Review of Convergent and Divergent Plate Boundaries

III. Plate interactions (cont.)B. Convergent boundaries

1. Oceanic – continental plate collision- ocean plate more dense- ocean plate subducts- ocean trench- volcanoes form on continental side of O-C boundary

Nazca plate (left), S. American Plate (right)

Example: Oceanic-ContinentalPlate Boundary

Example: Volcanic Arcs at Ocean-Continental Plate BoundariesThe Cascade Range

Island Arcs

Ocean Trenches

III. Plate interactions (cont.)B. Convergent boundaries (cont.)

2. Oceanic-oceanic plate collision a. Ocean trenches (thousands of m long, 8-11 km deep) b. Island Arcs and Volcanoes

• Subduction: older plate is colder, thus, denser• water & subducting plate heated, plate may melt• resulting magma rises to form volcanic chain• parallel to plate boundary• on continental side

Oceanic continentalPlate plate

Mariana Islands & Marianas TrenchActive Volcanoes on Mariana Islands

Volcanic Arcs (Island Arcs) at Ocean-Ocean Plate BoundariesMarianas Islands & Associated Volcanoes

Older DenserPacific PlateSubducts

III. Plate interactions (cont.)B. Convergent boundaries (cont.) 3. Continental-continental plate collision

• little or no subduction• extensive deformation (Mountain building)• collision of Indian & Asian plate forms

Himalayas

History of IndianContinent &Formation ofHimilayas(ex. Mt Everest)

40 mya

140 mya

History of Himalayas

Indian “continent” moves overtime

140 mya: O-O collision,subduction and vulcanism onAsian plate

Sea continues to close

40 mya: Indian “continent”collides with Asian continent

40 mya to PresentC-C plate collision formsHimalays

40 mya

140 mya

180 mya

210 mya

65 mya

PresentPresent

III. Plate interactions (cont.)C. Divergent boundaries

1. Zones where plates move apart• formation of new lithosphere• rising magma creates new lithosphere at trailing edge

Plate boundarynot here (oldboundary)

Plate boundary here

III. Plate interactions (cont.)C. Divergent Boundaries (cont.)

2. Mid-ocean Rise and Ridge Systema. seafloor spreading

Rise and RidgeSystem

Ridge

III. Plate interactions2. Mid-ocean Rise and Ridge System (cont.)

b. Rift valleys: description and examples i. Iceland, mid-Atlantic Ridge above sea level

Review Of Geographic Features at Plate Boundaries

Boundary Feature Examples Convergent O-O Island arcs,

Ocean Trenches, volcanism, subduction

Marianas Trench and Islands

Convergent O-C Volcanic arcs, Ocean trenches, volcanism, subduction

Cascades

Convergent C-C Deformation, Mountain formation

Himalayas

Divergent Ocean Ridges, Rises (undersea mountain chains), Rift valleys, Spreading centers (note, no subduction)

Mid-Atlantic Ridge, Rift Valley = Red sea, Atlantic Ocean, volcanism

Transform Faults

Deformation San Andreas