GEOL EXAM 3 Review

What is the age of the oldest seafloor?

Terms to Know 

Supercontinent Pangaea: All of Earth’s continents combined 245 mya and since have split and drifted

Alfred Wegener: Came up with the theory of Pangaea, he had 5 pieces of  evidence

Magnetics: Magnetic stripes were found, bands of ocean floor basalt with  alternating high and low intensities mirrored across the ridge Natural Remnant Magnetism (NRM): Fe- bearing minerals become  magnetized and align themselves with Earth’s magnetic field; igneous  magmas and lavas once cooled below ~500 degrees C. We can tell how the  poles looked when the rock was molten

Magnetization of Oceanic crust: basaltic magma flows into the crack  along the ridge axis solidifies and locks in earth’s magnetic field at that time. Magma comes up and records the magnetic field, happens almost daily. Age of the sea floor: the oldest oceanic crust is 180 mya. When oceanic  crust gets really old, it begins to sink within the earth and it is recycled. Sea-floor spreading: mechanism of spreading and creation of new oceanic  crust at mid-ocean ridges. The mechanism that causes continents to drift,  putting in new material pushes continents apart

What is another word for volume change?

Plate tectonics theory: continental drift and sea floor spreading. Basically,  took credit for Alfred Wegener’s idea

Convection: mechanism by which material moves due to differences in  density, usually due to heat If you want to learn more check out What is the purpose of diodes?

Convection cells: drive plate movement, heat from the center of the earth Oceanic crust: Basalt= ferromagnesian silicates, relatively dense (~3.3  gm/mL), 0-10 km thick

Transform boundary: plates slide horizontally past each other, shear  “slides laterally”, connects 2 divergent boundaries, e.g. San Andreas fault  system If you want to learn more check out What are natural resources?

Divergent boundary: plates move apart and create new lithosphere, pulls  apart or “thins”

Convergent boundary: plates collide and one is pulled into the mantle and  recycled. Pushed together or “thickens”

How are ridges different from valleys?

Lithosphere: rigid, rocky portion of the crust and uppermost mantle Asthenosphere: relatively soft, plastic, flowing zone within the upper  mantle beneath the lithosphere

Mid ocean ridge: oceanic crust, 1-3 km high

Continental rift: continental crust, e.g. east African rift system, may  progress to form an ocean basin

Ocean-ocean convergent boundary: forms “island arcs” e.g. Japan Continent-ocean convergent boundary: forms “continental volcanic arc”  e.g. Andes

Continent-continent convergent boundary: e.g. HimalayasIf you want to learn more check out What ways is the social construction of gender the foundation of the oppression of women and transgender people via sexism, patriarchy and misogyny?

Hot spots: localized zones of deep-seated melting, i.e. beneath the  lithosphere, e.g. Hawaiian islands

Structural geology: deformation of earth materials

Deformation: a change in shape and/or volume, can be seen in glacial ice Distortion: shape change at constant volume

Dilation: volume change

Stress: force/area, pressure, PSI, kilobars

Strain: result of stress, what we actually see in a rock, e.g. faults and folds,  deals with changes in lengths of lines

Intergranular flow: grains rotate and slide past each other Tensional stress: pulling apart, thins and extends, ex: divergent boundary Compressional stress: pushing together, thickens and shortens, ex:  convergent

Shear stresses: deal with shear couples, right handed (dextral)  “clockwise”, left handed (sinistral) “anti clockwise”

Hydrostatic stress: stress comes from all directions, what a sub feels lithostatic, = confining pressure

Strike: bearing of a horizontal line on an inclined plane Don't forget about the age old question of How is the media biased towards women in politics?

