Brazil Geology 1

Brazil Geology and Morphology Part 1

According to, a salient feature of the Brazilian relief is the contrast between the area of ​​high lands, very ancient, which is commonly given the name of Brazilian Plateau, and the region of low lands, mostly of more recent origin, indicated by the name of Amazonian lowland. But even a cursory examination of the map soon leads to the distinction of two other highland areas in the Brazilian area, the Guianas plateaus and the Atlantic ranges, and two other lowland areas, the Paraguayan Depression and the coastal plain.

Of the three high land areas, the one which, due to its structure and geographical position, is called massiço central (“Brasilia”, massif or shield of South America) is by far the largest. Mainly constituted in its central part and in its eastern and southern sections of archaic rocks (gneiss or granite), which attest to its belonging to a primordial conitinent “brasiletiopico” (see South America), the central massif, extended over an area of about 3 million square kilometers, it offers mainly in its western, northern and Greek sections, tabular mountains formed almost exclusively of sandstone. Chapadas or chapadões these are precisely the extensions of slightly inclined sandstones that rest on crystalline rocks and primary folded deposits, emerging here and there in torres and torrinhas, clearly identified by erosion. The limits of the massif or complex of plateaus which, in its highest part, has altitudes ranging between 800 and 1400 meters, and extends for more than 3200 km. from west to east and for about 2750 from north to noon, they are almost always clearly marked by escarpments that determine jumps and waterfalls in the watercourses, such as those of Madeira along the western edge, and those of Paulo Affonso, on the São Francisco, along the eastern edge The reason for the contrast between the flat expanses prevalent in the massif and the steep escarpments at its edges can be traced to the coexistence of forms of various ages in a terrain of equal geological structure.

Both the central massif and the Guianas rialto rest on the same crystalline base of ancient granites and gneiss, so we can speak of a Brazilian Guian rialto (the eastern anti-country of geologists, extreme western region of the continent of Gondwana), which only in very recent times has reached its current level, following vertical thrusts. The Guiana rialto has morphological characteristics such as to make it very difficult to delimit the action of successive erosion cycles and that of fractures that displaced and altered the primitive continuous surface. It is separated from the Amazon basin by a series of isolated massifs of granite and gneissic rocks, divided by low thresholds through which one passes from the side of the Rio Branco to that of the Essequibo; these massifs, which have not very remarkable different heights (1500 m. Serra de Acarahy, 800 m. M. Tumuc-Humac), give way to the west to an enormous layer of sandstone that covers the archaic rocks. Here we meet the Roraima plateau which rises, according to the most recent calculations, to 2620 m. and that it is a characteristic tabular block of pink sandstone, the southern wall of which drops precipitously to the extreme northern border of Brazil.

Morphologically it constitutes a region in itself, at the SE edge. of the central massif, the complex of reliefs with general direction SO.-NE., in some stretches rising directly from the sea, in other stretches bordered by a coastal plain of a few kilometers and which is given the name of maritime or eastern system, while the whole of the vast plateaus in the watershed area between the Amazons, the Tocantins and Paraguay and between the San Francisco and Paraná is called the centralor Goyano system.

With the name of maritime system, the Serra do Mar and the da Mantiqueira are generally indicated.

The first denomination in the strict sense is typical of a short area between the 25th and the 26th parallel, but in a broad sense it is also applied to indicate the Serre do Paranapiacaba, Cadia and Geral, i.e. the entire outer escarpment of the plateau in the section south-east between the state of Rio de Janeiro and that of Rio Grande do Sul, i.e. between the 22nd and 30th parallel, where the coastal reliefs actually take on the character of an impervious chain, justifying the name of greenhouse with which they are commonly distinguished, although in Brazil the chapadões or taboleiros of the interior are also called serra, which do not have the character of a chain at all.

The Serra da Mantiqueira rises north of the tropic with direction OSO.-ENE., Separated from the Serra do Mar by the Tieté and Parahyba do Sul valleys: the Grecale section joins the southern offshoots of the Serra do Espinhaço (which forms the east of the upper S. Francisco valley), while in the libecial part it includes the Itatiaya massif, an important hydrographic node, which culminates in the Agulhas Negras, climbed in 1871 by the botanist Ghasiou who assigned the supreme peak the altitude of 2713 meters, while it would rise to 2979 m. according to Orville Derby; recent calculations would instead give it a height of 2790 m. The mountain mass of Itatiaya, which was until now considered the peak of the whole of Brazil, is surpassed, according to recent measurements, by the Pico da Bandeira (M. Caparão: m. 2861) in the so-called Serra Geral,

Brazil Geology 1