Transcript Types of Plate Boundaries

Bell Work
10/08/13
What features do scientists use to mark the boundaries
(edges) of the lithospheric plates (plate boundaries)?
Mid Ocean Ridges and
deep sea trenches.
Types of Plate Boundaries
Theory of Plate Tectonics
• Explains the following:
– How oceans formed
– How continents formed
– How mountains formed
– Cause of earthquakes
– Cause of volcanoes
Plate Boundaries
• Plate tectonics states that the Earth’s
crust is broken up into tectonic plates.
• These tectonic plates move over the
Earth’s surface.
• Where two tectonic plates meet is
called a PLATE BOUNDARY.
• Tectonic plates can be destroyed or
created at these plate boundaries.
Plate Boundaries
• Plate boundaries mark the edge of a
tectonic plate. Where two plates meet.
• There are three general types:
– Convergent (plates move towards each
other)
– Divergent (plates move away from each
other)
– Transform (plate move past each other).
Divergent Plate Boundary
• There are two types:
– Mid Ocean ridge – involves creation of new
seafloor (oceanic crust).
– Rift Valley – involves breaking up a
continent (continental crust).
• What’s Happening?: A Divergent plate
boundary is where two plates are moving
away from each other creating new
seafloor.
Divergent Plate Boundary - MOR
Rift Valley
Shallow EQ
Volcanoes
Where do DPB Occur?
• MOR: Mid-ocean ridges occur in the center of ocean basins
• Rift Valley: Rift valleys occur within a plate involving
continental crust.
Mid-Ocean Ridge Landforms
• Shallow EQ
• Non-explosive
volcanoes with basaltic
magma.
• Pillow basalts on
seafloor
• Hydrothermal vents
Rift Valley Landforms
• Shallow EQ
• Both explosive & nonexplosive volcanoes.
• Weird magmas
• Thinning crust
• Long linear valleys
• Faulting in crust
Mid-Ocean Ridge of Iceland
Rift Valley of
Africa
Red Sea Rift Zone
Transform Plate Boundary
Characteristics
What’s happening? Two plates are sliding past
each other. Crust is neither created nor
destroyed.
• There are two kinds of transform plate
boundaries:
– Transform fault – associated with continental plate
– Fracture zone – associated with mid-ocean ridges
• Landforms found on this type of boundary is:
– Linear mountains (moderate height)
– NO volcanoes
– Off set landforms
– Moderate earthquakes with a moderate
depth
Transform Plate
Boundary
SAN ANDREAS
FAULT
Fracture Zone
Caused by the
spherical shape of
the Earth
Convergent Plate Boundaries
(CPB)
• Ocean crust is destroyed at convergent plate
boundaries or landmasses collide.
• Each depends on the type of crust involved:
• There are three types of Convergent Plate
Boundaries
– Ocean vs. Ocean crust (subduction zone)
– Continental vs. Ocean crust (subduction zone)
– Continent vs. Continent crust (collision zone)
Subduction Zone
• Defined as a convergent plate
boundary where one tectonic plate
is destroyed underneath another
tectonic plate.
• Ocean crust is destroyed at a
subduction zone.
• Trenches mark the spot where
subduction occurs.
Ocean-Ocean CPB Characteristics
• Plate made of ocean crust is being
destroyed by subducting under another
plate of ocean crust.
• Also called a subduction zone.
• The older, colder crust will be subducted
because it is more dense.
• Large (9.0+) powerful earthquakes with
tsunamis are common.
• Earthquakes are deep (near asthenosphere)
Ocean-Ocean Subduction Zone
Deep EQ
O – O Subduction Landforms
• Deep trenches that parallel volcanic islands.
• Explosive volcanoes with andesitic magma.
• Associated with the ring of fire in the
Pacific.
• Volcanic island chains (island arcs) form
due to ocean to ocean subduction.
• Examples: Japan, Indonesia, Philippines,
and Aleutian Islands in Alaska
Oceanic – Oceanic Subduction Zone
Oceanic –
Oceanic
Subduction
Zone
Oceanic – Oceanic Subduction Zone
Continent-Ocean CPB Characteristics
• Plate made of ocean crust is being
destroyed by subducting under a
continental landmass.
• Also called a subduction zone.
• Ocean crust is subducted because it is more
dense.
• Large (9.0+) powerful earthquakes with
tsunamis are common.
• Earthquakes are deep (near asthenosphere)
Continent-Oceanic Subduction Zone
Volcanic
Mountain
Chain
Trench
Deep EQ
O-C Subduction Plate Landforms
• Subduction zones are marked by trenches.
• Deep, powerful EQ occur at all types
• Explosive land volcanoes with andesitic
magma.
• Continental volcanic mountain ranges occur
with Ocean to Continent subduction.
• Examples: Andes, Cascades in N. America,
Mexico & Central America
Continental – Oceanic Subduction Zone
Continent-Continent CPB
Characteristics
• AKA “Collision Zone”
• Crust is shortened and folded but NOT
subducted.
• Thick continental crust will not subduct.
• Large, inter-continent (9.0+) powerful
earthquakes
• Earthquakes are deep (near asthenosphere)
Continent - Continent Collision Zone
No Volcanoes
Folded
Mountain
Range
Shallow EQ
Deep EQ
C – C Collision Landforms
• Large folded mountain ranges mark where
collision occurred.
• NO Volcanoes because there is no
subduction.
• Crust is shortened and thickened.
• Examples: Himalayan Mountains, Alps
Formation of Himalayas