The following sections of this BookRags Literature Study Guide is offprint from Gale's For Students Series: Presenting Analysis, Context, and Criticism on Commonly Studied Works: Introduction, Author Biography, Plot Summary, Characters, Themes, Style, Historical Context, Critical Overview, Criticism and Critical Essays, Media Adaptations, Topics for Further Study, Compare & Contrast, What Do I Read Next?, For Further Study, and Sources.
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The following sections, if they exist, are offprint from Beacham's Encyclopedia of Popular Fiction: "Social Concerns", "Thematic Overview", "Techniques", "Literary Precedents", "Key Questions", "Related Titles", "Adaptations", "Related Web Sites". (c)1994-2005, by Walton Beacham.
The following sections, if they exist, are offprint from Beacham's Guide to Literature for Young Adults: "About the Author", "Overview", "Setting", "Literary Qualities", "Social Sensitivity", "Topics for Discussion", "Ideas for Reports and Papers". (c)1994-2005, by Walton Beacham.
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Since the late 1970s, the term ophiolite has been used to describe sections of oceanic crust and upper mantle, along with sedimentary rocks deposited on the sea floor, emplaced as thrust slices onto continental lithosphere. This process, called obduction, results from continent-continent collision following subduction of oceanic crust and the closure of oceans or back-arc basins. A typical ophiolite suite comprises (from base to top):
Many ophiolites have undergone high pressure-low temperature, blueschist metamorphism in subduction zones prior to their emplacement. Blueschists are named after blue-colored glaucophane and other sodium-rich amphiboles formed in rocks of appropriate composition. Eclogite facies metamophism occurs when rocks are subducted to greater depth. In eclogites, pyroxene, olivine, and plagioclase recrystallize to sodium-rich pyroxene and garnet. During collision, blueschists plus or minus eclogites are thrust as a series of imbricate slices onto lower-grade, continental rocks. Ophiolites may be overprinted by greenschist facies metamorphic assemblages and exhumed during collapse of a thrust-thickened orogen.
Ophiolites in orogenic (mountain building) belts represent sutures between two continental plates. Their recognition is therefore important in tectonic reconstructions. Ophiolites host a range of mineral deposits. Ultramafic and gabbroic rocks may contain deposits of chromium or platinum-group elements. Chrysotile asbestos occurs in serpentinites. Copper, zinc, cobalt and nickel sulfides (marine exhalatives) may occur in economic amounts. Some ophiolites host shear controlled epithermal or mesothermal gold mineralization.