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.

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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