Geological History of NZ
543 ma first signs of multicellular life in NZ
290ma first signs of terrestrial life in NZ
84ma NZ separated from Antarctic continent
65-50ma sea floor spreading in the Tasman Sea began
Plate tectonics
Evidence
– similarity between continental coastlines
– submarine margins of continents “fit”
– bands of similar geology can be aligned
eg Australia and Antarctica
- same fossil species found on the complimentary
continents
The plates of crust are floating on a viscous semi-molten layer
of mantle. At active zones (eg mid-ocean ridges) mantle
material brought near to the surface – crust grows on each side
of the ridge. This forces the plates apart.
-on new side- oceans are created
-on the old side of the plate – pressure
- collides with other plates
- raising mountain ranges
- subduction (under plate mantle recycled)
Continental crust, thicker, high proportion of light elements
eg.Al
Oceanic crust, thinner, rich in heavy metals eg. Fe, Mn, Mg
Continents less dense – float higher.
More evidence of Plate tectonics
Shallow earthquakes associated with mid-ocean ridges
Outer edges of tectonic plates associated with
-steep mountain ranges (Southern Alps)
- deep oceanic trenches (Tonga Kermadec trench)
- terrestrial volcanoes (Pacific ‘Ring of Fire”)
-deep earthquakes under the volcanoes
Sediments are thicker further away from the oceanic ridge
showing the older sea floor crust is further away from the
oceanic ridge.
The rise and fall of greater NZ
Cretaceous Period (144-65ma)
The Australia + India + Antarctica + NZ part of Gondwana
separates from Africa and rotates to take NZ to a near polar
position.
Greater NZ mountains –attract rain - eroded plains
Continental crust lowered.
NZ is attached to Australia but begins to separate from
Antarctica (80ma)
Tertiary period NZ = archipelago of loose islands (not good
for life)
Late Miocene (23-5ma) New period of mountain building –
raising South and North islands.
NZ land mass today
Modern NZ land mass straddles the boundary between the
Pacific and Indo Australian plates
South Island – Indo Australian plate is dipping under
North Island – Indo Australian plate moving over Pacific plate
Along NZ – West side being transported North. (alpine fault
gives numerous shallow earthquakes. N.Island fault runs
along the Kermadec ridge)
The changing climate
80ma rift between NZ and Antarctica – change in climate.
Antarctica originally centred on South Pole
-forested, cold temperate climate.
Ocean currents came between NZ and NZ and Antarctica.
Circumpolar current lowered the temperature of continents.
NZ cool and wet until middle Miocene