{"id":558130,"date":"2025-08-25T20:46:47","date_gmt":"2025-08-25T23:46:47","guid":{"rendered":"https:\/\/revistapesquisa.fapesp.br\/?p=558130"},"modified":"2025-08-25T21:27:46","modified_gmt":"2025-08-26T00:27:46","slug":"map-exposes-oldest-structures-in-south-america","status":"publish","type":"post","link":"https:\/\/revistapesquisa.fapesp.br\/en\/map-exposes-oldest-structures-in-south-america\/","title":{"rendered":"Map exposes oldest structures in South America"},"content":{"rendered":"

Tomography techniques, like those used to examine inside the human body, have revealed an unexpected fragmentation of the layers up to 600 kilometers (km) below the earth\u2019s surface. The images led to the redefinition of boundaries, revealed deep structures about which only indications had previously existed, and reinforced the idea that surface mapping is insufficient for outlining the rocky skeleton of South America.<\/p>\n

The images at different depths are produced by analyzing different types of waves generated by earthquakes, also known as seismic tremors. Initially captured by devices called seismographs, they cross the interior of the earth at speeds which vary according to the density of the rocks: the speed is faster where the lithosphere\u2014the solid outermost layer of the earth\u2014is thicker, and cold and slower where it is thinner and hot. It is a way of seeing the boundaries of what are known as cratons, blocks of rock that extend for hundreds and thousands of kilometers, sometimes covered by sedimentary rocks or soil. Generally formed between 1 billion and 2 billion years ago, when the earth was still very hot, they form the framework of the geological structure of the continents, around which other rocky structures accumulate (see<\/em> Pesquisa FAPESP issue n\u00ba 188<\/em><\/a>).<\/p>\n

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Serra do Cip\u00f3 National Park<\/span>The Espinha\u00e7o mountain range, which extends for around 1000 km in the states of Minas Gerais and Bahia, marks the eastern edge of the S\u00e3o Francisco cratonSerra do Cip\u00f3 National Park<\/span><\/p><\/div>\n

In one of the most recent and comprehensive surveys, described in an article published in November in the journal Gondwana Research<\/em>, physician Bruna Chagas de Melo, from Belo Horizonte, and colleagues from the Dublin Institute for Advanced Studies in Ireland, showed that the Amazonian craton, until now seen as a single, oval structure, through the middle of which flows the Amazon River, may actually be made up of two parts, separated laterally at about 200 km below the surface.<\/p>\n

Also, in accordance with this study, the boundaries of another craton, the S\u00e3o Francisco craton, are broader and located more to the southwest than shown by previous mapping. Three ancient units of the continental geological structure, proposed by geologist Umberto Cordani, from the Institute of Geosciences of the University of S\u00e3o Paulo (IGC-USP), in the early 1980s, gained clearer contours. They are the Rio de la Plata craton, which covers parts of the state of Rio Grande do Sul, Uruguay, and Argentina, and two cratonic blocks, named because they are covered by sedimentary basins: the Parna\u00edba, in Piau\u00ed, and the Paran\u00e1 (or Paranapanema), located beneath the Paran\u00e1 River basin in the states of S\u00e3o Paulo and Mato Gross do Sul.<\/p>\n

An increased understanding of this ancient rocky structure\u2014at greater depths\u2014helps to detail both the geological and biological evolution of the continent. As the Andes mountain range formed to the west, it reversed the flow of the rivers, shaped the surface, and blocked moisture from the Atlantic, favoring the emergence of new species of plants and animals, especially in the Amazon region (see<\/em> Pesquisa FAPESP issue<\/em> n\u00ba 334<\/em><\/a>). It also helps explain the origin of mineral provinces, including the areas most likely to contain diamonds, which form at depths of at least 150 km, and reinforces the history of landscapes, such as those associated with volcanic activity, which occurs in regions with a thinner lithosphere.<\/p>\n

Particularly to the east of the Amazon and south of Par\u00e1, almost 2 billion years ago, there were dozens of volcanoes and rivers of lava flowing over the surface (see<\/em> Pesquisa FAPESP issues 81<\/a>, 174<\/a>, 250<\/a><\/em>). In more recent times, magma also rose in the regions occupied by Maraj\u00f3 Island, in Par\u00e1, and Dourados, in Mato Gross do Sul, and there are magma channels, although inactive, beneath the archipelagos of Fernando de Noronha, Trindade, and Martin Vaz.<\/p>\n

