Earth Science Plate Tectonics Chapter 12

The Structure of the Earth Earth was molten ball (liquefied rock) that cooled – denser/heavier materials sank towards interior and lighter/less dense ones floated to surface Lighter materials – silicon, oxygen – SILICATES  CRUST (upper mantle – lithosphere)

The Structure of the Earth Crust – made of solid rock Crust & Uppermost mantle – lithosphere Upper mantle but below lithosphere - asthenosphere 2 types of tectonic plates – continental plates (granite) and ocean plates (dense rock)

The Structure of the Earth Crust: solid rock plates which float on the liquid mantle. Mantle: thickest layer, fluid, flows like “thick toothpaste” Outer Core: liquid, very hot, under fairly high pressure, mostly Fe & Ni. Inner and outer core rotate at different speeds which may be responsible for Earth’s magnetic field Inner Core: solid, under high pressure, mostly Fe.

The Structure of the Earth The rock plates are called “tectonic plates” and they are always in motion. The reason for this is the mantle’s CONVECTION CURRENTS Crust Molten rock near the core heats up and rises. As it reaches the crust it cools and moves back down to the core, creating a circular current. Hotter less dense material rises Mantle convection – driving force behind plate movement Radioactive decay of elements like uranium heats up the mantle Liquid Mantle

Tectonic plates Convergent boundary – tectonic plates collide Divergent boundary – tectonic plates are spreading apart Transform fault – a break in the rock layers due to movement of plates Transform boundary – regions where rocks slide past rock but no mountains or volcanoes form

The Structure of the Earth Mantle convection – ridge as magma reaches earths surface at spreading centers If this happens on land – RIFT VALLEY Magma cools and pushes older material aside – RIDGE PUSH Subduction at TRENCH, pulls plate w/ it (Slab PULL)

The Structure of the Earth Magma pushed through spreading centers – cools and creates new rock which pushes older material away from ride – RIDGE PUSH

The Theory of Plate Tectonics Describes the idea that the Earth’s outer rigid shell is made up of moving plates the movement is responsible for volcanoes and earthquakes, mountain building, and ocean ridges. the plate boundaries have “fault zones” around them where many volcanoes & earthquakes occur. Transform Fault zone – zones where rock slides past rock but no mountains or volcanoes form at a plate boundary Can create breaks in rock layers

The Theory of Plate Tectonics there are 3 kinds of faults (plate boundaries) colliding (moving together) (convergent) rifting (tearing apart) (divergent) sliding sideways (transform) The way in which tectonic plates interact depends on two main factors: The type of plate The direction of plates moving in relation to one another

Examples: Convergent Boundary Oceanic - Continental Deep underwater valley – trench (Marianas trench is 10.9 km deep) As subducting plates moves down – parts melt off and turn into rock – magma can come to surface and create volcano Juan de Fuca plate & North American Plate (continental) – created chain of volcanoes in North America Creates coastal mountains, often with a volcanic belt as oceanic plate is subducted.

Examples: Convergent Boundary Oceanic - Oceanic Subduction occurs then cooling will make one plate denser – denser one slides down – can produce chain of volcanoes The denser plate moves down and a chain of volcanoes are produced.

Examples: Convergent Boundary Continental - Continental Plates similar densities so no subduction – edges fold and crumple – collision of Indian & Asian continent The two plates fold and crumple, creating mountain ranges.

Examples: Divergent Boundary Creates mountain ranges Creates new seafloor or land called rifts or ridges that are basically new mountains.

Examples: Transform Boundary Transform boundary – plates slide past each other If breaks in rock occur at boundary – transform faults Rocks slide past each other and faults are created. No volcanoes or mountains are formed.

Assignment Homework: Workbook Pages 210, 212, 218, 219