Oceans plates

Authigenic barium sulfate or barite [13462-86-7] is found in relatively high concentrations in sediments covering active diverging oceanic plate boundaries. It occurs as rounded masses containing up to 75% BaSO or as a dispersed constituent of the sediment. Its origins are uncertain, but it is likely that it is associated with hydrothermal actions. 

Ocean Basins. Known consohdated mineral deposits in the deep ocean basins are limited to high cobalt metalliferous oxide cmsts precipitated from seawater and hydrothermal deposits of sulfide minerals which are being formed in the vicinity of ocean plate boundaries. Technology for drilling at depth in the seabeds is not advanced, and most deposits identified have been sampled only within a few centimeters of the surface. 

Model 4 is also a plate kinematic model. The retreat of a fore arc plate forms a back-arc basin. This model seems attractive. Jackson et al. (1975) found the periodicities of rotational motions of the Pacific plate. When the direction of the Pacific plate changed and obliquely subducted, the compressional force of oceanic plate to continental plate decreases. That means that the retreat of fore arc plate occurs. 

Masuda, F. (1984) Sedimentary basins in arc-trench system as a high-sensitive recorder of oceanic plate motion. Mining Geology, 34, 1-20 (in Japanese). 

One example of half-space diffusion is the cooling of an oceanic plate. The oceanic plate when created at the mid-ocean ridge is hot, with a roughly uniform temperature of about 1600 K. It is cooled at the surface (quenched by ocean water) as it moves away from the ocean ridge. For simplicity, ignore complexities... 

Figure 1-8 Heat and mass diffusion in a semi-infinite medium in which the diffusion profile propagates according to square root of time, (a) The evolution of temperature profile of oceanic plate. The initial temperature is 1600 K. The surface temperature (at depth = 0) is 275 K. Heat diffusivity is 1 mm /s. (b) The evolution of profile in a mineral. Initial in the mineral is l%o. The surface is 10%o. D= 10 m /s.

Figure 1-8 Half-space diffusion profiles (cooling of oceanic plate) 43...

Continent-ocean convergence A convergent boundary where an oceanic tectonic plate collides with and subducts underneath a continental tectonic plate. The volcanoes of the Andes Mountains result from the Nazca oceanic plate subducting under the continental South American plate. 

Continental plate A tectonic plate largely consisting of continental rather than oceanic crust (compare with oceanic plate). 

Island arc A chain of volcanic islands that are commonly associated with the subduction of an oceanic plate underneath another oceanic plate (ocean-ocean convergence zone). The Aleutian Islands of Alaska are an example of an island arc. 

Ocean-ocean plate convergence A convergent plate tectonic boundary consisting of an oceanic plate subducting under another oceanic plate. 

Subduction A key process in plate tectonics that involves the movement of an oceanic plate and some of its associated sediments underneath a continental plate or another oceanic plate. 

The source of diamond-bearing kimberlites is uncertain but the stability field of diamond implies a deep-seated origin. Kimberlites are generally believed to have resulted from metamorphism or melting at the deep end of a subducted oceanic plate, the source material being the oceanic lithosphere with... 

Two other metamorphic facies are formed on a regional scale and under unique circumstances. The blueschist facies forms in the low-temperature, high-pressure environment in the upper portion of a subduc-tion zone. Land-derived sediments accumulated deep on the cold ocean floor are driven into an area of high pressure during subduction of an oceanic plate. These rocks often look blue when seen in outcrops. 

Shield volcano— A broad, low profile volcano consisting of layers of basaltic rock, typically formed in the middle of oceanic plates or on continental rifts. 

Powerful inorganic feedbacks do exist. If a volcanic event degasses huge amounts of carbon dioxide (e.g. eruption of a major plume head), then the air will become warmer and hence wetter, and more acid. Weathering will become more intense bicarbonate will flow off the land and eventually carbonate will be deposited in sediment and in new oceanic plate, to return the carbon dioxide to the deep continental crust and to the mantle. But this process depends on the availability of exposed land to be weathered, on the rate of erosion, and on the rate of plate motion. Weathering reaches only a certain depth ... 

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