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11.3 Mountains and Plates Mountains and Plates. Mountains and Plates: Mountains and Plates  Mountain building still occurs in many places worldwide.

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Presentation on theme: "11.3 Mountains and Plates Mountains and Plates. Mountains and Plates: Mountains and Plates  Mountain building still occurs in many places worldwide."— Presentation transcript:

1 11.3 Mountains and Plates Mountains and Plates

2 Mountains and Plates: Mountains and Plates  Mountain building still occurs in many places worldwide.  The jagged mountain peaks of the Grand Teton Range in Wyoming began to form about a million years ago and is still rising to this day.  In contrast, older mountain ranges, such as the eastern Appalachians, are deeply eroded.

3 Convergent Boundary Mountains  With the development of the theory of plate tectonics, a widely accepted model for mountain building became available.  Most mountain building occurs at convergent plate boundaries.

4 Convergent Boundary Mountains  Colliding plates provide the compressional forces that fold, fault, and metamorphose the thick layers of sediments deposited at the edges of landmasses.  The partial melting of mantle rock also provides a source of magma that intrudes into and further deforms these landscapes.

5 Convergent Boundary Mountains Ocean-Ocean convergence:  The convergence of two oceanic plates mainly produces volcanic mountains.  Recall that this process occurs where oceanic plates converge in a subduction zone.  The result of this is the formation of a volcanic island arc on the ocean floor.

6 Convergent Boundary Mountains Ocean-Continental Convergence:  The convergence of an oceanic plate and a continental plate produces volcanic mountains and folded and faulted mountains.  Mountains develop in two belts that run parallel to the edge of a continent.  Continental volcanic arcs form when an oceanic plate is subducted beneath a continental plate.

7 Convergent Boundary Mountains Ocean-Continental Convergence:  The belt of mountains that is created is made up of volcanoes and intrusive igneous rocks mixed with metamorphic rocks.  A prime example is the Andes Mountains in South America. The Andes formed through the subduction of the Nazca Plate beneath the South American Plate.

8 Convergent Boundary Mountains  Another process forms a belt of coastal mountains made up of folded and faulted rocks.  During subduction, sediment is eroded from the land and scraped from the subducting plate.  This sediment becomes stuck against the landward side of the trench.

9 Accretionary wedges  Along with scraps of oceanic crust, the sediment forms an accretionary wedge.  A long period of subduction can build an accretionary wedge that stands above sea level.  California’s coastal ranges formed by this process.

10 Continent-Continent Convergence Continent-Continent Convergence:  At a convergent boundary, a collision between two plates carrying continental crust will form folded mountains.  The reason for this is the continental crust is not dense enough, compared with the denser crust of the mantle, to be subducted.  An example of such a collision began about 45 million years ago when India collided with the Eurasian Plate to form the Himalayas.

11 Continent-Continent Convergence Continent-Continent Convergence:  Before this event, India was part of Antarctica. It slowly moved thousands of kilometers north of millions of years.  The result of this collision was the formation of the Himalayan Mountains.  Most of the oceanic crust that separated these landmasses was subducted, but some was caught up in the collision zone, along with the sediment along the shoreline.

12 Continent-Continent Convergence Continent-Continent Convergence:  Today, these sedimentary rocks and slivers of oceanic crust are elevated high above sea-level.  The closing up of the ocean between India and the Eurasian plate is an example of how plate motions can destroy a sedimentary basin.

13 Divergent Boundary Mountains Divergent Boundary Mountains:  Most mountains are formed at convergent boundaries, but some are formed at divergent boundaries, usually on the ocean floor.  These mountains form a chain that curves along the ocean floor at the ocean ridges.  This mountain chain is over 70,000 kilometers long and rises 2000 to 3000 meters above the ocean floor. Sea-floor spreading produces Ocean mountain chains

14 Divergent Boundary Mountains Divergent Boundary Mountains:  The mountains that form along ocean ridges at convergent plate boundaries are fault-block mountains made of volcanic rock.  The mountains are elevated because of isostosy. Rock at the ridge is hotter and less dense, so it rises higher than older, colder oceanic crust.

15 Non-Boundary Mountains Non-Boundary Mountains:  Some mountains occur well within plate boundaries.  Volcanic mountains at hot spots, as well as some upward mountains and fault- block mountains, can form far from boundary plates.  The Hawaiian islands are a well known example of volcanic mountains at a hot spot.

16 Non-Boundary Mountains Non-Boundary Mountains:  Mountains formed by upwarping and faulting include the southern Rocky Mountains.  The southern rocky Mountains began to form about 60 million years ago with the subduction of an oceanic plate more than 1600 kilometers away.

17 Non-Boundary Mountains Non-Boundary Mountains:  At first, compressional forces deformed the crust. Than the subducting plate separated from the lithosphere above.  This allowed hot rock to upwell from the mantle, pushing up the crust and forming the southern Rockies.

18 Non-Boundary Mountains Non-Boundary Mountains:  As the crust bent upwards, tensional forces stretched and fractured it, forming the fault-block mountains of the Basin and Range region.


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