Plate Tectonics

Brief Structure of the Earth Divided into layers: Core, mantle, crust

Brief Structure of the Earth Lithosphere Crust and upper part of the mantle About 100 km thick Rigid Asthenosphere Plastic (gooey) layer beneath the lithosphere More dense than the lithosphere

Brief Structure of the Earth Continental Crust Made up of continents and “edges” of the oceans Light Oceanic Crust Made up of ocean floor More dense than continental crust Older oceanic crust is more dense than younger oceanic crust

Theory of Plate Tectonics Developed in 1960’s Combined continental drift and seafloor spreading.

Theory of Plate Tectonics Stated that: The crust and upper mantle (lithosphere) of the earth are broken into sections called plates. These plates sit on top of the plastic (gooey) part of the mantle (asthenosphere). These plates can move apart, converge, or slide past one another through time.

Divergent Boundaries Where plates are moving apart and new crust is forming. Example: Mid-ocean ridges

Convergent Boundaries Where two plates collide and crust is destroyed. Subduction zone Area where a dense oceanic plate sinks under a light continental plate or another less dense oceanic plate Forms volcanoes. When two continental plates collide high mountains are formed.

Transform Boundary Where one plate is sliding past another plate. The plates may be going in opposite directions or the same direction at different rates. Earthquakes are common

Modern Theories for Cause of Plate Tectonics All include convection currents in the mantle.

Convection Current Cycle of heating, rising, cooling, sinking Caused by differences in density due to differences in temperature Example – boiling pan of water

Forces Movement of plates result in three types of forces: Tension – pulls rocks apart Compression – pushes rocks together Shearing – pushes rocks past each other

Fault Surface where rock has broken apart and moved. 3 types Normal fault Reverse fault Transform (or strike-slip) fault

Faults Normal fault Reverse fault Transform fault Rock above the fault moves down. Formed by tension. Reverse fault Rock above the fault plane moves up. Formed by compression. Transform fault Bodies of rock slide past each other. Formed by shearing.

Features of Tension Forces Mid-ocean ridge Where oceanic crust is being pulled apart. Rift Valley Where continental crust is being pulled apart.

Features of Compression Forces Mountains Continental-continental collisions Very high mountains (folded mountains) are formed. Oceanic-continental collisions Volcanic mountains are formed. Oceanic-oceanic collisions Island arcs (volcanoes that reach above the surface of the ocean) are formed.

Features of Shearing Earthquakes Rocks on each side of a strike-slip fault become stuck in one place for a time and then move, releasing energy in the form of an earthquake.

Tracking Plate Movement Plate movement is tracked using satellites and lasers. Current rates of movement range from about 1 cm to about 12 cm per year.