The Formation of Basic Magmas at a Hot Spot

1
The Formation of Basic Magmas at a Hot Spot
This diagram identifies the main processes and
features associated with the movement of an
oceanic plate across a hot spot located over a
rising magmatic plume in the mantle
2
Extinct Hot Spot Volcanoes
Active Hot Spot Volcano
Extinct and submerged hot spot volcanoes known
as sea mounts
Sea Level L
PLUME
Mantle drag carries plate across magmatic plume
3

• The Formation of Basaltic Magmas at a Hot
  Spot Volcano
• An oceanic plate passes across a rising magma
  plume within the
• asthenosphere.
• This raises the temperature at the base of the
  lithosphere causing
• partial melting.
• The base of the lithosphere partially melts and
  thins leaving a thinner and lighter lithosphere
  of approx. 70 kms.
• Isostatic adjustment causes this thinner
  lithosphere to rise.
• As it rises fractures develop within the plate.
• The partially molten ultrabasic peridotite
  produces a melt of basic magma.
• This melt migrates through the oceanic plate
  producing an active basic
• lava shield volcano on the oceanic plate
  termed a hot spot volcano.
• In time mantle drag causes the hot spot volcano
  to be carried away
• from the hot spot, and volcanic activity
  ceases. (Meanwhile a new
• basaltic volcano will have developed in its
  place over the hot spot).
• The lithosphere becomes progressively thicker and
  heavier with
• distance from the convection plume.
• Isostatic adjustment causes this thicker denser
  lithosphere to sink.
• As it sinks the extinct hot spots become
  submerged to form sea mounts.

4
Extinct hot spot volcano
Active hot spot volcano
Extinct submerged hot spot volcanoes or sea
mounts
Basic Oceanic Crust
Partial Melting
Ultrabasic Frozen Upper Mantle
Plume