IGNEOUS ACTIVITY/IGNEOUS ROCKS Chapter 3

 

A.             Overview:  The Rock Cycle  pp. 52-53---see Figure 3.1, p. 52

1.     Materials

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

2.     Processes

a.   Solidification, Weathering, Lithification, Metamorphism, Melting

 

B.             Magma

1.     Origin---lower crust/upper mantle  p. 64-65 (note: text goes into more detail than covered in class)

2.     Composition

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

a.     Less dense, therefore, moves upward

b.     Assimilation p. 68

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

 

C.            Bowen’s Reaction Series   pp. 66-67, know Fig 3.19  (note: covered in more detail in class than in the test)

1.         Bowen’s Series gives the sequence of crystallization of major minerals from a cooling magma

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

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

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

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

 

D.            Classification of Igneous Rocks pp. 57-58----note Table 3.1, Figure 3.6 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 (see table 4.1) volcanic glass----obsidian

d.         Porous (see table 4.1) volcanic (amorphous) rock with sponge-like appearance----pumice

 

2.         Composition

a.         Composition ranges from about 45% silica to about 80% silica.

b.         Mineralogy varies with composition (see Table 3.1, Figure 3.6)

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

 

SILICA RICH   INTERMEDIATE   SILICA POOR   ULTRAMAFIC

COARSE GRAIN    Granite             Diorite                          Gabbro             Peridotite

FINE GRAINED     Rhyolite            Andesite                        Basalt                  ____ 

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

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