Igneous Intrusions
Figures
Types of Magma (Lava)
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Felsic (Rhyolitic; Granitic magma)
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Intermediate (Andesitic)
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Mafic (Basaltic)
Igneous Intrusions
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Plutons - large igneous intrusive bodies
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Discordant plutons - cut across existing structures
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Batholiths - largest intrusions; huge(>100 km2)
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Stock - like batholith but smaller (<100 km2)
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Dike - tabular; < cm to > km thick; often occur in swarms
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Volcanic pipe - circular cross-section
Igneous Intrusions (cont.)
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Concordant plutons - parallel to existing structure
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sill - tabular
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laccolith - mushroom shaped; more viscous magma (usually granitic); generally
less than a few km wide
Igneous Intrusions (cont.)
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How do you distinguish a buried lava flow from a sill in the field?
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vesicles (lava)
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filled fractures on top and bottom (sill)
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baked margins on top and bottom (sill)
Hydrothermal Veins
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Heat of pluton drives convection of aqueous fluids (hot fluids)
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hydrothermal fluids dissolve minerals; precipitate in veins (quartz, gold,
silver)
Plutonism and Plate Tectonics
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Batholiths found in cores of mountains; associated with subduction zones
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feed magma to form other intrusive bodies
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Dikes swarms (sheeted dikes) at mid-ocean ridges feed undersea volcanism;
form ocean crust