IGNEOUS ACTIVITY/IGNEOUS ROCKS Chapter 4

A. Overview: The Rock Cycle p. 18 (Chap. 1) ---see Figure 1.15

1. Materials

a. Magma, Igneous Rocks, Sediment, Sedimentary Rocks, Metamorphic Rocks

2. Processes

a. Solidification, Weathering, Lithification, Metamorphism, Melting

3. Schematic Diagram Figure 1.15 p. 18

B. Magma (pp. 76-81; some of this material will be covered in the next topic, Volcanoes)

1. Origin---lower crust/upper mantle p. 76

2. Composition p76=77

a. “Top 8 elements”---O, Si, Al, Fe, Ca, Na, K, Mg

b. Other less common elements

c. Dissolved “gases”---notably water

3. Movement toward surface p.78

a. Less dense, therefore, moves upward

b. Assimilation

4. Cooling of a magma

a. Cools over a long period of time and solidifies over a very large temperature range

b. Completely solidifies (crystallizes) before reaching the surface: INTRUSIVE = PLUTONIC IG. ROCKS

c. Some molten material reaches the surface: EXTRUSIVE = VOLCANIC IGNEOUS ROCKS

5. Other igneous deposits (ore bodies, pegmatites, veins)

C. Bowen’s Reaction Series pp. 78, know Fig 4.3, p.79; (note: covered in more detail in class than in the text)

NOTE: Bowen’s Series gives the sequence of crystallization of major minerals from a cooling magma

1. Normal L. Bowen

2. The Diagram for Bowen’s Reaction Series see Figure 4.3

3. What you need to know for the test

a. Note: first minerals to crystallize (at higher T) are Mg, Al, Fe and Ca rich (Mafic)

b. Note: last minerals to crystallize (at lower T) are Na, K, Si rich (Silicic)

c. Multiple rocks can form from a single magma----crystal settling/differentiation (p. 67)

D. Classification of Igneous Rocks pp. 84-87----note Figures 4.10, p. 85 and also Table 4.1 page 87

1. Texture---size, shape and relationship among mineral grains/crystals in a rock

a. Coarse grained (individual grains/crystals) visible (Intrusive Rocks)

b. Fine grained (individual grains/crystals NOT visible (Extrusive Rocks)

c. Glassy volcanic glass----obsidian see Fig 4.14, p. 88, but the table below is what you need to know

d. Porous volcanic (amorphous) rock with sponge-like appearance----pumice

2. Composition

a. Composition ranges from about 45% silica to about 80% silica. See p. 84

b. Mineralogy varies with composition see Fig 4.10, p. 85

c. As silica content decreases, iron content increases and color goes from light to dark

3. The Classification Chart (this is the one you need to know for the test)

SILICA RICH INTERMEDIATE SILICA POOR ULTRAMAFIC

COARSE GRAIN Granite Diorite Gabbro Peridotite

FINE GRAINED Rhyolite Andesite Basalt ____

GLASSY ---------------------------------Obsidian-------------------------

POROUS ----------------------------------Pumice--------------------------

4. Rock Photographs (shown in lecture)