EPS SCI 15 Lab Review

Why does the MAR spread apart at lower rates than the EPS?

Slow spreading rates, the newly formed oceanic crust cools down and contracts before spreading far from the ridge. This forms steeper slopes and smaller volume.

Where does the MAR have a deep rift valley?

Along its crest

Why is the EPS less steep than the MAR?

Fast spreading rates relative to the MAR; the newly formed oceanic crust spreads faster than it cools, retaining a lower denistu/larger volume far from the ridge

Is there a rift valley associated with the EPS?

No, just a smooth volcanic summit with a crack along the crest

The distance from the island of Hawaii to Pearl Reef is about 2,000 km. What has been the approximate velocity of seafloor movement in centimeters per year (cm/yr), during the last 20 million years (i.e., since Pearl Reef was formed over the hot spot)?

Velocity = 200,000,000 cm/20,000,000 years = 10cm/yr

Ocean-ocean convergence

subduction of one plate underneath the other; older, colder plate is subducted under the younger warmer one

associated with deep trenches and volcanic island arcs parallel to trenches

Ocean-continent convergence

Subduction of more dense oceanic plate beneath continental plate

associated with deep ocean trenches near continental volcanic arcs

Continent-continent convergence

Since both plates are low density, neither is forced to subduct into asthenosphere: they both are pushed up

mountain building occurs, crust becomes ohighly deformed

How are island arcs created?

Stationary plumes of magma erupt through a plate that is moving over it, forms chains of extinct volcanic islands terminating at the active (youngest) volcanic island

ex. Hawaii

Determine factors that determine sediments’ geographic distribution. Consider their depth/location in respect to the continents, mid-ocean ridges, other ocean features, upwelling/biological productivity, and the CCD.

Terrigenous sediments

1. Shallow to deep, coarse to fine, close to continents, near margins

2. N/a

3. N/a

Determine factors that determine sediments’ geographic distribution. Consider their depth/location in respect to the continents, mid-ocean ridges, other ocean features, upwelling/biological productivity, and the CCD.

Abyssal clays

1. Deep ocean basins, very fine grained, far from continents

2. N/a

3. N/a

Determine factors that determine sediments’ geographic distribution. Consider their depth/location in respect to the continents, mid-ocean ridges, other ocean features, upwelling/biological productivity, and the CCD.

Calcerous (Foraminiferal or Coccolith) oozes

1. shallow, near MOR, low-latitude regions (i.e. warm regions)

2. high biological productivity

3. above CCD

Determine factors that determine sediments’ geographic distribution. Consider their depth/location in respect to the continents, mid-ocean ridges, other ocean features, upwelling/biological productivity, and the CCD.

Siliceous (Diatom or Radiolorian) Oozes

1. deep, abyssal plains, high latitude regions (cold water)

2. high biological activity, upwelling regions

3. Below CCD

Determine factors that determine sediments’ geographic distribution. Consider their depth/location in respect to the continents, mid-ocean ridges, other ocean features, upwelling/biological productivity, and the CCD.

Volcanogenic sediments

1. Near sites of volcanism (convergent volcanic arcs, hot spots), depth varies

2. N/a

3. N/a

Determine factors that determine sediments’ geographic distribution. Consider their depth/location in respect to the continents, mid-ocean ridges, other ocean features, upwelling/biological productivity, and the CCD.

Glacial marine sediments

1. variable depth (depends on location of icebergs)

2. N/a

3. N/a

Identify the 4 types of planktonic organisms most important in the calcerous and siliceous deep-sea oozes.

Caclerous phytoplankton: coccolithophores

Siliceous phytoplankton: diatoms

Calcerous zooplankton: foraminifera

Siliceous zooplankton: radiolaria

What are the 3 most important factors in controlling the accumulation of siliceous oozes?

1. concentration of dissolved silica

2. productivity in surface ocean

3. sedimentation rate

How can you tell the difference between calcerous (chalk) and siliceous (diatomite) sedimentary rocks?

Apply 1 drop of hydrochloric acid to scratched surface of rock. The chalk will fizz, while the diatomite will not.

How does the depth of the CCD change with latitude?

It gets shallower when moving from the equator towards the poles

What physical differences and chemical processes might cause this variation?

The water gets colder and hence has more CO2 dissolved when getting closer to the poles: the water is more corrosive for carbonate