Volcanoes and Igneous Rocks
Magma: Molten material consisting of liquid, gas, and a few xls.
1) Basaltic magma: 50% SiO2
2) Granitic magma: 65-77% SiO2
Magma which reaches the surface and erupts from a volcano is termed extrusive, such as lavas and ash clouds. That which xlizes underground is called intrusive or plutonic.
Crystallization:
Generally, the Si-O tetrahedra are the first things to form, then the other 8 abundant elements, and many other accessory elements, combine with these tetrehedra to form the basic rock-forming minerals.
Bowen's Reaction Series:
When 50% of a magma has xlized, the remaining magma will be depleted in Fe, Mg, Ca because those elements would have gone into the Ol, Pyx, Amph, Ca-plag.
VOLCANOES
Basaltic eruptions:
-gases can be 70% water, 15% CO2, 5% N,S, and then some other compounds of Cl, H, and Argon.
Basaltic lava flows form Shield volcanoes.
Silicic eruptions:
-Violent because there are lots of gases in silicic magmas. Gas is prevented from escaping by the viscous magma, and pressure builds. When released, the euption tends to be violent.
- As ash falls to the ground, it compresses into a hot ASH-FLOW TUFF. These hot ash clouds and gases can race down the side of a mountain at near 125 mph wiping out everything in its path. These are called Nuee Ardentes. When ash becomes saturated with water, by rain, it can flow down valleys. These are called Lahars.
-Volcanoes with alternating layers of ash and lava flows are termed stratovolcanoes or composite volcanoes. Mt. St. Helen's is an example.
Igneous Rocks
-magma which never reaches the surface, but xlizes underground instead.
Batholith and stock:
Distribution of igneous activity:
1) Divergent plate boundaries:
2) Convergent plate boundaries:
3) Hot spots.
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