There are still clear signs of magmatism, such as the Pico de Cabugi Peak, in Rio Grande do Norte, which has a height of 590 m and preserves the shape of a volcano, and other more subtle examples. The municipality of Po\u00e7os de Caldas, in Minas Gerais, for example, is expanding on the edge of a volcanic crater, through which magma rose around 60 million years ago.<\/p>\n\n \n \n \n <\/picture>Alexandre Affonso \/ Revista Pesquisa FAPESP<\/span>\n

\u201cThe magma was only able to rise because the lithosphere was, and still is, thinner in this region, between the S\u00e3o Francisco craton and the Paranapanema block. A thinner lithosphere means that the asthenosphere, the hottest layer directly below the lithosphere, was shallower, enabling the fusion of rocks, at a depth of between 100 and 200 km,\u201d comments physicist Marcelo de Sousa Assump\u00e7\u00e3o, of the Institute of Energy and Environment (IEE) at USP and coauthor of the article in Gondwana Research<\/em>. He has been studying the movements of the earth\u2019s crust since the mid-1970s (see Pesquisa<\/em> FAPESP issues 53<\/a> and 256<\/a><\/em>), was Melo\u2019s master\u2019s degree advisor, and helped her take her PhD in one of the major international geophysics research centers, in Ireland.<\/p>\n

Melo arrived in Dublin in December 2018 with the intention of applying the method that her advisor, Russian geophysicist Sergei Lebedev, had developed to analyze large quantities of seismic data\u2014records of the waves created by earthquakes. In just a few months, she gathered information on approximately 970,000 seismic waves, resulting from around 300,000 tremors, recorded by 9,259 seismographic stations worldwide, including those in Brazil, collected since 1994, at depths of up to 600 km.<\/p>\n

\u201cIt\u2019s a formidable amount of data, I\u2019ve never seen anything like it,\u201d admires geologist Reinhardt Adolfo Fuck, professor emeritus at the University of Bras\u00edlia (UnB), who has been studying the evolution of the lithosphere in Brazil for 50 years (see<\/em> Pesquisa FAPESP issue n\u00ba 122<\/em><\/a>). \u201cThey took great care in making the necessary corrections and excluding what needed to be discarded.\u201d<\/p>\n

Six months later, at a congress in Vienna, Austria, Melo presented the first evidence that the Amazonian craton could be two, one to the north and another to the south of the Amazon River. \u201cI didn\u2019t see the entire block at any depth,\u201d she commented in November, reviewing her work.<\/p>\n

With another seismic wave analysis methodology, fewer data\u2014112 tremors and 1,311 seismic stations\u2014and also a lower maximum depth, of 500 km, geophysicist Caio Ciardelli had already raised the possibility that the deeper areas of each side of the craton had thinned, due to movements within the earth\u2019s interior, and had broken, as detailed in his PhD, completed in 2021 at USP\u2019s Institute of Astronomy, Geophysics, and Atmospheric Sciences (IAG), and in an article from January 2022 in the Journal of Geophysical Research: Solid Earth<\/em>. \u201cOther seismotomography results varied, showing either continuity or separation,\u201d says Assump\u00e7\u00e3o, who supervised Ciardelli\u2019s PhD and is currently undertaking a postdoctoral fellowship at Northwestern University in the USA. \u201cBruna settled the debate, by showing there was a thinning or wear along the Amazon River.\u201d<\/p>\n

Marcelo Rocha, a physicist from UnB, who has been working with tomography of the lithosphere since 2001, disagrees. \u201cShe didn\u2019t settle it. Any conclusion is still premature, because we have little data on the region, one of the least studied in Brazil. There are few seismographic stations there, and they are 800 or 1,000 km apart,\u201d he says. \u201cIn fact, the Amazonian craton is neither one nor two, but many, with different ages, ranging from 3.1 billion to 1 billion years.\u201d The fact that there are rocks with the same ages on each side, as verified decades ago by geologists, suggests that the craton must have once been a single block, that, at some point, split in two, at least on the surface, opening a valley that would later be occupied by the Amazon River.<\/p>\n<\/div>

\n \n \n \n <\/picture>Alexandre Affonso \/ Revista Pesquisa FAPESP<\/span><\/div>
\n

The group from Dublin argues that the magma may have risen during at least two periods, between around 550 million and 200 million years ago, through a fissure\u2014or rift\u2014in a thinner region of the lithosphere near Manaus, separating the two parts of the craton. Rocha, once again, disagrees: \u201cIt was not a complete rupture, crossing the entire craton, from east to west.\u201d Fuck adds: \u201cThe rupture did not progress, forming a sea between the two blocks, but gave rise to the sedimentary basins of the Amazon and Solim\u00f5es.\u201d<\/p>\n