Dip: maximum inclination of the plane, measured perpendicular to strike Fold axis (hinge line): line of maximum curvature on a folded surface Axial surface: surface connecting all of the fold axes, a mirror plane Anticline: makes A shape, oldest rocks will be found In the center, concave  down, units dip away from center, oldest units in the core

Syncline: youngest rocks in the center, concave up, units dip toward center, almost always found in pairs

Ridges: cherts and sandstones

Valleys: shales and limestones

Physiography: topography directly reflects underlying bedrock and its  structure

Plunging anticline: plunging axis, contacts “V” in map view, contacts  plunge in cross sections, contact “V’s” point in direction of plunge, otherwise  rules for anticline hold

Plunging syncline: plunging axis, contacts “V” in map view, contacts  plunge in cross sections, contact “V’s” point in direction of plunge, otherwise  rules for syncline hold

Dome: doubly plunging anticline, most rules of anticline hold, e.g. Nashville  Dome We also discuss several other topics like What is the role of septal nuclei?

Basin: doubly plunging syncline, most rules of synclines hold, e.g. Michigan  basin

Hanging wall: block that lies above fault

Footwall: block that lies beneath fault

Dip-slip fault: parallel to dip

Strike-slip fault: parallel to strike

Thrust sheet: thin sheets of rock moved by thrust faults (~1 km thick, 100  km wide, ~2000 km long)

Strike slip faults: conserve thickness and area of crust, transform  boundaries, right lateral = San Andreas, left lateral = Great Glen fault Joints: fractures with little (<1cm) or no movement along them, most form  due to pressure release  

Quiet eruptions: nonexplosive, generally mafic lavas, e.g. Hawaii Explosive eruptions: deadly, intermediate and felsic lavas, e.g. Mt St  Helens

Viscosity: the measure of how easily a fluid flows, high viscosity=pasty, low  viscosity=watery

Pahoehoe: lava with a ropey texture, smoother texture, easier to walk on,  forms when basaltic lava flows cease flowing and solidify simultaneously Aa: lava that is angular and jagged, cindery blocks, solidifies at the surface  before flow ceases We also discuss several other topics like Who is the main character of the piece "an emily for rose"?

Shield Volcano: largest type of volcano, low angles on the sides, very  shallow, islands of Hawaii are completely composed of these, low viscosity  basaltic lavas, almost exclusively lava (no ash)

Composite volcano: large (usually ~8000 feet high), classic volcano shape, concave upward slopes (15 degrees at base, ~30 degrees at top), mostly  intermediate compositions, lava flows mixed with pyroclastic eruptions, ex:  Mt St Helens, Mt Fuji. Mt St Helens in on a continental subduction zone,  alternating layers of tephra and solidified lava

Lava flows: hard, resistant

Pyroclastic material: soft, easily eroded

Nuees ardentes (fiery cloud): deadly, super heated pyroclastic flow, >800 degrees Celsius, glows, hovercraft effect, clocked at 100 mph Cinder cone volcano: smallest type of volcano, very steep slopes (30-40  degrees), exclusively pyroclastic material, generally subsidiary structures on  the flanks of larger volcanoes, simple conical pile of tephra Fissure eruptions: lava spews out from a fracture, common in east Africa  and Iceland. Low viscosity

Caldera eruptions: Yellowstone is most famous, lava pushes up o the crust, doming reaches a critical state and the crust collapses

Vesicles: gas cavities due to degassing

Angle of repose: maximum slope where unconsolidated material becomes  stable, important for cinder cones, sunset crater

Flood basalts: area of volcanic activity that has covered the land in large  amounts of lava, at continental rifts, vast bodies of basaltic lava flow forth  from fissures

Body waves: earthquake waves that pass through the interior of earth,  generally travel the fastest, include both S and P waves

Surface waves: cause most of the damage to buildings during earthquakes Hypocenter (focus): the point within earth where an earthquake takes  place

Epicenter: the point of earth’s surface directly above the point where an  earthquake occurs

Mercalli scale: earthquake intensity scale that assesses the effects of an  earthquake on humans and human made structures

Tsunami: an earthquake generated sea wave that can sometimes destroy  coastal cities thousands of kilometers for its source

Pressure release: change in shape, induced by stress

Important Questions 

What were Wegener’s 5 pieces of evidence?

