The continent-ocean boundary (COB) or continent-ocean transition is the boundary between

continental crust Continental crust is the layer of igneous, sedimentary, and metamorphic rocks that forms the geological continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called '' sial' ...

and

oceanic crust Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramafi ...

on a

passive margin A passive margin is the transition between oceanic and continental lithosphere that is not an active plate margin. A passive margin forms by sedimentation above an ancient rift, now marked by transitional lithosphere. Continental rifting cre ...

. The identification of continent-ocean boundaries is important in the definition of plate boundaries at the time of break-up when trying to reconstruct the geometry and position of ancient continents e.g. in the reconstruction of

Pangaea Pangaea or Pangea () was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 millio ...

Techniques used in identification

* Gravity data inversion - Moho depth can be derived by the inversion of satellite gravity data and thereby crustal thickness * Magnetic stripe data - Most areas of oceanic crust show characteristic stripes due to periodic

magnetic reversals A geomagnetic reversal is a change in a planet's magnetic field such that the positions of magnetic north and magnetic south are interchanged (not to be confused with geographic north and geographic south). The Earth's field has alternated ...

during formation at a

mid-oceanic ridge A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a diverge ...

. The continental crust is by contrast typically magnetically quiet. * Wide-angle seismic refraction and reflection data - These data give a precise location for the COB by determining the

P-wave A P wave (primary wave or pressure wave) is one of the two main types of elastic body waves, called seismic waves in seismology. P waves travel faster than other seismic waves and hence are the first signal from an earthquake to arrive at an ...

velocities along a profile. The two types of crust have distinct P-wave velocities.

Economic importance

hydrocarbon exploration Hydrocarbon exploration (or oil and gas exploration) is the search by petroleum geologists and geophysicists for deposits of hydrocarbons, particularly petroleum and natural gas, in the Earth using petroleum geology. Exploration methods Vi ...

moves further offshore to look for the remaining potential on passive margins, understanding the location of the COB is critical to predicting possible hydrocarbon occurrence. This is both from the likely location of source and reservoir rocks and the need to model the thermal effects of break-up in basin modelling.

References

{{Reflist Structure of the Earth