Dynamic Earth
Impact Metamorphism
-meteorite impats
-one killed the dinosaurs
-generate heat and impact
Contact Metamorphism
-hot magma chamber
-high temperature
-low pressure
Fault Zone Metamorphism
-rocks slide across each other
-cold rocks-fault breccia (broken)
-hot rocks- flow to make mylonite
Hydrothermal Metamorphism
along mid-ocean ridges
Regional Metamorphism
-continent-continent collision
-cold near surface, hot deeper down
-low temp/low pressure
-high temp/high pressure
Subduction Zone Metamorphism
-low temp/high pressure
-slab is cold, takes a while to heat up
Law of Superposition
-sedimentary rocks deposited younger over older
Law of Original Horizonality
sediments deposited in horizontal beds
Law of Cross-Cutting Relations
-younger features transect older ones
-light-colored granitic dike cuts older, banded metamorphic rock
Inclusions
(Relative Age Dating)
-Older material encolosed within younger
igneous, sedimentary, or metamorphic
Angular Uncomformities
Uncomformities
(Relative Age Dating)
-sedimentary rock over tilted/folded/eroded strata (sedimentary rock)
Disconformity
Uncomformities
(Relative Age Dating)
-sedimentary rock over emergence and erosion (sedimentary rock)
Noncomformity
Uncomformities
(Relative Age Dating)
-sedimentary rock over eroded igneous rock (had intruded sedimentary rock)
Fossil Succession
-gives definate interval of geologic time
-fossils appear in geologic record in a definite order
-based on succession of fossils found in vertical sequences of sedimentary rocks
Dendrochronology
(Tree-Ring dating)
Absolute dates
measurement of annual ring widths at tree heights
isotopes
-different number of neutrons
-frequently used in radiometric dating
Alpha Decay
(Radioactive Decay)
-alpha particle emission
-lower atomic number and atomic mass
-lose an atom
Beta decay
(Radioactive Decay)
-beta (electron) emission
-higher atomic number
-same atomic mass
-neutron transforms into electron
Electron Capture
(Radioactive Decay)
-electron capture
-lower atomic number
-same atomic mass
-electron into neutron
Radiometric dating
constant rate-> half-life
Radiometric Dating of Rocks
conditions
-CLOSED SYSTEM (no parent or daughter leaves the rock)
-different teperatures
Igneous
Radiometric Date Meaning
-time since crystallization from magma
Metamorphic
Radiometric Date Meaning
time since metamorphism or recrystallization
Sedimentary
Radiomentry Date Meaning
not closed (water in it)
age of clasts
Marine Magnetic Anomalies
-magenetic reversals of seafloor spreading
-calibrated by radiometrically dated lavas on land
Acasta Gneisses(Canada)
-oldest rocks
-4030 million years old
Archaean Period
-3.8 to 2.5 million years ago
-reducing atmosphere-little oxygen,
-toxic to most current life
-continental plates began to form
-stromatolites abundant
Hamelin pool stromatolites
-oldest organisms on earth
-fossils 3.5 billion years ago
-formed by single-cell organism: cyanobacteria
Banded Iron Formations
-2.5-1.8 billion years ago
-oxygen (waste product of plants) banded with abundant dissolved iron to yield minerals like magnetite and hematite
-amount of oxygen locked up in banded iron beds-20x volume of oxygen in atmosphere today
-important source of iron ore
Proterozoic Era
-2.5 billion to 543 million years ago
-stable continents appear and acrete
-first abundant fossils of living organisms (bacteria and archaenas)
Prokaryotes vs. eukaryotes
-pro-dna organized in single chromosome, no nucleus, no mitosis

-euk-dna organized in multiple chromosomes inside a nucleus, mitotic division

Ediacaran fauna
-late proterozoic era fossil
-found on underside of course sandstone/mudstone- suggests a rapid burial
-worldwide presence
-not found after onslought of mineralized organisms in Cambrian period
Snowball Earth
-time when Earth must have been covered by a sheet of ice
-rapid greenhouse warming from carbon dioxide took Earth out of icy tomb
-repeated cycle
-abundant co2 held in limestones
-led to proliferation of animals
Paleozoic
Age of Invertebrates, Fish, Amphibians
Mesozoic
Age of Reptiles
Cenozoic
Age of Mammals, humans develop
Deformation
-general term for changes in volume or shape of rock masses in response to applied forces
-caused mainly by gravity
Stress
-CAUSE of deformation
-force applied to volumes of rock
Strain
EFFECT of deformation resulting from applied stresses
Uniform Stresses
-same in all directions
-simply pressure
