12.07.2015 Views

Chapter 2 Plate Tectonics: A Scientific Revolution Unfolds ...

Chapter 2 Plate Tectonics: A Scientific Revolution Unfolds ...

Chapter 2 Plate Tectonics: A Scientific Revolution Unfolds ...

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

Convergent plate boundaries Older portions of oceanic plates are returned to the mantle in thesedestructive plate margins Surface expression of the descending plate is an ocean trench Also called subduction zones Average angle of subduction = 45° Types of convergent boundaries Oceanic-continental convergence Denser oceanic slab sinks into the asthenosphere Along the descending plate partial melting of mantlerock generates magma Resulting volcanic mountain chain is called acontinental volcanic arc (Andes and Cascades) Types of convergent boundaries Oceanic-oceanic convergence When two oceanic slabs converge, one descends beneaththe other Often forms volcanoes on the ocean floor If the volcanoes emerge as islands, a volcanic island arcis formed (Japan, Aleutian islands, Tonga islands Types of convergent boundaries Continental-continental convergence Continued subduction can bring two continentstogether Less dense, buoyant continental lithosphere does notsubduct Resulting collision between two continental blocksproduces mountains (Himalayas, Alps, AppalachiansTransform fault boundaries <strong>Plate</strong>s slide past one another and no new lithosphere is created or destroyed Transform faults Most join two segments of a mid-ocean ridge along breaks inthe oceanic crust known as fracture zones A few (the San Andreas fault and the Alpine fault of NewZealand) cut through continental crustTesting the model Hot spots and mantle plumes Caused by rising plumes of mantle material Volcanoes can form over them (Hawaiian Island chain) Mantle plumes Long-lived structures Some originate at great depth, perhaps at the mantlecoreboundary

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!