Deep Structure of the Santos Basin, Offshore Brazil From 3D Inversion of magnetotelluric Data

The relationship between deep crustal structure and the deformation in the overlying sedimentary wedge in Santos basin, Brazil is not well understood, and the origin and evolution of the salt‐related “Albian Gap (AG)” remain a topic of debate. We investigate the deep structure using three‐dimensional inversion of full tensor marine magnetotelluric (MT) data (of 10−1 to 104 s period bandwidth) from 92 stations along three NW–SE lines in 50–1,700 m water depth, one crossing the Cretaceous hinge line (CHL), AG, and Cabo Frio Fault (CFF). The geological validity of the resulting MT resistivity models was determined using resistivity logs from 11 wells and seismic data. The model shows two regionally persistent electrically conductive layers (C2 and C3) related to key Cenozoic and Cretaceous unconformities in the upper part of the sedimentary wedge. Beneath this wedge, the resistive continental crust is ∼35 km thick across the CHL until the 200 m isobath and thereafter thins rapidly seaward to ∼21 km over a lateral distance of ∼80 km defining a domain of highly extended and faulted crust. Our models show a mantle‐associated basement high and evidence of significant uplift of the lower part of the sedimentary wedge at 100–150 km distance along our central profile which spatially coincides with the AG and a previously proposed Moho high. This implies a mantle‐driven deformation of the crust and basin fill. We propose that mantle flow and magmatism may have played a significant role in the inferred displacement at the AG. Plain Language Summary How the deformation observed in the sedimentary wedge of Santos basin, Brazil is related to deep crustal and/or upper mantle processes is not well understood. We investigate the deep structure beneath Santos basin using a three‐dimensional magnetotelluric resistivity model crossing the Cretaceous hinge line (CHL), Albian Gap (AG), and Cabo Frio Fault (CFF). The geology‐calibrated resistivity model shows a top electrically conductive sedimentary wedge, underlain by the resistive crust that thins seawards as a result of basin evolution through continental rifting and extension characteristic of passive margin basins. The resistive continental crust is ∼35 km thick across the CHL and thins rapidly seaward to ∼21 km beneath the CFF, defining a domain of ∼80 km with highly extended and faulted crust. Our model suggests a mantle‐associated basement high and shows evidence of significant displacement over a wide zone across a prop