Plate Tectonics
Saturday, September 17, 2022
11:50 PM
Plate Tectonics Theory
• States that the Earth’s layer is fragmented into either small
or large plate that interact in various ways
• Had its beginnings in 1915 when Alfred Wegener proposed
his Theory of Continental Drift.
Lithosphere
• Consists of layers; the crust and the upper mantle.
• The solid, outer part of the Earth.
Types of Crusts
• The earth’s outer surface is its crust, a cold, thin, brittle
outer shell made of rock.
• The crust is very thin relative to the radius of this planet.
• Extends from surface to about 32 km below, underneath
some mountains, the crusts thickness extends to 72 km.
1. Continental Crust
• Forms the land that we see today.
• Made up of many different types of igneous,, metamorphic,
and sedimentary rocks.
• The average composition is granite, which is much less dense
than basaltic rocks of the oceanic crust..
• Less dense and therefore more buoyant than oceanic crust
(4 billion y/o).
• Contains some of the oldest rocks on Earth
• Mostly composed of granite.
2. Oceanic Crust
• Composed of mafic magma that erupts on the seafloor to
create basalt lava flows or cools deeper down to create the
intrusive igneous rock gabro.
• Relatively thin and lies above the mantle.
• The age of the oceanic crust does not go back farther than
about 200 million years, thus making it younger than
continental crust.
• Subduct under continental plates, which makes it more
dense.
Tectonic Plates
• Massive, irregularly-shaped slab of solid rock, generally
composed of both continental and oceanic crust
• A rigid sections of the lithosphere that move as a unit.
Major Tectonic Plates
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African
Antarctic
Eurasian
North-American
South-American
Indo-Australian
Pacific
Minor Plates
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Arabian
Caribbean
Nazca
Scotia
Philippine
Cocos
Juan de Fuca
How are plates divided?
• Most geologic activity stems from th interplay where
the plates meet or divide
• The movement of the plates create three types of
tectonic boundaries;
a. Convergent - where plate moves into one
another
b. Divergent - where plates move apart
c. Transform fault - where plates move sideways
in relation to each other