Divergent Boundaries Two plates moving AWAY from each other and forming a gap or RIFT. Mostly...
-
Upload
gwendoline-george -
Category
Documents
-
view
219 -
download
2
Transcript of Divergent Boundaries Two plates moving AWAY from each other and forming a gap or RIFT. Mostly...
Divergent Boundaries
Two plates moving AWAY from each other and forming a gap or RIFT.
• Mostly associated with OCEANIC crust[seafloor spreading = Mid-Atlantic Ridge]– as molten rock [MAGMA] from the mantle rises
the plates move apart, and fills the space between the plates.
– as it cools, it hardens onto the edges of the plates and creates new crust.
1
Divergent Boundaries
• Some involve the CONTINENTAL crust
– when it begins to separate, the stretched crust forms a long, narrow, depression called a RIFT VALLEY
• it is currently happening between the African and Arabian plates Red Sea is therefore widening
4
Convergent BoundariesTwo plates moving TOWARDS each other.
• Direct COLLISION of one plate with
another one.
• There are three POSSIBILITIES:– CONTINENTAL – OCEANIC– OCEANIC – OCEANIC– CONTINENTAL – CONTINENTAL
8
CONTINENTAL - OCEANIC • As the plates are colliding, the denser plate will be
forced downwards
• Since the oceanic crust is denser than the continental crust, the ocean plate is pushed under continental plate. [crust destruction]The area is called a SUBDUCTION ZONE, and forms a deep-ocean trench
• As the plate sinks into the mantle, it melts and becomes magma. The magma rises through the continental plate and forms a volcanic chain
9
OCEANIC – OCEANIC • The more dense of the 2 will go under and form
a subduction zone / OCEAN TRENCH• The new mantle material produced from the
melting of the subducted plate will eventually resurface to produce chain of volcanic islands on the ocean floor called ISLAND ARCS
• As magma accumulates over time, the volcanoes may rise above sea level to form volcanic islands:
Mariana trench and the Mariana Islands in the west Pacific ocean
16
CONTINENTAL - CONTINENTAL• As the 2 continental plates are colliding,
neither plate is subducted i.e. neither plate goes beneath the other WHY?
– because the Continental crust is too buoyant to sink into the mantle.
• The colliding edges buckle and are pushed upward to form mountain ranges.
Indian/Australian plate collide with the Eurasian plate to form the HIMALAYAS.
22
Transform BoundariesTwo plates PASSING each other.
• Plates are grinding past each other and the crust is either cracked or deformed.
• Motion is not smooth but rather in spurs of sudden moves generating EARTHQUAKES*
• They are followed by periods of low or no activity San Andreas Fault
* Earthquakes can occur / are common along all boundaries27
Tectonic plates can include
A. only asthenosphere.
B. only oceanic crust
C. only continental crust
D. both oceanic and continental crust.
30
Features found at divergent boundaries include ____.
A. ocean ridges
B. deep-sea trenches
C. crumpled mountains
D. island arc volcanoes
31
Continental-continental plate collisions produce ____.
A. island arcs
B. rift valleys
C. deep-sea trenches
D. very tall mountain ranges
32
The theory that explains why and how continents move is called
A. continental drift
B. paleomagnetism
C. plate tectonics
D. sea-floor spreading
33
The Himalaya Mountains were formed in a collision at a
A. divergent boundary
B. convergent boundary
C. transform boundary.
D. fracture zone
34
Crust is neither destroyed nor formed along which of the following
boundaries?
A. convergent
B. divergent
C. transform
D. magnetic
35
36
SUMMARY
Direction of movement
Type of Boundary/ impact on crust
Plates involved Geological activities/features
Examples
Importance of plate tectonics
• Theory provides an explanation of Earth’s major surface processes
• Geologists have found explanations for the geologic distribution of earthquakes, volcanoes and mountains and the distributions of plants and animals fossils.
What causes Plate Movement?
While several models have been proposed to explain the
DRIVING MECHANISM responsible for their movement,
there is no doubt that the Earth’s internal heat is the DRIVING
FORCE.
42
DRIVING MECHANISM
Convection Currents the rising-sinking action of magma due to the heat in Earth’s core
Magma close to the core is heated, It expands, lowering its density, and then rises
Closer to the crust, the magma cools, it contracts, increasing its density, and then sinks due to gravity
43
The driving mechanism of tectonic plates movement are related to
convection currents in Earth’s ____.
A. crust
B. mantle
C. inner core
D. outer core
46
The downward part of a convection current causes a sinking force that ____.
A. pulls tectonic plates toward one another
B. moves plates apart from one another
C. lifts and splits the lithosphere
D. creates a divergent boundary
47
Which of the following is an example of a divergent plate boundary?
A. [Option 1]
B. [Option 2]
C. [Option 3]
D. [Option 4]
48
At what type of plate boundary does sea-floor spreading occur?
A. convergent oceanic-oceanic boundaries
B. convergent oceanic-continental boundaries
C. divergent oceanic-oceanic boundaries
D. transform boundaries
49
The force behind the movement of Earth’s plates is
A. cooling of magma cells that rises to the Earth’s surface
B. magnetic attraction between Earth’s iron core and its poles
C. temperature differences between Earth’s oceanic and continental plates
D. the Earth’s internal heat producing convection currents in the mantle.
50