I. Introduction: The Origin and Shaping of Continents
A. Permanency of continental lithosphere: once it forms, it rarely
gets subducted (too buoyant)
B. Basic structure of continents
1. Craton: continental shield, platform: Interior of the continent
2. Continental borders: mountains, coastal plains, continental
shelves: edges of the continent
II. Very Early History of North America
A. 4.6-2 billion years ago
1. Original Earth was probably Moon-like
2. Differentiation of Earth (Iron Catastrophe)
B. Early continents
1. Many (hundreds?) of microcontinents
2. By about 2 billion years ago, these microcontinents all had
been swept together and formed first supercontinent "Pangea
I"
C. By about 1.3 b.y.a., Pangea I broke up, but North American
craton stayed together and has remained basically intact
III. Late Precambrian and Paleozoic 1 b.y.a.-260 m.y.a.
A. Series of collisions with South America, Africa and Europe
build the Appalachian Mts. in 3 stages
B. When continents separate, pieces from one sometimes remain
stuck on the other continent
C. Interior of N.A. craton flooded by inland sea that rose and fell,
depositing the platform rocks, including vast Pennsylvanian swamps that
formed coal deposits
IV. Mesozoic ("Age of reptiles and dinosaurs") 260-65 m.y.a.
A. Separation of continents, opening of modern Atlantic Ocean
B. Small pieces of Europe and Africa stayed stuck to the N.A.
continent (Florida, some of East Coast)
C. Small pieces of N.A. rode off with Africa and Europe
D. Again, the interior of N.A. was flooded
E. The building of western North America: subduction zone and
accretion of displaced terranes
VII. Cenozoic action (most recent)
A. Subduction continues off west coast
B. A mid-ocean ridge subducts, motion changes to shearing along San
Andreas transform fault
C. Hot spot in Oregon and Washington causes volcanism (Columbia
River Basalts, Snake River Basalts, Yellowstone)
D. Divergence (rifting) in Basin and Range province
E. Subduction continues under Oregon and Washington (Cascades are
the volcanic arc)
F. Very recent events
1. At least 5 major periods of glaciation in last 5 million years
2. Sea level is low when glaciers are at their largest
3. Bering Strait is very shallow, was dry land. Animals and humans
walked over land bridge
|