Exam 1 Flashcards
What is geology?
- the study of physical structure and composition of all solid planetary bodies
- the physical processes that act on and within these planets
- geologic history
Why natural science core classes?
- jobs
- science minded voting public
- science is objectively amazing
How many Americans believe the sun revolves around the earth?
26%
How many Americans believe the earth is less than 10,000 years old?
26%
How many Americans reject evolution?
38%
What is scientific literacy?
- science involves ideas, theories, and facts
- behind the facts is a rigorous, repeatable process
- any unbiased/objective method to solve a problem involves the scientific method
Steps of the scientific process
make observations
think of interesting questions
formulate hypotheses
develop testable predictions
(refine, alter, expand, reject hypotheses)
gather data to test predictions
develop general theories
Example of theory = Newton’s theory of gravity:
determines the force of gravity between two objects
developed in 1680s, still used
accurately predicted planet locations in solar system
not perf, failed to account for gravitational force of more than two objects (sun pulls on mercury but so do other planets)
Albert Einstein’s theory relatively took over in 1916
What do geologists do?
- petroleum / coal industry exploration
- water management (hydrogeologist)
- floods (hydrologists / geomorphologists)
- economic geology
- environmental geology (cleaning, testing, etc.)
- earthquakes (seismologists)
- volcanoes (volcanologists)
- paleontologists (dino, fossils)
- ## planetary geologists
When was the origin of our solar system?
4.6 years ago
How did our solar system begin?
from hot gasses and dust, the remnants of a dead star (Nebula - step A)
What is step A in the origin of our solar system?
protoplanetary nebula stage (a collection of gasses)
What occurs in the protoplanetary nebula stage? (A)
the gasses come from a star that recently died, when a star reaches the end stages it can explode or lose its shell of gasses for space, the gasses are weakly attracted to each other by gravity
the composition (elements) of the gas is dependent on the elements that were in the original star (hydrogen&helium most abundant but also could be oxygen, carbon, iron, etc. - these elements are made inside of the star by nuclear fusion
a new star and planets will coalesce from these gasses
What happens to a dying star?
gasses are shed from the exterior, it can no longer hold them, the gasses that escape into space can coalesce again under gravity to form a new star and planetary system
Supernova explosion:
much more massive stars (giants/supergiants) die catastrophically and explode, the nebula of hot gasses can coalesce under gravity to form a new star and planetary system
What is step B of the origin of our solar system?
a protoplanetary disc: gasses collapse under gravity and begin to rotate around a center of mass (our protosun) in a disc
What occurs in the protoplanetary disc stage (B)?
the gasses will begin to attract to each other due to gravity, the sneer of mass of the nebula, in the region of the original star/explosion, has the highest concentration of gas, coalescing the gas here may birth a new star (a protosun) if enough mass can accumulate to initiate nuclear fusion
the protosun is the hot center of the disc, the gravitational attraction of the protosun controls/holds remaining gasses and a disc of gas develops, they are still very hot (hundreds of degrees)
What is step C in the origin of our solar system?
accretionary disc, gas cools and metals begin to solidify (Fe, Al, Mg, K, Ca, Si) larger objects attract to each other by gravitational attraction
What occurs in the accretionary disc stage (C)?
as the gasses in the protoplanetary disc cool, the gas particles turn to liquid droplets, and then eventually to solid particles, metal elements turn solid first and some gaseous elements never turn solid (like hydrogen) the solid particles in the disc begin as just small grains of dust, as they whip around the sun, they attract each other (by gravity) and collide
Accretion
the process where solid particles attract each other due to gravity, collide, and make larger objects (this process is responsible for making larger mass objects in our solar system like the sun and other planets)
Accretion in depth:
the “seed” of a planet begins as nothing more than a slightly larger piece of dust that attracts (by gravity) even smaller pieces of dust to it, as that seed becomes larger, it attracts more and more fragments of material due to gravity (more massive objects have more gravitational force) this makes the seed larger and larger, eventually a larger planetoid emerges and begins to clear out everything in its orbit (pluto is an example of a small planetary body - a dwarf planet that even today, has not cleared out its orbit completely this is why it is no longer considered a planet)
Definition of a planet:
- is in a stable elliptical orbit around the sun (can’t find colliding w sun for example)
- has sufficient mass reach hydrostatic equilibrium (round) [outward pressure=gravitational pressure]
- has cleared the neighborhood of other objects in the same orbit around the sun (where pluto fails) [can’t share orbit w another]
Hydrostatic equilibrium
state of balance by which the internal pressure of body exactly balances its gravitational pressure [self gravity=internal pressure] (gravity pulls the planet inward, exerting inward directed pressure, internal heat is trying to escape outwards {space}, exerting outward pressure, thus creating a balance –> h.e.
