GEOL 1001 Chapter : Chapter 4
Document Summary
Igneous rocks- form by solidification or molten (liquid) rock. In the crust: 95% igneous, 5% sedimentary: on the surface: 25% igneous, 75% sedimentary. Therefore, magma forms within the earth through melting. Temperatures high enough to promote melting to produce magma occur in the mantle. Magmas ascend because silicate liquids are less dense than equivalent solid rocks. General characteristics of magma: rocks formed from lava are extrusive, or volcanic rocks, rocks formed from magma at depth are intrusive, or plutonic rocks. Some magma reaches the surface and is extruded. Most magma ponds and solidifies within the mantle or crust and is intruded. Magma can be extruded (erupted) gently as lava or explosively as pyroclastic material. The lava cools and solidifies at the earth"s surface. Intrusive igneous activity: most magma is emplaced at depth in the earth, types of intrusive igneous features, dike tabular, discordant pluton, sill tabular, concordant pluton, laccolith similar to a sill, arches overlying rock layers upward.
