Continental crust - long lived Lithosphere 2

What is the main mineral constituent of the upper mantle rock peridotite?

• Olivine

• Quartz

• Feldspar

• Calcite

Who discovered that the deep cratonic roots of the continents have chemical and physical characteristics that distinguish them from surrounding mantle rocks?

• Thomas H. Jordan

• Anne Peslier

• Isaac Newton

• Marie Curie

Describe how fragments of mantle peridotites are drawn up from great depths and preserved.

Why are cratonic roots thought to be more buoyant than the rest of the lithosphere?

• Due to the chemical composition of the minerals from which they are formed

• Because they are closer to the surface

• Because they contain more water

• Due to their higher temperature

What effect does an increase in water content have on olivine at high pressure and temperature?

• It weakens the structure, making it less viscous and more likely to 'creep'

• It strengthens the structure, making it more rigid

• It increases the melting point

• It causes olivine to turn into quartz

What is the maximum depth to which cratonic roots can persist into the mantle, according to the text?

• 250 km (155 miles)

• 500 km (310 miles)

• 100 km (62 miles)

• 400 km (248 miles)

Which process allows geologists to study materials from the base of the cratons?

• Analysis of xenoliths brought up by deep-seated extinct volcanoes

• Direct drilling into the mantle

• Satellite imaging

• Chemical weathering

Why is it difficult to obtain direct samples from the deep cratonic roots?

• No borehole can be drilled to such depths due to intense pressure and temperature

• The roots are too soft to sample

• There is too much water in the mantle

• The roots are radioactive

What is the main reason cratonic roots are resistant to erosion or deformation?

• Their effective viscosity or stiffness is much greater than typical asthenospheric rocks

• They are constantly replenished by volcanic activity

• They are made of ice

• They are located near the surface

How does the water content of olivine from deep cratonic xenoliths compare to that of typical asthenospheric rocks?

• It is much lower, less than 10 parts per million

• It is much higher, over 1000 parts per million

• It is the same as typical asthenospheric rocks

• It contains no water at all