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Deep Ocean Topography
Mid-Ocean
Ridges
and
Hydrothermal
Vents
Sarah Fawcett
Mid-Ocean Ridges
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Linear mountain chains.
Some of the largest
features on Earth.
5km-2.6km deep.
Roughly symmetrical in
cross section.
Thousands of kilometers
wide.
Volcanoes, earthquakes,
hills and mountains.
Location of Ridges
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Mid-Atlantic Ridge
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1855 - Fontaine Maury
identified “shallow middle
ground”.
1950s - Heezen & Ewing
proposed a continuous
mountain range.
East Pacific Rise
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Largest oceanic ridge.
1870s - Challenger
Expedition
1950-60s - described by
Heezen and Ewing.
Formation of Ridges
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Divergent tectonic
plate motions.
Tensional forces =
thinning of oceanic
crust and upwelling of
magma, forming
ridges.
Seafloor Spreading
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Lava buried by sediment as seafloor spreads
away from ridge.
Spreading Rates:
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Slow - 10mm/yr (Southwest Indian Ridge)
Fast - up to 160mm/yr (East Pacific Rise)
Correlation between global spreading rates
and transgression of ocean waters onto the
continents.
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Early Cretaceous - Global spreading rates uniformly high
Marine sediments
Seafloor Dating
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Paleomagnetic dating
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Curie Point
Use spreading rate to
calculate age of rock.
Age of the Seafloor
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Gets older further from
the ridge.
Hydrothermal Vents
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Localized discharges of heated
seawater.
Cold water percolates down
into the crust through fissures.
Heated water rises and seeks
a path to the surface.
Bursts into the ocean as hot as
400ºC but intense pressure
from overlying ocean prevents
it from boiling.
Accounts for amount of the
Earth’s heat loss.
Growth of Vents
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Chimneys
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“Black Smokers”
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Minerals leached from
the crust - Zn, Fe, Cu.
Rapid growth rate.
Hottest vents.
Iron monosulfide.
“White Smokers”
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Cooler vents.
Compounds of Ba, Ca
and Si.
Discovery of Vents
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1977 on East Pacific Rise
Near Galapagos Islands
ALVIN
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Research submersible.
Wood’s Hole
Oceanographic Institute.
Viewports, searchlights,
mechanical arm, cameras.
First temperature
measurement.
Location of Hydrothermal
Vents
Life at Hydrothermal Vents
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Harsh environment, yet
abundant life:
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Tubeworms
Crabs
Shrimp
Clams
Anemones
CHEMOSYNTHETIC BACTERIA
No photosynthesis
Bacteria convert sulfur to
energy by chemosynthesis,
forming base of foodchain.
Animals eat bacteria or
bacteria live inside their
bodies.
Origin of Life?
Flow at Vents
QuickTime™ and a
Sorenson Video decompressor
are needed to see this picture.
Baker, Cormier, Langmuir and Zavala
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Hydrothermal plumes along segments of contrasting magmatic
influence, 15º20’ - 18º30N, East Pacific Rise: Influence of axial faulting.
Geochemistry Geophysics Geosystems. Volume 2. September 2004. AGU and
the Geochemical Society.
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Theory: Greater incidence of hydrothermal vents on faster spreading ridge
segments, not always the case - Tectonic forces can dominate.
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Segment of ridge between Orozco and Rivera transform faults (15º18’N 18º30’N).
133 rock cores.
Comparison of hydrothermal environment of three adjacent but distinctly different
segments.
Prediction:17ºN segment should have less extensive hydrothermal plumes
than16º segments - slower spreading rate.
Opposite is true.
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17ºN segment: plume incidence = mean of super fast
spreading segments on the southern EPR.
Local permeability environment in the region controls
amount of hydrothermal activity:
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Conclusion:
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16ºN segment: little indication of faulting, model for fast spreading rates, may
have hydrothermal activity suppressed by volcanic flows that act as an
impermeable cap over much of the segment.
Tectonic forces can control the extent and nature of hydrothermal
activity.
Documented for several sites on the Mid-Atlantic Ridge.
On a global scale, however this portion of the ridge
follows the existing global correlation between plume
incidence and spreading rate.