Plate Tectonics…What’s It All About? Chapter 7: Plate Tectonics

Earth’s Structure The Earth is not just a ball of solid rock…some parts are liquid as well We can divide the Earth into 3 main layers: crust, mantle, and core The crust can be continental (thick and less dense) or oceanic (thin and more dense) The crust and the uppermost part of the mantle make up the lithosphere The lithosphere is broken up into pieces called plates, which “glide” on the plastic- like asthenosphere

Structure Cont’d The asthenosphere and the mesosphere together make up the mantle Below the mantle is the core which has two parts: inner and outer The outer core is liquid iron and nickel The inner core is made of the same stuff as the outer core, but is SOLID because of the pressure applied by the layers above it

Tectonic Plates The lithosphere is broken up into pieces called plates Many are named after continents or bodies of water 10 major plates: North American, South American, African, Antarctic, Eurasian, Nazca, Pacific, Indo- Australian, Indian, Philippine Places where these plates meet are called boundaries Stress builds up along these boundaries as the plates move, creating volcanoes and earthquakes

Why Do The Plates Move? The Theory of Plate Tectonics states that the Earth’s lithosphere is divided into tectonic plates that move around on top of the asthenosphere So what is the driving force behind plate movement? Convection! What is convection? When hot, less dense mantle material rises and cooler, more dense mantle material sinks. It’s like a huge conveyor belt that carries the plates with it!

When Plates Collide A collision between plates creates a convergent boundary Compression pushes the plates together Depending on the type of crust, there are three possibilities: 1.Continental-continental: crust gets pushed upward to form mountains (Himalaya Mountains) 2.Oceanic-oceanic: the more dense oceanic plate is pulled down under the other oceanic plate, creating volcanic islands (Aleutian Islands, Japan) 3.Continental-oceanic: also called subduction, the more dense oceanic plate is pulled under the less dense continental plate, creating trenches and volcanoes along coastlines (Western coasts of North & South America)

Divergent and Transform Where plates move away from one another due to tension, a divergent boundary is created. An example is the Mid-Atlantic Ridge. The most common feature at a divergent boundary is a mid-ocean ridge or rift zone. Where plates move past each other horizontally, a transform boundary is created. Shearing is the stress that makes the plates move past one another, as seen at the San Andreas Fault in California. Here, the Pacific plate is moving to the northwest past the North American plate. The movement along transform boundaries is rarely smooth. Instead, there are lots of jerks and jolts along the way. Sometimes, the plates will get stuck for long periods of time and then jerk past each other very suddenly, creating violent earthquakes all along the San Andreas Fault.