Melo responds: \u201cWe don\u2019t know the exact shape and size of the rift or whether the lithosphere was already segmented beforehand, facilitating its spread in a certain direction.\u201d<\/p>\n

With the team from Dublin, she also redefined the boundaries and the shape of the S\u00e3o Francisco craton, limited, to the east, by the Espinha\u00e7o mountain range, which extends for around 1000 km in the states of Minas Gerais and Bahia, with a maximum altitude of 2,072 m. In this new version, instead of a single block, as indicated by geological surface measurements, the craton appears more elongated, with a deeper central region in the middle and two smaller regions, to the northeast and southwest.<\/p>\n

In the tomography, due to the limit of resolution, the Paranapanema cratonic block could be attached to the S\u00e3o Francisco craton, but it is still unclear. \u201cThe largest block just to the south of the S\u00e3o Francisco craton is too close to the central block for the tomography to be able to distinguish the two,\u201d says Melo. In the analyses of the S\u00e3o Francisco craton performed by Rocha\u2019s group and published in July 2019 in Geophysical Journal International<\/em>, the two blocks appear separated.<\/p>\n

Another divergence: Ciardelli identified the Paranapanema block as a single piece, while Melo saw it as fragmented. The conclusions differ because of the methodological approach, since the analyses relied on different seismic waves, better suited for defining the depth or width of the lithospheric blocks. \u201cIt will probably take a few years until we conclude which is the best model for analyzing geophysical data,\u201d remarks Rocha.<\/p>\n

Despite the uncertainties and indirect measurements, such studies represent an advance, by suggesting the probable shape of the blocks of rock hundreds of kilometers beneath the surface, far beyond our capacity to directly observe the interior of the earth. The deepest well, drilled from 1970 to 1989 on the Kola Peninsula in Russia, is 12.2 km.<\/p>\n

The story above was published with the title “600 km below the surface<\/strong>” in issue in issue 348 of february\/2025.<\/p>\n

Projects
\n1. <\/strong>The Pantanal, Chaco, and Paran\u00e1 basins (PCPB): Evolution and seismic structure of the crust and upper mantle (n\u00ba 13\/24215-6<\/a>); Grant Mechanism Thematic Project; Principal Investigator<\/strong> Marcelo Sousa de Assump\u00e7\u00e3o (USP); Investment<\/strong> R$7,188,833.62.
\n2<\/strong>.Waveform tomography in South America with spectral-element and adjoint methods (n\u00ba 16\/03120-5<\/a>); Grant Mechanism <\/strong>Doctoral Fellowship; Supervisor<\/strong> Marcelo Sousa de Assump\u00e7\u00e3o (USP); Beneficiary<\/strong> Caio Henrique Ciardelli; Investment<\/strong> R$275,045.61.<\/p>\n

Scientific articles<\/strong>
\nCIARDELLI, C. et al<\/em>. Adjoint waveform tomography of South America<\/a>. Journal of Geophysical Research-Solid Earth.<\/strong> Vol. 127, no. 2. Jan. 2, 2022.
\nCHAGAS de MELO, B. de et al<\/em>. The lithosphere of South America from seismic tomography: Structure, evolution, and control on tectonics and magmatism<\/a>. Gondwana Research. <\/strong>Vol. 138, pp. 139\u201367. Feb. 2025.
\nROCHA, M. P. et al<\/em>. Delimiting the Neoproterozoic S\u00e3o Francisco Paleocontinental Block with P<\/em>-wave traveltime tomography<\/a>. Geophysical Journal International<\/strong>. Vol. 219, no. 1, pp. 633\u201344. July 19, 2019.<\/p>\n","protected":false},"excerpt":{"rendered":"Tomography techniques redefine boundaries of rock structures formed billions of years ago","protected":false},"author":17,"featured_media":558131,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_exactmetrics_skip_tracking":false,"_exactmetrics_sitenote_active":false,"_exactmetrics_sitenote_note":"","_exactmetrics_sitenote_category":0,"footnotes":""},"categories":[159],"tags":[],"coauthors":[5968],"class_list":["post-558130","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-science"],"acf":[],"_links":{"self":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts\/558130","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/users\/17"}],"replies":[{"embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/comments?post=558130"}],"version-history":[{"count":6,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts\/558130\/revisions"}],"predecessor-version":[{"id":560841,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts\/558130\/revisions\/560841"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/media\/558131"}],"wp:attachment":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/media?parent=558130"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/categories?post=558130"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/tags?post=558130"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/coauthors?post=558130"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}