Resumo:
Abstract Between 1993 and 2000, a total of 101 magnetotelluric stations were acquired by the National Observatory along the southeastern edge of the Parnaiba basin. The stations were distributed in 10 NW-SE profiles. The objective of the present research is to propose a model of electrical resistivity from the 3D inversion in order to characterize the crustal structures of the southeastern border of the basin. The impedance tensor was estimated through the robust processing of the time series of the electric and magnetic fields. Subsequently, the Rhoplus method was applied to correct the outliers estimates from the apparent resistivity and the phase curves. The dimensionality analysis revealed a predominantly 3D behavior, and all components of the impedance tensor were thus inverted. The 3D inversion model corroborated the grabenform structures previously described in diferent publications, and contributed to define a differentiated thickening of the sedimentary layer, deeper in the southern portion (~ 500 m), shallower in the northern portion (~ 200 m), and a sedimentary thickening of up to 1 km in the central part. Moreover, the results evidenced the presence of low resistivity regions located in the upper crust along the southeast edge of the basin. Due to the distribution of the stations in the extension of the three northern, central and southern structural domains of Borborema Province (adjacent to the eastern border of the Parnaba basin), these regions were related to the geodynamic events of Borborema Province in Neo-proterozoic. The conductor located in the extension of the northern domain, was related to graphite precipitation, defined by the metamorphism that occurred in the western zone of the Seridó Belt. In the extension of the central domain, the conductive anomaly was related to the reactivation of the Pernambuco fault. In the extension of the southern domain, the low resistivity region was associated with the serpentinization processes, caused by the hydration of mafic and ultramafic rocks of the Brejo Seco complex in a context of oceanic subduction. Finally, the 3D model evidenced the location of the Senador Pompeu and Pernambuco shear zones previously defined through aerogravimetric and aeromagnetic data.
