What is the Barberton Greenstone Belt?

About Barberton Greenstone Belt

• It is situated on the eastern edge of the Kaapvaal Craton in South Africa.
• It is known for its gold mineralisation and for its komatiites, an unusual type of ultramafic volcanic rock named after the Komati River that flows through the belt. 
• Some of the oldest exposed rocks on Earth (greater than 3.6 Ga) are located in the Barberton Greenstone Belt of the Eswatini–Barberton areas, and these contain some of the oldest traces of life on Earth, second only to the Isua Greenstone Belt of Western Greenland.
• The Makhonjwa Mountains make up 40% of the Baberton belt.
• Geological sampling indicates that some rock formations in these mountains are 3.2 to 3.6 billion years old.

What are ultramafic rocks?

• Ultramafic (or ultrabasic) rocks are dark-colored igneous and meta-igneous rocks that are rich in minerals containing magnesium and iron ("mafic" minerals) and have a relatively low content of silica.
• They are generally composed of more than 90 percent mafic minerals—that is, they have a high content of magnesium oxide (more than 18 percent MgO) and iron oxide (FeO). Their silica content is less than 45 percent, and their potassium content is low.
• The Earth's mantle is thought to be composed of ultramafic rocks.
• Most of the exposed ultramafic rocks have been found in orogenic (mountain-forming) belts. 

Q1) What are Igneous Rocks?

Igneous rocks are one of three main types of rocks (along with sedimentary and metamorphic), and they include both intrusive and extrusive rocks.Igneous rocks form when magma (molten rock) cools and crystallizes, either at volcanoes on the surface of the Earth or while the melted rock is still inside the crust. All magma develops underground, in the lower crust or upper mantle, because of the intense heat there. Igneous rocks can have many different compositions, depending on the magma they cool from.

Source: Oldest evidence of earthquakes found in strange jumble of 3.3-billion-year-old rocks from Africa