Igneous Rocks

2. Igneous Rocks • Make up 95% of earths crust • Most common are on the continents - Andesite and Granite • Most common on the ocean floor – basalt • All Igneous rocks originate as magma or molten rock from the earths interior

3. Igneous Rocks • Rocks start melting at 750 C • Temp increases about 30 C each km toward the center of the earth

4. Igneous Rocks Melting depends on pressure & water content Higher pressure – higher melting point More water – lower melting point Rocks with lower melting point will melt first and solidify (crystallize) first when cooled

5. Magma is classified by the amount of silica (SiO2) that it contains Basaltic – 50% silica Andesitic – 60% silica Granite – 70% silica

6. Igneous Rocks • Extrusive – Rocks that form at the earths surface (lava) • Intrusive – Rocks that form beneath the earths surface

7. Extrusive Lava – molten material from the earth and the rocks that form from it Fissure – outpouring of basaltic lava on the ocean floor Volcano – outpouring of lava through a vent

8. Fissure Flood Basalts produced the Colombia Plateau

9. Volcano – outpouring of lava through a vent Shield volcano – broad gentile slopes Cinder cone – smooth steep slopes and a bowl shaped summit Composite cones – steep sided summit – gradual slopes

10. Volcano

11. Formations Under Ground • Igneous rock formations – intrusive rock • Plutons – large intrusive rock body beneath the earths surface

12. Plutons

13. Plutons • Dike – formed by the intrusion of magma into fractures that cut across the layers of existing rock • Shiprock – New Mexico

14. Plutons • Sill – intrusion of magma into fractures that are parallel to the layering • Laccolith – mushroom shaped sill that pushes the rock layers upward

15. Plutons • Batholiths – large sill or laccolith having a surface area greater than 100 square kilometers – usually due to a number of intrusive events

16. Batholiths

17. Plutons