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Must know facts for exam 3 Bolded words/topics were stressed in class!!! Plate tectonics • Theory: continental drift+ sea-floor spreading o Continental- felsic o Ocean basin- ultramafic o Volcanic arc- intermediate o Explains § Chains in volcanoes § Earthquake belts § Why mountain belts border continents §Polar wandering: poles are not moving, continents are • Alfred Wegener o Five evidence § God fit of the continents § Good fit of the rocks and structures § Coal deposits line up (climate bands) § Glacier evidence § Fossil evidence o Failed to explain how his theory of plate tectonics function • The ocean floor is not flat o Due to magnetics o Oldest basalts on the ocean floor are about 180 million years old • Plate tectonic boundaries o Transform § Shear “slides past each other” o Divergent § Pulls apart “thins” § Type of divergent ú mid-ocean ridge (occurs in ocean) ú continental rift (rips continents) • may form ocean basin o Convergent § Push together “thickens” § Zones ú Ocean-ocean ú Continent-ocean ú Continent-continent Crustal formation • Stress= force/ area o Types of stress § Tensional: pulling apart
ú Divergent Thins and extends § Compressional: pushing together ú Convergent ú Thickens and shortens § Shear (or rotational): deal with shear couples ú Right handed (dextral) • Clockwise • Top goes right ú Left handed (sinistral) • Anticlockwise • Top goes left § Hydrostatic: stress comes from all directions ú Equal stress from all sides ú Most common ú Confining pressure • Strain= results of stress, what we actually see in a rock o Example: faults and folds o After a couple breaks up others can see how they react (the strain) they cry, scream, etc. Strike and dip • Strike: bearing of a horizontal line on an inclined plane o Never south o If a rock’s strike is vertical or horizontal there is no dip • Dip: maximum inclination of the plane, measured perpendicular to strike o The direction water would flow • A geological compass has the east and west switched Folds • Types of folds (smaller number represent older rocks) o Anticline § Trap fossil fuel ú Oil trap § Makes a frown or A shape § Concave down, units dip away form the center § Oldest unit in the core § “upright anticline”- horizontal axis, straight unit contacts in map view § occur in pairs o syncline§ concave up, units sip toward center § youngest unit in the core § makes a smile shape § “upright syncline”- horizontal axis, straight unit contacts
o dome: doubly plunging anticline § meets on all 4 sides ú oldest layers in the center § plunging anticline ú contacts “v” in map view • v points towards you • Pacman mouth opens toward you ú contacts plunge in cross sections o basin: doubly plunging syncline § depression ú youngest in the center Faults • Hanging wall: block that lies above fault • Foot wall: block that lies beneath fault o Types of faults § Normal: break ú Dip-slip fault ú Hanging wall moves down relative to footwall ú Emplaces younger rocks on older rocks • Younger on top of older ú Tensional stresses ú Extends and thins crust ú Form horsts (up thrown block- mountains) and gra-bens (downthrown block- rift valleys) § Reverse: compression ú Dip-slip fault ú Hanging wall moves up relative to footwall ú Emplaces older rocks on younger rocks • Older on top of younger ú Compressional stress ú Shortens and thickens crust ú Forms “trust” faults, low angle (<30˚ dip) faults § Thrust: shear ú Slide past each other ú Strike-slip faults • Joints: cracks that did have displacement o Most form due to pressure release Volcanoes • Eruptions o Yellowstone § Over 640,000 years ago o Mount St. Helens §May 18, 1980 • Types of eruptions (change viscosity)
o Quite § Non explosive, generally mafic lava ú Example: Hawaii volcanoes National park o Explosive § Deadly, intermediate and felsic lava, high viscosity ú Mount St. Helens o How to determine what kind of eruption it is? § The amount of silica found in the molten material that the volcano is erupting ú High silica content (more felsic in nature) this makes the material very viscus and allows it to trap a large quantity of dissolved gasses • This dissolved gas causes pressure to build up resulting in a volcanic eruption ú Low viscosity (more mafic in nature) the dissolves gasses are allowed to escape through the volcanic vent therefore pressure does not build up • No pressure means no explosion • Types of lava o A’A’ § Angular and jagged § Most often contains a rapid flow § Solidifies at the surface fracture irregulary o Pahoehoe § Forms when a basaltic lava flow ceases flowing and solidifies simultaneously § Easier to walk on than A’A’ § Has a smoother texture than A’A’ ú Ropey texture § Most often contains a slow flow • Types of volcanoes o Shield §Largest type of volcanoes § Shallow slopes § Basaltic lave- dark, black úLow viscosity úMafic § Almost exclusively lava o Composite § Concave upward slope § Mostly intermediate compositions §Layers § Adding silica makes it explosive úPyroclastic flow
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School: Auburn University
Course: Intro Geology
Term: Fall 2016
Tags: geology notes, Geology, Hawkins, and geology1010
Name: Study guide for geology 1100 exam 3
Description: This study guide contains important information on all topics covered in class for the test. The last few pages are potential test questions that you can use as a practice test. The bolded words were stressed in class.