Transcript Plate Tectonics ppt

PLATE TECTONICS
Plate Tectonics
Plate - large rigid slab of solid rock
Tectonics - from the Greek root “to build”
• A relatively new area of study.
• Formed 30 yrs ago, incorporating
seismology and paleontology
– Seismology - the study of earthquakes
– Paleontology - the study of fossils
Tectonic Plate Theory
• a solid lithosphere floating on top of the
asthenosphere gives an idea of how plates can float
Evidence to support Tectonic
Theory
– Initial ideas of continental drift
• jig saw puzzle or map fit of continents
Evidence to support Tectonic Theory
• map fit--already mentioned
• mountain chains formed on continents with longitudinal axes
perpendicular to movement of the continents--examples:
Himalayan, Rocky Mountain and Andes Mountain chains
• same fossils (in rocks),same rocks , mountain ranges, and
glacial features located on different continents in areas
representing prejoined positions prior to continental drift
Matching of Fossils from Common
Locations on Separated Continents
Matching of Mountain Chains from
Common Locations on Separated
Continents
Matching of Glacial Deposits from
Common Locations on Separated
Continents
Global Ocean Ridge
•presence and shape of global ocean ridge
–a ridge is a raised region on ocean basin which is believed to represent
prejoined or splitting area of separated continents--the shape of the ridge
contours shape of coast lines of separated continents--- this is most evident in the
mid Atlantic ocean
HEAT CAUSES PLATES
MOVEMENT
– convection cells in Earth’s interior is the force which split
the lithosphere and are the driving force in continental
separation
Plates of the World
• Seven large and many smaller plates
• 80 km thick
• THREE TYPES OF MOVEMENT.
– CONVERGENT - oceanic and continental
plates collide forcing the oceanic plate to
slide beneath.
– DIVERGENT - plates move away from each
other, where they diverge molten rock rises.
– TRANSFORM - plates move horizontally
past each other.
Features Created
• Plates move sideways, apart or together
• Movement produces three tectonic
processes…folding, faulting (diastrophism),
volcanism
• These movements create landform and
ocean features.
Divergent Plates
DIVERGENT PLATE BOUNDARY
Divergent Plates
• kinds of divergent plate boundaries--1)ocean basin
to ocean basin boundary;
example is the mid ocean ridge
Global Ocean Ridge
DRIFT AND PLATES
• 2) continental to continental boundary
Map of East Africa -- a so-called triple
junction (or triple point),
- three plates are pulling away
from one another:
the Arabian Plate, and the two parts
of the African Plate (the Nubian and
the Somalian) splitting along the East
African Rift Zone.
East Africa may be the site of the Earth's next
major ocean. Plate interactions in the region
provide scientists an opportunity to study first
hand how the Atlantic may have begun to form
about 200 million years ago. Geologists believe
that, if spreading continues, the three plates that
meet at the edge of the present-day African
continent will separate completely, allowing the
Indian Ocean to flood the area and making the
easternmost corner of Africa (the Horn of
Africa) a large island.
Convergent Plates
3 types of convergent plate boundaries
1) Ocean basin to continental boundary
(Example is the Cascade Mountain chain)
Convergent Plate boundary
2) Ocean basin to ocean basin boundary
(Examples are Aleutian Islands and Japan)
Aleutian Islands and Japan
3) Continental to continental plate boundary
(Example is India and Asian continent boundary)
Transform Plates
DRIFT AND PLATES
• transformed boundary--plates move parallel to
boundary
Example are those off the Coast of Western U.S.A.