chapter 5 · 10/17/2010 1 chapter 5 igneous processes and volcanism jordan, the essential earth 1e...
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10/17/2010
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Chapter 5
IGNEOUS PROCESSESAND VOLCANISM
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
This photo of the July 22, 1980, eruption of Mount St. Helens was taken by Mike Doukas, who was in a U.S. Geological Survey helicopter. Skamania County, Washington. [M. Doukas/U.S. Forest Service.]
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and CompanyPlate tectonic processes explain the global pattern of igneous processes
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
FIGURE 5.2 Igneous rocks were first classified by texture. Early geologists assessed texture with a small hand-held magnifying glass. Modern geologists have access to high-powered polarizing microscopes, which can produce photomicrographs of thin, transparent rock slices like those shown here. [John Grotzinger/Ramón Rivera- Moret/Harvard Mineralogical Museum. Photomicrographs by Raymond Siever.]
Granite as seen through a hand lens
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
FIGURE 5.2 Igneous rocks were first classified by texture. Early geologists assessed texture with a small hand-held magnifying glass. Modern geologists have access to high-powered polarizing microscopes, which can produce photomicrographs of thin, transparent rock slices like those shown here. [John Grotzinger/Ramón Rivera- Moret/Harvard Mineralogical Museum. Photomicrographs by Raymond Siever.]
FIGURE 5.2 Igneous rocks were first classified by texture. Early geologists assessed texture with a small hand-held magnifying glass. Modern geologists have access to high-powered polarizing microscopes, whichcan produce photomicrographs of thin, transparent rock slices like those shownhere. [John Grotzinger/Ramón Rivera- Moret/Harvard Mineralogical Museum.
Granite as seen through a polarizing microscope.
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and CompanyFIGURE 5.2 Basalt as seen through a polarizing microscope.
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Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
Basalt, a thin section as seen through a polarizing microscope.
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
FIGURE 5.3 Granitic intrusions (light-colored) cutting across metamorphosed sedimentary rock. [Tom Bean/DRK PHOTO.]
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and CompanyFIGURE 5.4 Igneous rock types can be identified by texture. [John Grotzinger/Ramón Rivera-Moret/Harvard Mineralogical Museum.]
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
Although rhyolite has the same mineral composition, its fine texture would eliminate it from consideration.
Classification model of igneous rocks.The vertical axis shows the minerals contained in a given rock as a percentage of its volume. The horizontal axis includes a scale of silica content by weight.
So if chem analysis shows a coarsely textured rock sample is ~70 percent silica, you could deduce that its composition is ~6 percent amphibole, 3 percent biotite, 5 percent muscovite, 14 percent plagioclase feldspar, 22 percent quartz, and 50 percent orthoclase feldspar. Your rock would be granite.
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
FIGURE 5.6 Bowen’s reaction series provides a model of fractional crystallization.
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
FIGURE 5.7 Fractional crystallization (a type of magma differentiation) explains the composition of the basaltic intrusion that forms the Palisades. [Zehdreh Allen-Lafayette.]
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Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
FIGURE 5.8 The basic forms of extrusive and intrusive igneous structures
Batholith = > 100 km2
Stock = < 100 km2
Sill is between layersDike cuts layers
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
FIGURE 5.9 Magmas make their way into country rock in three basic ways: by invading cracks and wedging open overlying rock, by breaking off pieces of rock, and by melting country rock. Pieces of broken-off country rock, called xenoliths, can become completely dissolved in the magma. If many xenoliths are dissolved and the country rock differs in composition from the magma, the composition of the magma will change.
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
FIGURE 5.10 (a) At Finger Mountain, situated in the Dry Valleys of Antarctica, sandstone beds are split by sills parallel to the bedding. [Colin
Monteath/AUSCAPE.] (b) A dike of igneous rock (dark) intrudes into shaley sedimentary rock (reddish brown) in Grand Canyon National Park, Arizona [Tom Bean/DRK PHOTO ]
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
FIGURE 5.11 A granite pegmatite vein. Note the large crystals. [John Grotzinger/Ramón Rivera-Moret/Harvard Mineralogical Museum.]
Pat’s note: if xtls are large, where is scale?
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
Idealized section of an ophiolite suite. The combination of deep-sea sediments, submarine pillow lavas, sheeted basaltic dikes, and mafic igneous intrusions indicates a deep-sea origin.
FIGURE 5.12
Ophiolite suites are fragments of ocean lithosphere emplaced on a continent as a result of plate collisions. Peridotite—a dominant rock in the mantle—undergoes decompression melting to form gabbro, which is then erupted to form volcanic pillow lavas (see Figure 5.13).
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
FIGURE 5.13Decompression melting creates magma at seafloor spreading centers. (HINT: Pressure cooker analogy!)
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FIGURE 5.13Decompression melting creates magma at seafloor spreading centers.
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
Plate motion generates a trail of progressively older volcanoes. (a) The Hawaiian Island chain and its extension into the northwestern Pacific reveal the northwestward movement of the Pacific Plate. (b) The Yellowstone volcanic track marks the movement ofthe North American Plate over a hot spot during the past 16 million years.
