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Partial Melting

Partial Melting

  • Melting in the mantle is a complex process which produces variable amounts of melted material of different mineral

  • Partial melting occurs when only a portion of a solid is melted

  • Partial melting occurs where the solidus and liquidus temperatures are different.( For single minerals this can happen when they exhibit solid solution, for example in olivine between iron and magnesium )

  • The two end-member cases are

: Batch or Equilibrium melting

: Rayleigh or Fractional melting

Partition or Distribution Coefficient

Background

  • Partial melting of Earth's mantle and crystal fractionation within a magma causes fractionation of trace elements

Compatible element: D>1

Incompatible element: D<1

  • The amount of fraction can be calculated for a given element if partition coefficients and mineral proportions of the residue/crystallizing assemblage are known and if and assumption is made about the style of melting (e.g., batch, rayleigh, etc.) and fractionation

Bulk Partition Coefficient

  • Trace elements are elements present in rock, mineral, or magma in quantities too low in most cases to affect the number or identity of the phases(minerals) present. Trace elements will be found in small quantities in all of the minerals that crystallize fro a magam

Batch Melting

  • Batch Melting is the melting process whereby the liquid remains in equilibrium with the residue until the liquid is removed
  • This implies that all crystals remain in contact with the melt until it is removed
  • Model the change in the concentration of element in liquid during "batch melting"
  • Batch or Equilibrium melting

  • Fractional or Rayleigh melting

  • Permeability thresold

Fractional or Rayleigh Melting

  • Crystals form and are immediately removed from the system and do not interact(equilibrate) with the melt subsequently
  • Crystal settling is usually involved. Disequilibrium process.
  • Model the change in the concentration of element in a liquid during "Rayleigh Melting"
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