continent and deposited the formerly submerged rocks onto the present west
coast of Norway. Slices of land called terranes residing in western Europe
migrated into the Iapetus from ancient Africa. In the same manner, slivers of
crust from Asia traveled across the ancient Pacific Ocean called the Pantha-
lassa, Greek for “universal sea,” to form much of western North America.
A large portion of the Alaskan panhandle, known as the Alexander Ter-
rane,began its existence as part of eastern Australia some 500 million years
ago.About 375 million years ago, it broke free from Australia, traversed the
proto–Pacific Ocean, stopped briefly at the coast of Peru, slid past California,
and rammed into the upper North American continent around 100 million
years ago. The entire state of Alaska is an agglomeration of terranes that were
pieces of ancient oceanic crust.Terranes are well exposed in the Brooks Range
(Fig. 71), a major east-west–trending mountain belt that makes up the spine
of northern Alaska. Basaltic seamounts that accreted to the margin of North
America traveled halfway across the ocean that preceded the Pacific.
Terranes (Fig. 72) are fault-bounded blocks. They range in size from
small crustal fragments to subcontinents, with geologic histories markedly dif-
ferent from those of neighboring blocks and of adjoining continental masses.Figure 71Steeply
dipping Paleozoic rocks of
the Brooks Range,
Anaktuvuk district,
Northern Alaska.
(Photo by J. C. Reed,
courtesy U.S. Navy and
USGS)
Historical Geology