GEOL 100 Lecture Notes - Lecture 8: Oceanic Crust, Partial Melting, Mafic
28 Feb 2019
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Mafic (dark colored)--lower in silica, higher in iron and magnesium. Felsic (light colored)--higher in silica, lower in iron and magnesium. Differ by proportion of silica to fe/mg minerals and physical properties. Major types of magma: (compositional groups)--named after type of mineral that dominates. Felsic (silicic)--high % felsic, low % mafic minerals. Mafic--lower % felsic, high % mafic minerals. As you go down, density of rock increases because iron and magnesium rich minerals are heavier. High viscosity: lava piles up (like honey or gum), lower temperature and abundant silicate chains. Low viscosity: lava spreads out (like water), higher temperatures and fewer silica chains. Source of melt (what is being melted in the first place) Continental crust (felsic)--magma will be felsic composition(white or light gray) Oceanic or mantle crust (mafic)--magma produced will be mafic in composition (black or dark grey) As magma rises, it melts rock it comes into contact with and those pieces get mixed into melt.
