EOS 316 Midterm 1 Flashcards
Where are igneous rocks sourced from?
Mantle-derived melts
How does the mantle melt? (3 ways)
(1) Increasing temperature
(2) Lower the pressure (adiabatic rise)
(3) Add volatiles (H2O)
What are the characteristics of the ocean crust (thickness, composition)?
10km thick, uniform stratigraphy, mafic, ophiolite suite top down (sediments, pillow basalt, sheeted dikes, massive gabbro)
What are the characteristics of the CC (thickness, composition)
~35km thick, highly variable composition (average: granodiorite), buoyant - unsubductable
Describe the composition and rheology of the mantle
ultramafic, mainly solid, viscous
Describe the composition and rheology of the earth’s core
Fe-Ni metallic alloy, outer core liquid, inner core solid
describe the pressure gradient as we move deeper inside the earth
Pressure increases linearly through the mantle (~1kbar every 3 km), increases more rapidly inside the core since the alloy is more dense
How does temperature change as we move deeper inside the earth?
-Thermal energy dominantly comes from the decay of radioactive elements in the mantle
-The lithosphere geotherm is approximately ~25ºC/km
-Mantle: small dT/dz - stays hot!
Lithosphere: Large dT/dz - temp drops fast!
how does the mantle melt to produce magmas at (a) divergent boundaries, (b) convergent boundaries, (c) hotspots?
a) decompression melting
b) flux melting
c) decompression melting
How do we classify igneous rocks? (3)
(1) Texturally: grain, crystallinity
(2) Modally: naming an igneous sock based on the percentage of each mineral present
(3) Chemically
What’s the difference between holocrystalline, hypo crystalline, and holohyaline?
holocrystalline: all crystal
hypocrystalline: part crystal, part glass
holohyaline: all glass
What is a porphyritic / phyric rock texture?
visibly large crystals in a finer-grained groundmass.
how-to QAP
(1) Analyze all minerals within the rock
(2) Normalize out any non-QAP (mafic / ultramafic)
(3) use new QAP minerals for analysis and name using chart
how-to non-QAP
(1) Analyze all minerals within the rock
(2) Normalize out any QAP (felsics)
(3) use new QAP minerals for analysis and naming scheme
When is normative mineralogy useful?
a) fine-grained, extrusive rocks: ~hypothetical mineral assemblage
b) helps distinguish between magma types
What are the types of silica saturation from normative minerals - Si:(Fe + Mg) ? (ratio and name)
(1) Quartz 1:n/a - ‘Si-oversaturated’
(2) Opx (hypersthene): 1:1 ‘Si-saturated’
(3) Olivine: 1:2 ‘Si-undersaturated’
What are Si-saturated rocks?
(1) Normative hypersthene, normative olivine
(2) no quartz, no feldspathoids
What are the types of silica saturation from normative minerals - Si:(Na + K) ? (ratio and name)
(1) Quartz
(2) Feldspathoids
(2a) Leucite: KAlSi2O6
(2b) Nepheline: (Na,K)AlSiO4
What are Si-oversaturated rocks?
(1) Normative quartz, normative hypersthene
(2) No feldspathoids, no olivine
What are Si-undersaturated rocks?
(1) Normative feldspathoids, normative olivine
(2) No quartz, no hypersthene
How can we subdivide rocks in the alkaline field? (3)
(1) Hi-K series
(2) K-Series
(3) Na-Series
How can we subdivide rocks in the sub alkaline field? (2)
Tholeiitic series
Calc-alkaline series
At what setting can you find alkaline magmas?
Convergent plate margins, oceanic plates, continental plates
At what setting do you find tholeiitic magmas?
Convergent plate margins, divergent plate margins, oceanic plates, continental plates
Ate what setting can you find calc-alkaline magmas?
convergent plate margins
What components are (/can be) in a magma? (4)
(A) melt (liquid)
(B) Crystals (solid)
(C) Volatiles (fluid = dissolved or exsolved gas)
(D) Possibly xenoliths or xenocrysts
Describe the melt of a magma
-linked silica tetrahedra
-can have non-binded oxygen making it impure
How do NBO’s affect the melt of a magma?
more NBO’s = depolymerized melt
less NBO’s = more H2O can dissolve
What are the most important volatiles in a magma (2)?
(1) H2O
(2) Sulphur
What controls magma behaviour? (4)
(1) Viscosity / composition
(2) Temperature
(3) Density
(4) Exsolution of dissolved volatiles
What variables affect viscosity? (4)
(1) composition (wt% SiO2)
(2) Temperature
(3) % Crystals
(4) % Dissolved volatiles (eg. H2O)
What is the top –> down order for an ophiolite sequence?
Pelagic sediments –> pillow basalts –> sheeted dikes –> gabbros
How do hydrothermal fluids interact with ocean magma?( 4)
(1) Hot upwelling fluids reacting with rock
(2) Hydrothermal metamorphism
(3) Some areas concentrate large volumes of upwelling fluids
(4) Metasomatism = rock changes compositionally and mineralogically via fluids
What is a phase?
A physically distinct, mechanically separable phase (liquid, solid, gas)
