Main points

Question 1

Hydrothermal activity

Answer 1

 Magma cools and solidifies – shrinks 
 Cracks and fissures open up 
 Mineral-rich fluids
 Concentrations of low temperature and incompatible elements 
 Crystallise in veins

Question 2

Hydrothermal Circulation

Answer 2

 Cold sea-water penetrates into cracks and fissures in the ocean crust
 Waters heated at depth by magmatic processes and minerals from host rock become dissolved
 Hot mineral-rich waters are buoyant and rise back to sea-floor
 White and black smokers

Question 3

Fractional crystallisation (island arcs)

Answer 3

o Water in the subducted ocean lithosphere ‘boils off’ from hydrous minerals
o Released water and soluble elements rise
o Slab of subducted peridotite, basalt and sediments melts to produce basaltic magma with enrichment of soluble elements
o On way to the surface the melt cools with crystallisation of silica poor minerals
o silica content of the remaining melt rises resulting in andesitic magma.

Question 4

Magmatic processes

Answer 4

• fractional crystallisation

- immiscibly liquids

Question 5

Ore formations

Answer 5

• magmatic processes

- hydrothermal activity