OffshoreMde Dios

Chile Offshore

Mocha Geographic Basin (North Chiloe Islands)

On this tentative interpretation of a Canvas autotrace of a seismic line of the Chile deepwater offshore, the subduction of the Nazca lithospheric plate (oceanic crust + pelagic deepwater sediments) under the South America plate is quite evident. Similarly, the Moho or Mohorovicic discontinuity (surface separating the Earth's crust from the underlying mantle) is, highly, plausible as picked. The overriding lithospheric plate ( South America plate) is, here, represented, mainly, by the distal part of the accretionary prism. The seismic line does reach the forearc basin, which is illustrated on the next plate.

The majority of the Chile forearc basins associated with the subduction of the Nazca lithospheric plate, as the one illustrated on this autotrace, show bottom simulating reflectors (BSR) and certain time free gas layer (BGR). BSRs are, roughly, parallel the seafloor reflection and they area supposed to be caused by the contrast between an overlying gas hydrate (crystalline solid formed of water and gas) and underlying gas-saturated sediments. The base of the free gas zone is, often, highlighted by a seismic reflector: the so called Base of the free Gas Reflector (or BGR) as illustrated on this tentative interpretation.