Plate Boundaries And Igneous Processes

Question 1

What creates the rheid anthenosphere?

Answer 1

Partial melting within the mantle. Not enough to classify it as a liquid. Pressure allows material to remain solid due to particle compaction

Question 2

What is geothermal gradient?

Answer 2

The change in temperature with depth (C/Km)

Question 3

What are convection currents?

Answer 3

They help with rock movement within the mantle. Happens because of heat transfer from the core to the lower mantle.
Rock gets hotter, expands (less dense) and rises. Here it gets cooler, contracts (more dense) then sinks.

Question 4

What is adiabatic heating?

Answer 4

Areas become hotter, despite no change in energy.
Contraction = heat energy shared over smaller volume (no gained energy). So the rock appears hotter

Question 5

What is adiabatic cooling?

Answer 5

Expansion = heat energy shared over larger volume (no energy loss). Rock appears to cool

Question 6

What is an adiabatic system?

Answer 6

No heat energy enters or leaves the system.
Happens in the mantle.

Question 7

How does partial melting happen?

Answer 7

Rising magma experiences a decrease in pressure = expansion = reduction in temp with the loss of heat as energy used to move particles apart. Melting occurs because melting point decreases as pressure decreases

Question 8

What are the 6 causes for magma formation at Earth’s surface?

Answer 8

Divergent boundary
Hotspots
Subduction zones
Oceanic-oceanic boundary
Continental-oceanic boundary
Continental-Continental boundary

Question 9

How is magma formed at divergent plates boundaries?

Answer 9

Mainly seen as MORs (e.g. MAR).
Mainly due to decompression melting by pressure release. As it stretches and thins, asthenosphere upwell and pressure reduced (lower MP).
Partial melting of ultramafic peridotite produces mafic magma.
Basalts are produced, usually as pillow lava. Dolerite sills and dykes below

Question 10

How is magma formed at hotspots?

Answer 10

Evidence of mantle plumes.
Magma rises from deep - decompression melting. Plumes carry heat upward in narrow rising columns of hot material, which spreads out when plume head reaches lithosphere.
Lower pressure = decompression + partial melting of mantle peridotite. Forming enormous volcanoes of basaltic lava

Question 11

How is magma formed at subduction zones

Answer 11

Oceanic crust present.
Magma production here must occur under ocean. Some water dragged down during subduction. Presence of water lowers melting point of minerals. This called flux melting