Week 1 Flashcards
Temperature
Average kinetic energy of the particles in a substance.
Scalar quantity units of Temperature, [T] = Kelvin (K)
P-hacking
Artificially producing statistically significant results
Heat
A form of energy that flows due to temperature differentiation. It is the total kinetic energy of the particles in a substance.
Units of Heat, [Q] = Joules (J)
Specific Heat Capacity
The amount of heat required to raise the temperature of one unit of mass of a substance by one degree Celsius.
It is a measure of a substance’s ability to store heat.
Units of specific heat capacity
[Cp] = J / kg / K
Latent Heat
The heat absorbed or released during a phase transition (e.g., from solid to liquid or liquid to gas) at constant temperature.
Latent heat can be either latent heat of fusion (melting/freezing) or latent heat of vaporization (boiling/condensation).
Thermal Conduction / Diffusion
The transfer of heat through a material due to molecular collisions. Heat flows from a hotter region to a colder region.
Earth’s Thermal Gradient
The rate at which temperature increases with depth in the Earth’s interior.
What is Earth’s Surface Heat Flux?
The rate at which heat flows from the Earth’s interior to the surface. It is influenced by factors such as the thickness of the crust, the presence of volcanic activity, and the thermal conductivity of rocks.
What is the source of Earth’s Internal Heat?
The primary sources of Earth’s internal heat are:
** Radioactive decay: The decay of radioactive elements within the Earth’s interior releases heat.
Accounts for 50% of present-day surface heat flow
- Gravitational potential energy: The conversion of gravitational potential energy into heat as the Earth contracts over time.
** Residual heat: Heat left over from the Earth’s formation.
Heat conductor and example
Small specific heat capacity
Gold, [Cp] = 0.13 J/kg/K
Heat insulators and example
Large specific heat capacity
Aluminium, [Cp] = 0.91 J/kg/K
What are the mechanisms of heat transfer?
- Conduction: The transfer of heat through a material due to molecular collisions.
- Convection: The transfer of heat by the movement of a fluid (liquid or gas).
- Electromagnetic Radiation: The transfer of heat through electromagnetic waves, which can travel through a vacuum.
Heat flux density
Is the amount of thermal energy
that flows across a unit area of a material per unit time.
[q] = J/m2/s = W/m2
Thermal conductivity
Rate of thermal energy transfer over unit distance per unit change in temperature.
[k] = W/m/K
Thermal diffusivity and equation
the relative thermal “mobility” of
different materials.
[Df] = m2/s
Fourier’s Second Heat Law
Assumes that the rate of change of internal heat is proportional to the spatial gradient of the heat flux density.
Earth’s surface heat flux
Continent
Ocean
Globally
Continent
Area = 2.073 x10^14
Heat Flow = 14.7
Mean Heat Flow = 70.9
Ocean
Area = 3.028 x10^14
Heat Flow = 31.9
Mean Heat Flow = 105.4
Global
Area = 5.101 x10^14
Heat Flow = 46.7
Mean Heat Flow = 91.6
How do you calculate the Earth’s
surficial heat flux
By independently measuring the thermal conductivity of crustal rocks
Define Convection / Buoyancy and there connection
Convection is buoyancy-driven circulating motion within fluids exposed to a thermal gradient.
Buoyancy is responsible for convection: hotter material is less dense (rises) and colder material is more dense (sinks).
Heat Engine
A heat engine is a device that converts thermal energy (heat) into mechanical/electrical energy.
exploit thermal expansion, e.g. during a phase transition (liquid->gas), to complete work.
It operates by absorbing heat from a high-temperature source, converting some of it into work, and rejecting the remaining heat to a lower-temperature sink.
Discontinuities depths and causes
Upper mantle contains distinct
discontinuities at 450km and 670km depth. They are associated chemical phase transitions.
Mantle convection
The temperature of the Earth increases with depth – a thermal gradient. On geological timescales the mantle is a viscous fluid and therefore convects.
Models for mantle convection
- Whole mantle convection
- Two-layer convection
What drives plate tectonic motion?
