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

Abstract

We present a new gravity map between 45°-70° W and 5°-40° S integrating open source terrestrial gravity data of Argentina with the South American Gravity Model 2004 (SAGM04), a 5 min-arc resolution gravity model. The Bouguer anomaly map reveals a 2,000 km long linear gravity feature from 15° S to 30° S at longitude 55° W, with a steep horizontal gradient separating two gravity domains. The eastern domain is the Paraná basin, with NE-SW trending Bouguer anomalies of-80 mGal in average. The western domain comprises the Chaco-Paraná, Chaco-Tarija and Pantanal basins, with circular positive anomalies of up to 20 mGal in amplitude. Previous seismic studies mapped a thinner crust of less than 35 km in the western domain and the present gravity models indicate a 10 to 20 kg/m³ denser crust. On the other hand, the eastern domain has a thicker crust of more than 40 km. Seismic tomography models also show P-and S-wave velocity reduction in the western domain whereas high-velocity characterises the Paraná basin. These geophysical data indicate that the gravity gradient marks a transition between two distinct lithospheres. The gravity gradient is associated with a tectonic feature referred to as the Western Paraná suture/shear zone. Granites of 530 to 570 Ma ages, located parallel or over the gravity gradient, suggest a Neoproterozoic to Early Cambrian age suture/shear zone, thus approximately synchronous and parallel to the Pampean belt. Sediment corrected residual gravity map and its vertical derivative allow us to define the limits of the Rio Apa, Rio de la Plata and Rio Tebicuary cratons. Their eastern and western limits are the Western Paraná suture and the Pampean belt, respectively. This study unravels Precambrian tectonic elements concealed by the Phanerozoic sedimentary basins adding new constraints for the amalgamation history of SW Gondwana. Research Highlights Gravity map reveals the Neoproterozoic 2,000 km long Western Paraná suture/shear zone Geophysical delimitation of the Rio Apa, Rio Tebicuary and Rio de la Plata cratons Gravity anomalies of the Amazonian and Rio Apa cratons are distinct New tectonic features of SW Gondwana final amalgamation revealed Key Words SW Gondwana; intracontinental basins; cratons; sutures; gravity Research Highlights Gravity map reveals the Neoproterozoic 2,000 km long Western Paraná suture/shear zone Geophysical delimitation of the Rio Apa, Rio Tebicuary and Rio de la Plata cratons Gravity anomalies of the Amazonian and Rio Apa cratons are distinct New tectonic features of SW Gondwana final amalgamation revealed

Deep Resistivity Structure of Basalt‐Covered Central Part of Paraná Basin, Brazil, From Joint 3‐D MT and GDS Data Imaging

“…4. Does the deep resistivity structure support or help improve our understanding of the previously observed seismic and potential field anomalies (Chaves et al, 2016;Dragone et al, 2017;VanDecar et al, 1995) as well as the heat flow anomalies (e.g., Hamza et al, 2005;Hurter & Pollack, 1996) in the study area?…”

“…In (a)–(f), the Paraná axial anomaly and coastal mantle anomaly (CMA) are shown to peak and fade out at different depths. In (c), the inset black box, red polygon shows the Western Paraná Suture and the dashed black line is another suture, both proposed by Dragone et al (). A possible offset to feature CMA is shown in (f) by the black dashed lines.…”

“…This is followed by joint MT and GDS inversion to image the deep crust and mantle but using the constraints derived for the upper crust. In section 5, we show similarities between our joint inversion model and the density and velocity models of Chaves et al () and also explain the anomalies observed by Dragone et al () and past workers in the region. The main conclusions from our studies are presented in section 6.…”

“…Some seismological studies have focused on Moho depth determination in South America as a way to better understand the geodynamics of the region and have led to revised Moho depth predictions (e.g., Assumpção, Feng, et al, 2013;Lloyd et al, 2010). There has been a renewed interest in regional-scale determination of the Moho depth using terrestrial and satellite gravity data (e.g., Dragone et al, 2017;Mariani et al, 2013;Uieda & Barbosa, 2017), but these are also conditioned on the revised seismological Moho depth predictions (e.g., Assumpção, Feng, et al, 2013). These studies were recently extended to examine the deeper lithosphere in the region and found densification (relatively high density and P wave velocity) anomalies in the lower crust and upper mantle to a depth of 250-300 km directly beneath the central part of Paraná basin (Chaves et al, 2016).…”

An Updated Crustal Thickness Map of Central South America Based on Receiver Function Measurements in the Region of the Chaco, Pantanal, and Paraná Basins, Southwestern Brazil

“…The exact mechanism for the extrusion of the magma is not known in detail; it could be related to a central source in the middle of the Paraná Basin or multiple sources spread throughout the entire province. Gravity data show a NE‐SW trending Bouguer high along the central axis of the Paraná Basin (e.g., Dragone et al, ), which had been interpreted as due to magmatic underplating in the lower crust related to the extrusion process. However, attempts to detect an underplated lower crust by seismic methods (An & Assumpção, , ; Julià et al, ; Shirzad et al, ) have not identified significantly higher velocities beneath the Paraná Basin.…”