Chapter 3.2 Based on Readings 67-76 8/29

Abundance and Distribution of Plutonic Rocks Granite is the most abundant plutonic igneous rock in mountain ranges (erosion and weathering expose this) Metamorphic and Plutonic are similar in age. Exposed in the grand canyon otherwise covered by sediment (Great Plains)

Abundance and Distribution of Plutonic Rocks Basalt and Gabbro make up the ocean floor. Andestine=Volcanoes Ultramfic rocks make up the mantle

How Magma Forms The mantle is not just a giant pool of Magma The heat required to melt rock comes from the core (5000 Degrees Celsius) Conducted

How Magma Forms Geothermal Gradient…Heat increases as you go deeper into the earth (3 Degrees every 100 meters) Rocks melt at all different ranges (because they are made up of so many different minerals) Two factors create magma (liquid rock) Heat and pressure. Minerals require more heat to melt at higher pressures.

Decomrpession Metling and Addition of Water Decompression Melting occurs when hot mantle rock rises to a lower pressure. This allows it to become liquid. Water breaks silicone and oxygen bonds Greatly lowers the melting point click here

How Magmas of different Compositions Evolve Why are the oceans made of basalt and continents made of granite? It depends on how these minerals cooled… Bowens reaction series Certain Minerals Crystallize at higher temperatures. Calcium to sodium more silica at the end

Explaining Igneous Activity Plate Tectonics explains the huge variety of igneous rocks. Divergent= Basalt, Gabbro Convergent= Andestine and Granite

Explaining Igneous Activity Igneous Processes at Convergent Boundaries Water pushed down into the asthenosphere. Lowers the melting point of ultramafic rock Creates Granite and Andestine Igneous Processes at Divergent Boundaries Crust beneath the worlds oceans is mafic (contains less sliica) Due to partial melting of the asthenosphere Closer to the surface in the oceanic crust Decomrpression Melting (Silica melts first and is removed) Ultramafic