Lithospheric structure and its relationship to rifting and magmatism in the Ceará Central domain of northwestern Borborema Province in Brazil revealed by 3-D magnetotelluric inversion

Long period (1 – 10000 s) magnetotelluric (MT) data were acquired along a 400 km N-S transect across the Ceará Central domain in northwestern Borborema Province to investigate the electrical structure of the lithosphere. The data were inverted for three-dimensional (3D) resistivity models which revealed a thinned lithosphere between the Transbrasiliano Lineament and the Senador Pompeu Shear Zone in the Ceará Central domain. The basic structure across Ceará Central consists of a steep, electrically resistive lithospheric block (R3) bounded by deep-reaching conductors extending to depths of ∼100 km overlying a deeper conductive substratum (C3). In the upper crust, the raised thickest parts of R1a coincide spatially to the Archaean inlier Tróia-Tauá massif, while R1b coincides with the Tamboril Santa Quitéria calc-alkaline magmatic arc downdip, implying northward subduction. Our results are consistent with the past 3D MT models for the region, and we show that the above basic structure is repeated to the north and south in the adjoining tectonic domains. Integrating past and present results reveals a consistent lithospheric structure along-strike while dip-sections show lithospheric segmentation with structural wavelengths of ∼180-250 km and coinciding with the compartmentalisation of surface-mapped tectonic terrains. We interpret the gross structure across the region as suggesting the presence of multiple north-dipping (or south-verging) deep lithospheric roots or fossil subduction (and roll-back) systems. The shear zones are through-going, their high conductivity suggesting the reactivation of inherited structures, mineralisation or deep fluid circulation. Some of the shear zones are also associated with rift basin inversion. We therefore suggest that such terrains may be important for future exploration for geothermal and natural hydrogen resources.