Midterm 1 Flashcards
Geology:
Derived from the Greek
words “geo” meaning _____
and “logia” meaning _____
Earth
knowledge
5 subdisciplines of geology
Geochemistry • Mineralogy • Geophysics • Paleontology • Geomicrobiology/Geobiology
Three big ideas in geological sciences that form a framework for
understanding the Earth and Earth
processes
• Geological Time (“deep” time) -earth been around 4.6 billion years • Uniformitarianism -principle of how geological processes happen slowly and uniformally over time • Plate Tectonics
Geological record
-Geological time scale is a calender broken into Eons, eras,periods, and epochs
• Geologists examine Earth’s past (rocks) to learn about the
present (processes that form new rocks or features)
• The geologic record is information preserved in rocks
• Rocks contain information about their formation, e.g., fossils,
features such as ripples
ripples
rock found near beach formed by water movement
before ___ million years ago life was only unicellular
542
Uniformitarianism
• Assumption that geologic processes occurring today have
been the same through geologic history
• Imply that changes to the Earth over geologic history have
been a gradual process, not just a series of major
catastrophic events
Earth’s shape is a ______ _______
oblate spheroid
_____ forces cause Earth to bulge near equator, creating an oblate spheroid
rotational
Geodesy: study of
earths size and shape
Everest is in Nepal, North of ____
india
Mount Chimborazo
.technically higher then Everest because of bulge at the equator where it is located
• Inactive volcano in Ecuador – last
eruption ~550 AD
.
at equator Earths radius is __ km greater at the equator
21
_____ ____is used as a reference for all Earth
elevations
Sea level is used as a reference for all Earth elevations, refers to “mean sea level” which is a historic average of sea level measurements
Mariana Trench and Everest are similar because they are both found at the edge of …
interacting plates
Marianas Trench:
contains the deepest point in the ocean, the challenger deep
Earths Layers
Crust-where we are
0-40 km
0.4% of mass
Mantle
40-2890km
67.1%
Outer Core-liquid
2890-5150km
30.8% of mass
Inner core-solid
5150-6370km
1.7%
You can measure a position on Earth using…2
radius of the earth or mean sea level
-radius used for earths layers
the earths layer: _____ is the one with the most mass %
Mantle: 67.1%
Deep vs. Shallow layers in terms of density and main rock type components
Deeper layers of the earth are more dense and contain more Iron-nickel
-iron and nickel form alloys
Shallower layers are less dense and have high concentrations of silica
8 elements which make up about 99% of earth
Magnesium
Calcium
Iron
Nickel
Aluminum
Silica
Oxygen
Sulfur
Oxygen makes up mostof the Earth at __%
30
The Inner core of the earth contains about __% iron and about __% silica
The Earths crust contains about __% iron and __% silica
94, 0
6, 28
As you move deeper into the earth the ammount of Oxygen, Silica, and Aluminum ______
decreases
-Iron and nickel increase
DEFINATELY A QUESTION ON THIS
T OR F
THE CRUST IS HOMOGENOUS
FALSE
It is not homogeneous: it is layered
-based on density difference between continental crust and oceanic crust
Continental Crust: __ g/cm
ocean crust: __ g/cm
Mantle density: __g/cm
2.8
3
3.4
Moho Discontinuity
seperation between Continental/oceanic crust and mantle
.depth: ~40 km below continental, ~7 km below oceanic crust
The Boundary between the Crust and the
Mantle is called the
Moho Discontinuity
T OR F
More dense continental
crust floats on less dense
mantle
F
Less dense continental
crust floats on denser
mantle
T OR F
continental crust
is less dense than
oceanic crust.
T
Crust vs. Lithosphere
The lithosphere is composed of the Earth’s crust and the
uppermost part of the Earth’s mantle. It is solid and divided
into huge plates that move over the surface of the Earth.
