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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
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