GEOPHYS FINAL Flashcards
Alfred’s Evidence of Continental Drift
- Continents fit like a puzzle
- Fossil assemblages & migrations across continents
- Direction of past glacier movements
Three Types of Margins
- Constructive: Plates move apart (creates oceanic crust)
- Destructive: Continuous upwelling of molten material (creates volcanic arcs)
- Strike-Slip Faults: Two plates sliding past each other (nothing created or destroyed)
What are Earth’s heat sources? What do they control?
- Sun’s radiation –> controls surface water cycle, rainfall, erosion
- Interior heat –> controls tectonics, metamorphism, evolution of core
4 Modes of Heat Transfer
- Conduction: Vibrating of neighboring molecules (strongest in solids- closest together)
- Convection: Movement of fluid particles
- Radiation: Propagation of waves or photons (no medium required)
- Advection: Movement of heated “bulk mass” (mostly in liquids or gas
What modes of heat transfer are found in different portions of the Earth?
Solid Lithosphere: CONDUCTION
Solid Mantle: CONVECTION
Fluid Outer Core: CONVECTION
Solid Inner Core: CONDUCTION
RADIATION: Induced by hot lava and radioactive minerals.
ADVECTION: Through erosion, faulting, isostatic rebound, and tectonic movement.
Geotherm & Geothermal Gradient
Geotherm: A line or surface within or on the Earth connecting points of equal temperature.
Geothermal Gradient: The rate of change of temperature with respect to increasing depth.
Why was Kelvin’s calculated age of the Earth so wrong?
He didn’t consider temperatures at different depths– Earth is not homogeneous. In addition, convection and radioactive heat generation was unknown at the time.
Rayleigh-Bénard Convection
A buoyancy-driven flow in a container with a temperature gradient. As the fluid at the bottom heats up, its density decreases, so buoyant forces push the less-dense fluid up towards the cooler end of the container.
Does mantle convection also produce the geomagnetic field? Explain.
No. It’s not electrically conductive like the core.
Types of Induced Magnetization
- Diamagnetic: Weak magnetitsm in opposite direction (ie halite, quartz, calcite).
- Paramagnetic: Weak magnetism in the same direction as the field (ie pyrite, biotite, hematite).
- Ferromagnetic: Strong magnetism in the same direction (magnetite, ilmenite, pyrrhotite).
Curie Temperature & Curie Point Depth
Curie Temperature: The temperatures above which magnetic materials lose their magnetic properties.
Curie Point Depth: The depth at which rocks reach the Curie Temperature.
What causes geomagnetic storms (weakening field)?
Solar activity like sunspots and flares interacting with our magnetic field when its differential spin “unravels”.
What are sunspots?
Areas if intense magnetic field localization– formed by the tangling of magnetic field lines (differential rotation).
Apparent Polar Wander vs True Polar Wander
Apparent: The perceived movement of Earth’s paleomagnetic poles relative to a continent assuming it’s FIXED IN PLACE.
True: ACTUAL movement of the poles due to whole-Earth rotation to its spin axis. The pole shift is due to variations in movement spin inertia (mass redistribution).
Acceleration due to gravity is maximum where in Earth?
The Core-Mantle Boundary!! This is where gravitational acceleration reaches a maximum.
What is the Geoid & Geoid Height?
Geoid: The “equipotential” surface that defines the SEA LEVEL. Everywhere on the sea surface, gravitational potential is equal.
Geoid Height: The distance between the geoid and reference ellipsoid of the Earth. If there is no “gravity anomaly”, the geoid IS the reference ellipsoid!
What can cause a geoid anomaly?
- Continental collisions
- Postglacial rebounds
- Subduction and more plate tectonic consequences.
How do mountains affect the geoid?
Excess mass, above or below the reference ellipsoid, ELEVATES the geoid, while deficient mass depresses it.
Types of Gravity Corrections
- Latitude Correction: At any given latitude. (Subtracted)
- Elevation Correction: If the measurement is made above the reference geoid. (Added)
- Bouguer (Topography) Correction: For extra mass above the reference geoid. (Subtracted)
- Terrain & Tidal Corrections: For steep topography or gravitational effects from the Sun/Moon.
Describe the Wilson Cycle
- Rift → breaking up rocks like a zipper. Once there’s a gap, oceanic crust can form.
- Drift (outwards) → mid ocean ridge spreads stuff outwards
- Initiate Subduction → the spread stuff reaches continental crust and subducts
- Drift (inwards) → this pushes things together
- Collisions & Mountain Building → makes mountains
- Supercontinent.
Explain the Geodynamo Theory (Steps)
- Internal heat source from the inner core drives outer core convection
- Convection causes flow of molten iron; electrically conductive
- Earth’s rotation induces “helical” patterns of convective flow
- Magnetic field!
Why is the Geodynamo Self-Sustaining?
A current moving along a helical path produces a magnetic field, and helical flows twist magnetic field lines to produce a current.
1 km = ?m
1 mu m = ?m
1km = 1000 m
1 mu m = 1.0x10^-6 m
What’s a Concordia diagram?
Describes the U-Pb parent and daughter ages in a closed system if there were no initial Pb isotopes. DISCORDIA is the real line of parent/daughter ratios, caused by a disturbance and the system to lose Pb. The intersection of conc and disc is the AGE OF FORMATION (time the disturbance occurred).
______________________ dating is widespread. It can be used on most rocks.
Potassium-Argon (K-Ar)
What is postglacial rebound/glacial isostatic adjustment?
The rise of land masses that were depressed by the huge weight of ice sheets. This makes the “water level decrease” (in some areas like the Hudson Bay).
What is a half-life and what does it tell us?
The time required to disintegrate half of the original parent atoms.
It tells us which isotope dating is suitable for a certain age range!
Which radioactive dating should we use when?
The expected age range should be about the same order as the dating half-life. For old rocks, short half-life isotopes may have already vanished!
U-Pb = 10^6 (OLD)
C-N = 1000 (YOUNG)
Curie vs Closure Temperature
Curie: The temp at which rocks begin holding a magnetic signature.
Closure: The temp at which a rock isotopically stars recording an age (it has cooled enough so there is no diffusion of the parent/daughter out of the system).
Why are meteorites good for dating the Earth?
- Closed system
- Pb to Pb isochrones
Types of Seismic Waves
Body Waves:
1. P Waves
2. S Waves
Surface Waves:
3. Love Waves
4. Rayleigh Waves
P Wave
- Move along the direction of propagation
- Fastest; travels through all media
- Early warning
S Wave
- Move perpendicular to the direction of propagation
- Slower than P waves; travels only through solids
- Stronger than P waves
- Vertical and horizontal components (SV & SH)
Love Wave
- Interaction of SH waves on the surface
- Move along the horizontal
- Slower than body waves but faster than rayleigh
- Powerful and damaging
Rayleigh
- Interaction of P & SV waves on the surface
- Move along horizontal and perpendicular (rolling motion)
- Slower than love waves
- Powerful and damaging
Why are surface waves so destructive?
The amplitude of surface waves lasts longer over a longer distance than body waves.
