Origins and structure of ocean basins - 3 Flashcards
What is isostasy?
Mass balance of an object floating upon a fluid medium
What control elevation of an object floating on a liquid medium?
Thickness of mass, density of mass and the density of the medium
Why are continents higher than the ocean floor?
Continents are thicker and less dense so rise above the supporting mantle rocks more than the sea floor
When was the first ever geological map of the sea floor made?
1977
What is echo-sounding?
Type of SONAR, time between emission and return of pulse used to measure depth … (multiply half the time from the signals outgoing pulse to its return by the speed of sound in water)
What is the approximate speed of sound in water?
1460 m/s
What is multi beam?
Echo sounding, fan of sound waves emitted, swathe of depth readings from one pulse
What is altimetry used for?
Measuring height and sea surface level and bathymetry
What is the lithosphere?
Crust and uppermost mantle
What is the asthenosphere?
Partially melted mantle rocks with plastic properties
What is the mesosphere?
Deeper, rigid mantle zone
Properties of the earth’s core
Molten outer and solid inner, dense, iron-nickle
What are the three distinct physiographic provinces of the ocean?
- Continental margin
- Deep-sea basin
- Mid-ocean ridge
What are the sections of a continental margin?
Continental shelf, continental slope and continental rise
Below what depth are rocks in the mantle no longer plastic?
350km
Define Bathymetry
Submarine topography
What % of the earths crust projects above sea level?
29%
What is a Moho?
The sharp boundary between crust and upper mantle. It lies deeper below the ground beneath continents than it does beneath ocean.
What is an ocean basin?
Large portion of ocean floor that lies deeper than 2 km
Define tension
Pull apart force
Define compression
Pull together force
What is & where do you find normal faults?
When crustal rock is displaced vertically, occur along the edges of rift valleys
What is a transform fault?
Fracture in the crust where movement of rocks is horizontal
Where is the strongest magnetic field?
At the poles
‘Magnetic lines of force are vertically oriented’ meaning …
Out at S Pole and in at N Pole
What is paleomagnetism
When minerals align themselves to the geomagnetic field, recording strength and direction of the geomagnetic field at a given point in time
What is a continental margin?
Submerged edge of the continents … they can be divided into 3 parts
What is the continental shelf?
Top of the clastic wedge, slopes seaward at 0.5º from the shoreline to the shelf break, terminates in water between 130-200m deep
What is the continental slope?
Extends downwards from the shelf, slopes at 4º to a dept of around 2-3km, can be cut with submarine canyons
What is the continental rise?
Vast sedimentary plain, begins at the bottom of the slope, inclines at 1º and merges with the deep ocean at a depth of 4km
What are deep ocean provinces?
Located between the continental margin and the mid-oceanic ridge
What is an abyssal plain?
Flattest area on earth, depths of 3-5km, sediment itself can reach a depth of 1km
Who first proposed continental drift?
Alfred Wegener
What is seismicity?
Frequency, Magnitude and Distribution of earthquakes
What is a Benioff Zone?
An area of increasingly deeper seismic activity