Asthenonsphere
Where rock hits a melting temperature making it ductile and allowing it to move, stretch, and convect
Most of the earths crust has a temperature gradient, how much it heats up as you go down, of about
25 degree per km
Convection in mantle
over very long periods of time, cold rocks move down and hot rocks move upwards through mantle
.generates the Earths Magnetic field
Mantle plumes
columns of hot rock rise through the mantle
ex: volcanism in Hawaii results from mantle plumes
Continental Drift
• Alfred Wegener first developed the continental drift
hypothesis, which he based upon several observations:
• Fit of the continents
• Rock record
• Fossil distribution
• Paleoclimate
- **PANGEA
- WEGENER COULD NEVER EXPLAIN HOW IT HAPPENED
- Newfoundland and ireland and scotland
- East coast of greenland and scandinavia
Paleoclimate
the study of what climates were like in different regions historically
Adding to Wegener’s Pangea theory, what modern, new evidence gave crucial clues to the mechanism of “continental drift” (3)
- Exploration of the ocean floor
- Palaeomagnetism
- Presence of the aesthenosphere
Bathymetry
study of the underwater topography
-mapping ocean floor with sonar
How plate tectonics came about
using bathymetry, people discovvered that between continental margins mid-ocean ridges existed
.evidence of seafloor spreading
-crust contained basalt and gabbro
-ocean floor is covered by a thin sediment layer, thinner the sediment layer, younger the rock
-youngest at mid-oceanic ridge as little deposition
-less heat flow at edges of continents, most heat flow and magma coming up at oceanic ridge
-earthquakes most commonly occur at oceanic ridges, not random
Basalt and Gabbro
mafic rocks enriched in magnesium and are heavier and more dense
evidence of seafloor spreading
1-crust contained basalt and gabbro
2-ocean floor is covered by a thin sediment layer, thinner the sediment layer, younger the rock
3-youngest at mid-oceanic ridge as little deposition
4-less heat flow at edges of continents, most heat flow and magma coming up at oceanic ridge
5-earthquakes most commonly occur at oceanic ridges, not random
6-paleomagnetism: earths geomagnetic field switches polarity
7-the prescence of the aesthenosphere, confirmed in 1960 using seismic waves from an earthquake in chili finnally confirmed plate tectonic as the aesthenosphere moves
Explain seafloor spreading
Molten rock rises up beneath mid-ocean ridges and
solidifies to form new oceanic crust (Hess/Dietz model)
-at edges of continent, say east coast of canada we have a passive margin with little to no volcanic activity
-at the other sie, west coast, we we the active margin where old oceanic floor moves back down and causes earthquakes
Paleomagnitism
as rocks are forming, little tiny particles of iron will be randomly oriented in lava, not aligning with earths magenetic field
-as they cool and harden into rock, they match the direction of the magenetic field giving us a history of the direction of the magenetic field over time
Tuzo Wilson
in 1965 first described tectonics in terms of
rigid plates moving over Earth’s surface – not just
continentals moving over the surface
• Characterized three principal types of plate boundaries
• Basic theory of plate tectonics was established in 1968 and
embraced by 1970 due to this large body of evidence
KNOW THEMAJOR TECTONIC PLATE NAMES (11)
North American Plate * Eurasia Plate Australia Plate Nazca Plate South America Plate* Scotia Plate Africa Plate* Antarctic Plate India Plate Carrabian Plate Arabia Plate *Pacific Plate, cocos plate, Juan de fuca plate, folipinno plate
3 Types of Plate Boundaries
- Divergent Boundaries
a) Oceanic plate separation
b) Continental plate separation - Convergent Boundaries
a) Ocean-ocean convergence
b) Ocean-continent convergence
c) Continent-continent convergence - Transform-Fault Boundaries
• Mid-ocean ridge transform fault
• Continental transform fault
T OR F
When continental crust and oceanic crust meet at a
convergent continental margin, the less dense
