Chapter Questions
Why do mafic magmas tend to reach the surface much more often than silicic magmas?
What role does the asthenosphere play in generating magma at (a) a comvergent boundary; (b) a divergent boundary?
How do batholiths form?
How would you distinguish, on the basis of minerals present, among granite, gabbro, and diorite?
How would you distinguish andesite from a diorite?
What rock would probably form if magma that was feeding volcanoes above subduction zones solidified at considerable depth?
Why is a higher temperature required to form magma at the oceanic ridges than in the continental crust?
What is the difference between feldspar found in gabbro and feldspar found in granite?
What is the difference between a dike and a sill?
Describe the differences between the continuous and the discontinuous branches of Bowen's reaction series.
A surface separating different rock types is called aa. xenolithb. contactc. chill zoned. none of the preceding
The major difference between intrusive igneoas rocks and extrusive igneous rocks isa. where they solidifyb. chemical compositionc. type of mineralsd. all of the preceding
Which is not an intrusive igncous rock?a. gabbrob. dioritec. granited. andesite
By definition, stocks differ from batholiths ina. sizcb. shapec. chemical compositiond. all of the preceding
Which is not a source of heat for melting rock?a. geothermal gradientb. the hotter mantlec. mantle plumesd. water under pressure
The geothermal gradient is, on the average, abouta. $1^{\circ} \mathrm{C} / \mathrm{km}$b. $10^{\circ} \mathrm{C} / \mathrm{km}$c. $30^{\circ} \mathrm{C} k \mathrm{~km}$d. $50^{\circ} \mathrm{C} / \mathrm{km}$
The discontinuous branch of Bowen's reaction series contains the minerala. pyroxeneb. amphibolec. biotited. all of the preceding
The most common igncous rock of the continents isa. basaltb. granitec. rhyolited. ultramafic
Granitic magmas are associated witha. convergent boundaries and magmatic underplatingb. divergent boundaries and differentiationc. convergent boundaries and decompression meltingd. divergent boundaries and water release
The difference in texture between intrusive and extrusive rocks is primarily due toa. different mineralogyb. different rates of cooling and crystallizationc. different amounts of water in the magma
Mafic magma is generated at divergent boundaries because ofa. water under pressureb. decompression meltingc. magmatic underplatingd. melting of the lithosphere
A change in magma composition due to melting of surrounding country rock is calleda. magma mixingb. assimilationc. crystal settingd. partial melting
The continuous branch of Bowen's reaction series contains the minerala. pyroxeneb. plagioclasec. amphiboled. biotite