The Sea Floor

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The Sea Floor
Image source http//www.npaci.edu/online/v6.12/he
llyslides.html
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plate tectonics is a geotectonic theory
comprehensive set of idea that explains
development of regional geologic features
supported extremely well by data and
observations not the first theory (e.g.
shrinking Earth geosynclines)
main observations for plate tectonics
from http//www-personal.umich.edu/vdpluijm/gs20
5.html
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note that not all oceans and continents are
separate plates
Pacific plate is all oceanic, but North American
is both oceanic and continental (passive margin
along eastern North America)
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Methods of Studying the Sea Floor

• Techniques
• Dredge Hauls
• Echo Sounding
• Seismic Profiling
• Features of the Sea Floor
• Continental Shelves and Continental Slopes

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Rock Dredge Haul
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Sediment Corer
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Sea Floor Sediment Core
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JOIDES Resolution
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Echo Sounding
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Sea Floor Seismic Profile
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South Pacific Seafloor
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Sea floor Topographic Profiles
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Continental Shelf - Slope
Slope angle is only 4-5
NB that topographic profile is shown with 25x
vertical exaggeration
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Passive Margins and Transitional Crust
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Submarine Canyons

• Turbidity Currents
• Passive Continental Margins
• The Continental Rise
• Abyssal Plains

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Submarine Canyons and Abyssal Fans
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Sand Fall off Baja, CA
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Submarine Cable Breaks
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Contour Currents
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Active Continental Margins

• Oceanic Trenches
• The Mid-Oceanic Ridge
• Geologic Activity on the Ridge
• Biologic Activity on the Ridge

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Global Distribution of Trenches
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Trench Morphology
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Global Mid-Ocean Ridge System
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Mid-Atlantic Ridge seafloor spreading
(divergence) sea-floor bathymetry
axial valley (slow spreading)
NORTH AMERICA
AFRICA
spreading
from http//www.geo.duke.edu/geo41/sfs.htm
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Mid-Atlantic ridge is exposed in Iceland.
fracture zone
both from http//pubs.usgs.gov/publications/text
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Ridge Crest Hydrothermal Circulation
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Black Smoker
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Sea Floor Features

• Transform faults and Fracture Zones
• Seamounts, Guyots, and Aseismic Ridges
• Reefs - Atolls

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Transform Faults - Fracture Zones
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Southwest Indian spreading ridge note transform
fault and apparent deformation in seafloor
deformation
transform fault
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what are transform faults? offsets of the
spreading ridge
displacement across transforms is dictated by
seafloor spreading
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from Structural Analysis, CD-ROM, Declan DePaor
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Guyot Formation
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Aseismic Ridges - Hotspot Tracks
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absolute plate motion hot spots are fixed
points --narrow plume of upwelling that rises
from great depth and interacts with the base
of plates, forming basaltic volcanoes at
surface
Mauna Loa volcano
to visualize, hold a pencil vertically and
move a piece of paper over it, marking spots
motion of Pacific plate over hot spot below
Hawaii
both from http//pubs.usgs.gov/publications/text
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hot spot track forms as plate continues to move
over hot spot
direction
Hawaii-Emperor chain (hot spot track)
gives rate and direction of plate
rate age of volcano / distance from hot
spot direction trend of island chain
because time is long, distance is wide and easily
measured
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Atoll Development
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Atoll Animation
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Sediments of the Sea Floor

• Oceanic Crust and Ophiolites
• The Age of the Sea Floor
• The Sea Floor and Plate Tectonics

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Pelagic Sediment Thickness on Ridge Crest
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Oceanic Crust and Typical Ophiolite Sequence
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Pillow Basalts
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Offshore Drilling
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South Pacific Absyssal Plain Manganese Nodules at
5.3 km sea water depth