Asteroids
(few cm to 10 km in size) rocky bodies (sometimes icy) that are not large enough to be considered planets
may not have coalesced into large planets (accumulated enough debris via accretion) or are remnants of failed planets (planets that exploded due to large collisions during accretion phase
(ex. our moon formed from a large collision between earth and a mars sized object (thea) early on in the accretion disc
Protoplanets
(100s of km in size)
small planetary bodies that did not form into a full planet, they are almost round (ex. vesta is the largest still in our solar system, in the asteroid belt, never managed to coalesce because there wasn’t enough debris in its neighborhood)
Dwarf planets
(about 1000 km in size)
not full grown planets, relatively small, spherical bodies that look almost just as full planets, these never cleared out of their orbit the debris (other large bodies in their orbital path)
(ex. pluto in the outer solar system, ceres is the largest in the asteroid belt - between mars and jupiter)
Size of full planets
1000s to 10000s km in size
Why did the earth have a magma ocean phase?
around 4.5 billion years ago, heat collisions of objects (the formation of the moon) and radioactive elements within earth during and immediately after accretion phase leaves the early earth partially to mostly molten
What are the sources of heat from earth’s magma?
collision with other objects: even while this is still technically in accretion phase, large objects that are in unstable orbits collide with the earth (and all planets) some could completely melt
radioactive elements: this generates heat energy, radioactive elements decay over time, early earth had a lot that are now gone, the heat generated from those early elements kept the interior hot, today its a little cooler
Moon formation hypothesis:
Giant Impact Hypothesis: our moon formed from the debris ejected from earth due to impact of a mars sized body (thea) the moon is 4.56 billion years old - some of the ejected material recoalesced in orbit around earth as our moon
Heavy bombardment
the moon has large impact craters (now filled with old lava) they 100s of 1000s of km in size in diameter and represent heavy bombardment phase of our solar system that continues even after the formation of moon (ending ~3.9 billion years ago)
Why are earth’s interior parts separated?
elements in our molten planet begin the separate based on their relative density, dense elements sink in the magma ocean, less dense floats
differentiation
Differentiation
process of density settling of elements in the hot earth that leads to formation of core, mantle, and crust (each layer has a different composition- chemistry)
What are the most common risk forming elements on earth?
Fe - iron
O - oxygen
Si - silicon
Al - aluminum
Na - sodium
Ca - calcium
K - potassium
Mg - Magnesium
What are the two most abundant elements in our crust?
Silicon (Si) and Oxygen (O)
Is there more iron (along with nickel) towards the crust or the core?
core
How do we know how the earth is separated?
rocks are brought up from our mantle
upper mantle rocks may get incorporated into magma (liquid rock)
Differentiation:
density settling (sink towards core, lighter in density floats up)
crust, mantle, and core is compositional zonation
Plate tectonics:
how plates move and interact w each other
when plates collide, the lower crust and sometimes the upper mantle are uplifted to the surface
brings deep materials to the surface
controversial until 1960s
Xenolith
a piece of rock that is foreign to the rock surrounding it
ex. piece black basalt volcanic rock from crust surrounding green chunk from our upper mantle
Xenolith
a piece of rock that is foreign to the rock surrounding it
ex. piece of black basalt volcanic rock from crust surrounding green chunk from our upper mantle
Two ways to classify core, mantle, and crust:
- composition
- phase of matter
Lithosphere
solid outer shell of Earth, contains the crust and part of the upper mantle, ridged, broken up into plates, brittle, directly above asthenosphere, biggest plate on planet, movement of this is what causes earthquakes
Asthenosphere
a more plastic-like sphere of the Earth, mostly solid, but is partially molten in parts, is ductile (a solid that can bend and flow) we call a solid that expresses that kind of ductile behavior a plastic solid (not actually a plastic like you think of plastic) this is a portion of the uppermost mantle of Earth
Mesosphere
the solid portion of the mantle (the rest of the mantle) this material is still hot enough that it can flow (a bit) and some ways does behave like a plastic, but its still completely solid and does not flow as easily as the asthenosphere
Outer core
the only entirely liquid interior sphere of the earth, the outer core is Fe and Ni in composition, but it is entirely molten
Inner core
also made of Fe and Ni, but it is under too much pressure to turn liquid, it is plenty hot enough to be liquid, but the confining pressure of the entire planet prevents the atoms from phase changing to liquid
Is there magma (liquid rock) beneath us?
not until you get to the core, around 3000 km down, magma/lava comes from crust/upper mantle and requires specific circumstances to stay, the mantle is almost all solid but behaves like plastic
How do we know the phases of matter inside the Earth?
earthquakes
Summary of earth’s internal structure
crust, mantle, and core is a compositional classification scheme (based on differences in elemental composition)
the lithosphere, asthenosphere, etc. is a classification scheme based on the phase of matter (solid, liquid, etc.).