continental crust will move up over the denser oceanic
crust
T
Divergent boundaries
.continental plate seperation
- new plate forming from one plate spliting ( or extending)
- new lithosphere forms
- Rift valleys, mountains, volcanoes, and earthquakes
ex: East Africa Rift valley
East Africa Rift valley is an example of…
Divergent continental plate boundaries
Convergent boundaries
- Ocean-Ocean convergence
- subduction zone
- ocean trench, volcanic island, deep earthquakes
- volcanic activity in middle of ocean creating volcanic island arcs - Ocean-Continent
- trench, volcanic arc, earthquakes
- volcanic activity under continental crust - Continent-Continent
- crustal thickening, folded mountain and earthquakes
- basically being squished together
ex: Himalayan Mountains
Himalayan mountains are an ex of
- Continent-Continent convergence
- crustal thickening, folded mountain and earthquakes
- basically being squished together
ex: Himalayan Mountains
Angle at which down-going plate subductsdetermines characteristics of convergent boundaries. Talk about each
Moderate (__-__ degrees)
Steep angle(>__ degrees)
Flat-Slab(
30-70
> 70
• Characterized by deep trenches,
volcanic arcs, marginal seas
• E.g., Mariana trench
<30 • Creation of wide mountain belts • Inland deformation, volcanism • E.g., west coast of S. America; Laramide orogeny (The Rockies)
Marianas Trench is an example of
Steep angle(>70 degrees)
• Characterized by deep trenches,
volcanic arcs, marginal seas
• E.g., Mariana trench
Transform Plate Boundaries
• Conservative: lithosphere neither created or destroyed • Lateral (transform) fault and earthquakes • E.g., the San Andreas Fault in California
.At midatlantic ridge to accomodate stress of divergent plates a transform fault will exist to accomodate it
San Andreas Fault is at a ______ plate boundary
transorm
Mid Atlantic ridge
• Divergent Boundary with transform faults • ~16,000 km in length • Spreads 1 to 10 cm/year • Rift currently spans 80 to 120 km • Volcanoes, earthquakes, hydrothermal fields • Mostly underwater -alot of life down there
Iceland example
• Located on Mid‐Atlantic Ridge
• Geologically young and active
• Rift valley, volcanism,
hydrothermal fields
Columnar Basalt
form as the cooling mafic rock contracts quickly under a glacier- ex: iceland
Divergent Plate boundaries and Paleomagnetism
• Two plates pull apart • Mafic magma rises through rift zone forming new basaltic rock on either side of the rift. • Like conveyer belts, the newer crust travels away from the centre on each side. • Oceanic crust records reversed and normal polarity episodes
The magnetic polarity of the sea floor
rocks can be measured using a
magnetometer towed behind a ship.
Normal Polarity=
Reversed Polarity=
magnetic polarity-same as today
reversed polarity-opposite of today
Isochrons
Seafloor isochrons are lines of equal age
________ drives movement of lithospheric plates
Mantle convection
Mineral
is a naturally-occurring, inorganic, crystalline solid
with a definite, but sometimes variable, chemical
composition.
T OR F
Vitamin and Mineral pills arenot minerals in the geological sense
T
In the vitamin context, monerals refers to essential elements (iron, calcium)
Naturally Occuring Minerals
• Minerals are formed in nature, by geological
processes, and not produced by humans
• Example: diamond [C]
Crystalline Solid
The atoms that comprise minerals are arranged in an orderly, repeating, three‐dimensional structure
Halite
Salt (NaCl)
Ice forming on the river of saskatoon is an example of a
mineral
Mineraloids
• Mineraloids have some but not all of the characteristics of minerals
• E.g., Opal do not have a regularly‐occurring crystal structure, it is is
amorphous (disordered) at the atomic level
• Opal has a structure (tiny stacked spheres), but not at the atomic
level
Atoms
the smallest components of nature with propertiesof a given substance
Biogenic Minerals
minerals formed by organisms
Order
orderly pattern which is regular like in ice
Opal
