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 BoundariesTypes of Plate Boundaries

• Explains the following:– How oceans formed– How continents formed– How mountains formed– Cause of earthquakes– Cause of volcanoes

Theory of Plate Tectonics

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).

• 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

Divergent Plate Boundary - MOR

Shallow EQ

Rift Valley

Volcanoes

• MOR: Mid-ocean ridges occur in the center of ocean basins

• Rift Valley: Rift valleys occur within a plate involving continental crust.

Where do DPB Occur?

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 &

non-explosive 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

Deep EQ

Trench

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

Folded Mountain Range

Deep EQ

Shallow EQ

No Volcanoes

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