The investigation of the deep structures of Precambrian mobile belts is crucial for defining the tectonic evolution of Phanerozoic intraplate basins. The magnetotelluric (MT) method provides high-resolution two-dimensional (2-D) electrical resistivity models for the major deep-basement structures of a passive margin in southern Brazil. We obtained the resistivity models by applying mathematical inversion of 106 MT stations distributed along four profiles. The resistivity contrast between basement and basin and lateral discontinuity between basement terranes outline the geometry of the basins and the variation of the block physical properties and terrane of the Sul-Rio-Grandense shield. This information allowed to characterize and delimit the main structures, such as the Dorsal do Canguçu Shear Zone (DCSZ), the Passo do Marinheiro Shear Zone (PMSZ), and the depth of sedimentary cover of the onshore portion of the Pelotas Basin along the coast of the state of Rio Grande do Sul (RS), Brazil. The resistivity models extend 15 km deep, several kilometers below the top of the Precambrian basement. The top of the Precambrian basement varies from one profile to another from meters to kilometers and is covered in some places by packages of sedimentary rocks of different ages. The passive basin sediments of the Pelotas Basin can reach up to 4 km in thickness with structural control due to the inherited basement lineaments. Our MT data combined with data from wells and gravimetry data support a tectonic model for main structures of Sul-Rio-Grandense Shield in Neoproterozoic and for Phanerozoic sedimentary basin thicknesses.

前寒武纪移动带深部结构的研究对于确定显生宙板内盆地的构造演化至关重要。大地电磁 (MT) 方法为巴西南部被动边缘的主要深基底结构提供高分辨率二维 (2-D) 电阻率模型。我们通过应用沿四个剖面分布的 106 个 MT 站的数学反演获得了电阻率模型。基底和盆地之间的电阻率对比以及基底地体之间的横向不连续性勾勒出盆地的几何形状以及 Sul-Rio-Grandense 地盾的块体物理性质和地体的变化。这些信息可以表征和划定主要结构，例如 Dorsal do Canguçu 剪切带 (DCSZ)、Passo do Marinheiro 剪切带 (PMSZ)、以及巴西南里奥格兰德州 (RS) 沿岸 Pelotas 盆地陆上部分的沉积覆盖深度。电阻率模型深达 15 公里，在前寒武纪基底顶部以下几公里。前寒武纪基底的顶部从一个剖面到另一个剖面从几米到几公里不等，并且在一些地方被不同时代的沉积岩包裹。Pelotas 盆地的被动盆地沉积物厚度可达 4 公里，由于继承的基底线受到结构控制。我们的 MT 数据与井数据和重力测量数据相结合，支持了新元古代 Sul-Rio-Grandense Shield 主要结构和显生宙沉积盆地厚度的构造模型。