a mineraloid, as it does not have a regular occuring crystal structure
Definite Chemical composition
a fixed or varied within a set defined limits chemical formula
Olivine
mafic rock can vary from a magnesium or iron composition
- Fosterite-Mg
- Faysite-Fe
same mineral but vary over definite range of chemical compositions
Impurities
trace elements can alter the appearence of minerals
ex: corundum will vary in colour
- with cromium its purple
- with iron its blue
Elements
are different types of atoms with different numbers of protons
Atomic number
is the number of protons in the nucleus
Mass number
is the total bumber of neutrons + protons in the nucleaus
Isotopes
atoms with the same number of protons but differing numbers of neutrons (hence differing mass numbers)
Electron shells
s shell-2 electrons
p shell-8 electrons
d shell-8 electrons
electrons are used to balance number of protons
Ions
Anion: negatively charges atom
Cation: positively charges atom
- Na^2+
Compound
pure compounds are molecules (atoms bound together by chemical bonds) that have regular composition
ex: water
Mineral VS. Compound
.compounds can be organic
.compounds dont necessarily have regular crystal structures, they dont have to be solid (ex: liquid water)
.compounds can be produces naturally or synthetically in a lab (mminerals are only produced naturally)
.minerals are a subset of compounds
Minerals, atoms, and bonds
Atoms in minerals form bonds to achieve a stable electron configuration
.atoms bond to balance the number of electrons in their outer shell
-this is eight electrons for most elements: the octet rule
Ionic Bonding
- electrostatic interaction (interaction involving electrons) between oppositely charged ions
- electrons transfer from the atomwith an extra electron (Na) to the atom with a missing electrons (Cl) in the outer shell
- the Na atom becomes a cation (Na+) and the Cl atoms becomes an anion (Cl-)
- strength of bond decreases as distance between nucleii increases
covalent bonding
electrons are shared by atoms that do not readily form ions
generally stronger than ionic bonds
covalent bonds produce very stable molecules and minerals
T OR F covalent bonds are less likely then ionic bonds to dissolve in water
T
Hydrogen Bonds
.electrostatic interaction between hydrogen atom in a molecule and nearby molecules that have uneven charge distributions around them ex: water
ex: hydrogen bonds hold the water molecules in ice in a lattice
Hydrogen Bonds
.electrostatic interaction between hydrogen atom in a molecule and nearby molecules that have uneven charge distributions around them ex: water
ex: hydrogen bonds hold the water molecules in ice in a lattice
- dipole
Hydrogen Bonds
.electrostatic interaction between hydrogen atom in a molecule and nearby molecules that have uneven charge distributions around them ex: water
ex: hydrogen bonds hold the water molecules in ice in a lattice
- dipole based on placement of charges
Metallic bonding
.metals have a tendency to lose electrons and form cations
.freely mobile electrons are shared and dispersed, metals share a sea of electrons
.the metalic bonding in metals for ttwo of their important properties:
-they conduct electricity
-they are malleable
How do minerals form
Minerals form by crystalization where atoms of a gas or liquid combine to form a solid
-crustals can have sharp corners, planar surfaces, and straight edges
Precipitation
formation of minerals in water
Deposition
crystallization from a gas
ex: horefrost
Mineral Formation (5)
- Solidification of magma- basalt rock
- Precip from a solution- halite
- Mineralization/deposition around fumeroles-sulfur
- Biomineralization-Geothite
- Freezing of a liquid
Crystallization
atoms organize in an ordered, three dimensional way
-crystal appearance that we observe in hand samples reflects atomic level organization
- ions arrange themselves in minerals as the minerals crystallize according to both size and charge of ions
ex: olivine having both magnesium and iron
euhedrul crystals vs
anhedral crystals
.well formed with easily recognized faces
