Plate Tectonics is theory of global tectonics (geologic structural deformations) that has served as a master key in modern geology for understanding the structure, history, and dynamics of the earth's crust. The theory is based on the observation that the earth's solid crust is broken up into about a dozen semirigid plates. The boundaries of these plates are zones of tectonic activity, where earthquakes and volcanic eruptions tend to occur. Plate Tectonics also are the cause of major features that exist in the World ocean today such as ocean basins.
The Pacific is the oldest of the existing ocean basins, its oldest rocks having been dated at about 200 million years. The major features of the basin and rim have been shaped by the phenomena associated with plate tectonics. The coastal
As the ocean widens, arkoses, sandstones, and shales may accumulate in clastic wedges along the continental margin, and marine limestones may be deposited. The successions on the coasts of Brazil and West Africa record symmetrically the change from nonmarine clastic sandstones and shales, via evaporites (about 120 million to 110 million years old), to marine sandstones and limestones. This sequence records the incoming of seawater into a continental rift valley, widened via a Red Sea-type narrow ocean into a mature ocean.
shelf, which extends to depths of about 180 m (about 600 ft), is narrow along North and South America but is relatively wide along Asia and Australia. The East Pacific Rise, a submarine ridge-and-trough system, extends some 9650 km (about 6000 mi) from Antarctica t
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