How/when did plate tectonics become an accepted theory?
Continental Drift:
German meteorologist Alfred Wegener:
The Origins of Oceans and Continents published in 1915.
Pangaea supercontinent = “Fit” of the continents.
Developed hypothesis of continental drift.
Paleoclimatic Evidence (for Pangea)
~250 Myr old Glacial deposits (evidence of thick sheets of ice) near the equator today.
~250 Myr old tropical swamp deposits (coal) in present day eastern US.
~250 Myr old tropical coral reefs in present day midwest/southern US.
Subtropical deserts across North America and Europe (~250 Myr).
Fossil Evidence (for Pangea)
Fossils - lithified remains of tracks, traces, or body parts of organisms.
Similar land fossils of similar age (300 to 250 Myr) that span 5 continents that are now separated.
Southern part of Pangaea super-continent in picture below called Gondwanaland/Laurasia (South America, Africa, India, Antarctica, Australia).
These animals could not have possibly crossed the Atlantic Ocean. The best explanation is that the Atlantic Ocean didn’t exist when these animals were alive. Instead, South America and Africa must have been together.
Matching geology (for Pangea)
Geologic structures & mountain belts.
Rock types & ages.
(ex. Appalachians vs Atlas Mountains, Scottish Highlands
Ocean Floor Mapping: Post WW2 (for Pangea evidence)
In the 1950s, ocean bathymetry was measured (seafloor elevation) sound waves
Discovered…
An elevated ridge near center of every ocean basin.
Also found deep ocean trenches adjacent to large mountain ranges that stick up out of the water (Bathymetric profile of the Atlantic Ocean showing a Mid-Ocean Ridge, Bathymetric profile of the east Pacific Ocean showing an oceanic trench)
Magnetic rocks
- Fe-rich, silicate rocks found on the ocean floor (basalt)
- Contain magnetic minerals (magnetite)
- These rocks were formed by volcanism (lava)
- Magnetites aligned with Earth’s magnetic dipole (think of a bar magnet with a north and south magnetic pole)
- detected by magnetometers on ships
(ex. magnetite, basalt)
Magnetite/magnetization
- (Fe3O4) cools and crystallizes from magma/lava
- When magnetite cools to its Curie temperature (~570° C) it aligns with Earth’s magnetic dipole (north aligns to north, south to south)
Curie temperature:
the temperature below which magnetism sets in (with Fe-bearing magnetic minerals)
What do magnets have to do with plate tectonics?
When the magnetites formed in lava, they lined up with Earth’s magnetic field
Magnetic Anomalies on Seafloor
Magnetometers towed behind ships…they discovered =
- Magnetism in the rocks oscillates from north polarity (+) to south (-) as you move away from a Mid-Ocean Ridge.
- Linear belts (“stripes”) of + and - magnetization that parallel the Mid-Ocean Ridge.
Magnetism & Plate Tectonics
our magnetic field flips repeatedly but that the seafloor was/is spreading from the center of the ridge
Magnetic Field Reversals
Time average of reversals is ~450,000 years but it is highly variable
illustrates the switch of Earth’s polarity, normal (or positive) polarity is when Earth’s magnetic pole is pointing north, reverse polarity (or negative) is when the north magnetic pole points south
What movements occurred in the breakup of Pangea?
- spreading ridge offset by transform faults
- subduction zone
- motion of plate
Modern Evidence that Plates Move:
- earthquakes and volcanoes occur along specific boundaries – these correspond to the plate boundaries
- age of rocks on seafloor: Warm tones = young rocks/Cool tones = oldest rocks (The seafloor rocks also have “age stripes”. The youngest rocks are being erupted as lava from the crack at the Mid Ocean Ridge. As the plates spread out, the young rocks get pushed away from the central crack)
How can we measure plate motion?
Precision Global Positioning Systems (GPS) can be used to measure plate motion today - Average = 2 cm/yr
set up on top of crust, detects subtle movements
What formed due to plate tectonics?
ocean basins and continents
Why is there crust that rests above sea level and crust that rests below sea level? (large basins vs continents)
Isostasy & plate tectonics
Isostasy
a state of balance (equilibrium) in how the lithosphere is supported by the squishy/plastic upper mantle (asthenosphere)
easily demonstrated by floating anything on a fluid or plastic substance, iceberg is 10% above water and 90% below, lithosphere is iceberg and asthenosphere is water
Crust/Lithosphere Types
plates are made up of both oceanic crust/lithosphere and continental crust/lithosphere (sometimes both) + have different thicknesses and are made of different rocks (have different density) – this is similar to the wood analogy
Earth’s Crust:
Continental Crust – thick and less dense
Oceanic Crust – thin and more dense
Why is oceanic crust thinner than continental?
plate tectonics, it’s made where the plates spread across from each other, crust will thin where it spreads apart → the opposite is where the plates collide, crust will thicken, compresses and squishes together
What do oceanic crust plates do?
diverge - spread apart
the crust thins where plates spread apart – making ocean basins
What do continental crust plates do?
converge - collide
the crust thickens where plates collide – making continents
Why is oceanic crust denser?
