Download Subduction Zone Divergent Plate Boundary

Subduction Zone
ocean trench
lithosphere
lithosphere
continental crust
('overriding')
ocean crust
uppermost
mantle
volcanoes,
mountains
world's largest earthquakes
happen in this area
ocean crust is destroyed
Notes:
and
recycled into the mantle
1. Overriding plate can also have oceanic
imbedded in it.
2. Continental crust will not subduct into the mantle;
it is too light (low density). Thus, if both plates have continental crust in them, a
continental collision occurs, and large mountains form.
3. Examples of subduction zones and volcanoes:
Much of the Pacific Ocean is bounded by subduction zones - The Ring of Fire.
Northwest U.S. - Cascade mountains and volcanoes (Mt. St. Helens, Mt. Rainier, etc.)
Alaska - the Alaska Range - Mt. Spur, Mt. Augustine, etc.
West coast of Central and South America - Andes Mtns.
Western Pacific (oceanic crust on overriding plate) - Phillipines, Japan.
Divergent Plate Boundary
ocean crust
lithosphere
ocean crust
uppermost
mantle
new ocean crust is formed here;
as the plates move apart, it is added onto
both plates
Notes:
Ocean crust that is newly formed at the divergent plate boundary is relatively warm and therefore
less dense than older, colder ocean crust. Consequently, it floats a bit better on the mantle - that's
why there are mid-ocean ridges at a divergent plate boundaries. As the crust slowly moves away
from the plate boundary (and younger crust is added to the plate), the crust ages, cools, contracts
and sinks.
M.Bunds, Dept. of Earth Science, Utah Valley State College, 1/03