Igneous Rocks and Processes (A2)

Question 1

What are four factors which control melting?

Answer 1

Temperature, Pressure, Volatile content, Mineral mix

Question 2

Define Serpentinite

Answer 2

Chemically weathered gabbro or peridotite through the hydrothermal alteration of olivine

Question 3

What is an example of a fast spreading ridge?

Answer 3

East Pacific Rise

Question 4

What is an example of a slow spreading ridge?

Answer 4

Mid Atlantic Ridge

Question 5

Define Ocean Core Complex

Answer 5

Uplifted footwalls of very large offset, low angle normal faults that exhume lower crust and mantle rocks onto the sea floor at slow spreading ridges

Question 6

Define Hot Spot

Answer 6

Area of volcanism that is located far from plate boundaries. Produced by mantle plume

Question 7

Define Mantle Plume

Answer 7

Zones of hot solid mantle rising to the surface

Question 8

What are two characteristics of a mantle plume?

Answer 8

Hot and Solid

Question 9

What are four characteristics of eruptions associated with hot spots?

Answer 9

Low silica content, Low viscosity, Thin lava flows, Effusive eruptions

Question 10

Define Igneous Provinces

Answer 10

Huge outpourings of basalt from a fissure eruption e.g. Deccan Traps

Question 11

Define Flux Melting

Answer 11

If something can be added to the mantle, it could cause the solidus and liquidus temperatures to be lowered to the extent that the solidus could become lower than the geothermal gradient and result in partial melting without having to raise the geothermal gradient

Question 12

What is evidence of water being added to the mantle at subduction zones?

Answer 12

Volcanoes release water vapour when erupting

Question 13

Why can’t melt be generated at subduction zones via decompressional melting?

Answer 13

Decompressional melting occurs at divergent plate boundaries where hotter material rises to lower pressure. At subduction zones pressure increases with depth

Question 14

Define Crustal Anatexis

Answer 14

Partially melting of continental crust

Question 15

What are three potential mechanisms for making granite?

Answer 15

Magmatic processes, Underplating, Orogenesis

Question 16

What does 147Sm decay into?

Answer 16

143Nd

Question 17

Define Lopolith

Answer 17

Saucer shaped igneous body e.g. Bushveld Complex

Question 18

Define Laccolith

Answer 18

Forcible intrusion with flat bottom and rounded top

Question 19

Why are the minerals closer to the bottom of Bowen’s Reaction Series less likely to weather?

Answer 19

Formed at lower temperatures so more stable at earth’s surface

Question 20

Define Differentiation

Answer 20

The way in which you can change the composition of magma by separating it into two different fractions

Question 21

Define Fractional Crystallisation

Answer 21

The removal and segregation from the melt of mineral precipitates. This leads to a change in composition of a magma (always more quartz rich)

Question 22

Define Gravity Settling

Answer 22

Dense minerals fall to the bottom of the magma chamber or igneous body

Question 23

Define Cumulates

Answer 23

Layer at the bottom of the magma chamber/igneous body formed by gravity settling

Question 24

Define Assimilation

Answer 24

Addition of country rock to a magma will cause it to change composition. Rocks get incorporated via stoping

Question 25

Define Stoping

Answer 25

Magma forces its way through cracks then rips off part of the country rock to incorporate into melt

Question 26

Define Xenolith

Answer 26

Blocks of country rock not fully melted. Adds new elements into the magma when the xenolith is melted

Question 27

Define Enclave

Answer 27

Blob of magma with a different composition to the main host that is left after incomplete melting