NZ’s plate margin

Review

• What do the spatial patterns of fossils like Lystrosaurus (page 8) tell us about natural processes from the past?

• What do the global patterns of spreading plate margins (page 5) tell us about natural processes at work now?

Key Ideas• New Zealand owes its

origins and present shape to tectonic processes

• These processes are directly responsible for NZ’s relief features

• The variety of volcanic landscapes found in NZ’s North Island relates to the downward movement of the subducting Pacific plate

A complex margin

• For the last 15-20 million years NZ has been situated along the margins of a collision zone

20 mm/yr

60 mm/yr

40 mm/yr

50 mm/yr

Plate boundaries• When two plates grind together they create

friction• This friction melts the crustal rock along the

margin, causes earthquakes and buckles and cracks the overlying plate (Australian)

• Magma varies according to its source along a subduction zone– Shallow magma contains more surface materials

• Feldspar, silica, water and gas– Deep magmas contain more mantle material

• Iron and magnesium

How is NZ affected by its location on a plate margin

• Look at page 14 and summarise the ways in which NZ has been affected by its plate margin location into one paragraph

• You can use diagram(s) to help you

Viscosity

• The viscosity (resistance to flow) of magma is related to its temperature and mineral content.

• This varies with depth– Magma forming close to the surface highly viscous• does not flow easily because it is cool and thick

– Magma forming at great depths is non-viscous• Flows easily because it is hot and liquid

Types of Lava

• Look at the table on page 16 of the text and copy into your book

• Use text on page 17 to add in examples of volcanoes that have erupted this lava type in NZ