tailieunhanh - Geography and Oceanography - Chapter 5

Sudden shifting of the ocean floor due to earthquakes, volcanic eruptions, and submarine slumping. open ocean: short heights, long wavelengths (100 km), and long periods 400500 mph!!! shallow water: their length shortens and their height increases dramatically. These are NOT tidal waves | Creation, Aging and Recycling of the Ocean Floor How is the ocean floor made? Why does the ocean floor get deeper with age? How are volcanic arcs made and why are they so dangerous? Formation of Ocean Lithosphere Formation of Ocean Lithosphere Mid-ocean ridges -- global circuit of plate divergence -- youngest ocean floor -- shallowest ocean floor Architecture of oceanic plates -- seismic profiling -- ocean drilling -- fossil slivers of ocean floor Seismic Profiling (sound energy) Ocean Drilling International program (20 nations; began 1968) 2-month cruises Deepest hole: 2 km But, new vessel will drill to >6km! Fast vs. Slow Spreading Fast Spreading Ridge (10-20 cm/yr) Slow Spreading Ridge (1-5 cm/yr) Mid-Ocean Ridges Uniform process of mantle melting, lava freezing - magma chambers - effects of spreading rate - segmentation Ocean Crust Layering Superfast Spread Crust Mission to Hole 1256D Hole 1256D is located in the eastern Pacific in crust formed between 19 and 12 million years ago (Ma) on the Cocos-Pacific plate boundary. The recognition of an interval of superfast spreading rates, up to 220 mm/yr full rate (24), led to the choice of ODP Site 1256 (Fig. 2) as the optimal site for deep drilling (25). Superfast Spread Crust Mission to Hole 1256D Mineralized Volcanic Breccia (1027-1029 mbsf) o o 10 cm Similarly, there is little evidence for tilting (at most a few degrees) in Hole 1256D and no evidence for significant faulting. In contrast, the upper crust exposed at Hess Deep shows significant faulting and rotations within the dike complex (33). The ponded flow at Site 1256 indicates that faults of ~50-100 m must exist in superfast spread crust to provide the necessary relief for ponding of the flow, but faulting and rotations in the dike section must be less common than in crust formed at fast spreading rates, if observations from Hess Deep are widely applicable. The ~800 m-thick lava sequence is much less hydrothermally | Creation, Aging and Recycling of the Ocean Floor How is the ocean floor made? Why does the ocean floor get deeper with age? How are volcanic arcs made and why are they so dangerous? Formation of Ocean Lithosphere Formation of Ocean Lithosphere Mid-ocean ridges -- global circuit of plate divergence -- youngest ocean floor -- shallowest ocean floor Architecture of oceanic plates -- seismic profiling -- ocean drilling -- fossil slivers of ocean floor Seismic Profiling (sound energy) Ocean Drilling International program (20 nations; began 1968) 2-month cruises Deepest hole: 2 km But, new vessel will drill to >6km! Fast vs. Slow Spreading Fast Spreading Ridge (10-20 cm/yr) Slow Spreading Ridge (1-5 cm/yr) Mid-Ocean Ridges Uniform process of mantle melting, lava freezing - magma chambers - effects of spreading rate - segmentation Ocean Crust Layering Superfast Spread Crust Mission to Hole 1256D Hole 1256D is located in the eastern Pacific in crust formed