Dynamic Earth

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Dynamic Earth

• Class 6
• 26 January 2006

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Big Island Field Trip

• April 28-30, 2006
• Purchase your own ticket
• Meet Friday at Hilo airport no later than 6 PM
• Leave Hilo Sunday after 5 PM
• Ground Transportation
• We have reserved 6 minivans
• Accommodations
• Kiluea Military Camp (semi-private dorms)
• Costs estimate 99 plus airfare
• Roundtrip air fare your best deal
• 2 days van and fuel, food (2 breakfasts and
  picnic lunch), 2 nights lodging
• Payment (cash or check made out to JenPac Travel)
• Non-refundable deposit of 50 due by February 17
• Final payment of 49 due by March 17
• Meeting
• Important meeting Friday, April 21 at 130 PM
• Location to be announced attend or find out what
  happened

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Mistake on Syllabus

• First exam will be on February 14, 2006
• Listed as February 15th on hard copy
• Second exam will be on March 9, 2006
• Listed as March 17th on hard copy
• Exam dates correct on the online syllabus
  http//www.soest.hawaii.edu/GG/FACULTY/POPP/GG101.
  html
• Links to photos of last field trip online

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Any Questions?
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The Deep The beginnings of Plate
Tectonics(Chapter 2)
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Plate Tectonics

• Fundamental Concept and Unifying Theory in Earth
  Science
• Idea is gt 100 yrs old
• Acceptance only within the past 30 yrs

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Inside the Earth
Fig. 1.12
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Drilling into the seafloor provided more evidence
supporting sea-floor spreading

• Micropaleontology of sediments
• Dating of the underlying lavas

Drilling ship Glomar Challenger
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Age of Seafloor Crust
Realizing that the ocean basins are very young
was key to acceptance of Plate Tectonics Theory
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Ocean crust records magnetic reversals
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Seafloor Spreading Hypothesis

• Geopoetry of Harry Hess Robert Dietz
• New seafloor forms by upwelling at the center of
  MOR and moves laterally
• Older crust is destroyed in the subduction zones
  at the trenches
• Seafloor is younger than 200 MY
• Solved Continental Drift problem

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The moving plates describe a process
calledConvection
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Convection
Water boiling in a pan on your stove is an
example of convection
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Convection in a Pot
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Convection in the Mantle
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Increased Heat with Depth
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Convection in the Mantle
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Convection within the Earth
The Lithosphere is created at spreading
centers It is destroyed at Trenches (Subduction
Zones)
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Upper Mantle Convection as a Possible Mechanism
for Plate Tectonics
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Plates

• Rigid Lithosphere with definite boundaries
• Can have both oceanic and continental crust or
  just one kind.

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Mosaic of Earths Plates
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Rates of plate motion

• Mostly obtained from magnetic anomalies on
  seafloor
• Fast spreading 10 cm/year
• Up to 20 cm/year
• Slow spreading 3 cm/year

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Relative Velocity and Direction of Plate Movement
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Mid-Atlantic Ridge
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Earthquakes in mid-ocean areas
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Earthquakes in mid-ocean areas
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Anatomy of a Plate
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Types of Plate Margins
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Continental Collision forms Mountains
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Three possible mechanisms for the movement of
lithosphere over the asthenosphere
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Ocean crust records magnetic reversals
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Magnetic Anomalies in the Atlantic
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We can map spreading centers with swath
bathymetry
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We can look at new sea floor on land

• Thingvellir, Iceland America to the left,
  Eurasia to the right, a rift down the middle.

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Iceland is being pulled apart as it sits astride
the Mid-Atlantic Ridge.
Gudmundur E. Sigvaldason, Nordic Volcanological
Institute
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Nothing beats going down there in person, or at
least observing from a remotely-operated vehicle
Mir (sub)
Alvin (sub)
Jason II (ROV)
Ropos (ROV)
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UH/HURL Submersibles
Pisces IV
Pisces V
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At spreading centers, you can look at the ocean
crust in cross section
Pillow lava
Feeder dikes
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At fracture zones, you can look at the ocean
crust in cross section
Surface flows
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Sometimes, sea floor gets thrust up on land to
form what is called an ophiolite
Oman, on the Persian Gulf
Pillow lava
Sheeted dikes
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How we think the oceanic crust forms

• Hot rock rises and partially melts
• The melt is erupted to form a layer of basalt
  lava flows and pillows

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How we think the oceanic crust forms

• The feeders to the flows are vertical sheets
  called dikes
• Below the dikes, massive gabbro (like basalt,
  but with larger crystals) solidifies from the
  melt.

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How do we figure out the deep structure?

• Remote Sensing from the surface
• Echo sounding using high-frequency sound (several
  KHz thousand cycles per second
• But high-frequencies bounce off the hard rocks
• We need low frequency sound (5-100 Hz) to
  penetrate through the rock beneath the seafloor
  this is called seismic prospecting

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How do we figure out the deep structure?
Then explosives
Now Air Guns
Maurice Ewing
Seismic streamer
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Multichannel seismics - measure structure in two
and even three dimensions
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Sea floor structure
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What do we find right at the spreading axis?
Black smokerHydrogen sulfide
Giant tube worms and clams live onthe Black
smokers
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What do we find right at the spreading axis?
A single spot on the East Pacific Rise (pictures
about a year apart)
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How does it work?

• Cold sea water circulates down through cracks
• Water heats up as it passes through hot rock
• Water interacts with rock -- dissolves minerals
  and becomes laden with dissolved sulfides

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How does it work?

• Sulfides precipitate on exposure to cold water
  (black smoker)
• Bacteria oxidize the sulfides (chemosynthesis)
• Worms have a symbiotic relationship with the
  bacteria in their guts

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How does it work?

• Crabs live on dead worms, bacterial mats, and
  snow
• A complete complex food chain is established

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Were submarine hot springs the origin of life on
Earth?
Maybe
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What are those offsets in the spreading center,
and what are those parallel ridges?
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What are those offsets in the spreading center,
and what are those parallel ridges?
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The problem was solved by the Canadian
Geophysicist J. Tuzo Wilson
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Transform Faults offset Spreading Centers
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Notice how Wilsons theory explain depth offsets
across fracture zones
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The San Andreas FaultA transform fault
separating the Pacific and North American Plates
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Tuzo Wilsons other great contribution was the
concept of a stationary hot spot
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Hawaiian-Emperor chain
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Long-lived Global Hot Spots
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A compass points North because theneedle is made
of iron. It becomes aligned in the Earths
magnetic field.
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Magma formed at spreading centers contains minute
pieces of iron that become aligned in the
direction of the Earths magnetic field.
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Apparent polar wander

• Either the North Magnetic Pole or the continents
  must have moved.

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Homework 2Due next TuesdayJanuary 31st

• Find it on the Web Site

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Tuesday

• Video
• Journey to the Ocean Floor