- ridge-push and slab-pull, induced by negative
buoyancy of cold oceanic lithosphere,
* “suction” force of the overlying plate(s)
- Mantle convection (basal drag)
Plate-tectonic probable position “relative”
To other tectonic plates
Isochron
Magnetic anomalies + Fracture zone picks.
A line joining points of equal time intervals or ages.
Polar-wander path
The path that the magnetic pole appears to take according to the data on a continent.
The Wilson Cycle
Stage A
Stage A: Continental Rifting
Initiation: A mantle plume or hot spot upwells beneath a stable continental craton.
Magmatism and Extension: The increased heat from the mantle plume causes the overlying crust to thin, stretch, and develop a rift system. Magmatism often accompanies this process, leading to the formation of basaltic volcanic rocks.
The Wilson Cycle
Stage B
Stage B: Oceanic Divergence
Seafloor Spreading: As the continental crust continues to rift, a new oceanic basin begins to form. Seafloor spreading occurs along the divergent plate boundary, creating oceanic crust.
Passive Margins: The edges of the separating continents become passive margins, characterized by thick sedimentary wedges deposited from erosion of the adjacent landmasses.
The Wilson Cycle
Stage C
Stage C: Ocean Basin Maturation
Continued Spreading: The oceanic basin continues to widen as seafloor spreading progresses.
Sedimentation: Sedimentation rates on the passive margins gradually decrease as the distance from the continents increases.
The Wilson Cycle
Stage D
Stage D: Oceanic Convergence
Subduction Initiation: A subduction zone forms at one or both margins of the oceanic basin, leading to the convergence of tectonic plates.
Oceanic-Continental Subduction: In the most common scenario, oceanic crust subducts beneath continental crust due to its higher density.
The Wilson Cycle
Stage E
Stage E: Continent-Continent Collision
Mountain Building: As the subducting oceanic plate carries continental margin sediments and volcanic arcs towards the overriding continent, intense deformation and metamorphism occur, leading to the formation of a collisional mountain belt (orogeny).
Magmatism: Magma generated from the subduction zone can rise to the surface, forming volcanic arcs and intrusive igneous rocks.
The Wilson Cycle
Stage F
Stage F: Post-Collisional Orogeny
Erosion and Isostasy: The collisional mountain belt is subjected to intense erosion, gradually reducing its elevation over time. Isostatic adjustment occurs as the thickened crust rebounds due to the removal of overlying material.
Sedimentation: Sedimentation in foreland basins occurs as eroded material is transported and deposited.
The Wilson Cycle
Stage G
Stage G: Peneplanation
Long-term Erosion: Over extremely long-time scales, the collisional mountain belt may be reduced to a peneplain, a flat surface formed by erosion.
Supercontinents Throughout Earth’s History and there ages
Vaalbara: Formed around 3.6 billion years ago from the collision of the Kaapvaal and Pilbara cratons. It was the earliest known supercontinent.
Kenorland: Assembled around 2.7 billion years ago, consisting of parts of present-day North America, Greenland, Scandinavia, and southern Africa.
Columbia (or Nuna): Existed between 2.1 and 1.8 billion years ago, formed from the amalgamation of several smaller continents.
Rodinia: Formed around 1.1 billion years ago and broke apart around 750 million years ago. It was a massive supercontinent that included most of Earth’s landmass.
Pannotia: Assembled around 600 million years ago from the fragments of Rodinia. It was a short-lived supercontinent that existed for about 60 million years.
Pangaea: Formed around 335 million years ago and began breaking apart around 175 million years ago. It was the most recent supercontinent and is well-known for its C-shape.
The plate tectonics pump
Evolution can be driven by continents and continental shelves and moving them to different latitudes and recombining them.
What are the driving and resisting forces acting on tectonic plates
List nine.
RESISTING:
TF = TRANSFORM FAULT FRICTION
DF, CD = BASAL DRAG (CD ON CONT)
CR = CONTINENTAL RESISTANCE
SR = SLAB RESISTANCE BY MANTLE
DRIVING:
RP = RIDGE PUSH
SP = SLAB PULL
SU = SLAB SUCTION
DF = DRAG FORCES CAN PULL PLATES ALONG
What drives plate tectonics?
