntico, rochas ?gneas intrusivas (diques e soleiras) e extrusivas, de composi??o b?sica,
acomodaram-se na Bacia do Parna?ba, que, do ponto de vista estratigr?fico, foram divididas em
duas unidades: Forma??o Mosquito Eojur?ssica e Forma??o Sardinha Eocret?cea. A presente
pesquisa tem por objetivo principal a cartografia geof?sica regional desses corpos magm?ticos
com base em dados aeromagn?ticos e uma t?cnica de mapeamento semiautom?tico (SOM). O
Matched Filter foi aplicado com o objetivo de decompor o Campo Magn?tico An?malo (CMA)
da bacia em componentes relacionadas a fontes magn?ticas em diferentes profundidades. Com
isso, foram obtidos os campos magn?ticos profundo (CMP), intermedi?rio (CMI) e raso (CMR).
Como o CMI apresenta principalmente uma contribui??o causada por fontes magn?ticas em
profundidades mais rasas na crosta superior, caracter?stica dos corpos magm?ticos da bacia,
aplicamos as t?cnicas de filtragem espectral Amplitude do Sinal Anal?tico e Derivada Vertical
nas anomalias magn?ticas do CMI, com o objetivo de real?ar ainda mais a resposta geof?sica
dessas fontes magn?ticas, aumentando a resolu??o espacial do m?todo investigativo. Com base
nas anomalias de alta amplitude e curto comprimento de onda, delimitamos dom?nios e
lineamentos magn?ticos nos mapas aeromagn?ticos, correlacionando-os com os poss?veis corpos
causadores. Assim, integrando os mapas geof?sicos com essas assinaturas magn?ticas ao SOM e
ao mapa geol?gico, ? apresentado um mapa interpretativo com a distribui??o superficial das
anomalias magn?ticas associadas ao Magmatismo Mesozoico da bacia. Os resultados indicaram
que o Magmatismo Mosquito tem grande ocorr?ncia nas bordas oeste e sul da bacia, e o
Magmatismo Sardinha est? concentrado nas por??es centro-leste e nordeste. Os dados de
susceptibilidade magn?tica medidos nas rochas vulc?nicas da bacia individualizaram o
Magmatismo Mesozoico, constatando que a Forma??o Sardinha exibe susceptibilidade magn?tica
m?dia de 25,2 x 10-3 SI, aproximadamente duas vezes maior que a susceptibilidade magn?tica
m?dia da Forma??o Mosquito de 11,46 x 10-3 SI, revelando uma diferencia??o composicional
destes dois eventos magm?ticos. Associa??es entre as se??es s?smicas, os dados magn?ticos e o
mapa geol?gico demonstraram que as anomalias do CMA e da ASA est?o relacionadas ?s
soleiras e diques intrusivos, geralmente nos grupos Serra Grande, Canind? e Balsas, e s?o
sensivelmente influenciadas por rochas ?gneas aflorantes ou subaflorantes. Por fim, as dire??es
dos lineamentos magn?ticos revelaram que riftes de dire??es ENE-WSW e NNE-SSW,
associados ? desagrega??o do Gondwana Oeste, e trends estruturais E-W e NE-SW, associados ?
Zona de Cisalhamento Transbrasiliano, exerceram controle estrutural sobre o Magmatismo
Mesozoico da bacia do Parna?ba. === The Parna?ba Basin occupies a large area in the NE portion of Brazil, covering several states. It is
a Paleozoic syneclise that contains records from the formation and break-up of the Gondwana
supercontinent. The basin is supported by a crystalline basement developed after the collision
between the Amazonian and Brazilian platforms. During the Mesozoic break-up of the Pangea
megacontinent, which contributed to the opening of the Atlantic Ocean, intrusive igneous (dykes
and sills) and extrusive rocks took place in the Parna?ba Basin. In the stratigraphic context, those
igneous rocks were divided into two units: Early Jurassic Mosquito and Early Cretaceous
Sardinha formations. The main objective of this research is a regional geophysical mapping of
these magmatic bodies based on aeromagnetic data and self-organizing map technique (SOM).
Matched Filter was applied in order to decompose the Total Magnetic Intensity anomalies (TMI)
of the basin in their components related to magnetic sources at different depths: Deep (DMF),
Intermediate (IMF), and Shallow Magnetic Fields (SMF). As the IMF anomalies mainly present
contributions from magnetic sources at shallower depths in the upper crust, characteristics of
such magmatic bodies, spectral filtering techniques (Analytic Signal Amplitude and Vertical
Derivative) were applied to IMF data in order to enhance the geophysical response of these
magnetic sources, increasing the spatial resolution of the investigative method. Based on high
amplitude and short wavelength anomalies, magnetic domains and lineaments were delimited in
aeromagnetic maps and correlated with the possible causative bodies. Thus, the correlation of the
geophysical maps with SOM solutions and the geological map allowed to propose an interpretive
map with the surface distribution of magnetic anomalies associated with Mesozoic Magmatism in
the Parna?ba basin. The results indicated that the Mosquito Magmatism has great occurrence at
the western and southern basin edges and the Sardinha Magmatism is located at the centraleastern
and northeastern parts. Magnetic susceptibility data, measured in the magmatic rocks,
permitted individualizing the Mesozoic Magmatism.The Sardinha Formation displays average
magnetic susceptibility of 25.2 x 10-3 SI, about two times higher than the values of 11.46 x 10 -3
SI obtained to Formation Mosquito, revealing a compositional differentiation of these two
magmatic events. Associations between seismic sections, magnetic data and geological map
showed that the high amplitude anomalies in the Analytic Signal and TMI maps are associated
with sills and dykes intruded usually within Balsas, Canind? and Serra Grande groups, and are
significantly influenced by outcropping or at near-surface buried igneous rocks. Finally, the
directions of the magnetic lineaments revealed that ENE-WSW and NNE-SSW oriented rifts,
associated with the break-up of West Gondwana, and E-W and NE-SW structural trends,
associated with Transbrasiliano Shear Zone, exercised structural control over the Mesozoic
Magmatism of the Parna?ba basin.
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