Test 1 Flashcards
Arctic ocean…
Too small to be considered a real ocean basin, really part of the atlantic
Northern boundary for southern ocean
Antarctic convergence at approx 60 degrees s, no geographical boundary but still isolated by physical oceanographic processes
Surface elevations
Bimodal because there are two different types of crust
Geoid
The shape of the earth as defined by its gravitational field, position of the geoid is sea leaves equilibrium, earths gravitational field is everywhere perpendicular to the geoid
Conduction
Movement of thermal energy without movement of material
Occurs in lithosphere
Convection
Movement of energy as a result of movement of material
Always faster than conduction
Occurs in asthenosphere and mesosphere
MOHO
10-40 km depending on type of crust
Caused by a change in the type of rock
Change between crust and mantle
100 km discontinuity
Seismic wave activity decreases (increases at all other discontinuities)
Caused by a decrease in rigidity (partial melting) of mantle material
400 km discontinuity
Olivine undergoes polymorphic transition
Atoms rearrange themselves into beta spinel, a more rigid/dense material
Gradually changes to gamma spinel from 400-650 km
650-700 km discontinuity
Gamma spinel and pyroxene change to perovskite
Kimberlites
“Diamond pipes”
Represent upper mantle material that has moved upwards as the surface of the earth eroded
Hypocenter
The exact location of earthquake
Represents the actual place the rock breaks and the potential energy is released; defined by latitude longitude and depth
Usually less than 60 km deep because deeper, rock is too warm to develop strain
Epicenter
Defined by latitude and longitude, not depth
Right above the hypocenter
Transverse waves
The earth is moving at right angles to the direction of the wave
Longitudinal wave
The earth is moving in the same direction as the wave
P waves
Longitudinal motion only, first to arrive (greatest speeds)
Velocity increases as rigidity increases
Velocity decreases as compressibility and density increase
S waves
Transverse motion only, arrive second Velocity increases as rigidity increases Velocity decreases as density increases Does not depend on compressibility Do not travel through liquids
Seismic discontinuity
Represents a surface where there is a significant change in wave velocity
Composition of oceanic and continental crust
Oceanic is mafic igneous rock
Continental is felsic igneous rock
(Mantle is ultra mafic)
Geotherm
The actual temperature we think exists in the earths core
Anisotropic
Different characteristics in different directions
Poles
Defined as the points where the magnetic field is perpendicular
Dielectric material
Does not conduct electricity
Mantle is made of this
Does not impact the earths magnetic field
Diamagnetic materials
Only paired electrons
Can not be magnetized
Paramagnetic material
Have unpaired electron(s)
Can be magnetized but not permanently
Ferromagnetic material
Unpaired electrons
Can become permanently magnetized if they cool below the Curie temperature in the presence of an external magnetic field
Most common is magnetite
Earths magnetic field is produced by…
Convection currents in the liquid outer core
Flood basalts
Large outpourings of lava
2-12 km thick
Adiabatic decompression
Solid material moves up until about 100 km below the surface, then melts
Layer 1 of crust
Sediment layer
Average thickness 1 km in open ocean, can be up to 15 km in continental margin areas
Absent along ridges/rises
Slow accumulation of sediments (about 1 cm per 1000 years)
Layer 2 of crust
Basement layer
About 2 km thick
Layer 2A- tholeiitic sheet and pillow basalts
Layer 2B- tholeiitic basaltic dikes
Intrusive igneous rock
Form deep within the earth, cool slowly
Large crystals
Extrusive igneous rock
Cool rapidly
Small crystals
Layer 3 of crust
Oceanic layer
Not present under ridge/rise crests
About 6 km thick
Composed of tholeiitic gabbro (intrusive)
Homogeneous accretion theory
Describes what we think happened with the formation of the earth from the formation of the solar system
Planetary differentiation
Describes how the earth rearranged itself from a homogeneous mass into a heterogenous structure
Impact with a mars-sized object allowed beginning
About 90% of water in earths surface today was released during planetary differentiation
Isostatic equilibrium
The vertical balance between gravity and buoyancy in the earths lithosphere
Driving force for plate tectonics is…
Movement of thermal energy from inside earth to outside
Relative plate motion
Arrows indicate plate motion relative to ridges/rises, etc. (whatever is at the boundary)
Divergent motion
Two plates moving apart
Ridges and rises (called spreading centers)
Convergent motion
Two plates moving together
Trenches (called subduction zones)
Continent-continent collision zones (no trench, ex. Himalayas)
Tangential motion
Two plates slide past one another
Transform faults
Tholeiitic magma
Source material for new sea floor
Results from the partial melting of peridotite
Mature oceanic lithosphere
100 million years old
About 100 km thick
Magnetic anomalies
Small deviations from the average strength of the earths geomagnetic field
Subduction zones
Deepest and highest magnitude earthquakes associated with these zones because the subducting lithosphere is cool enough to develop strain-Benioff zone
Island arc system
Usually produced by cooler, less buoyant subducting lithosphere
Like a mini spreading center
Deep subduction angle
Continental arc
Usually produced by younger, warmer, more buoyant subducting lithosphere
Shallow subduction angle
Soft collisions
Occur when lithospheric plates carry geological features into continental subduction zones
Hard collisions
Continent-continent collision Thrust wedges (oceanic crust) caught, squeezed, and uplifted forming suture zone -marked by ophiolites (rock layer that may contain all 4 layers of oceanic lithosphere)
Hot spot
Anomalous hot areas at the CMB, loses density and slowly rises to the surface, hot spot magma produced at about 100 km from surface
Wilson cycle
Describe the birth, death and decay of ocean basins
Embryonic, juvenile, mature, declining, terminal, suturing
About 1/2 billion years to complete one cycle
Normal faulting indicates…
Tensional geological forces
Ridges and rises
Exotic terranes
Small fragments of unusual crustal material attached to continental edges via soft collision
Conrad discontinuity
Broad seismic discontinuity in continental crust separating felsic rocks above from mafic rocks below
Back arc basin
Small ocean basic that separates volcanic arc in an oceanic subduction zone from land basin, grows in width with time
Deep sea fans
“Delta like” sediment deposits at the foot of submarine canyons, formed by turbidity currents
Apparent gravitational acceleration
The vector sum of the true gravitational acceleration and centrifugal acceleration caused by the earths rotation
Turbidity current
High density mixture (slurry) of sediments and water that moves downward through submarine canyons
