Transcript Plate Tectonics

Plate Tectonics
ISCI 2001
Chapters 22-24
Plate Activities – Divergent Plate
Boundaries
 (1). Plates may ‘diverge’
 Plates move apart
 Lava fills spaces in between
 (2). What types of structures are produced?
 Volcanic mountains
 Rift valleys
 (3). Examples
 Mid-Atlantic Ridge
 Great Rift Valley (Africa near Nairobi Kenya)
Rift Valley in Kenya
Mid-Atlantic Ridge
Convergent Boundaries
 (1). When two plates collide
 One plate usually subducts
 Most dense or oldest plates
 (2). Types of convergence
 Oceanic – Oceanic
 Trench formation (Marianas Trench)
 11,000 m or 7.0 miles deep
 Pacific and Phillipine Plates collide
 Formation of volcanic islands or arcs
 Subduction plate mantle rock melts comes to the surface and cools
 Oceanic – Continental
 Oceanic basaltic plate (more dense) subducts under granitic continental plate
 Mantle rock melts, magma rises and cools forms island chains
 Volcanic Arcs (Peru)
 Continental – Continental
 Massive plate collisions (both granitic)
 No subduction, why?
 Both have same density
 Massive mountains are formed
 Himalayas
Marianas Trench
Oceanic – Continental
The convergence of the Nazca and South American Plates has deformed and pushed up
limestone strata to form the towering peaks of the Andes, as seen here in the Pachapaqui
mining area in Peru.
Continental – Continental
Transform Plate Boundaries
 (1). ‘Sliding Plate’ Boundaries
 Slipping of plates causes ‘faults’
 (2). Slipping causes plate movements
 Boundaries move in opposite directions against each
other
 (3). Where are they normally found?
 Mostly ocean basins
 Continental plate: San Andreas Fault
San Andreas Fault
Types of Faults
 (1). Dip-Slip (See figure 24.5)
 Hanging wall and vertical wall move vertically along
the fault plane
 Movement is vertical
 (2). Strike-Slip
 Movement is horizontal
 San Andreas Fault motion
 (3). Oblique
 Move horizontally and vertically
Slip-Dip
Conjugate Normal faults, Canyonlands
National Park, Utah
Fault Types
Folding
 (1). Bending in Rock layers
 Caused by compression
 (2). Results
 Anticlines or synclines
 (1). Folded Mountains
 During formation continental crust thickens and wrinkles
into vertical folds from compression
 Appalachians, Rockies and Himalayas
 (2). Unwarped
 Domed shaped
 Single anticline (crust is heaved upwards; no folds produced)
 Adirondack mountains NY
 (3). Fault-Block
 Land is ‘uplifted’ , stretched and elongated
 Very steep profile
 Tetons (Wyoming); Sierra Nevada (California)
Mountain Formation
Folded Mountain –
Antarctica
Mountain Formation
Adirondack
Mountains –
unwarped
Mountain Formation- (Fault-Block)
 (1). Earthquakes
 Transform faults
 Compression and tension caused by stress of plate movements - Slipping
 Focus location
 Rock is snapped or broken releasing ‘elastic’ energy
 (2). Types
 Intraplate (10%)
 Away from plate boundaries
 New Madrid, Missouri
 Interplate (90%)
 Plate boundaries
 Transform plates (mild Eqs)
 Subduction zones (strong)
Earthquakes
Subduction Zones – Ring of Fire!
80% of all interplate EQs occur here
Powerful Interplate EQs and Tsunamis
 (1). Coast of Sumatra
 Indian and Burma Plate collision
 Megathrust quake
 100 billion tons of TNT
 (2). Production of a Tsunami
 Quake took place in the Indian ocean
 As subduction occurred
 The seafloor bent as the other plate sank
 Stress caused rock to snap and thrust upwards
 Force caused water to creat large wave
 30m +/- above sea level
Earthquakes – San Francisco 1906
Magnitude of Earthquakes –Richter Scale
 (1). Logarithmic scale
 Each point represents a 10-fold increase in quake
shaking strength
 Measures shaking
 Also indicates 30 fold increase in energy output
 1 thru 10
 Examples
 1906 San Francisco (8.2)
 Sumatran 2004 (9.0)
Richter Scale
Sumatra EQ and Tsunami
184,000 People died