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CH. 3 IGNEOUS ROCKS AND INTRUSIVE ACTIVITY: Concept Checks
3.1
1. What is magma? How does magma differ from lava?
2. List the three major components of magma.
3. What is melt? What is a volatile?
3.2
1. In what basic settings do intrusive and extrusive igneous rocks originate?
3.3
1. Igneous rocks are composed mainly of which group of minerals?
2. Differentiate between felsic and mafic igneous rocks.
3. In what way are the dark (ferromagnesian) silicate minerals different from the light (nonferromagnesian) silicate minerals?
3.4
1. How does the rate of cooling influence crystal size? What other factors influence the texture of igneous rocks?
2. The statements that follow relate to terms used to describe igneous rock textures. For each statement, identify the appropriate term.
a. openings produced by escaping gases
b. obsidian exhibits this texture
c. a matrix of fine crystals surrounding phenocrysts
d. crystals are too small to be seen without a microscope
e. a texture characterized by two distinctly different crystal sizes
f. coarse-grained, with crystals of roughly equal size
g. exceptionally large crystals exceeding 1 centimeter in diameter
3. Why are the crystals in pegmatites so large?
4. What does a porphyrictic texture indicate about an igneous rock?
3.5
1. The classification of igneous rocks is based largely on two criteria. Name these criteria.
2. How are granite and rhyolite different? In what way are they similar?
3. Compare and contrast each of the following pairs of rocks:
Compare
a. granite and diorite
Contrast
b. basalt and gabbro
c. andesite and rhyolite
3.6
1. What is the geothermal gradient?
2. Describe decompression melting.
3. How does the introduction of volatiles trigger melting?
4. In which plate tectonic settings would you expect magma to form?
3.7
1. What is magmatic differentiation? How might this process lead to the formation of several different igneous rocks from a single magma?
2. Relate the classification of igneous rocks to Bowen’s reaction series.
3. What is partial melting?
4. How does the composition of a melt produced by partial melting compare with the composition of the parent rock?
3.8
1. Describe each of the four basic intrusive features:
a. dike
c. laccolith
b. sill
d. batholith
2. What is the largest of all intrusive igneous bodies? Is it tabular or massive? Concordant or discordant?
3.9
1. List two types of hydrothermal deposits.