Chapter 19

Plate Tectonics

Question:

Why do we have mountain ranges, ocean basins, volcanism, earthquakes, similar plants and animals on different continents?

Answer: Because there is plate tectonics.

Alfred Wegener: developed the hypothesis of continental drift, named "Pangea" (land mass at the end of the Paleozoic), no mechanism recognized

Evidence for Continental Drift

-continental fit

-similarities of rock sequences and mountain ranges

-glacial evidence

-fossil evidence

-paleomagnetism and polar wandering

Sea-Floor Spreading

Harry Hess (1962): proposed hypothesis

-plates move with respect to each other (not continents move across oceanic crust)

-two types of crust: oceanic and continental

-driving mechanism are thermal convection cells within the mantle

-oceanic crust is produced at mid-ocean ridges, and recycled at oceanic trenches where subduction occurs

Plate Boundaries

-divergent: mid-ocean ridge, production of new oceanic crust

-convergent: zone of collision of plates

-continent-ocean collision (volcanic arc on continent)

-continent-continent collision (huge mountain range)

-ocean-ocean collision (volcanic island arc)

-transform boundary: plates slide laterally past one another along transform faults

-hot spots: e.g. Hawaiian islands