Exam II: Generation and Crystallization of Basaltic Magma

The following concepts will be covered on Exam II.

Part I. Generation of Basaltic Magma

• Potential source materials within the asthenosphere
• Pyrolite
• Spinel lherzolite

• Critical Melt Fraction
• Dihedral angle
• Batch melting (within the Forsterite-Quartz-Diopside Ternary)
• Effect of pressure on phase relationships within this same system.

• Decompression Melting
• steady-state convective geotherm
• upwelling asthensophere during extension

• Controls on melt composition
• importance of invariant points "cusps" on the solidus
• the effect of increasing pressure
• changes in mineral assemblage

• Formation of Large Layered Igneous Complexes
• Cumulate Terminology (cumulus, intercumulus, orthocumulate, mesocumulate, adcumulate, heteradcumulate,

crescumulate, oikiocryst, chedacryst, poikiolytic, ophitic)
• Origin of Modal Layering
• Origin of Cryptic Layering
• Processes that operate during crystallization of Large Layered Igneous Complexes
• gravitational settling
• magma replenishment
• assimilation
• effect on the order of crystallization and appearance of opx and calcic-plagioclase.
• Application of phase diagrams to understanding these processes.

• Variation Diagrams
• Fractionation Indices (Why do we use them?)
• Geochemical Coherence (What is meant by this?)
• Inflection Points (What is their significance?)
• Liquid Line-of-Descent
• What does this signify?
• What is meant by "Crystal-liquid fractionation processes are reproducible at different times".
• Causes of scatter.
• Graphical Solutions to petrographic problems.
• Use of extraction polygons on two-oxide variation diagrams.
• Quantitative mixing calculations for explaining compositional variation (lever-rule).

• Distribution coefficient (Kd)
• Incompatible element behavior
• Compatible element behavior
• C = Co(1/F)
• Uses in solving petrologic problems
• calculation of percent crystallization
• determination of equilibrium between olivine and melt
• identification of Mg# of primary liquids