Figures

Types of Magma (Lava)

• Felsic (Rhyolitic; Granitic magma)
• Intermediate (Andesitic)
• Mafic (Basaltic)

• Plutons - large igneous intrusive bodies
• Discordant plutons - cut across existing structures
• Batholiths - largest intrusions; huge(>100 km2)
• Stock - like batholith but smaller (<100 km2)
• Dike - tabular; < cm to > km thick; often occur in swarms
• Volcanic pipe - circular cross-section

• Concordant plutons - parallel to existing structure
• sill - tabular
• laccolith - mushroom shaped; more viscous magma (usually granitic); generally less than a few km wide

• How do you distinguish a buried lava flow from a sill in the field?
• vesicles (lava)
• filled fractures on top and bottom (sill)
• baked margins on top and bottom (sill)

• Heat of pluton drives convection of aqueous fluids (hot fluids)
• hydrothermal fluids dissolve minerals; precipitate in veins (quartz, gold, silver)

• Batholiths found in cores of mountains; associated with subduction zones
• feed magma to form other intrusive bodies
• Dikes swarms (sheeted dikes) at mid-ocean ridges feed undersea volcanism; form ocean crust