plate motions-2
TRANSCRIPT
Solid Earth Geophysics
Ali [email protected].
saDepartment of Earth SciencesKFUPM
Today’s class: Plate MotionsReading: Fowler Chapters 2-3
http://neic.usgs.gov/neis/plate_tectonics/plates.html
OVERVIEW:PLATE TECTONICS
Basic concept:The outermost layer (LITHOSPHERE) is divided in a small number of “rigid” plates in relative motion one respect to the other. It FLOATS on the weak ASTHONOSPHERE.
Basic assumption: As a result of DISCOVERY, the plates are made up of both oceanic and continental material, whereas the ONLY oceanic parts of plate are created or destroyed. However, it is hard to understand why continental material usually is not destroyed at convergent plate boundaries. Sea floor spreading at the mid ocean ridges produces only oceanic lithosphere.
From: Fowler, the solid Earth
How many plates?
What is the largest plate and smallest plate?
Ocean or continent?
Oceanic crust is primarily basaltContinental crust is primarily graniteWhat are the differences between these 2
rock types?
What are the criteria for deciding whether Earth’s crust any location is
oceanic or continental in origin?
Why does the Pacific plate
subduct?
As new crust cools, it thickens and becomes denser.
Blue (cool) colors on this map show older crust, warm colors show younger crust.
Crustal Density: 2.8X103 kgm-3
Mantle Density: 3.3 X103 kgm-3
PARALLEL VALLEYS; VOLCANOES AND EARTHQUAKES.
Oceanic- Continental Plate Separation
Mid-Atlantic Ridge
East AfricanRift Valley
VOLCANOES AND EARTHQUAKES CONCENTRATE
Divergent Boundaries
DEEP-SEA TRENCH; VOLCANIC
ISLAND ARC.
Convergent Boundaries
Ocean-Ocean Convergence
Mariana Islands Marianas
Trench
AndesMountains
SouthAmericanPlate
Peru-Chile Trench
Ocean-Continent Convergence
A VOLCANIC BELT OF MOUNTAINS FORMS
Transform-Fault Boundaries
Mid-Ocean Ridge Transform Fault
Spreading centers offset.Offset
continental crust.
Continental Transform
As platesmove past each other...
…creek beds are offset
SanFrancisco
Los Angeles
San Andreas fault
Seismicity Depth
DistributionWhere are the deepest parts of the oceans?
Why here?
Which ocean is surrounded by the most volcanic and earthquake activity?
http://www.ncedc.org/anss/maps/cnss-depth.html
South
America
Japan Alaska
Tonga
Depth Cross-
Sections
South America
Tonga
Depth Cross-
Sections
Japan
Alaska
Basics
Con
verg
en
t
Con
str
ucti
ve
Transform LL
Transform RL
Plate Motions on a Flat Earth
Question
Spreading center with half rate of 2 cm/yr between plates A and B. What is happening at the eastern boundary between plates A and B?
