The Río de la Plata craton is one of the five craton

Craton

A craton is an old and stable part of the continental lithosphere. Having often survived cycles of merging and rifting of continents, cratons are generally found in the interiors of tectonic plates. They are characteristically composed of ancient crystalline basement rock, which may be covered by...

s (ancient nuclei) of the South American continent

Continent

A continent is one of several very large landmasses on Earth. They are generally identified by convention rather than any strict criteria, with seven regions commonly regarded as continents—they are : Asia, Africa, North America, South America, Antarctica, Europe, and Australia.Plate tectonics is...

. The other four cratons are: Amazonian, São Francisco

Sao Francisco craton

The São Francisco craton is located in the eastern part of South America. Outcrops in the Brazilian states of Minas Gerais and Bahia.It includes a number of different blocks of the Archean basement, separated by orogenic belts. The belts are characterized by sediment basins and passive continental...

, Río Apa and Arequipa–Antofalla

Arequipa–Antofalla craton

The Arequipa-Antofalla craton or terrane is a basement unit underlying the central Andes in northwestern Argentina, western Bolivia, northern Chile and southern Peru. The Arequipa-Antofalla craton collided and amalgamated with the Amazonian craton about 1000 Ma ago during the Sunsás orogeny....

.

It crops out

Outcrop

An outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. -Features:Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficial deposits are covered by a mantle of soil and vegetation and cannot be...

 in southern Uruguay

Geology of Uruguay

The geology of Uruguay combines areas of Precambrian-aged shield units with a region of volcanic rock erupted during the Cretaceous and copious sedimentary facies the oldest of which date from the Devonian...

 and parts of Argentina

Argentina

Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...

. Crystalline rocks of the Río de la Plata Craton are dated between 2200 and 1700 million years ago, such as rocks in Uruguay which are dated at 1790 ±5 Ma. Dikes

Dike (geology)

A dike or dyke in geology is a type of sheet intrusion referring to any geologic body that cuts discordantly across* planar wall rock structures, such as bedding or foliation...

 trending ENE in the same area are dated by argon-argon dating

Argon-argon dating

Argon-argon dating is a radiometric dating method invented to supersede potassium-argon dating in accuracy. The older method required two samples for dating while the newer method requires only one...

at 1727 ±10 Ma. The craton has a size of about 20,000 square kilometres.