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the Mid-Atlantic Ridge (Original)

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Author Topic: the Mid-Atlantic Ridge (Original)  (Read 13615 times)
Carolyn Silver
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Posts: 4611

« Reply #60 on: July 28, 2008, 11:45:19 pm »

Figure 10. Worldwide distribution of oceanic plateaus (black). (Reprinted with permission from Storetvedt,1997. Copyright by Fagbokforlaget and K.M. Storetvedt.)

    There are over 100 submarine plateaus and aseismic ridges scattered throughout the oceans, many of which were once above water. They make up about 10% of the ocean floor. Many appear to be composed of modified continental crust 20-40 km thick -- far thicker than 'normal' oceanic crust. They often have an upper 10-15 km crust with seismic velocities typical of granitic rocks in continental crust. They have remained obstacles to predrift continental fits, and have therefore been interpreted as extinct spreading ridges, anomalously thickened oceanic crust, or subsided continental fragments carried along by the 'migrating' seafloor. If seafloor spreading is rejected, they cease to be anomalous and can be interpreted as submerged, in-situ continental fragments that have not been completely 'oceanized'.
    Shallow-water deposits ranging in age from mid-Jurassic to Miocene, as well as igneous rocks showing evidence of subaerial weathering, were found in 149 of the first 493 boreholes drilled in the Atlantic, Indian, and Pacific Oceans. These shallow-water deposits are now found at depths ranging from 1 to 7 km, demonstrating that many parts of the present ocean floor were once shallow seas, shallow marshes, or land areas [10]. From a study of 402 oceanic boreholes in which shallow-water or relatively shallow-water sediments were found, E.M. Ruditch concluded that there is no systematic correlation between the age of shallow-water accumulations and their distance from the axes of the midoceanic ridges, thereby disproving the seafloor-spreading model. Some areas of the oceans appear to have undergone continuous subsidence, whereas others experienced alternating episodes of subsidence and elevation. The Pacific Ocean appears to have formed mainly from the late Jurassic to the Miocene, the Atlantic Ocean from the Late Cretaceous to the end of the Eocene, and the Indian Ocean during the Paleocene and Eocene [11]. This corresponds closely to the theosophical teachings on the submergence of Lemuria in the Late Mesozoic and early Cenozoic, and the submergence of Atlantis in the first half of the Cenozoic [12].
    Geological, geophysical, and dredging data provide strong evidence for the presence of Precambrian and younger continental crust under the deep abyssal plains of the present northwest Pacific. Most of this region was either subaerially exposed or very shallow sea during the Paleozoic to early Mesozoic, and first became deep sea about the end of the Jurassic. Paleolands apparently existed on both sides of the Japanese islands, and they were submerged during Paleogene to Miocene times. There is also evidence of paleolands in the southwest Pacific around Australia and in the southeast Pacific during the Paleozoic and Mesozoic.
    Oceanographic and geological data suggest that a large part of the Indian Ocean, especially the eastern part, was land (called by some scientists 'Lemuria') from the Jurassic until the Miocene. The evidence includes seismic and pollen data and subaerial weathering which suggest that the Broken and Ninety East Ridges were part of an extensive, now sunken landmass; extensive drilling, seismic, magnetic, and gravity data pointing to the existence an Alpine-Himalayan foldbelt in the northwestern Indian Ocean, associated with a foundered continental basement; data that continental basement underlies the Scott, Exmouth, and Naturaliste plateaus west of Australia; and thick Triassic and Jurassic sedimentation on the western and northwestern shelves of the Australian continent with characteristics pointing to a western source.

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