- made of heavier things
- Granite (very common) it contains silicon and oxygen which is silicate, granite has aluminum in it (important metal in the rock) - Basalt, dominant metal is iron - Both of these are cooled magma, our crust is made from magma *these share silicates but their metals are different
The heavier things are here also due to plate tectonics!
What makes the crust/lithosphere?
cooled magma/lava by volcanism
magmas/lavas have a different elemental composition because they come from different parts of the Earth (crust vs. mantle)
Examples of new crust being made by volcanism:
- Iceland = oceanic crust
- Mt. St. Helens (Washington state) = continental crust
Why is the ocean crust made of Fe-rich silicates and continental Al-rich silicates?
- New crust is made by the cooling of magma/lava (volcanism).
- Note that magma is made at both divergent and convergent plate boundaries (more on this later).
- But, notice that the magma comes from a deeper mantle source where plates spread apart (divergence). More Fe in these lava rocks.
Which crust is more dense?
oceanic crust (resting lower in asthenosphere due to basins), continental is less (rests higher than asthenosphere, land we live on)
Lithosphere/Crust Type Classification:
Oceanic – Oceanic
Continental – Oceanic
Continental – Continental
Relative Motion Classifications:
Convergent
Divergent
Transform
Plate boundary combinations for divergent
Continent – Continent Divergent
Ocean – Ocean Divergent
Plate boundary combinations for convergent
Continent – Ocean Convergent
Ocean – Ocean Convergent
Continent – Continent Convergent
Plate boundary combinations for transform
Ocean – Ocean Transform
Continent – Continent Transform
Continent - continent divergent margin
Divergence in a continent generates a rift valley (thinning of crust)
The rift is bounded on either side by faults, where quakes occur
Center of the crust collapses along the faults as plates move apart
(ex. East African rift valley (in cross section), forming because the African continent is splitting apart, the valley in the middle (now filled with lakes and some volcanoes) is an expression of this divergence)
Which boundary are volcanoes commonly associated with?
divergent
Why is there volcanism at a divergent boundary?
- Remember: The mantle is normally solid (if not plastic) all the way through!
- The mantle is plenty hot enough to melt rock, so why isn’t it completely molten!
- The mantle is under intense pressure from overlying rock…too much pressure for the molecules to move.
- Release of pressure at divergent plate boundaries causes the upper mantle to partially melt (decompression melting).
Decompression melting
you can melt a very hot object by simply reducing the pressure on that object, you don’t have to raise its temperature
Ocean - ocean divergent
new ocean
As continental rifting progresses, a new ocean basin forms
Modern rifting in continental crust leading to new ocean
(ex. Red Sea - a location where the contents have split apart enough that sea water has begun to fill in the rift valley, This is the birth of a new ocean. Not simply because sea water is filling in a rift valley, but because as divergence continues and the crust thins, lava will emerge from the upper mantle and new, Fe-rich oceanic crust (basalt) will be born)
Ocean - ocean divergent margin
As rifting continues, the mantle melts can eventually reach the surface.
This produces thin, Fe-rich oceanic crust (basalt)!
The resultant rift valley/basin starts to fill with water to form an early sea and then an ocean.
Ocean crust is born
(ex. Mid-Atlantic Ridge)
Continent – Ocean Convergent
If new crust is created (divergence), old crust must be destroyed (convergence)
(a thin oceanic plate collides with a thick continental plate - The result of this kind of collision is a process known as subduction)
Ocean - Continent Convergent Plate Boundary
Ocean crust is recycled back into the mantle at *subduction zones
Subduction
process by which lithosphere/crust is destroyed or recycled back into the mantle
Why does the oceanic crust sink relative to continental crust? (oceanic crust subducts beneath continental crust, why is it never is the other way around)
Ocean crust is thin and dense (Fe-bearing silicate rocks)
Also note the depression (trench) that occurs at the plate boundary…trenches indicate plate subduction
(ex. oceanic crust is colliding with continental crust near central America. The trench is the plate boundary. At the trench, the oceanic crust is folding downwards as it slides under the continental plate, you may also notice that there are volcanoes on the continental plate here)
Why is there volcanism at an Ocean-Continent Convergent margin?
- “Wet oceanic crust” has a lower melting temp than dry crust
- Subducting oceanic plate melts, magma rises and melts cont. crust
- This magma may erupt on surface producing volcanoes
- as subducts brings surface water with it. Its not that the ocean water itself subducts. But, ocean water does hydrate the rocks on the seafloor. The sediment and lava rocks on the seafloor absorb (in a way) some of the sea water (technically, the seafloor rocks experience chemical alteration that results in rock hydration).
