craton, the stable interior portion of a continent characteristically composed of ancient crystalline basement rock. A shield is that part of a craton in which (usually) Precambrian basement rocks crop out extensively at the surface.

What makes a craton?

Cratons are generally found in the interiors of continents and are characteristically composed of ancient crystalline basement crust of lightweight felsic igneous rock such as granite. They have a thick crust and deep roots that extend into the mantle beneath to depths of 200 km.

How do you identify a craton?

Cratons have thick lithospheric roots. Mantle tomography shows that cratons are underlain by anomalously cold mantle corresponding to lithosphere more than twice the typical 100 km (60 mi) thickness of mature oceanic or non-cratonic, continental lithosphere. At that depth, craton roots extend into the asthenosphere.

How do shields and cratons form?

Where cratons are exposed, they form “shields” dominated by crystalline and metamorphic rocks; where younger, weakly deformed cover overlies cratonic basement, these areas are referred to as “platforms”. Shields and platforms are physiographic terms rather than tectonic entities.

What are the three major shields in South America?

The Amazonian (Brazilian) Shield on the eastern bulge portion of South America. Bordering this is the Guiana Shield to the north, and the Platian Shield to the south.

What is the difference between a craton and a shield?

craton, the stable interior portion of a continent characteristically composed of ancient crystalline basement rock. A shield is that part of a craton in which (usually) Precambrian basement rocks crop out extensively at the surface.

What is the minimum age of a craton?

Most continents contain a core of rock known as a craton, a sort of geologic nucleus at least a billion years old that acts like a stable base upon which continents build. Until now, though, the oldest continental crust found on Zealandia was dated to roughly 500 million years ago—relatively youthful in geologic terms.

Where is the craton plate?

One of those original continents is the North American craton, located mostly in the Canadian part of North America. The history of the Earth’s oldest continental plates is vague, because details of their interiors are hidden from geologists.

What is the difference between a craton and a mobile belt?

The cratons are relatively rigid blocks, but have a history of ductile and brittle deformations. The surrounding mobile belts are either high-strain, high-grade metamorphic belts or folded basins. Thus, the relatively rigid cratons are surrounded by more ductile zones of mobility.

What is a Craton and why is it important?

Cratons are pieces of continents that have been stable for a over a billion years. Economically they are very important – most of the world’s diamonds come from cratonic areas as do many other valuable deposits. Cratons are stable because they are strong.

How are shields formed?

Plate tectonics refers to the movement and collision of the Earth’s outer crust. When these crustal plates collide they may weld together, forming larger landmasses. The Shield can be thought of as a jigsaw puzzle of different crustal blocks, sometimes known as “provinces,” welded together over time.

How is a shield landform formed?

A shield’s rocks are igneous and metamorphic in origin and contain some of the oldest rocks on Earth. In zones of tectonic plate convergence, mountain systems that are actively building often mark the edges of shields. Younger-aged sedimentary rocks hide large areas of most shields.

How do clasts form?

Clastic sedimentary rocks are made up of pieces (clasts) of pre-existing rocks. Pieces of rock are loosened by weathering, then transported to some basin or depression where sediment is trapped. If the sediment is buried deeply, it becomes compacted and cemented, forming sedimentary rock.

What is the Brazilian Shield?

The Brazilian Shield extends over much of South America to the east of the Andean Chain, and is partly covered by Phanerozoic sedimentary rocks. The Neoproterozoic Brasiliano Cycle belts contain 5% of juvenile crust in central and southern Brazil, but are dominantly derived from reworking of older crust.

What are ancient shield areas?

A shield is a large area of exposed Precambrian-age crystalline igneous and high-grade metamorphic rocks that form tectonically stable areas. In all cases, the age of these rocks is greater than 570 million years and sometimes dates back 2 to over 4 billion years.

How many continental shields are there in the world?

The Six Geological Provinces and Continental Shield. The entire Earth has been divided into several Geological Provinces on the basis of their origin.