What is a subduction zone? What happens at subduction
zones?
What is a slab?
Deep earthquakes, Benioff zones and the evidence
for subduction
Where do slabs go?
Lecture XIII- March 24,
1998
Carolina Lithgow-Bertelloni
GS 270- Plate Tectonics
How subduction zones were
"discovered"
Critical discoveries
and established notions
Deep Trenches (Veining-Meinesz)
Earthquakes: Wadati-Benioff
Zones (1927)
Inclined plane of seismicity
Ring of fire
Volcanism and high heat flow
Seismicity
reverse faults-compressional stresses
Critical papers
1967- Oliver and Isacks 1967- Jason Morgan 19678- Isacks, Oliver and Sykes
From Isacks et al. (1968)
Evidence for subduction:
Trenches, Volcanism, Earthquakes
Marianas Trench
Evidence for subduction:Benioff
Zones
Inclined plane of seismicity, i.e. Benioff
Zone
(earthquakes in the Japan subduction zone)
Subduction Zone Structure
Trench
Island Arc or Volcanic Arc
Slab
Subduction Zones and Plate
Tectonics
A subduction zone is an
area of convergence,
where oceanic material is destroyed.
It is the convergent
plate boundary.
Subduction is the mechanism
by which plates are reunited and continents amalgamated
Convergent Plate Boundary
Generation of Magma at Subduction
Zones
Subduction leads to CONTINENTAL
COLLISION
Another view of a continent-continent collision
SUBDUCTION: Examples
Three types of subduction
Ocean-Continent convergence
(Andes, Cascades)
Ocean-Ocean convergence
(Marianas, Japan)
Continent-Continent
convergence (Himalayas)
(animation)
What is the fate of slabs?
Cross section under North
America
Blue represents fast seismic
velocities, which we interpret as slabs.
This is an image of the
Farallon slab.
A plate that almost completely subducted under North America. The only
piece left is a tiny plate called the Juan de Fuca plate which subducts
under the Pacific Northwest.
