EARTH232 Lecture Notes - Lecture 3: Magma Chamber, Silicate Minerals, Biotite
26 Aug 2016
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Lecture 3: going down the brs (olivine to biotite) silica content increases. Density contrast between mineral and melt: larger more efficient. Viscosity of magma: higher less efficient. Shapes of crystals: spheres most efficient. Filter differentiation/ filter press action: flowing magma enters fractures. Bigger crystals can get stuck in a bottle neck and sepeates from the rest: crystals settling rearrange and tend to expel free liquid, less dense felsic magmas separate and float to the top of the chamber. Flow differentiation/segregation: grain dispersive pressure, shearing forces between grains and walls cause a force to applied perpendicular to the flow and causes crystals to accumulate near the centre of the chamber. Zoning: normal zoning: higher temp core forms anorthite, lower temp rims are where albite forms, oscillatory zoning: general progression from an-rich core to ab-rich rim, but w/some reversals. Magma next to growing crystal is depleted in ca, takes time to resupply.
