ophiolite belts, consisting of marine sedimentary rocks, pillow basalts, sheeted
dike complexes, gabbros, and peridotites.
Terranes also played a major role in the creation of mountain chains along
convergent continental margins. For example, the Andes appeared to have been
raised by the accretion of oceanic plateaus along the continental margin of South
America.Along the mountain ranges in western North America, the terranes are
elongated bodies due to the slicing of the crust by a network of northwest-trend-
ing faults. One of these is the San Andreas Fault in California, which has under-
gone some 200 miles of displacement in the last 25 million years.
Around 500 million years ago, North America was a lost continent.
South America, Africa, Australia, Antarctica, and India had assembled into the
supercontinent Gondwana. However, North America and a few smaller con-
tinental fragments were drifting freely on their own. At this time, North
America was situated a few thousand miles off the western coast of South
America, placing it on the western side of Gondwana.About 750 million years
ago, North America lay at the core of an earlier supercontinent called
Rodinia,when Australia and Antarctica bordered the west coast of the North
American continent.
North and South America apparently abutted one another at the begin-
ning of the Ordovician (Fig. 74), placing what would be present-day Wash-
ington, D.C., close to Lima, Peru.A limestone formation in Argentina contains
Figure 74North
America (top) abutted
South America (center)
during the early
Ordovician.ORDOVICIAN VERTEBRATESAFRICASOUTH
AMERICANORTH
AMERICAAUSTRALIAINDIA BALTICA