Page 431 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

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JUAN DE FUCA PLATE
PACIFIC PLATE
PACIFIC OCEAN
Seafloor spreading centre
Transform boundary (transform faults)
Convergent boundary (subduction zone)
Relative plate motion
At the Mendocino Triple Junction, a transform fault links the San Andreas fault with the Cascadia subduction zone and the spreading centre between the Pacific and Juan de Fuca plates.
NORTH AMERICAN PLATE
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(a) The western margin of North America is the meeting point of three plates with different types of boundaries. Between the Juan de Fuca and Pacific plates is a spreading centre with transform faults linking mid-ocean ridges. Between the Juan de Fuca and North American plates is the Cascadia subduction zone. The San Andreas transform fault separates the Pacific and North American plates. The meeting point of three plates is a “triple junction.”
▲Figure 13.12 Plate boundaries of western North america and the San andreas fault. [(a) Bobbé Christopherson (b) Lloyd Cluff/Corbis.]
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South America and the Eurasian–Himalayan sys- tem, which stretches from the Alps across Asia to the Himalayas. Go to the MasteringGeography website to view a map of world structural regions, including these mountain systems.
No orogeny is a simple event; many involve previous developmental stages dating back far into Earth’s past, and the processes are ongoing today. Major mountain ranges, and the latest re- lated orogenies that caused them, include the following (review Figure 12.1 for orogeny dates within the context of the geologic time scale):
• Appalachian Mountains and the folded Ridge and Valley Province of the eastern United
(b) The San Andreas fault, San Luis Obispo County, California.
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Gulf of California
125 250 KILOMETRES
Gulf of Mexico
Linear valley or trough
NORTH AMERICAN PLATE
PACIFIC PLATE
Chapter 13 Tectonics, Earthquakes, and Volcanism 395
The San Andreas fault occurs along a transform plate boundary that crosses a continental plate.