Neoproterozoic and Cretaceous crustal structures revealed by a 3-D magnetotelluric investigation of the onshore Espírito Santo Basin and the contiguous Araçuaí Orogen (SE Brazil)

Abstract

SUMMARY The study region in southeastern Brazil is composed of two domains: the Cretaceous onshore Espírito Santo Basin and the Neoproterozoic Araçuaí Orogen. In this region, associations among geological evolution, observed structures and geophysical data are limited. Therefore, this study aimed to further investigate this region using magnetotelluric (MT) data obtained from 22 W-E spanning stations over the Espírito Santo State. Because the dimensionality analysis revealed a substantial 3-D characteristic of the data, a 3-D MT inversion using the ModEM code was performed to generate a regional geoelectric model, and potential and well data were used as qualitative support for the interpretation. The resistivity profile obtained from the model revealed a resistive pattern for the Precambrian terrain and a conductive pattern for the sedimentary rocks of the onshore Espírito Santo Basin. The basement of the basin was delimited in the resistivity model, revealing consistency with the basement depths from the well data. Furthermore, three crustal conductors inserted in a resistive Precambrian orogen were identified. These conductors may be related to the recent circulation of saline fluids associated with plume action during the Upper Cretaceous and Cenozoic. However, the structures in which these fluids circulate exhibit different genesis along the resistivity profile. The conductors to the west of the profile may be related to plutons and dykes associated with the NNW Colatina Lineaments generated by the gravitational collapse of the orogen (530–490 Ma). Conversely, the conductor to the east under the Espírito Santo Basin appears to be related to the primary detachment rift fault generated during the Cretaceous breakup of Gondwana.