Extrusive igneous rock - - Form when magma solidifies at the surface
- Can be explosion or flowing
*Features*:
- Lava flows Fluid, viscous, or sluggish (Ex. Central Chilean Andes) - Fissure eruptions
- Volcanoes (many different types) Volcanic ash, lava, volcanic tuff (pyroclastic flow) ("tuff" layers in a
tunnel)
-. ex*rhyolite, andesite, basalt, komatilite*
intrusive igneous rock - - Form at depth from magma that crystallizes slowly
- Not lava but called *plutonic rocks*
- A large body of intrusive rock is called a *pluton*
-- Formed at great depth and later exposed at surface by erosion (Ex. Stawamus Chief Squamish, BC)
-ex. *granite, diorite, gabbro, peridotite*
batholith - Regional scale intrusive body from main mantle - Yosemite (Sierra Nevada batholith)
laccolith - Local intrusive body with other rocks below (fed by dykes or sill)
- Devils Tower (Wyoming) - Mont Royal (Montreal) and the Montreregian Hills, Quebec
- Torres del Paine, Chile
sills - sheetlike intrusions that are oriented parallel to previous rock units
- Dark sill of Gabbro, Brock River (NWT)
- Mount McKay eroded sill (thunder bay ON)
dykes - - Dyke intruding ash layers (New Zealand)
- Volcanic dykes in sedimentary rock (Scotland)
,melt - (component of magma)
- A liquid portion composed of mobile ions
solids - (component of magma)
- If any, are silicate minerals that have already crystallized from the melt
volatiles (gases dissolved in the melt) - (component of magma)
- Include water vapour, carbon dioxide (CO2) and sulphur dioxide (SO2)
- Volatiles make magma lighter (so it rises)
melting - - Confining pressure drops slightly
- Temperature increases slightly
- Volatiles (fluids, gases) are introduced
divergent plates - where the greatest amount of igneous activity occurs
geothermal gradient - temperature increases within Earth's upper crust. (average 25C per km)
- Rocks in the lower crust and upper mantle are near their melting points
decompression melting - melting due to a drop in confining pressure that occurs as rock rises
crystallization - cooling magma results in the systematic arrangement of ions into crystal structures
- Silicon and oxygen atoms link together to form silicate minerals
- A single volcano may extrude different lava compositions
magmatic differentiation - formation of one or more secondary magmas from a single parent magma
- Magma content evolves during eruption or crystallization
, mafic (basaltic) magma - low silica content, low viscosity (thin and runny), higher temperature
- Primary magmas - mafic magmas that originate from direct melting of mantle rock (peridotite) usually
in ocean ridges
- High composition of DARK (ferromagnesian) silicates *Pyroxene, Ca-plagioclase Feldspar, olivine,
amphibole, basalt, gabbro*
- Flowing lava; can travel long distances
- Shield volcanoes, basalt plateaus
Andesitic/felsic Magma - - Found only within continents (normally at margins)
- Mixing of mafic magma and melted continental crust
- High composition of light (non ferromagnesium) silicates *Quartz, mica, Na-plagioclase feldspar,
granite, K-orthoclase feldspar, rhyolite*
*FOR FELSIC (RHYOLITIC) LAVAS:*
- shorter, thick flows & explosive
- volcanic domes, pyroclastic flows
bowen reaction series - N.L. Bowen demonstrated that as a magma cools, minerals crystallize in a
systematic fashion based on their melting points
Felsic Composition (granitic/rhyolite) - - Composed of light-coloured silicates
- Rich in silica (SiO2) ~ 70%
- Major constituents of continental crust
- melts at lowest temperatures
- increased potassium and sodium
-*ex. K-feldspar, quartz, muscovite mica*
intermediate composition (andesitic/diorite) - - feldspar and amphibole gives salt and pepper look
- Contain at least 25% dark silicate minerals
- Associated with volcanic activity on continental margins
ex. *amphibole, plagioclase feldspar*
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