Fractionated plateau and Flank zone

Fractionated plateau

The fractioned plateau is the longest mountain chain on the earth’s surface submerged under the sea. This plateau is formed when there is spreading of the seafloor is really slow.

As the rate of seafloor spreading is very slow, this allows the accumulation of large amounts of lava. The lava forms the fractioned plateau more rich in iron and magnesium (Mafic) than the lava that flows in the rift valley. This is the reason a Fractionated plateau is referred to as a “Magma Pile”.

Fractionated plateau and Flank zone

Flank zone

The fractionated plateau is a zone in which there is a lot of intense volcanic activity. Also, lava found in this zone is often highly varied in composition.

This varied composition in lava is due to a variety of sources that include mantle, oceanic crust and also the sediments that lie on the seafloor.

Also, lava fractionation happens due to the result of different melting points of various minerals that are present in it. It is characterized by a central rift system at the crest.

Characteristics of the Flank Zone

This zone is characterized by secondary geological formations and features that are influenced by the primary geological processes associated with the main feature.

For example, in the context of a volcano, the flank zone would include the areas on the sides of the volcano. In this zone, you might find various volcanic features and deposits, such as lava flows, pyroclastic flows, ash deposits, and volcanic rocks. These secondary formations are the result of past volcanic activity and can provide valuable information about the history and behaviour of the volcano.

The flank zone is often studied by geologists to better understand the geological history and hazards associated with the main geological feature. It can also be important for assessing the potential risks to communities and infrastructure located in these areas, as volcanic or tectonic activity in the flank zone can have significant impacts.

Habitat in the fractionated plateau

In the ocean ridge system, the fractionated plateau is an important feature. This is because it provides a habitat for a wide range of marine life.

This plateau has a number of seamounts that rise above the surrounding seafloor providing a habitat of various fishes, invertebrates and algae.

some of the characteristics of a fractionated plateau:

  • It is a broad, flat summit.
  • It is formed by slow rates of seafloor spreading.
  • The lava that forms it is typically more mafic than the lava that forms the rift valley.
  • It is a zone of intense volcanic activity.
  • The lava that forms it is often highly varied in composition.
  • It is an important habitat for a variety of marine life.


The flanks are marked by sets of mountains that are elongated and run parallel to the ridge trend. Oceanic ridges are offset by transform faults and fracture zones.

* * All the Notes in this blog, are referred from Tamil Nadu State Board Books and Samacheer Kalvi Books. Kindly check with the original Tamil Nadu state board books and Ncert Books.
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