Page 435 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

13.2
MOUNTAIN BUILDING AT CONVERGENT BOUNDARIES
Three different types of lithospheric plate collisions result in mountain building:
• oceanic plate–continental plate
• oceanic plate–oceanic plate
• continental plate–continental plate Each plate interaction leads to a different kind of orogenesis.
Oceanic plate–continental plate
Where a dense oceanic plate collides with a less-dense continental plate, a subduction zone forms and the oceanic plate is subducted. Magma forms above the descending plate. Where the magma erupts to the surface through the continental plate, volcanic mountains form. Magma may also harden beneath the surface, forming batholiths. Example: The Andes of South America formed as a result of the subduction of the oceanic Nazca plate beneath the continental South American plate.
Accumulated sediments
Volcanic mountains
South American plate
Andes Mountains
Andes, Peru: Ancient Incan city of Machu Pichhu [vdLee/Shutterstock.]
Oceanic lithosphere
(a)
Subduction zone
Ocean trench Oceanic crust
Uppermost mantle
Asthenosphere
Continental crust
Nazca plate
Metamorphic processes
Moho
Uppermost mantle
Continental lithosphere
Philippine plate
Oceanic plate–oceanic plate
Partial melting
Where two oceanic plates collide, one plate is subducted beneath the other. Magma forms above the descending plate, giving rise to a volcanic island arc.
Mayon volcano, Philippines
[suronin/Shutterstock.]
Oceanic lithosphere
(b)
Himalayas, Nepal [Purepix/Alamy.]
(c)
Example: As part of the “Ring of Fire,” there are many volcanic island arcs where the Pacific plate interacts with other oceanic plates. These arcs extend from the southwestern Pacific (shown here) through Indonesia, the Philippines, and Japan to the Aleutians.
Pacific plate
Ocean
trench Oceanic crust
Uppermost mantle
Asthenosphere
Continental crust
Uppermost mantle
Asthenosphere
Island arc
Volcano
Continental
crust
Uppermost mantle
Partial melting Asthenosphere
Mountain range
Mariana trench
Subduction zone
Continental lithosphere
Indo-Australian plate
Eurasian plate
Himalayan Mountains
Collision zone
Continental crust
Uppermost mantle
Oceanic crust
Continental plate–continental plate
Indo-Australian plate
Infer: Why doesn’t subduction occur when two continental plates collide?
Continental lithosphere
Where two continental plates collide, neither plate is subducted. Instead, the collision subjects the plates to powerful compression forces that fold, fault, and uplift the crust, pushing up huge mountain ranges. Example: The Himalayas formed as a result of the ongoing collision of the Indian and Eurasian plates. The Himalayas are part of a long east–west mountain belt, stretching from Europe across Asia, formed by similar collisional processes.
GEOquiz
1. Predict: Will the Himalayas keep growing higher and 2. Compare: In terms of orogenesis and plate tectonics, how higher indefinitely? Explain your answer. are the Alps and the Andes similar? How are they different?
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geosystems in action 13 MOunTAin BuiLDinG