Occurrence of Trace Elements

1
Occurrence of Trace Elements

• Solid solution
• trace minerals
• interstitial defects in crystal lattice
• occluded zones trapped in minerals
• melts
• other fluids

2
Dilute Solutions
Ideal solution ai Xi
1
Real solution
activity
Henrys Law ai kiXi
0
0
1
Mole fraction
3
Distribution Coefficients
melt
Co
olivine
4
Distribution Coefficients
5
Fractional Crystallization

• Continuous re-equilibration with melt
• Equilibrium Crystallization
• Surface Equilibrium
• Diffusion in crystal lt diffusion in melt
• continuous removal of crystals
• Rayleigh Fractionation

6
Rayleigh Fractional Crystallization
Magma
Magma
Crystals
Time 1
Time 2
7
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8
Equilibrium Fractional Crystallization
Magma
Magma
Crystals
Crystals
Time 1
Time 2
9
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10
Can alkali basalts be derived from ocean
tholeiites by fractional crystallization?
Rayleigh Fractionation
Data K Rb OT 0.08 1 ppm AB 0.9 18
ppm D 0.02 0.02
Results F xyst K 0.085 91.5 Rb 0.052 94.8
11
Partial Melting

• Equilibrium throughout melting
• batch melting
• Continuous removal of melt as it forms
• fractional fusion

12
Rayleigh Partial Melting
Melt
Rock
Rock
Time 1
Time 2
13
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14
Equilibrium Batch Melting
Melt
Rock
Rock
Time 1
Time 2
15
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16
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