Hydrous (“Flux”) Melting
Addition of water to rock lowers the melting temperature of rock so that it is easier to melt (melts at lower temperatures and pressures).
Where do volcanoes occur on convergent/subduction zones?
Volcanoes do not occur on the plate boundary at a convergent margin (subduction zone)
They occur on the overriding plate – hundreds of miles inland of the boundary
Where do earthquakes occur at subduction zones?
Where plates collide & rub together here.
Earthquakes get deeper as you move inland at subduction zones.
(Shallow quakes are more dangerous to people (quakes are closer to surface).
Greater quake danger lies in being close to the coastline here.
Eventually, quakes go away at depth as the plate becomes too “mushy”/ductile.)
Wadati-Benioff zone
zone of seismic activity at subduction zone
Ocean - ocean convergent / subduction - what happens when ocean plates collide?
one ocean plate dives under the other
(Island arc: chain of volcanic islands produced by subduction)
ex. Marianas Trench - deepest point on the surface of the Earth (10.9 km)
Continent - continent convergent margins
What happens when two thick continents collide?
- Earthquakes, large mountains, and no volcanism!
- Shallow or no subduction – both plates are too thick for subduction
- simply crumble into huge mountains
(ex. The Himalayas, there are ocean fossils up here due to plate tectonics!)
Transform Plate Margin
- Where plates slide together
- Creates shallow earthquakes and no volcanics
ex. San Andreas Fault (North American Plate and Pacific Plate)
What causes plate tectonics?
- The asthenosphere and lower mantle can flow (even though they are not (mostly) liquid)
- mantle convection
- This process, including gravity, helps to push and pull plates across the surface of Earth
Mantle Convection
Hot, less dense mantle material slowly rises from the outer core.
As it rises, it hits lithosphere, cools and then sinks again.
Convection
motion induced by density changes in a fluid or mobile solid
Where do the elements we use in everyday objects (smartphones) come from? (they have economic value)
from minerals inside of rocks
What makes a mineral a mineral?
- Natural
- Inorganic, meaning no organic molecules, this does not mean life does not play a role (although life plays a major role in making minerals)
- Solid
- Ordered structure
- Specific chemical composition (NaCl, SiO2)
- More than 4,000 known!!!!
Structure of minerals
- Disordered (Amorphous) = Liquid/Glass
- Crystalline structure based on atomic patterns
*Ordered!
Rapid lava quenching
rapid cooling locks in the random ordering of atoms that is more typical of liquids – produces glass!
*elements need time to organize
Crystal lattice (of minerals)
Created by bonding between atoms (atomic)
Ordered atoms form a 3-D lattice.
Controls:
Crystal form/habit (shape of crystal)
Mineral properties (ex. hardness, cleavage)
How are minerals made?
- Start with atoms
- Atoms bond
- Crystals grow
Electrons:
The outer shell (valence shell) can hold up to 8 electrons. All atoms would prefer to have 8 electrons in their outer shell. Therefore, electrons with too few electrons in their outer shell can share or loan electrons to another atom to fill this outer shell with 8 electrons.
(Fluorine has two electron shells. Flourine has 7 valence electrons (outer shell electrons). Fluorine is electronically neutral (9 electrons and 9 protons)
How is the periodic table organized?
by electron shells
- Columns reflect number of electrons in outer shell (valence electrons)
- Rows reflect number of electron shells
- Last column = outer shells filled for noble gases
Fluorine’s electrons…
Outer shell of fluorine can hold one more electron – 8 electrons are possible in this shell.
When it is in proximity to an atom with one extra electron in its outer shell, it can bond with that other atom.
Na+1F-1
ionic bond type, an electronically neutral molecule, a cation and an anion
Cation
positively charged atom
Anion
negatively charged atom
Ion
atom with a positive or negative charge (lost or gained an electron)
Different bond types (as electronic interactions)
covalent bond - sharing
ionic bond - loaning
metallic bond - free flow
inter molecular force - stick together
Example of Bond Strength & Lattice Shape
Diamond and graphite (both made of only carbon):
- Diamond – Strong covalent bond, close packing, hardest mineral.
- Graphite – Weak Vander Waal bond, loose packing, soft mineral.
Minerals primarily form in two ways:
- magma/lava crystallization (mostly silicates) like feldspar
- crystallize out of water (salts, sulfates, carbonates) like halite/salt
Mineral growth
When water becomes saturated with a mineral dissolved in solution, Evaporation of water leads to mineral saturation
Crystal growth
Starts from a “seed” crystal (nucleation site).
Atoms attach to surfaces.
Expands outward.
Space determines size and quality of crystal form - Minerals can grow to large size and have well-defined crystal forms if given space and time to grow.
