Heterogeneous crust and upper mantle across the SE Brazilian Highlands and the relationship to surface deformation as inferred from magnetotelluric imaging

摘要

We provide evidence for lateral structural zoning of the crust and uppermost mantle across the southeast Brazilian Highlands from two-dimensional magnetotelluric (MT) imaging of a 250 km long NW-SE profile extending from the Archaean S?o Francisco craton to near the Atlantic coast. Our model shows the presence of an electrically resistive cover layer of variable thickness (2–20 km) and an underlying 5–15 km thick conductive marker horizon, atop a resistive segmented layer extending to 60–70 km depth. Two structurally different lithospheric provinces are suggested based on conductor geometry and lateral segmentation in the model. The northwestern half of the profile is characterized by flat to shallowly dipping crustal conductors (interpreted as a fold-and-thrust belt) while the southeastern half consists of major steeply dipping lithospheric conductors with spatially coincident high amplitude magnetic anomalies (interpreted as a strike-slip fault belt). The boundary between both provinces may be associated with a suture but lies 35 km NW of a previously suggested boundary between the Occidental and Oriental terranes. The marker horizon is coincident with a low P wave velocity layer and appears to be raised by about 5 km across a 85 km wide belt hosting a Neoproterozoic magmatic arc in the southeastern province. We propose a link between basement heterogeneity and surface deformation in the region.