||A flat region of the deep ocean floor (with a slope less than 1:1,000) that was formed
by the deposition of pelagic and gravity-current sediments, which obscure the pre-existing
topography. Vast areas of the ocean floor fall within this setting, which can be subdivided
into smaller basins based on regional topography.
|Convergent Active Continental Margin
||Intense areas of active magmatism, where the oceanic lithosphere is subducted beneath
the continental lithosphere. This results in chains of volcanoes near the continental
margin; the leading edge of the continental plate is usually studded with steep mountain
|Divergent Active Continental Margin
||Areas where tensional tectonic forces result in the crustal rocks being stretched
and—ultimately—split apart or rifted. These areas are marked by subsidence and a continental
||An elongate zone of unusually irregular topography (on the deep seafloor) that often
separates basins and regions of different depths; fracture zones commonly follow (and
extend beyond) offsets of the mid-ocean ridge.
||Spreading centers are areas where tectonic plates are moving apart, allowing new oceanic
crust to reach the surface of the sea floor.
||An extremely large, global spreading center. The mid-ocean ridge is a continuous,
seismically active, median mountain range extending through the North Atlantic, South
Atlantic, Indian, and South Pacific Oceans. It is a broad, fractured swell with a
central rift valley and usually extremely rugged topography. The ridge is 1-3 kilometers
in height, about 1,500 kilometers in width, and over 84,000 kilometers in length.
Sections of this feature are sometimes named based on the ocean region in which this
feature occur (for example, Mid-Atlantic Ridge).
|Passive Continental Margin
||The transition between oceanic and continental crust that is not an active plate margin.
This feature was constructed by sedimentation above an ancient rift, now marked by
transitional crust. Major tectonic movement is broad, whereas regional vertical adjustment,
earthquakes, and volcanic activity are minor and local.
|Transform Continental Margin
||A feature defined by the transform fault that develops during continental rifting.
These margins differ from rifted or passive margins in two key ways; they have a narrow
continental shelf (less than 30 kilometers) and a steep ocean-continent transition
zone (Keary et al. 2009).
||A narrow, elongate depression of the deep seafloor associated with a subduction zone.
These can be oriented parallel to a volcanic arc and are commonly aligned with the
edge of the adjacent continent, between the continental margin and the abyssal hills.
Trenches are commonly greater than 2 kilometers deeper than the surrounding ocean
floor, and they may be thousands of kilometers long.