Geology 12 Name: Mix and Match: Igneous Rocks Refer to the following list. Block: porphyritic volatiles mafic glassy magma mixing concordant discontinuous reaction series igneous vesicular partial melting fractures wallrock chilled margins fractional crystallization country rock pegmatite phenocrysts assimilation felsic intrusions discordant continuous reaction series pluton groundmass From this list, select the terms which answer the following questions. 1. Which terms are used to discuss the melting of rocks to form magmas? 2. Which terms are used to describe the crystallization of magmas? 3. Which terms represent ways to alter the compositions of magmas? 4. Which terms are used to describe, or observe, textures of igneous rocks? 5. Which terms are used to describe characteristics of intrusive rock structures?
Matching: Match the rock name with its composition. Some choices may be used more than once, and some may not be used at all. 6. granite A) ferromagnesians and plagioclase 7. andesite B) plagioclase, ferromagnesians, with a little K-feldspar 8. basalt C) all ferromagnesians 9. gabbro D) quartz & K-feldspar with lesser amounts of plagioclase 10. rhyolite E) quartz, plagioclase, and ferromagnesians Fill in the Blanks: 11. Based on their origin, there are two types of igneous rocks, the volcanic or igneous rocks, and the plutonic or igneous rocks. 12. If pressure is lessened on rocks at great temperatures, the rocks may begin to 13. Dissolved water and various gases found in magmas are called 14. The effect of increased volatiles in a magma is to the melting temperatures of the individual minerals. 15. The melting temperature of a mixture of minerals is always than the melting temperatures of the individual minerals. 16. Local sources of heat within the crust or mantle include concentrations of radioactive elements, and caused by plate motions. 17. According to Bowen s reaction series, the first minerals to crystallize from a silicate magma will be relatively in silica. 18. The continuous reaction series applies to the minerals.
19. The discontinuous reaction series applies to the minerals. 20. In the continuous branch of Bowen s reaction series, as the magma cools, rich plagioclase feldspar reacts with the melt to form rich plagioclase feldspar. 21. A magma that is rich in magnesium and iron and relatively poor in silica is called a magma. 22. In the process of, early formed crystals may settle out of the magma, thus changing the composition of the remaining melt. 23. The process by which a magma incorporates the rock around it is called 24. In magma mixing, magmas combine to produce a hybrid melt intermediate in composition. 25. If an igneous rock has experienced two phases of cooling, one slowly at depth and a second more quickly on the surface, then it develops a texture. 26. An extrusive rock with holes, due to escaping gases, has a texture. 27. In a porphyry, a finer surrounds the larger sized 28. A plutonic rock which consists almost completely of olivine and pyroxene would be described as 29. The most common volcanic rock, which makes up the seafloor, is
30. Magmas with high have great difficulty flowing through narrow cracks or other openings in country rock. 31. An igneous rock in which most crystals exceed one centimetre in size is called a 32. The most abundant mineral in ultramafic rocks is 33. A rock composed of fine-grained ash particles is classified as a 34. is generally a dark coloured volcanic glass with a conchoidal fracture, whereas is a vesicular volcanic glass. 35. When magma solidifies in the subsurface, it forms a rock body called a 36. A pluton is said to be if the contacts are parallel to the structure of the country rock. 37. A tabular, discordant pluton is called a and a tabular concordant one is a 38. The difference between a batholith and a stock is that a batholith has a surface area greater than square kilometres. 39. Chilled margins can be recognized because they will be than the interior of the pluton. 40. If magma is flowing as it cools, crystals may align in a parallel fashion. Such an intrusion exhibits
Fill in the Chart: Complete the skeleton of Bowen s reaction series by filling in the blanks with correct mineral names or other terms. True/False Plus: Indicate if the statement is true or false. If it is false, change the underlined part(s) to make it true. 49. Extrusive igneous rocks form from magma cooling in the subsurface. 50. Felsic igneous rocks are richer in silica than mafic igneous rocks. 51. Magma generally cools quickly because rock is a good conductor of heat. 52. The higher the viscosity of a lava, the faster it will flow. 53. A felsic magma has a lower viscosity than a mafic magma. 54. Most magma originates from Earth s molten outer core.
55. As a magma cools, the first minerals to form are olivine and calcium-rich plagioclase. 56. The discontinuous series consists of nonferromagnesian minerals. 57. Assimilation refers to two magmas mixing together. 58. The texture of an igneous rock is determined by the cooling history of the magma. 59. The mantle is believed to be composed primarily of basalt. 60. The richer a magma is in silica, the lighter in colour it will generally be. 61. It would not be unusual to see olivine phenocrysts in a porphyritic basalt. 62. Obsidian is a common constituent of intrusive igneous rocks. 63. Granite is exposed on the surface only after uplift and erosion of the overlying rocks. 64. Batholiths are the largest of all plutons. 65. The presence of inclusions of country rock in a granite is evidence of crystal settling. Drawings and Figures: 66. What two types of igneous intrusions are shown in this picture?
67. Refer to the following diagram: a) What is the identity of a fine grained igneous rock consisting of 15% quartz, 52% potassium feldspar, 10% plagioclase feldspar, 15% biotite, and 8% hornblende? b) What is the identity of a coarse grained igneous rock consisting of 15% quartz, 52% potassium feldspar, 10% plagioclase feldspar, 15% biotite, and 8% hornblende? c) What is the identity of a phaneritic rock consisting of 20% plagioclase, 8% hornblende, 56% pyroxene, and 16% olivine? d) What is the identity of an aphanitic rock consisting of 20% plagioclase, 8% hornblende, 56% pyroxene, and 16% olivine? e) What is the identity of an intrusive rock consisting of 60% plagioclase, 1% biotite, 31% hornblende, and 8% pyroxene? f) What is the identity of an extrusive rock consisting of 60% plagioclase, 1% biotite, 31% hornblende, and 8% pyroxene?
68. Label the indicated features on the following diagram: Short Answers: 69. What is partial melting, and how could this influence the composition of a forming silicate melt? 70. What is a concordant pluton? Give two examples. 71. What is a discordant pluton? Give two examples. 72. Most volcanic glasses are rhyolitic in composition. Compositional layering is more often observed in mafic than in felsic plutons. What property of a magma may have a bearing on both of these observations? Explain.