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UO / Geology / GEOL 306 / What are the three theories of tectonics?

What are the three theories of tectonics?

What are the three theories of tectonics?


School: University of Oregon
Department: Geology
Course: Volcanoes and Earthquakes
Professor: Bindeman
Term: Summer 2015
Cost: 50
Name: Midterm Study Guide
Description: Hey guys, here is my study guide for the Volcanoes and Earthquakes midterm. The guide includes information from the slides, discussions, and textbook homework. I hope this helps you with your midterm prep! Good luck everyone!
Uploaded: 10/29/2015
7 Pages 59 Views 1 Unlocks

Geology Midterm Study Guide

What are the three theories of tectonics?

Lecture and Discussion Notes

General Information  

 The Earth is ever-changing and is never in a state of “sameness”  Some structures like the Grand Canyon and Yellowstone would  still be there 200 million years ago as the Earth is nearly 6 billion  years old

 The continents are never in fixed locations and always moving   Plates have the potential to collide (creating mountains or larger  continents) as well as split apart and create seas and oceans  The movement of plates can cause climate changes, volcanoes,  mountains, earthquakes, extinctions, fossil distribution

General Information about Plate Tectonics 

 The globe is divided up into an infinite number of plates that  which the continents and land masses sit upon

What is the density of the asthenosphere?

 The ocean is getting simultaneously created and consumed by  other plates

 Mountain belts are created by continental land masses (plates  that land masses sit on) colliding into each other and pushing  matter upwards Don't forget about the age old question of What are the economic, social, and political characteristics of developing countries?

 The motion from plates can cause earthquakes and volcanoes

Theory of Plate Tectonics 

 Earthquakes tend to occur at plate boundaries where plates are  shifting and creating tension and friction on one another; they  can be divergent or transforming

 Volcanoes tend to occur at plate margins where heat is  excessively produced

 Plates are always moving – hence the almost constant  earthquake activity

 The evolution of flora and fauna could be due to the plates  moving as they grow but separate from each other, causing  changes in species that resemble one another at plate  boundaries

What is a type of rock that is granite, basalt, gabbro?

Three Theories of Tectonics 

 Continental drift hypothesis (1912-1960’s)

 Fixed land masses (before 1960’s)

 Modern plate tectonics (1960-current)Don't forget about the age old question of What type of third-party beneficiary has no rights in the contract?

1912 Continental Drift Theory 

 Matching Continental Plate Boundaries – if one was to cut up  continents and paste them together as puzzle pieces, they would match up almost perfectly aside from slight erosion  Don't forget about the age old question of What is considered the skin of the earth?

 Similarities of floras and faunas – animal and plant species are  similar at continental boundaries (see puzzle analogy above)  Alternative Explanations:  

o Ice or wood rafting – animals/plants could have been  transferred from one land to another by raft

o Land bridges – small portions of land may have been  connected to continents and allowing flora and fauna to  relocate

Ocean Floor Discoveries 

 Central rift valleys indicating tension between plates  Central rift valley having high heat flow and having volcanism  Deep ocean trenches are usually the deepest parts of the ocean  and are usually long and narrow

 Unable to determine ocean flooding older than 200 million years  by drilling and dredging


 Magnetic field changes with time  

 Magnetic pole and rotational pole are averaged to change over  thousands of years

 Magnetic reversal happens roughly every .5 to 1 million years  (Switching North and South poles) Don't forget about the age old question of What is cranial never #3?

Polar “Wandering” 

 From 1950 to 1960

 The magnetic field in young lavas in Eurasia pointed toward our  North pole, but in older lavas would point to other locations or  South pole

 This caused poles to “wander” or assume continental movement

Spreading and Subduction 

 Explained by Henry Hess from Princeton

 When oceanic crust is slowly pulled apart from the middle,  magma and molten rock seeps in between the cracks and  fractures to create the new oceanic crust

 Convection cells move downward and bring the plate down and  the seafloor is gradually deepened

 Ocean floor always young because always renewed  Divergent/Extensional – spreading

 Convergent/Compressional – SubductionIf you want to learn more check out How is sexuality shaped by culture?

 Slip – Transform

Plate Boundaries 

 Earth’s surface area is never increasing, only renewing  Spreading and subduction are both “faults”

Geometry and Kinematics of Plate Motion 

 Poles of rotation are when the plate’s angular velocity remains  the same but linear velocity increases away from the pole of  rotation

 Triple junctions are where convergent, divergent, or transform  plate boundaries meet in various combinations to accommodate  movements on a sphere’s surface  

o The Earth could not only be made up of one type of  faulting – has to adjust to the crust and area  Don't forget about the age old question of What is the difference between qualitative and quantitative research methods and philosophies?

