Transcript Sep 8 - University of San Diego

I.
Geology
B.
Plate Tectonics
2.
Mid-Ocean Ridge System
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3.
Discovered from sea floor mapping with SONAR during
and after World War II
Largest geological feature on Earth
Ridges displaced in some areas by transform faults
Trenches
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Conspicuous sea floor features
Especially common in the Pacific Ocean
http://www.ngdc.noaa.gov/mgg/image/global_topo_large.gif
Fig. 2.5
I.
Geology
C.
Plate Tectonics - Evidence
1.
“Ring of Fire”
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Geological activity (e.g. earthquakes, volcanoes)
associated with mid-ocean ridges and with trenches
Fig. 2.6
I.
Geology
C.
Plate Tectonics - Evidence
1.
“Ring of Fire”
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2.
Geological activity (e.g. earthquakes, volcanoes)
associated with mid-ocean ridges and with trenches
Closer to ridges
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3.
Younger rock
Thinner covering of sediment
Magnetic anomalies
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Caused by magnetic field reversals
Symmetrical on either side of ridge axis
Fig. 2.7
I.
Geology
D.
Plate Tectonics - Mechanism
1.
Sea-Floor Spreading
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Mid-ocean ridges contain rifts where two pieces of
crust are moving apart and new oceanic crust is being
created (spreading rate ca. 2-18 cm y-1)
As rift widens, hot mantle material rises through rift,
cools and solidifies to form new oceanic crust
Ridges = spreading centers
Theory generated by induction explains observations
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Younger rock closer to ridges
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Thinner sediment closer to ridges
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Patterns of magnetic anomalies
Fig. 2.8
I.
Geology
D.
Plate Tectonics - Mechanism
1.
Sea-Floor Spreading
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Lithosphere made up of lithospheric plates
Plates may contain continental crust, oceanic crust, or
both
Plates rest on asthenosphere (plastic upper mantle)
Plate boundaries correspond to locations of mid-ocean
ridges and to trenches
Not all plates completely characterized yet
Fig. 2.9
I.
Geology
D.
Plate Tectonics - Mechanism
2.
Subduction
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Old crust destroyed when one plate dips below
another
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Oldest oceanic crust ~200 million years old
Denser plate subducted beneath less dense plate
Locations – oceanic trenches = subduction zones
Recycles crust and supports volcanic activity
May result from collisions between
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Continental plate and oceanic plate (oceanic plate
subducted; usually forms volcanoes)
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Two oceanic plates (denser plate subducted;
usually forms island arc)
Fig. 2.10
Fig. 2.11
I.
Geology
E.
Geological History
1.
Continental Drift
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All
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continents joined together ~200 mya
Pangaea – “supercontinent”
Panthalassa – single ocean  Pacific Ocean
Tethys Sea – Shallow sea between Eurasia &
Africa  Mediterranean Sea
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Sinus Borealis  Arctic Ocean
Laurasia separated from Gondwana ~180 mya
Fig. 2.14
Fig. 2.14
Fig. 2.14
Fig. 2.14
Fig. 2.14
Global Plate Tectonics
Jurassic to Present Day
By
L.A. Lawver, M.F. Coffin, I.W.D. Dalziel
L.M. Gahagan, D.A. Campbell, and R.M. Schmitz
2001, University of Texas Institute for
Geophysics
February 9, 2001
We wish to thank the
PLATES’ sponsors
for their support:
Conoco, TotalFinaElf,
Exxon-Mobil,
Norsk Hydro, and Statoil.
For more information, contact:
Lisa M. Gahagan
Institute for Geophysics
4412 Spicewood Springs Rd.,
Bldg. 600
Austin, TX 78759
[email protected]
Earth – Future Drift
Earth – Future Drift
Earth – Future Drift
Earth – Future Drift
Earth – Future Drift
Link
I.
Geology
F.
Geological Provinces
1.
Continental Margins
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a.
b.
c.
2.
3.
4.
Boundaries between continental and oceanic crust
Accumulate sediment deposits from rivers and streams
Continental shelf
Continental slope
Continental rise
Deep-Ocean Basins
Mid-Ocean Ridges
Hot Spots
Fig. 2.17
I.
Geology
F.
Geological Provinces
1.
Continental Margins
a.
Continental shelf
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Shallowest part of continental margin
Underlie ~8% of ocean surface
Richest, most productive parts of ocean
Some parts exposed during times of low sea level and
eroded by rivers and glaciers now are submarine
canyons
California Coastline
Monterey Canyon
Fig. 2.19
I.
Geology
F.
Geological Provinces
1.
Continental Margins
a.
Continental shelf
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Shallowest part of continental margin
Underlie ~8% of ocean surface
Richest, most productive parts of ocean
Some parts exposed during times of low sea level and
eroded by rivers and glaciers now are submarine
canyons
Varies in width from 1 km (Pacific coast of S Am) to
750+ km (Arctic coast of Siberia)
Ends at shelf break, usually at 120-200 m but up to
400+ m depth.
I.
Geology
F.
Geological Provinces
1.
Continental Margins
b.
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Continental slope
Transition from continent to ocean
Furrowed with submarine canyons in many areas
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c.
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Canyons channel sediment and debris to deep sea floor
Continental rise
Accumulated sediment, including deep-sea fans
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May be extensive in areas where large rivers discharge
into ocean
I.
Geology
F.
Geological Provinces
1.
Continental Margins
d.
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Active margins
Geologically active
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Usually subduction or
transform fault
Steep, rocky shoreline
Narrow continental shelf
Steep continental slope
Usually lack welldeveloped continental
rise
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Sediment removed
by geological activity
Fig. 2.20
I.
Geology
F.
Geological Provinces
1.
Continental Margins
e.
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Passive margins
Not geologically active
Flat coastal plain
Wide continental shelf
Gentle continental slope
Usually well-developed
continental rise
Fig. 2.20
Fig. 2.20
I.
Geology
F.
Geological Provinces
2.
Deep-Ocean Basins
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Mostly between 3000 and 5000 m
Predominantly abyssal plain
I.
Geology
F.
Geological Provinces
2.
Deep-Ocean Floor
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Mostly between 3000 and 5000 m
Predominantly abyssal plain
Seamounts – Undersea mountains
Guyots – Flat-topped seamounts
Rises – Large table-like features
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Common in Pacific
California Coastline
Monterey Canyon
Fig. 2.19
I.
Geology
F.
Geological Provinces
3.
Mid-Ocean Ridges
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Central region – rift valley
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Fractures allow sea water to seep into crust
Fig. 2.23
I.
Geology
F.
Geological Provinces
3.
Mid-Ocean Ridges
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Central region – rift valley
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Fractures allow sea water to seep into crust
Water is heated by rock and rises back to surface of
sea floor
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Hot water picks up dissolved minerals (iron,
manganese, sulfides)
Hot, mineral-rich water contacts cold sea water
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Precipitate forms
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Black smokers
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May be very hot (350 oC or more)
Fig. 2.25