Page 400 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

364 part III The Earth–Atmosphere Interface
▼Figure 12.14 Continents adrift, from 465 m.y.a. to the present. Observe the formation and breakup of Pangaea and the types of motions occurring at plate boundaries. [(a) From r. K. Bambach, “Before Pan- gaea: The geography of the Paleozoic
60°
world,” American Scientist 68 (1980): 26–38, reprinted by permission.
(b–e) From r. S. Dietz and J. C. Holden, Journal of Geophysical Research 75,
no. 26 (September 10, 1970): 4939–4956, © The American geophysical Union.]
GONDWANA
120° 60° 40° 80°
P
160° 120°
(b)
80°
0°
40° 80°
120° 160°
Pangaea all Earth, Panthalassa all seas—no Atlantic Ocean. The Appalachian Mountains in the eastern U.S. and the Lesser Atlas Mountains of northwestern Africa are portions of this older range; Africa connected to North and South Americas.
A
N
G
A
E
A
L
A
U
A
I
R
A
S
E
E
U
U
R
R
D
N
O
G
O
O
E
P
O
P
P
U
E
E
160° 120°
(d)
NORTH AMERICA
SOUTH AMERICA
AFRICA
ASIA
INDIA
80°
120° 160°
Along the Mid-Atlantic Ridge, seafloor spread some 3000 km in 70 million years. The rifting along where the Red Sea would form began. Of all the major plates, India travelled
the farthest—almost 10 000 km.
(NORTH AMERICA)
(SOUTH AMERICA)
(EURASIA)
(ANTARCTICA) 225 million years ago
70°
AFRICA
New seafloor is highlighted (purple tint). An active spreading centre rifted North America away from landmasses to the east. India moved toward its collision with Asia, a spreading centre to the south and a subduction zone to the north.
New sea floor 160° 120°
Sea-floor spreading ridge
NORTH AMERICA
SOUTH AMERICA
ASIA
INDIA
80° 120° 160° Subduction zone
ANTARCTICA
65 million years ago
PACIFIC
160°
AFRICA
40°
60°
ANTARCTICA Today
From 65 m.y.a. until the present, more than half of the ocean floor was renewed. The northern reaches of the India plate underthrust the southern mass of Asia through subduction, forming the Himalayas. Plate motions continue to this day.
120°
40°
Animation
Plate Motions Through Time
KAZAKHSTANIA
10°
TETHYS SEA
(AFRICA)
(INDIA)
(a)
PANTHALASSA
BALTICA
(AUSTRALIA)
AUSTRALIA
(c)
CHINA
SIBERIA 40° 20°
LAURENTIA
NAZCA (e)
AUSTRALIA
NORTH
AMERICA 80° 120°
80° 40° 0°
SOUTH AMERICA
A S I A
465 million years ago
W
A
N
A
ANTARCTICA 135 million years ago
AUSTRALIA
R
E