.lacking well-formed crystals faces or shape
-because they were crowded as they formed
Graphite vs Diamond
graphite and diamond both are formed by carbon
.minerals with the same composition but different crystal structure
-diamons are extremely hard and are gems
-graphite pourous and soft, ex: pencil led
example of polymorphs
What creates polymorphs
temperature and pressure can effect ohysical and chemical characteristics
- density, hardness, colour, shape, bonding, structure, shape
graphite: formed at lower pressure, not have to structure self in tight way
Ferrihydrite –> Geotite
mineral that recrystallizes over time to form more chemically stable minerals
rock
is a naturally occurring solid aggregate of minerals
Classes of rock forming minerals (8)
- Carbonates: -CARBONATE(C03)
- ex: calcite (calcium carbonate) or dolomite(calcium magnesium) - Oxides:
- OXIDE (03)
- Hematite(iron), Uraninite(Uranium), Magnetite - Sulphides:
- SULPHUR(S2-)
- sulphide mineral weathering is a global environmental issue
- principal ore of many valuable metals
- Galena(lead), Chalcopyrite(copper), Sphalerite(Zinc), Pyrite (iron)
* they are ORE minerals used to get main substances - Sulfates:
- S04
- evaporite deposits, hydrothermal viens
- anhydrite(calcium), gypsum( hydrated version of anhydrite) - Halides:
- Halogen group
- halide anions bonded to metallic cations
- mine it because its primary ore mineral for potash
- halite (sodium chloride), sylvite(potassium chloride), fluorite(calcium floride) is purple - Phosphate Minerals:
- PHOSPHATE ion bonded with cationic metals (P04)
- marine sedimentary deposits, or poop deposits in caves
- Struvite(calcium) helps make up teeth enamel - Native Elements
- gold panning, natural copper, silver, sulphur
- often occur in tiny amount in rock
8.Silicates
.>90% of earths crust
.silicon-oxygen tetrahedron is the basic building of all silicate minerals
-silicon ion(Si^4+) surrounded by four oxygen ions(O^2-)
-ends up with -4 charge in total
-bound covalently, strong bond
.will often be bound with cations
Mineral Hydration
.some minerals change with the additions of water, water molecules attached
Metalic Cations
balance negative charges through ionic bonds
.substitute for other cations
Independent Tetrahedra ex: olivine
.separate tetrahedra
-charge is balanced by ionic bonds with fe^2+ and/or Mg^2+
Single Chain silicates ex: pyroxene
single chain tetrahedra:
.each tetrahedra shares two oxygen atoms
.charge is balanced by ionic bonds with fe^2+, Mg^2+, or Ca^2+
.Pyroxene at spreading centres in ocean/mafic rock
Double Chain silicates: ex: Amphibole
.double chain tetrahedra
- charge is balanced by ionic bonda with fe^2+, Mg^2+, Ca^2+ or other cations
- hexagonal spaces may be occupied by large anions including OH^- or F^-
Sheet Silicates: ex:Mica
.continuous sheets of tetrahedra form a hexagonal network
-easy to break as there ionic bonds, hence it breaks off in sheets easily
-charge is balanced by K^+, Fe^2+,Mg^2+ or other cations
.compositions include:
-ex: biotite(black), muscovite(white)
Framework Silicates
.Three Dimensional framework -Quartz( SiO2) .ex: feldspar -substitution of Al^3+ for Si^4+ gives framework excess negative charge, then negative charge is balanced by Na^+,Ca^2+ .Potassium Feldspar(K+) .Plagioclase Feldpspar(Na+)
Silicates Mineral types: 5
- Independen tetrahedra
- Single Chain silicates
- Double Chain silicates
- Sheet Silicates:
- Framework Silicates
Physical Properties of Minerals (9)
- Hardness
- Cleavage/fracture
- Lustre
- Colour/Streak
- Specific Gravity and Density
- Crystal Form
- Crystal Habit
- Magnetism
- Acid reaction
Malachite
has a very distinct colour
-copper carbonate mineral light green
Silicate Colours
Dark vs. Light
Dark vs. Light
- light=felsic
- high Silica content, low iron and magnesium
- ex: feldspar, quartz
- dark=mafic
- high iron and magnesium, low silica content
- olivine, amphibole, pyroxene
Mohs scale is
.hardness scale
Which class of rock forming minerals do diamond and graphite fall into?
