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Geology of gold ore deposits 91

morphism. Immature sandstones and shales form phyllites, marbles and
quartzites evolve from limestone and quartz sandstones. The basement batho-
liths are metamorphosed into gneisses and migmatites. The old divergent
continental wedge of sediments and batholiths plus superimposed volcanoes is
uplifted along major thrust faults to form towering mountains such as the Andes
of South America and the Cascades in Northern America.

Continent-continent plate collision
Figure 2.14 is a schematic representation of a cross-section of the Earth showing
the components of subduction types of convergence that result in the collision of
two continents. The ocean has closed and mountain building has many of the
same elements as island arc-continent collision, hinterland, foreland, suture
zone, and a towering mountain range. There are, however, two foreland basin
clastic wedges, one filled with sediments from a volcanic arc the other from a
cordilleran mountain; and two suture zones of melange with a great variety of
igneous and metamorphic rocks.
The Himalayan Mountains of India were formed as the result of collision
between the Continent of India, which moved across the southern ocean to
collide with the Continent of Asia. The Himalayas are still being pushed up;
Mount Everest is rising two centimetres per year. Coincidentally with the rise,
the Himalayas are being denuded by very severe erosion due to the extreme
weather conditions.

2.14 Three stages of collision of two continents.