Historical Geology Understanding Our Planet\'s Past

ated on an oceanic plate retain their shapes until they collide and accrete to a

continent. They are then subjected to crustal movements that modify their

overall dimensions.The assemblage of terranes in China is being stretched and

displaced in an east-west direction due to the continuing squeeze India is

exerting onto southern Asia as it raises the Himalayas.

Granulite terranes are high-temperature metamorphic belts formed in

the deeper parts of continental rifts. They also comprise the roots of moun-

tain belts created by continental collision, such as the Alps and Himalayas.

Northof the Himalayas is a belt of ophiolites, which marks the boundary

between the sutured continents.Terrane boundaries are commonly marked by

Figure 73Upper
Devonian radiolarians
from the Kandik Basin,
Yukon Region, Alaska.
(Photo by D. L. Jones,
courtesy USGS)

Historical Geology