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Rift |
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rift1
Geology a long narrow zone of faulting resulting from tensional stress in the earth's crust rift2 US 1. a shallow or rocky part in a stream 2. the backwash from a wave that has just broken rift [rift] (geology) A narrow opening in a rock caused by cracking or splitting. A high, narrow passage in a cave. rift The direction in which stone splits most readily; characteristic of granite or other stone not having visible stratification or foliation. Rift a major linear tectonic structure of the earth’s crust hundreds and thousands of kilometers long that forms when the crust is horizontally extended; this process usually occurs where there is a vast arching uplift. It is believed that the entire thickness or a significant part of the thickness of the earth’s crust is being extended. A rift consists mainly of a series of fractures, among which faults with inclined surfaces predominate; the crustal sector lying above the surface of a fault is also dislocated downward. The sum of the horizontal components of all such shifts compensates for the horizontal extension of the crust. The dip of a fault is usually 60°-70°, and the vertical amplitude of the shift along a fault may reach 5 km. The crustal extension can be several kilometers, and in some cases, several tens of kilometers long. Various types of grabens and horsts are found within a rift. The graben is the chief structural form. A rift usually begins to form, however, with a gentle upward bend of the crust in the form of a tectonic arch; the arch later breaks up and separates into grabens and horsts. Very large rifts are called rift zones or systems. V. V. BELOUSOV Want to thank TFD for its existence? Tell a friend about us, add a link to this page, add the site to iGoogle, or visit the webmaster's page for free fun content. |
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