Regional geophysical mapping of the Mesozoic magmatism in the Parnaíba Basin
DOI:
https://doi.org/10.11606/issn.2316-9095.v17-455Keywords:
Magnetics, Seismic Interpretation, Self-organizing Mapping, Magnetic Susceptibility, Mosquito and Sardinha Formations, Parnaíba Basin.Abstract
During the Mesozoic break-up of the Pangaea megacontinent and opening of the Atlantic Ocean, intrusive and extrusive igneous rocks took place in the Parnaíba Basin in Early Jurassic and Early Cretaceous times, resulting in the Mosquito and Sardinha igneous successions, respectively. The main aim of this research is a regional geophysical mapping of these magmatic bodies based on techniques of magnetic anomaly enhancement and self-organizing maps (SOM). The final geophysical maps indicate that the Mosquito Magmatism has widespread distribution at the western and southern edges of the basin, whereas the Sardinha Magmatism is distributed at the center-eastern and northeastern portions. Magnetic susceptibility data measured in magmatic rocks outcrops allowed distinguishing the two main Mesozoic magmatic activities. The igneous successions associated with the Sardinha Formation displays averaged magnetic susceptibility about two times higher than the Mosquito Formation. This difference of physical property reveals a compositional differentiation of these two magmatic events. Comparative analysis between seismic sections, magnetic and surface geology data shows that the occurrence of magmatic rocks is much more extensive in the subsurface and the sills and dykes occur mainly intercalated in the Paleozoic tectonic-sedimentary sequences. Finally, the magnetic lineaments revealed: 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 Brasiliano shear zones. This tectonic heritage partially controlled the emplacement of the Mesozoic magmatism in the Parnaíba Basin. Finally rifts structures lying unconformably on Parnaiba sedimentary sequences point out to a close relationship with ENE-WSW and NNE-SSW oriented magnetic trends. On the other hand, deep anisotropies associated to the Transbrasiliano Lineament revealed E-W and NE-SW structural trends, governing the pattern of emplacement of Mesozoic magmatism in the Parnaíba Basin.
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