 The Atlantic Ocean is a largely passive continental margin  The Pacific Ocean (including the Ring of Fire) is an active  continental margin

 The Indian Ocean is both passive and active

Subduction Zones 

 Three kinds of convergent margins

o Oceanic to continental (ocean crust meeting continental  crust)

o Oceanic to Oceanic (ocean crust meeting ocean crust) o Continental to Continental (continental crust meeting  continental crust)

 The density of the subducting plate will always be greater than  the underlying plate

o Asthenosphere – 3.25 g/cm3

o Continental Lithosphere – 3.10 g/cm3

o Old Oceanic Lithosphere – 3.28 g/cm3

o Young Oceanic Lithosphere – 3.26 g/cm3

 Continental Crust is rarely subducted  

Volcanoes and Earthquakes at Convergent Boundaries  Volcanism happens when the mantle above the subducting plate  melts due to dewatering

 Seismicity is when there is friction between the plates that cause earthquakes

Transform Plate Boundaries 

 No new crust is created  

 Usually occurring in ocean basins

 The act of sliding back and forth, with no volcanism

 Creates the strongest earthquakes with friction

 San Andreas Fault

o Has power to offset river deltas

o In the future, Baja California would be located where Alaska currently sits

Plate Tectonics and Volcanism 

 Melting of the mantle

o Partial melting usually occurs

 Melting in mid-ocean ridges and hotspots common and aids in  spreading

 Peridotie is the most abundant rock on Earth and most other  planets

 Makes up the mantle and it’s core

 Not seen often on surface or upper crust

Plumes and Hot Spots 

 Has a mushroom appearance with a thick and wide head and  narrow tail

 The plume materials at the shallower depths are partially molten  Seen on the surface as a hot spot

 Mantle plumes are narrow areas of hot plastic rock that rise  through the mantle

Density and Viscosity 

 Oil is less dense than water and will float

 Oil is more viscous than water and doesn’t flow as easily

Thermal Expansion 

 When something is heated, it expands and becomes less dense  and less viscous

Hot Spots 

 Credited with ability to form oceanic islands  

 Appear to move but always staying still and moving plates slide  over and form islands (Hawaiian Islands)

 Leaving tracks on moving plates  

 Can produce medium to high volumes of basaltic magma  Large volumes in the first .1 – 2 million years but gets weaker  with younger islands


 Granite, Sand, Sandstone, Quartzite

 Types of rocks

o Igneous – granite, basalt, gabbro

o Sedimentary – sandstones, limestone

o Metamorphic – schist, gneiss

 SiO2 (silica) concentration in rock and magma determines the  chemical and physical properties of rocks: color, mineral  composition, density, viscosity, etc.

 Peridotite makes up most of the mantle

 Basalt makes up most of the oceanic crust

 Andesite makes up most of the continental margins  Rhyolite and granite make up most of the continents

Igneous Rocks 

 Volcanic – erupted on the surface

o Containing glass and vesicles

o Usually fine-grained

o Effusive (lava)

o Pyroclastic (volcanic ash, scoria, pumice, bombs)

 Plutonic – cooled and crystallized at depth

o Contains larger crystals

 Magma is melted crystals and gas

 Lava is magma that has lost its gas

 Igneous rock is solid that was made from cooled and fully crystallized (plutonic) or partially crystallized (volcanic) magma

Volcanism and Plate Tectonics 

 5 types of volcanism

 Midocean ridges – basaltic, almost completely underwater, less  viscous, shield volcanoes, quite effusive eruptions

 Hot spots – when under continents, form huge calderas and  rhyolitic eruptions

 Subduction zones – above water level, viscous, explosive  pyroclastic eruptions and form island arcs

 Intraplate volcanism – mostly basalt, more explosive  Magmatism of continental collision zones – mostly granite, little  basalt, little volcanism

Textbook Notes

Chapter 2

 Distinction between mantle and crust based on rock composition  Lithosphere the stiff and rigid outer rind of Earth containing  tectonic plates

 Asthenosphere has inner, hotter, and more easily deformed rock

 Elevation difference between continental and oceanic crusts is  explained by isostacy (buoyancy)  

 Earth’s plates move up to 11 cm per year

 Eruptions occurring daily along oceanic ridge systems  Spreading centers in continents pull apart at much slower rates  and don’t usually form plate boundaries

 High Cascades volcanoes are an example of Convergent  boundaries (subduction) where the oceanic crust is diving  underneath the continental crust

 San Andreas Fault has moved California at least 350 kilometers  so far

 Transform faults generate the most earthquake, and all have  potential to be catastrophic

 1 to 2 dozen rigid lithosphere plates make up the outer 60 to 200 kilometers of Earth

 Continent-to-continent collision is where the tallest mountains  are formed and largest earthquakes

Chapter 6

 Melting temperature controlling when a rock becomes magma  Magma chambers are large masses of molten magma that rise  through Earth’s crust and usually erupt to form volcanoes  Rhyolitic magma flows extremely thick and stiff

 Fissure is when a crack opens in the floor and erupts a large  basalt flow

 Pahoehoe lava is very easy-flowing

 A-a lava is blocky and hard-flowing

 Volcanic Explosivity Index (VEI) quantifies the eruption size,  volume, and violence

 Phreatic eruptions are violent steam-driven explosions generated by vaporization of shallow water in the ground  

 Strombolian eruption is fed by magma that interacts with  groundwater or seawater  

 Vulcanian eruptions include ash falls that dominate   Mauna Loa is Hawaii’s largest volcano that has erupted 33 times  since 1843

 Etna’s eruptions feature occasional violent episodes   Cinder cones are basalt but characterized by small size, low  viscosity, steep sides, and moderate volatile content

 Stratovolcanoes have moderate volume and size, moderate  viscosity and slope, and moderate volatile content

 The tectonic environment dictates the volcano distribution, type,  composition, and behavior

 Volcanoes that are not near plate boundaries are generally  situated over hotspots

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