CONVERGENT BOUNDARIES: ORIGIN 14
OF MOUNTAINS
INTRODUCTION
Convergent Boundaries: Origin of Mountains
CHAPTER OUTLINE
1.
2.
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3.
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4.
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5.
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6.
LEARNING OBJECTIVES/FOCUS ON CONCEPTS
14.2 List and describe
14.4 Summarize
14.6 Explain
TEACHING STRATEGIES
Clicker Questions:
Muddiest Point:
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1. Isostasy
o Other Activities on Isostasy:
2. Connecting Tectonic Processes and Mountain Building
o
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TEACHER RESOURCES
Web Resources:
Areas associated with mountain-building processes:
oThe Himalayan Orogeny
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o Basin and Range Provinces
Imagery, Animations, and Videos:
Images
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Animations
Videos
ANSWERS TO QUESTIONS IN THE CHAPTER:
CONCEPT CHECKS
14.1 MOUNTAIN BUILDING
1. Orogenesis is a collective term for the processes that produce a mountain belt. Orogenic
2. Convergent plate boundaries, where oceanic lithosphere subducts into the mantle, are
associated with most of Earths mountain belts.
14.2 CONVERGENCE AND SUBDUCTING PLATES
1. The four main structures of a subduction zone are: a volcanic arc that is built on the overlying
14.3 SUBDUCTION AND MOUNTAIN BUILDING
1. The primary basaltic magmas produced at depth rise due to buoyancy and eventually reach
the base of the continental crust. Here, the basaltic magmas undergo magmatic differentiation
2. A batholith is a massive igneous pluton exposed at the surface. Batholiths are currently being
3. The Sierra Nevada is an excellent example of the structures of an Andeantype subduction
zone. These are both areas of continental-margin orogenesis driven by the subduction of
4. An accretionary wedge forms where unconsolidated sediments and fragments of oceanic crust
are scraped off and plastered to the edge of an overriding plate. Accretionary wedges are
5. The United States eastern (Atlantic) coast is a passive margin. Passive margins are those
6. Once formed, a volcanic arc continues to travel on the oceanic plate where it formed.
Eventually, the volcanic arc will be transported towards a convergent boundary where the
14.4 COLLISIONAL MOUNTAIN BELTS
1. A terrane is a crustal fragment consisting of a distinct and recognizable series of rock
2. It is thought that India was relatively undeformed compared to Asia during the formation of
3. In newly formed collisional mountain belts crust is thickened and shortened considerably.
4. The Appalachian Mountains are a collisional-type mountain belt that formed in the late
Paleozoic. Here, Europe, northern Africa, and North America collided and were all part of the
5. Slices of oceanic crust are known to be accreted to continental margins at subduction zones.
14.5 FAULT-BLOCK MOUNTAINS
1. When tensional forces stretch and thin the lithosphere, upwelling of hot mantle rock can heat
the thinned lithosphere, elevating it topographically. Simultaneously, stretching elongates the
2. Fault-block mountains develop in areas where widespread uplift causes fragmentation of the
brittle, upper crust. Stresses are tensional; deformation involves horizontal stretching and
3. The Basin and Range region consists of more than 100 fault-block mountains that were
generated during the past 20 million years. Upwelling of hot mantle rock and perhaps
14.6 WHAT CAUSES EARTHS VARIED TOPOGRAPHY?
1. Isostasy is the concept of low-density crust floating on top of the high-density mantle in a
gravitational balance.
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2. In portions of North America extensive ice cover, in some places over 3 km thick, during the
3. When weight is added to a floating object, the object sinks until it achieves a new isostatic
4. When compressional mountains are young, they are composed of thick, low-density crustal
5. Gravitational collapse involves ductile spreading at depth and normal faulting and subsidence
in the upper, brittle portion of Earths crust. Without compression forces to support them,
EYE ON EARTH
EOE #1 INTERBEDDED STRATA NEAR MARIN HEADLANDS, CALIFORNIA
2. Accretionary wedges form along continental-oceanic convergent margins.
3. Today, a transform boundary is found in the San Francisco Bay area. These folded layers
GIVE IT SOME THOUGHT
1.
a. The continental margin of the west coast of South America is characterized by a deep offshore
trench and a topographically high mountain range along the coast. The continental margin of
the east coast of South America is characterized by a continental shelf and slope that leads
into a deep ocean basin.
2. A sliver of oceanic crust in the interior of a continent would not refute the theory of plate tectonics.
Rather, this sliver would serve as supporting evidence for the theory because the location of the
3. The Ural Mountains mark the closure site of an ancient marine basin that once existed between
4. The Appalachians are an Alpinetype mountain belt formed from the collision of the formerly
separated North America and ancestral Africa continental block more than 250 million years ago;
6. The uplift and subsequent erosion of major mountain belts would also lead to isostatic adjustment
7. Students should compare Figures 2.11 and 14.1, and recognize that young mountain belts are
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