GEY 101 - Introductory Geology: Exploring Planet Earth
Plutonic and Other Igneous Activity

Plutonic Activity

Most magma is emplaced at depth in the earth; an underground igneous body, once colled and solidified, is called a pluton

Classifications

• Shape
  • Tabular or sheetlike
  • Massive
• Orientation
  • Discordant - cuts across sed rocks
  • Concordant - parallel to sed rocks

Types

• Dikes -- Discordant
• Sills -- concordant with layering
• Laccolith
• Batholith -- (>100km2)
• Stocks -- (<100km2)
• Pegmatites
• Hydrothermal Veins

Emplacement

• Magma at deth is much less dense than the surrounding rock
• At shallower depths, the host rock is cooler and exhibits brittle deformation
• Overall, the emplacement of magma is very similar to the emplacement and intrusion of salt domes

Distribution of Igneous Activity

• Divergent margins -- spreading centers
• Convergent Margins -- subduction zones
• Hot spots

Volcanoes and are concentrated near plate boundaries.
Basalts form at divergent plate margins.
Andesites form at convergent margins where oceanic basalts are subducted along with water-laden sediments.
Rhyolites and granites form where basalts, and older continental crust are remelted at subduction zones.

Other volcanoes form at hotspots. Yellowstone and Hawaii are examples of hot spot volcanism.

Volcanoes and Climate

• Explosive eruptions produce large amounts of gasses and debris which can filter out the sun
• Examples
  • Mt. Tambora, Indonesia - 1815
  • Krakatau, Indonesia - 1883
  • Mt. Pinatubo, Philippines - 1991

Additional Study Guide

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