Geoscience Reference
In-Depth Information
Figure 24.11
Tectonics and related land-
systems in the Himalayas and
East Asia region. Collision,
indentation and lateral extension
continue to elevate orogens and
pull rifts and ocean basins apart.
Source: Modified from Windley (1995)
Baikal rift
a
Tibet
A
Collision
Crustal extension
Extension fault
A-subduction
B-subduction
Lateral extrusion
Strike-slip faults
0
1000
km
subducting beneath North Island along the Kermadec-
Hikurangi trench, generating volcanic activity centred on
the andesitic volcanoes of Mount Egmont (2,518 m) and
Ruapehu (2,796 m), volcanic springs around the Lake
Taupo caldera and the Rotorua
ignimbrite
plateau. In
direct contrast, the Pacific plate takes South Island
over
subducting Indo-Australian plate. Both zones are
connected by the transform Alpine Fault which has been
the focus for uplift of the Southern Alps for the past 5 Ma
(
Figure 24.13
).
Mesozoic oceanic sediments, thrust and
metamorphosed against Palaeozoic granite batholiths,
form a steady-state cordillera 2-3.5 km high and 750 km
long. Peaks reach 2·5-3·8 km, including New Zealand's
highest, Mount Cook (3,764 m), in its 240 km-long core.
Rapid horizontal plate movement
45 mm yr
-1
is
consumed mostly in crustal shortening, creating an
asymmetrical range 100-150 km wide rising dramatically
from the west coast before falling a further 25-70 km
across the eastern coastal plain. With among Earth's
highest uplift rates at 2 cm yr
-1
, some blocks have been
elevated by 1 km (the height of Britain's highest moun-
tains today) in
250 ka, harnessing vigorous westerly air
streams to trigger intense Quaternary fluvial and glacial
erosion. The Southern Alps enjoy some of Earth's most
dramatic dissection and erosion rates and the size,
character and latitude of modern New Zealand make it a
reasonable analogue for parts of volcano-tectonic Britain
during the Lower Palaeozoic.
The Alpine landsystem
The Alpine landsystem develops its distinctive character
through the integration of glacial, cryonival, slope and
fluvial elements within the higher and spatially more
