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单词 Wilson cycle
释义
Wilson cycle

Geology and Earth Sciences
  • The hypothesis, named after Tuzo Wilson who proposed it, that an ocean basin has a lifespan with several stages: from opening, through development, to final closing and the destruction of the basin. Six stages, and the plate tectonic processes involved, have been identified in different parts of the Earth today, and have been postulated for orogenic belts back to the early Proterozoic. The earliest (embryonic) stage involves uplift and crustal extension with the formation of rift valleys (e.g. the E. African Rifts). The young stage involves further subsidence, plus sea-floor spreading; the result is a narrow, parallel-sided sea, possibly with evaporites from intermittent desiccation (e.g. the Red Sea). At this stage, if the uplift was broadly domal with a pattern of three radial rifts forming a triple junction, two of the rifts may widen leaving the third to form an aulacogen (e.g. the Ethiopian Rift). The next (mature) stage is exemplified by the Atlantic Ocean, a wide ocean basin flanked by continental shelves and with the production of new, hot, oceanic crust along an oceanic ridge. Eventually this expanding system becomes unstable, and part of the cooled lithosphere, away from the ridge, sinks into the asthenosphere, forming an oceanic trench with an associated island arc. The shrinking Pacific Ocean is thought to be at this stage. Further shrinking, with the compression, metamorphism, and uplift of accretionary wedges to form young mountain ranges, marks the terminal stage (e.g. the Mediterranean). Finally, all the oceanic crust between the continental masses has subducted and the continents converge in a collision zone, being joined along a suture. The suture (e.g. the Indus–Yarlung Zangbo suture in the Himalayas) marks the relic scar between the plates, and the plate margin finally becomes inactive.


Geography
  • A description of the aggregation and break-up of supercontinents. Initially, a hot spot rises up under a craton, heating it, causing it to swell upward, stretch, and thin, not only splitting a continent in two, but also creating a new divergent plate boundary. A new ocean basin is generated between the two new continents, and as this widens (possibly by thousands of miles), wedges of divergent continental margins’ sediments accumulate on both new continental edges. All of the above is the opening phase of the Wilson cycle. The closing phase of this cycle begins when a new subduction zone forms at the margin of one of the continents.

    Once this zone is active, the ocean basin begins to be subducted, causing the two continents to draw nearer. Magma is generated deep in the subduction zone, rising to the surface to form a cordillera of volcanoes, accompanied by metamorphism, folding, and faulting. When the two continents finally collide, the closing phase of the Wilson cycle is technically over. Because the subduction zone acts as a ramp, the continent with the subduction zone slides up over the edge of the other one. After this collision, the cordillera will be eroded to a peneplain. Most of the upper continent will be eroded away, and the lower continent will eventually return to the Earth’s surface. See Russo and Silver (1996) Geology 24 for further explanation on cordillera formation and the Wilson cycle.

    http://csmres.jmu.edu/geollab/Fichter/Wilson/Wilson.html Information about the Wilson cycle.


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