Which is the oldest mountain of South America continent ?

Question

UnlockIAS · Accepted Answer

Correct — D, Pacaraima. The Pacaraima or Pakaraima Mountains run for over 800 kilometres from west to east across southern Venezuela, northern Brazil and southwestern Guyana, forming the watershed between the Orinoco basin to the north and the Amazon basin to the south and marking long stretches of the Brazil–Venezuela and Brazil–Guyana borders. Geologically they sit on the Guiana Shield, one of the three cratons of the South American Plate and a Precambrian formation about 1.7 billion years old. The range itself is a sandstone plateau resting on horizontal Precambrian strata — the Roraima Supergroup, whose quartz sandstones, quartzites and conglomerates are dated to roughly 1.8 to 1.4 billion years — and its oldest basement rocks are older still, the Archean gneisses of the Imataca Complex. Erosion of that sandstone has carved the plateau into the flat-topped table mountains the region is famous for, the tepuis, of which Mount Roraima at 2,810 metres, ringed by 300-metre cliffs and standing at the tri-point of Brazil, Guyana and Venezuela, is the best known. Nothing else on this page is remotely as old. The Andes, printed here as 'Andese Mountain', are the youngest large range on the continent — an active fold belt still being pushed up by the subduction of the Nazca plate, with most of its uplift belonging to the Cenozoic, the last few tens of millions of years. Set 50 million years beside 1,700 million and the comparison is not close. Note the honest limit of this answer. The Tumucumaque uplands, printed here as 'Turmuc-Humuk', sit on the same Guiana Shield and share its Precambrian basement, so they cannot be excluded on the age of the rock alone; they are excluded because they are a low eastern extension with no comparable claim attached to them, while it is Pacaraima and Roraima that geological and reference sources single out for extreme antiquity.

Why the other options are wrong — (a) The Andes — printed here with the Commission's own spelling — are the obvious answer and the wrong one, because they are the continent's YOUNGEST major range, not its oldest. They run some 7,000 kilometres down the western edge of South America and are still rising, thrown up by the subduction of the oceanic Nazca plate beneath the South American plate; the belt is seismically and volcanically active along most of its length. Size and fame are not age.  (b) The Brazilian Highlands do rest on ancient cratonic basement — the Brazilian Shield is the second of the continent's three cratons — but they are described in physical geography as a plateau rather than as a mountain range, and their present relief owes much to Mesozoic basaltic outpourings and later uplift and erosion. The option is also a loose name rather than a recognised range.  (c) The genuine near-miss, and the reason this answer is argued rather than asserted. The Tumucumaque range, printed here as the Commission spells it, lies on the same Guiana Shield along the Brazil–Suriname and Brazil–French Guiana border and shares the same Precambrian basement. It is excluded not on rock age but because it is a low eastern extension of the uplands with no documented claim to being the continent's oldest range, while the Pacaraimas carry that claim through the Roraima Supergroup and the tepuis.

Concept: South America divides into four great physical regions, and holding them is worth more than any single fact about them. In the west run the Andes, a young Cenozoic fold belt raised by plate subduction. In the north-east lies the Guiana Shield, with its higher ground the Guiana Highlands, a 1.7-billion-year-old Precambrian craton carrying the Pacaraima Mountains, the Tumucumaque uplands and the tepuis. In the east and south-east lies the Brazilian Shield, the second ancient craton, surfacing as the Brazilian Highlands. Between the two shields lies the Amazon basin, a vast sedimentary trough drained by the world's largest river by volume. The Guiana Highlands are also the source of some of the world's most famous waterfalls — Angel Falls in Venezuela, the highest uninterrupted waterfall on Earth, and Kaieteur Falls in Guyana, which drops from the Pacaraima plateau itself.

State PCS 2025 Q18 — Geography PYQ with Answer

State PCS 2025 Q18 — Geography PYQ with Answer