Example of how lattice influences properties
Crystal Shape/Habit
- If crystals have space and time to grow, they will take on the ideal shape
Mineral characteristics (shape/structure):
- cubic (fluorite)
- Pyramidal/Octahedral (diamond)
- Hexagonal (quartz)
- prismatic (andalusite)
- rosette (gypsum)
How and why do we identify and classify minerals?
Physical properties:
- Crystal habit/form
- Color
- Streak
- Luster
- Hardness
- Cleavage
- Fracture
(others: Transparent/translucent, Taste, Smell, Feel, Magnetism, Effervescence (calcite/dolomite), Electrical properties, Striations (only plagioclase)
Mineral colors
Shade and color of a mineral can be helpful and deceptive at the same time.
Different minerals can be the same color!
Same mineral can be multiple colors (impurities).
Streak
Color of a mineral crushed on unglazed porcelain.
- Useful diagnostic property.
Magnetite (Fe3O4) – Black mineral; black streak.
Pyrite (fools gold) (FeS2) – Gold mineral; black streak.
Hematite (Fe2O3) – Metallic silver or red mineral; redish-brown streak.
Luster
Luster – The way in which light reflects off minerals.
- Metallic (always opaque, light can’t pass through)
- Nonmetallic (Earthy, Glassy, Pearly, Dull, Silky)
Hardness
Resistance to scratching (Determined by internal structure and bond types)
Mohs Hardness Scale
A 1 – 10 scale for relative mineral hardness. (1 = soft) (10 = hard)
Cleavage
- Ability of a mineral to break along plane(s) of weakness
- Minerals can have weaker and stronger bond types within them
- If these weak points occur along a “plane” we call it cleavage
ex. halite
No Cleavage/Fracture
Many minerals do not contain internal planes of weakness.
These minerals shatter/fracture into irregular pieces when they break.
ex. quartz (used to make glass, which breaks in shatters)
Special Properties of Minerals
Reaction with Acid
- Effervescence: bubbling of a mineral through a chemical reaction with (typically) acid.
ex. calcite
Magnetism
- Magnetite (Fe3O4) is a strongly magnetic mineral (there are other weakly magnetic minerals.
Mineral element compostions
Only about 50 minerals are abundant.
98.5% ~ 8 elements.
Every mineral contains elements and the elements are what we’re trying to extract for resources.
Mineral classes
Minerals are classified by their dominant anion.
Silicate minerals
Igneous rocks that form from magma/lava and make up the bulk of our crust are made of only these 9 common rock forming minerals.
Mineral Precipitation from Water
The most common (natural) dissolved compounds in water are…
- Halides (Cl)
Halite (table salt) = NaCl
- Carbonates (CO3)
Calcite (lime) = CaCO3
- Sulfates (SO4)
Gypsum = CaSO4* H2O
- Oxides (O)
Hematite = Fe2O3
Igneous rocks:
rocks that form from the crystallization (cooling) of magma or lava
How is Magma Made?
Magma is made at three geologic settings…
- Divergent plate boundaries (review): Decompression melting
- Convergent plate boundaries (subduction zones) (review): Flux melting (addition of water)
- Hot spots (mantle plumes) (new topic): Addition of heat
(Remember: lithosphere, asthenosphere, and lower mantle (mesosphere) are normally solid)
Decompression melting:
(divergent plate boundaries - rifting)
release of pressure allows the hot mantle to flow and partially turn liquid (partial melts)
What makes magma at Hawaii?
- Mantle Plumes & Hot Spots
each island is made of basaltic volcanoes
(Mauna Loa)
the melts/magmas here can’t form by decompression or hydrous melting like at the other locations
Mantle Plumes & Hot Spots
Hot, less dense mantle material (mantle plumes) from the core-mantle boundary sometimes rises to the base of the crust, partially melting the crust
Why are there chains of volcanoes?
Plate moving over a stable mantle plume (movement of plate over stationary hot spot)
- Plume stays in one spot while the plate moves over it, creating a chain of volcanoes
Famous hotspots
Hawaii
Yellowstone
Iceland
Properties of Igneous Rocks & Classification
- crystal (grain) size
- composition (% light/dark minerals) (crust or mantle melts)
Magma/lava Crystallization
Minerals cool and crystallize in a magma/lava forming an interlocking texture of minerals (like a puzzle without spaces between minerals).
What’s an example of how minerals grow?
together in the magma and therefore fit perfectly together like a puzzle
Different crystal/grain sizes
- fine (Majority of crystals can’t be seen with naked eye (may be a few larger ones)
- coarse (All crystals can be seen with naked eye)
Cooling rate of fine grained
Fast cooling rate (extrusive)
- Minerals do not have time to organize and grow before the melt solidifies.
- Cools over seconds -> days
- Usually happens when magma reaches the surface (we call it lava then).
