Igneous rocks: - Check out this comprehensive web site on igneous rocks.- It gives a good overview
Form from magmas. Textures show evidence that minerals crystallized from a liquid (silicate melt = magma)
Usually consist of four or five different minerals.
The minerals reflect the chemistry of the melt and the temperature at which the rock hardened (T at which melt crystallized). The chemistry depends on the composition of the rock that was melted and the amount of melting. Not all of the starting minerals melt at the same temperature.
The melting and also the crystallization temperature depends on:
Bowen's reaction series summarizes information on the melting and crystallization temperatures of the minerals.
2- the amount of water dissolved in magma
3- pressure - this is controlled by the depth of burial
The size of the grains gives information on rate of crystal growth and thus on whether the rock cooled at or near the surface (cooled rapidly) or cooled before reaching the surface (cooled slowly)
Information from volcanoes:
Distribution - volcanic belts coincide with earthquake belts. However:
-volcanic belts are not as continuous as earthquake belts. In the middle east, south Asia no volcanoes but plenty of earthquakes
- volcanoes do occur in areas with few major earthquakes such as in Hawaii
Volcanic products
- determine the nature of the eruption and shape of the surface feature formed during eruption
- may change during eruptive history, reflecting changes in magma
- vary geographically (oceanic vs. continental)
- give clues to the earth's interior
- provide new solid, liquid and gaseous material to the surface of the earth
- remove material from the interior, so are involved in the continuing process of earth differentiation and evolution
CHECK OUT THE VIDEOS OF VOLCANOES ON RESERVE IN COLLIER LIBRARY
Mechanisms of magma rise and eruption
- primarily due to gravity - magma has a lower density than solid rock
- may be an explosive component associated with boiling off dissolved gases
- hot magma and gases may open new passageways but the rise of magma is mainly limited to existing zones of weakness.