Magmatic room

A magmatic room (less running: magmatic pocket ) is a vast zone under ground, present in the Lithosphère containing magma (=roche in fusion). The magma comes from the fusion of deeper rocks and feeds the room by one or more conduits. The magma in the magmatic room can go up on the surface and give rise to Volcan S, effusive, explosive, of Strombolian type or with a Caldeira.

Located between 10 and 50 kilometers of depth, the room is connected to surface by the conduit (or the chimney) volcanic, in general very narrow. One often represents the magmatic room like an enormous pocket full with magma. It should rather be represented like an enormous rock sponge.

The magma, if it is not expelled at the time of an volcanic eruption, can remain in this room during several centuries and undergo important physicochemical transformations. In particular, of minerals crystallize. It is said that crystallization is split, because the minerals do not have the same composition as the magma. Thus, the composition of the magma evolves/moves during crystallization, and in particular, its density decreases. The reduction in the density of the magma can facilitate its increase on the surface, forming a volcano then. The contents of the room can also crystallize completely and give rise to plutonic rocks (example: Granite or Gabbro).

A magmatic room is due to the increase of a magma which accumulates because it is found blocked (for example, when it crosses mediums less dense than him). An increase of magma can occur:

in context of border of tectonic plates (in a zone of Subduction, one in a zone of Collision of the plates, one finds mainly volcanos explosive (example: The Andes), while in a zone of stretching of the plates rather one finds volcanicity effusive (ex: Iceland)
in context intra-plate: it is the hot case of the Point S (ex: Yellowstone, the Meeting…).

Internal bonds

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