1. Good fit of the continents

2. Good fit of the rocks and structures (rock types match)

3. Coal swamps (there shouldn’t be coal in the tip of Greenland, but there is)

4. Ancient glacial patterns (striations match and line up)

5. Geographic ranges of fossils

What was the name of the book Wegener published? The Origin of Continents and Oceans

Who proved Wegener wrong with science?

Sir Harold Jeffreys

In the 1950s-60s, the US dept of defense mapped the ocean floor to  understand its…

1. Topography

2. Magnetics

3. Gravity

What are earth’s major tectonic plates?

1. North American  

2. South American

3. African  

4. Eurasian

5. Antarctic

6. Indian- Australian

7. Pacific

What geological features does the plate tectonics theory explain? 1. Chains of volcanoes

2. Earthquake belts

3. Why mountain belts border continents

4. Polar wandering

What are the mechanisms of plastic deformation?

a. Mechanical dislocations

b. Recrystallization

c. Intergranular flow

What are the 4 types of stress?

1. Tensional

2. Compressional

3. Shear (or rotational)

4. Hydrostatic

What are the characteristics of normal faults?

a. Dip slip fault

b. Hanging wall moves down relative to footwall

c. Emplaces younger rocks on older rocks

d. Tensional stresses

e. Extends and thins crust

f. Form horsts (upthrown block) and grabbers (downthrown block) What is the evolution of continental rifts?

1. Upwelling leads to doming of the crust

2. Crust is broken and stretched producing a rift valley

3. Continental rifting eventually produces a linear sea

4. If spreading continues, it will develop into an ocean

What are the characteristics of reverse faults?

a. Dip-slip fault

b. Hanging wall moves up relative to footwall

c. Emplaces older rocks on younger rocks

d. Compressional stress

e. Shortens and thickens crust

f. Forms “thrust” faults, low angle (<30 degree dip) faults Some eruptions are explosive, and some are not, why? a. Deals with the high viscosity of magma

b. High viscosity magmas clog the piping system. Gases build up in the  magma chamber and it explodes (high viscosity= bigger eruptions) What does composition have to do with eruptive style? a. Mafic= quiet and free flowing (Hawaii)

b. Intermediate= explosive with periods of quieter lava flows (Mt St  Helens)

c. Felsic= totally explosive (Yellowstone)

The hot spot track associated with the Hawaiian islands and  emperor seamounts _____

- Shows that the pacific plate has been moving northwest for the last 30  million years

If, during an earthquake, a hanging wall slides upward relative to a  footwall, the fault is termed _______ if the fault is steep (closer to  vertical than horizontal)

- Reverse

If, during an earthquake, a hanging wall slides upward relative to a  footwall, the fault is termed ______ if the fault is shallow (much  closer to horizontal than vertical)

- Thrust

If, during an earthquake, a footwall slides upward relative to a  hanging wall, the fault is termed ______

- Normal

If a fault is nearly vertical in orientation and the two walls of rock on opposite sides slide past one another horizontally, the fault is  termed ________

- Strike-slip

What are faulting and earthquakes examples of?

- Brittle behavior

Which type of earthquake wave travels fastest?

- P-wave

How many seismic stations are necessary to find the epicenter of  an earthquake?

- 3

Earthquakes are likely to occur along _____

- all 3 major types of plate boundaries

Intermediate and deep earthquakes occur along _____ - convergent plate boundaries

A body of rock affected by tensile stress will likely undergo ______ - stretching

A body of rock affected by compressive stress will likely undergo  ______

- shortening

The distinction between joints and faults is that _______ - faults are fractures along which displacement has occurred;  displacement does not occur aong joints

Normal, reverse and thrust are all examples of ________ faults. - Dip-slip