Download - Chapter 5 · 10/17/2010 1 Chapter 5 IGNEOUS PROCESSES AND VOLCANISM Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company This photo of the July 22,

10/17/2010

1

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


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


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.

10/17/2010

2


Basalt, a thin section as seen through a polarizing microscope.


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.]


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.


FIGURE 5.6 Bowen’s reaction series provides a model of fractional crystallization.


FIGURE 5.7 Fractional crystallization (a type of magma differentiation) explains the composition of the basaltic intrusion that forms the Palisades. [Zehdreh Allen-Lafayette.]

10/17/2010

3


FIGURE 5.8 The basic forms of extrusive and intrusive igneous structures

Batholith = > 100 km2

Stock = < 100 km2

Sill is between layersDike cuts layers


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.


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 ]


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?


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).


FIGURE 5.13Decompression melting creates magma at seafloor spreading centers. (HINT: Pressure cooker analogy!)

10/17/2010

4


FIGURE 5.13Decompression melting creates magma at seafloor spreading centers.


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.


FIGURE 5.16 Volcanoes transport magma from Earth’s interior to its surface, where rocks are formed and gases are injected into the atmosphere.


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.


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.]


FIGURE 5.19 Two forms of basaltic lava, ropy pahoehoe, produced by Mauna Loa on the island of Hawaii. [John Grotzinger.], and…

10/17/2010

5


…jagged blocks of aa, produced by Mauna Loa on the island of Hawaii. [John Grotzinger.]


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.]


May 18th 1980 Plinian eruption

of Mount St. Helens. View is

to the north about !:00 PM.


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.


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.]


FIGURE 5.22 Vesicular basalt sample. [John Grotzinger.]

10/17/2010

6


FIGURE 5.23 An explosive eruption at Arenal volcano, Costa Rica. [Gregory G. Dimijian/Photo Researchers.]


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.]


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.]


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.]


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.]

10/17/2010

7



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.]


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.]


FIGURE 5.31 [B. Myers et al./USGS.]

Volcanic hazards associated with composite volcanoes.


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.]


FIGURE 5.33 Mount Rainier, seen from Tacoma, Washington, is one of the world’s most hazardous volcanoes. [Alamy.]

Download - Chapter 5 · 10/17/2010 1 Chapter 5 IGNEOUS PROCESSES AND VOLCANISM Jordan, The Essential Earth 1e © 2008 by W. H. Freeman and Company This photo of the July 22,

Top Related