Note the relationship between the igneous rock names and Bowen's discontinuous and continous reaction series.
Plutonic Igneous Activity
• Plutons - Igneous bodies emplaced at depth.
o Dike
Discordant, tabular body formed when magma injected into fractures.
May be feeders for lava flows.
o Pipe or Neck - Vertical feeder for volcanoes.
o Sill - Concordant tabular body often formed when magma injected along sedimentary bedding surfaces.
o Laccolith - Lens shaped sill of more viscous magma.
o Batholith
Largest intrusive body.
May be one large magma chamber or more likely composed of many coalesced magma chambers spanning a large range of geologic ages.
Believed to be the roots of volcanoes and volcanic chains.
Batholiths of western North America.
• Emplacement of batholiths.
o Upward migration versus granitization.
o Granitization - the conversion of country rock to granite.
o Upward migration
From subducting slabs.
By buoyancy and pushing aside the country rock.
Similar to the emplacement of salt domes.
o Stoping
Assimilation
Incorporation of xenoliths (country rock fragments)
Enlarging the conduit
Plate Tectonics and Igneous Activity
• Global distribution of igneous activity is not random.
• Spreading center volcanism.
o Plates pull apart and basaltic magma moves up to fill the voids.
o Short path to the surface.
o Produces mid-oceanic ridges.
• Subduction zone volcanism.
o Water-rich plates descend into the hot mantle and melting occurs.
o Long path to the surface.
o Dominant magma is andesitic - much assimilation.
o Produces chains of volcanoes parallel to the subduction zone; sometimes on the continent and sometimes as island arcs.
o Water and other volatiles contribute to the explosive nature of the volcanism.
o Ring of fire
• Intraplate igneous activity
o Plumes of hot mantle rock; may extend to the core-mantle boundary in some cases ("hot spots").
o Hawaiian islands and Yellowstone are two examples.
o Remelting of the continental crust - process poorly understood.