Geology of Brazil
Brazil is totally contained in the South American
Platform, whose basement is of very complex geologic evolution, that originated
in the Archean period. Brazil had its consolidation completed between the
Proterozoic Superior period and the beginning of the Palaeozoic period,
with the closing in the Brazilian cycle.
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Crystalline shields |
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Sedimentary basins |
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The basement of the South American Platform is essentially structured
on metamorphic rocks of amphibolite to granulite facies and granitoids
of Archean age, associated with the Proterozoic units that are represented
usually by folded strips of green schist facies and sedimentary and volcanic
coverings, (seldom metamorphosed) and several granitoids.
That basement is widely exposed in great shields, separated from each
other by fanerozoic coverings, whose limits extend to the neighboring countries.
Prominent are the shields of Guyana, Central Brazil and Atlantic.
The shield of Guyana extends to the north of the basin of Amazonas.
The shield of the Brazil-central, or Guaporé extends to the interior
of Brazil and south of that basin, while the Atlantic shield is exposed
in the oriental portion reaching the Atlantic border. These shields are
exposed in more than 50% of the area of Brazil.
On that platform were developed in Brazil, in stable conditions of ortho-plataform,
starting from Ordovician-Silurian, the sedimentary and volcanic coverings
that filled spatially three extensive basins with sineclisis character:
Amazonas, Paraíba and Paraná. Besides those basins, several
other smaller basins, including coastal basins and other sedimentary areas,
occur exposed on the platform.
Geomorphology
The relief of Brazil, in agreement with Aziz Ab'Saber's classification,
it is divided in two great plateau areas and three plain areas as follows:
Plateau of Guyana, embracing the mountainous area and the Amazon
North Plateau. Located in the extreme north of the country, it is an integral
part of the shield of Guyana, presenting crystalline rocks of the Precambrian
period. This area includes the highest elevation in Brazil - the Pico da
Neblina, with an altitude of 3,014 m.
Brazilian plateau, subdivided in Central, Maranhão-Piauí,
Northeastern Brazil, mountains and plateau of the East and Southeast, Southern
and Uruguayan-Riograndense, it is formed by quite worn crystalline lands
and sedimentary basins. It is located in the central part of the country,
and encompasses great areas of the national territory.
Plains and amazon low lands. Located in the North region of the
country, below the Plateau of Guyana, it presents three different altimetric
levels - valleys, constituted by lands of recent formation near the margins
of the rivers; fluvial terraces, with maximum altitudes of 30 m and periodically
flooded; and low-plateaus, formed by lands of Tertiary.
Plain of the Pantanal, located in the area west of the state of
Mato Grosso do Sul and Southwest of Mato Grosso, it is formed by lands
of Quaternary.
Plains and coastal low lands, accompanying the Brazilian coast from
Maranhão to the south of the country, it is formed by lands of the
Tertiary and for current lands of Quaternary.
It should be noted that the Brazilian relief doesn't present formation
of very high mountainous chains, prevailing altitudes are below 500 m,
since it was developed on an old geologic base, without recent tectonic
movements.
The information given here was extracted of the
site Brazilian Environmental
Mall
