1. Igneous Rocks December 7-8, 2015

2.   Melted rock that cools & crystallizes at or below the surface Igneous Rocks

3. Where do igneous rocks form?  Extrusive (volcanic): forms when lava cools at the surface  Intrusive (plutonic): forms when magma cools beneath the surface

4. Extrusive Igneous Rocks  Lava flows in Hawaii

5. Intrusive Igneous Rocks  This granite cooled 30 km below the surface Quartz Amphibole K Feldspar Plagioclase Feldspar

6. Where do magma & lava come from?  The crust and mantle are solid rock.  Magma is created in the lower crust and upper mantle (at depths of 50-200 km) by: 1.Raising the temperature 2.Reducing pressure 3.Adding water

7. Where do magma & lava come from?  At convergent plates, the crust descends into the mantle, is heated, and dehydrates. The fluid reduces the melting point of the rock causing melting.

8. Where do magma & lava come from?  At divergent boundaries, hot mantle rock ascends to zones of lower pressure, triggering melting even without additional heat.

9. Where do magma & lava come from?

10. The Geothermal Gradient Silica-rich rocks (with Quartz, K-feldspar) melt at cooler temperatures.  Melts are viscous Silica-poor rocks (with Olivine, Pyroxene, Ca- feldspar) melt at higher temperatures  Melts are very fluid Hot Cool

11. Crystallization of Magma  Crystallization of magma depends on: 1.Composition of the magma  Different minerals crystallize at different temperatures 2.Temperature of the melt  Different minerals crystallize at different temperatures 3.Cooling environment  Slower cooling = larger crystals  Rapid cooling = very small, intergrown crystals

12. Crystallization of Magma  Bowen’s Reaction Series Molten- VERY Hot No solids Molten- Not so hot 100% Solid