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Volcanism Definition
the manifestation at the surface of a planet or satellite of internal thermal processes through the emission at the surces of solid, liquid or gaseous products.
Sources of Heat in the Earth
premordial (accretional) heat
radioactive decay
dissipation of tidal energy
Mean heat flow
heat leaking away from the earth (87 milliwatts per square meter (mW m-2)
Main LT Radiation
258 u, 235 u, 232 Th, 40 K
Abundant heat source for the early earth
Aluminium
26 Al very short half life
What is Accretional Heating
the kinetic enery liberated during impact events - Meteors hitting a planet
What is dissipation of tidal energy
tides case a braking effect that liberates energy - kneading the mantle and causing heat
Earth secular cooling rate
100 degrees C per billion years
Chondritic Earth Model
the bulk composition of the earth was the same as a primative C1 condrule (small mineral spherule metorite)
xenolith
(Greek: foreign stones) small chunks of mantle carried up with some basalt magmas
kimberlites
form of xenolith - diamonds
What is the mantle made of
silicate minerals oliven and pyroxen together form a rock called peridotite
What is a depleted mantle
uppermost part of the mantle the is deficient in incompatible elements (potassium and rubidium - large ions)
pyroclastic rocks
(Greek: fire broken) solid fragments ejected from volcanoes
tephra
Ash fall
Scoria
rocks with a fragmented cindery texture "dung in Greek"
plutonic rocks
rocks that don't make it to the surface
7 mineral familys of volcanic minerals
6 are silicates and one is not
The silicates: Olivines, Pyroxens, Amphiboles, Micas, Faldspar (and feldspathoids), Quartz and Oxides.
phenocrysts
mass of tiny interlocking needle-like crystals
When do groundmass crystals form
before and after an eruption
What causes volcanic glass (ryholite melt)
polymerized by chilling so no crystals form.
most silicic and basic composition
Rhyolite then Dacite
alkali
basals, andesites or rhyolites

more sodium and potassium
similar to andesite or rhyolite, but even more alkali
pholoites and trachytes