Density and P‐wave velocity structure beneath the Paraná Magmatic Province: Refertilization of an ancient lithospheric mantle

Abstract

We estimate density and P‐wave velocity perturbations in the mantle beneath the southeastern South America plate from geoid anomalies and P‐wave traveltime residuals to constrain the structure of the lithosphere underneath the Paraná Magmatic Province (PMP) and conterminous geological provinces. Our analysis shows a consistent correlation between density and velocity anomalies. The P‐wave speed and density are 1% and 15 kg/m3 lower, respectively, in the upper mantle under the Late Cretaceous to Cenozoic alkaline provinces, except beneath the Goiás Alkaline Province (GAP), where density (+20 kg/m3) and velocity (+0.5%) are relatively high. Underneath the PMP, the density is higher by about 50 kg/m3 in the north and 25 kg/m3 in the south, to a depth of 250 − 300 km. These values correlate with high‐velocity perturbations of +0.5% and +0.3%, respectively. Profiles of density perturbation versus depth in the upper mantle are different for the PMP and the adjacent Archean São Francisco (SFC) and Amazonian (AC) cratons. The Paleoproterozoic PMP basement has a high‐density root. The density is relatively low in the SFC and AC lithospheres. A reduction of density is a typical characteristic of chemically depleted Archean cratons. A more fertile Proterozoic and Phanerozoic subcontinental lithospheric mantle has a higher density, as deduced from density estimates of mantle xenoliths of different ages and composition. In conjunction with Re‐Os isotopic studies of the PMP basalts, chemical and isotopic analyses of peridodite xenoliths from the GAP in the northern PMP, and electromagnetic induction experiments of the PMP lithosphere, our density and P‐wave speed models suggest that the densification of the PMP lithosphere and flood basalt generation are related to mantle refertilization. Metasomatic refertilization resulted from the introduction of asthenospheric components from the mantle wedge above Proterozoic subduction zones, which surrounded the Paraná lithosphere. The high‐density PMP lithosphere is presently gravitationally unstable and prone to delamination.

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

“…Both basins had very similar evolution with the first subsidence stage in the Paleozoic, and both had a significant magmatic event in the Mesozoic, producing large volumes of flood basalts. This difference in crustal thickness may be compensated by differences in the upper mantle, such as a thick lithospheric lid beneath the Paraná Basin with high velocities (Feng et al, ; Schaeffer & Lebedev, ; Rocha et al, ) and high density (Chaves et al, ), whereas beneath the Parnaíba Basin high Pn velocities were found only along a small 400‐ to 500‐km section in its center (Soares et al, ). This may imply that the cratonic block beneath the Parnaíba Basin is smaller and thinner compared with that of the Paraná Basin in the south.…”

Tectonic control of the oil-rich large igneous-carbonate-salt province of the South Atlantic rift

“…The results indicate that in the northern and central parts of the Parana magmatic province, where the thickest and largest volume of basalts were emplaced, lithospheric mantle down to 250-300 km is characterized by high-velocity perturbation (> 0.5 %) and high-density contrast (> 30 kg/m3). According to Chaves et al (2015) these results, when correlated with a geoeletrical model obtained by deep electromagnetic induction studies (GDS), which exhibits low-resistivity in relation to typical values obtained in cratons, preclude the idea of a cratonic block (Paranapanema) beneath the central Parana magmatic province. …”

“…Individual plumes such as Tristan da Cunha, along the eastern margin of the African large low shear velocity province (llsvp) (White & McKenzie, 1995;Torsvik, 2006Torsvik, , 2009) and decompression melting farther to the south (Gladczenko et al, 1997;Blaich et al, 2011;Stica et al, 2013) each played some role in this progressive breakup of Pangea from Triassic time. Chaves et al (2015) suggested delamination of the continental lithosphere; according to these authors, lowering of melting temperature may be caused by the presence of metasomatic fluids in the delaminated or detached continental lithosphere. A major pulse of heat flow from the Earth's core is suggested by the near-antipodal position of the SAMP to the early Cretaceous Ontong-Java Plateau in the Pacific.…”

“…Investigating the physical properties of the lithosphere and the mantle below the Parana magmatic province, Chaves et al (2015) obtained new density and P-wave velocity models to 1000 km depth by inverting residual geoid anomalies derived from EGM2008 after crustal, lower mantle and core effects being removed. The P-wave model was derived by inverting 8686 manually picked teleseismic travel-time delays, starting with an initial model and using the LSQR method.…”

Petrological and volcanological insights into acid lavas from the Paraná-Etendeka Magmatic Province on the surroundings of Guarapuava city, Paraná, Southern Brazil: a contribution of detailed textural characterization combined with in situ Sr isotopes in plagioclase phenocrysts

“…The same authors points to notable isotopic differences between the PEMP basalts and ocean islands along the Tristan da Cunha track, indicating a minor role of the plume. Recent geophysical investigation points to a high-density lithosphere underlying the PMP, attributed to a highly altered and fertile lithosphere (Chaves et al, 2016).…”