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Abstract

How the lithospheric structure of the coast-parallel orogenic belts in SE Brazil is related to the petroliferous offshore rifted margin is not well understood. We present a three-dimensional magnetotelluric (MT) resistivity model of the Southeastern Brazilian onshore-offshore margin from 174 long period and broadband amphibious MT soundings distributed in NW-SE profiles crossing orthogonally the regional coast-parallel Serra da Mantiqueira and Serra do Mar mountain belts. Dimensionality analysis from phase tensor (PT) along the two main profiles outline the character of the subsurface: i) Onshore, there is a marked three-dimensional behavior with spatially changes over Brasília (BrB) and Ribeira (ROB) Orogenic belts and the PT minimum phase varies over the periods suggesting segmentation in the crust and between the crust and mantle.; ii) Offshore, PT ellipses are mostly 1-D in nature for shorter periods with high minimum phases corresponding to thick conductive sediments in the Santos basin and low minimum phases marking the resistive basement. We undertook 3D inversion of the data incorporating topography/bathymetry. 3-D MT resistivity model shows a highly heterogeneous crust beneath the BrB and a major sub-lithospheric suture zone beneath ROB. Crustal conductivity anomalies distinguish a wide antiformal structure below the BrB and a megasynform structure below the ROB, which provide evidence for both compressional and extensional tectonic regimes beneath the Southeast Brazil.