Dec 21, 2015
Mafic
Intermediate
Felsic
- The mantle is made up of peridotite (ultramafic composition)
- So why/how do we end up with so many different magma compositions?
Textbook Figure 6.6a
Bowen’s Reaction Series
Obsidian (felsic)
-extrusive - cooled very quickly above surface
- “glassy” texture
Granite (felsic)
- intrusive – cooled slowly below surface
- “phaneritic” texture – mineral crystals are visible
Rhyolite (felsic)
- extrusive – cooled above surface
- “aphanitic” texture – mineral crystals are not visible to eye
IGNEOUS ROCK TEXTURES
Magma composition….
So what minerals are in a:
Felsic rock?Intermediate rock?Mafic rock?
Granite (felsic) – Intrusive – phaneritic texture
Rhyolite (felsic) – extrusive – aphanitic texture
Similar felsic composition, different cooling history
Diorite – intrusive – phaneritic texture
Andesite – extrusive – aphanitic texture
Similar intermediate composition, different cooling history
Gabbro – intrusive – phaneritic texture
Basalt – extrusive – aphanitic texture
Similar mafic composition, different cooling history
Page 177
Stock sizedbody
Textbook Figure 6.11a
Dike
Textbook Figure 6.11 b and c