Petrology Midterm Review

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Petrology Midterm Review

• 2/11/08

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What underlies the crust?

• What we know of the mantle comes from
• - ophiolites and ocean floor samples
• - geophysics (especially seismology)
• - cosmochemistry (constraints on the bulk
• composition of the earth)
• - study of mantle rocks brought to the surface

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Seismic structure of the earth
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mineralogical significance of seismic structure?
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Phase Transitions
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Compositional heterogeneity in the mantle

• Be able to interpret compositional trends on
  ternary diagrams

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Compositional heterogeneity in the mantle

• Peridotite vs. eclolgite
• Lines of evidence
• Potential implications

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Ultramafic rock classification
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the norm and classification - 1
Qtz
SiO2
Ab
pyroxene Na2SiO3
X
X
olivine Na4SiO4
Ne
Al2O3
Na2O
NaAlO2
Co
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Physical properties of magmas

• Know and understand factors influencing magma
  viscosity and density
• composition (degree of polymerization)
• P,T (which has bigger effect?)
• Fluids (H2O, CO2 solubility)
• Crystallization (non-Newtonian viscosity)

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Composition
Water content
Also temperature, pressure
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Solubility of fluids
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(No Transcript)
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Daly Gap
crustal density
critical viscosity
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Temperature and pressure effects on density
significance for terrestrial magma ocean
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Phase Diagrams

• T-X diagrams basic reading skills, Lever Rule,
  describing melting/xllization path

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One-Component Phase Diagrams (especially P-T)

• Slopes of boundaries between fields
• Projections of fields with lowest G onto a single
  plane
• µ-P diagrams, H-S diagrams
• Phase Rule

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One-component thermodynamics

• Know definitions of each energy (E, F, G, H)
  independent variables for each case
• Chemical potential, various definitions
• Situations in which each set of independent
  variables is relevant

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this difference in slope underlies our
understanding of how most magmas on earth are
produced
solidus (0.015 C/bar)
liquid
isentrope (0.0015 C/bar)
solid
note that T is a dependent variable
i.e., initially solid material cools slightly as
it ascends, but because of the steeper slope of
the solidus, it begins to melt