Native- mostly made up of just Carbon alone
Cleavage
number of planes, pattern, and angles of cleavage are key identifiers of rock forming minerals
-tie back to atomic scale structure of mineral
Cleavage Planes vs. Crystal face
are repeated
single surface
Fracture
ex: Quartz
- curved lines similar if you break windows
- NO cleavage planes
Lustre (2)
-interaction of light with mineral surface
- Metallic lustre: ex: Pyrite
- shiny like metal, opaque as you cant see through them
- may dull after a while - Vitreous lustre: ex: Quartz, diamond
- adamantine means it sparkles, shiny and clear like glass
Streak
- fine deposit of mineral powder left on an abrasive surface
- ex: hematite has redy brown streak
Specific Gravity
.measure of density, heavyness
Crystal Form
Geometry of a crystal:
- external expression of internal arrangement
- shape of crystal
crystal habit
.characteristic clusters and shapes as minerals grow
ex: garnet has tiny little crystals that develops
- hematite has bubbles
Form vs. Habit for Hematite
form: tabular crystals
habit: bubbly look, earthy habit
______ react to acid
____ tastes salty
____ tastes bitter
____ smells when scratched
____ is magnetic
carbonates
halite
sylvite(potash core mineral)
sulphur
magnetite
_____ is a potash core mineral
sylvite
Rock
naturally occurring solid aggregates of minerals, or in some cases non mineral solid matter
How to identify a rock? 2
Texture:
.shape and size of mineral crystals
.patterns of mineral grains or other features in the rock fabric
Composition: .which minerals are present and in what quantities
.bulk composition(in silicate rocks, felsic vs mafic)
Three types of major rock
- Igneous:
- melting of rocks in hot, deep crust and upper mantle
- crystallization/solidification of magma or lava
- ex:Granite, basalt
2.Metamorphic:
.rocks under high temps and pressures in deep crust and upper mantle
-recrystallization of new minerals in solid state
-ex: Gneiss, marble
- Sedimentary:
- weathering and erosion of rocks exposed at surface
- deposition, burial, and lithification
- ex: sandstone, limestone, chalk
Name one or more plate tectonic environments where you would expect to find igneous rocks forming
.divergent
.subduction zone
.volcanoes
-convergent
dont see it at continent- continent collision
Igneous rocks 2
.form from solidification of liquid rock
Extrusive igneous rock:
.form when magma and volcanic ash are ejected at earths surface
Intrusive igneous rock:
solidification occurs at depth below earths surface
Called ____ when about earths crust
called ____ when below earths crust
lava
magma
dyke
any intrusive igneous rock that is cutting through other rocks
Stawamus Chief
shows example of mafic dyke where intrusive igneous rock went through granite
How to identify and classify igneous rock
- Texture: crystal size, amount of air bubbles, particle sizes
- Mineralogy and elemental composition
Four main igneous textures
- Pyroclastic texture
- Porphyritic texture
- Aphanitic Texture
- Phaneritic texture
Intrusive rock
.cool and solidify slowly, over thousands of years
- mineral crystals can grow to larger sizes because of the slower cooling
- produces coarse-grained phaneritic texture
ex: granite
phaneritic means
coarse grained
extrusive igneous rocks
cool and solidify quickly, minutes to months
- mineral crystals DO NOT have time to grow in size
- produces glassy to find grained (aphanitic) textures
ex: basalt
aphanitic
fine-grained
Pahoehoe
smooth and ropy
-volcanic rock, megma ejected at surface
Aa
- sharp and jagged
- form when magma ejected at surface
- THINK AHH HURTS TO WALK ON CAUSE JAGGED
Pyroclasts-2 types
.fragments of lava ejected into air during eruption
- Volcanic ash:
- <2mm rsulting from magma shattering and cooling suddently in volcanic explosions, largely composed of glass - Bombs
- >64mm, cool and solidify before hitting ground
Pumice
forms during explosive volcanic eruptions
- bubbles trapped during rapid cooling of gas rick lava
- felsic rock, floats on water
- LIGHTER THEN SCORIA
Scoria
- basaltic equivalent of pumice
- also frothy with voids from gas bubbles
- heavier so doesn’t float on water
- DARKER THEN PUMMICE
OBSIDIAN
.rapid cooling prevents atoms from arranging in crystalline structure
.glassy with smooth, uniforms texture with conchoidal fracture
-broken edges very sharp, excellent materials for knives
Porphoritic texture
- igneous rock with distinct difference in crystal size
- larger crystals(phenocrysts) within relatively fine grained matric
- can find extrusive and intrusive examples of porphyritic texture rock matric can either be aphanitic or phaneritic