Differential Stresses
vary with direction
Hydrostatic Stress
(type of Uniform Stress)
like on the bottom of a swimming pool
Lithostatic stress
(type of Uniform STress)
“felt” by rocks deep in the earth from overburden and surrounding rocks
Normal Stress
(type of Differential Stress)
directed perpendicular to surfaces
Shear Stress
(type of Differential Stress)
directed parallel to surfaces, causing sliding
Compressional Stress
(type of Differential Stress)
directed inward, leads to shortening of rock
Tensional Stress
(type of Differential Stress
directed outward and can lead to stretching of rock
types of changes from STRAIN
-length changes
-volume changes
-angular changes: between lines; surfaces sliding past one another
Strength
-resistance to deformation
-function of pressure and depth- the deeper in the Earth, the stronger the rocks
Elastic Deformation
completely and instantly recoverable
Brittle Deformation
-creates sharp discontinuities
-when rocks pushed beyond elastic limit
(ie earthquakes)
Ductile (Plastic) Deformation
-continuous deformation
-begins at critical strength:YIELD STRENGTH
-strength of ductile material governed by composition, temp, rate of deformation
-strength lower for greater T or lower strain
Active Areas
-where deformations take place on Earth
-marked by earthquakes and surface deformation
-plate boundaries: ridges, subduction zones, and transfrom faults where plates pull apart, converge and slide past another can result in extreme thinning or thickening of the crust
Strike
to define a plane in space
-to describe faults and folds
compass direction in horizontal plane
Dip
to define a plane in space
-to describe faults and folds
-inclination of plane normal to strike
in the vertical plane
-max inclination of the plane
Joints
(example of Crustal Deformation)
-cracks/fractures in rock with little/no visible displacement
-common-exploited by weathering
-commonly in parallel arrays or networks
-(alligned squares)
Faults
(example of Crustal Deformation)
-fractures with obvious displacement
-common-shallow crustal deformation
-classified according to direction of displacement (and strain)
-(shifted/displaced squares)
Divergence
(example of Crustal Deformation)
-vertical compression from gravity
results in horizontal extension

-example of divergent boundary-oceanic ridges
-oceanic crust made at the ridge
-lithosphere thickens and subsides as it cools

What happens with a normal fault?
-before- nice horizontal layers
-small offset- hanging wall drops down relative to footwall
-large offset- active fault, hanging wall sliding downwards
-erosion- fault line scarp
Convergence
(example of Crustal Deformation)
-horizontal compression
-results in horizontal shortening

-examples:
-Thurst Fault: hanging wall moves UP relative to foot wall
-older rocks move over younger rocks

Formation of Himalayas
collision of India and Asia
Surface features along a strike-slip fault
-rocks move past each other horizontally
-stand on one side of fault surface, see where the other side moves to determine which type of lateral strike-slip fault it is
-drainage offets
-linear valley along fault
-active and inactive fault traces
Folds
(example of Crustal Deformation)
-tilted and bent rock layers
-caused by layer-parallel shortening
-common-deeper level crustal deformation
-classified by shape/geometry
anticline
(type of fold)
2 sandstones incline away from each other
syncline
(type of fold)
-2 sandstones folding the same direction together
-big “U” shape
Dome
-N-S and E-W folding
-circular area where strata pushed up relative to what’s around it
-hot targets for oil/gas
-exposed by erosion- younger rocks on outside, bottom
Basin
-N-S and E-W folding
-rocks in center pushed down relative to what’s around them
-Older rocks on the outside, top
Earthquake causes
-weak ones from volcanoes
-strong- motion along faults, disconnect between rocks on either side of the fault, motions occur and release energy
Elastic Rebound Theory
(Earthquakes)
-Earthquake- elastic rebound of previously stored elastic strain energy in the rocks on either side of the fault
-energy released is based on how much slick there is, how much rocks aredeformed, over how much area the fault moved
p-waves
(generated by earthquake)
(body wave-travel through earth)
-compressional waves
-horizontal pressure
-~6km/s FASTER than S waves
-SLOWER in liquids than in solids
s-waves
(generated by earthquake)
