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Physical Processes in Earth and Environmental Sciences Phần 8

Chương 5 Xây dựng tấm midocean núi biên giới Tấm ranh giới bảo thủ ở đại dương biến đổi lỗi hoặc lục tấn công chống trượt lỗi cảm giác của chuyển động tấm trên sườn núi (thông thường, nhưng không phải lúc nào cũng trực giao với trục sống núi). | 224 Chapter 5 Constructive plate boundary at midocean ridge Conservative plate boundary at oceanic transform fault or continental strike-slip fault Sense of plate motion across ridge usually but not always orthogonal to ridge axis Destructive plate boundary at trench filled barbs on side of overriding plate Zone or suture of continent-to-continent ỹ collision unfilled barbs on overthrust terrain Fig. 5.35 Outline of major plates. Ca Caribbean plate Co Cocos plate Ph Philippine plate JF Juan de Fuca plate. approaching the partial melt curve for mantle rock Section 5.1 that allows the whole process of plate tectonics to operate. The asthenosphere behaves as a high-viscosity r.4-1019 Pa s fluid in this scheme of things. Plate thickness varies according to whether continental or oceanic crust is involved in the upper layers oceanic plate thickens laterally from zero at the ocean ridge to a maximum of 80 km while the thickest continental lithosphere may be greater than 200 km. It is a key fact that unlike the isostatic equilibrium of crust and mantle Section 3.6 oceanic lithospheric is denser than the underlying asthenosphere. This inverted density stratification leads to the production of negative buoyancy forces which drive plate destruction by subduction at the oceanic trenches. 5.2.2 A brief historic overview It is instructive to briefly review the development of plate tectonics because the logic developed to account for various key components comes from a range of subject areas paleontology paleoclimatology geology geophysics and geochemistry. Alfred Wegener a meteorologist by training developed his theory of continental drift in 1915 starting from the basis that a supercontinent called Pangea Greek all Earth progressively broke up over r.250 million years My into today s separate continental masses. Wegener and later du Toit Wegener tragically died during an Arctic meteorological expedition assembled much fossil and geological evidence to support the theory of .