THE SLABS DRIVE PLATE TECTONIC
SLAB PULL ~ 1X10 14 N/M
Mueller and Phillips (1991)
analysed force balance on
oceanic margins
They concluded that you
needed between 7x10 12 N/m to
1x10 13 N/m to initiate subduction on a passive margin.
The only force big enough to
do this is a mature subduction
zone.
FLEXURE RESISTANCE ~ 8X10 12 N/M
SHEAR RESISTANCE (OCEAN TRENCH FAULT) ~ 1X10 12 N/M
SLAB RESISTANCE ~ 8X10 12 N/M
RIDGE PUSH ~ 3X10 12 N/M
BASAL DRAG ~ 1X10 12 N/M
What is the Transition Zone?
Give an example of a minerals journey?
Between 410km and 670km
Olivine transforms first to Wadsleyite
Then to Ringwoodite
It transforms in bridgmanite and ferropericlase in the
lower mantle.
Each phase is denser than the ones above.
Key point – the 670 km transition is endothermic. This
means in happens in the warm mantle before the cold
slabs – could prevent slabs from getting through.
Picture the D Layer. Describe what you see
Convergent Boundaries CC and OC Explain how each works
OC: The Oceanic plate is denser and cooler than the continental crust and therefore subducts below it. It has negative density greater than a thin hot crust and will go down preferentially.
CC: In this case both crusts are relatively light and hot from the lithosphere. Buoyancy must be balanced and mountain belts start to form.
Divergent boundaries
OO: Tectonic plates pull apart, causing the mantle to rise and fill the gap. This mantle material is very hot (around 1300 °C) and low in density, making it buoyant. As it cools, it forms new oceanic crust, creating a ridge that sits higher than the surrounding ocean floor. Over time, as the crust cools and becomes denser, it sinks lower, leading to varying ocean depths—2.5 km at the ridge and around 5 km in deeper ocean basins.
CC: As the plates pull apart it forms rift valleys. Normal faults develop on both sides of the rift vally to form on both sides. This process thins and drops the crust, often resulting in significant geological features like the East African Rift Valley (graben).
Transform boundaries
Transform boundaries occur where tectonic plates slide past each other horizontally. They serve to connect segments of divergent boundaries.
The mid-ocean ridges, where plates move in opposite directions on either side. In oceanic settings, transform faults between ridge segments are seismically active. Once past the ridge segments, the transform fault becomes a fracture zone with no relative motion and no seismic activity.
On continents, transform faults, like the San Andreas Fault, can be dramatic, causing significant earthquakes due to accumulated stress. This differential motion highlights the dynamic interactions of plates across various tectonic settings.
What is the Ophiolite Suite?
What are are the layers and depths?
Mean age? Average Age?
It is the Oceanic crusts uniform stratigraphy
- Sediments
- Pillow Basalts
- Sheeted Dikes
- Gabbros
Mean Thickness ~ 9km
Average Age ~ 180Ma
List all the major tectonic plates
What is Plate Tectonic Theory?
What are the key aspects?
Earth’s outer, cool, rigid shell is divided into fragments called “plates.”
Plates float on a viscous, weaker layer beneath them.
Plate movements include collision, sliding past each other, and breaking apart.
Two types of plates exist, differing in density and composition:
Continental: Thicker, less dense, older.
Oceanic: Thinner, denser, short-lived and recycled into Earth’s interior through subduction.
Earthquake Source Locations
Large earthquakes were routinely located using the
WWSN. It quickly became evident that earthquakes cluster along somewhat linear structures.
The correlation between earthquake locations, and deep sea trenches and mid-ocean ridges, was quite obvious.
Topographic nature of Earth’s crust?
Picture the graph. Where is mass distributed in relation to altitude/depth?
Continental Crust
Average Age?
Average thickness?
Picture elevation globally
Mean Thickness ~ 38km (20-90km)
Average Age ~ 2Ga
Physical properties of the Earth’s interior?
Each Layer