(body wave-travel through earth)
-shear waves
-diagonal pressure
-3.5 km/s
-slower than P waves
-can ONLY travel through solid
Raleigh waves
(generated by earthquake)
(surface wave)
like ocean waves
love waves
(generated by earthquake)
(surface wave)
horizontal “shimmy”
seismograph record
-P-waves arrive first (travel faster)
-then S-waves
-then surface waves
one unique epicenter
-3 seismic stations
-triangulation
Intensity
Mercalli scale
-meaure of the degree of earthquake shaking at a given locale
-based on the amount of damage
-scale: I-XII
Richter Magnitude Scale
-Estimates the amount of energy released at the source of the earthquake
-large eq: 9
-based on amplitude of the largest seismic wave recorded (p or s)
-RMS of 2 is 10 times greater than RMS of 1
Calculating RMS
-log(amplitude) + (distance correction)
distance correction is time difference between P and S wave arrival
First Motion of an earthquake
versus an atomic bomb
-distinct quadrants of push or pull
versus all regions experiencing an initial push away from epicenter
large earthquakes to fewer occur on…
-subduction zones (Alaska, Japan)
-collision zones (Himalayas by India/Asia)
-(both on convergent plate boundaries)
-strike-slip plate boundaries on land (SF)
-divergent plate boundaries (East African Rift)
the most subduction occurs in
the Pacific Basin
liquefaction
-from EQ shaking
-caused large slope failure
-cracks develop in crust
Tsunami
-Earthquake waves in the sea
-low amplitude (increases rapidly as seafloor shallows and speed and wavelength decrease)
-long wavelength
Earthquake prediction
short-term (hours, days, weeks)
-based on precursor changes
-uplift/subsidence of land surface
periods of renewed/reduced minor seismicity
-changes in gasses emitted from wells
-abnormal animal behavior
long term earthquake prediction (years, decades, centuries)
-based on probabilities
-risk assessment maps based on historical data
-seismic “gaps” :buildup of strain along plate boundary
Seismology
(geophysics-indirect investigations)
tells:
-earthquake: location, strength, physical properties, movements
-seismic refraction
-seismic reflection
magnetism
(geophysics-indirect investigations)
-tells core dynamics, paleomagnetics (plate motions, reversals, etc)
-mass flow
heat flow
(geophysics-indirect investigations)
tells convection/conduction, lithosphere thickness
gravity
(geophysics-indirect investigations)
density distributions near surface
seismic refraction
Seismology
(geophysics-indirect investigations)
velocity, physical properties, layer thinknesses
seismic reflection
Seismology
(geophysics-indirect investigations)
-internal gemoetry
-waves bouncing off earth
-mapping the subsurface (under ocean or inside the earth)
Seismic Tomography
Seismology
(geophysics-indirect investigations)
MRI of the Earth
velocity of compressional waves (p-waves)
higher velocity in higher density
refraction
Snell’s Law
-bending-path bends away from normal to interface with increasing density (and velocity)
-travel more where you can travel quickly so biggest angle in highest density
increase velocity with increase depth- waves move faster inside Earth
liquid outer core proved by:
-P and S wave shadow zone
-P waves refracted off liquid and placed constraints on radius of liquid core
-S waves ended at liquid
Lehmann Discontinuity
seperation between liquid outer core and and solid inner core
Moho
-seismic discontinuity of increasing P wave velocity with depth
-boundary between crust and uppermost mantle (within lithosphere)
Oceanic Crust
-thin (5-7 km)
-dense (basaltic)
-mostly young (<200 my old)
Continental Crust
-thick (20-70 km)
-less dense (granitic)
-mostly very old (<4500 my old)
Lithosphere
-thermal boundary layer
-includes crust and part of upper mantle
-thickness depends on temp (thin where hot and young)
Asthenosphere
-hot, weak part of upper mantle
-solid, but weak relative to lithosphere
-NOT molten, may have melt in it
Mesosphere
-strong lower part of mantle
-solid like lithosphere
-650-2800 depth
Conduction
-without any transfer of mass
from radioactive decay in Earth’s interior (near surface in granitic material)
-higher in young, thin lithosphere and areas of active magmatism
Convection
-heat because movement of mass/water
-movement of magma from mantle to surface
-seafloor spreading (formation/recycling of plates)
hydrothermal circulation (black smoker, geysers, etc.)
