NZ Geology Flashcards
What two geological layers are considered in tectonic plate theory?
Lithosphere (outside), asthenosphere (deep)
Outline the differences between the lithosphere and the asthenosphere.
Lithosphere = cooler, rigid, asthenosphere = hotter mechanically weaker.
Outline how tectonic drifting occurs. Comment on its geographic impact in the short and long term.
Due to the relative fluidity of the asthenosphere, the rigid lithosphere “floats” on top of it. The lithosphere is divided into tectonic plates which move over time. In the short-term, tectonic drifting can cause earthquakes which are damaging for humans in the short term, while over many millions of years tectonic drifting can divide or amalgamate continents.
Define the two types of lithospheres. Discuss the difference in density in the two types and comment on the impacts of this difference.
Continental and oceanic lithosphere. Oceanic lithospheres are denser than continental lithospheres because of their greater mafic content, causing oceanic lithospheres to generally lie below sea level while the continental lithospheres lie above sea level.
What are all seven main tectonic plates? Which two lie over New Zealand?
African, Antarctic, Australian, Eurasian, North American, South American, Pacific. Australian and Pacific plates lie over New Zealand.
Outline the timeline of super-continents.
1000 million years ago = Rodinia formed.
600 million years ago = Rodinia broke apart.
Pangea formed from these fragments which later split up into Laurasia and Gondwana.
What are the three types of plate boundary?
Transform = grind past each other.
Divergent = slide apart from each other.
Convergent (active margins) = slide towards each other.
What process may occur in an active margin (convergent boundary)?
A subduction zone might form if one plate slides under the other, or orogenic belt if they collide and compress.
Outline how earthquakes occur at transform faults.
Friction opposes the lateral motion of plates at transform faults. Eventually the stress forces overcome the slipping point of the rocks, and massive amounts of energy is released.
Discuss features of the alpine fault.
The alpine fault is a transform fault between the Australian and Pacific plates lying over the Southern Alps in New Zealand. The last major earthquake caused by the Alpine fault was in 1717 AD and scientists predict that another may occur in the next 50 years.
Comment on the trends of earthquakes that occur at transform faults.
They are usually shallow (<25km) and small in magnitude (<8.5).
Explain how a hotspot forms at a divergent boundary. Explain any consequences to renewable energy.
As the two plates diverge, the space left is filled molten asthenospheric material. Large convective cells may bring this hot material near the surface to break apart the lithosphere, forming a hotspot. Hotspots can allow efficient harvesting of geothermal power.
Outline how seafloor spreading occurs.
Divergent boundaries causes plate separation and a new crust to fill in the gap. The relative motion between the two sides of the boundary is seafloor spreading.
Outline how an oceanic trench forms.
When two oceanic plates, the denser one will be subducted under the other. As the subducted plate is driven into the asthenosphere, a trench forms at the point of subduction.
Outline how plate convergence can form a mountain range.
When two continential plates converge, neither is usually subducted because continental plates have low densities and resist downwards motion into the asthenosphere. The crust then buckles and is pushed upwards, forming a mountain range.
