A useful reference http://www.learner.org/interactives/dynamicearth/sitemap.html http://pubs.usgs.gov/gip/dynamic/dynamic.html#anchor19309449
Types of Plate Boundaries • Divergent - Pull apart- Mid Ocean Ridges • Convergent- Come together- subduction zones- Andes Mts. • Transform- sliding past each other- San Andreas fault zone California
Volcanoes • Mid Ocean volcanoes • Mostly basaltic • Source of magma is hot mantle area. • Shield type volcanoes • Continental Margins and Island Arcs • Source of Magma is mostly remelting of pre-existing rocks, through the continental crust, producing Andesite and Rhyolite lavas • Stratovolcanoes
Earthquakes • Earthquake locations are used to determine the plate boundaries. • Plates are the large pieces of the earth that have few earthquakes, the boundaries are where the earthquakes occur because this is where the blocks of the earth are interacting with each other, pushing into each other, sliding past each other
Mid-ocean Ridges with Transform FaultsThe orientation of Transform faults help to determine plate motion direction. These have shallow earthquakes
Trenches at Island ArcsThese have shallow to deep earthquakes and usually rhyolitic flows
The west coast shows aspects of both subduction in the north and transform motion in the south
The Formation of granitic bodies as a result of subduction and melting of surface rocks
Convective heat flow from inside the Earth is the ultimate cause of volcanoes, earthquakes, and plate motion. When the Earth cools completely –no more volcanoes etc.
Earthquake Waves • There are three types of seismic waves that travel through and on the earth • P waves - Compressional travel about 6 km/sec • Travel trough both solids and liquids • S waves – Shear waves travel about 4 km/sec • Travel only through solids (not the liquid outer core) • Surface waves- travel only along the surface at about 3.5 km/sec
Interior of the Earth • The earth’s interior is divided into Crust 0-35 km • Mantle 10-2900 km • Outer Core 2900-5200 km • Inner Core 5200-6000 km • From Earthquake studies • Also: Lithosphere 0-100 km • Asthenosphere 100-700 km • Based on rigid vs. plastic
Problems Not solved • Driving Mechanism • Why Hot Spots • How deep does convection take place
Types of mountains or mountain ranges • Volcanic- West coast –Mt. Rainer • Fault, trusting – Western U.S. Basin and Range area- Nevada • Folded – Appalachian Mts. Eastern Pa, West Virginia etc.
Reversal of the Earth’s magnetic Field Present world - arrows in at North Reversed field – arrows out at North
Before 500 years before middle of reversal Middle of reversal 500 year after middle of reversal
Example evidence from Igneous rocks: Lava flows and sea floor magnetic anomalies