important mechanism of cooling the Earth
generation of new oceanic lithosphere and recycling by plate tectonics- large scale convection of the planet
conductive cooling of lithosphere causes
-lithosphere-asthenosphere boundary move down at rate proportional to:
1/(age of lithosphere)^2
Earth’s magnetic field
function of matter and motion in the Earth’s magnetic outer core
Magnetic Reversals
show age of strips of oceanic crust worldwide
Earth’s gravity field g=
G(m1 x m2)/r^2
-m1=measuring device
-m2=mass between device and center of Earth
Gravity Anomoly
-negative=mass deficiency
-positive=mass excess
-show how actual gravity field differs from gravity of uniform/featureless Earth
Satellite Altimetry
-determine bathymetry based upon slight changes in elevation of sea surface from greater gravitational attraction of large rock masses on sea floor (volcanoes)
to learn topography of seafloor
-echo-sounding
-swath mapping
-satellite altimetry
to learn geology of ocean floor
-side-scan sonar (reflectivity of sound signal)
-ROVs (remotely operated vehicles)
-Alvin (submersible)
-Ocean drilling program
Passive continental margin
-margin (where continental crust transitions into oceanic crust) created by spreading at mid-ocean ridge
-WEST coast of South America
Active continental margin
-margin (where continental crust transitions into oceanic crust) adjacent to a subduction zone (or strike-slip boundary)
-contains oceanic trench
-EAST coast of US
Continental shelf
on Passive continental margin
-submerged extension of CONTINENT
-nearly horizontal
-thick
-(during Ice Age, was exposed)
continental slope
on Passive continental margin
-seaward edge shelf
-steeper
-boundary between continental/oceanic crust
continental rise
on Passive continental margin
-more gradual slope
-very wide (merges into abyssal plain)
-thick with sediments from continental slope
-turbidity currents make deep sea fans
deepest place on Earth
-deep ocean trenches
-~11 km below sea level
terrigenous
on ocean basin floor
-derived from land-mineral grains from continental rocks
biogenic
on ocean basin floor
derived from organisms- marine animal shells, organisms
precipitates
on ocean basin floor
derived from water- minerals crystallize out of water
mid-ocean ridge
may occupy as much as 1/3 of ocean basin
hotspots
long-lived, large volcanic features that are randomly distributed through the ocean basins (and on land)
seamounts
-smaller volcanoes that erupt commonly near the ridge axis
-generally, do not rise to sea surface
Coral Reefs and Atolls
marine structures composed mainly of coral (some live but mostly dead skeleton) and some algae and sediment
Coral Reef
-colonies of coral generally near the shore
-require warm temperature, clear sunlit water, and nutrients from ocean water
Atoll
-circular coral structure with an interior lagoon
-can be >1000 m thick
Mountain Belts
-area of high elevation
-belt of HIGHLY DEFORMED rocks resulting from contractional thickening and uplift of the crust
-thickening and uplift expose deep level metamorphic and igneous rocks
Andean type
of Orogenic/Mountain Belt
-magmatic arcs above subduction zones
-accreted terrains “smeared” onto them during subduction
-Foreland basins of sedimentary rocks
Collisional Type
of Orogenic/Mountain Belt
collided continental margins-at least one was a subduction zone (possibly both)
suture zone marks seam where 2 continents welded together
remnants of Andean type typically found
Continental shield
collage of old continental fragments and orogenic belts
old “cratons” are rifted and surrounded by somewhat younger orogenic belts
Wilson Cycle
Major Earth Process
oceans open and close
-rifting and continental margin development
-seafloor spreading
-subduction
-collision
-continued convergence
-new cycle…
tectonic extension
horizontal stretching, crust/lithosphere thinning, subsidence, sedimentation (burial)
*good sedimentary record, but deep rocks not exposed
tectonic extraction
horizontal shortening, uplift, crust/lithosphere thickening, erosion (exhumation)
*sedimentary record deposite far away, surface material removed and deep level rocks exposed
miogecline
rifted continental margin
once a rift and spreading center, not a plane interior
Suture Zone
marks the site of a former oceanic tract
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