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Convergent Plate Boundaries By Diana L. Duckworth Rustburg High School Campbell County, VA.

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Presentation on theme: "Convergent Plate Boundaries By Diana L. Duckworth Rustburg High School Campbell County, VA."— Presentation transcript:

1 Convergent Plate Boundaries By Diana L. Duckworth Rustburg High School Campbell County, VA

2 Features Deep sea trenches and Volcanic island arcs or Volcanic mountain ranges or Folded & faulted mountain ranges

3 Process Subduction One plate is pushed down into the mantle where it melts producing magma for volcanoes

4 Subduction Oceanic lithospheric plate dives under another plate Produces initially mafic lavas, but as islands grow, lavas become more felsic from subducted sediment Metamorphic rocks produced in subduction complex

5 Subduction Explains Why there are no abyssal plains in the Pacific Ocean (sediment goes into trenches) Why there are no continental rises in Pacific continental margins – (sediment goes into trenches) Why there is no old sea floor (it subducts & melts) Why there are explosive volcanoes in the ring of fire (subducted sediment contains water!)

6 Evidence Compressional earthquake foci get deeper under the continents (or island arcs) away from the trench. Angle is 45° ocean

7 Mantle Convection

8 Three Types of Convergent Plate Boundaries Oceanic – Oceanic lithospheric plates –Features include trench and volcanic islands Oceanic – Continental lithospheric plates –Features include trench and volcanic mountains Continental – Continental lithospheric plates –Features include folded and faulted mountains

9 Oceanic - Oceanic

10 Oceanic - Oceanic As volcanic islands increase in size More sediment contributed to trench Magma becomes more felsic due to melting of sediments subducted on plate Subduction of water & sea shells in sediments adds carbon dioxide and water vapor to magma – result explosive eruptions Island arc can be welded on to nearby continent as subduction continues.

11 Oceanic - Continental

12 Continental - Continental

13 Continental Collision Continental crust cannot be subducted Density is too low Remnants of subducted ocean crust provide uplift (low density) until it melts Erosion carves out mountain ranges & valleys Intense folding & faulting & metamorphism No volcanic activity remains; remnants of magma chambers become batholiths

14 Growth of Continents These processes cause continents to become larger through additions of terranes Subduction can cease & new trench forms seaward (Asia) Continental collision creates a thicker continental crust Rifting will occur somewhere else


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