Paraguay‐Araguaia Belt Conductivity Anomaly: A fundamental tectonic boundary in South American Platform imaged by electromagnetic induction surveys

Abstract

[1] We discovered and mapped a 1200 km-long zone of enhanced electrical conductivity through a large array of magnetometers, over a narrow corridor parallel to the Paraguay and Araguaia belts which surround the Amazon craton. The anomaly has been further studied using magnetotelluric measurements made along a 300 km profile crossing the Paraguay belt; modeling shows the anomaly at this location as a very strong 100 km-wide upper-crust to mid-crust conductor, located under a region where surficial rocks show an increase in deformation and metamorphism within the belt. From the high conductivity of the anomalous structure, its observed geometry and surface rock exposures, the most likely interpretation of its source is graphitized biogenic material in metasediments, now deeply underthrust in a Neoproterozoic or Early Cambrian suture zone. This result strongly supports the hypothesis that the collision between the Amazon plate and the western Paran a block has probably closed an ocean in the Paraguay belt region, contrary to former propositions of an ensialic evolution for this belt. Although the precise age of this ocean closure have been a matter of debate, our finding significantly constrains the tectonic setting of West Gondwana amalgamation involving the Amazon plate and its surrounding blocks.

Imaging three‐dimensional crustal conductivity structures reflecting continental flood basalt effects hidden beneath thick intracratonic sedimentary basin

“…Transient geomagnetic variations were recorded with three‐component fluxgate magnetometers [ Chamalaun and Walker , ] in several array deployments between 2002 and 2006, yielding a total of 212 sites in central and southern Brazil [ Bologna et al, ]. At each array deployment, the magnetic fields were recorded over periods of at least 6 weeks using a 60 s sampling interval, with at least one station common to two adjoining arrays being used as reference for calculation of the VTF.…”

Crustal framework of the northwest Paraná Basin, Brazil: Insights from joint modeling of magnetic and gravity data

“…This tectonic relief first resulted from the closing of a Precambrian ocean, limited by two crustal domains. Various authors have discussed the existence of this ocean Fuck, 1987, 1992;Brito Neves and Cordani, 1991;Almeida et al, 2000;Brito Neves et al, 2009;Cordani et al, 2009a,b;Cordani et al, 2010;Cordani et al, 2013;Bologna et al, 2014;Cordani et al, 2013;Brito Neves et al, 2014), while its association and/or relationship with the TBL is sometimes addressed indirectly or secondarily. We believe that an ancient suture zone was intensely reworked in the study area sector of the TBL.…”

Western Paraná suture/shear zone and the limits of Rio Apa, Rio Tebicuary and Rio de la Plata cratons from gravity data

“…Brazil (Bologna et al, 2014;Padilha et al, 2015), and regional seismological studies (Feng et al, 2007;Assumpção et al, 2013;Rosa et al 2016). This integration provides a more robust lithospheric physical model for this segment of the South American plate.…”