Electrical Structure of the Lithosphere From Rio de la Plata Craton to Paraná Basin: Amalgamation of Cratonic and Refertilized Lithospheres in SW Gondwanaland

Abstract

We conducted a magnetotelluric (MT) study from Paleoproterozoic Rio de la Plata Craton, in Uruguay, toward Paleozoic-Mesozoic Paraná Basin, in Brazil. The 850-km-long MT transect comprises 35 evenly spaced broadband electromagnetic soundings sites. In the Paraná Basin, 11 additional long-period measurements were acquired to extend the maximum depth of investigation. All data were inverted using two-and three-dimensional approaches obtaining the electrical resistivity structure from the surface down to 200 km. The Rio de la Plata Craton is >200-km thick and resistive (~2,000 Ωm). Its northern limit is electrically defined by a lithosphere scale lateral transition and lower crust conductive anomalies (1-10 Ωm) interpreted as a Paleoproterozoic suture at the southern edge of Rivera-Taquarembó Block. The latter is characterized by an approximately 100-km thick and moderate resistive (>500 Ωm) upper mantle. The Ibaré shear zone is another suture where an ocean-ocean subduction generated the 120-km thick and resistive (>1,000 Ωm) São Gabriel juvenile arc. Proceeding northward, a 70-to 80-km thick, 150-km wide, and inclined resistive zone is imaged. This zone could be remnant of an oceanic lithosphere or island arcs accreted at the southern border of Paraná Basin. The MT transect terminates within the southern Paraná Basin where a 150-to 200-km-thick less resistive lithosphere (<1,000 Ωm) may indicate refertilization processes during plate subduction and ocean closure in Neoproterozoic-Cambrian time. Our MT data support a tectonic model of NNE-SSW convergence for this segment of SW Gondwanaland.

Teleseismic P Wave Tomography Beneath the Pantanal, Paraná, and Chaco‐Paraná Basins, SE South America: Delimiting Lithospheric Blocks of the SW Gondwana Assemblage

“…The southern limit of the Paranapanema Block, as defined by Mantovani et al (), is roughly consistent with the decrease in the highest P ‐wave anomalies, but these reach the limit with the Riograndense Shield, where the boundary between them is marked by a low‐velocity anomaly. This low‐velocity anomaly is consistent with the high electrical‐conductivity anomaly presented by Bologna et al (), which, in both cases, indicates compositional and/or thermal (higher temperatures) changes in the lithosphere mantle, when compared to the cratonic regions, which present high velocities and low conductivities (or high resistivities), which is the behavior observed as we move towards the north. This low‐velocity anomaly could represent also the boundary between the Paranapanema Block and the RDLP Craton, consistent with the limit proposed by Rapela et al () and interpreted as a thinning of the lithosphere.…”

Aeromagnetic patterns in Southern Uruguay: Precambrian-Mesozoic dyke swarms and Mesozoic rifting structural and tectonic evolution

“…This last fact could suggest that it does not correspond to a deep-rooted structure. This observation is consistent with magnetotelluric data presented by (Bologna et al, 2019), which also fail in detecting this structure in depth. Fig.…”

“…594-584 Ma (Oyhantçabal et al, 2001(Oyhantçabal et al, , 2009. Magnetotelluric studies (Bologna et al, 2019) show that this sinistral shear zone has no significative expression in the lithosphere and does not represent a Neoproterozoic continental suture, as previously suggested (Bossi and Cingolani, 2009;Gaucher et al, 2011; among others).…”

“…1) is a complex collage of Archean to Neoproterozoic blocks, with different histories. It experienced a complex amalgamation since Paleoproterozoic times that ended with a Neoproterozoic orogenic event (Sánchez Bettucci and Rapalini, 2002 and references therein; Rossello et al, 2007;Sánchez Bettucci et al, 2010;Oyhantçabal et al, 2011;Masquelin et al, 2017;Núñez Demarco et al, 2018, 2019bBologna et al, 2019). Later, it suffered a Mesozoic extensional event related to the opening of the Atlantic Ocean.…”

“…Reactivation, inversion, deformation, displacement and obliteration of previous structures are common and not well understood. This makes it difficult to separate events and to understand their complex history (Masquelin et al, 2017;Núñez Demarco et al, 2018, 2019bBologna et al, 2019;among others).…”