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Deep Ocean Topography

Deep Ocean Topography. Mid-Ocean Ridges and Hydrothermal Vents Sarah Fawcett. Mid-Ocean Ridges. Linear mountain chains. Some of the largest features on Earth. 5km-2.6km deep. Roughly symmetrical in cross section. Thousands of kilometers wide.

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Deep Ocean Topography

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  1. Deep Ocean Topography Mid-Ocean Ridges and Hydrothermal Vents Sarah Fawcett

  2. Mid-Ocean Ridges • 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.

  3. Location of Ridges • Mid-Atlantic Ridge • 1855 - Fontaine Maury identified “shallow middle ground”. • 1950s - Heezen & Ewing proposed a continuous mountain range. • East Pacific Rise • Largest oceanic ridge. • 1870s - Challenger Expedition • 1950-60s - described by Heezen and Ewing.

  4. Formation of Ridges • Divergent tectonic plate motions. • Tensional forces = thinning of oceanic crust and upwelling of magma, forming ridges.

  5. Lava buried by sediment as seafloor spreads away from ridge. Spreading Rates: 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. Early Cretaceous - Global spreading rates uniformly high Marine sediments Seafloor Spreading

  6. Seafloor Dating • Paleomagnetic dating • Curie Point • Use spreading rate to calculate age of rock. • Age of the Seafloor • Gets older further from the ridge.

  7. Hydrothermal Vents • 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.

  8. Growth of Vents • Chimneys • Minerals leached from the crust - Zn, Fe, Cu. • Rapid growth rate. • “Black Smokers” • Hottest vents. • Iron monosulfide. • “White Smokers” • Cooler vents. • Compounds of Ba, Ca and Si.

  9. Discovery of Vents • 1977 on East Pacific Rise • Near Galapagos Islands • ALVIN • Research submersible. • Wood’s Hole Oceanographic Institute. • Viewports, searchlights, mechanical arm, cameras. • First temperature measurement.

  10. Location of Hydrothermal Vents

  11. Life at Hydrothermal Vents • Harsh environment, yet abundant life: • 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?

  12. Flow at Vents

  13. Baker, Cormier, Langmuir and Zavala • 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. • Theory: Greater incidence of hydrothermal vents on faster spreading ridge segments, not always the case - Tectonic forces can dominate. • 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.

  14. 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: • 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. • Conclusion: • 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.

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