Transcript Plate Tectonics and Boundaries

What we know…
 Wegener
collected evidence and
proposed the theory of Continental
Drift.
 Hess found the “mechanism” to
support the idea with his theory of
Sea-Floor Spreading.
Put the two together… we get the Theory
of Plate Tectonics.
Plate Tectonics

The Earth’s crust and rigid upper mantle are
broken into huge slabs called tectonic plates
(about a dozen major plates, and several
smaller ones).
 Tectonic
plates interact at places
called plate boundaries.
 This is where MOST of the action is
really taking place.
Divergent Boundaries



The place where two tectonic plates are pulling away from
each other (not always, but usually occurs on the seafloor).
A common feature associated with a divergent boundary is
a ridge/rift.
A good example of a divergent boundary is the MidAtlantic Ridge.
Another Picture of a Divergent
Boundary – A Mid-Ocean Ridge
Arguably the best example of a divergent
boundary – The Mid-Atlantic Ridge
Convergent Boundaries

: The place where two tectonic plates are pushing against each
other.
– Oceanic/Continental: Basalt/Granite (a trench and a
continental arc are formed)
– Oceanic/Oceanic: Basalt/Basalt (a trench and an island arc
are formed)
– Continental/Continental: Granite/Granite (folded mountains
are formed)
Convergent Boundaries Cont…


A common feature associated with a convergent boundary
is a subduction.
A good example of a convergent boundary is the Mariana
Trench / Mariana Island.
Transform Boundaries


The place where two tectonic plates are sliding past one
another.
A good example of a transform boundary is the San Andres
Fault in California.
More Photos of the San Andreas
Fault
The San Andreas near San Francisco
… in Central California