Ch13_As Presented

Ch13_As Presented - Chapter 13 Divergent Boundaries: Origin...

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Unformatted text preview: Chapter 13 Divergent Boundaries: Origin and Evolution of the Ocean Floor Mapping the ocean floor ¡ Depth was originally measured by lowering weighted lines overboard ¡ Echo sounder (also referred to as sonar ) • Invented in the 1920s • Primary instrument for measuring depth • Reflects sound from ocean floor Mapping the ocean floor ¡ Multibeam sonar • Employs an array of sound sources and listening devices • Obtains a profile of a narrow strip of seafloor Figure 13.2 Figure 13.4 Mapping the ocean floor ¡ Viewing the ocean floor from space • Satellites use radar altimeters to measure subtle differences of the ocean surface • Small variations reflect the gravitational pull of features on the seafloor Figure 13.5 Mapping the ocean floor ¡ Three major provinces of the ocean floor • Continental margins • Deep-ocean basins • Oceanic (mid-ocean) ridges Major topographic divisions of the north Atlantic Ocean Figure 13.6 Continental margins ¡ Passive continental margins • Found along most coastal areas that surround the Atlantic ocean • Not associated with plate boundaries • Experience little volcanism and few earthquakes Continental margins ¡ Features comprising a passive continental margin • Continental shelf • Flooded extension of the continent • Varies greatly in width • Gently sloping • Contains important mineral deposits • Some areas are mantled by extensive glacial deposits Continental margins ¡ Features comprising a passive continental margin • Continental slope • Marks the seaward edge of the continental shelf • Relatively steep structure • Boundary between continental crust and oceanic crust Continental margins ¡ Features comprising a passive continental margin • Continental rise • Found in regions where trenches are absent • Continental slope merges into a more gradual incline – the continental rise • Thick accumulation of sediment • At the base of the continental slope turbidity currents deposit sediment that forms deep-sea fans Provinces of a passive continental margin Figure 13.7 Continental margins ¡ Active continental margins • Continental slope descends abruptly into a deep-ocean trench • Located primarily around the Pacific Ocean • Accumulations of deformed sediment and scraps of ocean crust form accretionary wedges Active continental margin Figure 13.8 Features of the deep-ocean basin ¡ Deep-ocean trench • Long, relatively narrow features • Deepest parts of ocean • Most are located in the Pacific Ocean • Sites where moving lithospheric plates plunge into the mantle • Associated with volcanic activity Earth’s deep-ocean trenches Figure 13.9 Table 13.1 Features of the deep-ocean basin ¡ Abyssal plains • Likely the most level places on Earth • Sites of thick accumulations of sediment • Found in all oceans Features of the...
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This note was uploaded on 07/17/2008 for the course GS 121 taught by Professor Leavell during the Fall '07 term at Ohio State.

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Ch13_As Presented - Chapter 13 Divergent Boundaries: Origin...

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