Structural framework from gravity and magnetic data in the paleo/mesoproterozoic Araí rift-sag Basin, Central Brazil

Abstract

The Araí Basin comprises a paleo/mesoproterozoic rift-sag basin inverted in a thick-skinned regime during the Brasiliano Orogeny. Its depth to basement, geometry, and lateral extension remain unknown. We have aimed to determine this information based on geophysical/geologic data to clarify its main structures and gain an evolutional understanding. Gravity and magnetic data allowed us to delineate the rift system — its major faults and adjacent postrift sedimentary structures — over its entire length. The geophysical investigation included radial power spectrum analysis and Euler deconvolution alongside the application of edge structure enhancement filters on magnetic anomaly and matched filter grids. A 2.5D forward gravity model was generated using all results, with geophysical sources at depths of 35–42, 20.9–22.6, 11–15.6, 9.68, 8–2.3, and 0.37–0.54 km, respectively, interpreted as the Mohorovičić Discontinuity, Curie Surface, Conrad Discontinuity, granitic intrusions, basement depths, and superficial faults. The main interpreted tectonic framework of the entire area showed a preferential direction in N40E, comprising structures related to the Transbrasiliano Lineament and its reactivations. The basin magnetic signature trends N50-80E, with structures generated essentially in the Brasiliano Orogeny and those related to extensional rift faults reactivations (belonging to São Jorge-Alto Paraíso-Cormari, Cavalcante-Teresina, and Teresina-Nova Roma systems). These fault systems exhibit a magnetic signature at the average depth of 6 km, converging to a single fault detected up to 21.8 km. The main rift faults are in accordance with the Euler solutions and the matched filter interpretation, confirmed by mapped alluvial fans conglomerates. The current structural framework of the basin goes back to the Brasiliano Orogeny, when its sedimentary filling was limited by crustal blocks with distinct compositional, rheologic, and magnetic characteristics. These intrinsic characteristics of each block along with the resulting kinematics were responsible for delimiting the shape and depth of the basin.

The Acre Basin basement (NW Brazil) and the transition from the intracratonic to retroarc foreland basin system

“…de OLIVEIRA and VIDOTTI coverage is incomplete (e.g., de Castro et al, 2014;de Sousa Moro et al, 2018;Ferreira et al, 2019;Milani & Szatmari, 2020;Pedrosa Jr. et al, 2017;Pinto & Vidotti, 2019;Prezzi et al, 2018). This study integrated the gravity, magnetic, seismic and well data to identify the main geophysical structures of the Acre Basin while estimating for the first time the basement depth in the basin southern portion, positioning the Brazilian basin within the Andean foreland system and proposing a subdivision into two sub-basins based on the geophysical lineaments, depths of sources and gravity highs.…”

“…Although jointly potential field methods are a classic tool, computational advances and the expansion of the airborne survey data in the last decade allowed obtaining excellent results for structural framework and construction of geodynamic models, especially in sedimentary basins such as the Acre Basin, where the seismic coverage is incomplete (e.g., Curto, Vidotti, et al, 2015; de Castro et al, 2014; de Sousa Moro et al, 2018; Ferreira et al, 2019; Milani & Szatmari, 2020; Pedrosa Jr. et al, 2017; Pinto & Vidotti, 2019; Prezzi et al, 2018). This study integrated the gravity, magnetic, seismic and well data to identify the main geophysical structures of the Acre Basin while estimating for the first time the basement depth in the basin southern portion, positioning the Brazilian basin within the Andean foreland system and proposing a subdivision into two sub‐basins based on the geophysical lineaments, depths of sources and gravity highs.…”

Chapter 2

“…After these corrections are performed, the resulting measured magnetic field grid is subtracted from the IGRF to obtain the TFA. Aeromagnetic surveys provide magnetic anomaly maps (Corrêa et al, 2017;Dentith & Mudge, 2014;De Sousa-Moro et al, 2018). Large areas can be mapped quickly, without interpretation bias, irrespective of surface cover and with minimal terrain restrictions (Reeves, 2005).…”

“…The main applications of magnetometry are (Table 1) geological mapping (Oliveira, 2014a;Oliveira, 2014b;Silva, 2014), delineation of geological structures (De Sousa-Moro et al, 2018;Ramos et al, 2014), studies of porphyry copper/gold deposits and related hydrothermal alteration/mineralization (Heithersay & Walshe, 1995;Jhon et al, 2010), direct searches for iron oxide copper-gold (IOCG) systems, alkaline bodies containing diamonds and iron deposits (Nannini et al, 2017), and studies on continental-scale geotectonic trends (Kronenberg & Reeves, 2011).…”