Theories about the Hawaiian vsYellowstone hot spots.
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
FIGURE 5.16 Volcanoes transport magma from Earth’s interior to its surface, where rocks are formed and gases are injected into the atmosphere.
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
FIGURE 5.17 The active volcanoes of the world with vents on land or above the ocean surface are represented by red dots. Black lines represent plate boundaries. Not shown on this map are the numerous volcanoes of the mid-ocean ridge system below the water’s surface.
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
FIGURE 5.18 A central vent eruption from Kilauea, a shield volcano on the island of Hawaii, produces a river of hot, fast-flowing basaltic lava. [J. D. Griggs/USGS.]
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
FIGURE 5.19 Two forms of basaltic lava, ropy pahoehoe, produced by Mauna Loa on the island of Hawaii. [John Grotzinger.], and…
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Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
…jagged blocks of aa, produced by Mauna Loa on the island of Hawaii. [John Grotzinger.]
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
FIGURE 5.20 Mount St. Helens, a composite volcano in southwestern Washington State, before its cataclysmic eruptioin May 1980, which ejected about 1 km3 of pyroclastic material.[Before: Emil Muench/Photo Researchers. Erupting: U.S. Geological Survey. After: David Weintraub/Photo Researchers.]
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
May 18th 1980 Plinian eruption
of Mount St. Helens. View is
to the north about !:00 PM.
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
The collapsed northern flank of Mount St. Helens, May 19th, 1980, one day after its cataclysmic eruption. View is to the south. Spirit Lake in foreground.
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
FIGURE 5.21Phreatic explosion from Nisino-sima, a new volcano that rose above the sea in 1973 after a submarine eruption in the Pacific Ocean about 900 km south of Tokyo. [Japan Meteorological Agency.]
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
FIGURE 5.22 Vesicular basalt sample. [John Grotzinger.]
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FIGURE 5.23 An explosive eruption at Arenal volcano, Costa Rica. [Gregory G. Dimijian/Photo Researchers.]
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
FIGURE 5.24 A volcanologist examines a volcanic bomb ejected from Asama volcano, Japan. [Science Source/Photo Researchers.]
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company FIGURE 5.25 Volcanic breccia. [John Grotzinger.]
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
FIGURE 5.26 This pyroclastic flow plunged down the slopes of Mount Unzen, in Japan, in June 1991. Note the fireman and fire engine in the foreground, trying to outrun the hot ash cloud descending on them. Three scientists who were studying this volcano died when they were engulfed by a similar flow. [AP/Wide World Photos.]
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
FIGURE 5.27 The eruptive styles of volcanoes and the landforms they create are determined by the composition of magma [(a) U.S. Geological Survey; (b) Lyn Topinka/USGS Cascades Volcano Observatory; (c) Mark Hurd Aerial Surveys; (d) CORBIS; (e) Fabrizio Villa/AP/Wide World Photos; (f) Greg Vaughn/Tom Stack & Associates.]
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
FIGURE 5.28 In a fissure eruption, highly fluid basaltic lava flows rapidly away from fissures and forms widespread layers, rather than building up into a volcanic mountain. [After R. S. Fiske/USGS.] These volcanic cones lie along the Laki fissure in Iceland, which opened in 1783 and erupted the largest flow of lava on land in recorded history. [Tony Waltham.]
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Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
FIGURE 5.28 In a fissure eruption, highly fluid basaltic lava flows rapidly away from fissures and forms widespread layers, rather than building up into a volcanic mountain. [After R. S. Fiske/USGS.] These volcanic cones lie along the Laki fissure in Iceland, which opened in 1783 and erupted the largest flow of lava on land in recorded history. [Tony Waltham.]
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
FIGURE 5.30 (a) Cumulative statistics on fatalities caused by volcanoes since A.D. 1500. The seven eruptions that dominate the record, each of which claimed 10,000 or more victims, are named. These eruptions account for two-thirds of the total deaths. (b) Causes of volcano fatalities since A.D. 1500. [After T. Simkin, L. Siebert, and R. Blong. Science 291 (2001): 255.]
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
FIGURE 5.31 [B. Myers et al./USGS.]
Volcanic hazards associated with composite volcanoes.
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
FIGURE 5.32 Locations of potentially hazardous volcanoes in the United States and Canada. Volcanoes within each U.S. group are color-coded by time since their last eruption; those that have erupted most recently are thought to present the greatest cause for concern. (These classifications are subject to revision as studies progress and are not available for Canadian volcanoes.) Note the relationship between the volcanoes extending from northern California to British Columbia and the convergent boundary between the North American Plate and the Juan de Fuca Plate. [After R. A. Bailey, P. R. Beauchemin, F. P. Kapinos, and D. W. Klick/USGS.]
Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company
FIGURE 5.33 Mount Rainier, seen from Tacoma, Washington, is one of the world’s most hazardous volcanoes. [Alamy.]