masterThesis
Cartografia geofísica regional do magmatismo mesozoico (mosquito e sardinha) na Bacia do Parnaíba
Fecha
2016-08-04Registro en:
MOCITAIBA, Leonardo da Silva Ribeiro. Cartografia geofísica regional do magmatismo mesozoico (mosquito e sardinha) na Bacia do Parnaíba. 2016. 95f. Dissertação (Mestrado em Geodinâmica e Geofísica) - Centro de Ciências Exatas e da Terra, Universidade Federal do Rio Grande do Norte, Natal, 2016.
Autor
Mocitaiba, Leonardo da Silva Ribeiro
Resumen
The Parnaíba 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 Parnaíba 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 Parnaíba 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, Canindé 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 Parnaíba basin.