Subduction zones have several geomorphic features:1. A deep ocean trench, where the descending slab drags down the upper plate2. An accretionary wedge of material scraped off of the descending slab3. A forearc basin between the accretionary wedge and the volcanic arc4. A volcanic arc produced by the eruption of andesitic magmas 1 2 3 4
Convergent Plate Boundaries• Three Possible Collisions • Oceanic-Continental Collision • Oceanic-Oceanic Collision • Continental-Continental Collision
Oceanic-Continental Collision• Denser oceanic crust dives under continental crust• Oceanic crust is then recycled by melting back into the mantle• This massive collision creates deep ocean Subduction zones have several geomorphic features: 1. A deep ocean trench, where the descending slab drags down the upper plate 2. An accretionary wedge of material scraped off of the descending slab trenches, an accretionary wedge, a forearc basin, 3. A forearc basin between the accretionary wedge and the volcanic arc 4. A volcanic arc produced by the eruption of andesitic magmas and a volcanic arc.• Exactly like the 1 2 3 4 California landscape.
California’s ProﬁleAccretionary Forearc Volcanic Wedge Basin ArcCoast Ranges Central Valley Sierra Nevada
Oceanic-Oceanic Collision• One oceanic plate will subduct under another• Creates deep ocean trenches arc, separate from a A volcanic island continent is created by the subduction of• Creates volcanic island arcs oceanic crust under oceanic crust• Japan Example: the Aleutian Islands in Alaska or Eurasian Plate Pacific Plate Japan
Continental-Continental Collision• ThisIndo-Australiancontinental crust is riding occurs when on a subducting plate and then smashes Eurasian into another continent Plate Plate India Tibet Continental Continental crust crust
Indo-Australia Eurasia Plate Plate Himalayas India Tibetan plateau Suture
Transform fault boundaryIn the simplest form, plates slide past each other
Transform Faults connectother plate boundaries.They frequently offsetmid-oceanic ridges (whichcan be thought of asjagged tears); in this casethe transform faultsconnect two portions ofa spreading center. Onlybetween the offsetportions of the spreadingcenter are rocks moving inopposite directions (theactive region of thetransform fault; beyondthe ridge segments, rockis moving in the samedirection and there is nofault (inactive region), onlya fracture zone.
San Andreas Fault North American PlatePacific Plate
In Review Three plate boundaries1. Spreading Center: two plates created and diverge; oceanic crust forms2. Subduction Zone: two plates converge and one is recycled; continental crust forms3. Transform Fault: two plates slide past one another