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3 Mountain Formation PLATE TECTONICS.ppt
1. In Order to Get Lecture Credit!
1. Answer all warm up questions
2. Answer all concept check questions
3. Underline or highlight the key
points (stuff you think I would
make you write)
2. 1) If erosion stripped off the top of a dome, what would
be found?
a. The oldest rocks are exposed in the center.
b. The oldest rocks are exposed along the edges of the
dome.
c. The youngest rocks are exposed in the center.
d. The rocks in the center are the same age as those
along the edges.
2) The convergence of two continental plates would
produce
a. trenches. c. folded mountains.
b. rift valleys. d. island arcs.
3) What type of mountains are produced by ocean-
ocean convergence?
a. a continental volcanic arc
b. mainly volcanic mountains
c. parallel belts of uplifted mountains and volcanic
mountains
d. parallel belts of folded mountains and volcanic
mountains
4. Mountain Building at Convergent
Boundaries
With the original development of the
theory of plate tectonics, an
accepted model for orogenesis
emerged
Most mountain building occurs at
convergent plate boundaries
Colliding plates provide the
compressional forces that fold, fault,
and metamorphose the thick layers
of sediments deposited at the edges
of landmasses
5. Ocean-Ocean Convergence
Ocean-ocean convergence mainly
produces volcanic mountains
These features tend to be long-lived
The accumulation of sediment
scraped off of the subducting plate
increases the volume of the crust
Examples: Aleutian Islands (Alaska)
and Japan
8. Ocean-Continental Convergence
The convergence of the continental block and
the subduction of the oceanic plate leads to
deformation and metamorphism of the
continental margin
Partial melting of mantle rock above the
subducting plate generates magma that
migrates upward
Accretionary wedge - the accumulation of
different sedimentary and metamorphic rocks
with some scraps of ocean crust that gathers
on the landward side of a trench
The types of mountains formed by ocean-
continental convergence are volcanic mountains
and folded mountains
Examples: Andes (South America) and
Cascades
13. Continent-Continent Convergence
Continental crust floats too much to be
subducted
At a convergent boundary between two plates
carrying continental crust, a collision between
the continental fragments will result and form
folded mountains
Most of the oceanic crust that separated
landmasses, before a collision, is subducted,
but some gets caught up in a collision zone and
raised above sea level
Examples: Himalayas (Asia), Urals (Russia),
and Appalachians
16. Mountain Building at Divergent
Boundaries
Most mountains are formed at
convergent boundaries, but some are
formed at divergent boundaries
The mountains that form along ocean
ridges at divergent plate boundaries
are fault-block type mountains
Example: the 65,000 kilometer long
mid-ocean ridge system
20. Continental Accretion
Accretion – the process by which fragments
collide with a continental plate and become
stuck or embedded into the continent
Terrane – any crustal fragment that has a
geologic history distinct from the adjoining
terranes
Terranes can contain anything from sediment
off the ocean floor to volcanic island arcs
The newly added material increases the width
and thickness of the continental crust
The accretion of larger crustal fragments, such
as a mature island arc (Hawaii), may result in a
mountain range
Because of its buoyancy, an island arc will not
subduct beneath the continental plate
25. Isostasy
Isostasy – concept of a floating crust in
gravitational balance
Many mountain belts stand high above the
surface because they have buoyant (less
dense) crustal “roots” that extend deep into the
mantle
Isostatic adjustment – the processes of
establishing a new level of gravitational
equilibrium
As weight is added to the top of a mountain,
the crust subsides, and as weight is lifted, the
crust will rebound
Because of isostasy, deformed and thickened
crust will undergo regional uplift both during
mountain building and for a long period
afterward
29. Assignment
Read Chapter 11, Section 3 (pg. 317-324)
Do Chapter 11 Assessment #1-36 (pg. 329-
330)
For Section 3: Do #’s 7, 9, 19-21, 23, 25,
26, 28, 35, & 36
Study for the Unit 2 Test (chapters 8-11)
Collect Notes (Total of 13, including this
one!)
