Metamorphic
Lithostatic vs differential pressure
Lithostatic: The general pressure of burial (~3kbar/km)
Differential/Directed: Is due to shear or compressional forces. Causes recrystallization, foliation, recrystallization, or folding
Partial Melting
incomplete melting of parent rock to produce a molten rock of different chemical composition (due to different melting points)
explosivity controls
Silica content --> higher Si=more explosive
Gas content --> higher = more explosive
Causes of the formation of mineral deposits
Weathering
Flow of aqueous solutions
interxn w/ hydrothermal solutions
cooling/crystalization
precipitates
wave action
Isochemical vs metasomatic
isochemical: no change in the chemical composition - just a rearrangement
Metasomatic: significant changes in chemical comp
Decompression melting: decrease in pressure w/ no temperature change
Hydration melting: addition of a volatile that better distributes heat in cracks
Heat transfer/rising magma: buoyant magma rises to crust and melts rock there
Viscosity controls
Composition --> higher Si=more viscous
Temperature --> higher temp=lesss viscous
Residual mineral deposits
Chemical weathering occuring on newly exposed/unstable rock results in a concentration
obtain and sort minerals by smelting
Contact metamorphism
Molten rock comes into contact with cooler rock
There's a series of alteration zones in adjacent rocks
Fractionation
Runaway Rxn
-when there's gas in a viscous magma, as soon as the pressure is released the geological shift causes a release in pressure and allows the gases to expand even further and increase explosivity
deposit of heavy minerals that have been concentrated by a mechanical process
usually waves or currents
Dynamic metamorphism
Moderate to high pressure and fluids, usually at fault zones
Causes of fractionation
Fractional Crystallization: a temp drop causes denser and earlier formed materials to settle
Assimilation: hot magma flows into and melts country rock --> leaves behind xenoliths
Magma Mixing: two magma plumes of varying mafic quality meet and mix
Basaltic vs Andesitic magma composition
Basaltic --> 50% SiO2, gas-poor, ketchup
Andesite --> 60% SiO2, gas-rich, asphalt
Sedimentary mineral deposits
local concentration formed through sedimentation
evaporites, chemical precipitates
Regional metamorphism
Intensense compression and pressure, deep burial, high temps
orogeny along plate edges
Rhyolitic and Granitic magma composition
70% SiO2, gas-rich, peanut butter
Magmatic mineral deposits
occurs during the cooling/crystalization of magmatic bodies causing a concentration of:
pagmatites, kimberlites, or layered intrusions