- phenocrysts often euhedal form due to crystallization within magma at depth, able to form large crystals
extrusive porphyritic rock
matrix is fine grained- aphanitic
intrusive porphyritic rock
matrix is phaneritic with larger grains
composition of igneous rock is generally based on dark or light
.if its black or dark it is mafic, ex basalt
-lighter is most likely felsic, ex: granite
Felsic to Mafic Continuum
Felsic-80 to 20%
-GRANITE, rhyolite
Intermediate-70 to 30
-DIORITE, andesite
Mafic- 50 to 50
-GABBRO, BASALT
Ultramafic- 10 to 90
-peridotite, KOMATITITE
caps is higher percentage, first is lighter coloured minerals, darker minerals is second
- lighter rocks are intrusive
- darker are extrusive
Trends in Felsic to Mafic rocks
Felsic:
- higher silica content
- more sodium and potassium
- felsic has higher interconnectedness between tetrahedra(ex: quartz)
Mafic:
- lower silica content
- higher iron, magnesium, and calcium content
- mostly independent tetrahedra at mafic side(ex: olivine)
- more cations needed which is why there is more Mg, Ca, and Fe
Felsic composition rocks
Intrusive: Granite
Extrusive: Rhyolite
-plagioclase and potassium felspar, quartz, biotite, and/or amphibole
Intermediate Composition
Intrusive: Diorite
Extrusive: Andesite
-plagioclase, biotite, amphibole, pyroxene
Mafic Composition
Intrusive: Gabbro
Extrusive: Basalt
- pyroxene, plagioclase, amphibole, and olivine
- hawain and Icelandic rock types
- no more quartz or potassium feldspar at this level
Ultramafic Composition
intrusive: peridotite
extrusive: komatiite
- olivine, pyroxene
Where would you find gabbro and basalt in plate tectonic environment?
mafic rocks
- mid ocean ridge, divergent plates
- volcanic island arcs like Hawaii and Iceland in ocean rocks
- also maybe in a continent continent divergent plates where basaltic rock comes up
Where would you find Diorite and Andesite in plate tectonic environment?
bit more felsic
- subduction zones, where melting occurs
- along coast of BC
Where would you find Granite and Rhyolite plate tectonic environment?
- subduction zone
- continental hotspots like Yellowstone national park
- lots of rhyolite
Diorite look s like a
smashed up oreo cookie
Magma Formation
.complete melting rarely occurs at a single temperature
melting points are controlled by four principal factors:
temp,pressure, water content, compositon
melting points are controlled by four principal factors:
temp
pressure
water content
composition
Melting temp depends on whether rocks are more felsic or mafic
felsic: around 700 degrees
- lower magma density
- higher magma viscosity
ultramafic around 1200 degrees
- higher magma density
- lower magma viscosity
Partial Melting
.if a rock has some felsic and some mafic, at lower temps the felsic will melt and move out while the mafic remains hard and stays
-felsic is erupted first at volcanoes as it melts first when rock is subducted
to find 1000 degrees celcius, generally need to be atleast __km unless your at an ocean ridge or hot spot where it will get hotter much faster
40
how does pressure and water content effect melting
.rocks dont melt as easily at higher pressure
.water lowers the melting temp of rock
Decompression melting
fluid induced melting
.pressure decrease lowers melting temp
.increase in water content lowers melting temp
geothermal gradient
.gradients differ in different plate tectonic environments
- the deeper we get in the lithosphere, the hotter it has to be to melt rock
- at mid oceanic ridge, the gradient gets hotter much faster
- at hotspot it also gets hotter faster, not as fast as mid ocean
- subduction zone with water lowers solidus to melt rock at lower temp, similar to normal situation
Solidus
at what point rock will melt in specific tectonic environments
decompression melting happens at
mid oceanic ridges and hotspots
fluxes
are substances that lower the melting temp of a material
Magma Differentiation 4
- Crystal Setting
- starting to cool, mafic crystal first - Magma mixing
- magma moving up into other chambers - Wall-rock assimilation
- country rock will melt and become part of magma
4.Magma migration
Crystal setting
first mafic crystals like olivine begin to form, and as the magma continues to cool the crystals start to include more felsic crystals, by lower temps the magma is almost entirely felsic
wall rock assimilation
xenoliths(country rock) op into magma, if it cools very quickly xenoliths hanging from top of chamber may harden in place
Bowen’s Reaction Series
describes the order and process of magma crystallization