Cooling rate of coarse grained
Slow cooling rate (intrusive)
- Minerals have a long time to grow before the melt solidifies.
- Cools over thousands to millions of years.
- Usually happens when magma gets stuck deep under ground
Where is fast cooling and where is slow cooling melts (magma/lava)
fast - on top within volcanoes (extrusive, fine)
slow - down underground (intrusive, coarse)
What gives magma its differing “flavors”?
silicate minerals
Silicate minerals
Igneous rocks are made of these 9 common rock forming minerals in different combinations.
These minerals are your “ingredients” in lava/magma.
Composition of Igneous Rocks
We determine composition first by the relative percentage of light colored vs. dark colored silicate minerals.
Felsic (igneous rocks)
High Si
(Si, O, Al, K, Na – rich)
Less than 30% dark minerals
Intermediate (igneous rocks)
Mod Si
(Si, O, Al, Na, Ca, Fe – rich)
50 – 70% dark minerals
Mafic (igneous rocks)
Lower Si
(Fe, Mg, Ca – rich, Si, O)
More than 70 - 80% dark minerals
Igneous rocks are made of these 9 common rock forming minerals
- olivine m
- pyroxene m
- amphibole m
- biotite f
- muscovite f
- ca-pagioclase feldspar m
- na-pagioclase feldspar f
- orthoclase feldspar f
- quartz f
Naming Igneous Rocks:
Texture
- Fine grained
- Coarse grained
Composition
- Felsic
- Intermediate
- Mafic
Extrusive examples:
basalt, rhyolite
Intrusive examples:
gabbro, granite
Does ocean crust & mantle contain more mafic or felsic?
mafic
Does continental crust & crust contain more mafic or felsic?
felsic
A magma’s composition/ flavor is based on:
Where the melt originally forms, and…
- Magma from deeper depths has more Fe and less Si, O.
- Magma from shallower depths has less Fe and more Si, O.
How long the melt resides in the crust.
Mafic rocks =
Partial Melts of Mantle
Is Hawaii mafic or felsic?
mafic - basalt
The Mantle Plume in Hawaii
Mantle plume is melting mafic, oceanic lithosphere to produce mafic lavas.
Felsic rocks =
Melted Crust Rocks (more Si)
What can change magma composition/flavors?
When a magma resides in the thick continental crust for a long time, it changes composition chemically (density settling, assimilation, magma mixing, fractional crystallization, different sources)
Where are intermediate to felsic rocks made on Earth?
- Magma typically starts mafic in composition, but can change to felsic.
- Where does this happen? places where magma from upper mantle gets trapped in crust for long periods of time.
- This happens most often at subduction zones – mafic melt gets trapped during its ascent through the thick continental crust.
- Melt fractionally crystallizes (density settles) and assimilates the surrounding continental crust to become more felsic.
- Melts at mid-ocean ridges pass through thin oceanic crust, so they have a more similar composition to the mantle.
Is every volcano the same?
no, different shapes, levels of explosively, materials (ash, lava, etc)
800 million people live within 100 km (about 60 miles) of a volcano
Effusive volcano
small lava fountains and gentle lava flows (geyser) emerge from rifts and shield volcanoes
Explosive volcano
generate high ash (fragmented lava) clouds and dangerous ash flows (pyroclastic flows) lava torn to pieces, tall stratovolcanoes
Types of volcano edifices:
strato, caldera, shield, fissure/rift
Mafic volcanism example
Iceland
at a divergent plate boundary
Spreading of the plates creates rift volcanoes that erupt mafic lava (basalt)
takes on shield volcano shape
Are mafic volcanoes effusive or explosive?
effusive (gentle, no large ash cloud)
Shield volcano
broad, low-sloping (< 3 - 10°) edifice where runny lava erupts from as single point for a long period of time
largest on earth, forming at location w steady magma source, no ash cloud
Why are mafic volcanoes (like Iceland) not explosive? (effusive)
Mafic lava (basalt) has a low viscosity (its runny!)
Viscosity
measure of the resistance to flow
Low viscosity
runny
High viscosity
sticky
What type of viscosity does mafic lava (basalt) have
low
What type of viscosity does felsic lava (rhyolite) have
high
What type of viscosity does felsic lava (rhyolite) have
high
Basaltic lava characteristics
pahoehoe: runniest, travels far from vent, thinner, ropey lava
aa: lessy runny, thicker, blocky
Why is Mafic Lava Runny?
Mafic lavas come from melting of mantle.
The mantle is hot!!
