Chapter Two- The Sea Floor Flashcards
measured and estimated from gravity data derived from satellite altimetry and shipboard depth soundings
Global Seafloor topography
Explains how different topographic heights can exist at the earth’s surface. The crust “floats” at an elevation that depends on its thickness and density
Isostasy
is an igneous, volcanic rock that forms commonly in the oceanic crust and parts of the continental crust.
Basalt
made up of dark-colored mineral, basalt; denser than continental crust; younger than continental crust ( less than 200millions years old) Rich in iron and magnesium
Oceanic Crust
light-colored, mostly granite; less dense; some crust as old as 3.8 billion years old. Rich in sodium, potassium, calcium, and aluminum
Continental Crust
Research vessels Earth’s surface is covered by a series of lithospheric plates.
The ocean floors are constantly moving; spreading in the center and sinking at the edges and being regenerated.
Convection currents beneath the plates assist movement.
The heat from the mantle drives these currents.
Main Features of Plate Tectonics
Mid-Oceanic Ridges
Geomagnetic Anomalies
Island arcs
Evidence for Plate tectonics
The mid-oceanic ridges are a chain of submarine volcanic mountains that rise from the ocean floor.
At regular intervals, the ridge is displaced by faults in the Earth’s crust called transform faults.
Sediment accumulates; therefore being thicker away from the ridges, means that the crust further from the ridge is older.
Mid-Oceanic Ridges
At random intervals, the Earth’s magnetic field reverses.
New rock formed from magma records the orientation of Earth’s magnetic field at the time the magma cools.
Studies of the seafloor have revealed “stripes” of alternating magnetization parallel to the mid-oceanic ridges.
(See Fig. 2.10.)
Once minerals solidifies into a rock it cannot change is magnetic orintation (direction)
Geomagnetic Anomalies
Chains of islands are found throughout the oceans, especially in the western Pacific.
These island arcs are usually situated along the continental side of deep sea trenches.
These observations, along with many other studies of our planet, support the theory that underneath the Earth’s crust is a layer of heated rock driving the creation of a new ocean floor.
Island Arcs
Terrigenous, Biogenous, hydrogenous and cosmogeneous
More evidence is available in ocean sediment thickness
Marine Sediments
break-down of rocks on land
Particle size is important to the transportation and settlement of these sediments
Terrigenous
from skeleton and shells ( Siliceous and calcareous)
30% more of the total of these sediments, bottom sediments are called oozes
Biogenoues
chem-precipitation act of seawater
Manganese nodules, phosphorite nodules, and evaporites
Hydrogenous
tektites
Cosmogenous