Hot fluids are runnier than cold
Silica (SiO2) in correspondence to viscosity
a polymerizing molecule
- Its presence promotes bonding of atoms and molecules (into complex lattices) in a fluid which makes it more viscous (sticky)
- Mafic lavas (basalt) have less SiO2 than felsic lavas (rhyolite)
Is Hawaii on a plate boundary like Iceland?
no, but same basaltic lava composition
Where do Hawaiian volcanoes form?
from melting mafic oceanic crust – this produces mafic lava
What kind of volcanoes are the Hawaiian islands?
Shield volcano (large shields)
The lava has a low viscosity
The lava can travel far from the vent (miles, to build up broad)
The lava does not pile up right at the vent
But what does viscosity have to do with explosivity?
Pressure from trapped gas!
Gas in lava:
All lava has gas trapped in it (H2O, CO2, and H2S)
Because basalt has a low viscosity (runny), gas can easily and safely escape to the atmosphere during an eruption, has big vesicular so gas can escape
(causes lava fountaining, thus causing scoria cone (small cone around lava) when erupting, then turns degassed)
What are the types of felsic volcanoes you would see
plinian, strato (viscous, thick, steep/tall, composed of ash)
What kind of lava in stratovolcanoes
Viscous Intermediate to Felsic Lava
Most famous subduction mountain range on earth
Andes (named by intermediate rock andesite)
Tiny vesicles
gas has a hard time getting out (like pumice)
Gas pressure
Gas pressure builds up in sticky/viscous felsic lava
Lava reaches surface and pressure is released catastrophically
Classic example locations for felsic to intermediate volcanism (explosive volcanism)
Cascades, Andes
Ash
fragmented lava
Pyroclastic fall
Ash falling like snow from the eruption plume, will fall gently like snow
Pyroclastic flow
Collapsed portions of the plume flow along ground (hundreds of mph) dangerous and hazardous
VEI
Volcanic Explosivity Index
the relative size of volcanic eruptions on Earth, it is technically based on the volume of an eruption in cubic kilometers of equivalent lava
Largest eruption of the century
Tonga (2022)
VEI=6
10km^3 of lava
death toll of 3
Most abundant rock type on earth:
igneous
What rock type is derived from weathering?
sedimentary
Clastic rocks
sedimentary rocks formed from pieces (clasts) of other rock
Layering
Water, wind, ice (even gravity) deposits sediment in layers over time (key characteristic of sedimentary)
Each layer or bed represents a single depositional event. That depositional event could represent a storm or just the daily flow of a river into a lake or ocean (for example).
Layers can tell time. The layers at the bottom of this stack are older than the layers at the top.
What is the goal to studying sedimentary rocks?
understand earth’s history, and some economic things too
Clast size of gravel
coarse grained
Clast size of sand
medium grained
Clast size of silt and clay
fine grained
Clast size of silt and clay
fine grained
How are clastic sedimentary rocks almost always classified?
based on grain/clast size (with exceptions)
What does grain size tell us?
Depositional environment = environment in which the rock forms/deposits
What does size of clast have to do with traveling?
clast size decreases with increasing transport distance (ex. clay would have traveled far while boulder would not have)
Sediment can be deposited and form a sedimentary rock anywhere along this journey
What type of environment has high/low energy when it comes to transporting?
a glacier/mountainous environment would be high energy, and water would be low because it can only move small/medium clasts (unless fast moving waves, etc), not boulders
coarse grained takes more energy, fine takes less/low
Common dispositional environment of gravel:
rivers/streams
Common dispositional environment of sand:
beach waves or dune winds
Common dispositional environment of silt:
shallow ocean
Common dispositional environment of clay:
deep ocean
What do the angularity of clasts have to do with transportation?
the more angular, the less they traveled
the more rounded, the farther they traveled
sub angular or rounded are the in betweens
Characteristics of well sorted sand:
Deposited in an environment that sorts out one clast size
Wind, waves, slow moving water
Same size mostly
Characteristics of poorly sorted sand:
Deposited in a high energy environment that can carry multiple particle sizes
Gravity, fast rivers, glaciers!
Differing sizes
What does sorting have to do with transportation?
the farther traveled, the more well sorted it is, the less traveled is more poor sorted
Texture has to do with (rocks)
grain size and angularity
Sorting has to do with (rocks)
deposition environment interpretation
Which mineral cannot chemically react to water and oxygen and become clay?
quartz
is the most chemically and physically stable of common igneous minerals
Clay minerals
microscopic, mica-like minerals that are the by-products (a residue) of the hydrous (water) chemical breakdown of silicate igneous minerals (except quartz)
clay is a size and a mineral
Texture and Mineralogy Tell Us Something About Time/Distance of Transport
Sediment evolution with time/distance.
- Texture - Average grain size; roundness and sorting
- Composition – Becomes more quartz and clay dominated
- Clay carried out to ocean, larger quartz left on beach
more transport = more mature
Two of the most common sedimentary rocks on Earth? We call these mineralogically mature sedimentary rocks!
quartz sandstone (from beach)
shale (from marine)
